Telecom dictionary
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This document defines telecommunications terms from A to C. Key terms defined include: - Analog-to-digital conversion (A-D) which is the transmission of a continuously varying signal as a discretely varying signal. - A-law algorithm, a standard compression algorithm used in European digital systems to optimize the dynamic range of analog signals for digitizing. - Abandoned call, a call where the originator disconnects before the call is established. - Absolute gain, the ratio of output to input signal levels of a device under specified conditions, usually expressed in decibels. - Acceptance, the condition where a system meets specified performance and security requirements. -
![sawtooth waves are produced by certain types of electronic oscillators, and by a low-end uninterruptible
power supply (UPS) when it is operating from its battery. Irregular AC waves are produced by audio
amplifiers that deal with analog voice signals and/or music.
The voltage of an AC power source can be easily changed by means of a power transformer. This allows the
voltage to be stepped up (increased) for transmission and distribution. High-voltage transmission is more
efficient than low-voltage transmission over long distances, because the loss caused by conductor resistance
decreases as the voltage increases.
The voltage of an AC power source changes from instant to instant in time. The effective voltage of an AC
utility power source is usually considered to be the DC voltage that would produce the same power
dissipation as heat assuming a pure resistance. The effective voltage for a sine wave is not the same as the
peak voltage. To obtain effective voltage from peak voltage, multiply by 0.707. To obtain peak voltage from
effective voltage, multiply by 1.414. For example, if an AC power source has an effective voltage of 117 V,
typical of a household in the United States, the peak voltage is 165 V.
Accept -In data transmission, an Accept is the condition assumed by a primary or secondary station upon
correct receipt of a frame for processing.
Acceptance - The condition that exists when a system or functional unit meets the specified performance
and security requirements.
Access - 1. The ability and means necessary to store data in, to retrieve data from, to communicate with, or
to make use of any resource of a system. 2. To obtain the use of a resource. 3. (COMSEC) [The] capability and
opportunity to gain detailed knowledge of or to alter information or material. 4. (AIS) [The] ability and means
to communicate with (i.e., input to or receive output from), or otherwise make use of any information,
resource, or component in an AIS. Note [for 3 and 4]: An individual does not have "access" if the proper
authority or a physical, technical, or procedural measure prevents him/her from obtaining knowledge or
having an opportunity to alter information, material, resources, or components. 5. An assigned portion of
system resources for one data stream of user communications or signaling. 6. [An] opportunity to make use
of an information-system (IS) resource.
Access Arrangement - An arrangement to transport access traffic between an end office and an IC POT
(interexchange carrier point of termination) and may be either direct routed, tandem routed, or a
combination of direct and tandem routed. (In the case of direct routed only, the access arrangement and
access connection are synonymous.)
Acceptance Angle - In fiber optics, half the vertex angle of that cone within which optical power may be
coupled into bound modes of an optical fiber. Note 1: The axis of the cone is collinear with the fiber axis, the
vertex of the cone is on the fiber end-face, and the base of the cone faces the optical power source. Note 2:
The acceptance angle is measured with respect to the fiber axis. Note 3: Rays entering an optical fiber at
angles greater than the acceptance angle are coupled into unbound modes.
Acceptance Cone - In fiber optics, the cone within which optical power may be coupled into the bound
modes of an optical fiber. Note: The acceptance cone is derived by rotating the acceptance angle about the
fiber axis.
Acceptance Criterion - See acceptance test. A test of a system or functional unit to ensure that contractual
requirements are met. Note: An acceptance test may be performed at the factory or user premises by the
user, vendor, or a third party.
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![Acceptance Limit (AL) - The bound on performance that is allowed at service turnup or interexchange carrier
(IC) acceptance of a circuit or connection, or when corrective action is taken to restore a parameter after an
immediate action limit (IAL) failure. Performance as measured by a parameter is satisfactory if the value of
the parameter is equal to or better than the limit.
Acceptance Pattern - 1. Of an antenna, for a given plane, a distribution plot of the off-axis power relative to
the on-axis power as a function of angle or position. Note: The acceptance pattern is the equivalent of a
horizontal or vertical antenna pattern. 2. Of an optical fiber or fiber bundle, a curve of total transmitted
power plotted against the launch angle.
Acceptance Test - A test of a system or functional unit to ensure that contractual requirements are met.
Note: An acceptance test may be performed at the factory or user premises by the user, vendor, or a third
party.
Acceptance Testing - Operating and testing of a communication system, subsystem, or component, to
ensure that the specified performance characteristics have been met.
Acceptance Trial - A trial carried out by nominated representatives of the eventual military users of the
weapon or equipment to determine if the specified performance and characteristics have been met.
Accepted Interference - Interference at a higher level than that defined as permissible interference and
which has been agreed upon between two or more administrations without prejudice to other
administrations.
Access - 1. The ability and means necessary to store data in, to retrieve data from, to communicate with, or
to make use of any resource of a system. 2. To obtain the use of a resource. 3. (COMSEC) [The] capability and
opportunity to gain detailed knowledge of or to alter information or material. [NIS] 4. (AIS) [The] ability and
means to communicate with (i.e., input to or receive output from), or otherwise make use of any
information, resource, or component in an AIS. Note [for 3 and 4]: An individual does not have "access" if the
proper authority or a physical, technical, or procedural measure prevents him/her from obtaining knowledge
or having an opportunity to alter information, material, resources, or components. [NIS] 5. An assigned
portion of system resources for one data stream of user communications or signaling. 6. [An] opportunity to
make use of an information-system (IS) resource.
Access is commonly defined as the process used for communication between your computer and the
Internet. Access is simply being able to get to what you need. Data access is being able to get to (usually
having permission to use) particular data on a computer. Web access means having a connection to the
World Wide Web through an access provider or an online service provider such as America Online.
For data access, access is usually specified as read-only access and read/write access.
Access Attempt - The process by which one or more users interact with a telecommunications system to
enable initiation of user information transfer. Note: An access attempt begins with an issuance of an access
request by an access originator. An access attempt ends either in successful access or in access failure.
Access Barred Signal - In a communications system, a signal sent in the backward direction to indicate that a
call will not be completed because of a call-originator or a call-receiver facility requirement. Note: An access
barred signal may occur for many reasons, such as the failure of a closed user group validation check on an
incoming calls-barred facility.
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![Access Category - A class to which a user, such as a person, program, process, or equipment, of a system
may be assigned, based on the resources each user is authorized to use.
Access Channel - A designated part of the information transfer capability having specified characteristics,
provided at the user-network interface.
Access Charge - 1. A fee charged by a local exchange carrier for the use of its local exchange networks. 2. A
charge made by a local exchange carrier for use of its local exchange facilities for a purpose such as the
origination or termination of traffic that is carried to or from a distant exchange by an interexchange carrier.
Access Code - 1. The preliminary digits that a user must dial to be connected to a particular outgoing trunk
group or line. 2. A uniform code assigned by the telephone company to an individual customer in the form
101xx and 950-xx.
Access Connection - In ISDN technology, a connection (using either the B-Channel or a logical link on the D-
Channel) established between the user equipment and a packet-mode handier function, over which packet-
mode calls (incoming and outgoing) are established.
Access Contention - In ISDN applications, synonym contention. - 1. A condition that arises when two or more
data stations attempt to transmit at the same time over a shared channel, or when two data stations
attempt to transmit at the same time in two-way alternate communication. Note: A contention can occur in
data communications when no station is designated a master station. In contention, each station must
monitor the signals and wait for a quiescent condition before initiating a bid for master status. 2.
Competition by users of a system for use of the same facility at the same time.
Access Control - 1. A service feature or technique used to permit or deny use of the components of a
communication system. 2. A technique used to define or restrict the rights of individuals or application
programs to obtain data from, or place data onto, a storage device. 3. The definition or restriction of the
rights of individuals or application programs to obtain data from, or place data into, a storage device. 4.
Limiting access to information system resources only to authorized users, programs, processes, or other
systems.5. That function performed by the resource controller that allocates system resources to satisfy user
requests.
Access Control List - 1. In security, a list of entities, together with their access rights, that are authorized to
access a resource. 2. [A] mechanism implementing discretionary and/or mandatory access control between
subjects and objects.
Access Control Mechanism - 1. In security, a hardware, software, or firmware feature, operating procedure,
or management procedure that (a) permits authorized access to a system, such as a communications,
computer, and data processing system, (b) prevents unauthorized access to the system, and (c) is considered
to have failed when unauthorized access is permitted or when authorized access is prevented. 2. [A] Security
safeguard designed to detect and deny unauthorized access and permit authorized access in an information
system (IS).
Access Control Message - A message that is a user request, a resource controller response, or a
request/response between resource controllers.
Access Coupler - Deprecated term. See directional coupler.
Access Denial - 1. Access failure caused by the issuing of a system blocking signal by a communications
system that does not have a call-originator camp-on feature. 2. Access failure caused by exceeding the
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![maximum access time and nominal system access time fraction during an access attempt. Synonym system
blocking.
Access-Denial Time - The time between the start of an access attempt and access failure caused by access
denial, i.e., system blocking. Note: Access denial times are measured only on access attempts that result in
access denial.
Access Digit - In automatic direct outward telephone dialing, a digit, often a 1, or a 9, that (a) enables access
to an outside facility, e.g., a PBX or local exchange, and (b) is prefixed to the specific number being dialed.
Note 1: Throughout the United States, an access digit, usually 1, must be prefixed to an area code before
dialing the area code and the specific number to which a connection is desired. Note 2: The access digit 9 is
often used to establish a connection between a PBX and a local exchange.
Access Failure - In a communications system, an unsuccessful access that results in termination of an access
attempt in any manner other than initiation of user information transfer between the intended source and
destination (sink) within the specified maximum access time. Note: Access failure can be the result of access
denial, access outage, user blocking, or incorrect access.
Access Function - A set of processes in a network that provides for interaction between the user and a
network.
Access Group - A group of one or more stations having identical rights to use the available resources on a
PBX, network or host computer.
Access Level - 1. In security, the level of authority required from an entity to access a protected resource.
Note: An example of access level is the authority to access information at a particular security level. 2. [The]
hierarchical portion of the security level used to identify sensitivity of information-system (IS) data and the
clearance or authorization of users. Access level, in conjunction with the nonhierarchical categories, forms
the sensitivity label of an object.
Access Line - 1. A transmission path between end user terminal equipment and a switching center. 2. A
channel between an end user's network interface and local end office. Synonym [loosely] loop. 3. A
communications facility extending from a customer's premises to a serving central office comprising a
subscriber line and, if necessary, a trunk facility, e.g., a WATS access line, TWX access line.
Access Lines - A telephone line running from the telephone company’s central office to a point on your
property.
Access Line Equivalents - A representation of the number of access lines that a system could hold.
Access List - 1. In information systems (IS), a compilation of users, programs, or processes and the access
levels and types to which each is authorized. 2. In COMSEC, a roster of persons authorized admittance to a
controlled area.
Access Loop - See attendant access loop.
Access Node - In switching systems, the point where user traffic enters and exits a communications network.
Note: Access node operations may include various operations, such as protocol conversion and code
conversion.
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![Access Originator - The functional entity responsible for initiating a particular access attempt. Note: An
access attempt can be initiated by a source user, a destination user, or the telecommunications system.
Access Path - The steps required to obtain the use of a system or device. Note: Examples of access paths are
(a) the operations required of a database management system to obtain access to a database and (b) the
sequence of steps required to reach a file.
Access Period - In security, a segment of time, generally expressed in days or weeks, during which specified
access rights prevail.
Access Permission - All of a subject's access rights with respect to some object.
Access Phase - In an information-transfer transaction, the phase during which an access attempt is made.
Note: The access phase is the first phase of an information-transfer transaction.
Access Point - 1. A point where connections may be made for testing or using particular communications
circuits. 2. In telephony, a junction point in outside plant consisting of a splice at a junction between a branch
feeder cable and distribution cables.
Access Profile - 1. In security, a profile that associates each user with a list of protected objects that the user
may access. 2. [An itemization that] associates each user with a list of protected objects the user may access.
Access Provider - 1. An organization that provides users with access to a computer network. Any
organization that arranges for an individual or an organization to have access to the Internet. Access
providers are generally divided into two classes: Internet access providers (ISPs) and online service providers
(OSPs). ISPs can be local businesses that pay for a high-speed connection to one of the companies (such as
AT&T, Sprint, or MCI in the U.S.) that are part of the Internet. They can also be national or international
companies that have their own networks (such as AT&T's WorldNet or IBM's Global Services). OSPs,
sometimes just called "online services," also have their own networks but provide additional information
services not available to non-subscribers. America Online is the most successful example of an OSP. 2. A
party responsible for traffic originating and terminating in jurisdictional areas defined by regulatory agencies.
Access Request - 1. A control message issued by an access originator for the purpose of initiating an access
attempt. 2. A signal sent to a network for the purpose of initiating the establishment of a network
connection. In this definition, a signal may take the form of a message.
Access Right - Permission for a subject to access a particular object for a specific type of operation. Note: An
example of an access right is the permission for a process to read a file but not write to it.
Access Service Area - A geographic area established for the provisioning and administration of
telecommunications service. An access service area encompasses one or more exchanges, which are grouped
in access service areas to serve common social, economic, and other purposes. Contrast with LATA.
Access System - In communications, computer, and data processing systems, a program that (a) allows an
operator to call up different parts of the program package and (b) usually allows functions to be selected
from menus in the same way as other commands. Note: An example of an access system is the program
supplied with a common spreadsheet program that (a) allows the computer to shift between the
spreadsheet program and a graph-printing facility and (b) provides access to various support functions.
Access Tandem - 1. A telephone company or centralized equal access provider switching system that
provides a concentration and distribution function for originating or terminating traffic between end offices
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![and a customer-designated premises. 2. An exchange carrier switching system that provides a traffic
concentration and distribution function for inter-LATA traffic originating/terminating within a LATA.
Access Time - 1. In a telecommunication system, the elapsed time between the start of an access attempt
and successful access. Note: Access time values are measured only on access attempts that result in
successful access. 2. In a computer, the time interval between the instant at which an instruction control unit
initiates a call for data and the instant at which delivery of the data is completed. 3. The time interval
between the instant at which storage of data is requested and the instant at which storage is started. 4. In
magnetic disk devices, the time for the access arm to reach the desired track and the delay for the rotation
of the disk to bring the required sector under the read-write mechanism.
Access Type - 1. In computer security, a type of operation specified by an access right. Note: Examples of
access type are "read," "write," "execute," "append," "modify," "delete," and "create." [2382-pt.8] 2. [The]
privilege to perform action on an object. Read, write, execute, append modify, delete, and create are
examples of access types.
Access Unit - See medium access unit (MAU).
Access Unit Interface - Synonym attachment unit interface.
Acceptability - Section 508, an amendment to the United States Workforce Rehabilitation Act of 1973, is a
federal law mandating that all electronic and information technology developed, procured, maintained, or
used by the federal government be accessible to people with disabilities. Technology is deemed to be
"accessible" if it can be used as effectively by people with disabilities as by those without. To demonstrate
that a product or Web service is in compliance with Section 508, the creator completes a Voluntary Product
Accessibility Template (VPAT), an "informational tool" that describes exactly how the product or service does
or does not meet Section 508 standards. The completed VPAT gets posted on the creator's Web site to
provide government officials and consumers with access to the information.
The scope of Section 508 is limited to the federal sector. It includes binding, enforceable standards, as well as
compliance reporting requirements and a complaint procedure. Section 508 doesn't apply to the private
sector, nor does it impose requirements on the recipients of federal funding. Because the federal
government has so much purchasing power, however, it is hoped that Section 508 will encourage the dev
elopement of products and Web-based services that meet accessibility standards. To that end, the United
Stated Department of Education now requires states funded by the Assitive Technology Act State Grant
program (a grant program that supports consumer-driven state projects to improve access to assistive
technology devices and services) to comply with Section 508.
Accessibility policies like Section 508 vary from country to country, but most countries, including the
European Union (EU), have adopted standards based on the Web Content Accessibility Guidelines of the
World Wide Web Consortium. Section 508 is based on W3C Priority 1 checkpoints.
Accountability - 1. The property that ensures that the actions of an individual or an institution may be traced
uniquely to that individual or institution. 2. In information systems (IS), the process of tracing IS activities to a
responsible source.3. In COMSEC, the principle that an individual is entrusted to safeguard and control
equipment, keying material, and information and is answerable to proper authority for the loss or misuse of
that equipment or information.
Accounting Management - In network management, a set of functions that (a) enables network service use
to be measured and the costs for such use to be determined and (b) includes all the resources consumed,
the facilities used to collect accounting data, the facilities used to set billing parameters for the services used
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![by customers, maintenance of the data bases used for billing purposes, and the preparation of resource
usage and billing reports.
Accreditation - 1. In computer security, the authorization and approval--granted by a designated authority to
a data processing system, computer network, organization, or individual--to process sensitive information or
data. 2. Formal declaration by a designated approving authority that an information system (IS) is approved
to operate in a particular security mode using a prescribed set of safeguards at an acceptable level of risk.
Accrediting Authority - Synonym designated approving authority.
Accumulator - 1. A register in which one operand can be stored and subsequently replaced by the result of
an arithmetic or logic operation. 2. A storage register. 3. A storage battery.
Accuracy - The degree of conformity of a measured or calculated value to its actual or specified value.
AC Current - Alternating Current.
ACD - Automatic Call Distributor
AC-DC Ringing - Telephone ringing that makes use of both ac and dc voltages and currents. Note: An
alternating current may be used to operate a ringer and direct current to aid the relay action that stops the
ringing when the called telephone is answered.
Achromat - A usually two-element lens that is corrected to bring two specified or distinct wavelengths to a
common focal point. Note 1: The term "achromatic" literally means "without color." This is not strictly true,
however. Early lenses consisted of only a single element, and therefore could bring only a single wavelength
to a given focal point; i.e., they suffered from what is termed "chromatic aberration." The invention of lenses
with two elements meant that two distinct wavelengths could be brought to a common focus. This
represented a vast improvement over the single-element lens; hence the designation "achromat(ic)." Note 2:
The residual chromatic aberration manifested in the image produced by an achromat (and other multi-
element lenses) is usually referred to as the "secondary spectrum." Synonyms achromatic doublet,
achromatic lens.
Achromatic Double - Synonym achromat.
Achromatic Doublet - Synonym achromat.
Achromatic Lens - Synonym achromat.
ACK - Abbreviation for acknowledge character.
Acknowledge Character (ACK): A transmission control character transmitted by the receiving station as an
affirmative response to the sending station. Note: An acknowledge character may also be used as an
accuracy control character.
Acknowledgement - 1. A response sent by a receiver to indicate successful receipt of a transmission. Note:
An example of an acknowledgement is a protocol data unit, or element thereof, between peer entities, to
indicate the status of data units that have been successfully received. 2. A message from the addressee
informing the originator that the originator's communication has been received and understood.
Acknowledgement Delay Period - Synonym [loosely] sliding window.
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![ADSL (Asymmetric Digital Subscriber Line) - A new modem technology that allows existing twisted pair
telephone lines to access the Internet at T-1 speeds. A technology for transmitting digital information at a
high bandwidth on existing phone lines to homes and businesses. Unlike regular dial up phone service, ADSL
provides continously-available, "always on" connection. ADSL is asymmetric in that it uses most of the
channel to transmit downstream to the user and only a small part to receive information from the user. ADSL
simultaneously accommodates analog (voice) information on the same line. ADSL is generally offered at
downstream data rates from 512 Kbps to about 6 Mbps. A form of ADSL, known as Universal ADSL or G.lite,
has been approved as a standard by the ITU-TS.
ADSL was specifically designed to exploit the one-way nature of most multimedia communication in which
large amounts of information flow toward the user and only a small amount of interactive control
information is returned. Several experiments with ADSL to real users began in 1996. In 1998, wide-scale
installations began in several parts of the U.S. In 2000 and beyond, ADSL and other forms of DSL are
expected to become generally available in urban areas. With ADSL (and other forms of DSL), telephone
companies are competing with cable companies and their cable modem services.
ADSL Modem - An ATU-R (ADSL Terminal Unit - Remote) is a hardware unit that is installed in any computer
that uses a telephone company connection with Asymmetric Digital Subscriber Line (ADSL) service. The ATU-
R connects to an Ethernet network interface card (NIC) in the computer and, on the other side, to a
telephone jack in the home or business. Ideally (for less interference), the telephone jack hooks up to a new
wire that goes to a signal splitter that the telephone company installs at the telephone company
demarcation point (the place where the outside phone company wire or wires connect to the network of
phone lines within the customer's building). The splitter divides the signal into low frequencies for voice and
high frequencies for data.
Advanced Data Communication Control Procedures (ADCCP) - A bit-oriented Data-Link-Layer protocol used
to provide point-to-point and point-to-multipoint transmission of data frames that contain error-control
information. Note: ADCCP closely resembles high-level data link control (HDLC) and synchronous data link
control (SDLC).
Advanced Intelligent Network (AIN) - 1. A telecommunications network architecture that uses databases to
facilitate call processing, call routing, and network management, allowing carriers to change the routing of
both inbound and outbound calls from moment to moment. [FCC-5] 2. A proposed intelligent-network (IN)
architecture that includes both IN/1+ and IN/2 concepts.
Advanced Mobile Phone Service (AMPS) - A standard system for analog signal cellular telephone service in
the United States and is also used in other countries. It is based on the initial electromagnetic radiation
spectrum allocation for cellular service by the Federal Communications Commission (FCC) in 1970.
Introduced by AT&T in 1983, AMPS became and currently still is the most widely deployed cellular system in
the United States.
Advanced Television (ATV) - A family of television systems that is intended to be improvements over current
commercial-quality television. Note: The ATV family includes improved-definition television (IDTV),
extended-definition television (EDTV), and high-definition television (HDTV).
AECS - Abbreviation for Aeronautical Emergency Communications System. See Aeronautical Emergency
Communications System Plan.
Aerial Cable - A communications cable designed for installation on, or suspension from, a pole or other
overhead structure.
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![Aerial Insert - In a direct-buried or underground cable run, a cable rise to a point above ground, followed by
an overhead run, e.g., on poles, followed by a drop back into the ground. Note: An aerial insert is used in
places where it is not possible or practical to remain underground, such as might be encountered in crossing
a deep ditch, canal, river, or subway line.
Aeronautical Advisory Station - An aeronautical station used for advisory and civil defense communications
primarily with private aircraft stations. Synonym UNICOM station.
Aeronautical Broadcast Station - An aeronautical station which makes scheduled broadcasts of
meteorological information and notices to airmen. (In certain instances, an aeronautical broadcast station
may be placed on board a ship.)
Aeronautical Earth Station - An Earth station in the fixed-satellite service, or, in some cases, in the
aeronautical mobile-satellite service, located at a specified fixed point on land to provide a feeder link for the
aeronautical mobile-satellite service.
Aeronautical Emergency Communications System (AECS) Plan - The AECS Plan provides for the operation of
aeronautical communications stations, on a voluntary, organized basis, to provide the President and the
Federal Government, as well as heads of state and local governments, or their designated representatives,
and the aeronautical industry with an expeditious means of communications during an emergency situation.
Aeronautical Fixed Service - A radio communication service between specified fixed points provided
primarily for the safety of air navigation and for the regular, efficient and economical operation of air
transport.
Aeronautical Fixed Station - A station in the aeronautical fixed service.
Aeronautical Mobile (OR) [off-route] Service - An aeronautical mobile service intended for communications,
including those relating to flight coordination, primarily outside national or international civil air routes.
Aeronautical Mobile (R) [route] Service - An aeronautical mobile service reserved for communications
relating to safety and regularity of flight, primarily along national or international civil air routes.
Aeronautical Mobile-Satellite Service - A mobile-satellite service in which mobile Earth stations are located
on board aircraft; survival craft stations and emergency position-indicating radio beacon stations may also
participate in this service.
Aeronautical Mobile-Satellite (OR) [off-route] Service - An aeronautical mobile-satellite service intended for
communications, including those relating to flight coordination, primarily outside national and international
civil air routes.
Aeronautical Mobile-Satellite (R) [route] Service - An aeronautical mobile-satellite service reserved for
communications relating to safety and regularity of flight, primarily along national or international civil air
routes.
Aeronautical Mobile Service - A mobile service between aeronautical stations and aircraft stations, or
between aircraft stations, in which survival craft stations may participate; emergency position-indicating
radio beacon stations may also participate in this service on designated distress and emergency frequencies.
Aeronautical Multicom Service - A mobile service not open to public correspondence, used to provide
communications essential to conduct activities being performed by or directed from private aircraft.
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![at the equipment originating the AIS signal or upstream of that equipment. 2. A signal transmitted in lieu of
the normal signal to maintain transmission continuity and indicate to the receiving terminal that there is a
transmission fault located either at the transmitting terminal or upstream of the transmitting terminal.
Alarm Indicator - A device that responds to a signal from an alarm sensor. Note: Examples of alarm
indicators include bells, lamps, horns, gongs, and buzzers.
Alarm Sensor - 1. In communications systems, any device that (a) can sense an abnormal condition within
the system and provide a signal indicating the presence or nature of the abnormality to either a local or
remote alarm indicator, and (b) may detect events ranging from a simple contact opening or closure to a
time-phased automatic shutdown and restart cycle. 2. In a physical security system, an approved device used
to indicate a change in the physical environment of a facility or a part thereof. Note: Alarm sensors may also
be redundant or chained, such as when one alarm sensor is used to protect the housing, cabling, or power
protected by another alarm sensor.
Alarm Status - A set of attributes that describes the alarms currently defined for an object, for example,
perceived severity, alarm state, etc. The alarm status of an object is a subset of the global status of that
object.
Alarm Surveillance - A set of functions that enables the monitoring or interrogation (or both) of the
telecommunications network concerning alarm-related events or conditions.
A-law - See a-law algorithm.
A-Law Algorithm - A standard compression algorithm, used in digital communications systems of the
European digital hierarchy, to optimize, i.e., modify, the dynamic range of an analog signal for digitizing.
Note: The wide dynamic range of speech does not lend itself well to efficient linear digital encoding. A-law
encoding effectively reduces the dynamic range of the signal, thereby increasing the coding efficiency and
resulting in a signal-to-distortion ratio that is superior to that obtained by linear encoding for a given number
of bits.
ALE - Abbreviation for automatic link establishment.
Alerting Signal - A signal used by the network to indicate the presence of an incoming call. It consists of a
ringing signal periodically interrupted by silent (no ringing signal) intervals.
Algorithmic Language - An artificial language established for expressing a given class of algorithms.
Algorithm Identifier - In encryption, a unique identifier or recognizer for a given encryption or hash
algorithm, together with any required parameters.
Alias - 1. See aliasing. 2. In networking, one of a set of domain names of an Internet resource. [2382-pt.35] 3.
Synonyms personal number, UPT number.
Aliasing - In any technology or process involving (a) sampling a signal, e.g., an electrical signal or (a series of
images of) a moving subject; (b) processing, storing, or transmitting representations of the samples; and (c)
replicating the original signal from the representations: the production of artifacts as a result of sampling at
intervals too great to permit faithful replication of the original signal. Note 1: A common example of aliasing
in video or motion picture technology is the apparent slowing, freezing, or even reversing of direction of, the
motion of spokes in the wheels on a moving vehicle. Note 2: In the sampling and replication of electrical
signals, if the sampling interval is too great, high-frequency components may, for example, be replicated as
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![low-frequency components, distorting the replicated signal. Note 3: Faithful reproduction of a sampled
electrical signal requires a theoretical sampling interval not greater than one-half the inverse of the highest
Fourier frequency component in the sampled signal (Nyquist interval). In practice, to achieve a given level of
fidelity in the replicated signal, the sampling interval must usually be somewhat shorter than the theoretical
(Nyquist) interval, because the samples are usually processed, stored, or transmitted in digital form, and
quantization errors in the digitizing process will also result in distortion of the (waveform of the) replicated
signal. Note 4: The effects of aliasing in the replicated signal may be avoided by filtering the original signal to
remove frequency components that are higher than those desired in the replicated signal. Note 5 (from
SMPTE): Video images are sampled in two or three dimensions, and computer graphics are sampled in three.
In a composite (complex) spectral channel, any cross talk of the information cannot be eliminated by
filtering, and will produce aliasing, for example as cross-color and/or cross-luminance. In a rectilinearly
sampled system, lines not parallel to a sampling axis will appear stepped unless anti-aliasing processing
algorithms have been applied.
Alias Point Code - 1. A Signaling System No. 7 (SS7) address that is shared by more than one system
supporting the same GTT (global title translation) function (or other SS7 function). It allows other systems to
address the function instead of maintaining the status of multiple point codes. [T1.711-1999] 2. A point code
that may be assigned to more than one signaling point, each of which is also assigned a "real" point code.
Note: Each of the signaling points having the same "alias" point code is capable of providing a predefined
functionality (capability) in the network. As an example for management of global translation capability, an
STP (signaling transition point) and its mate can be assigned the same "alias" point code. This provides the
capability such that if a message that requires global title translation is routed based on "alias" point code,
then either STP answering to the "alias" point code can provide the global title translation functionality.
Synonym capability code.
Aligned Bundle - A bundle of optical fibers in which the relative spatial coordinates of each fiber are the
same at the two ends of the bundle. Note: Such a bundle may be used for the transmission of images.
Synonym coherent bundle.
Alignment Error Rate Monitoring - A procedure by which the error rate of a signaling link is measured during
the initial alignment process.
Alignment Jitter - The short-term variations between the optimum sampling instants of a digital signal and
the sampling clock derived from it.
Allan variance - One half of the time average over the sum of the squares of the differences between
successive readings of the frequency deviation sampled over the sampling period. Note: The Allan variance is
2
conventionally expressed by y ( ). The samples are taken with no dead-time between them. Synonym
two-sample variance.
Allcall - In adaptive high-frequency (HF) radio automatic link establishment (ALE), a general broadcast that
does not request responses and does not designate any specific addresses. Note: This essential function is
required for emergencies ("HELP"), sounding-type data exchanges, and propagation and connectivity
tracking.
All-Glass Fiber - Synonym all-silica fiber.
Allocation (of a frequency band) - 1. Entry in the Table of Frequency Allocations of a given frequency band
for the purpose of its use by one or more (terrestrial or space) radio communication services or the radio
astronomy service under specified conditions. This term shall also be applied to the frequency band
concerned. 2. The process of designating radio-frequency bands for use by specific radio services.
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![Antenna Lobe - A three-dimensional section of the radiation pattern of a directional antenna, bounded by
one or more cones of nulls or by regions of diminished irradiance.
Antenna Matching - The process of adjusting impedance so that the input impedance of an antenna equals
or approximates the characteristic impedance of its transmission line over a specified range of frequencies.
Note: The impedance of either the transmission line, or the antenna, or both, may be adjusted to effect the
match.
Antenna Noise Temperature - The temperature of a hypothetical resistor at the input of an ideal noise-free
receiver that would generate the same output noise power per unit bandwidth as that at the antenna output
at a specified frequency. Note 1: The antenna noise temperature depends on antenna coupling to all noise
sources in its environment as well as on noise generated within the antenna. Note 2: The antenna noise
temperature is a measure of noise whose value is equal to the actual temperature of a passive device.
Anti-Clockwise Polarized Wave - Synonym left-hand polarized wave.
Anti-Interference - Pertaining to equipment, processes, or techniques used to reduce the effect of natural
and man-made noise on radio communications.
Anti-Jam - Measures ensuring that intended transmitted information can be received despite deliberate
jamming attempts.
Anti-Node - A point in a standing wave at which the amplitude is a maximum.
Antireflection Coating - A thin, dielectric or metallic film, or several such films, applied to an optical surface
to reduce its reflectance and thereby increase its transmittance.Note: For minimum reflection of a normal
incident wave of a single wavelength, the antireflection coating may consist of a single layer and must have
(a) a refractive index equal to the square root of the refractive indices of the materials bounding the coating,
and (b) a thickness equal to one-quarter the wavelength in question (i.e., the wavelength within the material
of which the coating consists). For minimum reflection of multiple wavelengths, additional layers must be
added.
Anti-Spoof - 1. Measures taken to prevent an unauthorized person/entity from impersonating an authorized
person/entity to gain access to a data system. [DoJ] 2. Measures preventing an opponent's participation in
an information system (IS).
Anti-Virus Program - A computer program designed to detect computer-file viruses and possibly to suggest
or take corrective action. Synonym vaccine program.
Anycall - In adaptive high-frequency (HF) radio automatic link establishment, a broadcast in which (a) the
called stations are unspecified, (b) stations receiving the call stop scanning, and (c) each station
automatically responds in pseudorandom time slots.
AP - Abbreviation for anomalous propagation.
APC - Abbreviation for adaptive predictive coding.
APD - Abbreviation for avalanche photodiode. Note: apd and a.p.d. are also used.
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![Aramid Yarn - Generic name for a tough synthetic yarn that is often used in optical cable construction for the
strength member, protective braid, and/or rip cord for jacket removal.
Architecture - See computer architecture, network architecture.
Archive File - A software file that has been set aside, often in a redundant storage medium, as a security
measure or for later retrieval, e.g., for research or verification.
Archiving - The storing of files, records, and other data for reference and alternative backup.
Area Broadcast Shift - The changing from listening to transmissions intended for one broadcast area to
listening to transmissions intended for another broadcast area. Note 1: An area broadcast shift may occur
when a ship or aircraft crosses the boundary between listening areas. Note 2: Shift times, on the date a ship
or aircraft is expected to pass into another area, must be strictly observed or the ship or aircraft will miss
messages intended for it. Synonym radio watch shift.
Area Code - In the North American telephone system, an area code is a three-digit code delineating a "toll"
area in the United States, Canada, and Mexico. Area codes are distributed according to the North American
Number Plan (NANP). The area code is also referred to as a Number Plan Area or NPA. See access code, code,
country code, NXX code. Also See Telephone Area Codes of North America.
Area Loss - When optical fibers are joined by a splice or a pair of mated connectors, a power loss that is
caused by any mismatch in size or shape of the cross section of the cores of the mating fibers. Note 1: Any of
the above conditions may allow light from the core of the "transmitting" fiber to enter the cladding of the
"receiving" fiber, where it is quickly lost. Note 2: Area loss may be dependent on the direction of
propagation. For example, in coupling a signal from an optical fiber having a smaller core to an otherwise
identical one having a larger core, there will be no area loss, but in the opposite direction, there will be area
loss.
Argument - 1. An independent variable. 2. Any value of an independent variable. Note: Examples of
arguments include search keys, numbers that identify the location of a data item in a table, and the in sin .
Arithmetic and Logic Unit (ALU) - A part of a computer that performs arithmetic, logic, and related
operations.
Arithmetic Overflow - 1. In a digital computer, the condition that occurs when a calculation produces a
result that is greater than a given register or storage location can store or represent. 2. In a digital computer,
the amount that a calculated value is greater than a given register or storage location can store or represent.
Note: The overflow may be placed at another location. Synonym [loosely] overflow.
Arithmetic Register - A register that holds the operands or the results of operations such as arithmetic
operations, logic operations, and shifts.
Arithmetic Shift - A shift, applied to the representation of a number in a fixed radix numeration system and
in a fixed-point representation system, and in which only the characters representing the fixed-point part of
the number are moved. An arithmetic shift is usually equivalent to multiplying the number by a positive or a
negative integral power of the radix, except for the effect of any rounding; compare the logical shift with the
arithmetic shift, especially in the case of floating-point representation.
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![Artifact - In facsimile or television, a defect or distortion of the image, introduced along the sequence from
origination and image capture to final display. Note 1: Artifacts may arise from the overload of channel
capacity by excess signal bandwidth. Note 2: In general, artifacts may result from (a) sampling effects in
temporal, spatial, or frequency domains, (b) processing by the transfer functions, (c) compromises and
inadequacies in the system employed, (d) cascading of minor defects, or (e) any other departure of the total
system from "complete transparency."
Artificial Intelligence (AI) - The capability of a device to perform functions that are normally associated with
human intelligence, such as reasoning and optimization through experience. Note: AI is the branch of
computer science that attempts to approximate the results of human reasoning by organizing and
manipulating factual and heuristic knowledge. Areas of AI activity include expert systems, natural language
understanding, speech recognition, vision, and robotics.
Artificial Transmission Line - A four-terminal electrical network, i.e. an electrical circuit, that has the
characteristic impedance, transmission time delay, phase shift, and/or other parameter(s) of a real
transmission line and therefore can be used to simulate a real transmission line in one or more of these
respects. Synonym [loosely] art line.
Art Line - Synonym [loosely] artificial transmission line.
ARU - Abbreviation for audio response unit.
ASCII (pronounced: ask-ee) - ASCII is an acronym for American Standard Code for Information Interchange, a
code that represents the most basic letters of the Roman alphabet, numbers, and other characters used in
computing. ASCII characters allow us to communicate with computers, which use their own language called
binary made up of 0s and 1s. ASCII files are also called text files.
ASCII is the standard code used for information interchange among data processing systems, data
communications systems, and associated equipment in the United States. Note 1: The ASCII character set
contains 128 coded characters. Note 2: Each ASCII character is a 7-bit coded unique character; 8 bits when a
parity check bit is included. Note 3: The ASCII character set consists of control characters and graphic
characters. Note 4: When considered simply as a set of 128 unique bit patterns, or 256 with a parity bit,
disassociated from the character equivalences in national implementations, the ASCII may be considered as
an alphabet used in machine languages. Note 5: The ASCII is the U.S. version of International Reference
Alphabet (IRA) No. 5 (formerly International Alphabet No. 5, or "IA5") as specified in ITU-T Recommendation
T.50.
ASP - Abbreviation for adjunct service point.
Aspect Ratio - 1. In facsimile or television, the ratio of the width to the height of a scanning field or image.
Note: For example, the classical NTSC television standard specifies an aspect ratio of 4:3, and the new high-
definition television standard specifies 16:9. - For 4:3, the traditional TV aspect ratio, a 32-inch TV would be
25½ inches wide and 19 inches tall. A 16:9 widescreen 32-inch TV is closer to a movie screen than a
traditional TV, and would be 28 inches wide and 16 inches tall. 2. The ratio of the width to the height of any
video or scanned image display.
ASR ( Automated Speech Recognition) - Is a technology that allows users of information systems to speak
entries rather than punching numbers on a keypad. ASR is used primarily to provide information and to
forward telephone calls.
In recent years, ASR has become popular in the customer service departments of large corporations. It is also
used by some government agencies and other organizations. Basic ASR systems recognize single-word
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![entries such as yes-or-no responses and spoken numerals. This makes it possible for people to work their
way through automated menus without having to enter dozens of numerals manually with no tolerance for
error. In a manual-entry situation, a customer might hit the wrong key after having entered 20 or 30
numerals at intervals previously in the menu, and give up rather than call again and start over. ASR virtually
eliminates this problem.
Sophisticated ASR systems allow the user to enter direct queries or responses, such as a request for driving
directions or the telephone number of a hotel in a particular town. This shortens the menu navigation
process by reducing the number of decision points. It also reduces the number of instructions that the user
must receive and comprehend.
For institutions that rely heavily on customer service, such as airlines and insurance companies, ASR makes it
possible to reduce the number of human call-center employees. Those people can then be trained for other
jobs that are more profitable and interesting, such as complaint resolution, customer retention, or sales.
The technology of speech recognition has been around for some time. It is improving, but problems still
exist. An ASR system cannot always correctly recognize the input from a person who speaks with a heavy
accent or dialect, and it has major problems with people who combine words from two languages by force of
habit. Marginal cell-phone connections can cause the system to misinterpret the input. And, although the
cost is gradually diminishing, ASR systems are still too expensive for some organizations.
Assemble - To translate a computer program expressed in an assembly language into a machine language.
Assembler: A computer program that is used to assemble. Synonym assembly program.
Assembly - In logistics, an item forming a portion of an equipment that can be provisioned and replaced as
an entity and which normally incorporates replaceable parts or groups of parts.
Assembly Language - A computer-oriented language (a) in which instructions are symbolic and usually in
one-to-one correspondence with sets of machine language instructions and (b) that may provide other
facilities, such as the use of macro instructions. Synonym computer-dependent language.
Assembly Program - Synonym assembler.
Assembly Time - The elapsed time taken for the execution of an assembler.
Asset - 1. In security, a resource or information that is to be protected. 2. Any system or component (e.g.,
subsystem, hardware, firmware, software, database, or interconnection communications network or facility)
that is part of a communications system or an information system.
Assigned Frequency - 1. The center of the assigned frequency band assigned to a station. [RR] 2. The
frequency of the center of the radiated bandwidth. Note: The frequency of the rf carrier, whether
suppressed or radiated, is usually given in parentheses following the assigned frequency, and is the
frequency appearing in the dial settings of rf equipment intended for single-sideband or independent-
sideband transmission. 3. The frequency coinciding with the center of an authorized bandwidth of emission.
[47CFR] 4. The center of the frequency band assigned to a station.
Assigned Frequency Band - The frequency band within which the emission of a station is authorized; the
width of the band equals the necessary bandwidth plus twice the absolute value of the frequency tolerance.
Where space stations are concerned, the assigned frequency band includes twice the maximum Doppler shift
that may occur in relation to any point of the Earth's surface.
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![ATSC Tuner - Often called an ATSC receiver or HDTV tuner, allows reception of DTV signals broadcast over-
the-air by TV stations. May be integrated into a television set, VCR, DVR, or set-top box.
Attachment - In e-mail, a computer file that is transmitted with an e-mail message. Note: Attachments are
converted by an e-mail manager program, or by an add-on, to a MIME (multipurpose Internet mail
extension) or binary format. The files are recovered by the recipient's e-mail manager program or by an add-
on into their original, usually application-specific, format.
Attachment Unit Interface (AUI) - In a local area network, the interface between the medium access unit
(MAU) and the data terminal equipment within a data station.
Attack - 1. An attempt to violate computer security. Note: An example of an attack is malicious logic. 2. [An]
intentional act of attempting to bypass one or more of the following security controls of an information
system (IS): nonrepudiation, authentication, integrity, availability, or confidentiality.
Attack Time - The time between (a) the instant that a signal at the input of a device or circuit exceeds the
activation threshold of the device or circuit and (b) the instant that the device or circuit reacts in a specified
manner, or to a specified degree, to the input. Note: Attack time occurs in devices such as clippers, peak
limiters, compressors, and voxes.
Attendant Access Loop - A switched circuit that provides an attendant with a manual means for call
completion and control. Note: An attendant access loop might be given a specific telephone number.
Synonym access loop.
Attendant Conference - A network-provided service feature that allows an attendant to establish a
conference connection of three or more users.
Attendant Position - The part of a switching system used by an attendant, i.e., an operator, to assist users in
call completion and use of special services.
Attention Character - In [a] trusted-computing-base (TCB) design, a character entered from a terminal that
tells the TCB the user wants a secure communications path from the terminal to some trusted node to
provide a secure service for the user.
Attention Signal - The attention signal to be used by AM, FM, and TV broadcast stations to actuate muted
receivers for inter-station receipt of emergency cuing announcements and broadcasts involving a range of
emergency contingencies posing a threat to the safety of life or property.
Attenuation - The decrease in intensity of a signal, beam, or wave as a result of absorption of energy and of
scattering out of the path to the detector, but not including the reduction due to geometric spreading. Note
1: Attenuation is usually expressed in dB. Note 2: "Attenuation" is often used as a misnomer for "
attenuation coefficient," which is expressed in dB per kilometer. Note 3: A distinction must be made as to
whether the attenuation is that of signal power or signal electric field strength.
Attenuation Coefficient - The rate of diminution of average power with respect to distance along a
transmission path. Note: The attenuation coefficient is often calculated as the sum of the absorption
coefficient and the scattering coefficient. Synonym attenuation rate.
Attenuation Constant - 1. The real part of the propagation constant in any electromagnetic propagation
medium. Note 1: The attenuation constant is usually expressed as a numerical value per unit length. Note 2:
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![Audio Dubbing - 1. In videotape editing, a process or technique employed to (a) enhance (e.g., remove noise
from, or introduce some kind of special effect into), (b) add to, or (c) replace totally, the originally recorded
audio (if any), without modifying the originally recorded video signal. 2. In audiotape editing or mixing, a
process analogous to any of the above, performed (a) on a single audio channel, or (b) on one or more audio
channels of a multi-track recording without modifying the other channel(s). 3. The copying of one or more
audio signals from one storage medium, location, or format to another with or without modification or
enhancement.
Audio-Follow-Video - A video recording, mixing or switching technique or process in which the audio signal
associated with any given video signal is recorded, switched, or mixed with that video signal.
Audio Frame - A presentation unit of the audio channel; a group of consecutive audio samples. The preferred
number of samples in an audio frame depends on the audio sample rate. These audio frames have no
relationship to the frames designated by certain audio/speech codecs.
Audio Frequency (AF) - The band of frequencies (approximately 20 Hz to 20 kHz) that, when transmitted as
acoustic waves, can be heard by the normal human ear.
Audio Response Unit (ARU) - A device that provides synthesized voice responses to dual-tone
multifrequency signaling input by processing calls based on (a) the call-originator input, (b) information
received from a host data base, and (c) information in the incoming call, such as the time of day. Note: ARUs
are used to increase the number of information calls handled and to provide consistent quality in
information retrieval.
Audit - 1. To conduct an independent review and examination of system records and activities in order to
test the adequacy and effectiveness of data security and data integrity procedures, to ensure compliance
with established policy and operational procedures, and to recommend any necessary changes. 2.
Independent review and examination of records and activities to assess the adequacy of system controls, to
ensure compliance with established policies and operational procedures, and to recommend necessary
changes in controls, policies, or procedures.
Audit Record Field - A field containing information regarding all entities in a transaction, and indicators of
the types of processing performed by those entities.
Audit Review File - A file created by executing statements included in a computer program for the explicit
purpose of providing data for auditing.
Audit Trail - 1. A record of both completed and attempted accesses and service. 2. Data in the form of a
logical path linking a sequence of events, used to trace the transactions that have affected the contents of a
record. 3. [In INFOSEC, a] chronological record of system activities to enable the reconstruction and
examination of the sequence of events and/or changes in an event. Note: Audit trail may apply to
information in an information system (IS), to message routing in a communications system, or to the transfer
of COMSEC material.
AUI - Abbreviation for attachment unit interface.
Aurora - Sporadic radiant emission from the upper atmosphere that usually occurs about the North and
South magnetic poles of the Earth. Note 1: Auroras are most intense at times of intense magnetic storms
caused by sunspot activity. The distribution of auroral intensity with altitude shows a pronounced maximum
near 100 km above the Earth. Auroras may occasionally be observed within 40° or less of the equator. Note
2: Auroras interfere with radio communications. Note 3: In the Northern hemisphere, the aurora is called the
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![Aurora Borealis (Northern Lights). In the Southern hemisphere, the aurora is called the Aurora Australis
(Southern Lights).
Authenticate - 1. To establish, usually by challenge and response, that a transmission attempt is authorized
and valid. 2. [To] verify the identity of a user, user device, or other entity, or the integrity of data stored,
transmitted, or otherwise exposed to unauthorized modification in an information system (IS), or establish
the validity of a transmission. 3. A challenge given by voice or electrical means to attest to the authenticity of
a message or transmission.
Authentication - 1. [Any] Security measure designed to establish the validity of a transmission, message, or
originator, or a means of verifying an individual's authorization to receive specific categories of information.
2. A security measure designed to protect a communications system against acceptance of a fraudulent
transmission or simulation by establishing the validity of a transmission, message, or originator. 3. Evidence
by proper signature or seal that a document is genuine and official.
Authentication Algorithm: An encryption process or tool in which the results of text encryption depend on
all relevant authentication elements.
Authentication Element - A contiguous group of characters or bits that are corruption-protected by being
processed by the authentication algorithm.
Authentication Exchange - A mechanism intended to ensure the identity of an entity by means of an
information exchange.
Authentication Information - Information used to establish the validity of a claimed identity of an entity.
Authentication Key - A (data-encryption algorithm) key used to authenticate data in accordance with specific
encryption standards.
Authentication System - [A] cryptosystem or process used for authentication.
Authenticator - 1. A symbol or group of symbols, or a series of bits, selected or derived in a prearranged
manner and usually inserted at a predetermined point within a message or transmission for the purpose of
attesting to the validity of the message or transmission. 2. A letter, numeral, group of letters or numerals, or
any combinations of these, attesting to the authenticity of a message or transmission. 3. a means used to
confirm the identity of a station, originator, or individual.
Authorization - 1. The rights granted to a user to access, read, modify, insert, or delete certain data, or to
execute certain programs. 2. Access privileges granted to a user, program, or process.
Authorization Certificate - Any of several types of attribute certificates containing information used in the
authorization process. Note: Authorization information may also be contained in a public key certificate, in
which case that public key certificate also serves as an authorization certification
Authorized Bandwidth - 1. Authorized bandwidth is, for purposes of this Manual, the necessary bandwidth
(bandwidth required for transmission and reception of intelligence) and does not include allowance for
transmitter drift or Doppler shift. 2. The maximum bandwidth authorized to be used by a station as specified
in the station license. This shall be occupied bandwidth or necessary bandwidth, whichever is greater. 3. The
maximum width of the band of frequencies permitted to be used by a station. This is normally considered to
be the necessary or occupied bandwidth, whichever is greater.
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![Authorized Frequency - 1. A frequency that is allocated and assigned by a competent authority to a specific
user for a specific purpose. 2. The frequency, or frequency range, assigned to a station by the Commission
[FCC] and specified in the instrument of authorization. See assigned frequency.
Authorized Signatory - The highest level issuer of authorization certificates in an organization. Note:
Authorized signatories are designated in a signatory certificate, which is issued to an organization by an
agreed signatory authority.
Authorized User - In security, a user who may, according to an organization's security policy, perform an
operation.
AUTODIN - Acronym for automatic digital network. See Defense Data Network.
Auto Fax Tone (CNG ) - This tone is produced by virtually all FAX machines when it dials the receiving FAX
machine’s number from memory. Older FAX machines and some current models that do not have speed-dial
memory will not produce CNG. CNG is a medium-pitch tone (1100 Hz) that last 1/2 second and repeats every
3-1/2 seconds. A FAX machine will produce CNG for about 45 seconds after it dials the receiving FAX number.
Automated Attendant - An automated attendant system allows the caller to be automatically be transferred
to a user's extension without the intervention of a receptionist. A receptionist can be reached by pressing 0
on most systems. There is a dial-by-name directory like 411 to find user on a system. The dial-by-name
directory is usually set up last name followed by first name. Once the user ID is announced you can press # or
it will automatically ring the extension. Express messaging is used when you don't want to disturb the user or
are calling a guest mailbox without a phone.
A phone can be set to "Do Not Disturb" to forward all calls directly to voicemail without ringing the
extension.
On some systems there is a message-only information so that a company can give directions to their office,
job offerings etc. Theese mailboxes are forwarded to the receptionist after each message plays or the user
can return to the main menu.
Some colleges have telephone registration where the user uses the key pad or voice response to register for
courses, check for grades, etc.
Other features of automated attendant systems include transferring to another outside line, connecting two
companies via wide area networking, incorporating Outlook Express to have Unified Messaging.
Automated Data Medium - Synonym machine-readable medium. - A medium capable of storing data in a
form that can be accessed by an automated sensing device. Note: Examples of machine-readable media
include (a) magnetic disks, cards, tapes, and drums, (b) punched cards and paper tapes, (c) optical disks, and
(d) magnetic ink characters.
Automated Information System (AIS) - 1. An assembly of computer hardware, software, firmware, or any
combination of these, configured to accomplish specific information-handling operations, such as
communication, computation, dissemination, processing, and storage of information. 2. any equipment or
interconnected system or subsystems of equipment that is used in the automatic acquisition, storage,
manipulation, management, movement, control, display, switching, interchange, transmission or reception
of data and includes computer software, firmware, and hardware. Note: Included are computers, word
processing systems, networks, or other electronic information handling systems, and associated equipment.
3. See information systems security.
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![Automatic Calling - Calling in which the elements of the selection signal are entered into the data network
contiguously at the full data signaling rate. The selection signal is generated by the data terminal equipment.
Note: A limit may be imposed by the design criteria of the network to prevent more than a permitted
number of unsuccessful call attempts to the same address within a specified period.
Automatic Calling Unit (ACU) - A device that enables equipment, such as computers and card dialers, to
originate calls automatically over a telecommunications network.
Automatic Coin Telephone System (ACTS) - is a public coin-operated telephone service that completes a
variety of phone calls, times the calls, and collects payment without the aid of an operator.
Automatic Data Handling (ADH): 1. A generalization of automatic data processing to include the aspect of
data transfer. 2. Combining data processing and data transfer.
Automatic Data Processing (ADP) - 1. An interacting assembly of procedures, processes, methods,
personnel, and equipment to perform automatically a series of data processing operations on data. Note:
The data processing operations may result in a change in the semantic content of the data. 2. Data
processing by means of one or more devices that use common storage for all or part of a computer program,
and also for all or part of the data necessary for execution of the program; that execute user-written or user-
designated programs; that perform user-designated symbol manipulation, such as arithmetic operations,
logic operation, or character-string manipulations; and that can execute programs that modify themselves
during their execution. Note: Automatic data processing may be performed by a stand-alone unit or by
several connected units. 3. Data processing largely performed by automatic means. 4. That branch of science
and technology concerned with methods and techniques relating to data processing largely performed by
automatic means.
Automatic Data Processing Equipment (ADPE) - Any equipment or interconnected system or subsystems of
equipment that is used in the automatic acquisition, storage, manipulation, management, movement,
control, display, switching, interchange, transmission, or reception, of data or information (i) by a Federal
agency, or (ii) under a contract with a Federal agency which (i) requires the use of such equipment, or (ii)
requires the performance of a service or the furnishing of a product which is performed or produced making
significant use of such equipment. Such term includes (i) computer, (ii) ancillary equipment, (iii) software,
firmware, and similar procedures, (iv) services, including support services, and (v) related resources as
defined by regulations issued by the Administrator for General Services. . . . [Public Law 99-500, Title VII, Sec.
822 (a) Section 111(a) of the Federal Property and Administrative Services Act of 1949 (40 U.S.C. 759(a))
revised.]
Automatic Dialing - See automatic calling unit.
Automatic Digital Network (AUTODIN) - Formerly, a worldwide data communications network of the
Defense Communications System, now replaced by the Defense Switched Network (DSN).
Automatic Error Correction - See error-correcting code.
Automatic Exchange - In a telephone system, an exchange in which communications among users are
effected by means of switches set in operation by the originating user equipment without human
intervention at the central office or branch exchange.
Automatic Fax Switch - A device that allows a single phone line to be shared for multiple devices. Common
applications include any variation of voice, a fax machine, fax/modem and/or modem(s). Incoming calls are
automatically routed to the proper device(s). If the call comes in and it is a fax call, the call is automatically
routed to the fax machine or fax.modem. If the call is a modem call, it is routed to the correct modem. Voice
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![that provides the billing number of the line or trunk that originated a call. 3. A system that identifies the
billing account for a call. For 911 systems, the ANI identifies the calling party and may be used as a call back
number.
Automatic Operation - The functioning of systems, equipment, or processes in a desired manner at the
proper time under control of mechanical or electronic devices that operate without human intervention.
Automatic Personal Deregistration - The process by which a user's location registration is automatically
canceled without any explicit action from the user.
Automatic Personal Registration - The process by which a user's location registration is automatically
updated without any explicit action from the user.
Automatic Redial - A service feature that allows the user to dial, by depressing a single key or a few keys, the
most recent telephone number dialed at that instrument. Note: Automatic redial is often associated with the
telephone instrument, but may be provided by a PBX, or by the central office. Synonym last number redial.
Automatic Reload - See bootstrap.
Automatic Remote Rekeying - [In INFOSEC, a] procedure to rekey a distant crypto-equipment electronically
without specific actions by the receiving terminal operator. [INFOSEC-99] Note: Automatic remote rekeying
may also apply to non-crypto devices.
Automatic Remote Reprogramming and Rekeying - The procedure by which distant equipment is
reprogrammed or rekeyed electronically without specific actions by the receiving terminal.
Automatic Repeat-Request (ARQ) - See ARQ.
Automatic Ringdown Circuit - A circuit providing priority telephone service, typically for key personnel; the
circuit is activated when the telephone handset is removed from the cradle causing a ringing signal to be
sent to the distant unit(s). See verified off-hook.
Automatic Route Selection (ARS) - Electronic or mechanical selection and routing of outgoing calls without
human intervention.
Automatic Secure Voice Communications Network (AUTOSEVOCOM) - A worldwide, switched, secure voice
network developed to fulfill DOD long-haul, secure voice requirements.
Automatic Sequential Connection - A service feature in which the terminals at each of a set of specified
addresses are automatically connected, in a predetermined sequence, to a single terminal at a specified
address.
Automatic Signaling Service - Synonym hotline.
Automatic Sounding - The testing of selected channels or paths by providing a very brief beacon-like
identifying broadcast that may be used by other stations to evaluate connectivity, propagation, and
availability, and to identify known working channels for possible later use for communications or calling.
Note 1: Automatic soundings are primarily intended to increase the efficiency of the automatic link
establishment (ALE) function, thereby increasing system throughput. Note 2: Sounding information is used
for identifying the specific channel to be used for a particular ALE connectivity attempt.
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![Automatic Switching System - 1. In data communications, a switching system in which all the operations
required to execute the three phases of information-transfer transactions are automatically executed in
response to signals from a user end-instrument. Note: In an automatic switching system, the information-
transfer transaction is performed without human intervention, except for initiation of the access phase and
the disengagement phase by a user. 2. In telephony, a system in which all the operations required to set up,
supervise, and release connections required for calls are automatically performed in response to signals from
a calling device.
Automatic Voice Network (AUTOVON) - Formerly, the principal long-haul, unsecure voice communications
network within the Defense Communications System, now replaced by the Defense Switched Network (DSN).
Automation - 1. The implementation of processes by automatic means. 2. The investigation, design,
development, and application of methods of rendering processes automatic, self-moving, or self-controlling.
3. The conversion of a procedure, a process, or equipment to automatic operation.
Autonomous System - Internet (TCP/IP) terminology for a collection of gateways (routers) that fall under one
administrative entity and that cooperate using a common interior gateway protocol (IGP). [Bahorsky] Note:
Routers pertaining to different autonomous systems must agree on a common exterior gateway protocol in
order to communicate with each other effectively.
Auto-Reply - In e-mail systems, a message sent automatically upon receipt of incoming e-mail. Note: Auto-
replies are used to acknowledge delivery of e-mail and to provide receipts for e-mail messages.
AUTOSEVOCOM - Acronym for Automatic Secure Voice Communications Network.
AUTOVON - Acronym for Automatic Voice Network. Superseded by Defense Switched Network.
Auxiliary Operation - An offline operation performed by equipment not under control of the processing unit.
Auxiliary Power - Electric power that is provided by an alternate source and that serves as backup for the
primary power source at the station main bus or prescribed sub-bus. Note 1: An offline unit provides
electrical isolation between the primary power source and the critical technical load whereas an online unit
does not. Note 2: A Class A power source is a primary power source, i.e., a source that assures an essentially
continuous supply of power. Note 3: Types of auxiliary power services include Class B, a standby power plant
to cover extended outages of the order of days; Class C, a 10-to-60-second quick-start unit to cover short-
term outages of the order of hours; and Class D, an uninterruptible non-break unit using stored energy to
provide continuous power within specified voltage and frequency tolerances.
Auxiliary Storage - 1. Storage that is available to a processor only through its input / output channels. 2. In a
computer, any storage that is not internal memory, i.e., is not random access memory (RAM). Note:
Examples of auxiliary storage media are magnetic diskettes, optical disks including CD ROM, and magnetic
tape cassettes.
Availability - 1. The degree to which a system, subsystem, or equipment is operable and in a committable
state at the start of a mission, when the mission is called for at an unknown, i.e., a random, time. Note 1: The
conditions determining operability and committability must be specified. Note 2: Expressed mathematically,
availability is 1 minus the unavailability. 2. The ratio of (a) the total time a functional unit is capable of being
used during a given interval to (b) the length of the interval. Note 1: An example of availability is 100/168 if
the unit is capable of being used for 100 hours in a week. Note 2: Typical availability objectives are specified
in decimal fractions, such as 0.9998. 3. Timely, reliable access to data and information services for authorized
users.
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![Background Noise - The total system noise in the absence of information transmission.
Background Processing - The execution of lower priority computer programs when higher priority programs
are not using the system resources. Note: Priorities may be assigned by system software, application
software, or the operator.
Backhaul - 1. The practice of routing telecommunications traffic beyond its intended destination, and then
back to the intended destination, usually for the purpose of taking advantage of tariffs or prices that are
lower than those afforded by direct routing. 2. In security, to bring a call that has been routed along a
particular path (usually via satellite) to some earlier position in the switching sequence (also using satellites).
Note: The technique supports CALEA, the Communications Assistance to Law Enforcement Act and LAES,
Lawfully Authorized Electronic Surveillance. 3. In commercial telephone networks, referring to a trunk or line
between two central offices that may not share the same facilities or geographic location, and which trunk is
used to support special services, e.g., orderwires, off-premises extensions, common exchange number
routing, or least-cost routing of customer centrex services. 4. In mission programs requiring contingency
networking, referring to a link that provides feedback to the mission control center to verify that the
transmission via a primary communications has been successful. Note: In cases where the primary path fails
to deliver the transmission, the communications may occur over the backhaul connection or an alternative
network connection. 5. In contingency networking, an alternative connection that is routed via a diversified
path, e.g., an alternative frequency, satellite facility, cable, trunk, or time slot.
Backscattering - 1. Radio wave propagation in which the direction of the incident and scattered waves,
resolved along a reference direction (usually horizontal) are oppositely directed. A signal received by
backscattering is often referred to as "backscatter." 2. In optics, the scattering of light into a direction
generally opposite to the original one.
Back-to-Back Connection - 1. A direct connection between the output of a transmitting device and the input
of an associated receiving device. Note: When used for equipment measurements or testing purposes, such
a back-to-back connection eliminates the effects of the transmission channel or medium. 2. A direct
connection between the output of a receiving device and the input to a transmitting device. Note: The term
"direct," as used in both definitions, may be construed as permitting a passive device such as a pad
(attenuator) to accommodate power level constraints.
Backup - 1. [A] copy of files and programs made to facilitate recovery, if necessary. 2. See backup file.
Backup File - A copy of a file made for purposes of later reconstruction of the file, if necessary. Note: A
backup file may be used for preserving the integrity of the original file and may be recorded on any suitable
medium. Synonym job-recovery control file.
Backward Channel - 1. In data transmission, a secondary channel in which the direction of transmission is
constrained to be opposite to that of the primary, i.e., the forward (user-information) channel. Note: The
direction of transmission in the backward channel is restricted by the control interchange circuit that
controls the direction of transmission in the primary channel. 2. In a data circuit, the channel that passes
data in a direction opposite to that of its associated forward channel. Note 1: The backward channel is
usually used for transmission of supervisory, acknowledgement, or error-control signals. The direction of
flow of these signals is opposite to that in which user information is being transferred. Note 2: The backward-
channel bandwidth is usually less than that of the primary channel, i.e., the forward (user information)
channel.
Backward Indicator Bit (BIB) - A signal unit (or sequence of bits) that (by changing its status) is used to
request retransmission by the remote end whenever it receives a signal unit that is out of sequence.
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![Backward Recovery - The reconstruction of an earlier version of a file by using a newer version of data
recorded in a journal.
Backward Sequence Number (BSN) - A field in a signal unit that contains the forward sequence number of a
correctly received signal unit being acknowledged in the signal unit that is being returned to the sender.
Backward Signal - A signal sent from the called to the calling station, i.e., from the original data sink to the
original data source. Note: Backward signals are usually sent via a backward channel and may consist of
supervisory, acknowledgment, or control signals.
Backward Supervision - The use of supervisory signal sequences from a secondary to a primary station.
Bacterium - A program that attempts to propagate itself by e-mailing a copy of itself to e-mail addresses
found on a recipient's hard drive. This is done without the consent or knowledge of the recipient. Note: In
many cases, this type of program does not attempt to cause any direct damage to user's system, but rather
attempts to overload the e-mail distribution system, much as a successful chain letter would do to the postal
system. Synonym [in cryptosystems] chain letter.
Bad Sectoring - A technique for copy protection in which bad sectors are intentionally written on a diskette.
Balance - In electrical circuits and networks, to adjust the impedance to achieve specific objectives, such as
to reach specified return loss objectives at a hybrid junction of two-wire and four-wire circuits.
Balanced - Pertaining to electrical symmetry.
Balanced Code - 1. In PCM systems, a code constructed so that the frequency spectrum resulting from the
transmission of any code word has no dc component. 2. In PCM, a code that has a finite digital sum variation.
Balanced Line - A transmission line consisting of two conductors in the presence of ground, capable of being
operated in such a way that when the voltages of the two conductors at all transverse planes are equal in
magnitude and opposite in polarity with respect to ground, the currents in the two conductors are equal in
magnitude and opposite in direction. Note: A balanced line may be operated in an unbalanced condition.
Synonym balanced signal pair.
Balanced Modulator - A modulator constructed so that the carrier is suppressed and any associated carrier
noise is balanced out. Note 1: The balanced modulator output contains only the sidebands. Note 2: Balanced
modulators are used in AM transmission systems.
Balanced Signal Pair - Synonym balanced line. A transmission line consisting of two conductors in the
presence of ground, capable of being operated in such a way that when the voltages of the two conductors
at all transverse planes are equal in magnitude and opposite in polarity with respect to ground, the currents
in the two conductors are equal in magnitude and opposite in direction. Note: A balanced line may be
operated in an unbalanced condition.
Balance Return Loss - 1. A measure of the degree of balance between two impedances connected to two
conjugate sides of a hybrid set, coil, network, or junction. 2. A measure of the effectiveness with which a
balancing network simulates the impedance of a two-wire circuit at a hybrid coil.
Balancing Network - 1. In a hybrid set, hybrid coil, or resistance hybrid, a circuit used to match, i.e., to
balance, the impedance of a uniform transmission line, i.e., twisted metallic pair, over a selected range of
frequencies. Note: A balancing network is required to ensure isolation between the two ports of the four-
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![automatically prefixed to, and printed out as part of, a printing job, as a means of identifying uniquely the
output belonging to a given user of a shared printer. Note: A banner may, in addition to identifying the
owner of the printout, also identify the file name, queue, and server involved. Synonym banner page. 4. [A]
display on an information system (IS) that sets parameters for system or data use.
Banner Page - Synonym banner. In computer networking, a page that is automatically prefixed to, and
printed out as part of, a printing job, as a means of identifying uniquely the output belonging to a given user
of a shared printer. Note: A banner may, in addition to identifying the owner of the printout, also identify the
file name, queue, and server involved.
Bar Code - A code representing characters by sets of parallel bars of varying thickness and separation that
are read optically by transverse scanning. Note: Bar code uses include identifying merchandise, sorting mail,
and inventorying supplies.
Barge-In Protection- When installed on an incoming telephone line before ALL telephone equipment
(extension wall jacks or multi-line phone systems), The Barge-In Protection feature will protect any voice or
data call from being accessed by other telephone equipment on the same line. Any phone device that goes
"off-hook" during a conversation or data transmission will receive a silent line or a busy signal depending on
the product.
Barn Doors - This term is used in television production to describe the effect that occurs when a 4:3 image is
viewed on a 16:9 screen. When this happens, viewers see black bars, or, "barn doors," on the sides of the
screen.
Barrage Jamming - Jamming accomplished by transmitting a band of frequencies that is large with respect to
the bandwidth of a single emitter. Note: Barrage jamming may be accomplished by presetting multiple
jammers on adjacent frequencies or by using a single wideband transmitter. Barrage jamming makes it
possible to jam emitters on different frequencies simultaneously and reduces the need for operator
assistance or complex control equipment. These advantages are gained at the expense of reduced jamming
power at any given frequency.
Base - 1. In the numeration system commonly used in scientific notation, the real number that is raised to a
power denoted by the exponent and then multiplied by the coefficient to determine the value of the number
represented without the use of exponents. Note: An example of a base is the number 6.25 in the expression
1.5
2.70 × 6.25 42.19. The 2.70 is the coefficient and the 1.5 is the exponent. In the decimal numeration
system, the base is 10 and in the binary numeration system, the base is 2. The value e 2.718 is the natural
base. 2. A reference value. 3. A number that is multiplied by itself as many times as indicated by an
exponent.
Base Address - 1. An address that is used as the origin in the calculation of addresses in the execution of a
computer program. 2. A given address from which an absolute address is derived by combination with a
relative address. Note: Base addresses are primarily used by computer programmers rather than by
computer users.
Baseband - 1. The original band of frequencies produced by a transducer, such as a microphone, telegraph
key, or other signal-initiating device, prior to initial modulation. Note 1: In transmission systems, the
baseband signal is usually used to modulate a carrier. Note 2: Demodulation re-creates the baseband signal.
Note 3: Baseband describes the signal state prior to modulation, prior to multiplexing, following
demultiplexing, and following demodulation. Note 4: Baseband frequencies are usually characterized by
being much lower in frequency than the frequencies that result when the baseband signal is used to
modulate a carrier or subcarrier. 2. In facsimile, the frequency of a signal equal in bandwidth to that between
zero frequency and maximum keying frequency.
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![amplification and selectivity (filtering) are provided. 2. A frequency produced by mixing two or more signals
in a nonlinear device.
Beeping - Synonym paging, radio paging. - The use of a pocket-size radio receiver capable of alerting its
wearer that there is a phone call, either from a displayed phone number or to a predesignated number.
Note: Beeping (Radio paging) may be considered a subset of paging.
B8ZS (bipolar 8-zero substitution, also called binary 8-zero substitution, clear channel, and clear 64) - is an
encoding method used on T1 circuits that inserts two successive ones of the same voltage - referred to as a
bipolar violation - into a signal whenever eight consecutive zeros are transmitted. The device receiving the
signal interprets the bipolar violation as a timing mark, which keeps the transmitting and receiving devices
synchronized. Ordinarily, when successive ones are transmitted, one has a positive voltage and the other has
a negative voltage.
B8ZS is based on an older encoding method called alternate mark inversion (AMI). AMI is used with
Dataphone Digital Service, the oldest data service still in use that uses 64 Kbps channels. AMI, however,
requires the use of 8 Kbps of the 64 Kbps of each channel to maintain synchronization. In a T1 circuit, there
are 24 channels. This loss adds up to 192 Kbps, which means that in reality only 56 Kbps is available for data
transmission. B8ZS uses bipolar violations to synchronize devices, a solution that does not require the use of
extra bits, which means a T1 circuit using B8ZS can use the full 64 Kbps for each channel for data. B8ZS is not
compatible with older AMI equipment.
T1 technology is used in the United States and Japan. In Europe, a comparable technology called E1 provides
32 channels instead of 24 and uses an encoding scheme called high-density bipolar 3 (HDB3) instead of B8ZS.
A T-carrier line code in which bipolar violations are deliberately inserted if user data contains a string of 8 or
more consecutive zeros. Note 1: B8ZS is used to ensure a sufficient number of transitions to maintain system
synchronization when the user data stream contains an insufficient number of "ones" to do so. Note 2: B8ZS
is used in the European hierarchy at the T1 rate.
bel (B): A unit of measure of ratios of power levels, i.e., relative power levels. Note 1: The number of bels for
a given ratio of power levels is calculated by taking the logarithm, to the base 10, of the ratio.
Mathematically, the number of bels is calculated as B = log10(P 1/P 2) where P 1 and P 2 are power levels. Note
2: The dB, equal to 0.1 B, is a more commonly used unit.
Bell (BEL) Character - A transmission control character that is used when there is a need to call for user or
operator attention in a communications system, and that usually activates an audio or visual alarm or other
attention-getting device.
Bell-La Padula Security Model - [A] formal state-transition model of a computer security policy that
describes a formal set of access controls based on information sensitivity and subject authorizations.
Bell Operating Company - (see BOC). Historically, any of the 22 operating companies that were divested
from AT&T by court order. Note: Cincinnati Bell Telephone Co. and Southern New England Bell Telephone Co.
were not included.
Bell Operating Company is a term for any of the 22 original companies (or their successors) that were
created when AT&T was broken up in 1983 and given the right to provide local telephone service in a given
geographic area. The companies had previously existed as subsidiaries of AT&T and were called the "Bell
System." The purpose of the breakup was to create competition at both the local and long-distance service
levels. BOCs compete with other, independent companies to sell local phone service. In certain areas, long-
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![distance companies, including AT&T, can now compete for local service. Collectively, companies offering
local phone service are referred to legally as local exchange carriers (local exchange carrier).
BOCs are not allowed to manufacture equipment and were initially not allowed to provide long-distance
service. The Telecommunications Act of 1996 now permits them to engage in long-distance business under
certain circumstances. As of 1996, the BOCs consisted of original and successor companies to:
Bell Telephone Company of Nevada, Illinois Bell, Indiana Bell, Michigan Bell, New England Telephone and
Telegraph Company, New Jersey Bell, New York Telephone Company, U S West Communications Company,
South Central Bell, Southern Bell, Southwestern Bell, Bell Telephone of Pennsylvania, The Chesapeake and
Potomac Telephone Company, The Chesapeake and Potomac Telephone Company of Maryland, The
Chesapeake and Potomac Telephone Company of Virginia, The Diamond State Telephone Company, The
Ohio Bell Telephone Company, The Pacific Telephone and Telegraph Company, and the Wisconsin Telephone
Company.
Bend Loss - See macrobend loss, microbend loss. In an optical fiber, that loss attributable to macrobending.
Synonym curvature loss.
Benign - A condition of cryptographic data that cannot be compromised by human access.
Benign Environment - [In security, a] nonhostile environment that may be protected from external hostile
elements by physical, personnel, and procedural security countermeasures.
BER (bit error rate) - In telecommunication transmission, the BER is the percentage of bits that have errors
relative to the total number of bits received in a transmission, usually expressed as ten to a negative power.
For example, a transmission might have a BER of 10 to the minus 6, meaning that, out of 1,000,000 bits
transmitted, one bit was in error. The BER is an indication of how often a packet or other data unit has to be
retransmitted because of an error. Too high a BER may indicate that a slower data rate would actually
improve overall transmission time for a given amount of transmitted data since the BER might be reduced,
lowering the number of packets that had to be resent. BER - Abbreviation for bit error ratio.
BERT - Acronym for bit error ratio tester. - A testing device that compares a received data pattern with a
known transmitted pattern to determine the level of transmission quality.
Beta Test - A secondary software product test involving select or voluntary participants before the product is
marketed to the general public. Note: Participants agree to provide detailed feedback to the product's
manufacturer in return for their being allowed to preview, use, and contribute to the final form of the
product.
BETRS - Abbreviation for basic exchange telecommunications radio service. - A commercial service that can
extend telephone service to rural areas by replacing the local loop with radio communications. Note: In the
BETRS, non-government ultra high frequency (UHF) and very high frequency (VHF) common carrier and the
private radio service frequencies are shared.
Between-the-lines Entry - Unauthorized access to a momentarily inactive terminal, of a legitimate user,
assigned to a communications channel.
BEX - Abbreviation for broadband exchange. A communications switch capable of interconnecting channels
having bandwidths greater than voice bandwidth.
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![Binary Number - A number that is expressed in binary notation and is usually characterized by the
arrangement of bits in sequence, with the understanding that successive bits are interpreted as coefficients
of successive powers of the base 2.
Binary String - Synonym bit string. - A sequence of bits. Note: In a bit stream, individual bit strings may be
separated by data delimiters.
Binary Synchronous (bi-sync) Communication - A character-oriented, data-link-layer protocol. Note: The bi-
sync protocol is being phased out of most computer communication networks in favor of bit-oriented
protocols such as SDLC, HDLC, and ADCCP.
Binding - 1. In computer, communications, and automatic data processing systems, assigning a value or
referent to an identifier. Note: Examples of binding include assigning a value to a parameter, assigning an
absolute address to a virtual or relative address, and assigning a device identifier to a symbolic address or
label. 2. [In security, the] process of associating a specific communications terminal with a specific
cryptographic key or associating two related elements of information.
Biometric - Any specific and uniquely identifiable physical human characteristic, e.g., of the retina, iris,
acoustic spectrum of the voice (i.e., voiceprint), fingerprint(s), handwriting, pattern of finger lengths, etc.,
that may be used to validate the identity of an individual. Note: Biometrics provide a highly secure means of
identification, for purposes of security involving, e.g., Internet communications and cryptosystems.
Biometrics - Automated methods of authenticating or verifying an individual based upon a physical or
behavioral characteristic.
Biphase Modulation - Synonym phase-shift keying. - 1. In digital transmission, angle modulation in which the
phase of the carrier is discretely varied in relation either to a reference phase or to the phase of the
immediately preceding signal element, in accordance with data being transmitted. 2. In a communications
system, the representing of characters, such as bits or quaternary digits, by a shift in the phase of an
electromagnetic carrier wave with respect to a reference, by an amount corresponding to the symbol being
encoded. Note 1: For example, when encoding bits, the phase shift could be 0° for encoding a "0," and 180°
for encoding a "1," or the phase shift could be -90 for "0" and +90° for a "1," thus making the
representations for "0" and "1" a total of 180° apart. Note 2: In PSK systems designed so that the carrier can
assume only two different phase angles, each change of phase carries one bit of information, i.e., the bit rate
equals the modulation rate. If the number of recognizable phase angles is increased to 4, then 2 bits of
information can be encoded into each signal element; likewise, 8 phase angles can encode 3 bits in each
signal element.
Bipolar 8-Zero Substitution (B8ZS, binary 8-zero substitution, clear channel, and clear 64) - is an encoding
method used on T1 circuits that inserts two successive ones of the same voltage - referred to as a bipolar
violation - into a signal whenever eight consecutive zeros are transmitted. The device receiving the signal
interprets the bipolar violation as a timing mark, which keeps the transmitting and receiving devices
synchronized. Ordinarily, when successive ones are transmitted, one has a positive voltage and the other has
a negative voltage (see B8ZS).
Bipolar Signal - 1. A signal that may assume either of two polarities, neither of which is zero. Note 1: A
bipolar signal may have a two-state non-return-to-zero (NRZ) or a three-state return-to-zero (RZ) binary
coding scheme. Note 2: A bipolar signal is usually symmetrical with respect to zero amplitude, i.e., the
absolute values of the positive and negative signal states are nominally equal. 2. A pseudoternary signal,
conveying binary digits, in which successive "ones" (marks, pulses) are of alternating, positive (+) and
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![given polarity or phase at one stage in a circuit, the 1 is represented by the opposite polarity or phase at the
next stage.
Bitmap - In computer graphics, a representation of an image (which category includes characters) by code or
a coding scheme that defines (a) the position of pixels by row (horizontal position) and column (vertical
position), and (b) individual pixel characteristics such as gray scale and color. Loosely synonymous with
raster.
Bitmapped Graphics - In computer graphics, an image created with, or represented by, a matrix of pixels.
Synonym [loosely] raster graphics.
Bit Masking - In embedded ADPCM (adaptive differential pulse-code modulation), the process of discarding
the enhancement bits.
BITNET - Abbreviation for Because It's Time NETwork. An early (ca. 1981) store-and-forward digital
communications network interconnecting universities and research institutions worldwide. Note: BITNET,
which is now obsolete, had a purpose akin to that of the present Internet, but was not nearly so robust, and
at a speed of only 9600 b/s, it could not support the data rates presently attainable via the Internet.
Bit Padding - is the addition of one or more extra bits to a transmission or storage unit to make it conform to
a standard size. Some sources identify bit padding as a type of bit stuffing.
Bit Pairing - The practice of establishing, within a code set, a number of subsets that have an identical bit
representation except for the state of a specified bit. Note: An example of bit pairing occurs in the
International Alphabet No. 5 and the American Standard Code for Information Interchange (ASCII), where the
upper case letters are related to their respective lower case letters by the state of bit six.
Bit Period (T) - The amount of time required to transmit a logical one or a logical zero
Bit Position - A character position in a word in a binary notation.
Bit Rate (BR) - 1. In a bit stream, the number of bits occurring per unit time, usually expressed in bits per
second. Note: For n-ary operation, the bit rate is equal to log 2 n times the rate (in bauds), where n is the
number of significant conditions in the signal. 2. The rate of transmission of information in binary (two state)
form in bits per unit time.
Bit-Rate•Distance Product - See bandwidth•distance product. - Of an optical fiber, under specified
launching and cabling conditions, at a specified wavelength, a figure of merit equal to the product of the
fiber's length and the 3-dB bandwidth of the optical signal. Note 1: The bit-rate•distance product is usually
stated in megahertz • kilometer (MHz •km) or gigahertz •kilometer (GHz•km). Note 2: The bit-rate•distance
product, which is normalized to 1 km, is a useful figure of merit for predicting the effective fiber bandwidth
for other lengths, and for concatenated fibers.
Bit Robbing - In digital carrier systems, the practice or technique of preempting, at regular intervals and for
the purpose of transmitting signaling information, one digit time slot that (a) is associated with the given
user channel for which signaling is required, and (b) is used primarily for transporting encoded speech via
that channel. Note 1: Bit robbing is an option in networks compatible with T-carrier, e.g., an ISDN. Note 2: In
conventional T-carrier systems, bit robbing uses, in every sixth frame, the time slot associated with the least
significant bit. Synonym speech digit signaling.
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![For example, the timing or bit rate of T-carrier system signals is constantly synchronized between any
terminal device and an adjacent repeater or between any two repeaters. The synchronization is achieved by
detecting the transition in polarity for 1 bits in the data stream. (T-1 signalling uses bipolar signaling, where
each successive bit with a value of 1 is represented by voltage with a reverse polarity from the previous bit.
Bits with a value of 0 are represented by a no-voltage time slot.) If more than 15 bits in a row are sent with a
0 value, this "lull" in 1 bits that the system depends on for synchronization may be long enough for two end
points to become out of synchronization. To handle this situation (the sequence of more than 15 0 bits), the
signal is "stuffed" with a short, unique bit pattern (which includes some 1 bits) that is recognized as a
synchronization pattern. The receiving end removes the stuffed bits and restores the bit stream to its original
sequence.
In another example of bit stuffing, a standard HDLC packet begins and ends with 01111110. To make sure
this sequence doesn't appear again before the end of the packet, a 0 is inserted after every five consecutive
1s.
Bit stuffing is defined by some to include bit padding or the addition of bits to a tranmission to make the
tranmission unit conform to a standard size.
Note 1: Stuffed bits should not be confused with overhead bits. Note 2: In data transmission, bit stuffing is
used for various purposes, such as for synchronizing bit streams that do not necessarily have the same or
rationally related bit rates, or to fill buffers or frames. The location of the stuffing bits is communicated to
the receiving end of the data link, where these extra bits are removed to return the bit streams to their
original bit rates or form. Bit stuffing may be used to synchronize several channels before multiplexing or to
rate-match two single channels to each other. Synonym positive justification.
Bit Stuffing Rate - See nominal bit stuffing rate. - The rate at which stuffing bits are inserted when both the
input and output bit rates are at their nominal values.
Bit Synchronization - Synchronization in which the decision instant is brought into alignment with the
received bit, i.e., the basic signaling element.
Bit Synchronous Operation - Operation in which data circuit terminating equipment (DCE), data terminal
equipment (DTE), and transmitting circuits are all operated in bit synchronism with a clock. Note 1: In bit
synchronous operation, clock timing is usually delivered at twice the modulation rate, and one bit is
transmitted or received during each clock cycle. Note 2: Bit synchronous operation is sometimes erroneously
referred to as digital synchronization.
BIU - Abbreviation for bus interface unit. See network interface device.
BLACK - 1. [A] designation applied to telecommunications and automated information systems, and to
associated areas, circuits, components, and equipment, in which only unclassified signals are processed.
Note: Encrypted signals are unclassified. 2. Designation applied to information systems, and to associated
areas, circuits, components, and equipment, in which national security information is not processed.
Blackbody - A totally absorbing body that does not reflect radiation. Note: In thermal equilibrium, a
blackbody absorbs and radiates at the same rate; the radiation will just equal absorption when thermal
equilibrium is maintained.
Black Box - is any device, sometimes highly important, whose workings are not understood by or accessible
to its user. According to Edward Tenner, writing in The Washington Post, the first black box was a gun sight
carried on World War II Flying Fortresses, with hidden components that corrected for environmental
variables, such as wind speed. The crew probably didn't know how the device worked, but they knew it
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![Blurring - In television and video systems, a global distortion over the entire image, characterized by reduced
sharpness of edges and limited spatial detail.
BNC connector - A type of bayonet (twist-lock) coaxial connector commonly used in applications involving
small (e.g., RG-59, RG-62) coaxial cables.
Board - In computers, a board, depending on usage, can be short for motherboard, the physical arrangement
of a computer's basic components and circuitry, or it can refer to an expansion board (or card or adapter),
which fits into one of the computer's expansion slots and provides expanded capability.
BOC (Bell operating company) Abbreviation for Bell Operating Company. - is a term for any of the 22
original companies (or their successors) that were created when AT&T was broken up in 1983 and given the
right to provide local telephone service in a given geographic area. The companies had previously existed as
subsidiaries of AT&T and were called the "Bell System." The purpose of the breakup was to create
competition at both the local and long-distance service levels. BOCs compete with other, independent
companies to sell local phone service. In certain areas, long-distance companies, including AT&T, can now
compete for local service. Collectively, companies offering local phone service are referred to legally as local
exchange carriers (local exchange carrier).
BOCs are not allowed to manufacture equipment and were initially not allowed to provide long-distance
service. The Telecommunications Act of 1996 now permits them to engage in long-distance business under
certain circumstances. As of 1996, the BOCs consisted of original and successor companies to:
Bell Telephone Company of Nevada, Illinois Bell, Indiana Bell, Michigan Bell, New England Telephone and
Telegraph Company, New Jersey Bell, New York Telephone Company, U S West Communications Company,
South Central Bell, Southern Bell, Southwestern Bell, Bell Telephone of Pennsylvania, The Chesapeake and
Potomac Telephone Company, The Chesapeake and Potomac Telephone Company of Maryland, The
Chesapeake and Potomac Telephone Company of Virginia, The Diamond State Telephone Company, The
Ohio Bell Telephone Company, The Pacific Telephone and Telegraph Company, and the Wisconsin Telephone
Company.
Historically, a BOC is any of the 22 operating companies that were divested from AT&T by court order. Note:
Cincinnati Bell Telephone Co. and Southern New England Bell Telephone Co. were not included.
Boltzmann's Constant (k): The number that relates the average energy of a molecule to its absolute
-23
temperature. Note: Boltzmann's constant is approximately 1.38 × 10 J/K (joules/ kelvin).
Bond - An electrical connection that provides a low-resistance path between two conducting surfaces.
Bonding - 1. In electrical engineering, the process of connecting together metal parts so that they make low
resistance electrical contact for direct current and lower frequency alternating currents. [JP1] 2. The process
of establishing the required degree of electrical continuity between two or more conductive surfaces that
are to be joined.
Bookmark - A name or address of an Internet resource, stored in a software file at a user's site, e.g., in a
desktop computer, for convenient future use. Note: An example of a bookmark is an entry in a bookmark file
(or bookmark list) such as maintained within or by a Web browser for the convenience of the user in
revisiting a previously visited Web site.
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![messages are sent to them (e.g., the messages can be sent as they are received by the list
server or saved, compiled, and then sent).
pokerbot A bot that automatically plays the game of poker in various on-line forums. Note: Many on-line
games have had bots designed to play them, e.g., a chessbot or a bridgebot.
portal A bot that serves as a starting point for browsers. A portal will often include a search engine.
robot See bot.
robotic Synonym search engine.
librarian
search bot Synonym search engine.
search A bot that accepts words or phrases from an Internet user via a browser, searches a database
engine for matching web pages, and displays a list of those pages that match the search criteria.
spambot A bot that sends unwanted, unrequested, and usually repetitive e-mail or messages directly to
a user or to a message forum. In most cases, this unwanted information is commercial
advertisements, although the message can be propaganda supporting a cause or nonsense
messages designed to fill up a user's mailbox.
spider Synonym web crawler.
web crawler A bot that searches the world wide web for new and updated web pages. Found pages are
categorized by subject and placed in a database. Typically, an associated search engine will
access that database.
wizard A bot that has some ability to make informed decisions. For example, a wizard might determine
the city from which you are accessing the network and provide to you the current weather
report for your area.
Bounce - To return, to the sender, e-mail that is, for whatever reason, undeliverable to its intended
destination. Note 1: There are various reasons why e-mail may be bounced. Examples are an incorrect
address, problems with local network facilities, and problems with telecommunications links. Note 2:
Bounced e-mail is often accompanied by an error message describing the reason that it was not delivered.
Bouncing Busy Hour (BBH) - The hour in which the highest usage is measured for any day. The readings are
on the hour or half hour. The selected clock hour will vary from day to day, depending on the measured
usage.
Boundary - 1. [In security,] Software, hardware, or a physical barrier that limits access to a system or part of
a system.2. Synonym [in networking] section boundary.
Bound Mode - In an optical fiber, a mode that (a) has a field intensity that decays monotonically in the
transverse direction everywhere external to the core and (b) does not lose power to radiation. Note: Except
for single-mode fibers, the power in bound modes is predominantly contained in the core of the
fiber.Synonyms guided mode, trapped mode.
Bound Ray - In an optical fiber, a ray that is confined primarily to the core.
BPI ( bpi) - See bits per inch. - A unit used to express the linear bit density of data in storage. Note: The
abbreviation " bpi" is not in accordance with international standards, and is therefore deprecated.
BPS - (See bits per second). - In data communications, bits per second is a common measure of data speed
for computer modems and transmission carriers. As the term implies, the speed in bps is equal to the
number of bits transmitted or received each second.
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![sections of a communications circuit. Such conversion is necessary when repeaters are introduced in a 2-wire
circuit.
Bridging Connection - A parallel connection used to extract some of the signal energy from a circuit, usually
with negligible effect on the normal operation of the circuit.
Bridging Loss - At a given frequency, the loss that results when an impedance is connected across a
transmission line. Note: Bridging loss is expressed as the ratio, in dB, of the signal power delivered, prior to
bridging, to a given point in a system downstream from the bridging point, to the signal power delivered to
the given point after bridging.
Brightness - An attribute of visual perception in which a source appears to emit a given amount of light. Note
1: "Brightness" should be used only for nonquantitative references to physiological sensations and
perceptions of light. Note 2: "Brightness" was formerly used as a synonym for the photometric term
"luminance" and (incorrectly) for the radiometric term " radiance."
Brillouin Diagram - See Brillouin scattering. - In a physical medium, scattering of lightwaves, caused by
thermally driven density fluctuations. Note: Brillouin scattering may cause frequency shifts of several
gigahertz at room temperature.
Brillouin Scattering - In a physical medium, scattering of lightwaves, caused by thermally driven density
fluctuations. Note: Brillouin scattering may cause frequency shifts of several gigahertz at room temperature.
Broadband - 1. Synonym [in analog technology] wideband. 2. A descriptive term for evolving digital
technologies that provide consumers a signal-switched facility offering integrated access to voice, high-speed
data service, video-demand services, and interactive delivery services.
Broadband Exchange (BEX) - A communications switch capable of interconnecting channels having
bandwidths greater than voice bandwidth.
Broadband Internet Connection - A connection capable of carrying high quality VoIP conversations, and is
much more cheap and efficient than a traditional telephone line.
Broadband ISDN (B-ISDN) - An Integrated Services Digital Network (ISDN) offering broadband capabilities.
Note 1: B-ISDN is an ITU-T proposed (originally a CCITT-proposed) service that may (a) include interfaces
operating at data rates from 150 to 600 Mb/s, (b) use asynchronous transfer mode (ATM) to carry all services
over a single, integrated, high-speed packet-switched network, (c) have LAN interconnection capability, (d)
provide access to a remote, shared disk server, (e) provide voice/ video /data teleconferencing, (f) provide
transport for programming services, such as cable TV, (g) provide single-user controlled access to remote
video sources, (h) handle voice/video telephone calls, and (i) access shop-at-home and other information
services. Note 2: Techniques used in the B-ISDN include code conversion, information compression,
multipoint connections, and multiple-connection calls. Current proposals use a service-independent call
structure that allows flexible arrangement and modular control of access and transport edges. The service
components of a connection can provide each user with independent control of access features and can
serve as the basis of a simplified control structure for multipoint and multiconnection calls. Such a network
might be expected to offer a variety of ancillary information processing functions.
Broadband Phone - is a type of voice based communications system, which can be created using a regular
touch tone telephone, a broadband connection, and a connecting adapter.
Broadband System - See [in analog technology] wideband.
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![Broadcasting-Satellite Service - A radiocommunication service in which signals transmitted or retransmitted
by space stations are intended for direct reception by the general public. In the broadcasting-satellite
service, the term "direct reception" shall encompass both individual reception and community reception.
Broadcasting Satellite Space Station - A space station in the broadcasting-satellite service (sound
broadcasting).
Broadcasting Service - A radiocommunication service in which the transmissions are intended for direct
reception by the general public. This service may include sound transmissions, television transmissions or
other types of transmissions.
Broadcasting Station - A station in the broadcasting service.
Broadcast Operation - The transmission of signals that may be simultaneously received by stations that
usually make no acknowledgement.
Broadcast Spectrum - An entire range of frequencies used for radio and television transmission.
Broadcasting - Using radio waves to distribute radio or TV programs, which are available for reception by the
general public.
Broadside Antenna - Synonym billboard antenna. - An array of parallel dipole antennas with flat reflectors,
usually positioned in a line or plane. Note 1: The spacing and dimensions of the dipoles depend on the
wavelength. Note 2: The main lobe of a fixed billboard antenna may, within limits, be steered by appropriate
phasing of the respective signals to individual elements of the array.
Brouter - A combined bridge and router that operates without protocol restrictions, routes data using a
protocol it supports, and bridges data it cannot route.
Browser - A software program that allows you to view HTML documents and navigate on the WWW. Any
computer software program for reading hypertext. Note 1: Browsers are usually associated with the Internet
and the World Wide Web (WWW). Note 2: A browser may be able to access information in many formats,
and through different services including HTTP and FTP.
Browsing - [The] act of searching through information-system (IS) storage to locate or acquire information
without necessarily knowing of the existence or the format of the information being sought.
Brute-Force Attack - In security, an attack that requires trying all (or a large fraction of all) possible values
until the right value is found. Synonym [loosely] exhaustive attack.
b/s - Abbreviation for bits per second.
BSA - Abbreviation for basic serving arrangement.
BSE - Abbreviation for basic service element.
BSI - Abbreviation for British Standards Institution.
B6ZS - Abbreviation for bipolar with six-zero substitution. A T-carrier line code in which bipolar violations
are deliberately inserted if user data contain a string of 6 or more consecutive zeros. Note 1: B6ZS is used to
ensure a sufficient number of transitions to maintain system synchronization when the user data stream
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![Capacity - See channel capacity, traffic capacity. The maximum possible information transfer rate through a
channel, subject to specified constraints.
Card - A card (or expansion card, board, or adapter) is circuitry designed to provide expanded capability to a
computer. It is provided on the surface of a standard-size rigid material (fiberboard or something similar) and
then plugged into one of the computer's expansion slots in its motherboard (or backplane). Cards may come
in one of two sizes designed to match standard slot dimensions. A card can actually contain the capability
within its circuitry (as a video card does) or it can control (through an extended connection) a device (such as
a hard disk drive).
Carrier - In the telecommunications industry, a carrier is a telephone or other company that sells or rents
telecommunication transmission services. A local exchange carrier (LEC) is a local phone company and an
inter-exchange carrier (IEC or IXC) carries long-distance calls.
Carrier and Data Tone - very loud screech that is produced when the FAX machines or MODEMs are actually
transferring data. Unlike CNG or DTMF, carrier and data will be constantly changing.
Carrier Power (of a radio transmitter) - 1. The average power supplied to the antenna transmission line by a
transmitter during one radio frequency cycle taken under the condition of no modulation. Note: The concept
does not apply to pulse modulation or frequency-shift keying. 2. The average unmodulated power supplied
to a transmission line.
Carrier Frequency - 1. The nominal frequency of a carrier wave. 2. In frequency modulation, synonym center
frequency. 3. The frequency of the unmodulated electrical wave at the output of an amplitude modulated
(AM), frequency modulated (FM), or phase modulated (PM) transmitter. 4. The output of a transmitter when
the modulating wave is made zero.
Carrier System - A multichannel telecommunications system in which a number of individual circuits (data,
voice, or combination thereof) are multiplexed for transmission between nodes of a network. Note 1: In
carrier systems, many different forms of multiplexing may be used, such as time-division multiplexing and
frequency-division multiplexing. Note 2: Multiple layers of multiplexing may ultimately be performed upon a
given input signal; i.e., the output resulting from one stage of modulation may in turn be modulated. Note 3:
At a given node, specified channels, groups, supergroups, etc., may be demultiplexed without demultiplexing
the others. Synonym [loosely] carrier.
Carrier Wave - Synonym carrier (cxr).
CATV - Abbreviation for cable TV.
CCIR - Abbreviation for International Radio Consultative Committee, a predecessor organization of the ITU-R.
CCITT - Abbreviation for International Telegraph and Telephone Consultative Committee; a predecessor
organization of the ITU-T.
CCS (centum call second) - also known as the hundred call second -- is a unit of telecommunications traffic
density that is the equivalent of one call (including call attempts and holding time) in a specific channel for
100 seconds in an hour. The 100 seconds need not be, and generally are not, in a contiguous block.
In digital telecommunications, the voice signals are compressed. This makes it possible for one channel to
carry numerous calls simultaneously by means of multiplexing. In theory, there are many ways in which a
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![In a communications system, the part that connects a data source to a data sink. 7. A virtual area where
Internet Relay Chat (IRC) users communicate (exchanging text messages) in real time. Note: There are
thousands of channels located on the Internet. 8. An IRC conduit designated for the real-time exchange of
text messages. 9. An electrical path suitable for the transmission of communications between two or more
points, ordinarily between two or more stations or between channel terminations in Telecommunication
Company central offices. A channel may be furnished by wire, fiber optics, radio or a combination thereof.
10. The portion of the electromagnetic spectrum assigned by the FCC for one emission. In certain
circumstances, however, more than one emission may be transmitted on a channel.
Channel-Associated Signaling - Signaling in which the signals necessary to switch a given circuit are
transmitted via the circuit itself or via a signaling channel permanently associated with it.
Channel Bank - A device at a telephone company central office (public exchange) that converts analog
signals from home and business users into digital signals to be carried over higher-speed lines between the
central office and other exchanges. The analog signal is converted into a digital signal that transmits at a rate
of 64 thousand bits per second (Kbps). This 64 Kbps signal is a standard known as a DS0 signal. The signal is
multiplexed with other DS0 signals on the same line using time-division multiplexing (TDM) . Usually, the
digital information is put on each DS0 signal using pulse code modulation (PCM).
Channel Capacity - The maximum possible information transfer rate through a channel, subject to specified
constraints.
Channel Scan - Channel Scan will search for digital broadcast channels that are available in your area; once
the scan is completed, you will be able to tune to the digital channels received by your antenna.
Character - 1. A letter, digit, or other symbol that is used as part of the organization, control, or
representation of data. 2. One of the units of an alphabet.
Character Interval - In a communications system, the total number of unit intervals required to transmit any
given character, including synchronizing, information, error checking, or control characters, but not including
signals that are not associated with individual characters. Note: An example of a time interval that is
excluded when determining character interval is any time added between the end of a stop signal and the
beginning of the next start signal to accommodate changing transmission conditions, such as a change in
data signaling rate or buffering requirements. This added time is defined as a part of the intercharacter
interval.
Chroma Keying - In television, nearly instantaneous switching between multiple video signals, based on the
state, i.e., phase, of the color (chroma) signal of one, to form a single composite video signal. Note 1: Chroma
keying is used to create an overlay effect in the final picture, e.g., to insert a false background, such as a
weather map or scenic view, behind the principal subject being photographed. Note 2: The principal subject
is photographed against a background having a single color or a relatively narrow range of colors, usually in
the blue or green. When the phase of the chroma signal corresponds to the preprogrammed state or states
associated with the background color, or range of colors, behind the principal subject, the signal from the
alternate, i.e., false, background is inserted in the composite signal and presented at the output. When the
phase of the chroma signal deviates from that associated with the background color(s) behind the principal
subject, video associated with the principal subject is presented at the output. Synonyms color keying,
[loosely] blue-screening, [in security] keying.
Chromatic Dispersion - A commonly used (but redundant) synonym for material dispersion. See dispersion.
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![Coating - See primary coating. - The plastic overcoat in intimate contact with the cladding of an optical fiber,
applied during the manufacturing process. Note 1: The primary coating typically has an outside diameter of
approximately 250 to 750 m, and serves to protect the fiber from mechanical damage and chemical attack. It
also enhances optical fiber properties by stripping off cladding modes, and in the case where multiple fibers
are used inside a single buffer tube, it suppresses cross-coupling of optical signals from one fiber to another.
Note 2: The primary coating should not be confused with a tight buffer, or the plastic cladding of a plastic-
clad-silica (PCS) fiber. Note 3: The primary coating, which typically consists of many layers, may be color-
coded to distinguish fibers from one another, e.g., in a buffer tube containing multiple fibers. Synonyms
primary polymer coating, primary polymer overcoat.
Coaxial - Coaxial inputs (sometimes just called "cable") provide a simple and common way to transmit video.
Now coaxial inputs are mostly used for connecting a TV set to an antenna or cable system.
Coaxial Adapter - Device for connecting a coaxial cable to a TV with a Twin Lead cable connection port.
Coaxial Cable (coax) - 1. A cable consisting of a center conductor surrounded by an insulating material and a
concentric outer conductor and optional protective covering, all of circular cross-section. Synonym (when
combined with others under a common sheath) coaxial tube. 2. A cable consisting of multiple coaxial tubes
under a single protective sheath. Note: Coaxial cables are used primarily for CATV and other wideband,
video, or rf applications.
COBOL - Acronym for common business oriented language. A programming language designed for business
data processing.
Code - 1. A set of unambiguous rules specifying the manner in which data may be represented in a discrete
form. Note 1: Codes may be used for brevity or security. Note 2: Use of a code provides a means of
converting information into a form suitable for communications, processing, or encryption. 2. [In COMSEC,
any] system of communication in which arbitrary groups of letters, numbers, or symbols represent units of
plain text of varying length. Note: Codes may or may not provide security. Common uses include: (a)
converting information into a form suitable for communications or encryption, (b) reducing the length of
time required to transmit information, (c) describing the instructions which control the operation of a
computer, and (d) converting plain text to meaningless combinations of letters or numbers and vice versa. 3.
A cryptosystem in which the cryptographic equivalents, (usually called "code groups") typically consisting of
letters or digits (or both) in otherwise meaningless combinations, are substituted for plain text elements
which are primarily words, phrases, or sentences. 4. A set of rules that maps the elements of one set, the
coded set, onto the elements of another set, the code element set. Synonym coding scheme. 5. A set of
items, such as abbreviations, that represents corresponding members of another set. Synonym encode. 6. To
represent data or a computer program in a symbolic form that can be accepted by a processor. 7. To write a
routine.
Codec - Term is short for "Coder-decoder." A codec is a device that converts analog video and audio signals
into a digital format for transmission. It also converts received digital signals back into an analog format.
Code-Division Multiple Access (CDMA) - A coding scheme, used as a modulation technique, in which
multiple channels are independently coded for transmission over a single wideband channel. Note 1: In some
communication systems, CDMA is used as an access method that permits carriers from different stations to
use the same transmission equipment by using a wider bandwidth than the individual carriers. On reception,
each carrier can be distinguished from the others by means of a specific modulation code, thereby allowing
for the reception of signals that were originally overlapping in frequency and time. Thus, several
transmissions can occur simultaneously within the same bandwidth, with the mutual interference reduced
by the degree of orthogonality of the unique codes used in each transmission. Note 2: CDMA permits a more
uniform distribution of energy in the emitted bandwidth.
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![principal subject, the signal from the alternate, i.e., false, background is inserted in the composite signal and
presented at the output. When the phase of the chroma signal deviates from that associated with the
background color(s) behind the principal subject, video associated with the principal subject is presented at
the output.
Color Subcarrier - In analog color television technology, a signal superimposed upon the picture (gray scale)
information for the purpose of conveying the associated color information. Note: The color information is
conveyed by the instantaneous phase of the color subcarrier with respect to that of the color burst.
.com - 1. A top-level domain name-suffix originally intended to designate commercial entities such as
corporations and companies. 2. A filename suffix indicating an executable file. Note: Usually, ".com"
programs are smaller and simpler than programs with the ".exe" suffix.
Combinational Logic Element - A device having at least one output channel and one or more input channels,
all characterized by discrete states, such that at any instant the state of each output channel is completely
determined by the states of the input channels at the same instant.
Command - 1. An order for an action to take place. 2. In data transmission, an instruction sent by the
primary station instructing a secondary station to perform some specific function. 3. In signaling systems, a
control signal. 4. In computer programming, that part of a computer instruction word that specifies the
operation to be performed. 5. Loosely, a mathematical or logic operator.
Command and Control (C2): The exercise of authority and direction by a properly designated commander
over assigned forces in the accomplishment of the mission. Command and control functions are performed
through an arrangement of personnel, equipment, communications, facilities, and procedures employed by a
commander in planning, coordinating, and controlling forces and operations in the accomplishment of the
mission.
Command, Control and Communications (C3) - The capabilities required by commanders to exercise
command and control of their forces.
Common Carrier - In a telecommunications context, a telecommunications company that holds itself out to
the public for hire to provide communications transmission services. Note: In the United States, such
companies are usually subject to regulation by Federal and state regulatory commissions. Synonyms carrier,
commercial carrier, communications common carrier, [and, loosely] interexchange carrier.
Common-Channel Signaling - 1. In a multichannel communications system, signaling in which one channel in
each link is used for signaling to control, account for, and manage traffic on all channels of the link. Note: The
channel used for common-channel signaling does not carry user information. 2. A signaling method in which
a single channel conveys, by means of labeled messages, signaling information relating to a multiplicity of
circuits or calls and other information, such as that used for network management.
Common Control - An automatic switching arrangement in which the control equipment necessary for the
establishment of connections is shared by being associated with a given call only during the period required
to accomplish the control function for the given call. Note: In common control, the channels that are used for
signaling, whether frequency bands or time slots, are not used for message traffic.
Common Gateway Interface - See CGI. A means for allowing programs or scripts (usually written in C++ or
Perl) to add functionality to the World Wide Web. Note: Examples are search engines, feedback forms, and
guestbooks.
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![Note: Communications security includes cryptosecurity, transmission security, emission security, and
physical security of COMSEC material. [INFOSEC]
• (a) cryptosecurity: [The] component of communications security that results from the provision of
technically sound cryptosystems and their proper use. [NIS]
• (b) emission security: Protection resulting from all measures taken to deny unauthorized persons
information of value which might be derived from intercept and analysis of compromising
emanations from crypto-equipment, AIS, and telecommunications systems. [NIS]
• (c) physical security: The component of communications security that results from all physical
measures necessary to safeguard classified equipment, material, and documents from access
thereto or observation thereof by unauthorized persons. [JP 1-02]
• (d) transmission security: [The] component of communications security that results from the
application of measures designed to protect transmissions from interception and exploitation by
means other than cryptanalysis.
Communications System - A collection of individual communications networks, transmission systems, relay
stations, tributary stations, and data terminal equipment (DTE) usually capable of interconnection and
interoperation to form an integrated whole. Note: The components of a communications system serve a
common purpose, are technically compatible, use common procedures, respond to controls, and operate in
unison.
Compact - See data compaction.
Compact Disc - Known by its abbreviation, CD, a compact disc is a polycarbonate with one or more metal
layers capable of storing digital information. The most prevalent types of compact discs are those used by
the music industry to store digital recordings and CD-ROMs used to store computer data. Both of these types
of compact disc are read-only, which means that once the data has been recorded onto them, they can only
be read, or played.
Competitive Local Exchange Carrier - A telephone company that competes with the larger incumbent
carriers (ILECs) through reselling the ILEC services and/or creating services that use the ILEC's infrastructure.
The Regional Bells are ILECs; local phone companies are frequently CLECs.
Compile - 1. To translate a computer program expressed in a high-level language into a program expressed in
a lower level language, such as an intermediate language, assembly language, or a machine language. 2. To
prepare a machine language program from a computer program written in another programming language
by making use of the overall logic structure of the program or by generating more than one computer
instruction for each symbolic statement as well as performing the function of an assembler.
Component - 1. An assembly, or part thereof, that is essential to the operation of some larger assembly and
is an immediate subdivision of the assembly to which it belongs. Note: For example, a radio receiver may be
a component of a complete radio set consisting of a combined transmitter-receiver, i.e., a transceiver. The
same radio receiver could also be a subsystem of the combined transmitter-receiver, in which case the IF
amplifier section would be a component of the receiver but not of the radio set. Similarly, within the IF
amplifier section, items, such as resistors, capacitors, vacuum tubes, and transistors, are components of that
section. 2. In logistics, a part, or combination of parts having a specified function, that can only be installed
or replaced as an entity. 3. In material, an assembly or any combination of parts, subassemblies, and
assemblies mounted together in manufacture, assembly, maintenance, or rebuild.
Component Video - Also known as "Y Pb Pr," this connector splits the video signal into three parts. With two
audio connections, this five-wire solution is the most common way to connect an EDTV to DVD player and
most HDTV monitors to their receivers or other set-top boxes.
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![COMSEC - Acronym for communications security.
COMSEC material: [An] item designed to secure or authenticate telecommunications. Note: COMSEC
material includes, but is not limited to, key, equipment, devices, documents, firmware or software that
embodies or describes cryptographic logic and other items that perform COMSEC functions.
Conference Controller - In audio and video teleconferences, the user in charge of the conference when the
service is invoked and the conference reaches the active state. Note: The conference controller may perform
any or all of the following actions: drop, floating, isolate, reattach, and split.
Configuration Management - 1. [The] management of security features and assurances through control of
changes made to hardware, software, firmware, documentation, test, test fixtures, and test documentation
throughout the life cycle of an information system (IS). 2. The control of changes--including the recording
thereof--that are made to the hardware, software, firmware, and documentation throughout the system life
cycle.
Congestion - 1. In a communications switch, a state or condition that occurs when more subscribers attempt
simultaneously to access the switch than it is able to handle, even if unsaturated. 2. In a saturated
communications system, the condition that occurs when an additional demand for service occurs.
Connection - In telecommunication and computing in general, a connection is the successful completion of
necessary arrangements so that two or more parties (for example, people or programs) can communicate at
a long distance. In this usage, the term has a strong physical (hardware) connotation although logical
(software) elements are usually involved as well.
A dialup (sometimes called a switched) connection is a telephonic arrangement that is set up only when
needed, using shared, circuit-switched communication lines (as in "plain old telephone service"). A dedicated
(sometimes called a nonswitched) connection is a continuous, always available connection (familiar to users
of Digital Subscriber Line or DSL service). A leased line is a line rented from a telephone company that
provides dedicated connection between two points (such as a headquarters office and a manufacturing
plant).
Connection - 1. A provision for a signal to propagate from one point to another, such as from one circuit,
line, subassembly, or component to another. 2. An association established between functional units for
conveying information. 3. A temporary concatenation of transmission channels or telecommunication
circuits, switching and other functional units set up to provide a route for a transfer of information between
two or more points in a telecommunication network.
Connectionless Data Transfer - See connectionless mode transmission.
Connectionless Mode Transmission - 1. In a packet-switched network, transmission in which each packet is
encoded with a header containing a destination address sufficient to permit the independent delivery of the
packet without the aid of additional instructions. Note 1: A packet transmitted in a connectionless mode is
frequently called a datagram. Note 2: In connectionless mode transmission of a packet, the service provider
usually cannot guarantee there will be no loss, error insertion, misdelivery, duplication, or out-of-sequence
delivery of the packet. However, the risk of these hazards' occurring may be reduced by providing a reliable
transmission service at a higher protocol layer, such as the Transport Layer of the Open Systems
Interconnection--Reference Model. 2. The transmission of a unit of data in a single self-contained operation
without establishing, maintaining, and releasing a connection.
Connectivity - The technical communications link between a computer system and the Internet.
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![Connector - A device for mating and demating electrical power connections or communications media. Note:
A connector is distinguished from a splice, which is a permanent joint.
Connect Signal - An off-hook condition applied to the network interface (NI) by the network that indicated
the network intends to complete a call attempt to the customer installation (CI) or intends to continue an
established connection .
Contamination - The introduction of data of one security [classification or] security category into data of a
lower security classification or different security category.
Content Hosting (hosting) - Storage and management of databases by a content provider.
Content Provider - An organization that creates and maintains databases containing information from an
information provider. Note: The content provider and the information provider may be the same
organization.
Control Character - A character that initiates, modifies, or stops a function, event, operation, or control
operation. Note: Control characters may be recorded for use in subsequent actions. They are not graphic
characters but may have a graphic representation in some circumstances.
Control Function - Synonym control operation. - An operation that affects the recording, processing,
transmission, or interpretation of data. Note: Examples of control operations include starting and stopping a
process; executing a carriage return, a font change, or a rewind; and transmitting an end-of-transmission
(EOT) control character.
Control Operation - An operation that affects the recording, processing, transmission, or interpretation of
data. Note: Examples of control operations include starting and stopping a process; executing a carriage
return, a font change, or a rewind; and transmitting an end-of-transmission (EOT) control character.
Synonym control function.
Controller - In an automated radio, the device that commands the radio transmitter and receiver, and that
performs processes, such as automatic link establishment, channel scanning and selection, link quality
analysis, polling, sounding, message store and forward, address protection, and anti-spoofing.
Converter Box - Also referred to as a “digital-to-analog converter box,” this is a stand-alone device that
receives, decodes, and converts over-the-air digital programming into analog. When connected to an analog
television, it permits digital programming to be displayed in analog.
Cookie -1. A small piece of information that is automatically stored on a client computer by a Web browser
and referenced to identify repeat visitors to a Web site and to tailor information in anticipation of the
visitor's interests. Note: Some privacy advocates have objected to the use of cookies without a user's
consent. 2. A general mechanism that server side connections (such as CGI scripts) can use both to store and
to retrieve information on the client side of the connection. Note 1: A server, when returning an HTTP object
to a client, may also send a piece of state information that the client will store. Included in that state object is
a description of the range of URLs for which that state is valid. Any future HTTP requests made by the client
that fall in that range will include a transmittal of the current value of the state object from the client back to
the server. The state object is called a cookie. This simple mechanism provides a tool that enables new types
of applications to be written for Web-based environments. Shopping applications can now store information
about the currently selected items, for-fee services can send back registration information and free the client
from retyping a user ID on subsequent connections, sites can store per-user preferences on the client, and
have the client supply those preferences every time that site is accessed. Note 2: Session cookies are volatile
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![Cross-Connection: Connections between terminal blocks on the two sides of a distribution frame, or
between terminals on a terminal block. Note: Connections between terminals on the same block are also
called straps. Synonyms cross-connect, jumper.
Cross Coupling - The coupling of a signal from one channel, circuit, or conductor to another, where it is
usually considered to be an undesired signal.
Crosstalk (XT) - 1. Undesired coupling of a signal from one circuit, part of a circuit, or channel, to another. 2.
Any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an
undesired effect in another circuit or channel. Note 1: In telephony, crosstalk is usually distinguishable as
speech or signaling tones. Note 2: In video, "ghost" images from one source appear in addition to the signals
of interest transmitted from another.
CRT- Cathode Ray Tube. Display screens used in TV sets and computer monitors that use a Cathode Ray
Tube, which is also called a "picture tube." Cathode Ray Tubes were found in all electronic television sets up
until the invention of the less bulky LCD screens.
Cryptanalysis - 1. Operations performed in converting encrypted messages to plain text without initial
knowledge of the crypto-algorithm and/or key employed in the encryption. 2. The study of encrypted texts.
CRYPTO - The marking or designator identifying COMSEC keying material used to secure or authenticate
telecommunications carrying classified or sensitive U.S. Government or U.S. Government-derived
information. Note: When written in all upper case letters, CRYPTO has the meaning stated above. When
written in lower case as a prefix, crypto and crypt are abbreviations for cryptographic.
Crypto-Algorithm - [A] well-defined procedure or sequence of rules or steps, or a series of mathematical
equations used to describe cryptographic processes such as encryption/decryption, key generation,
authentication, signatures, etc.
Crypto-Equipment - See cryptographic equipment. - Any device that embodies cryptographic logic or
performs one or more cryptographic functions (e.g., key generation, encryption, and authentication).
Cryptology - 1. The science that deals with hidden, disguised, or encrypted communications. It includes
communications security and communications intelligence. 2. [The] field encompassing both cryptography
and cryptanalysis.
Cryptographic - Pertaining to, or concerned with, cryptography.
Cryptographic Equipment (crypto-equipment) - Any device that embodies cryptographic logic or performs
one or more cryptographic functions (e.g., key generation, encryption, and authentication).
Cryptographic Logic - The embodiment of one (or more) crypto-algorithm (s) along with alarms, checks, and
other processes essential to effective and secure performance of the cryptographic process(es).
Cryptography - 1. [The] art or science concerning the principles, means, and methods for rendering plain
information unintelligible, and for restoring encrypted information to intelligible form. 2. The branch of
cryptology that treats of the principles, means, and methods of designing and using cryptosystems.
Cryptosecurity - See communications security. [The] component of communications security that results
from the provision of technically sound cryptosystems and their proper use.
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![current density. However, in some situations, current density varies in different parts of an electrical
conductor. A classic example is the so-called skin effect, in which current density is high near the outer
surface of a conductor, and low near the center. This effect occurs with alternating currents at high
frequencies. Another example is the current inside an active electronic component such as a field-effect
transistor (FET).
An electric current always produces a magnetic field. The stronger the current, the more intense the
magnetic field. A pulsating DC, or an AC, characteristically produces an electromagnetic field. This is the
principle by which wireless signal propagation occurs.
Curvature Loss - In an optical fiber, that loss attributable to macrobending. - Synonym macrobend loss.
Customer Controlled Call Forwarding Busy - Allows you the capability to activate and deactivate call
forwarding busy from your home telephone number using dial codes. Forwards calls to the number you have
pre-selected. To activate, press 82#. To deactivate, press 83#.
Customer Controlled Call Forwarding No Answer - Allows you the capability to automatically forward
unanswered incoming calls to another telephone number after a pre-selected number (2-7) of rings.
Forwards calls to the number you have pre-selected. Activate this feature by pressing 77#. To deactivate,
press 78#.
Customer Installation (CI) - All telecommunication equipment and wiring on the customer side of the
network interface.
Customer Premises Equipment (CPE) - Telephone or other service provider equipment that is located on the
customer's premises (physical location) rather than on the provider's premises or in between. Telephone
handsets, cable TV set-top boxes, and Digital Subscriber Line routers are examples. Historically, this term
referred to equipment placed at the customer's end of the telephone line and usually owned by the
telephone company. Today, almost any end-user equipment can be called customer premise equipment and
it can be owned by the customer or by the provider.
Custom Ring Service 1 - Allows you to receive calls dialed to two different telephone numbers without
having a second access line. Distinctive ringing will be provided for the second telephone number to facilitate
identification of incoming calls. One directory listing is provided for each Custom Ring number.
Custom Ring Service 2 - Allows you to receive calls dialed to three separate telephone numbers without
having a second or third access line. Distinctive ringing will be provided for each of the additional telephone
numbers to facilitate identification of incoming calls. One directory listing is provided for each Custom Ring
number. You must have Custom Ring Service 1 to have Custom Ring Service 2.
Cutoff Wavelength - 1. The wavelength corresponding to the cutoff frequency. 2. In an uncabled single-
mode optical fiber, the wavelength greater than which a particular waveguide mode ceases to be a bound
mode. Note 1: The cutoff wavelength is usually taken to be the wavelength at which the normalized
frequency is equal to 2.405. Note 2: The cabled cutoff wavelength is usually considered to be a more
functional parameter because it takes into consideration the effects of cabling the fiber.
CXR ( cxr) - Abbreviation for carrier.
Cybermall - An electronic site shared by a number of commercial interests, and at which users can browse,
shop, and place orders for the products listed at that site. [Bahorsky] Synonym Internet mall.
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![Display Device - An output unit that gives a visual representation of data.
Distinctive Ring - An inexpensive service that lets businesses and homes to have two or three different
phone numbers on one phone line. What distinguishes the different telephone numbers coming in on the
same line is their signature ring, a pattern of long and/or short rings. Each number has its own special ring.
Most telephone companies throughout the US and Canada offer distinctive ring. These "Distinctive Ring"
services go by different names depending on your phone company -custom Ringing by US West, SmartRing
by GTE, RingMaster by Bell South, RingMate by NYNEX, Personalized Ringing by Southwestern Bell and SBC,
Multi-Ring by Ameritech, Distinctive Ring by ATT and SBC and IdentaRing by Bell Atlantic.
Note: Without distinctive ringing, all the instruments on the party line will ring at the same time, selection
being made by the number of rings. Two popular Distinctive Ring Devices are the SR-Series Call Processors
and The Line Hunter. For deteailed info see Distinctive Ring Definition and Use.
Distinctive Ring Device - A device that tests a phone line for a distinctive ring signal and routes the call to a
specific device (example: phone, phone system, answering machine, fax machine. fax modem). For more info
see Fax Switch. For more info see Distinctive Ring Definition and Use.
Distinctive Ring Service - Provides a distinctive ringing pattern for up to six different telephone numbers on a
screening list. The telephone numbers on the screening list may be changed or reprogrammed at any time.
See Distinctive Ring. For more info see Distinctive Ring Definition and Use.
Distortion - 1. In a system or device, any departure of the output signal waveform from that which should
result from the input signal waveform's being operated on by the system's specified, i.e., ideal, transfer
function. Note: Distortion may result from many mechanisms. Examples include nonlinearities in the transfer
function of an active device, such as a vacuum tube, transistor, or operational amplifier. Distortion may also
be caused by a passive component such as a coaxial cable or optical fiber, or by inhomogeneities, reflections,
etc., in the propagation path. 2. In start-stop teletypewriter signaling, the shifting of the significant instants
of the signal pulses from their proper positions relative to the beginning of the start pulse. Note: The
magnitude of the distortion is expressed in percent of an ideal unit pulse length.
Distributed-Queue Dual-Bus (DQDB) [network] - A distributed multi-access network that (a) supports
integrated communications using a dual bus and distributed queuing, (b) provides access to local or
metropolitan area networks, and (c) supports connectionless data transfer, connection-oriented data
transfer, and isochronous communications, such as voice communications.
Distribution Frame - In communications, a structure with terminations for connecting the permanent wiring
of a facility in such a manner that interconnection by cross-connections may readily be made.
Distribution List Server - Synonym list server. - A functional unit (hardware and software) for operating a
computer conferencing system by acting as a repository for electronic messages and redistributing those
messages automatically or on-demand.
Diversity Combiner - A circuit or device for combining two or more signals carrying the same information
received via separate paths or channels with the objective of providing a single resultant signal that is
superior in quality to any of the contributing signals.
Divestiture - The court-ordered separation of the Bell Operating Telephone Companies from AT&T.
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![DMA - Designated Market Area. A term used by Nielsen Media Research to identify an exclusive geographic
area of counties in which the home market television stations hold a dominance of total hours viewed. There
are 210 DMA in the U.S.
DNS - See Domain Name System
DOD - Abbreviation for Department of Defense, direct outward dialing.
Dolby® Digital - A form of multi-channel digital sound, it provides efficient encoding and noise reduction for
high-quality surround sound — technology used in movie theaters and upscale home theater systems that
enhances audio. Home theater components with this technology work in conjunction with a "5.1-speaker"
system (five speakers plus a low-frequency subwoofer) to produce true-to-life audio that draws the listener
into the onscreen action.
Domain - 1. The independent variable used to express a function. Note: Examples of domains are time,
frequency, and space. 2. In distributed networks, all the hardware and software under the control of a
specified set of one or more host processors. [From Weik '89] 3. [A] unique context (e.g., access control
parameters) in which a program is operating; in effect, the set of objects a subject has the privilege to access.
Domain Name - A unique name that identifies an Internet site; the Domain Name will always have at least
two parts separated by dots (for example: tds.net or tdsnet.com). These names are granted and controlled
by a centralized Internet Network Information Center (InterNIC), administered by the National Science
Foundation.
Domain Name System (DNS) - A system by which one Internet host can find another. DNS translates words
(Domain Names) into numbers that Internet computers can understand.
Double Refraction - Synonym birefringence. - In a transparent material, anisotropism of the refractive index,
which varies as a function of polarization as well as orientation with respect to the incident ray. Note 1: The
term "birefringence" means, literally, " double refraction." Note 2: All crystals except those of cubic lattice
structure exhibit some degree of anisotropy with regard to their physical properties, including refractive
index. Other materials, such as glasses or plastics, become birefringent when subjected to mechanical strain.
Note 3: Birefringent materials, including crystals, have the ability to refract an unpolarized incident ray into
two separate, orthogonally polarized rays, which in the general case take different paths, depending on
orientation of the material with respect to the incident ray. The refracted rays are referred to as the
"ordinary," or "O" ray, which obeys Snell's Law, and the "extraordinary," or "E" ray, which does not.
Downconvert - A process by which a high-resolution signal is reduced to a lower resolution for display.
Usually, extra lines are simply ignored when drawing the lower resolution image; however, more
sophisticated methods are sometimes used.
Download - To transfer of a file or information from another computer to yours.
Downstream - 1. In communications, the direction of transmission flow from the source toward the sink. 2.
With respect to the flow of data in a communications path: at a specified point, the direction toward which
data are received later than at the specified point.
DQDB - Abbreviation for distributed-queue dual-bus. - A distributed multi-access network that (a) supports
integrated communications using a dual bus and distributed queuing, (b) provides access to local or
metropolitan area networks, and (c) supports connectionless data transfer, connection-oriented data
transfer, and isochronous communications, such as voice communications.
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![fiber optic and/or microwave links may be used between the studio and the broadcast station, or between
the broadcast station and local community networks.
DTTV provides a clearer picture and superior sound quality when compared to analog TV, with less
interference. DTTV offers far more channels, thus providing the viewer with a greater variety of programs to
choose from. DTTV can be viewed on personal computers. Using a split-screen format, a computer user can
surf the Web while watching TV.
In regions not served by cable, DTTV is generally impractical. For this reason, digital satellite TV (DSTV) has
become popular, especially in rural areas and in some small towns. A few city dwellers prefer DSTV even
when they have the option of subscribing to DTTV.
DTV - Digital Television. An advanced broadcasting technology that uses radio frequency (RF) to transmit
computer code and display it as pictures and sound. DTV is the umbrella term encompassing HDTV and
several other applications, including SDTV, datacasting, multicasting and interactivity.
Dual Bus - A pair of parallel buses arranged such that the direction of data flow in one bus is opposite to the
direction of data flow in the other bus.
Dual Seizure - The condition that occurs when, in both-way operation, two exchanges attempt to seize the
same circuit at approximately the same time. Synonyms call collision, glare [deprecated].
Dual Tone Multifrequency (DTMF)- This tone is commonly called "touch-tone". Not all push-button phones
are capable of producing the DTMF tones.
Duct - 1. In interfacility cabling, a conduit, which may be direct-earth buried or encased in concrete, used to
enclose communications or power cables. Note: For maximum resistance to rodent attack, direct-earth-
buried conduit should have an outside diameter equal to or greater than 6 cm (2.25 in.). 2. See atmospheric
duct.
Ducting - The propagation of radio waves within an atmospheric duct.
Duplex Communication - means that both ends of the communication can send and receive signals at the
same time. full-duplex communication is the same thing. half-duplex is also bidirectional communication but
signals can only flow in one direction at a time. Simplex communication means that communication can only
flow in one direction and never flow back the other way.
An ordinary telephone conversation is a duplex communication. Most inexpensive speakerphones in
conference rooms are half-duplex communication. (If you're speaking, you can't hear anyone else interrupt.
You have to pause to let others speak.)
DVI - Digital Video Interface. A high-quality digital connector. Similar to HDMI and sometimes with HDCP, DVI
can digitally transmit uncompressed, high-definition video, preserving perfect picture quality. Unlike HDMI or
Firewire, DVI requires a separate audio connection.
DVR - Digital Video Recorder. A device that records video in a digital format to a disk drive or other memory
medium within a device. The term includes stand-alone set-top boxes, Portable Media Players (PMP) and
software for personal computers, which enables video capture and playback to and from disk.
Dynamic Range - 1. In a system or device, the ratio of (a) a specified maximum level of a parameter, such as
power, current, voltage, or frequency to (b) the minimum detectable value of that parameter. Note: The
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![network mail server or host computer until it is examined and deleted. The mail program (e-mail client) in
your computer queries the mail server every so many minutes and alerts you if new mail has arrived.
E-mail Address - A computer mailing address to which electronic mail is sent.
E-mail Exploder - Synonym mail exploder, exploder. - Part of an e-mail delivery system that allows a
message to be automatically and efficiently delivered to a list of addresses, thus implementing mailing lists.
Emergency Video Description - Video descriptions are a way to inform people who are blind or have other
vision disabilities of what is happening on the television screen. Video description is the insertion of verbal
descriptions about the setting and/or action in a program when information about these visual elements is
not contained in the audio portion of the program. These descriptions supplement the regular audio track of
the program.
Emission - 1. Electromagnetic energy propagated from a source by radiation or conduction. Note: The
emission may be either desired or undesired and may occur anywhere in the electromagnetic spectrum. 2.
Radiation produced, or the production of radiation, by a radio transmitting station. For example, the energy
radiated by the local oscillator of a radio receiver would not be an emission but a radiation. 3. The
electromagnetic energy radiated from an antenna.
Emission Security - Protection resulting from measures taken to deny unauthorized persons information
derived from intercept and analysis of compromising emanations from crypto-equipment or an information
system (IS). [INFOSEC-99] Synonym [in INFOSEC] emissions security.
Encoding - See analog encoding. The portion of the analog-to-digital conversion process that samples an
analog signal and creates a digital signal that represents the value of the sample. Note: Multiple samples are
needed to digitize a waveform over a time interval.
Encryption - A way of making transmitted data, such as e-mails, unreadable to everyone except the receiver.
If the data is intercepted by anyone as it travels over a network, it cannot be read. Only those persons that
have the right type of decoding software can unscramble the message. Encryption is used to protect e-
commerce and financial transactions.
End Distortion - In start-stop teletypewriter operation, the shifting of the end of all marking pulses, except
the stop pulse, from their proper positions in relation to the beginning of the next start pulse. Note 1:
Shifting of the end of the stop pulse is a deviation in character time and rate rather than an end distortion.
Note 2: Spacing end distortion is the termination of marking pulses before the proper time. Note 3: Marking
end distortion is the continuation of marking pulses past the proper time. Note 4: The magnitude of the
distortion is expressed as a percentage of an ideal pulse length.
End Exchange - Synonym end office. - A central office at which user lines and trunks are interconnected.
Synonym end exchange.
End Instrument - A communication device that is connected to the terminals of a circuit.
End Office (EO) - A central office at which user lines and trunks are interconnected. Synonym end exchange.
End-of-Transmission-Block Character (ETB) - A transmission control character used to indicate the end of a
transmission block of data when data are divided into such blocks for transmission purposes.
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![End-of-Transmission Character (EOT) - A transmission control character used to indicate the conclusion of a
transmission that may have included one or more texts and any associated message headings. Note: An EOT
is often used to initiate other functions, such as releasing circuits, disconnecting terminals, or placing receive
terminals in a standby condition.
End-to-End Signaling - The capability changeover procedure to be used whenever the normal one cannot be
accomplished (i.e., in case of some failure in the signaling terminal equipment or in case of inaccessibility
between the two involved signaling points).
Enhanced 911 (E911) - Technology allowing 911 calls from cellular phones to be routed to the geographically
correct emergency station (a.k.a. PSAP: Public Safety Answering Point). VoIP users currently have limited
access to 911 services, and with some providers none, because VoIP is not geographically based.
Envelope - The boundary of the family of curves obtained by varying a parameter of a wave. See figure under
amplitude modulation.
EO - Abbreviation for End Office - A central office at which user lines and trunks are interconnected.
Synonym end exchange.
EOT - Abbreviation for end-of-transmission character.
EPG - Electronic Program Guide. An interactive list of upcoming TV programming that can be transmitted
along with a DTV program
Equilibrium Mode Distribution (EMD) - That condition in a multimode fiber wherein after propagation has
taken place for a certain distance, called the " equilibrium length," the relative power distribution among
modes becomes statistically constant and remains so for the course of further propagation down the fiber.
Note 1: In practice, the equilibrium length may vary from a fraction of a kilometer to more than a kilometer.
Note 2: After the equilibrium length has been traversed, the numerical aperture of the fiber's output is
independent of the numerical aperture of the optical source, i.e., beam, that drives the fiber. This is because
of mode coupling and stripping, primarily by small perturbations in the fiber's geometry which result from
the manufacturing and cabling processes. Note 3: In the ray-optics analogy, the equilibrium mode
distribution may be loosely thought of as a condition in which the "outermost rays" in the fiber core are
stripped off by such phenomena as microbends, and only the "innermost rays" continue to propagate. In a
typical 50-m core multimode graded-index fiber, light propagating under equilibrium conditions occupies
essentially the middle seven-tenths of the core and has a numerical aperture approximately seven-tenths
that of the full numerical aperture of the fiber. This is why in-line optical attenuators based on the principle
of gap loss may be ineffective or induce a lower-than-rated loss if they are inserted near the optical receiver.
To be fully effective, gap-loss attenuators should be inserted near the optical transmitter, where the core is
fully filled. Synonyms equilibrium mode power distribution, steady-state condition.
Erasure - [A] process intended to render magnetically stored information irretrievable by normal means.
Erlang - A unit of traffic density in a telecommunications system. One erlang is the equivalent of one call
(including call attempts and holding time) in a specific channel for 3600 seconds in an hour. The 3600
seconds need not be, and generally are not, in a contiguous block. In digital telecommunications, the voice
signals are compressed. This makes it possible for one channel to carry numerous calls simultaneously by
means of multiplexing. In theory, there are many ways in which a channel can carry a certain number of
erlangs. For example, a traffic density of 3 erlangs can consist of three simultaneous calls, each lasting for an
hour (a total of 10,800 seconds); it can consist of six calls, each of which are allocated 30 minutes (1800
seconds) of time during the hour; it might consist of 180 calls, each of which occupy one minute (60 seconds)
of time during an hour. Smaller units of traffic density are sometimes used. The hundred or centum call
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![second or CCS is the equivalent of one call for 100 seconds out of an hour. A traffic density of 1 CCS is equal
to 1/36 erlang. An erlang can be applied to the group of lines in a telephone trunk line or to the traffic in a
telephone call center.
The term is named after the Danish telephone engineer, A. K. Erlang, the originator of queueing theory.
Error - 1. The difference between a computed, estimated, or measured value and the true, specified, or
theoretically correct value. 2. A deviation from a correct value caused by a malfunction in a system or a
functional unit. Note: An example of an error is the occurrence of a wrong bit caused by an equipment
malfunction.
Error Control - Any technique that will detect or correct errors.
Error Message - In a computer or communications system, a message that indicates that an error has been
made and, sometimes, the nature or type of error.
Error Ratio - The ratio of the number of bits, elements, characters, or blocks incorrectly received to the total
number of bits, elements, characters, or blocks sent during a specified time interval. Note: For a given
communication system, the bit error ratio will be affected by both the data transmission rate and the signal
power margin.
Ethernet - A network link that can transmit approximately 10,000,000 bits per second. Ethernet is the most
widely-installed local area network ( LAN) technology. Specified in a standard, IEEE 802.3, Ethernet was
originally developed by Xerox from an earlier specification called Alohanet (for the Palo Alto Research Center
Aloha network) and then developed further by Xerox, DEC, and Intel. An Ethernet LAN typically uses coaxial
cable or special grades of twisted pair wires. Ethernet is also used in wireless LANs. The most commonly
installed Ethernet systems are called 10BASE-T and provide transmission speeds up to 10 Mbps. Devices are
connected to the cable and compete for access using a Carrier Sense Multiple Access with Collision Detection
(CSMA/CD ) protocol.
Fast Ethernet or 100BASE-T provides transmission speeds up to 100 megabits per second and is typically
used for LAN backbone systems, supporting workstations with 10BASE-T cards. Gigabit Ethernet provides an
even higher level of backbone support at 1000 megabits per second (1 gigabit or 1 billion bits per second).
10-Gigabit Ethernet provides up to 10 billion bits per second.
Ethernet was named by Robert Metcalfe, one of its developers, for the passive substance called
"luminiferous (light-transmitting) ether" that was once thought to pervade the universe, carrying light
throughout. Ethernet was so- named to describe the way that cabling, also a passive medium, could similarly
carry data everywhere throughout the network.
Evaluation - Assessment of an information technology (IT) product or system against defined security-related
functional and assurance criteria, performed by a combination of testing and analytic techniques.
Even Parity - See parity, parity check. - A test that determines whether the number of ones or zeros in an
array of binary digits is odd or even. Note: Odd parity is standard for synchronous transmission and even
parity for asynchronous transmission.
EWSD (Electronic Worldwide Switch Digital, or, in German, Elektronisches WaehlSystem [Digital]) - A
widely-installed telephonic switch system developed by Siemens. Siemens says that EWSD performs
switching for over 160 million lines in more than 100 countries. EWSD is a modular system in which some
switches in the system can be installed in a telephone company's centrex facility and other switches can be
located at the customer.
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![distribution facility, such as a broadcasting station in a network. 4. Pertaining to the function of inserting one
thing into another, such as in a feed horn, paper feed, card feed, and line feed.
Feedback - 1. The return of a portion of the output, or processed portion of the output, of a (usually active)
device to the input. Note 1: The feedback signal will have a certain magnitude and phase relationship relative
to the output signal or the input signal. This relationship can be used to influence the behavior, such as the
gain and stability, of the overall circuit. Note 2: If the feedback is regenerative (additive), it is called "positive
feedback," which increases gain and distortion, and decreases linearity and stability. Note 3: If the feedback
is degenerative (subtractive), it is called "negative feedback," which reduces the gain and distortion, and
increases linearity and stability. Note 4: Feedback may occur inadvertently, and be detrimental. 2.
Information returned as a response to an originating source.
Feedback Path - The signal path from the input of the bit-masking block to the output of the adaptive
predictor.
Feeder Echo Noise - Signal distortion resulting from reflected waves in a transmission line that is many
wavelengths long and mismatched at both the generator and the load ends.
Feeder Link - A radio link from an Earth station at a given location to a space station, or vice versa, conveying
information for a space radiocommunication service other than for the fixed-satellite service. The given
location may be at a specified fixed point, or at any fixed point within specified areas.
Feed-Forward Path - In the encoder, the signal path from the input of the PCM-to-uniform-PCM converter to
the output of the adaptive quantizer. In the decoder, the feed-forward path is the signal path from the input
of the feed-forward inverse adaptive quantizer to the output of the synchronous coding adjustment block.
FEP - Abbreviation for front-end processor. A programmed-logic or stored-program device that interfaces
data communication equipment with an input / output bus or memory of a data processing computer.
Fermat's Principle - A principle stating that a ray of light follows the path that requires the least time to
travel from one point to another, including reflections and refractions that may occur. Synonym least-time
principle.
Fetch Protection - 1. [An] AIS-provided restriction to prevent a program from accessing data in another
user's segment of storage. 2. [An] information-system (IS) hardware-provided restriction to prevent a
program from accessing data in another user's segment of storage.
FET photodetector: A photodetector using photogeneration of carriers in the channel region of a field-effect
transistor structure to provide photodetection with current gain.
Fiber - See optical fiber. A filament of transparent dielectric material, usually glass or plastic, and usually
circular in cross section, that guides light. Note 1: An optical fiber usually has a cylindrical core surrounded
by, and in intimate contact with, a cladding of similar geometry. Note 2: The refractive index of the core must
be slightly higher than that of the cladding for the light to be guided by the fiber.
Fiber Amplifier - A device that amplifies an optical signal directly, without the need to convert it to an
electrical signal, amplify it electrically, and reconvert it to an optical signal. Note 1: One type of fiber
amplifier uses a doped fiber (e.g., a fiber doped with erbium), which bears the communication signal, and
which is optically pumped with a laser having a high-powered continuous output at an optical frequency
slightly higher than that of the communication signal. The signal is intensified by Raman amplification. Note
2: Because neither optical-electrical conversion nor electrical amplification takes place, this type of amplifier
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![FIFO - Abbreviation for first-in first-out. A queuing discipline in which entities in a queue leave the queue in
the same order in which they arrive. Note 1: Service, when available, is offered to the entity that has been in
the FIFO queue the longest. Note 2: FIFO techniques are used in message switching.
File - 1. The largest unit of storage structure that consists of a named collection of all occurrences in a
database of records of a particular record type. 2. A set of related records treated as a unit, for example, in
stock control, a file could consist of a set of invoices.
File Archive - Synonym FTP archive. A collection of files that are available by using file transfer protocol
(FTP). Synonym file site.
File Name Extension - 1. A suffix that is preceded by a decimal (".") and that is appended to a computer file
name. Note: Common filename extensions with their meanings are:
.wpd = a type of word-processing document
.doc = a type of word-processing document
.exe = executable code or a self-extracting archive file.
.gif = a graphical interchange format (graphics file)
.txt = a text file.
2. Proprietary HTML tags that are recognized by a single Web browser or by those Web browsers developed
by a single company.
File-Oriented Applications - Applications concerned with the storage, manipulation, and exchange of
information between application processes in the form of files.
File Protection - 1. The execution of appropriate administrative, technical, or physical means to guard
against the unauthorized access to, modification of, or deletion of a file. [After 2382-8] 2. [The] aggregate of
processes and procedures designed to inhibit unauthorized access, contamination, elimination, modification,
or destruction of a file or any of its contents.
File Security - [A] means by which access to computer files is limited to authorized users only.
File Server - 1. A high-capacity disk storage device or a computer that each computer on a network can use
or access and retrieve files that can be shared among attached computers. 2. A program, running on a
computer, that allows different programs, running on other computers, to access the files of that computer.
File Site - Synonym FTP archive. A collection of files that are available by using file transfer protocol (FTP).
File Transfer - In networking, a service to move a part or the whole of a file's content over a computer
network.
File Transfer, Access, and Management (FTAM) - An application's service and protocol based on the concept
of virtual file store. Note: FTAM allows remote access to various levels in a file structure and provides a
comprehensive set of file management capabilities.
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![File Transfer Protocol (FTP) - A common method for sending and/or receiving files between Internet sites
using a login system. Publicly accessed FTP sites are often called anonymous FTPs.
Fill - See bit stuffing. The insertion of noninformation bits into data. Note 1: Stuffed bits should not be
confused with overhead bits. Note 2: In data transmission, bit stuffing is used for various purposes, such as
for synchronizing bit streams that do not necessarily have the same or rationally related bit rates, or to fill
buffers or frames. The location of the stuffing bits is communicated to the receiving end of the data link,
where these extra bits are removed to return the bit streams to their original bit rates or form. Bit stuffing
may be used to synchronize several channels before multiplexing or to rate-match two single channels to
each other. Synonym positive justification.
Fill Bit - See bit stuffing. The insertion of noninformation bits into data. Note 1: Stuffed bits should not be
confused with overhead bits. Note 2: In data transmission, bit stuffing is used for various purposes, such as
for synchronizing bit streams that do not necessarily have the same or rationally related bit rates, or to fill
buffers or frames. The location of the stuffing bits is communicated to the receiving end of the data link,
where these extra bits are removed to return the bit streams to their original bit rates or form. Bit stuffing
may be used to synchronize several channels before multiplexing or to rate-match two single channels to
each other.
Fill Device - [A] COMSEC item used to transfer or store key in electronic form or to insert key into a crypto-
equipment.
Filled Cable - A cable that has a nonhygroscopic material, usually a gel, inside the jacket or sheath. Note 1:
The nonhygroscopic material fills the spaces between the interior parts of the cable, preventing moisture
from entering minor leaks in the sheath and migrating inside the cable. Note 2: A metallic cable, such as a
coaxial cable or a metal waveguide, filled with a dielectric material, is not considered as a filled cable.
Fill-in Area - The area where the coverage contour of an FM translator or booster station is within the
protected contour of the associated primary station (i.e., predicted 0.5 mV/m contour for commercial Class B
stations, predicted 0.7 mV/m contour for commercial Class B1 stations, and predicted 1 mV/m contour for all
other classes of stations).
Fill-in Signal Unit (FISU) - A signal unit that is transmitted when there are no message signal units or link
status signal units to be transmitted. It contains only error control and delimitation information.
FILO - Abbreviation for first-in last-out. A queuing discipline in which entities in a queue leave the queue in
the reverse order from that in which they arrived. Note: An understanding of FILO techniques is important in
the understanding of store-and-forward capabilities in packing switching.
Filter - In electronics, a device which transmits only part of the incident energy and may thereby change the
spectral distribution of energy:
• (a) high pass filters transmit energy above a certain frequency;
• (b) low pass filters transmit energy below a certain frequency;
• (c) band pass filters transmit energy of a certain bandwidth;
• (d) band stop filters transmit energy outside a specific frequency band
Filtered Symmetric Differential Phase-Shift Keying (FSDPSK) - A method of encoding information for digital
transmission in which (a) a binary 0 is encoded as a +90° change in the carrier phase and a binary 1 is
encoded as a -90° change in the carrier phase, and (b) abrupt phase transitions are smoothed by filtering or
other functionally equivalent pulse shaping techniques.
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![Final Trunk Group - A last-choice trunk group that receives overflow traffic, may receive first-route traffic
and for which there is no alternate route. There are various types of final trunk groups, differentiated by the
type of traffic that they carry.
Finger - A computer-operating-system command for accessing limited network-user-account information.
Note: Finger is limited to providing information such as the full name of the account holder and address
information, intentionally made public by the account holder. Finger is also used to establish the existence of
an address and to discover whether or not the account is currently logged on.
Finished Call - 1. In an information transaction, a call in which the call originator or call receiver terminates
the communication and goes on hook, i.e., hangs up. 2. In an information transfer transaction, the
termination of the information transfer phase.
FIP - Acronym for Federal Information Processing.
FIP Equipment - In the Federal government, any equipment or interconnected system or subsystems of
equipment (as defined in 41CFR) used in the automatic acquisition, storage, manipulation, management,
movement, control, display, switching, interchange, transmission, or reception of data or information.
FIP System - In the Federal government, any organized combination of FIP equipment, software, services,
support services, or related supplies.
FIREFLY - [A] key management protocol based on public key cryptography.
Firewall - 1. A computer that (a) acts as an interface between two networks ( e.g., the Internet and an
private network, respectively), and (b) regulates traffic between those networks for the purpose of
protecting the internal network from electronic attacks originating from the external network. The firewall is
capable of handling the following tasks: (a) isolating internal and external traffic (a bridge service ); (b)
making internal addresses invisible and directly unaccessible from outside and passing through authorized
traffic after proper checking (a proxy service); (c) facilitating protected (encrypted) connections to
cooperative parties over public networks (a tunneling service); (d) filtering outgoing traffic for security and
network usage rules (filtering or monitoring service); (e) filtering incoming traffic for rogue data (viruses,
spam, inappropriate data (filtering), or improper actions ( port scanning, overload prevention, etc. ; (f)
blocking forbidden external services or addresses (blocking, "network nanny"-functions); (g) providing log -in
services for authorized outside users and simulating the approved outside user as an inside user (proxy, log-
in server ); (h) caching network traffic (cache service); (i) converting between different network protocols on
different protocol levels (bridge when handling lower level protocols, gateway when handling higher level
protocols); (j) traffic diverting ( e.g., for cost optimizing, accounting, network planning, monitoring);
(k)providing consistent, open entry to the internal network ( portal service) and facilitating public network
address and connection sharing (proxy service). 2. A system designed to defend against unauthorized access
to or from a private network. Firewalls can be implemented in both hardware and software, or a
combination of both.
Firmware - 1. Software that is embedded in a hardware device that allows reading and executing the
software, but does not allow modification, e.g., writing or deleting data by an end user. Note 1: An example
of firmware is a computer program in a read-only memory ( ROM ) integrated circuit chip. A hardware
configuration is usually used to represent the software. Note 2: Another example of firmware is a program
embedded in an erasable programmable read-only memory (EPROM) chip, which program may be modified
by special external hardware, but not by an application program. 2. A program recorded in permanent or
semipermanent computer memory.
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![Flicker - In video, any of several visual artifacts similar to ( i.e., manifested as) a stroboscopic effect ( jerkiness
), sometimes caused by or related to vertical synchronization characteristics or video field display rates.
Flip-Flop - A device that may assume either one of two reversible, stable states. Note 1: The flip-flop is used
as a basic control element in computer and communications systems. Note 2: In a flip-flop, the transition
from one stable state to the other is unstable, i.e., for the very short period during which the transition takes
place, both outputs may assume the same state, which state may be unpredictable. Synonyms bistable
circuit, bistable multivibrator, bistable trigger circuit.
Floating - See conference floating. In conference calling, the state in which the conference is active but
without a controller. This state is possible when two or more conferees exist on an active conference and the
controller successfully disconnects himself/herself.
Floating Head - A magnetic head floating on a layer of air away from the recording surface. Synonyms air-
floating head, flying head.
Floating-Point Coding Compaction - Data compaction accomplished by using coefficients, a base, and
exponents to specify the scale, range, or magnitude of numbers. Note: An example of floating -point coding
compaction is using 119.8 × 10 6 , 119.8(6), or 119.86 to represent 119,800,000. If the number is rounded to
120,000,000, it might be written as 1206 or 127 in which the last digit is the number of zeros to be appended
to the preceding digits. Thus, only three positions are required instead of nine to represent the number in
storage or in a message, which is only 33% of the original space and time requirement.
Float Operation - Operation of a dc system with the battery, rectifier, and load all connected in parallel. The
battery charger supplies the normal dc load plus any battery self-discharge current or recharge current
required after a discharge.
Flooding - Insertion of a large volume of data resulting in denial of service. Synonyms [in e-mail and forum
postings] mail bombing, spamming; [in radio and wireline communications] flood-search routing, pilot-
make-busy.
Flooding Compound - A substance surrounding the buffer tubes of a fiber -optic cable, to prevent water
intrusion into the interstices in the event of a breach of the jacket.
Flood Projection - In facsimile , the optical method of scanning in which the object is floodlighted and the
scanning spot is defined by a masked portion of the illuminated area.
Flood Search Routing - In a telephone network, nondeterministic routing in which a dialed number received
at a switch is transmitted to all switches, i.e., flooded, in the area code directly connected to that switch; if
the dialed number is not an affiliated subscriber at that switch, the number is then retransmitted to all
directly connected switches, and then routed through the switch that has the dialed number corresponding
to the particular user end instrument affiliated with it. Note 1: All digits of the numbering plan are used to
identify a particular subscriber. Note 2: Flood search routing allows subscribers to have telephone numbers
independent of switch codes. Note 3: Flood search routing provides the highest probability that a call will go
through even though a number of switches and links fail.
floppy disk - Synonym diskette. In computer technology, a small disk of flexible plastic, coated with a
magnetizable material and enclosed in a protective jacket, used to store digital data. Note: A diskette is
distinguished from a hard disk by virtue of the fact that it is flexible, and unlike most hard disks, is removable
from its drive.
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![flops - Acronym for floating -point operations per second. Note: For example, 15 Mflops equals 15 million
floating-point arithmetic operations per second.
Flowchart - A graphical representation in which symbols are used to represent such things as operations,
data , flow direction, and equipment, for the definition, analysis, or solution of a problem. Synonym flow
diagram.
Flow Control - See transmit flow control. In data communications systems, control of the rate at which data
are transmitted from a terminal so that the data can be received by another terminal. Note 1: Transmit flow
control may occur between data terminal equipment ( DTE ) and a switching center, via data circuit-
terminating equipment ( DCE ), or between two DTEs. The transmission rate may be controlled because of
network or DTE requirements. Note 2: Transmit flow control can occur independently in the two directions
of data transfer, thus permitting the transfer rates in one direction to be different from the transfer rates in
the other direction.
Flow Control Procedure - A procedure for controlling the rate of transfer of data among elements of a
network, e.g. , between a DTE ( data terminal equipment ) and a data switching exchange network, to
prevent overload.
Flow Diagram - Synonym flowchart. A graphical representation in which symbols are used to represent such
things as operations, data , flow direction, and equipment, for the definition, analysis, or solution of a
problem.
Flowline - On a flowchart, a line that (a) has an indicated direction, (b) represents a connection between
other symbols, and (c) indicates the sequence of operations or the transfer of control.
Flutter - Rapid variation of signal parameters, such as amplitude, phase, and frequency. Note: Examples of
flutter are (a) rapid variations in received signal levels, such as variations that may be caused by atmospheric
disturbances, antenna movements in a high wind, or interaction with other signals, (b) in radio propagation,
a phenomenon in which nearly all radio signals that are usually reflected by ionospheric layers in or above
the E-region experience partial or complete absorption, (c) in radio transmission, rapidly changing signal
levels, together with variable multipath time delays, caused by reflection and possible partial absorption of
the signal by aircraft flying through the radio beam or common scatter volume, (d) the variation in the
transmission characteristics of a loaded telephone circuit caused by the action of telegraph direct currents
on the loading coils, (e) in recording and reproducing equipment, the deviation of frequency caused by
irregular mechanical motion, e.g., that of capstan angular velocity in a tape transport mechanism, during
operation. Synonym [loosely] frequency flutter .
Flux - 1. The lines of force of a magnetic field. 2. Obsolete synonym for radiant power.
Flying Head - Synonym floating head. A magnetic head floating on a layer of air away from the recording
surface.
Flywheel Effect - In an oscillator, the continuation of oscillations after removal of the control stimulus. Note
1: The flywheel effect is usually caused by interacting inductive and capacitive circuits in the oscillator. Note
2: The flywheel effect may be desirable, such as in phase -locked loops used in synchronous systems, or
undesirable, such as in voltage-controlled oscillators. Synonym flywheeling.
Flywheeling - Synonym flywheel effect. In an oscillator, the continuation of oscillations after removal of the
control stimulus. Note 1: The flywheel effect is usually caused by interacting inductive and capacitive circuits
in the oscillator. Note 2: The flywheel effect may be desirable, such as in phase -locked loops used in
synchronous systems, or undesirable, such as in voltage-controlled oscillators.
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![considered full-motion in PAL and SECAM systems. Many proprietary video technologies produce 15 fps
video; 24 fps is considered full-motion in motion-picture technology.
Fractal - A mathematical formula or algorithm that constitutes or defines an efficient way of formulating
computer graphics. Fractal graphics translate the natural curves of an object into mathematical formulas,
from which the entire image can later be constructed. Fractals are self-similar in that any piece of the fractal
design contains a miniature of the entire design. A fractal is completely described by (a) one piece ( layer ) of
the design, and (b) a sublayer of the design, which sublayer shows how contiguous pieces (layers) fit
together. For this reason, fractal patterns (designs) require very little computer storage space. An example of
a fractal is a fern leaf design.
Fractional Frequency Deviation - Synonym fractional frequency offset . A measure of the deviation of the
frequency of a signal from a reference, expressed as a ratio. The ratio is dimensionless but typically
expressed as parts per million, ppm. For example, 4.6 ppm = 4.6/106. Fractional frequency offset = [(f-fr) / fr]
where: f = the actual frequency output of the signal in question, and fr = the reference frequency.
Fractional Frequency Fluctuation - The deviation of the frequency of an oscillator from its nominal constant
frequency, normalized to the nominal frequency.
Fractional Frequency Offset - A measure of the deviation of the frequency of a signal from a reference,
expressed as a ratio. The ratio is dimensionless but typically expressed as parts per million, ppm. For
example, 4.6 ppm = 4.6/106. Fractional frequency offset = [(f-fr) / fr] where: f = the actual frequency output
of the signal in question, and fr = the reference frequency. Synonym fractional frequency deviation.
Fractional T1 - A fractional T1 or T3 line is a T1 or T3 digital phone line in the North American T-carrier
system that is leased to a customer at a fraction of its data-carrying capacity and at a correspondingly lower
cost. A T1 line contains 24 channels, each with a data transfer capacity of 64 Kbps. The customer can rent
some number of the 24 channels. The transmission method and speed of transfer remain the same.
Overhead bits and framing are still used, but the unrented channels simply contain no data.
In telecommunications a fractional T1 is a portion of the 1.544 Mb/s (T1-aggregate) bit stream; the available
fractions being determined by the type of multiplexer used to achieve the T1 aggregate bit stream.
T3 lines (which offer 672 64 Kbps channels) are also sometimes offered as a fractional service. T1 and
fractional T1 service are sometimes advertised as "point-to-point" service (from the customer to the service
provider).
Fragmentation -1. The process in which an IP ( Internet protocol ) datagram is broken into smaller pieces to
fit the requirements of a given physical network; the reverse process of reassembly. 2. The physical
separation of portions of a file on a computer disk.
Frame -1. In data transmission, the sequence of contiguous bits delimited by, and including, beginning and
ending flag sequences. Note 1: A frame usually consists of a specified number of bits between flag sequences
and usually includes an address field, a control field, and a frame check sequence. Note 2: Frames usually
consist of a representation of the original data to be transmitted, together with other bits which may be
used for error detection or control. Additional bits may be used for routing, synchronization, or overhead
information not directly associated with the original data. 2. In the multiplex structure of pulse-code
modulation ( PCM ) systems, a set of consecutive time slots in which the position of each digit can be
identified by reference to a frame-alignment signal. Note: The frame-alignment signal does not necessarily
occur, in whole or in part, in each frame. 3. In a time-division multiplexing ( TDM ) system, a repetitive group
of signals resulting from a single sampling of all channels, including any required system information, such as
additional synchronizing signals. Note: "In-frame" is the condition that exists when there is a channel -to-
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![channel and bit-to-bit correspondence, exclusive of transmission errors, between all inputs of a time-division
multiplexer and the output of its associated demultiplexer. 4. In ISDN, a block of variable length, labeled at
the Data Link Layer of the Open Systems Interconnection--Reference Model. 5. In video display, the set of all
picture elements that represent one complete image. Note: In NTSC and other television standards used
throughout the world, a frame consists of two interlaced fields, each of which has half the number of
scanning lines, and consequently, half the number of pixels, of one frame. 6. In video display, one complete
scanned image from a series of video images. Note: A video frame is usually composed of two interlaced
fields. 7. In computer screen displays of HTML documents, a portion (usually rectangular) of the screen
where one usually finds the same types of fields/information displayed, in the same manner as one usually
finds the same or similar information displayed in the same segment of different copies of a printed form. 8.
An HTML feature that allows multiple Web pages to be viewed simultaneously (by means of scrolling or re-
sizing) through a browser window.
Frame Alignment - 1. In the reception of framed digital data, the extent to which a received frame is
correctly aligned with respect to the clock at the receiver. 2. The state in which the frame of the receiving
equipment is synchronized with that of the received signal.
Frame-Alignment Recovery Time - Synonym reframing time. The time interval between the instant at which
a valid frame-alignment signal is available at the receiving data terminal equipment and the instant at which
frame alignment is established. Note: The reframing time includes the time required for replicated
verification of the validity of the frame-alignment signal.
Frame-Alignment Signal - In the transmission of data frames, a distinctive sequence of bits used to
accomplish frame alignment. Note: A frame-alignment signal may also contain additional bits for status,
control, and error detection.
Frame-Alignment Time Slot - A time slot occupying the same relative position in every frame and used to
transmit the frame alignment signal.
Frame Check Sequence (FCS) - 1. An error-detection scheme that (a) uses parity bits generated by
polynomial encoding of digital signals, (b) appends those parity bits to the digital signal, and (c) uses
decoding algorithms that detect errors in the received digital signal. Note: Error correction, if required, may
be accomplished through the use of an automatic repeat-request (ARQ) system. 2. [An] error checking
mechanism that checks data integrity by computing a polynomial algorithm based checksum.
Framed Interface - An interface through which information flow is partitioned into physical, periodic frames
consisting of overhead information and an information payload.
Frame Duration - The time between the beginning of a frame and the end of that frame. Note: For fixed-
length frames, at a fixed data rate, frame duration is constant.
Frame Frequency - Synonym frame rate. The number of frames transmitted or received per unit time. Note
1: The frame rate is usually expressed in frames per second. Note 2: In television transmission, the frame rate
must be distinguished from the field rate, which in the NTSC and other systems, is twice the frame rate.
Frame Grabber - A device that can seize and record a single frame of video information out of a sequence of
many frames.
Frame Matching - The process of comparing one sequence of frames with another sequence of frames in
order to determine the correspondence between frames in each sequence and the correspondence of
individual frames. Note: One means to test the correspondence between two video frames is to compare
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![Frame Synchronization Pattern - In digital communications, a prescribed recurring pattern of bits
transmitted to enable the receiver to achieve frame synchronization.
Framing -1. In time-division multiplexing reception, synonym frame synchronization. 2. In video reception,
the process of adjusting the timing of the receiver to coincide with the received video synchronization pulse.
3. In facsimile, the adjustment of the facsimile picture to a desired position in the direction of line
progression.
Framing Bit -1. A bit used for frame synchronization. 2. In a bit stream, a bit used in determining the
beginning or end of a frame. Note 1: The framing bit occurs at a specific position in the frame. Note 2: In a bit
stream, framing bits are noninformation bits. Note 3: Framing in a digital signal is usually repetitive.
Framing Signal - See frame-alignment signal, framing bit. In the transmission of data frames, a distinctive
sequence of bits used to accomplish frame alignment. Note: A frame-alignment signal may also contain
additional bits for status, control, and error detection.
Fraunhofer Diffraction Pattern - Synonym far-field diffraction pattern. The diffraction pattern of a source
(such as an LED, ILD, or the output end of an optical fiber ) observed at an infinite distance from the source.
Note 1: A far- field pattern exists at distances that are large compared with s 2 / , where s is a characteristic
dimension of the source and is the wavelength. For example, if the source is a uniformly illuminated circle,
then s is the radius of the circle. Note 2: The far-field diffraction pattern of a source may be observed at
infinity or (except for scale) in the focal plane of a well-corrected lens. The far-field pattern of a diffracting
screen illuminated by a point source may be observed in the image plane of the source. Synonym Fraunhofer
diffraction pattern.
Fraunhofer Region - Synonym far-field region. The region where the angular field distribution is essentially
independent of distance from the source. Note 1: If the source has a maximum overall dimension D that is
large compared to the wavelength, the far-field region is commonly taken to exist at distances greater than
2
2D / from the source, being the wavelength. Note 2: For a beam focused at infinity, the far-field region is
sometimes referred to as the Fraunhofer region.
Free Net - A radio net in which any station may communicate with any other station in the net without first
obtaining the permission of the net- control station. Note: Permission to operate as a free net is granted by
the net-control station until such time as a directed net is established by the net-control station. See [for
Internet systems] freenet.
Freenet - A system of computer networks (usually funded by individuals or organizations) consisting of
community-based bulletin board systems with, e.g., e-mail, information services, interactive
communications, and conferencing, and that are available to the user free of charge, or for a small
membership fee. See [for radio communications] free net.
Freephone - In the U.K., Freephone is a type of Number Translation Service (NTS) that allows a phone user to
call a non-geographic number beginning with 0800 or 0500 without incurring a charge. All charges and
associated costs are charged to the organization that receives the call. Businesses and non-profit help lines
often offer Freephone numbers. Freephone is similar to 1-800 numbers used in the U.S.
Free Routing - The routing of messages in such a manner that they are forwarded toward their destination or
addressee over any available channel without dependence upon predetermined routing.
Free-Running Capability - In a synchronized oscillator, the capability to operate in the absence of a
synchronizing signal.
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![Frequency-Exchange Signaling - Frequency-change signaling in which the change from one significant
condition to another is accompanied by decay in amplitude of one or more frequencies and by buildup in
amplitude of one or more other frequencies. Note: Frequency-exchange signaling applies to supervisory
signaling and user - information transmission. Synonym two-source frequency keying.
Frequency Fluctuation - A short-term variation, with respect to time, of the frequency of an oscillator.
Frequency Flutter - A deviation of frequency that generally results from irregular motion of the recording
medium during the recording, duplication, or reproduction. Synonym [loosely] flutter.
Frequency Frogging -1. The interchanging of the frequencies of carrier channels to accomplish specific
purposes, such as to prevent feedback and oscillation, to reduce crosstalk, and to correct for a high
frequency-response slope in the transmission line. Note: Frequency frogging is accomplished by having
modulators, which are integrated into specially designed repeaters, translate a low-frequency group to a
high-frequency group, and vice versa. A channel will appear in the low group for one repeater section and
will then be translated to the high group for the next section because of frequency frogging. This results in
nearly constant attenuation with frequency over two successive repeater sections, and eliminates the need
for large slope equalization and adjustments. Singing and crosstalk are minimized because the high- level
output of a repeater is at a different frequency than the low-level input to other repeaters. 2. In microwave
systems, the alternate use of two frequencies at repeater sites to prevent feedback and oscillation.
Frequency Guard Band - A frequency band deliberately left vacant between two channels to provide a
margin of safety against mutual interference.
Frequency Hopping - The repeated switching of frequencies during radio transmission according to a
specified algorithm, to minimize unauthorized interception or jamming of telecommunications. Note: The
overall bandwidth required for frequency hopping is much wider than that required to transmit the same
information using only one carrier frequency.
Frequency-Hopping Spread Spectrum - A signal structuring technique employing automatic switching of the
transmitted frequency. Selection of the frequency to be transmitted is typically made in a pseudo-random
manner from a set of frequencies covering a band wider than the information bandwidth. The intended
receiver would frequency- hop in synchronization with the code of the transmitter in order to retrieve the
desired information. Note: In many cases, used as an electronic counter- countermeasure ( ECCM )
technique.
Frequency Hour - One frequency used for one hour regardless of the number of transmitters over which it is
simultaneously broadcast by a station during that hour.
Frequency Instability - See frequency stability. The degree to which variations of the frequency of an
oscillator deviate from the mean frequency over a specified period of time.
Frequency Lock - The condition in which a frequency -correcting feedback loop maintains control of an
oscillator within the limits of one cycle. Note: Frequency lock does not imply phase lock, but phase lock does
imply frequency lock.
Frequency Modulation (FM) - Modulation in which the instantaneous frequency of a sine wave carrier is
caused to depart from the center frequency by an amount proportional to the instantaneous value of the
modulating signal. Note 1: In FM, the carrier frequency is called the center frequency. Note 2: FM is a form of
angle modulation. Note 3: In optical communications, even if the electrical baseband signal is used to
frequency-modulate an electrical carrier (an "FM" optical communications system), it is still the intensity of
the lightwave that is varied (modulated) by the electrical FM carrier. In this case, the "information," as far as
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![FTTP (Fiber to the Premises) - A fiber-optic network that connects directly from the carrier network to the
user premises. Another fiber-optic network is FTTC (Fiber to the Curb) that connects from the carrier
network to the curb, and from there to the premises by copper wire or coaxial cable.
Full-Duplex (FDX) Circuit - A circuit that permits simultaneous transmission in both directions.
Full-Duplex (FDX) Operation - Synonym duplex operation. Operating method in which transmission is
possible simultaneously, in both directions of a telecommunication channel. [NTIA] [RR] Note 1: This
definition is not limited to radio transmission. Note 2: In general, duplex operation and semi-duplex
operation require two frequencies in radiocommunication; simplex operation may use either one or two.
Synonym two-way simultaneous operation.
Full Width at Half Maximum (FWHM) - An expression of the extent of a function, given by the difference
between the two extreme values of the independent variable at which the dependent variable is equal to
half of its maximum value. Note 1: FWHM is applied to such phenomena as the duration of pulse waveforms
and the spectral width of sources used for optical communications. Note 2: The term full duration at half
maximum (FDHM) is preferred when the independent variable is time.
Fully Connected Mesh Network - See network topology.
Fully Connected Topology - See network topology.
Functionality - The ability of equipment to operate as expected during actual service conditions in a central
office.
Functional Component (FC) - In intelligent networks, an elemental call-processing component that directs
internal network resources to perform specific actions, such as collecting dialed digits. Note: An FC is unique
to the intelligent-network-IN/2 architecture.
Functional Unit - An entity of hardware, software, or both, capable of accomplishing a specified purpose.
Fundamental - Of a periodic wave, the sinusoidal component, i.e., Fourier component, having the lowest
frequency. Note: Every periodic waveform may be expressed as the summation of the fundamental and its
harmonics. For example, a square wave may be expressed as the summation of sine waves equal in
frequency to the fundamental and all odd harmonics, each frequency having an appropriate amplitude and
phase. A pure sinusoidal wave has only one component, i.e., the fundamental.
Fundamental Mode - The lowest order mode of a waveguide. Note: In optical fibers, the fundamental mode
is designated LP01 or HE11.
Fusion - Synonym (in cryptosystems) linkage. - In computer security, the purposeful combining of data or
information from one data processing system with data or information from another system to derive
protected information.
Fusion Splice - In fiber optics, a splice created by localized heating of the ends of the two fibers to be joined.
Note: A properly made fusion splice results in a continuous length of material with minimal discontinuities at
the splice.
G
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![Gap-Loss Attenuator - An optical attenuator that exploits the principle of gap loss to reduce the optical
power level when inserted in-line in the fiber path; e.g., to prevent saturation of the receiver. Note: Gap-loss
attenuators should be used in-line near the optical transmitter.
Gaps - Periods of no speech activity or low-energy content signals present in the access channel of a
wideband packet network.
Garble - 1. An error in transmission, reception, encryption, or decryption that changes the text of a message
or any portion thereof in such a manner that it is incorrect or undecryptable. 2. In a telephone circuit or
channel, readily audible but unintelligible interference from another circuit or channel. Note: Garble may, for
example, take place in an FDM telephone carrier system in which an interfering signal from another channel
or system is demodulated in such a fashion that it has an objectionable audio power level but is nonetheless
unintelligible.
Gate - 1. A device having one output channel and one or more input channels, such that the output channel
state is completely determined by the input channel states, except during switching transients. 2. One of
many types of combinational logic elements having at least two inputs; e.g., AND, OR, NAND, and NOR.
Gateway - A system that translates incompatible networks or applications. Gateway is also commonly used
to refer to any system that provides access to another system. A gateway is a network point that acts as an
entrance to another network. On the Internet, a node or stopping point can be either a gateway node or a
host (end-point) node. Both the computers of Internet users and the computers that serve pages to users are
host nodes. The computers that control traffic within your company's network or at your local Internet
service provider (ISP) are gateway nodes.
In the network for an enterprise, a computer server acting as a gateway node is often also acting as a proxy
server and a firewall server. A gateway is often associated with both a router, which knows where to direct a
given packet of data that arrives at the gateway, and a switch, which furnishes the actual path in and out of
the gateway for a given packet.
1. In a communications network, a network node equipped for interfacing with another network that uses
different protocols. Note 1: A gateway may contain devices such as protocol translators, impedance
matching devices, rate converters, fault isolators, or signal translators as necessary to provide system
interoperability. It also requires that mutually acceptable administrative procedures be established between
the two networks. Note 2: A protocol translation/mapping gateway interconnects networks with different
network protocol technologies by performing the required protocol conversions. 2. [An] interface providing a
compatibility between networks by converting transmission speeds, protocols, codes, or security measures.
3. Loosely, a computer configured to perform the tasks of a gateway.
Gating - 1. The process of selecting only those portions of a wave between specified time intervals or
between specified amplitude limits. 2. The controlling of signals by means of combinational logic elements.
3. A process in which a predetermined set of conditions, when established, permits a second process to
occur.
Gaussian Beam - A beam of light whose electric field intensity distribution is gaussian.
Gaussian Filter - A filter having a response curve (magnitude versus frequency) that approximates an ideal
gaussian curve.
Gaussian Pulse - A pulse that has a waveform described by the gaussian distribution.
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![Guided Mode - Synonym bound mode. In an optical fiber, a mode that (a) has a field intensity that decays
monotonically in the transverse direction everywhere external to the core and (b) does not lose power to
radiation. Note: Except for single-mode fibers, the power in bound modes is predominantly contained in the
core of the fiber.
Guided Ray - In an optical fiber, a ray that is confined primarily to the core. Synonyms bound ray, trapped
ray.
Guided Wave - A wave having (a) energy concentrated near a boundary, or between substantially parallel
boundaries, separating materials of different properties and (b) a direction of propagation effectively parallel
to these boundaries.
H
H.323 - The standard call protocol for voice and videoconferencing over LANs, WANs, and the Internet,
allowing these activities on a real-time basis as opposed to a packet-switched network. Initially designed to
allow multimedia to function over unreliable networks, it's the oldest and most established of the VoIP
protocols. See also SIP and MGCP.
Hack - 1. To break into or use a computer network or use a system without authorization, as a hacker might
do. 2. Referring to a track used to bypass a flaw or a bug in an application program or application.
Hacker - 1. A person who breaks into, or attempts to break into, or use, a computer network or system
without authorization, often at random, for personal amusement or gratification, and not necessarily with
malicious intent. 2. [An] unauthorized user who attempts to or gains access to an information system. 3. A
technically sophisticated computer expert who intentionally gains unauthorized access to targeted protected
resources. 4. Loosely, a computer enthusiast. 5. A person who uses a computer resource in a manner for
which it is not intended or which is in conflict with the terms of an acceptable-use policy, but (unlike the
work of a cracker) is not necessarily malicious in intent. hack: 1. To break into or use a computer network or
use a system without authorization, as a hacker might do. 2. Referring to a track used to bypass a flaw or a
bug in an application program or application.
Hagelbarger Code - A convolutional code that enables error bursts to be corrected provided that there are
relatively long error-free intervals between the error bursts. Note: In the Hagelbarger code, inserted parity
check bits are spread out in time so that an error burst is not likely to affect more than one of the groups in
which parity is checked.
Half-Duplex (HDX) Operation - Operation in which communication between two terminals occurs in either
direction, but in only one direction at a time. Note: Half-duplex operation may occur on a half-duplex circuit
or on a duplex circuit, but it may not occur on a simplex circuit. Synonyms one-way reversible operation,
two-way alternate operation.
Halftone - Any photomechanical printing surface or the impression therefrom in which detail and tone
values are represented by a series of evenly spaced dots in varying size and shape, varying in direct
proportion to the intensity of tones they represent
Halftone Characteristic - 1. In facsimile systems, the relationship between the density of the recorded copy
and the density of the object, i.e., the original. 2. In facsimile systems, the relationship between the
amplitude of the facsimile signal to either the density of the object or the density of the recorded copy when
only a portion of the system is under consideration. Note: In an FM facsimile system, an appropriate
parameter other than the amplitude is used.
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![Hamming code: An error-detecting and error-correcting binary code, used in data transmission, that can (a)
detect all single- and double-bit errors and (b) correct all single-bit errors. Note: A Hamming code satisfies
m
the relation 2 n +1, where n is the total number of bits in the block, k is the number of information bits
in the block, and m is the number of check bits in the block, where m = n-k.
Hamming Distance - The number of digit positions in which the corresponding digits of two binary words of
the same length are different. Note 1: The Hamming distance between 1011101 and 1001001 is two. Note 2:
The concept can be extended to other notation systems. For example, the Hamming distance between
2143896 and 2233796 is three, and between "toned" and "roses" it is also three. Synonym signal distance.
Hamming Weight - The number of non-zero symbols in a symbol sequence. Note: For binary signaling,
Hamming weight is the number of "1" bits in the binary sequence.
Handoff - 1. In cellular mobile systems, the process of transferring a phone call in progress from one cell
transmitter and receiver and frequency pair to another cell transmitter and receiver using a different
frequency pair without interruption of the call. Synonym handover. 2. In satellite communications, the
process of transferring ground-station control responsibility from one ground station to another without loss
or interruption of service.
Handover - 1. In telephony, synonym handoff. 2. The transfer (permanent or temporary) of a component or
series of components to another application process. 3. The automatic rerouting of the radio portion of a call
for signal quality, traffic management, or other reasons.
Handshaking - 1. In data communications, a sequence of events governed by hardware or software,
requiring mutual agreement of the state of the operational modes prior to information exchange. 2. The
process used to establish communications parameters between two stations. Note: Handshaking follows the
establishment of a circuit between the stations and precedes information transfer. It is used to agree upon
such parameters as information transfer rate, alphabet, parity, interrupt procedure, and other protocol
features.
Handshaking Procedures - [The] dialogue between two information systems for synchronizing, identifying,
and authenticating themselves to one another.
Hangover - Synonym tailing. In facsimile systems, the excessive prolongation of the decay of the signal.
Hang-Up - Calling- or called-user placement of a telephone set or other unit of telecommunications
equipment in the quiescent state.
Hang-Up Signal - An on-hook signal sent from an end office toward the disconnect-control office indicating
either calling or called user hang-up and requesting the connection be disconnected. The interface remains
dedicated to the call until the disconnect-control office responds to the hang-up signal.
HA1-Receiver Weighting - A noise weighting used in a noise measuring set to measure noise across the HA1-
receiver of a 302-type or similar instrument. Note 1: The meter scale readings of an HA1 test set are in dBa
(HA1). Note 2: HA1 noise weighting is obsolete for new DOD applications.
Hard Copy - In computer graphics and in telecommunications, a permanent reproduction, on any media
suitable for direct use by a person, of displayed or transmitted data. Note 1: Examples of hard copy include
teletypewriter pages, continuous printed tapes, facsimile pages, computer printouts, and radiophoto prints.
Note 2: Magnetic tapes, diskettes, and nonprinted punched paper tapes are not hard copy.
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![Hard-Copy Key - [A] physical keying material, such as printed key lists, punched or printed key tapes, or
programmable, read-only memories (pROM).
Hard Disk - A flat, circular, rigid plate with a magnetizable surface on one or both sides of which data can be
stored. Note: A hard disk is distinguished from a diskette by virtue of the fact that it is rigid. Early in the
development of computer technology, hard disks, often multiple disks mounted on a common spindle, were
interchangeable and removable from their drives, which were separate from the processor chassis. This
technology is still in use, especially in conjunction with large mainframe computers, but physically smaller
computers use hard disks that are in sealed units, along with their control electronics and read /write heads.
The sealed units are usually installed permanently in the same chassis that contains the processor.
Hard-Drawn Copper Wire - Copper wire that has not been annealed after being drawn.
Hardened - Pertaining to the condition of a facility with protective features that enable it to withstand
destructive forces, such as explosions, natural disasters, or ionizing radiation.
Hard Limiting - See limiting. Any process by which a specified characteristic (usually amplitude) of the output
of a device is prevented from exceeding a predetermined value. Note 1: Hard limiting (" clipping ") is a
limiting action in which there is (a) over the permitted dynamic range, negligible variation in the expected
characteristic of the output signal, and (b) a steady-state signal, at the maximum permitted level, for the
duration of each period when the output would otherwise be required to exceed the permitted dynamic
range in order to correspond to the transfer function of the device. Note 2: Soft limiting is limiting in which
the transfer function of a device is a function of its instantaneous or integrated output level. The output
waveform is therefore distorted, but not clipped.
Hard Sectoring - In magnetic or optical disk storage, sectoring that uses a physical mark on the disk, from
which mark sector locations are referenced. Note: Hard sectoring may be done, for example, by punching an
index hole in a floppy diskette. When the presence of the index hole is recognized by an optical reader, a
reference signal is generated. All sector locations can be referenced from this signal.
Hardware - 1. Physical equipment as opposed to programs, procedures, rules, and associated
documentation. 2. The generic term dealing with physical items as distinguished from its capability or
function such as equipment, tools, implements, instruments, devices, sets, fittings, trimmings, assemblies,
subassemblies, components, and parts. The term is often used in regard to the stage of development, as in
the passage of a device or component from the design stage into the hardware stage as the finished object.
3. In data automation, the physical equipment or devices forming a computer and peripheral components.
Hardware Platform - Synonym platform. 1. The type of computer on which a given operating system or
application runs. Synonym hardware platform. 2. The operating system in use on a given computer. Synonym
operating system platform. 3. The application program in use on a given computer and operating system.
Synonym application platform. Note 1: The term platform, usually with some kind of accompanying
qualifying verbiage, may also be applied to any combination of the foregoing. Note 2: The term cross-
platform may be used to characterize an application program or operating system that may be run on more
than one platform.
Hardwire - 1. To connect equipment or components permanently in contrast to using switches, plugs, or
connectors. 2. To wire in fixed logic or read-only storage that cannot be altered by program changes.
Hardwired Key - [A] permanently installed key. Information (usually a sequence of random or pseudorandom
binary digits) used initially to set up and permanently installed for the operations performed in crypto-
equipment for the purpose of encrypting or decrypting electronic signals, for determining electronic counter-
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![countermeasures patterns (e.g., frequency hopping or spread spectrum), or for producing other key. Note:
"Key" has replaced the terms "variable," "key(ing) variable," and "cryptovariable."
Harmful Interference - 1. Any emission, radiation, or induction interference that endangers the functioning
or seriously degrades, obstructs, or repeatedly interrupts a communications system, such as a radio
navigation service, telecommunications service, radio communications service, search and rescue service, or
weather service, operating in accordance with approved standards, regulations, and procedures. Note: To be
considered harmful interference, the interference must cause serious detrimental effects, such as circuit
outages and message losses, as opposed to interference that is merely a nuisance or annoyance that can be
overcome by appropriate measures. 2. Interference which endangers the functioning of a radionavigation
service or of other safety services or seriously degrades, obstructs, or repeatedly interrupts a
radiocommunication service operating in accordance with these [Radio] Regulations.
Harmonic - 1. Of a sinusoidal wave, an integral multiple of the frequency of the wave. Note: The frequency of
the sine wave is called the fundamental frequency or the first harmonic, the second harmonic is twice the
fundamental frequency, the third harmonic is thrice the fundamental frequency, etc. 2. Of a periodic signal
or other periodic phenomenon, such as an electromagnetic wave or a sound wave, a component frequency
of the signal that is an integral multiple of the fundamental frequency. Note: The fundamental frequency is
the reciprocal of the period of the periodic phenomenon.
Harmonic Distortion - In the output signal of a device, distortion caused by the presence of frequencies that
are not present in the input signal. Note: Harmonic distortion is caused by nonlinearities within the device.
Hash Function - A mathematical function that maps values from a large (or very large) domain into a smaller
range, and that reduces a potentially long message into a "message digest" or "hash value" or that is
sufficiently compact to be input into a digital signature algorithm. Note: A "good" hash function is one that
results from applying the function to a (large) set of values that are evenly (and randomly) distributed over
the range.
Hashing - Computation of a hash total, which is: 1. The result obtained by subjecting a set of data to an
algorithm for purposes of checking the data at the time the algorithm is applied or for use at a later time
such as after transmission or retrieval from storage. 2. [A] value computed on data to detect error or
manipulation.
Hash Total - 1. The result obtained by subjecting a set of data to an algorithm for purposes of checking the
data at the time the algorithm is applied or for use at a later time such as after transmission or retrieval from
storage. 2. [A] value computed on data to detect error or manipulation. See checksum.
Hash Value - In cryptography, the result of applying a cryptologic hash function to a message.
Hashword - [The] memory address containing [a] hash total.
Hazards of Electromagnetic Radiation to Fuel (HERF) - The potential for electromagnetic radiation to cause
ignition or detonation of volatile combustibles, such as aircraft fuels.
Hazards of Electromagnetic Radiation to Ordnance (HERO) - The potential for electromagnetic radiation to
affect adversely munitions or electroexplosive devices.
Hazards of Electromagnetic Radiation to Personnel (HERP) - The potential for electromagnetic radiation to
produce harmful biological effects in humans.
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![H-bend - A smooth change in the direction of the axis of a waveguide, throughout which the axis remains in a
plane parallel to the direction of magnetic H-field (transverse) polarization. Synonym H-plane bend.
H-channel - In Integrated Services Digital Networks (ISDN), a 384-kb/s, 1472-kb/s, or 1536-kb/s channel,
designated as "H0", "H10", and "H11", respectively, accompanied by timing signals used to carry a wide variety
of user information. Note: Examples of types of user information representation forms include fast facsimile,
video, high-speed data, high-quality audio, packet-switched data, bit streams at rates less than the
respective H-channel bit rate that have been rate-adapted or multiplexed together, and packet-switched
information.
HDCP - Abbreviation for High Definition Content Protection. Technology used to prevent piracy of high-
quality uncompressed video, primarily over DVI connections.
HDLC - Abbreviation for high-level data link control. A Link-Level protocol used to facilitate reliable point-to-
point transmission of a data packet. Note: A subset of HDLC, known as " LAP-B," is the Layer-two protocol for
ITU-T Recommendation X.25.
HDMI - Abbreviation for High Definition Multimedia Interface. A high-quality digital connector. Similar to
DVI and sometimes with HDCP, HDMI can digitally transmit uncompressed high-definition video and audio on
the same cable, preserving picture and sound quality.
HDTV - Abbreviation for high-definition television. Television that has approximately twice the horizontal
and twice the vertical emitted resolution specified by the NTSC standard. The highest quality digital
television, generally widescreen 16:9. It consists of either 1080 interlaced or 720 progressively scanned lines
of resolution and includes the ability to transmit digital surround sound. Note that HDTV and DTV are not the
same thing — HDTV is one format of DTV. Note 1: In HDTV, the total number of pixels is therefore
approximately four times that of the NTSC standard. Note 2: HDTV may include any or all improved-
definition television (IDTV) and extended-television (EDTV) improvements. Note 3: HDTV employs a wide
aspect ratio.
HDTV Monitor (also HDTV-Ready) - A TV set with the inputs and capability to become an HDTV with the
addition of an HDTV tuner, HD cable set-top box, or HD satellite receiver.
HDTV Tuner (also known as Decoder or Receiver) - A device capable of receiving and decoding HDTV signals.
HDTV tuners can either be built into a TV set (called an Integrated Digital TV Set) or be a stand-alone device,
such as a set-top box.
HDX - Abbreviation for half-duplex (HDX) operation. Operation in which communication between two
terminals occurs in either direction, but in only one direction at a time. Note: Half-duplex operation may
occur on a half-duplex circuit or on a duplex circuit, but it may not occur on a simplex circuit. Synonyms one-
way reversible operation, two-way alternate operation.
Head - A device that reads, writes, and/or erases data on a storage medium.
Head End - See cable headend, headend. 1. A central control device required by some networks (e.g., LANs
or MANs) to provide such centralized functions as remodulation, retiming, message accountability,
contention control, diagnostic control, and access to a gateway. 2. A control center of a CATV system, where
incoming signals are amplified, converted, processed, and combined into a common cable for transmission
to customers. The headend usually includes antennas, preamplifiers, frequency converters, demodulators,
modulators, processors, and other related equipment. Synonym [in this sense] cable headend.
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![I2 - Abbreviation for Internet second generation. A proposed high-speed Internet for use exclusively by
government researchers and academic institutions.
IAL - Abbreviation for Immediate Action Limit. The bound on performance allowed for a circuit or
connection that is in service. When any parameter value exceeds the IAL, the circuit or connection is
considered defective and corrective action is necessary.
IANA - Abbreviation for Internet Assigned Numbers Authority. An organization directed by the Internet
Architecture Board (IAB) and which assigns IP numbers and protocol parameters such as port, protocol, and
enterprise numbers, and options, codes, and types.
Ia - The 4-wire (2-pair) bidirectional primary rate interface point on the network side of the termination
equipment (i.e., NT1, NT2), including the equipment connecting cord, or equivalent, on the user side of the
interface cable.
Ib - The 4-wire (2-pair) bidirectional primary rate (PR) interface point on the user side of the termination
equipment (i.e., NT1 and NT2), including the equipment connecting cord or equivalent on the network side
of the interface cable.
IC - Abbreviation for integrated circuit (IC): An electronic circuit that consists of many individual circuit
elements, such as transistors, diodes, resistors, capacitors, inductors, and other active and passive
semiconductor devices, formed on a single chip of semiconducting material and mounted on a single piece of
substrate material. Synonyms chip, microcircuit.
ICA - Abbreviation for International Communications Association.
ICI - Abbreviation for incoming call identification. A switching system feature that allows an attendant to
identify visually the type of service or trunk group associated with a call directed to the attendant's position.
ICMP - Abbreviation for Internet Control Message Protocol. An Internet protocol that reports datagram
delivery errors. Note 1: ICMP is a key part of the TCP/IP protocol suite. Note 2: The packet internet gopher
(ping) application is based on ICMP.
Icon - In computer systems, a small, pictorial representation of an application software package, idea, or
concept used in a window or a menu to represent commands, files, or options.
ICW - Abbreviation for interrupted continuous wave. Modulation in which there is on-off keying of a
continuous wave.
Identification - [The] process an information system (IS) uses to recognize an entity.
Identification, Friend or Foe (IFF) - A system using electromagnetic transmissions to which equipment
carried by friendly forces automatically responds, for example, by emitting pulses, thereby distinguishing
themselves from enemy forces. Note: The secondary surveillance radar (SSR) system used in modern air
traffic control systems is an outgrowth of the military IFF system used during World War II. The IFF
equipment carried by modern military aircraft is compatible with the transponder system used for civilian air
traffic control.
Identification Friend or Foe Personal Identifier - The discrete identification, friend or foe code assigned to a
particular aircraft, ship, or other vehicle for identification by electronic means.
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![Identification Information -A form of notification information that consists of the documentation of the
actual sequence of intermediate networks traversed by a signaling message. The documentation of the
sequence of networks traversed may also include the origination and destination networks. The
documentation that the message traversed a given network is performed by that network itself.
Intermediate networks that are not ISNI-capable are not identified. ISNI identification information can be
used to force a return error message, destined for the originating SEP, to transit the same intermediate
network(s) as the original message.
Identifier (ID) - 1. In telecommunications and data processing systems, one or more characters used to
identify, name, or characterize the nature, properties, or contents of a set of data elements. 2. A string of
bits or characters that names an entity, such as a program, device, or system, in order that other entities can
call that entity. 3. In programming languages, a lexical unit that names a language object, such as a variable,
array, record, label, or procedure. Note: An identifier is placed in a label. The label is attached to, is a part of,
or remains associated with, the information it identifies. If the label becomes disassociated from the
information it identifies, the information may not be accessible.
Identity Authentication - The performance of tests to enable a data processing system to recognize entities.
Note: An example of identity authentication is the checking of a password or identity token.
Identity Token - 1. A device, such as a metal key or smart card, used for identity authentication.2. [A] Smart
card, metal key, or other physical object used to authenticate identity.
Identity Validation - Tests enabling an information system to authenticate users or resources.
IDF - Abbreviation for intermediate distribution frame. In a central office or customer premises, a frame that
(a) cross-connects the user cable media to individual user line circuits and (b) may serve as a distribution
point for multipair cables from the main distribution frame (MDF) or combined distribution frame (CDF) to
individual cables connected to equipment in areas remote from these frames.
Idle-Channel Noise - Noise that is present in a communications channel when no signals are applied. Note:
The channel conditions and terminations must be stated for idle-channel noise measurements to be
meaningful.
Idle Character - A control character that is transmitted when no useful information is being transmitted.
Idle Code - A special sequence that indicates that no data are being sent on the channelized side.
Idle-Line Termination - A switch-controlled electrical network that maintains a desired impedance at a trunk
or line terminal that is in the idle state.
Idle State - The telecommunications service condition that exists whenever user messages are not being
transmitted but the service is immediately available for use.
Idle Time - A period during which a system, circuit, or component is not in use, but is available.
IDN - Abbreviation for integrated digital network. A network that uses both digital transmission and digital
switching.
IDTV - Abbreviation for improved-definition television. - Television transmitters and receivers that (a) are
built to satisfy performance requirements over and above those required by the NTSC standard and (b)
remain within the general parameters of NTSC standard emissions. Note 1: IDTV improvements may be
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![made at the TV transmitter or the receiver. Note 2: Examples of improvements include enhancements in
encoding, digital filtering, scan interpolation, interlaced line scanning, and ghost cancellation. Note 3: IDTV
improvements must allow the TV signal to be transmitted and received in the standard 4:3 aspect ratio.
Synonym enhanced-quality television.
IETF - Abbreviation for Internet Engineering Task force. One of the task forces (with more than 40 working
groups) of the Internet Architecture Board, responsible for solving short-term engineering needs of the
Internet.
IF - Abbreviation for intermediate frequency. A frequency to which a carrier frequency is shifted as an
intermediate step in transmission or reception.
I/F - I/F: Abbreviation for interface.- 1. In a system, a shared boundary, i.e., the boundary between two
subsystems or two devices. 2. A shared boundary between two functional units, defined by specific
attributes, such as functional characteristics, common physical interconnection characteristics, and signal
characteristics. 3. A point of communication between two or more processes, persons, or other physical
entities. 4. A point of interconnection between user terminal equipment and commercial communications
facilities. 5. To interconnect two or more entities at a common point or shared boundary. 6. [A] common
boundary between independent systems or modules where interactions take place. 7. The point of
interconnection between two distinct but adjacent communications systems having different functions. The
interface in the communication-satellite service is that point where communications terminal equipment of
the terrestrial common carriers or other authorized entities interconnects with the terminal equipment of
the communication-satellite earth station complex. The interface in the communication-satellite service shall
be located at the earth station site, or if this is impracticable, as close thereto as possible.
IFF - Abbreviation for identification, friend or foe.- A system using electromagnetic transmissions to which
equipment carried by friendly forces automatically responds, for example, by emitting pulses, thereby
distinguishing themselves from enemy forces. Note: The secondary surveillance radar (SSR) system used in
modern air traffic control systems is an outgrowth of the military IFF system used during World War II. The
IFF equipment carried by modern military aircraft is compatible with the transponder system used for civilian
air traffic control.
IF4 (Interface 4) - An interface suitable for multipoint concentration by polling.
IF1 (Interface 1) - An interface suitable for star concentration.
IFRB - Abbreviation for International Frequency Registration Board. See Radio Regulations Board. The Radio
Regulations Board was formerly called International Frequency Registration Board (IFRB). A permanent
organization of the International Telecommunication Union (ITU) that implements frequency assignment
policy and maintains the Master International Frequency Register (MIFR).
IF Repeater - See heterodyne repeater. In radio reception and retransmission, a repeater that converts the
original band of frequencies of the received signal to a different frequency band for retransmission after
amplification. Note: IF repeaters are used, for example, in microwave systems, to avoid undesired feedback
between the receiving and transmitting antennas.
IFS - Abbreviation for ionospheric forward scatter. See ionospheric scatter. ionospheric scatter: The
propagation of radio waves by scattering as a result of irregularities or discontinuities in the ionization of the
ionosphere. Synonym forward propagation ionospheric scatter.
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![rejection ratio is measured, the input signal levels of the desired and image frequencies must be equal for
the measurement to be meaningful. Synonym image frequency rejection ratio.
Imagery - Collectively, the representations of objects reproduced electronically or by optical means on film,
electronic display devices, or other media.
IMD - Abbreviation for intermodulation distortion. - Nonlinear distortion characterized by the appearance,
in the output of a device, of frequencies that are linear combinations of the fundamental frequencies and all
harmonics present in the input signals. Note: Harmonic components themselves are not usually considered
to characterize intermodulation distortion. When the harmonics are included as part of the distortion, a
statement to that effect should be made.
Imitative Communications - See communications deception. 1. Deliberate transmission, retransmission, or
alteration of communications to mislead an adversary's interpretation of the communications. 2. Use of
devices, operations, and techniques with the intent of confusing or misleading the user of a communications
link or a navigation system.
Immediate Action Limit (IAL) - The bound on performance allowed for a circuit or connection that is in
service. When any parameter value exceeds the IAL, the circuit or connection is considered defective and
corrective action is necessary.
Immediate Activation - In cryptology, a condition of readiness associated with a key having no effective date.
Note: A key is immediately activated (a) by the receiver when the RSM is sent in response to the KSM that
carried that key, and (b) by the sender when the RSM is received in response to the KSM that carried the key.
Immediate Message - A category of precedence reserved for messages relating to situations that gravely
affect the security of national/allied forces or populace and that require immediate delivery to the
addressee(s).
Immunity - The ability of an assembly, equipment, or a system to perform without degradation in the
presence of an electromagnetic disturbance.
IMP - Abbreviation for interface message processor. - A processor-controlled switch used in packet-switched
networks to route packets to their proper destination.
Impedance - The total passive opposition offered to the flow of electric current. Note 1: Impedance is
determined by the particular combination of resistance, inductive reactance, and capacitive reactance in a
given circuit. Note 2: Impedance is a function of frequency, except in the case of purely resistive networks.
Impedance Matching - The connection of an additional impedance to an existing one in order to accomplish
a specific effect, such as to balance a circuit or to reduce reflection in a transmission line.
Impersonating - [A] form of spoofing. Spoofing is the interception, alteration, and retransmission of a cipher
signal or data in such a way as to mislead the recipient. 2. (AIS) [An] attempt to gain access to an AIS by
posing as an authorized user. [NIS] 3. Unauthorized use of legitimate Identification and Authentication (I&A)
data, however it was obtained, to mimic a subject different from the attacker. Impersonating, masquerading,
piggybacking, and mimicking are forms of spoofing.
Implant - [In security, an] electronic device or electronic equipment modification designed to gain
unauthorized interception of information-bearing emanations.
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![Implicit Congestion Control - A scheme under which user terminals first detect a possible congestion
condition by means other than explicit congestion messages, and then take appropriate action to reduce
their throughput.
Improper Character - Synonym illegal character. A character, or a combination of bits, that is not valid in a
given system according to specified criteria, such as with respect to a specified alphabet, a particular pattern
of bits, a rule of formation, or a check code.
Improved-Definition Television (IDTV) - Television transmitters and receivers that (a) are built to satisfy
performance requirements over and above those required by the NTSC standard and (b) remain within the
general parameters of NTSC standard emissions. Note 1: IDTV improvements may be made at the TV
transmitter or the receiver. Note 2: Examples of improvements include enhancements in encoding, digital
filtering, scan interpolation, interlaced line scanning, and ghost cancellation. Note 3: IDTV improvements
must allow the TV signal to be transmitted and received in the standard 4:3 aspect ratio. Synonym enhanced-
quality television.
Improvement Threshold - See FM improvement threshold. The point in an FM receiver at which the peaks in
the rf signal equal the peaks of the thermal noise generated in the receiver. Note: A baseband signal-to-noise
ratio of about 30 dB is typical at the improvement threshold, and this ratio improves 1 dB for each decibel of
increase in the signal above the threshold.
Impulse - A short surge of electrical, magnetic, or electromagnetic energy. Synonym surge.
Impulse Excitation - The production of oscillation in a circuit or device by impressing a stimulus (signal) for a
period that is extremely short compared to the duration of the oscillation that it produces. Synonym shock
excitation.
Impulse Noise - Noise consisting of random occurrences of energy spikes having random amplitude and
spectral content. Note: Impulse noise in a data channel can be a definitive cause of data transmission errors.
Impulse Response - 1. Of a device, the mathematical function that describes the output waveform that
results when the input is excited by a unit impulse. 2. The waveform that results at the output of a device
when the input is excited by a unit impulse.
IN - Abbreviation for intelligent network. - 1. A network that allows functionality to be distributed flexibly at
a variety of nodes on and off the network and allows the architecture to be modified to control the services.
2. In North America, an advanced network concept that is envisioned to offer such things as (a) distributed
call-processing capabilities across multiple network modules, (b) real-time authorization code verification, (c)
one-number services, and (d) flexible private network services [including (1) reconfiguration by subscriber,
(2) traffic analyses, (3) service restrictions, (4) routing control, and (5) data on call histories]. Levels of IN
development are identified below:
• IN/1 A proposed intelligent network targeted toward services that allow increased customer control
and that can be provided by centralized switching vehicles serving a large customer base.
• IN/1+ A proposed intelligent network targeted toward services that can be provided by centralized
switching vehicles, e.g., access tandems, serving a large customer base.
• IN/2 A proposed, advanced intelligent-network concept that extends the distributed IN/1
architecture to accommodate the concept called " service independence." Note: Traditionally,
service logic has been localized at individual switching systems. The IN/2 architecture provides
flexibility in the placement of service logic, requiring the use of advanced techniques to manage the
distribution of both network data and service logic across multiple IN/2 modules.
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![Inactive Signaling Link - A signaling link that has been deactivated and cannot therefore carry signaling
traffic.
In-band - Using or involving the information digit time slots of a DS1 frame; i.e., bit assignments of a frame
exclusive of the framing bit.
In-band Control - Control effected by sending control information over the same channel as the one used to
send data.
In-band Noise Power Ratio - For multichannel equipment, the ratio of (a) the mean noise power measured in
any channel, with all channels loaded with white noise, to (b) the mean noise power measured in the same
channel, with all channels but the measured channel loaded with white noise.
In-band Signaling - Signaling that uses frequencies or time slots within the bandwidth or data stream
occupied by the information channel.
In Call - A UPT (Universal Personal Telecommunications) call type which permits a UPT user to have calls to
his/her UPT number routed to the terminal specified by the user.
In call Delivery - A feature by which incoming calls are presented at the terminal address registered
previously by in-call registration. This feature is invoked when originating parties or others call the UPT
(Universal Personal Telecommunications service) user.
In-call Registration - A feature that enables the UPT (Universal Personal Telecommunications service) user to
register from the current terminal address for incoming calls to be presented to that terminal address. When
registered, all incoming calls to the UPT number of the UPT user will be presented to the registered terminal
address, for the duration specified by the UPT user (duration may also be specified in terms of number of
incoming UPT calls), or until a specified deregistration time. A UPT user's in-call registration will cancel the
previous in-call registration of that UPT user's UPT number. Several UPT users may register for incoming calls
to the same terminal address simultaneously. The UPT user may also explicitly de-register for incoming calls.
Incident - 1. In information systems (IS), [an] assessed occurrence having actual or potentially adverse effects
on an IS. 2. In COMSEC, the occurrence that potentially jeopardizes the security of COMSEC material or the
secure electrical transmission of national security information or information governed by 10 U.S.C. Section
2315.
Incidental-Radiation Device - A device that radiates radio frequency energy during the course of its
operation although the device is not intentionally designed to generate radio frequency energy.
Inclination of an Orbit (of an Earth satellite) - The angle determined by the plane containing the orbit and
the plane of the Earth's equator.
Inclined Orbit - Any nonequatorial orbit of a satellite. Note: Inclined orbits may be circular or elliptical,
synchronous or asynchronous, and direct or retrograde.
Inclusion - A foreign object present within, for example, an optical fiber or a crystal.
Incoherent - In optics, characterized by a degree of coherence significantly less than 0.88.
Incoming Access - The ability of a user to terminate data calls via an ISDN.
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![Information Integrity - In a frame-relaying network, the condition when all frames relayed by the network
satisfy the frame check sequence check.
Information Origination/Termination Equipment - Equipment used to input into or receive output from the
telecommunications network.
Information processing - Synonym data processing.The systematic performance of operations upon data
such as handling, merging, sorting, and computing. Note: The semantic content of the original data should
not be changed. The semantic content of the processed data may be changed.
Information processing center (IPC): A facility staffed and equipped for processing and distributing
information. Note: An IPC may be geographically distributed.
Information Provider - An entity that collects information and makes it available to Internet users. Note: The
information can be provided directly to users, or provided via an Internet access provider or a content
provider.
Information Rate - For a frame relay logical connection, the average number of end user bits transferred per
second, in one direction, across a user-network interface as measured over an interval of duration 't'. The
measurement interval 't' is network dependent.
Information Security - The protection of information against unauthorized disclosure, transfer, modification,
or destruction, whether accidental or intentional.
Information Source - Synonym source user. The user providing the information to be transferred to a
destination user during a particular information transfer transaction.
Information Superhighway - Synonym National Information Infrastructure. A proposed, advanced, seamless
web of public and private communications networks, interactive services, interoperable hardware and
software, computers, databases, and consumer electronics to put vast amounts of information at users'
fingertips. Note: NII includes more than just the physical facilities (more than the cameras, scanners,
keyboards, telephones, fax machines, computers, switches, compact disks, video and audio tape, cable, wire,
satellites, optical fiber transmission lines, microwave nets, switches, televisions, monitors, and printers) used
to transmit, store, process, and display voice, data, and images; it encompasses a wide range of interactive
functions, user-tailored services, and multimedia databases that are interconnected in a technology-neutral
manner that will favor no one industry over any other.
Information System - 1. A system, whether automated or manual, that comprises people, machines, and/or
methods organized to collect, process, transmit, and disseminate data that represent user information. 2.
Any telecommunications and/or computer related equipment or interconnected system or subsystems of
equipment that is used in the acquisition, storage, manipulation, management, movement, control, display,
switching, interchange, transmission, or reception of voice and/or data, and includes software, firmware, and
hardware. 3. The entire infrastructure, organization, personnel, and components for the collection,
processing, storage, transmission, display, dissemination, and disposition of information.
Information Systems Security (INFOSEC and/or ISS) - [The] protection of information systems against
unauthorized access to or modification of information, whether in storage, processing or transit, and against
the denial of service to authorized users, including those measures necessary to detect, document, and
counter such threats.
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![Information Technology (IT) - The branch of technology devoted to (a) the study and application of data and
the processing thereof; i.e., the automatic acquisition, storage, manipulation (including transformation),
management, movement, control, display, switching, interchange, transmission or reception of data, and (b)
the development and use of the hardware, software, firmware, and procedures associated with this
processing.
Information Transfer - The process of moving messages containing user information from a source to a sink.
Note: The information transfer rate may or may not be equal to the transmission modulation rate.
Information Transfer Capability - The capability associated with the transfer of different types of
information through the ISDN. It can be used to characterize a telecommunication service or connection.
Values associated with this attribute are unrestricted digital, speech, 3.1-kHz audio, 7- kHz audio, 15-kHz
audio, and video.
Information Transfer Interface - Establishment of a communication (signaling) path and any required bearer
path between the RPT/RT and the radio port. For example, in TDMA and FDMA, time slots and frequencies
are identified, and in CDMA, sequence codes are identified.
Information Transfer Mode - The operational mode for transferring (transportation and switching) user
information through the ISDN. It can be used to characterize a telecommunication service or a connection in
the network. Values associated with the attribute are circuit mode and packet mode.
Information-Transfer Phase - In an information-transfer transaction, the phase during which user
information blocks are transferred from the source user to a destination user.
Information Transfer Rate - The transfer of digital information between two access points or reference
points. Values associated with this attribute are appropriate bit rate (in circuit mode) and throughput rate (in
packet mode).
Information-Transfer Transaction - A coordinated sequence of user and telecommunications system actions
that cause information present at a source user to become present at a destination user. Note: An
information-transfer transaction usually consists of three consecutive phases called the access phase, the
information-transfer phase, and the disengagement phase.
INFOSEC - Acronym for information systems security. [The] protection of information systems against
unauthorized access to or modification of information, whether in storage, processing or transit, and against
the denial of service to authorized users, including those measures necessary to detect, document, and
counter such threats.
Infrared (IR) - The region of the electromagnetic spectrum bounded by the long-wavelength extreme of the
visible spectrum (approximately 0.7 m) and the shortest microwaves (approximately 0.1 mm). See
electromagnetic spectrum.
Ink Vapor Recording - Recording in which vaporized ink particles are deposited directly upon the record
medium.
Infrastructure Assurance - Preemptive or reactive risk-management techniques designed to increase
confidence that disruption of a system will be minimized if its critical infrastructure is attacked.
Infrastructure Protection - Preemptive or reactive risk-management techniques designed to prevent
disruption of a system after its critical infrastructure is attacked.
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![Integrating Network - A network (circuit) that produces an output waveform that is the time integral of the
input waveform. Note: Integrating networks are used in signal processing, such as for producing sawtooth
waves from square waves.
Integrity - The quality of an information system (IS) reflecting the logical correctness and reliability of the
operating system; the logical completeness of the hardware and software implementing the protection
mechanisms; and the consistency of the data structures and occurrence of the stored data. Note that, in a
formal security mode, integrity is interpreted more narrowly to mean protection against unauthorized
modification or destruction of information.
Integrity Check Value - A checksum capable of detecting modification of an information system (IS).
Intelligent Agent - Synonym droid. 1. In the Internet, an intelligent search tool that automatically seeks out
relevant online information based on the user's specifications. Synonyms agent, bot, crawler, hotbot,
infobot, information agent, intelligent agent, Internet search engine, knowbot, knowledge robot, personal
agent, robotic librarian, search robot, spider, Web crawler, Web spider, wizard. 2. In artificial intelligence, an
entity with the ability to sense its environment and to act in such a way or to affect that environment;
typically knowledge-based entities that can communicate with each other through some message-passing
scheme.
Intelligent Network (IN) - 1. A network that allows functionality to be distributed flexibly at a variety of
nodes on and off the network and allows the architecture to be modified to control the services. 2. In North
America, an advanced network concept that is envisioned to offer such things as (a) distributed call-
processing capabilities across multiple network modules, (b) real-time authorization code verification, (c)
one-number services, and (d) flexible private network services [including (1) reconfiguration by subscriber,
(2) traffic analyses, (3) service restrictions, (4) routing control, and (5) data on call histories]. Levels of IN
development are identified below:
• IN/1 A proposed intelligent network targeted toward services that allow increased customer control
and that can be provided by centralized switching vehicles serving a large customer base.
• IN/1+ A proposed intelligent network targeted toward services that can be provided by centralized
switching vehicles, e.g., access tandems, serving a large customer base.
• IN/2 A proposed, advanced intelligent-network concept that extends the distributed IN/1
architecture to accommodate the concept called " service independence." Note: Traditionally,
service logic has been localized at individual switching systems. The IN/2 architecture provides
flexibility in the placement of service logic, requiring the use of advanced techniques to manage the
distribution of both network data and service logic across multiple IN/2 modules.
Intelligent Network Application Protocol (INAP) - A protocol for intelligent network applications contained
in Layer 7 (the Application Layer of the OSI model).
Intelligent Network (IN) Supported Service - A service provided using the capabilities of the intelligent
network.
Intelligent Peripheral (IP) - 1. A functional component that may be used most efficiently when accessed
locally. 2. An intelligent-network feature that provides specialized telecommunication capabilities required
by IN/2 service logic programs.
Intelligibility - For voice communications, the capability of being understood. Note: Intelligibility does not
imply the recognition of a particular voice.
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![Intelligible Crosstalk - Crosstalk from which information can be derived.
INTELSAT - Abbreviation for International Telecommunications Satellite Organization.
Intensity - The square of the electric field strength of an electromagnetic wave. Note: Intensity is
proportional to irradiance and may be used in place of the term "irradiance" when only relative values are
important.
Intensity Modulation (IM) - In optical communications, a form of modulation in which the optical power
output of a source is varied in accordance with some characteristic of the modulating signal. Note: In
intensity modulation, there are no discrete upper and lower sidebands in the usually understood sense of
these terms, because present optical sources lack sufficient coherence to produce them. The envelope of the
modulated optical signal is an analog of the modulating signal in the sense that the instantaneous power of
the envelope is an analog of the characteristic of interest in the modulating signal. Recovery of the
modulating signal is by direct detection, not heterodyning.
Interaction Crosstalk - Crosstalk caused by coupling between carrier and noncarrier circuits. Note: If the
interaction crosstalk is, in turn, coupled to another carrier circuit, that crosstalk is called "indexing."
Interactive - Pertaining to a communications environment in which more than one party is equipped and
ready to participate actively in a session or a protocol. [After X9.42] Note: Common usage of the term refers
to a session where at least one of the parties is human and another of the parties is a software application.
Interactive Data Transaction - A unidirectional message, transmitted via a data channel, that requires a
response in order for work to proceed logically.
Interactive Service - In an integrated services digital network (ISDN), a telecommunications service that
facilitates a bidirectional exchange of information among users or among users and hosts. Note: Interactive
services are grouped into conversational services, messaging services, and retrieval services.
Interactive Voice Response - In telephony, interactive voice response, or IVR, is a computerised system that
allows a person, typically a telephone caller, to select an option from a voice menu and otherwise interface
with a computer system. Generally the system plays pre-recorded voice prompts to which the person
presses a number on a telephone keypad to select the option chosen, or speaks simple answers such as
"yes", "no", or numbers in answer to the voice prompts.
The latest systems use natural language speech recognition to interpret the questions that the person wants
answered.
Other innovations include the ability to speak complex and dynamic information such as an e-mail, news
report or weather information using Text-To-Speech (TTS). TTS is computer generated synthesised speech
and is no longer the robotic voice people associate with computers. Real voices are used to create the
speech in tiny fragments that are glued together before being played to the caller.
IVR systems are found operating telephone banking services, voicemail systems are similar to IVR systems
but offer limited functionality. IVR systems can be used to create services from telephone banking, order
placement, caller identification and airline ticket booking. ACD systems are often the first point of contact
when calling many larger businesses. IVR systems are generally used at the front end of call centers to
identify what service the caller wants and to extract numeric information such as account numbers as well as
provide answers to simple questions such as account balances or allow pre-recorded information to be
heard.
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![IVR systems are often criticised as being unhelpful and difficult to use due to poor design and lack of
appreciation of the callers' needs. A properly designed IVR system should connect callers to their desired
service promptly and with a minimum of fuss.
IVR call flows are created in a variety of ways: while older systems depended upon proprietary programming
or scripting languages, modern systems are structured similar to WWW pages, using the VoiceXML or SALT
(http://www.saltforum.org/speechtek05/) language. This allows any Web server to act as an application
server, freeing the developer to focus on the call flow. Developers then also no longer require specialized
programming skills, as any Web developer already has all the tools needed to create an IVR call flow.
Interblock Gap - On a data recording medium, an area used to indicate the end of a block or physical record.
Note: Examples of interblock gaps are the gaps between blocks on magnetic tape and disks.
Intercept - 1. To stop a telephone call directed to an improper, disconnected, or restricted telephone
number, and to redirect that call to an operator or a recording. 2. To gain possession of communications
intended for others without their consent, and, ordinarily, without delaying or preventing the transmission.
Note: An intercept may be an authorized or unauthorized action. 3. The acquisition of a transmitted signal
with the intent of delaying or eliminating receipt of that signal by the intended destination user. 4. A call
disposition category for a call attempt to a non-operating number.
Intercept Call Request - An operator services call request initiated by the network because of the service
condition of the line of the called party (e.g., line out of service, etc.).
Interchange - Mutual acceptance and exchange of messages between entities.
Interchangeability - 1. The ability to exchange hardware components having the same form, fit, and
function, across platforms, without affecting the functionality of the system. 2. A condition which exists
when two or more items possess such functional and physical characteristics as to be equivalent in
performance and durability, and are capable of being exchanged one for the other without alteration of the
items themselves, or of adjoining items, except for adjustment, and without selection for fit and
performance.
Interchangeable Connectors - Connectors that share common installation geometry and have the same
transmission performance.
Interchange Circuit - A circuit that facilitates the exchange of data and signaling information between data
terminal equipment (DTE) and data circuit-terminating equipment (DCE). Note: An interchange circuit can
carry many types of signals and provide many types of service features, such as control signals, timing
signals, and common return functions.
Intercharacter Interval - In asynchronous transmission, the time interval between the end of the stop signal
of one character and the beginning of the start signal of the next character. Note: The intercharacter interval
may be of any duration. The signal sense of the intercharacter interval is always the same as the sense of the
stop element, i.e., "1" or "mark."
Intercom - 1. A telephone apparatus by means of which personnel can talk to each other within an aircraft,
tank, ship, or activity. [JP 1-02] 2. A dedicated voice service within a specified user environment.
Interconnect Facility - In a communications network, one or more communications links that (a) are used to
provide local area communications service among several locations and (b) collectively form a node in the
network. Note 1: An interconnect facility may include network control and administrative circuits as well as
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![the primary traffic circuits. Note 2: An interconnect facility may use any medium available and may be
redundant.
Interconnecting Networks (ICNs) - Two or more networks connected for purposes of call processing.
Interconnection - 1. The linking together of interoperable systems. 2. The linkage used to join two or more
communications units, such as systems, networks, links, nodes, equipment, circuits, and devices.
Interconnectivity - See interconnection. - 1. The linking together of interoperable systems. 2. The linkage
used to join two or more communications units, such as systems, networks, links, nodes, equipment, circuits,
and devices.
Interdigit Interval - A multifrequency (MF) and dual tone multifrequency (DTMF) signal timing interval that is
equal to the sum of the fall time, signal-off time, and rise time. The interdigit interval starts when the MF or
DTMF signal duration ends. The interdigit interval ends when the next MF or DTMF signal duration begins.
Interest Group - A gathering or category of network users who have a similar interest in a particular topic
and who share their opinions with each other via email or an internet forum.
Interexchange Carrier (IXC or IC) - 1. A communications common carrier authorized to provide interexchange
telecommunications services within world zone 1 using the North American numbering plan. 2. A
telecommunications common carrier authorized to provide telecommunications services between LATAs.
Note: The term "interexchange carrier" is also used to refer to any other entity that connects to the
exchange access network at a point of termination (POT).3. A carrier that provides connections between
LATAs, where the calling or called customer is located in the United States. Note: This definition has no
Canadian equivalent. However, the term "interexchange carrier" is used in the context of a carrier that
provides connections extending across borders to carriers in the United States. Synonyms [loosely] carrier,
common carrier, commercial carrier, communications carrier.
Interexchange Channel - A circuit which is included in the interexchange transmission equipment.
Interexchange Transmission Equipment - The combination of (a) interexchange cable and wire facilities, (b)
interexchange circuit equipment and, (c) associated land and buildings.
Interface (I/F) - 1. In a system, a shared boundary, i.e., the boundary between two subsystems or two
devices. 2. A shared boundary between two functional units, defined by specific attributes, such as
functional characteristics, common physical interconnection characteristics, and signal characteristics. 3. A
point of communication between two or more processes, persons, or other physical entities. 4. A point of
interconnection between user terminal equipment and commercial communications facilities. 5. To
interconnect two or more entities at a common point or shared boundary. 6. [A] common boundary between
independent systems or modules where interactions take place. 7. The point of interconnection between
two distinct but adjacent communications systems having different functions. The interface in the
communication-satellite service is that point where communications terminal equipment of the terrestrial
common carriers or other authorized entities interconnects with the terminal equipment of the
communication-satellite earth station complex. The interface in the communication-satellite service shall be
located at the earth station site, or if this is impracticable, as close thereto as possible.
Interface Data - The parameter within a primitive that is the unit of information transferred to/from the
upper layer or sublayer in a single interaction.
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![International Telecommunication Union (ITU) - A civil international organization established to promote
standardized telecommunications on a worldwide basis. Note: The ITU-R and ITU-T are committees under
the ITU. The ITU headquarters is located in Geneva, Switzerland. While older than the United Nations, it is
recognized by the U.N. as the specialized agency for telecommunications.
International Telegraph Alphabet Number 5 (ITA-5) - An alphabet in which (a) 128 unique 7-bit strings are
used to encode upper- and lower-case letters, 10 decimal numerals, special signs and symbols, diacritical
marks, data delimiters, and transmission control characters, (b) 12 of the 7-bit strings are not assigned to any
letter, numeral, or control character, and (c) the unassigned bit strings are open for use in a given country
that may have unique requirements, such as monetary symbols; diacritical marks, such as the tilde, umlaut,
circumflex, and dieresis, and (d) a two-condition 8-bit pattern may be used that consists of seven information
bits and a parity check bit. Note: ITA-5 is used for effecting information interchange. It is a result of a joint
agreement between the International Telegraph and Telephone Consultative Committee (CCITT), now ITU-T,
of the International Telecommunication Union (ITU) and the International Organization for Standardization
(ISO). It is published as CCITT (ITU-T) Recommendation V.3 and as ISO 646. It has also been adopted by NATO
for military use. The United States adaptation of ITA-5 is ASCII (American Standard Code for Information
Interchange) published by the American National Standards Institute (ANSI). Synonym International
Reference Alphabet (IRA).
International Telegraph and Telephone Consultative Committee (CCITT) - See ITU-T. Abbreviation for
International Telecommunication Union--Telecommunication Standardization Sector. The
Telecommunication Standardization Sector of the International Telecommunication Union (ITU). Note 1: ITU-
T is responsible for studying technical, operating, and tariff Questions and issuing Recommendations on
them, with the goal of standardizing telecommunications worldwide. Note 2: In principle, the ITU-T combines
the standards-setting activities of the predecessor organizations formerly called the International Telegraph
and Telephone Consultative Committee (CCITT) and the International Radio Consultative Committee (CCIR).
International Time Bureau (BIH) - See International Atomic Time. The time scale established by the Bureau
International des Poids et Mesures (BIPM--International Bureau of Weights and Measures in Sevres, France)
on the basis of atomic clock data supplied by cooperating institutions.
Internaut - Slang term for a user of the Internet. Synonym cybernaut.
Internet - A collection and interconnection of tens of thousands of independent global networks.
internet - Any interconnection among or between private, industrial or governmental computer (digital
communication) networks. Note: The term internet (spelled with a lower case "i") is distinguished from the
Internet (spelled with the "I" capitalized). "The Internet" refers to a specific, historic, ubiquitous worldwide
digital communications network.
Internet [the] - 1. A worldwide interconnection of individual networks a) with an agreement on how to talk
to each other, and b) operated by government, industry, academia, and private parties. Note: The Internet
originally served to interconnect laboratories engaged in government research, and has now been expanded
to serve millions of users and a multitude of purposes, such as interpersonal messaging, computer
conferences, file transfer, and consulting of files containing documents. 2. The international computer
network of both federal and nonfederal interoperable packet switched data networks.
Internet2 - See I2. Abbreviation for Internet second generation. A proposed high-speed Internet for use
exclusively by government researchers and academic institutions.
Internet 2 - A proposed high-speed Internet for use exclusively by government researchers and academic
institutions. See I2. Abbreviation for Internet second generation.
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![Internet Service Provider - See ISP. A company or organization that provides connections to the Internet to
companies or individuals via dial-up, ISDN, T1, or other connection.
Internet Society - See ISOC. A nongovernmental, international organization for global cooperation and
coordination for The Internet and its internetworking technologies and applications.
Internet Telephone - See Internet phone. A combination of software and hardware that allows a user to
approximate a telephone conversation over an Internet connection instead of using a traditional telephone
system. Note 1: The required hardware generally consists of a microphone and headphones. Note 2: The
sound quality of current Internet-phone systems is much less than that of traditional telephone systems.
Internet Telephony - See Internet phone. See Internet phone. A combination of software and hardware that
allows a user to approximate a telephone conversation over an Internet connection instead of using a
traditional telephone system. Note 1: The required hardware generally consists of a microphone and
headphones. Note 2: The sound quality of current Internet-phone systems is much less than that of
traditional telephone systems.
Internetwork - Synonym internet. 1. A worldwide interconnection of individual networks a) with an
agreement on how to talk to each other, and b) operated by government, industry, academia, and private
parties. Note: The Internet originally served to interconnect laboratories engaged in government research,
and has now been expanded to serve millions of users and a multitude of purposes, such as interpersonal
messaging, computer conferences, file transfer, and consulting of files containing documents. 2. The
international computer network of both federal and nonfederal interoperable packet switched data
networks.
Internetwork Connection - See gateway. 1. In a communications network, a network node equipped for
interfacing with another network that uses different protocols. Note 1: A gateway may contain devices such
as protocol translators, impedance matching devices, rate converters, fault isolators, or signal translators as
necessary to provide system interoperability. It also requires that mutually acceptable administrative
procedures be established between the two networks. Note 2: A protocol translation/mapping gateway
interconnects networks with different network protocol technologies by performing the required protocol
conversions. 2. [An] interface providing a compatibility between networks by converting transmission
speeds, protocols, codes, or security measures. 3. Loosely, a computer configured to perform the tasks of a
gateway.
Internetworking - The process of interconnecting two or more individual networks to facilitate
communications among their respective nodes. Note: The interconnected networks may be different types.
Each network is distinct, with its own addresses, internal protocols, access methods, and administration.
Iinternetwork Interface (INI) - The point of demarcation between networks when service is provided across
multiple networks.
Internetwork Packet Exchange - See IPX. A proprietary (LAN) protocol.
InterNIC (Internet Network Information Center) - The centralized organization run by the National Science
Foundation that provides various administrative services for the Internet, including Domain Name
registration. The association of providers of domain-name registration, information, and database services to
the Internet.
Interoffice Trunk - A single direct transmission channel, e.g., voice-frequency circuit, between central offices.
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![Job-Recovery Control File - Synonym backup file. A copy of a file made for purposes of later reconstruction
of the file, if necessary. Note: A backup file may be used for preserving the integrity of the original file and
may be recorded on any suitable medium.
Johnson Noise - Synonym thermal noise. The noise generated by thermal agitation of electrons in a
conductor. The noise power, P, in watts, is given by P = kT f, where k is Boltzmann's constant in joules per
kelvin, T is the conductor temperature in kelvins, and f is the bandwidth in hertz. Note 1: Thermal noise
power, per hertz, is equal throughout the frequency spectrum, depending only on k and T. Note 2: For the
general case, the above definition may be held to apply to charge carriers in any type of conducting medium.
Joint - For optical fibers, a splice or connector.
Joint Multichannel Trunking and Switching System - That composite multichannel trunking and switching
system formed from assets of the Services, the Defense Communications System, other available systems,
and/or assets controlled by the Joint Chiefs of Staff to provide an operationally responsive, survivable
communication system, preferably in a mobile/transportable/recoverable configuration, for the joint force
commander in an area of operations.
Joint Random Buried Plant - Telecommunications outside plant that is directly buried in the same trench
with power conductors, with no restriction regarding minimum separation between the two systems.
Joint Telecommunications Resources Board (JTRB) - The body required to be established by Section 2(b) (3)
of Executive Order No. 12472 to assist the Director of the Office of Science and Technology Policy in the
exercise of assigned nonwartime emergency telecommunications functions.
Joint Use Aerial Plant - Aerial telecommunications and power plant utilizing the same structure, such as
poles.
Journal - 1. A chronological record of data processing operations that may be used to reconstruct a previous
or an updated version of a file. Synonym log. 2. In database management systems, the record of all stored
data items that have values changed as a result of processing and manipulation of the data.
Joy Stick - In computer graphics, a lever (with at least two degrees of freedom) that is used as an input unit,
normally as a locator.
J-PEG [ or JPEG] - Abbreviation for Joint Photographic Experts Group. 1. A standardized, if relatively lossy, file
format for transporting, storing, and/or displaying data representing still images and graphical data. Note:
Along with .gif, it is one of the most common ways that photos are moved over the Web. 2. Images
compressed with the JPEG format and identified with the .jpg or .jpeg file-name extension. 3. An
international standards group functioning under ISO and IEC developing an international consensus on an
image compression algorithm for continuous-tone still color pictures.
Judder - A temporal artifact associated with moving images, which artifact occurs when the image is sampled
at one frame rate and converted to a different frame rate for display; as a result, motion vectors in the
display may appear to represent continuously varying velocities. Note: The subjective effect of the artifact
becomes more obvious when the frame-rate conversion is made by simple deletions or repetitions of
selected frames (or fields). It may become less obvious when interpolated frames (or fields) are generated by
using predictive algorithms.
Julian Date - 1. The sequential day count reckoned consecutively beginning January 1, 4713 B.C. Note: The
Julian date on January 1, 1990, was 2,446,892. 2. The sequential day count of the days of a year, reckoned
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![consecutively from the first day of January. Note: In modern times, the definition of Julian date has been
corrupted to use the first day of the year as the point of reference. To avoid ambiguity with the traditional
meaning, "day of year" rather than "Julian date" should be used for this purpose.
Jumper - Synonym cross-connection. Connections between terminal blocks on the two sides of a distribution
frame, or between terminals on a terminal block. Note: Connections between terminals on the same block
are also called straps.
Junction Point - Synonym node. 1. In network topology, a terminal of any branch of a network or an
interconnection common to two or more branches of a network. Synonyms junction point, nodal point. 2. In
a switched network, one of the switches forming the network backbone. Note: A node may also include
patching and control facilities. 3. A technical control facility (TCF). 4. A point in a standing or stationary wave
at which the amplitude is a minimum. In this sense, synonym null.
Jurisdiction - 1. In telecommunications, the functional separation of telecommunications networks. A
jurisdiction is one of the following four types: (a) local exchange carrier network; (b) interexchange carrier
network; (c) end user network; (d) some combination of the above. 2. Loosely, and in a more general sense,
the regulatory authority of the Federal Communications Commission as specified in the Communications Act
of 1934, supplements thereto, and numerous court decisions; and the regulatory authority of state
regulatory commissions as specified in the laws established by each state.
Justification - The process of changing the digit rate of a digital signal in a controlled manner so that it is in
accord with a digit rate different from its own inherent rate, usually without loss of information. Synonyms
[loosely] bit stuffing, de-stuffing, justify.
Justify - 1. To shift the contents of a register or a field so that the significant character at the specified end of
the data is at a particular position. 2. To align text horizontally or vertically so that the first and last
characters of every line, or the first and last line of the text, are aligned with their corresponding margins.
Note 1: In English, text may be justified left, right, or both. Left justification is the most common. Note 2: The
last line of a paragraph is usually only left justified. 3. To align data on a designated character position.
K
3
k - Abbreviation for kilo (SI prefix for 10 ). See International System of Units.
K - 1. Abbreviation for kelvin (s). See thermodynamic temperature. 2. When referring to data storage
10
capacity, 2 , or 1024 in decimal notation; however this usage of an upper case K is deprecated.
Kalman Filter - A computational algorithm that processes measurements to deduce an optimum estimate of
the past, present, or future state of a linear system by using a time sequence of measurements of the system
behavior, plus a statistical model that characterizes the system and measurement errors, plus initial
condition information.
KA9Q - A popular implementation of TCP/IP and associated protocols for amateur packet radio systems.
Kbps - Kilobytes per second. A kilobyte equals a thousand bytes.
KDC - Abbreviation for key distribution center. [A] COMSEC facility generating and distributing key in
electrical form.
Kelvin (K) - A unit of thermodynamic temperature, taken as one of the base units of the International System
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![of Units (SI). The kelvin is defined by setting the thermodynamic temperature of the triple point of water at
273.16 K. Note 1: The kelvin was formerly called "degree Kelvin." The term "degree Kelvin" is now obsolete.
No degree symbol is written with K, the symbol for kelvin(s). Note 2: In measuring temperature intervals, the
degree Celsius is equal to the kelvin. The Celsius temperature scale is defined by setting 0 °C equal to 273.16
K
Kelvin Temperature Scale - See thermodynamic temperature. See Kelvin (K).
Kendall Effect - A spurious pattern or other distortion in a facsimile record copy caused by unwanted
modulation products arising from the transmission of a carrier signal, and appearing in the form of a rectified
baseband that interferes with the lower sideband of the carrier. Note: The Kendall effect occurs principally
when the single-sideband width is greater than half of the facsimile carrier frequency.
Kermit - An early generation protocol [a file-transfer and terminal-emulation program] developed for
transfer of asynchronous data files, designed to help minimize the effects of interference and noise on
analog telephone circuits.
Kernel - A module of a program that forms a logical entity or performs a unit function. Note: The most
vulnerable portion of code in a secure operating system is a special case of a kernel.
Kerr Electro-Optic Effect - The creation of birefringence in a liquid that is not otherwise birefringent, by
subjecting the liquid to an electric field. Note 1: The degree of birefringence, which is manifested as a
difference in refractive indices for light of orthogonal linear polarizations, one of which is parallel to the
induced optical axis, is directly proportional to the square of the applied electric field strength. Note 2: In the
general case, the birefringence produced by the applied electric field can be used in conjunction with
polarizers to modulate light. Devices that use this principle are called Kerr cells.
Key - 1. Information (usually a sequence of random or pseudorandom binary digits) used initially to set up
and periodically change the operations performed in crypto-equipment for the purpose of encrypting or
decrypting electronic signals, for determining electronic counter-countermeasures patterns (e.g., frequency
hopping or spread spectrum), or for producing other key. Note: "Key" has replaced the terms "variable,"
"key(ing) variable," and "cryptovariable." 2. Usually a sequence of random or pseudorandom bits used
initially to set up and periodically change the operations performed in crypto-equipment for the purpose of
encrypting or decrypting electronic signals, or for determining electronic counter-countermeasures
patterns(e.g., frequency hopping or spread spectrum), or for producing other key.
Key Agreement - 1. A key establishment protocol whose secret key is a function of information contributed
by two or more participants, so that no party can predetermine the value of the key. 2. A method for
negotiating a key value on-line without transferring the key, even in an encrypted form, e.g., the Diffie-
Hellman technique.
Key Authentication - The assurance of the legitimate participants in a key agreement that no other entity
possesses the shared-secret key.
Key-Auto-Key - Cryptographic logic using previous key to produce key.
Keyboard - An input device used to enter data by manual depression of keys, which causes the generation of
the selected code element.
Keyboard Punch - Synonym keypunch. Historically, a keyboard-actuated punch that punches holes in a data
medium.
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![Keyboard Recorder - A hidden program in a computer that stores user-typed input or other input and sends
this data to the originator. Keyboard recorders are used for stealing user identifications, passwords, and
other sensitive information.
Key Bundle - An assemblage of two keys that are considered logically to be one key, in that one key alone
cannot be manipulated.
Key Component - One of two or more parameters that have the format of a cryptographic key that is added
modulo-1 with one or more like parameters to form a cryptographic key.
Key Confirmation - The assurance of the rightful participants in a key-establishment protocol that the
intended recipient (s) of the shared key actually possess the shared key.
Key Distribution Center (KDC) - [A] COMSEC facility generating and distributing key in electrical form.
Key Encrypting Key - 1. A key that is used exclusively for encrypting and decrypting keys. 2. Key that encrypts
or decrypts other key for transmission or storage.
Key Encrypting Key Pair - In public-key cryptography, two key encrypting keys used together to encrypt
other keys.
Key Establishment - 1. A protocol that reveals a secret key to its legitimate participants for cryptographic
use. 2. The procedure to share a common secret key among different parties by either key agreement or key
transport.
Key Generation Center - A facility within a group, which facility performs the function of generating keys for
any specific key exchange transaction.
Key Generator - A device, including associated alarms and self-tests, for generating cryptographic keys (and
where needed, initialization vectors).
Key Granularity - The number of individuals represented by a key, e.g., the finest granularity is one individual
represented by one key; a coarser granularity is a node key.
Keying - 1. The generating of signals by the interruption or modulation of a steady signal or carrier. 2. See
chroma keying.
Keying Material - 1. In encryption, the data (e.g., keys, certificates, and initialization vectors) necessary to
establish and maintain cryptographic keying relationships. 2. [A] key, code, or authentication information in
physical or magnetic form.
Keying Relationship - The state existing between two parties such that they share at least one cryptographic
key.
Keying Variable - Deprecated synonym for key.
Key Integrity - The assurance that a key (a) is always used in the proper order and key space, and (b) has not
been altered.
Key List - Printed sets of key settings for a specific cryptonet. Keylists may be produced in list, pad, or printed
tape format.
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![Key Loader - An electronic, self-contained unit which is capable of storing at least one key and transferring
that key, upon request, into cryptographic modules.
Key Management - Supervision and control of the process whereby key is generated, stored, protected,
transferred, loaded, used, and destroyed.
Key Management Facility - The physically protected enclosure (e.g., room or device) and its contents where
cryptographic elements (i.e., cryptographic hardware, software, firmware, keys, or initialization vectors)
reside.
Key Offset - 1. The process of applying a count value to a cryptographic key using the Boolean exclusive-OR
function. 2. The count so added.
Key Pair - 1. In public-key cryptography, a public key and its corresponding private key. 2. Two key-
encrypting keys that are used in concert to encrypt other keys.
Key Pair Updating - The recertification or replacement of a certificate authority's public/ private key pair.
Key Production Key - Key used to initialize a keystream generator for the production of other electronically
generated key.
Key-Pulse Signal - The first signal in an MF (multifrequency) outpulsing format; a control signal used to
prepare the customer installation (CI) to receive digits.
Key Pulsing - A system of sending telephone calling signals in which the digits are transmitted by operation
of a pushbutton key set. Note: The type of key pulsing commonly used by users and PBX operators is dual-
tone multifrequency signaling. Each pushbutton causes generation of a unique pair of tones. In military
systems, pushbuttons are also provided for additional signals, such as precedence. Synonym pulsing.
Keypunch - Historically, a keyboard-actuated punch that punches holes in a data medium. Synonym
keyboard punch.
Key Security - In cryptology, the protection of keys against compromise.
Key Service Message - A message used for transferring keys between subscribers.
Key Set - A multiline or multifunction user terminal device.
Key Set Identifier - A non-secret value that uniquely identifies a key set.
Key Storage - In cryptology, storage of cryptographic keys in such a manner as (a) to protect them against
unauthorized use, disclosure, or tampering, and (b) to erase them and re-initialize equipment upon
tampering.
Key Stream - [A] sequence of symbols (or their electrical or mechanical equivalents) produced in a machine
or auto-manual cryptosystem to combine with plain text to produce cipher text, control transmission
security processes, or produce key.
Keystroke Verification - With respect to data entry via a keyboard, determination of the accuracy of data
entry by the re-entry of the same data through the same (or another) keyboard.
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![Layer Entity - An active element within a layer.
Layer Function - A part of the activity of the layer entities.
Layer Interface - The boundary between two adjacent layers in the model.
Layer Service - A capability of the (N) layer and the layers beneath it, which is provided to (N + 1) layer
entities, at the boundary between the (N) layer and the (N + 1) layer.
Layer Service Elements - An indivisible component of the layer service made visible to the service user via
layer service primitives.
Layer Service Primitives - A means for specifying in detail the adjacent layer interactions
Layer User Data - Data transferred between corresponding entities on behalf of the upper layer or layer
management entities for which they are providing services.
Lay Length - In communications cables--including fiber-optic cables--having the transmission media wrapped
helically around a central member, the longitudinal distance along the cable required for one complete
helical wrap; i.e., the total cable length divided by the total number of wraps. Note 1: In many fiber-optic
cable designs, the lay length is shorter than in metallic cables of similar diameter, to avoid overstressing the
fibers during the pulling associated with the installation operation. Note 2: The wraps, i.e., turns, that are
referred to should not be confused with the twists given twisted metallic pairs, i.e., wires, to reduce
electromagnetic coupling. Pairs of optical fibers are not given such twists. Synonym pitch.
LBO - Abbreviation for line buildout. Synonym building out. - The process of adding a combination of
inductance, capacitance, and resistance to a cable pair so that its electrical length may be increased by a
desired amount to control impedance and loss characteristics.
LCD - Abbreviation for liquid crystal display. - A display device that creates characters by means of the action
of electrical signals on a matrix of liquid cells that become opaque when energized. Note: A liquid crystal
display may be designed to be viewed by reflected or transmitted light.
LCD TV - Abbreviation for Liquid Crystal Display Television. LCD televisions are sets that use LCD technology
to produce images. Benefits of LCD technology include lower weight and reduced power requirements when
compared to other display types. Often, LCD television screens can also be used as computer monitors.
LCN- Abbreviation for Local Communication Network - A communication network within a TMN
(telecommunications management network) that supports data communication functions (DCFs) normally at
[specified] reference points q1 and q2. LCNs range from the simple to the complex. LCN examples include
point-to-point connections and networks based on star and bus topologies.
LDAP - Abbreviation for lightweight directory access protocol. A simplified version of the X.500 standard,
which version consists of a set of protocols developed for accessing information directories.
LDM - Abbreviation for limited distance modem.
Leaky Bucket Counter - A counter that is incremented by one each time an event occurs and is decremented
by a fixed value periodically.
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![Line Load Control - A network-provided service feature that allows selective denial of call origination to
certain lines when excessive demands for service are required of a switching center.
Line Loop - See loop. - A pair of wires, or its equivalent, between a customer's station and the central office
from which the station is served. Synonym user line.
Line Loopback - A signal used to command the far-end receiver to loopback the received line signal. ]
Synonym [loosely] line loopback signal.
Line Loopback Signal - See line loopback.
Line Noise - In a telecommunications link or line facility, interference, from any source, that degrades
performance. Note 1: Line noise is usually measured as a signal-to-noise ratio and as a set parameter used by
engineers to determine the operating range of the system. Note 2: In analog lines, noise is usually measured
in dbrnc (dB relative to -90 dBm, with C-message weighting). Note 3: In digital lines, noise is usually
measured as a function of the number of errored bits per second or errors in the digital data stream. In
digital systems with signal buffers, these errors may be linked to alarms, and to circuitry that enables the
signal to be recovered to acceptable degree.
Line-Of-Sight (LOS) Propagation - Of an electromagnetic wave, propagation in which the direct ray from the
transmitter to the receiver is unobstructed, i.e., the transmission path is not established by or dependent
upon reflection or diffraction. Note: The need for LOS propagation is most critical at VHF and higher
frequencies.
Line-Rate Conversion - A translation of standardized, existing video systems (using 525, 625, and 1125 total
lines per frame) to proposed systems. Note: Current systems operate in a 2:1 interlace mode, i.e., with 262.5,
312.5, 562.5 lines per field and with concurrent temporal differences at field rates of 50.00, 59.94, or 60.00
fields per second. While simple transcoding by deletion or repetition can be applied, it is more commonly
done by applying an algorithm to stored information in order to generate predictive line structures in the
target system.
Line-Route Map - A map or overlay for signal communications operations that shows the actual routes and
types of construction of wire circuits in the field. It also gives the locations of switchboards and telegraph
stations.
Line Sharing - A technology that allows a single phone line to share incoming and outgoing access for
multiple phone line connected devices. Typically Line Sharing Technology allows voice (phones and
answering machine) and a fax machine or fax modem to operate on a shared phone line. Other applications
include any variation of voice, a fax machine, fax/modem and/or modem(s).
Incoming calls are automatically routed to the proper device(s). If the call comes in and it is a fax call, the call
is automatically routed to the fax machine or fax modem. If the call is a modem call, it is routed to the
correct modem. Voice calls are routes to phone(s) and/or answering machine. May require a security access
code (SAC) in the dialing string to automatically switch to the modem.
Since the need for to subscribe to a separate "fax line" from the local telephone company is eliminated, the
return on investment (ROI) is very high. The initial cost of the device is returned in savings in a few months.
After that you will save the monthly bills associated with fax, data or voice lines. For almost every business,
line sharing technology is a smart investment.
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![Line Side - The portion of a device that is connected to external, i.e., outside plant, facilities such as trunks,
local loops, and channels.
Line Source - 1. In spectroscopy, an optical source that emits one or more spectrally narrow lines as opposed
to a continuous spectrum. 2. In the geometric sense, an optical source having an emitting area in the form of
a spatially narrow line, e.g., a slit. Synonym slit source.
Line Spectrum - In optics, an emission or absorption spectrum consisting of one or more narrow spectral
lines, as opposed to a continuous spectrum.
Line Speed - See modulation rate. - The rate at which a carrier is varied to represent the information in a
digital signal. Note: Modulation rate and information transfer rate are not necessarily the same.
Line Terminating Equipment (LTE): Network elements that originate and/or terminate line signals. LTEs can
originate, access, modify, or terminate the transport overhead, or can perform any combination of these
actions.
Line-to-Line Vorrelation - In facsimile, the correlation of object information from scanning line to scanning
line. Note: Line-to-line correlation is used in two-dimensional encoding.
Line Traffic Coordinator (LTC): In a DDN switching center, the processor that controls traffic on a line.
Line Unit Network Termination (LUNT): The customer side of any digital subscriber line (DSL) that does not
terminate on the customer installation.
Line Verification - See busy verification. - In a public switched telephone network, a network-provided
service feature that permits an attendant to verify the busy or idle state of station lines and to break into the
conversation. Note: A 440-Hz tone is applied to the line for 2 seconds, followed by a 0.5-second burst every
10 seconds, to alert both parties that the attendant is connected to the circuit.
Linewidth - See spectral width. - The wavelength interval over which the magnitude of all spectral
components is equal to or greater than a specified fraction of the magnitude of the component having the
maximum value. Note 1: In optical communications applications, the usual method of specifying spectral
width is the full width at half maximum. This method may be difficult to apply when the spectrum has a
complex shape. Another method of specifying spectral width is a special case of root-mean-square deviation
where the independent variable is wavelength, , and f ( ) is a suitable radiometric quantity. Note 2: The
relative spectral width , / , is frequently used where is obtained according to note 1, and is the
center wavelength.
Link - See Hypertext Link. 1. The communications facilities between adjacent nodes of a network. Synonym
[loosely] telecommunications link. 2. A portion of a circuit connected in tandem with, i.e., in series with,
other portions. 3. A radio path between two points, called a radio link. 4. In communications, a general term
used to indicate the existence of communications facilities between two points. 5. A conceptual circuit, i.e.,
logical circuit, between two users of a network, that enables the users to communicate, even when different
physical paths are used. Note 1: In all cases, the type of link, such as data link, downlink, duplex link, fiber
optic link, line-of-sight link, point-to-point link, radio link and satellite link, should be identified. Note 2: A link
may be simplex, half-duplex, or duplex. 6. In a computer program, a part, such as a single instruction or
address, that passes control and parameters between separate portions of the program. 7. In hypertext, a
logical connection between discrete units of data, or a hypertext connection between Web pages. Synonyms
(in this sense) hotlink, hyperlink.
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![Local Area Network (LAN) - A data communications system that (a) lies within a limited spatial area, (b) has a
specific user group, (c) has a specific topology, and (d) is not a public switched telecommunications network,
but may be connected to one. Note 1: LANs are usually restricted to relatively small areas, such as rooms,
buildings, ships, and aircraft. Note 2: An interconnection of LANs within a limited geographical area, such as a
military base, is commonly referred to as a campus area network. An interconnection of LANs over a city-
wide geographical area is commonly called a metropolitan area network (MAN). An interconnection of LANs
over large geographical areas, such as nationwide, is commonly called a wide area network (WAN).
Local Battery - 1. In telegraphy, the source of power that actuates the telegraphic station recording
instruments, as distinguished from the source of power that furnishes current to the line. 2. In telephony, a
system in which each telephone instrument has its own source of power, as opposed to being powered from
the central office. 3. A source of local power for a telephone instrument.
Local call - 1. Any call using a single switching facility. 2. Any call for which an additional charge, i.e., toll
charge, is not made to the calling or called party. Note: Calls such as those via "800" numbers do not qualify
as local calls, because the called party is charged.
Local Central Office - Synonym central office. 1. A common carrier switching center in which trunks and/or
loops are terminated and switched. Note: In the DOD, "common carrier" is called "commercial carrier."
Synonym switch. Other synonyms [loosely] end office, exchange, local exchange, local office, switching
center (except in DOD DSN [formerly AUTOVON] usage), switching exchange, telephone exchange. 2. A
switching unit, in a telephone system which provides service to the general public, having the necessary
equipment and operations arrangements for terminating and interconnecting subscriber lines and trunks or
trunks only. There may be more than one central office in a building.
Local Channel - The portion of a private line circuit which is included in the exchange transmission plant.
However, common usage of this term usually excludes information origination/termination equipment.
Local Clock - A source of timing located in close proximity to an associated facility, such as a communications
station, central office, or node. Note: The same clock might be a remote clock relative to some other facility.
Local Communication Network (LCN) - A communication network within a TMN (telecommunications
management network) that supports data communication functions (DCFs) normally at [specified] reference
points q1 and q2. LCNs range from the simple to the complex. LCN examples include point-to-point
connections and networks based on star and bus topologies.
Local Exchange - Synonym central office. In telephone communication in the United States, a local exchange
office is an office in a locality to which subscriber home and business lines are connected on what is called a
local loop. The local exchange has switching equipment that can switch calls locally or to long-distance
carrier phone offices.
Local Exchange Carrier (LEC) - A local telephone company, i.e., a communications common carrier that
provides ordinary local voice-grade telecommunications service under regulation within a specified service
area.
Local Exchange Loop - An interconnection between customer premises equipment and telephone central
office.
Local Line - See loop. A communications channel from a switching center or an individual message
distribution point to the user terminal. Synonym subscriber line.
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![users. 4. In mobile communications, an arrangement of control circuits whereby only one receiver can feed
the system at a time. Synonym receiver lockout system. 5. An arrangement for restricting access to use of all,
or part of, a computer system. Synonym protection.
Log - Synonym journal. A chronological record of data processing operations that may be used to reconstruct
a previous or an updated version of a file.
Logical Circuit - Synonym virtual circuit. A communications arrangement in which data from a source user
may be passed to a destination user over various real circuit configurations during a single period of
communication. Note: Virtual circuits are generally set up on a per-call basis and are disconnected when the
call is terminated; however, a permanent virtual circuit can be established as an option to provide a
dedicated link between two facilities.
Logical Link Control (LLC) Sublayer - In a local-area-network/metropolitan-area-network (LAN /MAN) system,
the part of the link level that (a) supports medium-independent data link functions and (b) uses the services
of the medium access control sublayer to provide services to the network layer.
Logical Route - Synonym virtual circuit. A communications arrangement in which data from a source user
may be passed to a destination user over various real circuit configurations during a single period of
communication. Note: Virtual circuits are generally set up on a per-call basis and are disconnected when the
call is terminated; however, a permanent virtual circuit can be established as an option to provide a
dedicated link between two facilities.
Logical Signaling Channel - A logical channel that provides a signaling path within an information channel or
within a physical signaling channel.
Logical Topology - Of a network, the schematic configuration that reflects the network's function, use, or
implementation without regard to the physical interconnection of network elements.
Logic Bomb - 1. Malicious logic that causes damage to a data processing system when triggered by some
specific system condition. [2382-pt.8] 2. [A] resident computer program triggering an unauthorized act when
particular states of an information system (IS) are realized.
Log In - To perform a login procedure. Synonym log on.
Login - The procedure that is followed by a user in beginning a session, e.g., a period of terminal operation.
Synonym logon.
Login Name - The unique account name used to access a computer system. Also called user ID or user name,
it is a way people identify themselves to their online service or Internet access provider.
Log Off - To perform a log-off procedure. Synonym log out.
Log-Off - The procedure that is followed by a user in closing a session, e.g., a period of terminal operation.
Synonym log out.
Logon - Synonym login. The procedure that is followed by a user in beginning a session, e.g., a period of
terminal operation.
Log On - Synonym log in. To perform a login procedure.
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![LP Mode - Abbreviation for linearly polarized mode. - A mode for which the field components in the
direction of propagation are small compared to components perpendicular to that direction. Note: The LP
description is an approximation that is valid for a weakly guiding optical fiber, including typical
telecommunications grade fibers.
LP01 mode - Designation of the fundamental LP mode. See fundamental mode.
LPTV - Abbreviation for Low-Power TV. These are TV stations who are locally-oriented broadcasters --
operated by high schools/colleges, churches/religious groups, local governments, small/large businesses and
individual citizens. There is currently no deadline for these categories of stations to convert to digital
broadcasting
LQA - Abbreviation for link quality analysis. - In adaptive high-frequency (HF) radio, the overall process by
which measurements of signal quality are made, assessed, and analyzed. Note 1: In LQA, signal quality is
determined by measuring, assessing, and analyzing link parameters, such as bit error ratio (BER), and the
levels of the ratio of signal-plus-noise-plus-distortion to noise-plus-distortion (SINAD). Measurements are
stored at--and exchanged between--stations, for use in making decisions about link establishment. Note 2:
For adaptive HF radio, LQA is automatically performed and is usually based on analyses of pseudo-BERs and
SINAD readings.
LRC Abbreviation for longitudinal redundancy check. - A system of error control based on the formation of a
block check following preset rules. Note 1: The block check formation rules are applied in the same manner
to each character. Note 2: A combination of longitudinal and vertical redundancy check allows the detection
and correction of single bit errors.
LSB - Abbreviation for least significant bit, lower sideband.
LTC - Abbreviation for Line Traffic Coordinator - In a DDN switching center, the processor that controls traffic
on a line.
.l3 - A file-name extension that identifies a Motion Picture Experts Group (MPEG) audio file. [Bahorsky]
LTE - Abbreviation for Line Terminating Equipment - Network elements that originate and/or terminate line
signals. LTEs can originate, access, modify, or terminate the transport overhead, or can perform any
combination of these actions.
LUF - Acronym for lowest usable high frequency. - The lowest frequency in the HF band at which the
received field intensity is sufficient to provide the required signal-to-noise ratio for a specified time period,
e.g., 0100 to 0200 UTC, on 90% of the undisturbed days of the month.
Luminance Range - 1. In CRT displays, the difference in brightness between the lightest and the darkest
element of a scene or its display. 2. Of a CRT or other display device, the ratio of (a) the maximum brightness
that is (or can be) displayed to (b) the minimum brightness that is (or can be) displayed.
Luminance Signal - 1. In television technology, the signal that describes (a) the distribution of brightness
levels within the image and (b) the equation for deriving that information from the camera output. 2. In
composite color television, a signal that has major control of the brightness. Note: Luminance signal is a
linear combination of gamma-corrected primary color signals.
Luminescent Diode - See superluminescent LED. - A light-emitting diode in which there is stimulated
emission with amplification but insufficient feedback for oscillations to build up to achieve lasing action.
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![Maintainability - 1. A characteristic of design and installation, expressed as the probability that an item will
be retained in or restored to a specified condition within a given period of time, when the maintenance is
performed in accordance with prescribed procedures and resources. 2. The ease with which maintenance of
a functional unit can be performed in accordance with prescribed requirements.
Maintenance - 1. Any activity, such as tests, measurements, replacements, adjustments and repairs,
intended to restore or retain a functional unit in a specified state in which the unit can perform its required
functions. 2. [For materiel], All action taken to retain materiel in a serviceable condition or to restore it to
serviceability. It includes inspection, testing, servicing, classification as to serviceability, repair, rebuilding,
and reclamation. 3. [For materiel], All supply and repair action taken to keep a force in condition to carry out
its mission. 4. [For materiel], The routine recurring work required to keep a facility (plant, building, structure,
ground facility, utility system, or other real property) in such condition that it may be continuously used, at
its original or designed capacity and efficiency for its intended purpose.
Maintenance Control Circuit (MCC) - In a communications link, a circuit used by maintenance personnel for
coordination. Note: An MCC is not available to operations or technical control personnel.
Maintenance Hook - 1. A trapdoor in software that allows easy maintenance and development of additional
features and that may allow entry into the program at unusual points or without the usual checks. 2. Special
instructions (trapdoors) in software allowing easy maintenance and additional feature development. Since
maintenance hooks frequently allow entry into the code without the usual checks, they are a serious security
risk if they are not removed prior to live implementation.
Maintenance Key - Key intended only for in-shop use.
Major Lobe - See main lobe. - Of an antenna radiation pattern, the lobe containing the maximum power
(exhibiting the greatest field strength). Note: The horizontal radiation pattern, i.e., that which is plotted as a
function of azimuth about the antenna, is usually specified. The width of the main lobe is usually specified as
the angle encompassed between the points where the power has fallen 3 dB below the maximum value. The
vertical radiation pattern, i.e., that which is plotted as a function of elevation from a specified azimuth, is
also of interest and may be similarly specified.
Major Trading Area (MTA) – An area defined by the U.S. government and used by the Federal
Communications Commission (FCC) to designate personal communications services market areas.
Make Interval - 1. In dial-pulse signaling, that portion of the dial pulse in which the network applies a low
resistance between the tip and ring conductors at the network interface (NI). 2. In dial-pulse signaling, that
portion of the dial pulse in which the pulsing circuit is in its low-impedance condition.
Malicious Applets - Small application programs automatically downloaded and executed that perform an
unauthorized function on an information system.
Malicious Code - Software or firmware capable of performing an unauthorized function on an information
system (IS).
Malicious Logic - 1. A program implemented in hardware, firmware, or software, and whose purpose is to
perform some unauthorized or harmful action. Note: Examples of malicious logic are a logic bomb, a Trojan
horse, a virus, a worm. [2382-pt.8] 2. Hardware, software, or firmware capable of performing an
unauthorized function on an information system.
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![Martian - 1. [Slang] Pertaining to packets that are delivered to the wrong network as the result of bogus
routing entries. 2. [Slang] A packet that has a completely bogus (nonregistered or ill-formed) Internet
address.
m-ary code - See n-ary code.
m-ary signaling - See n-ary code.
MASER - Acronym for microwave amplification by stimulated emission of radiation. A member of the
general class of microwave oscillators based on molecular interaction with electromagnetic radiation.
Mask - 1. In communications systems, to obscure, hide, or otherwise prevent information from being derived
from a signal. Note 1: Masking is usually the result of interaction with another signal, such as noise, static,
jamming, or other forms of interference. Note 2: Masking is not synonymous with erasing or deleting. 2. In
computing and data processing systems, a pattern of bits that can be used to retain or suppress segments of
another pattern of bits.
Masked Threshold - The level at which an indistinguishable signal of interest becomes distinguishable from
other signals or noise. Note: In acoustics, the masked threshold is usually expressed in dB.
Masking - 1. In television and video technology, a process in which color signals are used to modify each
other for the purpose of altering their color rendition. Note: The process is often accomplished by suitable
cross coupling between primary color-signal channels. 2. One way of partial compensation for photo-
receptor cot sensitivity, nonoptimum color filters, nonideal display phosphors, unwanted dye absorption,
etc.
Masquerade - The pretense by an entity to be a different entity in order to gain unauthorized access.
Masquerading - A form of spoofing. Unauthorized use of legitimate Identification and Authentication (I&A)
data, however it was obtained, to mimic a subject different from the attacker.
Master Clock - A device that generates periodic, accurately spaced signals that are used for such purposes as
timing, regulation of the operations of a processor, or generation of interrupts.
Master File (MF) - The unique mandatory file containing access conditions and optionally DFs (dedicated
files) and/or EFs (extended frames).
Master Frequency Generator - In frequency-division multiplexing (FDM), equipment used to provide system
end-to-end carrier frequency synchronization and frequency accuracy of tones. Note: The following types of
oscillators are used in the Defense Communications System FDM systems:
• Type 1 - A master carrier oscillator as an integral part of the multiplexer set.
• Type 2 - A submaster oscillator equipment or slave oscillator equipment as an integral part of the
multiplexer set.
• Type 3 - An external master oscillator equipment that has extremely accurate and stable
characteristics.
Synonym master oscillator.
Mastergroup - See group.
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![Master Key - Within a hierarchy of encrypting keys and transaction keys, the highest level of key-encrypting
key.
Master Oscillator - In frequency-division multiplexing (FDM), equipment used to provide system end-to-end
carrier frequency synchronization and frequency accuracy of tones. Note: The following types of oscillators
are used in the Defense Communications System FDM systems:
• Type 1 - A master carrier oscillator as an integral part of the multiplexer set.
• Type 2 - A submaster oscillator equipment or slave oscillator equipment as an integral part of the
multiplexer set.
• Type 3 - An external master oscillator equipment that has extremely accurate and stable
characteristics.
Synonym master frequency generator.
Master-Slave Timing - Timing in which one station or node supplies the timing reference for all other
interconnected stations or nodes.
Master Station - 1. In a data network, the station that is designated by the control station to ensure data
transfer to one or more slave stations. Note: A master station controls one or more data links of the data
communications network at any given instant. The assignment of master status to a given station is
temporary and is controlled by the control station according to the procedures set forth in the operational
protocol. Master status is normally conferred upon a station so that it may transmit a message, but a station
need not have a message to send to be designated the master station. 2. In navigation systems using precise
time dissemination, a station that has the clock used to synchronize the clocks of subordinate stations. 3. In
basic mode link control, the data station that has accepted an invitation to ensure a data transfer to one or
more slave stations. Note: At a given instant, there can be only one master station on a data link.
Matched Junction - A waveguide component having four or more ports, and so arranged that if all ports
except one are terminated in the correct impedance, there will be no reflection of energy from the junction
when the fourth port is driven by a transmission line having a matching impedance.
Matching Gel - See gel. Index-matching material in the form of a gel.
Material Absorption - See absorption. - In the transmission of electrical, electromagnetic, or acoustic signals,
the conversion of the transmitted energy into another form, usually thermal. Note 1: Absorption is one cause
of signal attenuation . Note 2: The conversion takes place as a result of interaction between the incident
energy and the material medium, at the molecular or atomic level.
Material Dispersion - See dispersion. In optical fiber communication, the wavelength dependence of the
velocity of propagation (of the optical signal) on the bulk material of which the fiber is made. Note 1:
Because every optical signal has a finite spectral width, material dispersion results in spreading of the signal.
Note 2: Use of the redundant term " chromatic dispersion " is discouraged. Note 3: In pure silica, the basic
material from which the most common telecommunication-grade fibers are made, material dispersion is
minimum at wavelengths in the vicinity of 1.27 m (slightly longer in practical fibers).
Material Dispersion Coefficient [M ( )]: In an optical fiber, pulse broadening per unit length of fiber and
unit spectral width, usually expressed in picoseconds per (nanometer• kilometer). Note 1: For many silica-
based fibers, M ( ) approaches zero at a specific wavelength 0 between 1.3 m and 1.5 m. At
wavelengths shorter than 0, M ( ) is negative and increases with wavelength; at wavelengths longer than
0,, M ( ) is positive and decreases with wavelength.
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![2
talker volume, V, is given by V = V o+ 0.115 , where V o is the average of the talker volume distribution in
2
volume units (vu), and is the variance of the distribution.
Medium-Term Bit Error Rate - Bit error rate that can be encountered for relatively short time periods (e.g.,
minutes), due to temporary malfunctions of, for example, transmission equipment.
Megabyte (MB)- A million bytes or a thousand kilobytes.
6
Megahertz (MHz) - A unit of frequency denoting one million (10 ) Hz.
Memory - 1. All of the addressable storage space in a processing unit and other internal memory that is used
to execute instructions. 2. Loosely, the volatile, main storage in computers. See random access memory.
Memory Scavenging - The collection of residual information from data storage.
Menu - A displayed list of options from which a user selects actions to be performed.
MEO - Abbreviation for medium Earth orbit. An orbital path configuration, between altitudes of 8,000 and
20,000 km, used by communication satellites that provide communications capabilities for such services as
cellular telephone communications and GPS (global positioning system) signals.
Classification Orbital Altitude (km above the earth)
LEO 500-2,000
MEO 8,000-20,000
Geostationary Orbit 35,786
MERCAST - Acronym for merchant-ship broadcast system.
Merchant-Ship Broadcast System (MERCAST) - A maritime shore-to-ship broadcast system in which the
ocean areas are divided into primary broadcast areas each covered by a high-powered shore radio station
that broadcasts simultaneously on one medium frequency (MF) and one or more high frequencies (HF) for
routing messages to ocean-going ships. Note: In some instances, coast stations may repeat the messages.
Meridional Ray - In fiber optics, a ray that passes through the optical axis of an optical fiber (in contrast with
a skew ray, which does not).
Mesh Network - See network topology. A network topology in which there are at least two nodes with two
or more paths between them.
Mesh Topology - See network topology. A network topology in which there are at least two nodes with two
or more paths between them.
Mesochronous - The relationship between two signals such that their corresponding significant instants
occur at the same average rate.
Message - 1. Any thought or idea expressed briefly in a plain or secret language, prepared in a form suitable
for transmission by any means of communication. Note: A message may be a one-unit message or a
multiunit message. 2. [In telecommunications,] Record information expressed in plain or encrypted language
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![Metropolitan Area Network (MAN) - A data communications network that (a) covers an area larger than a
campus area network and smaller than a wide area network (WAN), (b) interconnects two or more LANs, and
(c) usually covers an entire metropolitan area, such as a large city and its suburbs.
MGCP (Media Gateway Control Protocol) - Another protocol competing with H.323 (see also SIP), MGCP
handles the traffic between media gateways and their controllers. Especially useful in multimedia
applications: the media gateway converts from various formats for the switched-circuit network, and the
controller handles conversion for the packet-switched network. Designed to take the workload away from IP
telephones themselves and thereby make IP phones less complex and expensive.
MHS (Message Handling System) - In the ITU-T X.400 Recommendations, the family of services and
protocols that provides the functions for global electronic-mail (e-mail) transfer among local mail systems.
MHz - Abbreviation for megahertz.
MIC - Abbreviation for Medium Interface Connector - In communications systems, the connector at the
interface point between the bus interface unit and the terminal, i.e., the medium interface point.
Microbend - In an optical waveguide, sharp curvatures involving local axial displacements of a few
micrometers and spatial wavelengths of a few millimeters. Note: Microbends can result from waveguide
coating, cabling, packaging, and installation. Microbending can cause significant radiative loss and mode
coupling.
Microbending - See microbend.
Microbend Loss - In an optical fiber, the optical power loss caused by a microbend.
Microwave (mw) - Loosely, an electromagnetic wave having a wavelength from 300 mm to 10 mm (1 GHz to
30 GHz). Note: Microwaves exhibit many of the properties usually associated with waves in the optical
regime, e.g., they are easily concentrated into a beam.
Mimicking - [A] form of spoofing.
Minimum Bend Radius - The radius below which an optical fiber or fiber-optic cable should not be bent.
Note 1: The minimum bend radius is of particular importance in the handling of fiber-optic cables. It will vary
with different cable designs. The manufacturer should specify the minimum radius to which the cable may
safely be bent during installation, and for the long term. The former is somewhat shorter than the latter.
Note 2: The minimum bend radius is in general also a function of tensile stresses, e.g., during installation,
while being bent around a sheave while the fiber or cable is under tension. Note 3: If no minimum bend
radius is specified, one is usually safe in assuming a minimum long-term low-stress radius not less than 15
times the cable diameter.
MIP - Abbreviation for Medium Interface Point - In communication systems, the location at which the
standards for the interface parameters between a terminal and the line facility are implemented.
MIS - Abbreviation for Management Information System - An organized assembly of resources and
procedures required to collect, process, and distribute data for use in decision making.
Miscellaneous Taxes - Like many other consumer goods and services, certain telephone services are taxed by
federal, state, and local governments. These charges may appear as a “gross receipts” tax.
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![Near Real Time - Near Real Time is defined as 1. Pertaining to the delay introduced, by automated data
processing, between the occurrence of an event and the use of the processed data, e.g., for display or
feedback and control purposes. Note 1: For example, a near-real- time display depicts an event or situation
as it existed at the current time less the processing time. Note 2: The distinction between near real time and
real time is somewhat nebulous and must be defined for the situation at hand. 2. Pertaining to the timeliness
of data or information which has been delayed by the time required for electronic communication and
automatic data processing. This implies that there are no significant delays.
Near-Vertical-Incidence Skywave - In radio propagation , Near-Vertical-Incidence Skywave is a wave that is
reflected from the ionosphere at a nearly vertical angle and that is used in short-range communications to
reduce the area of the skip zone and thereby improve reception beyond the limits of the ground wave.
Near Zone - Synonym near-field region. Near Zone is defined as 1. The close-in region of an antenna wherein
the angular field distribution is dependent upon distance from the antenna. Synonym near field. 2. In optical
fiber communications, the region close to a source or aperture . Note: The diffraction pattern in this region
typically differs significantly from that observed at infinity and varies with distance from the source.
NEC - Abbreviation for National Electric Code ® - NEC is a standard that governs the use of electrical wire,
cable, and fixtures, and electrical and optical communications cable installed in buildings. Note: The NEC was
developed by the NEC Committee of the American National Standards Institute ( ANSI ), was sponsored by
the National Fire Protection Association (NFPA), and is identified by the description ANSI/NFPA 70-XXXX, the
last four digits representing the year of the NEC revision.
Necessary Bandwidth -1. For a given class of emission, the width of the frequency band which is just
sufficient to ensure the transmission of information at the rate and with the quality required under specified
conditions. Note: Emissions useful for the adequate functioning of the receiving equipment, e.g., the
emission corresponding to the carrier of reduced carrier systems, must be included in the necessary
bandwidth. ( See Annex J of NTIA Manual of Regulations and Procedures for Federal Radio Frequency
Management for formulas used to calculate necessary bandwidth.) 2. The calculated spectral width of an
emission. Calculations are made using procedures set forth in part 2 of this chapter [of 47CFR ]. The
bandwidth so calculated is considered to be the minimum necessary to convey information at the desired
rate with the desired accuracy.
Need To Know -Need to Know is 1. The legitimate requirement of a person or organization to know, access,
or possess sensitive or classified information that is critical to the performance of an authorized, assigned
mission. 2. The necessity for access to, or knowledge or possession of, specific information required to carry
out official duties.
Negation Circuit - Deprecated synonym for inverter. 1. In electrical engineering, a negation circuit is a device
for converting direct current into alternating current. 2. In computers, a negation circuit is a device or circuit
that inverts the polarity of a signal or pulse.
Negative-Acknowledge Character (NAK) - A Negative-Acknowledge Character is a transmission control
character sent by a station as a negative response to the station with which the connection has been set up.
Note 1: In binary synchronous communication protocol , the NAK is used to indicate that an error was
detected in the previously received block and that the receiver is ready to accept retransmission of that
block. Note 2: In multipoint systems, the NAK is used as the not-ready reply to a poll.
Negative Feedback - See feedback. If the feedback is degenerative (subtractive), it is called " negative
feedback ," which reduces the gain and distortion, and increases linearity and stability. Note 1: Feedback may
occur inadvertently, and be detrimental. 2. Information returned as a response to an originating source.
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![Netiquette - [Slang] A contraction of network etiquette. The written or unwritten rules of etiquette that
govern online interaction between users on the Internet. Note: Some typical rules are a ban on profane or
offensive language, a requirement to respect other users, and a ban on floods of unsolicited advertisements.
Netiquette rules may be enforced by a moderator or may be self-policed by other users.
Net Loss - The overall loss of a transmission circuit.
Net Loss Variation - The maximum change in net loss occurring in a specified portion of a communication
system during a specified period.
Net Operation - The operation of an organization of stations capable of direct communication on a common
channel or frequency. Note: Net operations (a) allow participants to conduct ordered conferences among
participants who usually have common information needs or related functions to perform, (b) are
characterized by adherence to standard formats and procedures, and (c) are responsive to a common
supervisory station, called the " net control station," which permits access to the net and maintains net
operational discipline.
Net Radio Interface (NRI) - An interface between a single- channel radio station (usually in a radio net ) and
switched communications systems.
NETS - Abbreviation for Nationwide Emergency Telecommunications Service. See Government Emergency
Telecommunications Service.
Network - A network is the total infrastructure for transmitting phone and/or Internet messages. 1. An
interconnection of three or more communicating entities. 2. An interconnection of usually passive electronic
components that performs a specific function (which is usually limited in scope), e.g., to simulate a
transmission line or to perform a mathematical function such as integration or differentiation. Note: A
network may be part of a larger circuit. 3. In television, a communication system consisting of a group of
broadcasting stations that all transmit the same programs. (ABC, CBS, NBC)
Network Access Point (NAP) - A centralized point where Internet traffic is exchanged or shared.
Network Address - The signaling point code, containing for U.S. national networks, the network
identification, network cluster, and network cluster member fields (24 bits).
Network Administration - A group of network management functions that (a) provide support services, (b)
ensure that the network is used efficiently, and (c) ensure prescribed service -quality objectives are met.
Note: Network administration may include activities such as network address assignment, assignment of
routing protocols and routing table configuration, and directory service configuration.
Network Architecture - 1. The design principles, physical configuration, functional organization, operational
procedures, and data formats used as the bases for the design, construction, modification, and operation of
a communications network. 2. The structure of an existing communications network, including the physical
configuration, facilities, operational structure, operational procedures, and the data formats in use.
Network Availability - The probability a network can perform its required functions.
Network Browser - A computer program for browsing hyperlinked documents (especially on the Web ). Note
1: A network browser formats and displays information so obtained in a form useful to the viewer. Note 2: A
network browser may function in a graphical mode or in a text-only mode.
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![Network Performance - The qualitative level at which a network fulfills its function.
Network Provided Number (NPN) - An ISDN number, supplied by the calling user 's or the redirecting user's
network , which is associated with the calling user or the redirecting user. It is possible that the NPN may
have the same value as the user provided number (UPN) especially in cases where delivery of two calling
party numbers is supported. The NPN may also be accompanied by a subaddress.
Network Provider - The organization that maintains and operates the network components required for
intelligent network (IN) functionality. A network provider may also take more than one role, e.g., also acting
as service provider.
Network Reliability - See network survivability. The (a) ability of a network to maintain or restore an
acceptable level of performance during network failures by applying various restoration techniques, and (b)
mitigation or prevention of service outages from network failures by applying preventive techniques.
Network Restoration - Automatic or manual methods to return a network to its normal function in response
to a network failure.
Network Section - The network components that provide a virtual connection between two circuit sections.
A network section may be either an access network section or a transit network section.
Network Security: Protection of networks and their services from unauthorized modification, destruction, or
disclosure. It provides assurance the network performs its critical functions correctly and there are no
harmful side-effects.
Network Security Architecture - A subset of network architecture specifically addressing security -relevant
issues.
Network Service Part - The combination of the MTP ( message transfer part ) and the SCCP ( signaling
connection control part ).
Network Site -1. A collection of functional units that provide network services and that belong to one
management domain and are considered as a whole. [2382-pt.35] 2. A specific location that houses
telecommunications equipment entities and/or facility terminations at that location, or a specific location
that houses administrative operations . A location is usually designated as a network site when it houses one
or more network applications.
Network Surveillance - A process concerned with surveillance of the network as a whole. It includes
activities for coordination and assigning priorities to maintenance actions. The information necessary to
support this process comes from alarms, measurements, and indicators of operational (including congestion
) status.
Network Side - The side of the network interface or the network functions as seen from the interface.
Network Survivability - The (a) ability of a network to maintain or restore an acceptable level of
performance during network failures by applying various restoration techniques, and (b) mitigation or
prevention of service outages from network failures by applying preventive techniques.
Network Survivability Model - The analytical processes for estimating how well network services will be
affected and restored with transparencies to the users as a result of a failure.
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![Network Terminal Number (NTN) - In the ITU-T International X.121 format, the sets of digits that comprise
the complete address of the data terminal end point. Note: For an NTN that is not part of a national
integrated numbering format, the NTN is the 10 digits of the ITU-T X.25 14- digit address that follow the Data
Network Identification Code (DNIC). When part of a national integrated numbering format, the NTN is the 11
digits of the ITU-T X.25 14-digit address that follow the DNIC.
Network Terminating Interface (NTI) - Synonym for demarcation point. That point at which operational
control or ownership of communications facilities changes from one organizational entity to another. Note:
The demarcation point is usually the interface point between customer-premises equipment and external
network service provider equipment.
Network Termination - Network equipment that provides functions necessary for network operation of ISDN
access protocols. Note: Network termination provides functions essential for transmission services.
Network Termination 1 (NT1) - In Integrated Services Digital Networks ( ISDN ), a functional grouping of
customer-premises equipment that includes functions that may be regarded as belonging to OSI Layer 1, i.e.,
functions associated with ISDN electrical and physical terminations on the user premises. Note: The NT1
forms a boundary to the network and may be controlled by the provider of the ISDN services.
Network Termination 2 (NT2) - In Integrated Services Digital Networks ( ISDN ), an intelligent device that
may include functionality for OSI Layers 1 through 3 (dependent on individual systems requirements).
Network Topology - The specific physical, i.e., real, or logical, i.e., virtual, arrangement of the elements of a
network. Note 1: Two networks have the same topology if the connection configuration is the same,
although the networks may differ in physical interconnections, distances between nodes, transmission rates,
and/or signal types. Note 2: The common types of network topology are illustrated [refer to the figure on this
page] and defined in alphabetical order below:
• bus topology: A network topology in which all nodes, i.e., stations, are connected together by a
single bus.
• fully connected topology: A network topology in which there is a direct path (branch) between any
two nodes. Note: In a fully connected network with n nodes, there are n(n-1)/2 direct paths, i.e.,
branches. Synonym fully connected mesh network.
• hybrid topology: A combination of any two or more network topologies. Note 1: Instances can
occur where two basic network topologies, when connected together, can still retain the basic
network character, and therefore not be a hybrid network. For example, a tree network connected
to a tree network is still a tree network. Therefore, a hybrid network accrues only when two basic
networks are connected and the resulting network topology fails to meet one of the basic topology
definitions. For example, two star networks connected together exhibit hybrid network topologies.
Note 2: A hybrid topology always accrues when two different basic network topologies are
connected.
• linear topology: See bus topology. A network topology in which all nodes, i.e., stations, are
connected together by a single bus.
• mesh topology: A network topology in which there are at least two nodes with two or more paths
between them.
• ring topology: A network topology in which every node has exactly two branches connected to it.
• star topology: A network topology in which peripheral nodes are connected to a central node,
which rebroadcasts all transmissions received from any peripheral node to all peripheral nodes on
the network, including the originating node. Note 1: All peripheral nodes may thus communicate
with all others by transmitting to, and receiving from, the central node only. Note 2: The failure of a
transmission line, i.e., channel, linking any peripheral node to the central node will result in the
isolation of that peripheral node from all others. Note 3: If the star central node is passive, the
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![provide ready access to instrument packages or sensors at the focus. The engineering tradeoff of an off-axis
optical system is an increase in image aberrations.
Offered Load - The total load submitted to a trunk group. This value may be corrected for retrials during the
engineering process.
Off-Hook - If equipment is "off-hook", it is not idle but actively connected to the telephone line. - 1. In
telephony, the condition that exists when an operational telephone instrument or other user instrument is in
use, i.e., during dialing or communicating. Note: Off-hook originally referred to the condition that prevailed
when the separate earpiece, i.e., receiver, was removed from its switchhook, which extended from a vertical
post that also supported the microphone, and which connected the instrument to the line when not
depressed by the weight of the receiver. 2. One of two possible signaling states, such as tone or no tone and
ground connection versus battery connection. Note: If off-hook pertains to one state, on-hook pertains to
the other. 3. The active state, i.e., closed loop, of a subscriber or PBX user loop. 4. An operating state of a
communications link in which data transmission is enabled either for (a) voice or data communications or (b)
network signaling.
Off-Hook Service - Synonym hotline.
Off-Hook Signal - In telephony, of a circuit, a signal indicating seizure, request for service, or a busy
condition.
Office Classification - Prior to divestiture, numbers that were assigned to offices according to their
hierarchical function in the U.S. public switched telephone network. Note 1: The following class numbers are
used:
• Class 1: Regional Center (RC)
• Class 2: Sectional Center (SC)
• Class 3: Primary Center (PC)
• Class 4: Toll Center (TC) [Only if operators are present; otherwise Toll Point (TP)]
• Class 5: End Office (EO) [ Local central office]
Note 2: Any one center handles traffic from one center to two or more centers lower in the hierarchy. Since
divestiture, these designations have become less firm.
Off Line - 1. In computer technology, the state or condition of a device or equipment that is not under the
direct control of another device. 2. In computer technology, the status of a device that is disconnected from
service.
Off-Line -1. Pertaining to the operation of a functional unit when not under the direct control of the system
with which it is associated. Note 1: Off-line units are not available for immediate use on demand by the
system. Note 2: Off-line units may be independently operated. 2. Pertaining to equipment that is
disconnected from a system, is not in operation, and usually has its main power source disconnected or
turned off.
Off-Line Cryptosystem - A cryptosystem in which encryption and decryption are performed independently of
the transmission and reception functions.
Off-Line Recovery - The process of recovering nonprotected message traffic by use of an off-line processor or
central processing unit.
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![Operator Service Access Point (OSAP) - The functional entity that provides access to an operator service
from an exchange in the network. The operator service may be co-located with the exchange or located
elsewhere.
Operator Service Provider - The company accepting the billing information, initiating the validation process,
and recording the details of the call.
Operator Services - A set of services including toll and assistance, listing services and intercept, associated
with the originating connection network capability.
Operator System - A stored program electronic system associated with one or more toll switching systems
which provides centralized traffic service position functions for several local offices at one location.
Operator Trunks - A general term, ordinarily applied to trunks between manually operated switchboard
positions and local dial central offices in the same wire center.
OPSEC - Acronym for operations security. The process denying to potential adversaries information about
capabilities and/or intentions by identifying, controlling and protecting generally unclassified evidence of the
planning and execution of sensitive activities.
Optical Amplifier - See fiber amplifier. A device that amplifies an optical signal directly, without the need to
convert it to an electrical signal, amplify it electrically, and reconvert it to an optical signal. Note 1: One type
of fiber amplifier uses a doped fiber ( e.g. , a fiber doped with erbium), which bears the communication
signal, and which is optically pumped with a laser having a high-powered continuous output at an optical
frequency slightly higher than that of the communication signal. The signal is intensified by Raman
amplification. Note 2: Because neither optical-electrical conversion nor electrical amplification takes place,
this type of amplifier is well suited for a wide variety of applications, both digital and analog. Note 3: Because
this type of amplifier does not require extraordinary frequency ( wavelength ) control of the pumping laser, it
is relatively simple. optical repeater.
Optical Attenuator - In optical communications, a device used to reduce the power level of an optical signal.
Note 1: Optical attenuators used in fiber optic communications systems may use a variety of principles for
their functioning. Those using the gap - loss principle are sensitive to the modal distribution ahead of the
attenuator, and should be used at or near the transmitting end, or they may introduce less loss than
intended. Optical attenuators using absorptive or reflective techniques avoid this problem. Note 2: The basic
types of optical attenuators are fixed, step-wise variable, and continuously variable.
Optical Axis -1. Of a refractive or reflective optical element, the straight line that is coincident with the axis
of symmetry of the surfaces. Note: The optical axis of a system is often coincident with its mechanical axis,
but it need not be, e.g., in the case of an off-axis parabolic reflector used to transmit signals to, or receive
signals from, a geosynchronous satellite. 2. In a lens element, the straight line which passes through the
centers of curvature of the lens surfaces. 3. In an optical system, the line formed by the coinciding principal
axes of the series of optical elements. 4. In an optical fiber, synonym fiber axis [which is the preferred term].
Optical Beamsplitter - See beamsplitter. A device for dividing an optical beam into two or more separate
beams. Note: An example of a beamsplitter is a partially reflecting mirror.
Optical Cable - See fiber optic cable. A telecommunications cable in which one or more optical fibers are
used as the propagation medium. Note 1: The optical fibers are surrounded by buffers, strength members,
and jackets for protection, stiffness, and strength. Note 2: A fiber-optic cable may be an all-fiber cable, or
contain both optical fibers and metallic conductors. One possible use for the metallic conductors is the
transmission of electric power for repeaters.
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![Optically Active Material - A material that rotates the plane of polarization of light that passes through it.
Optical Mixing - Optical beating, i.e., the mixing , i.e. , heterodyning, of two lightwaves (incoming signal and
local oscillator ) in a nonlinear device to produce a beat frequency low enough to be further processed by
conventional electronic circuitry. Note: Optical mixing is the optical analog of heterodyne reception of radio
signals. [After FAA] Synonym optical heterodyning.
Optical Modulator - Any device used to modify any characteristic of an optical signal (lightwave) for the
purpose of conveying information.
Optical Multiplexing - See wavelength-division multiplexing.
Optical Network Unit (ONU) - A network element that is part of a fiber -in-the- loop system interfacing the
customer analog access cables and the fiber facilities.
Optical Path Length -1. In a medium of constant refractive index , n , the product of the geometric distance
and the refractive index. 2. In a medium of varying refractive index, the integral of n s , where s is an
element of length along the path, and n is the local refractive index. Note: Optical path length is proportional
to the phase shift that a lightwave undergoes along a path.
Optical Path Power Penalty - The extra optical power required to account for degradations due to
reflections, intersymbol interference, and mode partition noise.
Optical Power - See radiant power. The rate of flow of electromagnetic energy, i.e., radiant energy. Note 1:
optical power is usually expressed in watts, i.e., joules per second. Note 2: The modifier is often dropped and
"power" is used to mean "optical power".
Optical Power Budget - In a fiber -optic communication link, the allocation of available optical power
(launched into a given fiber by a given source) among various loss -producing mechanisms such as launch
coupling loss, fiber attenuation, splice losses, and connector losses, in order to ensure that adequate signal
strength (optical power) is available at the receiver. Note 1: The optical power budget is usually specified or
expressed in dB. Note 2: The amount of optical power launched into a given fiber by a given transmitter
depends on the nature of its active optical source ( LED or laser diode ) and the type of fiber, including such
parameters as core diameter and numerical aperture. Manufacturers sometimes specify an optical power
budget only for a fiber that is optimum for their equipment--or specify only that their equipment will operate
over a given distance, without mentioning the fiber characteristics. The user must first ascertain, from the
manufacturer or by testing, (a) the transmission losses for the type of fiber to be used, (b) the required signal
strength for a given level of performance. Note 3: In addition to transmission loss, including those of any
splices and connectors, allowance should be made for at least several dB of optical power margin losses, to
compensate for component aging and to allow for future splices in the event of a severed cable.
Optical Power Margin - In an optical communications link, the difference between (a) the optical power that
is launched by a given transmitter into the fiber, less transmission losses from all causes, and (b) the
minimum optical power that is required by the receive for a specified level of performance. Note 1: The
optical power margin is usually expressed in dB. At least several dB of optical power margin should be
included in the optical power budget. Note 2: The amount of optical power launched into a given fiber by a
given transmitter depends on the nature of its active optical source ( LED or laser diode ) and the type of
fiber, including such parameters as core diameter and numerical aperture.
Optical Receiver - A device that detects an optical signal, converts it to an electrical signal, and processes the
electrical signal as required for further use.
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![Parity - 1. In binary-coded data, a condition that is maintained such that, in any permissible coded
expression, the total number of 1s, or 0s, is always odd or always even. Note 1: Parity is used in error-
detecting and error-correcting codes. Note 2: For example, in the ASCII code or in the International Telegraph
Alphabet 5 (ITA-5) code as usually implemented, 7 bits are used to represent each character and 1 bit is used
as a parity check bit. 2. Bit(s) used to determine whether a block of data has been altered.
Parity Bit - An extra bit that can be added to a group of "0" bits and "1" bits to make the parity of the group
odd or even. Note: The parity bit is discarded when the message is received.
Parity Check - A test that determines whether the number of ones or zeros in an array of binary digits is odd
or even. Note: Odd parity is standard for synchronous transmission and even parity for asynchronous
transmission. Synonym odd-even check.
Parking Party - Representative of the served user who parks a call via "call park".
Par Meter - Abbreviation for peak-to-average ratio meter. A meter used to measure, calculate, and display
the ratio of the peak power level to the time -averaged power level in a circuit, i.e. , the peak-to-average
ratio ( p / a r). Note 1: A par meter is used as a quick means to identify degraded telephone channels. Note 2:
A par meter is very sensitive to envelope delay distortion. The par meter may also be used for idle channel
noise, nonlinear distortion, and amplitude-distortion measurements. Note 3: The peak-to-average ratio can
be determined for many signal parameters, such as voltage, current, power, frequency, and phase.
PARS - Abbreviation for paging and radiotelephone service. A radio service in which common carriers are
authorized to offer and provide paging and radiotelephone service to the general public. This service was
formerly titled Public Land Mobile Service.
Partial-Dial Condition - A condition in which outpulsing has commenced, insufficient information has been
received by the customer installation (CI) to process the call and no further outpulsing has been received
from the network within a timed interval.
Partitioned Security Mode - [An] information - system (IS) security mode of operation wherein all personnel
have the clearance, but not necessarily formal access approval and need-to-know, for all information
handled by an IS.
Party ID -1. The served user 's (or controller 's) reference to a particular party within the context of a call.
Note 1: Multiple parties may be associated with a given call, e.g., a conference call. Moreover, there may be
multiple connections associated with a single party, e.g., a simultaneous voice and video call. Note 2: This
service description assumes that there exists only one connection to a given party. 2. In a teleconference,
any participant.
Party Line - A line that serves more than one subscriber or user. In telephone systems, an arrangement in
which two or more user end instruments, usually telephones, are connected to the same loop. Note: If
selective ringing is not used, individual users may be alerted by different ringing signals, such as a different
number of rings or a different combination of long and short rings. Party lines remain primarily in rural areas
where loops are long. Privacy is limited and congestion often occurs. Synonym multiparty line.
Passband - The portion of spectrum , between limiting frequencies (or, in the optical regime, limiting
wavelengths), that is transmitted with minimum relative loss or maximum relative gain. Note 1: The limiting
frequencies are defined as those at which the relative intensity or power decreases to a specified fraction of
the maximum intensity or power. This decrease in power is often specified to be the half-power points, i.e. ,
3 dB below the maximum power. Note 2: The difference between the limiting frequencies is called the
bandwidth, and is expressed in hertz (in the optical regime, in nanometers or micrometers).
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![Peak Envelope Power (of a radio transmitter) [PEP, pX, PX]: The average power supplied to the antenna
transmission line by a transmitter during one radio frequency cycle at the crest of the modulation envelope
taken under normal operating conditions.
Peak Limiting - A process by which the absolute instantaneous value of a signal parameter is prevented from
exceeding a specified value.
Peer Entity - In layered systems, entities in the same layer but in different systems (nodes) that must
exchange information to achieve a common objective.
Peer-Entity Authentication - The corroboration that a peer entity in an association is the one claimed.
peer group - In Open Systems Interconnection (OSI)--Architecture, a group of functional units in a given layer
of a network in which all the functions performed by the functional units extend throughout the system at
the same layer.
Peering - The arrangement of information sharing between Internet Service Providers at various NAPs.
Peer Protocol - A formal language used by peer entities to exchange user data.
Peg Count -1. In communication systems, a count that is made of the number of times that an event or
condition occurs. [From Weik '89] 2. In telephone systems, the process that provides counts of the calls of
different service classes that occur during intervals of such frequency as to reliably indicate the traffic load.
3. A count of the attempts to seize, or a count of the actual seizures that occur, of various types of telephone
trunks, access lines, switches, or other equipment.
Pel - In a facsimile system, the smallest discrete scanning line sample containing only monochrome
information , i.e. , not containing gray-scale information.
Pen-Based Computer - A computer that uses pattern-recognition software to enable it to accept handwriting
as a form of input. A stylus, which may contain special electronic circuitry, is used to write on the computer
display or on a separate tablet. The earliest devices were limited to recognizing geometric shapes for
computer graphics applications and neatly printed alphabetic characters. Pattern recognition has improved
to the level where cursive input is now acceptable, especially in personal digital assistants , although such
input is not always accurately interpreted by the software. Some software requires the use of a specially
modified alphabet to enter data.
Penetration - 1. The intentional passage, through a building wall or partition, or an equipment enclosure or
chassis, of a signal -bearing communications medium, e.g., a cable, metallic or optical. 2. Unintended access
to the information within a communications or information-processing device via a metallic path intended
for another purpose, e.g., via the primary power connection. 3. [The] unauthorized act of bypassing the
security mechanisms of a system. 4. The passage of an rf signal through a physical barrier, such as a partition,
a wall, a building, or earth. 5. Unauthorized access to a data processing system.
Penetration Testing - Security testing in which evaluators attempt to circumvent the security features of a
system based on their understanding of the system design and implementation.
PEP - Deprecated abbreviation for peak envelope power. Either "PX" or "pX" is now preferred. See peak
envelope power, power.
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![Per-Call Key - A unique traffic encryption key generated automatically by certain secure telecommunications
systems to secure single voice or data transmissions.
Percentage Modulation -1. In angle modulation, the fraction of a specified reference modulation, expressed
in percent. 2. In amplitude modulation, the modulation factor expressed in percent. Note: Percentage
modulation may also be expressed in dB below 100% modulation.
Percent Break - In pulsed telephone signaling ( dialing ), the ratio, expressed in percent, of (a) the open-
circuit (break) time to (b) the sum of the open- and closed-circuit times of a single dial pulse cycle. Note: For
example, at a pulse rate of 10 per second, the pulse period is 100 milliseconds. If, during each pulse period,
the equipment generating the dial pulses ( e.g., a telephone set ) presents an open circuit (high impedance )
for 48 milliseconds, and a closed circuit (low impedance) for 52 milliseconds, the percent break is [48
ms/(48ms + 52ms)] = 0.48, or 48%.
Performance Measurement Period - The period during which performance parameters are measured. Note:
A performance measurement period is determined by required confidence limits and may vary as a function
of the observed parameter values. User time is divided into consecutive performance measurement periods
to enable measurement of user information transfer reliability.
Perfect Forward Secrecy - In cryptography, of a key -establishment protocol, the condition in which the
compromise of a session key or long-term private key after a given session does not cause the compromise
of any earlier session.
Performance Anomalies - A discrepancy between actual and desired characteristics of an item. An anomaly
may or may not affect the ability of an item to perform a required function.
Performance Management - In network management, (a) a set of functions that evaluate and report the
behavior of telecommunications equipment and the effectiveness of the network or network element and
(b) a set of various subfunctions, such as gathering statistical information, maintaining and examining
historical logs, determining system performance under natural and artificial conditions, and altering system
modes of operation.
Performance Measurement Period - The period during which performance parameters are measured. Note:
A performance measurement period is determined by required confidence limits and may vary as a function
of the observed parameter values. User time is divided into consecutive performance measurement periods
to enable measurement of user information transfer reliability.
Performance Parameter - A quality, usually quantified by a numerical value, which quality characterizes a
particular aspect, capability, or attribute of a system. Note: Examples of performance parameters are peg
count and mean time between failures.
Performance Primitives - Basic error events or other performance-related occurrences that may be detected
by monitoring a digital signal.
Performance Reliability - The ability of an item to perform a required function under given conditions for a
given time period. Note 1: It is generally assumed that the item is in a state to perform this required function
at the beginning of the time interval. Note 2: The term reliability is used as a measure of reliability
performance.
Performance Standard - A statement of general criteria that define a desired result without specifying the
techniques for achieving that result. Synonym performance-based standard.
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![Permissible Interference - Observed or predicted interference which complies with quantitative interference
and sharing criteria contained in these [Radio] Regulations or in CCIR Recommendations or in special
agreements as provided for in these Regulations.
Permuter - A device used in crypto-equipment to change the order in which the contents of a shift register
are used in various nonlinear combining circuits.
Persistent Data - Information that endures beyond a single instance of use, e.g., longer than one call
attempt.
Personal Agent - Synonym droid. See bot.
Personal Authenticating Information (PAI) - Information such as a secret password, a badge, or biometric
data —or any combination of these—used to authenticate a user's identity.
Personal Communications Service - See PCS. A set of capabilities that allows some combination of terminal
mobility, personal mobility, and service profile management. Note 1: The flexibility offered by PCS can
supplement existing telecommunications services, such as cellular radio, used for NS/EP missions. Note 2:
PCS and UPT are sometimes mistakenly assumed to be the same service concept. UPT allows complete
personal mobility across multiple networks and service providers. PCS may use UPT concepts to improve
subscriber mobility in allowing roaming to different service providers, but UPT and PCS are not the same
service concept.
Personal De-registration - The process by which end users cancel a previous registration to a terminal.
Personal Digital Assistant - [personal digital assistant] (PDA), lightweight, hand-held computer designed for
use as a personal organizer with communications capabilities. A typical PDA has no keyboard, relying instead
on special hardware and pen-based computer software to enable the recognition of handwritten input,
which is entered on the surface of a liquid crystal display screen. In addition to including such applications as
a word processor, spreadsheet, calendar, and address book, PDAs are used as notepads, appointment
schedulers, and wireless communicators for sending and receiving data, faxes, and electronic-mail messages.
Introduced in 1993, PDAs achieved only modest acceptance during the remainder of the decade due to their
relatively high price and limited applications.
Personal Identification Number (PIN) - A code or password, unique to or associated with, a specific user, and
entered into a data-processing device for purposes of verifying the identity of a person requesting, e.g., a
transaction or access.
Personal Mobility - In universal personal telecommunications (UPT), (a) the ability of a user to access
telecommunication services at any UPT terminal on the basis of a personal identifier, and (b) the capability of
the network to provide those services in accord with the user's service profile. Note 1: The personal mobility
aspects of personal communications are based on the UPT number. Note 2: Personal mobility involves the
network's capability to locate the terminal associated with the user for the purposes of addressing, routing,
and charging the user for calls. Note 3: "Access" is intended to convey the concepts of both originating and
terminating services. Note 4: Management of the service profile by the user is not part of personal mobility.
Personal Mobility Controller - In UPT (universal personal telecommunications), a facility that provides the
control logic for user authentication, service request validation, location management, alerting, user access
to service profile, privacy, access registration, and call management.
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![split evenly by the center taps. This cancels crosstalk from the phantom circuit to the side circuits. Synonym
[loosely] phantom facility.
Phantom Facility - A transmission facility derived with repeating coils from two or more pairs of wires.
Synonyms phantom circuit, phantom pair. Note: The name "phantom" is derived from the fact that
balanced, center-tapped transformers, called "repeat(ing)" coils in telephone parlance, can be used, e.g., in
conjunction with two twisted pairs, to create a third, electrically isolated transmission path ("phantom pair")
by splitting the latter's electrical signal between the two twisted pairs (called "side circuits") in such a fashion
as to cancel inductive interference from the phantom circuit to the side circuits, and vice versa.
Phantom Group - Three circuits that are derived from simplexing two physical circuits to form a phantom
circuit.
Phase - 1. Of a periodic, varying phenomenon, e.g., an electrical signal or electromagnetic wave, any
distinguishable instantaneous state of the phenomenon, referred to a fixed reference or another periodic
varying phenomenon. Note 1: Phase, i.e., phase time (frequently abbreviated simply to "phase" in informal
usage), can be specified or expressed by time of occurrence relative to a specified reference. Note 2: The
phase of a periodic phenomenon can also be expressed or specified by angular measure, with one period
usually encompassing 360&176; (2 radians). Note 3: Phase may be represented (a) in polar coordinates by
M , where M is the magnitude and is the phase angle, and (b) in Cartesian coordinates, i.e., an Argand
diagram, as (a + jb), where a is a real component and b is an imaginary component such that tan = (b /a),
2 2 ½
where is the phase angle, and the magnitude, M, is (a + b ) 2. A distinguishable state of a phenomenon.
3. That period of time during which a specified function occurs in a sequential list of functions.
Phase Angle - Of a periodic wave, the number of suitable units of angular measure between a point on the
wave and a reference point. Note 1: The reference point may be a point on another periodic wave. The
waves may be plotted on a suitable coordinate system, such as a Cartesian plot, with degrees or other
angular measure usually plotted on the abscissa and amplitude on the ordinate. Usually, at least one full
cycle of each wave is plotted, with 360&176; (2 radians) encompassing one full cycle. The reference points
may be any significant instants on the waves, such as where they cross the abscissa axis. Note 2: The use of
angular measure to define the relationship between a periodic wave and a reference point is derived from
the projection of a rotating vector onto the real axis of an Argand diagram. Note 3: The value of the phase
angle of a point on the wave is the point on the abscissa that corresponds to the point on the wave. Note 4:
The phase angle of a vector may be written as M , where M is the magnitude of the vector and is the
phase angle relative to the specified reference.
Phase Bandwidth - Of a network or device, the width of the continuous frequency range over which the
phase -vs.-frequency characteristic does not depart from linearity by more than a stated amount.
Phase Coherence - The state in which two signals maintain a fixed phase relationship with each other or with
a third signal that can serve as a reference for each.
Phase Coherent - See phase coherence.
Phase Constant - The imaginary part of the axial propagation constant for a particular mode, usually
expressed in radians per unit length.
Phased Array - A group of antennas in which the relative phases of the respective signals feeding the
antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired
direction and suppressed in undesired directions. Note 1: The relative amplitudes of--and constructive and
destructive interference effects among--the signals radiated by the individual antennas determine the
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![Phone Company Voice Mail - A phone company feature that answers calls and takes messages when you are
on the phone, on the internet, sending a fax, or not at home. This feature also works when the electrical
power is out. You can access your voicemail box through a local access number. You enter your PIN and
follow the appropriate prompts to use the service. There is a maximum capacity for messages, minutes per
message, and message retention length, as outlined in marketing information for your local phone company.
Call Forwarding Busy/No Answer must be ordered but will not be billed when Voice Mail is ordered.
Phone Jack - n : a jack for plugging in a telephone [syn: telephone jack].
Phone Fax Switch - A device that allows a single phone line to be shared for multiple devices. Typically a
Phone Fax Switch would allow voice (phones and answering machine) and a fax machine or fax modem to
operate on a shared phone line. Other applications include any variation of voice, a fax machine, fax/modem
and/or modem(s). Incomming calls are automatically routed to the proper device(s). If the call comes in and
it is a fax call, the call is automatically routed to the fax machine or fax .modem. If the call is a modem call, it
is routed to the correct modem. Voice calls are routes to phone(s) and/or answering machine. May require a
security access code (SAC) in the dialing string to automatically switch to the modem. Synonym Automatic
Line Sharing Device . Fax Switch , Automatic Fax Switch .
Phone Line Switch - - A device that allows one or more phone lines to be shared for multiple phone
connected devices. A common application would allow voice (phones and answering machine) and a fax
machine or fax modem to operate transparently on a single phone line thus eliminating the monthly costs
associated with a dedicated phone line. Applications include any variation of voice, a fax machine,
fax/modem and/or modem(s). Incoming calls are automatically routed to the proper device(s) with no
human intervention. If the call comes in and it is a fax call, the call is automatically routed to the fax machine
or fax modem. If the call is a modem call, it is routed to the correct modem. Voice calls are routes to
phone(s) and/or answering machine. May require a security access code (SAC) in the dialing string to
automatically switch to the modem. Synonym Automatic Line Sharing Device . Fax Switch , Automatic Fax
Switch .
Phone Line Sharing - A technology that allows a single phone line to share incoming and outgoing access for
multiple devices. Typically Phone Line Sharing Technology allows voice (phones and answering machine) and
a fax machine or fax modem to operate on a shared phone line. Other applications include any variation of
voice, a fax machine, fax/modem and/or modem(s).
Incoming calls are automatically routed to the proper device(s). If the call comes in and it is a fax call, the call
is automatically routed to the fax machine or fax modem. If the call is a modem call, it is routed to the
correct modem. Voice calls are routes to phone(s) and/or answering machine. May require a security access
code (SAC) in the dialing string to automatically switch to the modem. All outgoing calls access the line from
any device. Optional "barge-in protection" protects any voice or data call from being accessed by other
telephone equipment on the same line.
Since the need for to subscribe to a separate "fax line" or "modem line" from the local telephone company is
eliminated, the return on investment (ROI) is very high. The initial cost of the device is returned in savings in
a few months. After that you will save the monthly bills associated with fax, data or voice lines. For almost
every business, phone line sharing technology is a smart investment.
Photocurrent - The current that flows through a photosensitive device, such as a photodiode, as the result of
exposure to radiant power. Note 1: The photocurrent may occur as a result of the photoelectric,
photoemissive, or photovoltaic effect. Note 2: The photocurrent may be enhanced by internal gain caused by
interaction among ions and photons under the influence of applied fields, such as occurs in an avalanche
photodiode (APD).
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![DSL, and you have broadband; add VoIP, and you have a system that uses POTS, the PSTN, and the Internet
in one (ideally) seamless system.
Power - 1. The rate of transfer or absorption of energy per unit time in a system. 2. Whenever the power of a
radio transmitter etc. is referred to, it shall be expressed in one of the following forms, according to the class
of emission, using the arbitrary symbols indicated:
• peak envelope power (PX or pX);
• mean power (PY or pY);
• carrier power (PZ or pZ).
For different classes of emission, the relationships between peak envelope power, mean power and carrier
power, under the conditions of normal operation and of no modulation, are contained in CCIR
Recommendations which may be used as a guide. For use in formulae, the symbol p denotes power
expressed in watts and the symbol P denotes power expressed in decibels relative to a reference level.
Power Density - Deprecated synonym for irradiance. Radiant power incident per unit area upon a surface.
Note: Irradiance is usually expressed in watts per square meter, but may also be expressed in joules per
square meter.
Power-Law Index Profile - For optical fibers, a class of graded-index profiles Note 1: is often used in place
of g. Hence, this is sometimes called an alpha profile. Note 2: For this class of profiles, multimode distortion
is smallest when g takes a particular value depending on the material used. For most materials, this optimum
value is approximately 2. When g increases without limit, the profile tends to a step-index profile.
PPP - See Point to Point Protocol
Precedence - In communications, a designation assigned to a message by the originator to indicate to
communications personnel the relative order of handling and to the addressee the order in which the
message is to be noted. [After JP1] Note: The descending order of precedence for military messages is FLASH,
IMMEDIATE, PRIORITY, and ROUTINE.
Precise Time - A time mark that is accurately known with respect to an accepted reference time standard.
14
Note: Current uncertainty among international standards is approximately 1 part in 10 as of 1995.
Predetection Combining - A diversity combiner in which (a) the signals from each channel are added
together, (b) the gain of each channel is made proportional to the rms signal level and inversely proportional
to the mean square noise level in that channel, and (c) the same proportionality constant is used for all
channels. Synonym maximal-ratio combiner.
Preemption - The seizure, usually automatic, of military system facilities that are being used to serve a lower
precedence call in order to serve immediately a higher precedence call.
Prefix - In telephone communications, an indicator consisting of one or more digits, that allows the selection
of different types of number formats (e.g., local, national or international), transit networks and/or the
service. Note 1: Prefixes are not part of the number and are not signaled over internetwork and international
boundaries. Note 2: When prefixes are used, they are always entered by the user or by automatic calling
equipment.
Presentation Layer - Layer 6 of the See Open Systems Interconnection--Reference Model. This layer
responds to service requests from the Application Layer and issues service requests to the Session Layer. The
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![Presentation Layer relieves the Application Layer of concern regarding syntactical differences in data
representation within the end-user systems. Note: An example of a presentation service would be the
conversion of an EBCDIC-coded text file to an ASCII-coded file. See Open Systems Interconnection--
Reference Model.
Primary Coating - The plastic overcoat in intimate contact with the cladding of an optical fiber, applied
during the manufacturing process. Note 1: The primary coating typically has an outside diameter of
approximately 250 to 750 m, and serves to protect the fiber from mechanical damage and chemical attack. It
also enhances optical fiber properties by stripping off cladding modes, and in the case where multiple fibers
are used inside a single buffer tube, it suppresses cross-coupling of optical signals from one fiber to another.
Note 2: The primary coating should not be confused with a tight buffer, or the plastic cladding of a plastic-
clad-silica (PCS) fiber. Note 3: The primary coating, which typically consists of many layers, may be color-
coded to distinguish fibers from one another, e.g., in a buffer tube containing multiple fibers. Synonyms
primary polymer coating, primary polymer overcoat.
Primary Polymer Coating - Synonym primary coating.
Primary Polymer Overcoat - Synonym primary coating.
Primary Power - The source of electrical power that usually supplies the station main bus. Note 1: The
primary power source may be a Government-owned generating plant or a public utility power system. Note
2: A Class A primary power source assures, to a high degree of reliability, a continuous supply of ac electrical
power.
Primary Radar: A radiodetermination system based on the comparison of reference signals with radio signals
reflected from the position to be determined.
Primary Rate Interface (PRI) - An integrated services digital network (ISDN) interface standard (a) that is
designated in North America as having a 23B+D channels, (b) in which all circuit-switched B channels operate
at 64 kb/s, and (c) in which the D channel also operates at 64 kb/s. Note: The PRI combination of channels
results in a digital signal 1 (T1) interface at the network boundary.
Priority - 1. Priority, unless specifically qualified, is the right to occupy a specific frequency for authorized
uses, free of harmful interference from stations of other agencies. [NTIA] 2. Synonym priority level. 3. In
DOD record communications systems, one of the four levels of precedence used to establish the time frame
for handling a given message. 4. In DOD voice communications systems, one of the levels of precedence
assigned to a subscriber telephone for the purpose of preemption of telephone services.
Priority Level - In the Telecommunications Service Priority system, the level that may be assigned to an
NS/EP telecommunications service, which level specifies the order in which provisioning or restoration of the
service is to occur relative to other NS/EP or non-NS/EP telecommunication services. Note: Priority levels
authorized are designated (highest to lowest) "E," "1," "2," "3," "4," and "5" for provisioning and "1," "2," "3,"
"4," and "5" for restoration. Synonym priority.
Privacy - 1. In a communications system or network, the protection given to information to conceal it from
unauthorized persons having access to the system or network at large. Synonym segregation. 2. In a
communications system, protection given to unclassified information, such as radio transmissions of law
enforcement personnel, that requires safeguarding from unauthorized persons. 3. In a communications
system, the protection given to prevent unauthorized disclosure of the information in the system. Note 1:
The required protection may be accomplished by various means, such as by communications security
measures and by directives to operating personnel. Note 2: The limited protection given certain voice and
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![telecommunication service to a user, including all associated transmission, wiring, and equipment. 5. The
process of establishing and supplying telecommunications service to a user, including an associated
transmission, wiring, and telecommunications company equipment.
PSK - Abbreviation for phase-shift keying. - 1. In digital transmission, angle modulation in which the phase of
the carrier is discretely varied in relation either to a reference phase or to the phase of the immediately
preceding signal element, in accordance with data being transmitted. 2. In a communications system, the
representing of characters, such as bits or quaternary digits, by a shift in the phase of an electromagnetic
carrier wave with respect to a reference, by an amount corresponding to the symbol being encoded. Note 1:
For example, when encoding bits, the phase shift could be 0° for encoding a "0," and 180° for encoding a "1,"
or the phase shift could be -90 for "0" and +90° for a "1," thus making the representations for "0" and "1" a
total of 180° apart. Note 2: In PSK systems designed so that the carrier can assume only two different phase
angles, each change of phase carries one bit of information, i.e., the bit rate equals the modulation rate. If
the number of recognizable phase angles is increased to 4, then 2 bits of information can be encoded into
each signal element; likewise, 8 phase angles can encode 3 bits in each signal element.
Psophometer - An instrument that provides a visual indication of the audible effects of disturbing voltages of
various frequencies. Note: A psophometer usually incorporates a weighting network. The characteristics of
the weighting network depend on the type of circuit under investigation, such as whether the circuit is used
for high-fidelity music or for normal speech.
Psophometric Weighting - A noise weighting established by the International Consultative Committee for
Telephony (CCIF, which became CCITT and, more recently, ITU-T), designated as CCIF-1951 weighting, for use
in a noise measuring set or psophometer. Note: The shape of this characteristic is virtually identical to that of
F1A weighting. The psophometer is, however, calibrated with a tone of 800 Hz, 0 dBm, so that the
corresponding voltage across 600 ohms produces a reading of 0.775 V. This introduces a 1-dBm adjustment
in the formulas for conversion with dBa.
PSTN (Public Switched Telephone Network) - The network of wires, signals, and switches that lets one
telephone connect to another anywhere in the world. Some VoIP services provide a gateway from the
Internet to the PSTN and vice versa.
Public Key Cryptography - 1. The type of cryptography in which the encryption process is publicly available
and unprotected, but in which a part of the decryption key is protected so that only a party with knowledge
of both parts of the decryption process can decrypt the cipher text. Note: Commonly called non-secret
encryption in professional cryptologic circles. FIREFLY is an application of public key cryptography. 2. [An]
Encryption system using a linked pair of keys. What one pair of keys encrypts, the other pair decrypts.
Public Switched Network (PSN) - 1. Any common carrier network that provides circuit switching among
public users. Note: The term is usually applied to public switched telephone networks, but it could be applied
more generally to other switched networks, e.g., packet-switched public data networks. 2. A switched
network accessible by the public for the purpose of originating and terminating telecommunications
messages. 3. Any common carrier switched network, whether by wire or radio, including local exchange
carriers, interexchange carriers, and mobile service providers, that use the North American Numbering Plan
in connection with the provision of switched services.
Public Switched Telephone Network (PSTN) - The network of wires, signals, and switches that lets one
telephone connect to another anywhere in the world. Some VoIP services provide a gateway from the
Internet to the PSTN and vice versa.
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![purpose of providing and maintaining a specified degree of confidence in data integrity and accuracy
throughout the life cycle of the data, which includes input, update, manipulation, and output.
QOS (Quality of Service): Refers to the quality of the voice call over a VoIP network. A major issue in VoIP
communications, because the high quality of telephone calls has always been taken for granted. Latency,
packet loss, network jitter, and many other factors contribute to QOS measurements, and numerous
solutions have been offered by vendors of routers and other network components.
QRS - Abbreviation for quasi-random signal. A signal consisting of a bit sequence that approximates a
random signal. [T1.201-1989] The unframed QRS (QRSS, QRTS, QRW) for DS1 consists of a PRBS with a 20-
stage shift register with a constraint that forces the "put to a one" when the next 14 bits in the sequence
would be zeros. The QRS generates every combination of 20-bit words, repeats every 1,048,575 bits, and
contains high density sequences, low density sequences, and sequences that change from low density to
high density and vice versa. When transmitted as the payload of a DS1 signal (framed), the QRS meets the
pulse density definition "a" criteria, providing a maximum of 15-sequential zeros (14 + 1 when the frame bit
is a zero), but does not meet the pulse density definition "b" criteria. (ANSI Tl.403 states: 'the quasi-random
signal may be transmitted without meeting these pulse density constraints.') Contrast with pseudorandom
number sequence.
QRW - Abbreviation for quasi-random word.
Quad - A group of four wires composed of two pairs twisted together. Note: The pairs have a fairly long
length of twist and the quad a fairly short length of twist.
Quadded Cable - A cable formed of multiples of quads, paired and separately insulated, and contained under
a common jacket.
QUADRANT - [A] short name referring to technology that provides tamper-resistant protection to crypto-
equipment.
Quadratic Profile - Synonym parabolic profile. In an optical fiber, a power-law index profile with the profile
parameter, g, equal to 2.
Quadrature - 1. The state of being separated in phase by 90° ( /2 radians). 2. Pertaining to the phase
relationship between two periodic quantities varying with the same period, that is, with the same frequency
or repetition rate, when the phase difference between them is one-quarter of their period.
quadrature amplitude modulation (QAM): 1. Quadrature modulation in which the two carriers are
amplitude modulated. 2. In analog communications, the representation (i.e., transmission) of digital
information by encoding bit sequences of fixed, specified length (number of bits), and representing these bit
sequences as a function of (a) the amplitude of an analog carrier; or (b) a phase shift of the analog carrier
with respect to the phase that represented the preceding bit sequence, and where the permissible phase
shift is an integral multiple of /2 radians (90°, or one-quarter unit interval); or (c) both. Note 1: The name
quadrature originates from the stipulation that a phase shift, when required, must be an integral multiple of
p/2 radians, i.e., one-quarter of a cycle (unit interval, or baud). Note 2: A representative QAM table is
presented below. If the baud (carrier) rate is 1200 Hz (the usual case in modems used on conventional
telephone lines), this QAM scheme permits transmission of a data rate of 9600 b/s, which is the product of
the baud rate and the number of permissible phase-amplitude states.
Any continuous bit stream may be represented as a combination of the eight permissible bit sequences in
the above table, and transmitted as such. Note 3: According to mathematical theory, there is no limit to the
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![bandwidth, signal-to-noise ratio, and envelope delay distortion. When quasi-analog form of signaling is used
to convey message traffic over dial-up telephone systems, it is often referred to as voice-data. A modem may
be used for the conversion process.
Quasi-Analog Transmission - Transmission in which a special-purpose modulator is used to convert digital
signals into an analog form suitable for transmission over an analog voice-grade circuit. Note: A
complementary demodulator is used to recover the digital signal at the other end of the circuit. See modem.
Quasi-Associated Mode of Signaling - A limited case of the nonassociated mode of signaling in which the
path taken by a message through the signaling network is predetermined and fixed at a given point in time.
Quasi-Lossless Compression - In video and multimedia applications, the bit-rate reduction of an image
signal, by an algorithm that recognizes the high degree of correlation ascertainable in specific images. Note
1: The final image does not replicate the original when viewed in direct comparison, but the losses are
designed to be unrecognizable under the intended display conditions. Note 2: The algorithm may often apply
transform coding, predictive techniques, and other modeling to the image signal, along with some form of
entropy encoding. Note 3: While the image appears unaltered to normal human vision, it may show losses
and artifacts when analyzed by other systems (i.e., chroma key, computerized image analysis, etc.). Note 4:
The lost information cannot be extracted from the compressed bit stream.
Quasi-Random Signal (QRS) - See QRS. A signal consisting of a bit sequence that approximates a random
signal. [T1.201-1989] The unframed QRS (QRSS, QRTS, QRW) for DS1 consists of a PRBS with a 20-stage shift
register with a constraint that forces the "put to a one" when the next 14 bits in the sequence would be
zeros. The QRS generates every combination of 20-bit words, repeats every 1,048,575 bits, and contains high
density sequences, low density sequences, and sequences that change from low density to high density and
vice versa. When transmitted as the payload of a DS1 signal (framed), the QRS meets the pulse density
definition "a" criteria, providing a maximum of 15-sequential zeros (14 + 1 when the frame bit is a zero), but
does not meet the pulse density definition "b" criteria. (ANSI Tl.403 states: 'the quasi-random signal may be
transmitted without meeting these pulse density constraints.') Contrast with pseudorandom number
sequence.
Quaternary Phase-Shift Keying - Synonym quadrature phase-shift keying. Phase-shift keying in which four
different phase angles are used. Note: In QPSK, the four angles are usually out of phase by 90°.
Quaternary Signal - A digital signal having four significant conditions.
Query Call - In adaptive high-frequency (HF) radio, an automatic-link-establishment (ALE) call that requests
responses from stations having connectivity to the destination specified in the call.
Queue - A set of items, such as telephone calls or packets, arranged in sequence. Note: Queues are used to
store events occurring at random times and to service them according to a prescribed discipline that may be
fixed or adaptive.
Queue Traffic - 1. A series of outgoing or incoming calls waiting for service. 2. In a store-and-forward
switching center, the outgoing messages awaiting transmission at the outgoing line position.
Queuing - The process of entering elements into or removing elements from a queue.
Queuing Delay - 1. In a switched network, the time between the completion of signaling by the call
originator and the arrival of a ringing signal at the call receiver. Note: Queues may be caused by delays at the
originating switch, intermediate switches, or the call receiver servicing switch. 2. In a data network, the sum
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![Radiobeacon Station - A station in the radionavigation service the emissions of which are intended to enable
a mobile station to determine its bearing or direction in relation to the radiobeacon station.
Radiocommunication - Telecommunication by means of radio waves.
Radiocommunication Service - A service as defined in this Section [of the Radio Regulations] involving the
transmission, emission and/or reception of radio waves for specific telecommunication purposes. In these
regulations, unless otherwise stated, any radiocommunication service relates to terrestrial
radiocommunication.
Radio Detection and Ranging - See radar.
Radiodetermination - The determination of the position, velocity and/or other characteristics of an object,
or the obtaining of information relating to these parameters, by means of the propagation properties of
radio waves.
Radiodetermination-Satellite Service - A radiocommunication service for the purpose of radiodetermination
involving the use of one or more space stations. This service may also include feeder links necessary for its
own operation.
Radio Field Intensity - Synonym field strength. 1. The magnitude of an electric, magnetic, or electromagnetic
field at a given point. Note: The field strength of an electromagnetic wave is usually expressed as the rms
value of the electric field, in volts per meter. The field strength of a magnetic field is usually expressed in
amperes per meter 2. The electric field strength in the horizontal plane.
Radio Frequency - See RF. Of, or pertaining to, any frequency within the electromagnetic spectrum normally
associated with radio wave propagation. Note: For designation of subdivisions, see electromagnetic
spectrum and its associated diagram.
Radio Horizon - The locus of points at which direct rays from an antenna are tangential to the surface of the
Earth. Note: If the Earth were a perfect sphere and there were no atmospheric anomalies, the radio horizon
would be a circle. In practice, the distance to the radio horizon is affected by the height of the transmitting
antenna, the height of the receiving antenna, atmospheric conditions, and the presence of obstructions, e.g.,
mountains.
Radiolocation - Radiodetermination used for purposes other than those of radionavigation.
Radiological Monitoring - Synonym monitoring. - 1. The act of listening, carrying out surveillance on, and/or
recording the emissions of one's own or allied forces for the purposes of maintaining and improving
procedural standards and security, or for reference, as applicable. 2. The act of listening, carrying out
surveillance on, and/or recording of enemy emissions for intelligence purposes. 3. The act of detecting the
presence of radiation and the measurement thereof with radiation measuring instruments.
Radionavigation - 1. Radiolocation intended for the determination of position or direction or for obstruction
warning in navigation. 2. Radiodetermination used for the purposes of navigation, including obstruction
warning.
Radionavigation-Satellite Service - A radiodetermination-satellite service used for the purpose of
radionavigation. This service may also include feeder links necessary for its operation.
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![Radio Paging - The use of a pocket-size radio receiver capable of alerting its wearer that there is a phone call,
either from a displayed phone number or to a predesignated number. Note: Radio paging may be considered
a subset of paging. Synonym beeping.
Radio Regulations Board: A permanent organization of the International Telecommunication Union (ITU)
that implements frequency assignment policy and maintains the Master International Frequency Register
(MIFR). Note: Formerly International Frequency Registration Board (IFRB).
Radio Wave - An electromagnetic wave of a frequency arbitrarily lower than 3000 GHz. Synonym Hertzian
wave.
RAM - Acronym for random access memory. - A read /write, nonsequential-access memory used for the
storage of instructions and data. Note 1: RAM access time is essentially the same for all storage locations.
Note 2: RAM is characterized by a shorter access time than disk or tape storage. Note 3: RAM is usually
volatile.
Random Access Memory (RAM) - A read /write, nonsequential-access memory used for the storage of
instructions and data. Note 1: RAM access time is essentially the same for all storage locations. Note 2: RAM
is characterized by a shorter access time than disk or tape storage. Note 3: RAM is usually volatile.
Random Noise - Noise consisting of a large number of transient disturbances with a statistically random time
distribution. Note: Thermal noise is an example of random noise.
Raster - A predetermined pattern of scanning lines within a display space. Note: An example of a raster is the
pattern followed by an electron beam scanning the screen of a television camera or receiver.
Raster Graphics - Synonym [loosely] bitmapped graphics.
Ratio-Squared Combiner - A diversity combiner in which (a) the signals from each channel are added
together, (b) the gain of each channel is made proportional to the rms signal level and inversely proportional
to the mean square noise level in that channel, and (c) the same proportionality constant is used for all
channels. Synonym maximal-ratio combiner.
Ray - A geometric representation of a lightwave by a line normal to the electromagnetic wavefront; i.e., in
the direction of propagation of the wave.
Rayleigh Scattering - Of an electromagnetic wave propagating in a material medium, scattering caused by
refractive-index inhomogeneities that are small compared to the wavelength. Note 1: Rayleigh scattering
losses vary as the reciprocal of the fourth power of the wavelength. Note 2: Ionospheric scattering is caused
partly by Rayleigh scattering.
Ray Optics - Synonym geometric optics. The branch of optics that describes light propagation in terms of
rays. Note 1: Rays are bent at the interface between two dissimilar media, and may be curved in a medium in
which the refractive index is a function of position. Note 2: The ray in ray optics is perpendicular to the
wavefront in physical optics.
RBOC - Regional Bell Operating Company. In December 1983, a federal judge ordered AT&T to divide their 22
telephone companies into seven regional operating companies. The United States Department of Justice
placed several restrictions on the RBOCs: they were not allowed to provide long distance, equipment
manufacturing, or information services.
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![Read - [A] fundamental operation in an information system (IS) that results only in the flow of information
from an object to a subject.
Real Time Protocol (RTP) - Also known as Real Time Transport Protocol. Controls the transmission of packets
of data that demands low latency (such as audio and video). Supports real-time transmission over IP
networks and streaming as one means of delivery.
Received Noise Power - 1. The calculated or measured noise power, within the bandwidth being used, at the
receive end of a circuit, channel, link, or system. 2. The absolute power of the noise measured or calculated
at a receive point. Note: The related bandwidth and the noise weighting must also be specified. 3. The value
of noise power, from all sources, measured at the line terminals of telephone set's receiver. Note: Either flat
weighting or some other specific amplitude-frequency characteristic or noise weighting characteristic must
be associated with the measurement.
Receiver - The sink or terminator of any signal on a transmission medium.
Recipient - The switch or network to which a subscriber's directory number has been ported.
Recording Density - Synonym bit density.The number of bits recorded per unit length, area, or volume. Note:
Recording Density is the reciprocal of bit pitch.
Record Traffic - 1. Traffic that is recorded, in permanent or quasipermanent form, by the originator, the
addressee, or both. 2. Traffic that is permanently or semipermanently recorded in response to administrative
procedures or public law.
Recovery - In a database management system, the procedures and capabilities available for reconstruction
of the contents of a database to a state that prevailed before the detection of processing errors and before
the occurrence of a hardware or software failure that resulted in the destruction of some or all of the stored
data.
RED - Rural Economic Development. A program administered by TDS Telecom and other phone companies
which includes advocating for rural development funding at the Federal and State levels. This program is
designed to support local companies’ efforts with economic development projects in their communities.
Redundancy - 1. In the transmission of data, the excess of transmitted message symbols over that required
to convey the essential information in a noise-free circuit. Note: Redundancy may be introduced
intentionally (as in the case of error detection or correction codes) or inadvertently (such as by oversampling
a band-limited signal, inefficient formats, etc.). 2. In a communication system, surplus capability usually
provided to improve the reliability and quality of service.
Redundant Connectivity - A system of backup connections that ensures the network will continue
functioning even if a problem is encountered on one of the connections.
Reference Antenna - An antenna that may be real, virtual, or theoretical, and has a radiation pattern that
can be used as a basis of comparison with other antenna radiation patterns. Note: Examples of reference
antennas are unit dipoles, half-wave dipoles, and isotropic, i.e., omnidirectional antennas.
Reference Point - In ISDN, a logical point between two, nonoverlapping functional groups. Note: When
equipment is placed at a reference point, that reference point is designated an interface.
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![Rotary Hunting - Hunting in which all the numbers in the hunt group are selected in a prescribed order.
Note: In modern electronic switching systems, the numbers in the hunt group are not necessarily selected in
consecutive order.
Rotary Switching - In telephone systems, an electro-mechanical switching method whereby the selecting
mechanism consists of a rotating element using several groups of wipers, brushes, and contacts.
Rotational Position Sensing: [In magnetic media,] A technique used to locate a given sector, a desired track,
and a specific record by continuous comparison of the read / write head position with appropriate
synchronization signals.
Rounding - Deleting the least-significant digits of a number and applying some rule of correction to the part
retained.
Round-Trip Delay Time -1. The elapsed time for transit of a signal over a closed circuit. Note: Round-trip
delay time is significant in systems that require two-way interactive communication such as voice telephony
or ACK / NAK data systems where the round-trip time directly affects the throughput rate. It may range from
a very few microseconds for a short line-of-sight ( LOS ) radio system to many seconds for a multiple- link
circuit with one or more satellite links involved. This includes the node delays as well as the media transit
time. 2. In primary or secondary radar systems, the time required for a transmitted pulse to reach a target
and for the echo or transponder reply to return to the receiver.
Route - 1. In communications systems operations, the geographical path that is followed by a call or message
over the circuits that are used in establishing a chain of connections. 2. To determine the path that a
message or call is to take in a communications network. Note: In a Transmission Control Protocol / Internet
Protocol (TCP/IP) internet, each IP datagram is routed separately. The route a datagram follows may include
many gateways and many physical networks. 3. To construct the path that a call or message is to take in a
communications network in going from one station to another or from a source user end instrument to a
destination user end instrument.
Route Diversity - The allocation of circuits between two points over more than one geographic or physical
route with no geographic points in common.
Route Index - A pointer to a specific trunk group.
Route List - A specific list of trunk groups.
Route Matrix - In communications network operations, a record that indicates the interconnections between
pairs of nodes in the network, and is used to produce direct routes, alternate routes, and available route
tables from point to point.
Router - Highly sophisticated systems that connect local area networks (LANs). The router reads the network
layer address of all packets transmitted by a network, and forwards only those addressed to another
network.
Route Verification - Procedures that permit a signaling point to determine the accuracy and consistency of
its routing data by sending a test message and analyzing the response message to determine whether the
sent message traversed the expected route.
Routine - A computer program, called by another program, that may have some general or frequent use.
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![an inherent long-term instability. This instability relegates the rubidium standard to its status as a secondary
standard.
Run - The execution of one or more computer jobs or programs.
Run-Length Encoding - A redundancy -reduction technique for facsimile in which a run of consecutive picture
elements having the same state ( gray scale or color) is encoded into a single code word.
Rural Radio Service - A public radio service rendered by fixed stations on frequencies below 1000 MHz used
to provide (1) Basic Exchange Telecommunications Radio Service, which is public message communication
service between a central office and subscribers located in rural areas, (2) public message communication
service between landline central offices and different exchange areas which it is impracticable to
interconnect by any other means, or (3) private line telephone, telegraph, or facsimile service between two
or more points to which it is impracticable to extend service via landline.
Rural Subscriber Station -1. A fixed station in the rural radio service used by a subscriber for communication
within a central office station. 2. One or more fixed transmitters in the rural radiotelephone service that
receive service from central office transmitters.
RUS - Rural Utilities Service. The RUS is an agency of the United States Department of Agriculture. It’s a
source of financing and technical assistance for rural telecommunication systems.
RWI - Abbreviation for radio and wire integration.
RX - Abbreviation for receive, receiver.
RZ - Abbreviation for return-to-zero.
S
Safeguarding Statement - [A] statement affixed to a computer output or printout that states the highest
classification being processed at the time the product was produced and requires control of the product, at
that level, until determination of the true classification by an authorized person. Synonym [in INFOSEC]
banner.
Safety Service - Any radiocommunication service used permanently or temporarily for the safeguarding of
human life and property.
Sampled Data - Data in which the information content exists only for instantaneous values measured or
determined at or for discrete intervals. Note: Sampled data can be analog or digital.
Sampling - See signal sampling. The process of obtaining a sequence of instantaneous values of a particular
signal characteristic, usually at regular time intervals.
Sampling Frequency - See sampling rate. The number of samples taken per unit time, i.e., the rate at which
signals are sampled for subsequent use, such as for modulation, coding, and quantization.
Sampling Interval - The reciprocal of the sampling rate, i.e. , the interval between corresponding points on
two successive sampling pulses of the sampling signal.
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![Sampling Rate - The number of samples taken per unit time, i.e., the rate at which signals are sampled for
subsequent use, such as for modulation, coding, and quantization. Deprecated synonym sampling frequency.
Sampling Theorem - Synonym Nyquist's theorem. A theorem, developed by H. Nyquist, which states that an
analog signal waveform may be uniquely reconstructed, without error, from samples taken at equal time
intervals. The sampling rate must be equal to, or greater than, twice the highest frequency component in the
analog signal.
Sanitize - [In INFOSEC, the] process to remove information from media such that data recovery is not
possible. It includes removing all classified labels, markings, and activity logs.
Sanitizing - Of a recording medium, erasing or overwriting all data in such a manner that it cannot be
recovered, even by extraordinary, e.g., laboratory, means. Note: Sanitizing is distinguished from simply
"deleting" or "erasing" data. For example, a software-based deletion command may simply mark a file or
block of data to the effect that it may be overwritten during a subsequent "save" of different data. Until such
a save is performed, the deleted data may be recovered, sometimes by the simple expedient of executing a
software command. Likewise, digital data, for example, may be "erased," from a magnetic recording
medium, but still be recoverable if subjected to laboratory techniques that can identify residual magnetism
left after the erasure.
SAP - Abbreviation for service access point. - 1. A physical point at which a circuit may be accessed. 2. In an
Open Systems Interconnection (OSI) layer, a point at which a designated service may be obtained.
Satellite - A body which revolves around another body of preponderant mass and which has a motion
primarily and permanently determined by the force of attraction of that other body. Note: A parent body
and its satellite revolve about their common center of gravity.
Satellite Access - In satellite communications systems, the establishment of contact with a communications
satellite space station. Note: An example of satellite access is access at the moment at which an Earth station
commences to use a satellite space station as a signal repeater, i.e. , to use its transponder. Each radio
frequency (rf) carrier that is relayed by a satellite space station at any time occupies an access channel.
Accesses, i.e., channels, are distinguishable by various system parameters, such as frequency, time, or code.
Satellite Communications - A telecommunications service provided via one or more satellite relays and their
associated uplinks and downlinks.
Satellite Digital Audio Radio Service (SDARS) - 1. A satellite-based direct-broadcast radio service in which
digitally encoded audio entertainment material is broadcast to Earth-based receivers, either directly from an
orbiting satellite, or--in cases in which the receiver is in a shielded location--from the satellite to the receiver
via a repeater station. 2. A radiocommunication service in which audio programming is digitally transmitted
by one or more space stations directly to fixed, mobile, and/or portable stations, and which may involve
complementary repeating terrestrial transmitters, telemetry, tracking and control facilities. 3. A
radiocommunication service in which compact-disc quality programming is digitally transmitted by one or
more space stations.
Satellite Earth Terminal - Synonym Earth terminal. In a satellite link, one of the non-orbiting
communications stations that receives, processes, and transmits signals between itself and a satellite. Note:
Earth terminals may be at mobile, fixed, airborne, and waterborne Earth terminal complexes.
Satellite Emergency Position-Indicating Radiobeacon - An Earth station in the mobile-satellite service the
emissions of which are intended to facilitate search and rescue operations.
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![Secure Voice Cord Board - See SECORD. A desk-mounted patch panel that provides the capability for
controlling (a) sixteen 50-kb/s wideband or sixteen 2400-b/s narrowband user lines and (b) 5 narrowband
trunks to DSN or other narrowband facilities.
Security - 1. A condition that results from the establishment and maintenance of protective measures that
ensure a state of inviolability from hostile acts or influences. 2. With respect to classified matter, the
condition that prevents unauthorized persons from having access to official information that is safeguarded
in the interests of national security. 3. Measures taken by a military unit, an activity or installation to protect
itself against all acts designed to, or which may, impair its effectiveness.
Security Filter - 1. In communications security, the hardware, firmware, or software used to prevent access
to specified data by unauthorized persons or systems, such as by preventing transmission, preventing
forwarding messages over unprotected lines or circuits, or requiring special codes for access to read-only
files. 2. [An] AIS trusted subsystem that enforces security policy on the data that passes through it.
Security Kernel - 1. In computer and communications security, the central part of a computer or
communications system hardware, firmware, and software that implements the basic security procedures
for controlling access to system resources. 2. A self-contained usually small collection of key security-related
statements that (a) works as a part of an operating system to prevent unauthorized access to, or use of, the
system and (b) contains criteria that must be met before specified programs can be accessed. 3. Hardware,
firmware, and software elements of a trusted computing base that implement the reference monitor
concept.
Security Management - In network management, the set of functions (a) that protects telecommunications
networks and systems from unauthorized access by persons, acts, or influences and (b) that includes many
subfunctions, such as creating, deleting, and controlling security services and mechanisms; distributing
security-relevant information; reporting security-relevant events; controlling the distribution of
cryptographic keying material; and authorizing subscriber access, rights, and privileges.
Seek - To position selectively the access mechanism of a direct access [storage] device.
Seek Time - The time required for the access arm of a direct-access storage device to be positioned on the
appropriate track. Synonym positioning time.
Segment - In a distributed queue dual bus (DQDB) network, a protocol data unit (PDU) that (a) consists of 52
octets transferred between DQDB-layer peer entities as the information payload of a slot, (b) contains a
header of 4 octets and a payload of 48 octets, and (c) is either a pre-arbitrated segment or a queued
arbitrated segment.
Segmented Encoding Law - An encoding law in which an approximation to a curve defined by a smooth
encoding law is obtained by a number of linear segments. Synonym piecewise linear encoding law.
Segregation - In a communications system or network, the protection given to information to conceal it from
persons having access to the system or network.
Seizing - The temporary dedication of various parts of a communications system to a specific use, usually in
response to a user request for service. Note: The parts seized may be automatically connected, such as by
direct distance dialing (DDD), or may require operator intervention.
Seizure Signal - In telephone systems, a signal used by the calling end of a trunk or line to indicate a request
for service. Note: A seizure signal also locks out the trunk or line to other demands for service.
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![not objectionable, if the compression is limited to a few dB. Note 6: The original dynamic range of a
compressed signal may be restored by a circuit called an " expander." 2. In facsimile systems, a process in
which the number of pels scanned on the original is larger than the number of encoded bits of picture
information transmitted.
Signaling - 1. The use of signals for controlling communications. 2. In a telecommunications network, the
information exchange concerning the establishment and control of a connection and the management of the
network, in contrast to user information transfer. 3. The sending of a signal from the transmitting end of a
circuit to inform a user at the receiving end that a message is to be sent.
Signaling Message - 1. An assembly of signaling information pertaining to a call that includes, but is not
limited to, management transactions, that is transferred (between signaling points) as an entity. 2. An
assembly of signaling information that pertains to a call management transaction, and the like and that is
transferred as an entity.
Signals Intelligence (SIGINT) - 1. A category of intelligence comprising, either individually or in combination,
all communications intelligence, electronics intelligence, and foreign instrumentation signals intelligence,
however transmitted. [JP 1-02] 2. Intelligence derived from communications, electronics, and foreign
instrumentation signals.
SIGINT - Acronym for signals intelligence. 1. A category of intelligence comprising, either individually or in
combination, all communications intelligence, electronics intelligence, and foreign instrumentation signals
intelligence, however transmitted. 2. Intelligence derived from communications, electronics, and foreign
instrumentation signals.
Signal - 1. Detectable transmitted energy that can be used to carry information. 2. A time-dependent
variation of a characteristic of a physical phenomenon, used to convey information. 3. As applied to
electronics, any transmitted electrical impulse. 4. Operationally, a type of message, the text of which consists
of one or more letters, words, characters, signal flags, visual displays, or special sounds, with prearranged
meaning and which is conveyed or transmitted by visual, acoustical, or electrical means.
Signal Center - A combination of signal communication facilities operated by the Army in the field and
consisting of a communications center, telephone switching central and appropriate means of signal
communications.
Signal Compression - 1. In analog (usually audio) systems, reduction of the dynamic range of a signal by
controlling it as a function of the inverse relationship of its instantaneous value relative to a specified
reference level. Note 1: Signal compression is usually expressed in dB. Note 2: Instantaneous values of the
input signal that are low, relative to the reference level, are increased, and those that are high are
decreased. Note 3: Signal compression is usually accomplished by separate devices called "compressors." It is
used for many purposes, such as (a) improving signal-to-noise ratios prior to digitizing an analog signal for
transmission over a digital carrier system, (b) preventing overload of succeeding elements of a system, or (c)
matching the dynamic ranges of two devices. Note 4: Signal compression (in dB) may be a linear or nonlinear
function of the signal level across the frequency band of interest and may be essentially instantaneous or
have fixed or variable delay times. Note 5: Signal compression always introduces distortion, which is usually
not objectionable, if the compression is limited to a few dB. Note 6: The original dynamic range of a
compressed signal may be restored by a circuit called an "expander." 2. In facsimile systems, a process in
which the number of pels scanned on the original is larger than the number of encoded bits of picture
information transmitted.
Signal Contrast - In facsimile, the ratio of the level of the white signal to the level of the black signal. Note:
Signal contrast is usually expressed in dB.
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![The part of SS7 that provides additional functions to the MTP to cater to both connectionless as well as
connection-oriented network services and to achieve an OSI-compatible network service.
Signaling Data Link - A combination of two data channels operating together in a single signaling system.
Signaling Link - A transmission facility that consists of a signaling data link and its transfer control functions,
used for reliable transfer of a signaling message.
Signaling Message - 1. An assembly of signaling information pertaining to a call that includes, but is not
limited to, management transactions, that is transferred (between signaling points) as an entity. [T1.226-
1992] 2. An assembly of signaling information that pertains to a call management transaction, and the like
and that is transferred as an entity.
Signaling Path - In a transmission system, a path used for system control, synchronization, checking,
signaling, and service signals used in system management and operations rather than for the data, messages,
or calls of the users.
Signaling Rate - The aggregate rate at which data pass a point in the transmission path of a data transmission
system. Note 1: The DSR is usually expressed in bits per second. Note 3: For serial transmission in a single
channel, the DSR reduces to (1/T )log2n ; with a two-condition modulation, i.e. , n =2, the DSR is 1/T . Note 4:
For parallel transmission with equal unit intervals and equal numbers of significant conditions on each
channel, the DSR is (m /T )log2 n ; in the case of a two-condition modulation, this reduces to m /T . Note 5:
The DSR may be expressed in bauds, in which case, the factor log2ni in the above summation formula should
be deleted when calculating bauds. Note 6: In synchronous binary signaling, the DSR in bits per second may
be numerically the same as the modulation rate expressed in bauds. Signal processors, such as four-phase
modems, cannot change the DSR, but the modulation rate depends on the line modulation scheme, in
accordance with Note 4. For example, in a 2400 b/s 4-phase sending modem, the signaling rate is 2400 b/s
on the serial input side, but the modulation rate is only 1200 bauds on the 4-phase output side.
Signaling System No. 7 (SS7) - A common-channel signaling system defined by the CCITT in the 1988 Blue
Book, in Recommendations Q.771 through Q.774. Note: SS7 is a prerequisite for implementation of an
Integrated Services Digital Network (ISDN).
Signaling Time Slot - In TDM carrier systems, a time slot starting at a particular phase or instant in each
frame and allocated to the transmission of signaling (supervisory and control) data.
Signal Intelligence - 1. A category of intelligence comprising, either individually or in combination, all
communications intelligence, electronics intelligence, and foreign instrumentation signals intelligence,
however transmitted. 2. Intelligence derived from communications, electronics, and foreign instrumentation
signals.
Signal Level - In a communications system, the signal power or intensity at a specified point and with respect
to a specified reference level, e.g., 1 mW.
Signal Message - In communications systems, a message, i.e., an assembly of signaling information, that (a)
includes associated message alignment and service indications, (b) pertains to a call, and (c) is transferred via
the message transfer part.
Signal-Plus-Noise-Plus-Distortion to Noise-Plus-Distortion Ratio - See SINAD. - 1. The ratio of (a) total
received power, i.e., the received signal-plus-noise-plus-distortion power to (b) the received noise-plus-
distortion power. 2. The ratio of (a) the recovered audio power, i.e., the original modulating audio signal plus
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![procedure for up to seven more numbers. To call a speed-dial number wait for the dial tone and press the
one-digit code of the number you wish to call followed by #.
Spider - See bot, droid.
Splice - 1. To join, permanently, physical media that conduct or transmit power or a communication signal. 2.
A device that so joins conducting or transmitting media. 3. The completed joint.
Splice Organizer - In optical communication, a device that facilitates the splicing or breaking out of fiber optic
cables. Note: The organizer provides means to separate and secure individual buffer tubes, fibers, and/or
pigtails. It also provides means to secure mechanical splices or protective sleeves used in connection with
fusion splices, and has means to contain the slack fiber that remains after the splicing process is completed.
Splitter - See directional coupler, T-coupler, tee coupler. - A transmission coupling device for separately
sampling (through a known coupling loss) either the forward (incident) or the backward (reflected) wave in a
transmission line. Note: A directional coupler may be used to sample either a forward or backward wave in a
transmission line. A unidirectional coupler has available terminals or connections for sampling only one
direction of transmission; a bidirectional coupler has available terminals for sampling both directions.
Spontaneous Emission - Radiation emitted when the internal energy of a quantum mechanical system drops
from an excited level to a lower level without regard to the simultaneous presence of similar radiation. Note:
Examples of spontaneous emission include radiation from an LED, and radiation from an injection laser
below the lasing threshold.
Spoofing - 1. [The] interception, alteration, and retransmission of a cipher signal or data in such a way as to
mislead the recipient.2. [An] attempt to gain access to an AIS by posing as an authorized user. 3.
Unauthorized use of legitimate Identification and Authentication (I&A) data, however it was obtained, to
mimic a subject different from the attacker. Impersonating, masquerading, piggybacking, and mimicking are
forms of spoofing.
Spot Speed - In facsimile systems, the speed of the scanning or recording spot along the available line. Note:
The spot speed is usually measured on the object or on the recorded copy.
SS7 - Abbreviation for Signaling System No. 7. - A common-channel signaling system defined by the CCITT in
the 1988 Blue Book, in Recommendations Q.771 through Q.774. Note: SS7 is a prerequisite for
implementation of an Integrated Services Digital Network (ISDN).
SSL - The Secure Sockets Layer (SSL) is a common protocol for managing the security of data transmission
over the Internet. You can tell if a Web page is encrypted by looking for the "lock" graphic within your
browser window. Sites that need to transfer sensitive information such as passwords and credit card
information from the browser to the server must have SSL enabled. TDS uses SSL for your protection.
Standard - 1. Guideline documentation that reflects agreements on products, practices, or operations by
nationally or internationally recognized industrial, professional, trade associations or governmental bodies.
Note: This concept applies to formal, approved standards, as contrasted to de facto standards and
proprietary standards, which are exceptions to this concept. 2. An exact value, a physical entity, or an
abstract concept, established and defined by authority, custom, or common consent to serve as a reference,
model, or rule in measuring quantities or qualities, establishing practices or procedures, or evaluating
results. A fixed quantity or quality.
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![TCB - Abbreviation for trusted computing base. - [The] totality of protection mechanisms within a computer
system, including hardware, firmware, and software, the combination of which is responsible for enforcing a
security policy. Note: The ability of a trusted computing base to enforce correctly a unified security policy
depends on the correctness of the mechanisms within the trusted computing base, the protection of those
mechanisms to ensure their correctness, and the correct input of parameters related to the security policy.
TCF - Abbreviation for technical control facility. - A physical plant, or a designated and specially configured
part thereof, that (a) contains the equipment necessary for ensuring fast, reliable, and secure exchange of
information, (b) typically includes distribution frames and associated panels, jacks, and switches and
monitoring, test, conditioning, and orderwire equipment, and (c) allows telecommunications systems control
personnel to exercise operational control of communications paths and facilities, make quality analyses of
communications and communications channels, monitor operations and maintenance functions, recognize
and correct deteriorating conditions, restore disrupted communications, provide requested on-call circuits,
and take or direct such actions as may be required and practical to provide effective telecommunications
services.
T-Coupler - A passive optical coupler having three ports (three fibers). Note 1: Two isolated inputs may be
combined into one output; or one input, into two isolated outputs. Note 2: The amount of coupling loss,
usually expressed in dB, between ports is determined by the design and construction of the coupler. [After
FAA] Synonyms directional coupler, splitter, tee coupler.
TCP - Abbreviation for Transmission Control Protocol. In the Internet Protocol suite, a standard, connection-
oriented, full-duplex, host-to-host protocol used over packet-switched computer communications networks.
Note 1: TCP corresponds closely to the ISO Open Systems Interconnection--Reference Model (OSI--RM) Layer
4 (Transport Layer). Note 2: The OSI--RM uses TP-0 or TP-4 protocols for transmission control. See
Transmission Control Protocol/Internet Protocol
TCP/IP - Abbreviation for Transmission Control Protocol / Internet Protocol. Two interrelated protocols that
are part of the Internet protocol suite. Note 1: TCP operates on the OSI Transport Layer and breaks data into
packets. IP operates on the OSI Network Layer and routes packets. Note 2: TCP/IP was originally developed
by the U.S. Department of Defense.
TCP/IP Suite - The suite of interrelated protocols associated with Transmission Control Protocol / Internet
Protocol. Note 1: The TCP/IP Suite includes, but is not limited to, protocols such as TCP, IP, UDP, ICMP, FTP,
and SMTP. Note 2: Additional application and management protocols are sometimes considered part of the
TCP/IP Suite. This includes protocols such as SNMP.
TCS - Abbreviation for trusted computer system. 1. [An] information system (IS) employing sufficient
hardware and software assurance measures to allow simultaneous processing of a range of classified or
sensitive information. 2. A data processing system that provides sufficient computer security to allow for
concurrent access to data by users with different access rights and to data with different security
classification and security categories.
TCU - Abbreviation for teletypewriter control unit. - A device that controls and coordinates operations
between teletypewriters and message switching centers.
TDD - Abbreviation for Telecommunications Device for the Deaf. - A machine that uses typed input and
output, usually with a visual text display, to enable individuals with hearing or speech impairments to
communicate over a telecommunications network.
TDEA Decryption Operation - the transformation of a 64-bit block I into a 64-bit block O that is defined as
follows: O = DK1(EK2(DK3(I))). The standard specifies the following keying options for bundle (K1, K2, K3)
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![Tee Coupler - A passive coupler that has three ports. Synonyms directional coupler, splitter, T-coupler.
TEK - Abbreviation for traffic encryption key. - [A] key used to encrypt plain text or to superencrypt
previously encrypted text and/or to decrypt cipher text.
Teleaction Service - In Integrated Services Digital Network (ISDN) applications, a telecommunications service
that uses very short messages with very low data transmission rates between the user and the network.
Telecommand - The use of telecommunication for the transmission of signals to initiate, modify or terminate
functions of equipment at a distance.
Telecommunication - 1. Any transmission, emission, or reception of signs, signals, writing, images and
sounds or intelligence of any nature by wire, radio, optical or other electromagnetic systems. 2. Any
transmission, emission, or reception of signs, signals, writings, images, sounds, or information of any nature
by wire, radio, visual, or other electromagnetic systems.
Telecommunication Administration - An administration, or the part of a combined postal and
telecommunication administration, concerned with the provision of telecommunication service.
Telecommunication Architecture - See network architecture. - 1. The design principles, physical
configuration, functional organization, operational procedures, and data formats used as the bases for the
design, construction, modification, and operation of a communications network. 2. The structure of an
existing communications network, including the physical configuration, facilities, operational structure,
operational procedures, and the data formats in use.
Telecommunications - Telecommunications is any process that enables one or more users to pass to one or
more other users information of any nature delivered in any usable form, by wire, radio, visual, or
other electrical, electromagnetic, optical means. The word is derived from the Greek tele, "far off," and the
Latin communicare "to share."
Telecommunications Center - See communications center. - 1. An agency charged with the responsibility for
handling and controlling communications traffic. The center normally includes message center, transmitting,
and receiving facilities. 2. A facility that (a) serves as a node for a communications network, (b) is equipped
for technical control and maintenance of the circuits originating, transiting, or terminating at the node, (c)
may contain message-center facilities, and (d) may serve as a gateway.
Telecommunications Closet - In a premises distribution system, a telecommunications closet is an area for
connecting the horizontal and backbone wiring and for containing active or passive PDS equipment.
Telecommunications Device for the Deaf (TDD) - A machine that uses typed input and output, usually with a
visual text display, to enable individuals with hearing or speech impairments to communicate over a
telecommunications network.
Telecommunication Sector - The sector that includes the telecommunications service providers, network
operators, regulators, manufacturers, subscribers, and users.
Telecommunications Facilities - The aggregate of equipment, such as radios, telephones, teletypewriters,
facsimile equipment, data equipment, cables, and switches, used for providing telecommunications services.
Telecommunications Infrastructure - The organizations, personnel, procedures, facilities, and networks
employed to transmit and receive information by electrical or electronic means. Note 1: Telecommunications
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![facilities include, but are not necessarily limited to, terrestrial radio, metallic and optical fiber cables, artificial
Earth satellite communications, radio and television stations (traditional broadcast as well as cable and
satellite broadcast), public switched telephone network (s), etc. Note 2: Examples of advanced
telecommunications infrastructure facilities are direct broadcast satellite (DBS), digital audio broadcasting
(DAB), Advanced Digital Television, and the Global Positioning System (GPS), which is used extensively for
precise navigation and timing.
Telecommunications Link - A communications facility or channel, including feeder and local distribution
plant, having a termination in a center in the telecommunications network. Examples of such a link include
(but are not necessarily restricted to): optical-fiber cable, coaxial cable, metallic cables, transmitting and
receiving antenna.
Telecommunications Load Equipment - Equipment powered from a primary or secondary distribution of a
centralized dc power system owned or operated by exchange and interexchange carriers.
Telecommunications Management Network (TMN) - A network that interfaces with a telecommunications
network at several points in order to receive information from, and to control the operation of, the
telecommunications network. Note: A TMN may use parts of the managed telecommunications network to
provide for the TMN communications.
Telecommunications Network - A telecommunications network is a system of interconnected facilities
designed to carry traffic from a variety of telecommunications services. The network has two different but
related aspects. In terms of its physical components, it is a facilities network. In terms of the variety of
telecommunications services that it provides, it can support a set of many traffic networks, each
representing a particular interconnection of facilities.
Telecommunications Relay Center Fee/Charge/Surcharge - This state fee helps pay for the relay center that
transmits and translates calls for people who are deaf, hard-of-hearing or speech disabled. Mandated
nationally by Congress with the passage of the Americans with Disabilities Act, it may also be called
“Telecommunication Devices for the Deaf Tax.”
Telecommunications Security - See communications security. Measures and controls taken to deny
unauthorized persons information derived from telecommunications and to ensure the authenticity of such
telecommunications. Note: Communications security includes cryptosecurity, transmission security, emission
security, and physical security of COMSEC material. [INFOSEC]
• (a) cryptosecurity: [The] component of communications security that results from the provision of
technically sound cryptosystems and their proper use. [NIS]
• (b) emission security: Protection resulting from all measures taken to deny unauthorized persons
information of value which might be derived from intercept and analysis of compromising
emanations from crypto-equipment, AIS, and telecommunications systems. [NIS]
• (c) physical security: The component of communications security that results from all physical
measures necessary to safeguard classified equipment, material, and documents from access
thereto or observation thereof by unauthorized persons. [JP 1-02]
• (d) transmission security: [The] component of communications security that results from the
application of measures designed to protect transmissions from interception and exploitation by
means other than cryptanalysis.
Telecommunications Service - 1. Any service provided by a telecommunication provider. 2. A specified set of
user-information transfer capabilities provided to a group of users by a telecommunications system. Note:
The telecommunications service user is responsible for the information content of the message. The
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![telecommunications service provider has the responsibility for the acceptance, transmission, and delivery of
the message.
Telecommunications Service Priority (TSP) Service - A regulated service provided by a telecommunications
provider, such as an operating telephone company or a carrier, for NS/EP telecommunications. Note: The
TSP service replaced Restoration Priority (RP) service effective September 1990.
Telecommunications Service Priority (TSP) System - A system that provides a means for telecommunications
users to obtain priority treatment from service providers for the NS/EP telecommunications requirements.
Note: The TSP system replaced the Restoration Priority (RP) system effective September 1990.
Telecommunications Service Priority (TSP) System User - Any individual, organization, or activity that
interacts with the NS/EP TSP System.
Telecommunications System - See communications system. A collection of individual communications
networks, transmission systems, relay stations, tributary stations, and data terminal equipment (DTE) usually
capable of interconnection and interoperation to form an integrated whole. Note: The components of a
communications system serve a common purpose, are technically compatible, use common procedures,
respond to controls, and operate in unison.
Telecommunications System Operator - The organization responsible for providing telecommunications
services to users.
Teleconference - The live exchange of information among persons and machines remote from one another
but linked by a telecommunications system. Note: The telecommunications system may support the
teleconference by providing audio, video, and data services by one or more means, such as telephone,
telegraph, teletype, radio, and television.
Telegram - Written matter intended to be transmitted by telegraphy for delivery to the addressee. This term
also includes radiotelegrams unless otherwise specified. In this definition the term telegraphy has the same
general meaning as defined in the [1979 General Worldwide Administrative Radio Conference] Convention.
Telegraph - See telegraphy. A form of telecommunication which is concerned in any process providing
transmission and reproduction at a distance of documentary matter, such as written or printed matter or
fixed images, or the reproduction at a distance of any kind of information in such a form. For the purposes of
the Radio Regulations, unless otherwise specified therein, telegraphy shall mean a form of
telecommunication for the transmission of written matter by the use of a signal code.
Telegraphy - A form of telecommunication which is concerned in any process providing transmission and
reproduction at a distance of documentary matter, such as written or printed matter or fixed images, or the
reproduction at a distance of any kind of information in such a form. For the purposes of the Radio
Regulations, unless otherwise specified therein, telegraphy shall mean a form of telecommunication for the
transmission of written matter by the use of a signal code.
Telemeter - A measuring, transmitting, and receiving device used in telemetry. Any scientific instrument for
observing events at a distance and transmitting the information back to the observer.
Telemetered, Telemetering, Telemeters - To measure, transmit, and receive (data) automatically from a
distant source, as from a spacecraft or an electric power grid.
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![Telephoto - 1. Of or relating to a photographic lens or lens system used to produce a large image of a distant
object. 2. Of or relating to an instrument that electrically transmits photographs. 3. Pertaining to pictures
transmitted via a telecommunications system.
Telephotograph - 1. A telephoto. 2. A photograph transmitted and reproduced over a distance.
Telephotography - 1. The process or technique of photographing distant objects, using a telephoto lens on a
camera. 2. The technique or process of transmitting charts, pictures, and photographs over a distance.
Teleprinter - A typewriter-like terminal with a keyboard and built-in printer. It can be a desktop or portable
unit. Teleprinters were quite common years ago as input terminals for computers, but have given way to the
video screen. Teleprinter-like devices are still used in retail applications where receipts are necessary.
Teleprinters were widely used starting with the very first computers. They lived well into the 1970s as a
computer input device. Any keyboard and printing unit can be called a teleprinter.
Paper tape was widely used on teleprinters to record incoming data. The reel of tape in this picture is on the
lower left side of the unit. (Image courtesy of General Electric Company.)
A teletypewriter that can only receive data and does not have a keyboard for transmission.
Teleprocessing - The combining of telecommunications and computer operations interacting in the
automatic processing, reception, and transmission of data and/or information. [JP 1-02] Note:
Teleprocessing includes human-machine interface equipment.
Teleran - An air-traffic control system in which the image of a ground-based radar unit is televised to aircraft
in the vicinity so that pilots may see their positions in relation to other aircraft.
Teletext - An electronic communications system in which printed information is broadcast by television
signal to sets equipped with decoders. An international store-and-forward essentially error-free
communications service that is defined by the CCITT (now the ITU-T), has a data signaling rate (DSR) of 2400
b/s over switched telephone networks, and has a communications protocol that supports the CCITT Group 4
facsimile service.
Teletraining - Training that (a) in which usually live instruction is conveyed in real time via
telecommunications facilities, (b) that may be accomplished on a point-to-point basis or on a point-to-
multipoint basis, and (c) may assume many forms, such as a teleseminar, a teleconference, or an electronic
classroom, usually including both audio and video. Synonyms distance learning, distance training, electronic
classroom, virtual instruction.
Teletype - A trademark used for a teletypewriter.
Teletypewriter (TTY) - A printing telegraph instrument that has a signal-actuated mechanism for
automatically printing received messages. An electromechanical typewriter that either transmits or receives
messages coded in electrical signals carried by telegraph or telephone wires. Note 1: A TTY may have a
keyboard similar to that of a typewriter for sending messages. Note 2: Radio circuits carrying TTY traffic are
called "RTTY circuits" or "RATT circuits."
Teletypewriter Control Unit (TCU) - A device that controls and coordinates operations between
teletypewriters and message switching centers.
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![Teletypewriter Exchange Service (TWX) - A switched teletypewriter service in which suitably arranged
teletypewriter stations are provided with lines to a central office for access to other such stations.
Teletypewriter Signal Distortion - The shifting of signal pulse transitions from their proper positions relative
to the beginning of the start pulse. Note: The magnitude of the distortion is expressed in percent of a perfect
unit pulse length. Synonym start-stop TTY distortion.
Television (TV) - A form of telecommunication for the transmission of transient images of fixed or moving
objects.Note 1: The picture signal is usually accompanied by the sound signal. Note 2: In North America, TV
signals are generated, transmitted, received, and displayed in accordance with the NTSC standard.
Telex - 1. A communications system consisting of teletypewriters connected to a telephonic network
(automatic exchanges) to send and receive signals. 2. A message sent or received by such a system.
(TELetypewriter EXchange) An international, dial-up data communications service administered in the U.S. by
AT&T, MCI and other providers. Developed in the U.S. and other European countries in the 1930s, it was the
first data communications service that used typewriter-like terminals (teletypewriters). Prior to Telex,
telegrams and cablegrams were the primary method for delivering a text message. By the 1960s, Telex
became a worldwide, realtime, data communications service. Although diminishing each year, Telex is still
used for commerce in more than 200 countries.
Telex started out transmitting Baudot code at 50 bps. Although upgraded, it is still a low-speed data service.
It was originally administered worldwide by various carriers and the local PTTs. Western Union handled the
U.S., and in 1971, purchased and integrated the Bell System's TWX service. AT&T acquired Western Union's
Telex service in 1991.
Telex Machine - A character printer connected to a telegraph that operates like a typewriter
Telnet - A program that allows Internet users to login to computers other than their host. Telnet also refers
to the act of doing so. The TCP/IP standard network virtual terminal protocol that is used for remote terminal
connection service and that allows a user at one site to interact with systems at other sites as if that user
terminal were directly connected to computers at those sites.
TEM - Abbreviation for transverse electric and magnetic mode. - A mode whose electric and magnetic field
vectors are both normal to the direction of propagation. Note: The TEM mode is the most useful mode in a
coaxial cable.
TEMPEST - 1. [A] Short name referring to investigation, study, and control of compromising emanations from
information systems (IS) equipment. 2. To shield against compromising emanations.
Temporal Application - A video application requiring high temporal resolution, i.e., reduced jerkiness,
possibly at the expense of reduced spatial resolution. Note: An example of temporal applications is the
ability to accurately discern moving image features such as facial expressions and lip movements.
Temporal Edge Noise - In a video display, that form of edge busyness that is characterized by time-varying
sharpness at the edges of objects.
Terminal - A device capable of sending, receiving, or sending and receiving information over a
communications channel.
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![Terminal Type - The variety of terminal or the originator (e.g., dual-tone multifrequency (DTMF) phone, ISDN
terminal).
Terminating Endpoint - In a wideband packet node, the part of the node that receives packetized traffic,
depacketizes it, and then plays it back as channelized traffic.
Terminating Network Function - Of a UPT call, any network function associated with the termination of the
call to the destination terminal.
Termination - 1. The load connected to a transmission line, circuit, or device. Note: For a uniform
transmission line, if the termination impedance is equal to the characteristic impedance of the line, wave
reflections from the end of the line will be avoided. 2. In hollow metallic waveguides, the point at which
energy propagating in the waveguide continues in a nonwaveguide propagation mode into a load. 3. An
impedance, often resistive, that is connected to a transmission line or piece of equipment as a dummy load,
for test purposes.
Terminus - A device used to terminate, position, and hold an optical fiber within a connector.
Ternary Signal - A signal that can assume, at any given instant, one of three significant conditions, such as
power level, phase position, pulse duration, or frequency. Note: Examples of ternary signals are (a) a pulse
that can have a positive, zero, or negative voltage value at any given instant, (b) a sine wave that can assume
phases of 0°, 120°, or 240° relative to a clock pulse, and (c) a carrier wave that can assume any one of three
different frequencies depending on three different modulation signal significant conditions.
Terrestrial Broadcasting - A broadcast signal transmitted over-the-air to an antenna.
Terrestrial Microwave Radio - Terrestrial microwave radio is a transmission systems consisting of at least
two radio transmitter/receivers (transceivers) connected to high gain antennas (directional antennas
which concentrate electromagnetic or radiowave energy in narrow beams) focused in pairs on each other.
The operation is point-to-point, that is, communications are established between two and only two
antennas (installations) with line-of-sight visibility. This can be contrasted to point-to- multipoint systems like
broadcast radio or television.
Terrestrial Radiocommunication - Any radiocommunication other than space radiocommunication or radio
astronomy.
Terrestrial Station - A station effecting terrestrial radiocommunication. In these [Radio] Regulations, unless
otherwise stated, any station is a terrestrial station.
Test and Validation - Physical measurements taken (a) to verify conclusions obtained from mathematical
modeling and analysis or (b) for the purpose of developing mathematical models.
Test Antenna - An antenna of known performance characteristics used in determining transmission
characteristics of equipment and associated propagation paths.
Test Key - Key intended for testing of COMSEC equipment or systems.
Test Point - A point within a piece of equipment or an equipment string that provides access to signals for
the purpose of fault isolation.
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![Test Tone - A tone sent at a predetermined level and frequency through a transmission system for test
purposes, such as for facilitating measurements and for aligning gains and losses in the system.
Text Format vs. HTML Format - Some Web applications, such as e-mail or Web pages, can either be viewed
in Text or HTML formats. Text formats generally display only the words (text) in an e-mail or on a Web page
and not graphics, such as artwork or photos. HTML format allows display of both text and graphics.
TGM - Abbreviation for trunk group multiplexer.
THD - Abbreviation for total harmonic distortion. - Of a signal, the ratio of (a) the sum of the powers of all
harmonic frequencies above the fundamental frequency to (b) the power of the fundamental frequency.
Note 1: The THD is usually expressed in dB. Note 2: Measurements for calculating the THD are made at the
output of a device under specified conditions.
Thermal Noise: The noise generated by thermal agitation of electrons in a conductor. The noise power, P, in
watts, is given by P = kT f, where k is Boltzmann's constant in joules per kelvin, T is the conductor
temperature in kelvins, and f is the bandwidth in hertz. Note 1: Thermal noise power, per hertz, is equal
throughout the frequency spectrum, depending only on k and T. Note 2: For the general case, the above
definition may be held to apply to charge carriers in any type of conducting medium. Synonym Johnson
noise.
Thermal Radiation - 1. Electromagnetic radiations emitted from a heat or light source as a consequence of
its temperature; it consists essentially of ultraviolet, visible, and infrared radiations. [JP1] 2. The heat and
light produced by a nuclear explosion.
Thermodynamic Temperature - A measure, in kelvins (K), proportional to the thermal energy of a given body
at equilibrium. Note 1: A temperature of 0 K is called "absolute zero," and coincides with the minimum
molecular activity (i.e., thermal energy) of matter. Note 2: Thermodynamic temperature was formerly called
"absolute temperature." Note 3: In practice, the International Temperature Scale of 1990 (ITS-90) serves as
the basis for high-accuracy temperature measurements in science and technology.
The Stick - Business quality Single Line Automatic Call Processor. Line sharing device for small or home
business as well large corporations and organizations. Automatically routes calls to the assigned device. The
Stick allows up to three telecommunication devices plus an answering machine to share one single phone
line. This is our most popular fax switch. For more information: The Stick brochure , The Stick online manual.
THF - Abbreviation for tremendously high frequency. See electromagnetic spectrum.
Thin Client (computing) - A server-centric computing model in which the application software, data, and CPU
power resides on a network server rather than on the client computer (s). Note 1: This computing philosophy
allows administrators to purchase one relatively powerful and expensive server and be confident that any
external terminal, regardless of its power or sophistication, can run applications on the server. Most
"shopping" Web pages, for example, are thin-client applications (i.e., the client needs nothing more than a
browser and a connection to the network to be able to search the "shopping" page and to order products).
Local area networks can use thin-client modeling to install only one copy of necessary programs onto the
main server for many clients on the network to use. Note 2: Server software is required to interface clients
with the software on the server. Synonyms Internet appliance (computing), Internet box (computing),
network computer.
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![Thin-Client Software - Computer programs that reside on a server and react to external requests from a
client. Note: This is in contrast to software that is installed on each client computer in a network. Software
that resides only on a single server can be maintained and updated with minimal effort.
Thin-Film Laser - A laser that is constructed by thin-film deposition techniques on a substrate for use as a
light source, is usually used to drive thin-film optical waveguides, and may be used in integrated optical
circuits.
Thin-Film Optical Modulator - A modulator that consists of multilayered films of material of different optical
characteristics, is capable of modulating transmitted light by using electro-optic, electro-acoustic, or
magneto-optic effects to obtain signal modulation, and may be used as a component in integrated optical
circuits.
Thin-Film Optical Multiplexer - A multiplexer that consists of multilayered films of material of different
optical characteristics, is capable of multiplexing transmitted light by using electro-optic, electro-acoustic, or
magneto-optic effects to obtain signal multiplexing, and may be used as a component in integrated optical
circuits.
Thin-Film Optical Switch - A switch that consists of multilayered films of material of different optical
characteristics, that is capable of switching transmitted light by using electro-optic, electro-acoustic, or
magneto-optic effects to obtain signal switching, and is usually used as a component in integrated optical
circuits. Note: Thin-film optical switches may support only one propagation mode.
Thin-Film Optical Waveguide - A slab-dielectric waveguide that consists of multilayered films of material of
different optical characteristics, is capable of guiding an optical signal, and may be used as a component in
integrated optical circuits.
Third-Order Intercept Point - A point (a) that is an extrapolated convergence--not directly measurable--of
intermodulation distortion products in the desired output and (b) that indicates how well a receiver
performs in the presence of strong nearby signals. Note: Determination of a third-order intercept point is
accomplished by using two test frequencies that fall within the first intermediate frequency mixer passband.
Usually, the test frequencies are about 20 to 30 kHz apart.
Third Window - Of silica-based optical fibers, the transmission window at approximately 1.55 m. Note: The
third window is the minimum-loss window in silica-based fibers.
Thread - In computer conferencing, a set of sequential messages containing closely related information.
Threat - 1. Capabilities, intentions, and attack methods of adversaries to exploit, or any circumstance or
event with the potential to cause harm to, information or an information system. [NIS] 2. Any circumstance
or event with the potential to harm an information system (IS) through unauthorized access, destruction,
disclosure, modification of data, and/or denial of service.
Threat Analysis - Examination of information to identify the elements comprising a threat.
Threat Assessment - [A] formal description and evaluation of threat to an information system (IS).
Three-Way Calling - A switching system service feature that permits users to add a third party to an
established connection at a different number during a call, without the assistance of an attendant or
operator.
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![Ticket-Oriented - [In security, a] computer protection system in which each subject maintains a list of
unforgeable bit patterns called tickets, one for each object a subject is authorized to access.
TIE - Acronym for time interval error. - 1. The time difference between a real clock and an ideal uniform time
scale, after a time interval following perfect synchronization between the clock and the scale. 2. The
variation in time delay of a given timing signal with respect to an ideal timing signal over a particular time
period.
Tie Trunk - A telephone line that directly connects two private branch exchanges (PBXs).
TIFF (Tag Image File Format) - A common format for exchanging raster graphics (bitmap) images between
application programs, including those used for scanner images. A TIFF file can be identified as a file with a
".tiff" or ".tif" file name suffix. The TIFF format was developed in 1986 by an industry committee chaired by
the Aldus Corporation (now part of Adobe Software). Microsoft and Hewlett-Packard were among the
contributors to the format. One of the most common graphic image formats, TIFF files are commonly used in
desktop publishing, faxing, 3-D applications, and medical imaging applications.
TIFF files can be in any of several classes, including gray scale, color palette, or RGB full color, and can include
files with JPEG, LZW, or CCITT Group 4 standard run-length image compression.
Time - 1. An epoch, i.e., the designation of an instant on a selected time scale, astronomical or atomic. It is
used in the sense of time of day [JP1] 2. On a time scale, the interval between two events, or the duration of
an event. 3. An apparently irreversible continuum of ordered events. 4. That which characterizes, or is
characterized by, the observed and apparently irreversible continuum of ordered events.
Time Ambiguity - A situation in which more than one different time or time measurement can be obtained
under the stated conditions.
Time-Assignment Speech Interpolation (TASI) - An analog technique used on certain long transmission links
to increase voice-transmission capacity. Note: TASI works by switching additional users onto any channel
temporarily idled because an original user has stopped speaking. When the original user resumes speaking,
that user will, in turn, be switched to any channel that happens to be idle.
Time Block - An arbitrary grouping of several consecutive hours of a day, usually for a particular season,
during which it is assumed that propagation data are statistically homogeneous.
Time Bomb - 1. In COMSEC, a logic bomb to be activated at a predetermined time. 2. [A] resident computer
program that triggers an unauthorized act at a predefined time.
Time Code - A code used for the transmission and identification of time signals. Note: In telecommunications
systems, the format of the time code must be specified.
Time Code Ambiguity - The shortest interval between successive repetitions of the same time code value.
Note: For example, in a time code in which year-of-century is the most slowly changing field, the time code
ambiguity would be 100 years; for a digital clock in which hours and minutes up to a maximum of 11:59 are
displayed, the time code ambiguity would be 12 hours.
Time Code Resolution - The interval between two successive time code states. Note: Time code resolution is
determined by the most rapidly changing symbol position within the time code. For example, for a digital
clock that displays hours and minutes, the time code resolution would be 1 minute.
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![Time Marker - A reference signal, often repeated periodically, enabling the correlation of specific events
with a time scale, such as for establishing synchronization.
Time of Occurrence - The date of an event, i.e., the instant an event occurs, with reference to a specified
time scale.
Time-Out - 1. A network parameter related to an enforced event designed to occur at the conclusion of a
predetermined elapsed time. 2. A specified period of time that will be allowed to elapse in a system before a
specified event is to take place, unless another specified event occurs first; in either case, the period is
terminated when either event takes place. Note: A time-out condition can be canceled by the receipt of an
appropriate time-out cancellation signal. 3. An event that occurs at the end of a predetermined period of
time that began at the occurrence of another specified event. The time-out can be prevented by an
appropriate signal.
Time Scale - 1. A time measuring system defined to relate the passage of temporal events since a selected
epoch. Note: The internationally recognized time interval is the second. Time scales are graduated in
intervals such as seconds, minutes, hours, days, and years, and in fractions of a second, such as milliseconds,
nanoseconds, and picoseconds. 2. Time coordinates placed on the abscissa (x-axis) of Cartesian-coordinate
graphs used for depicting waveforms and similar phenomena.
Time Scale Factor - A multiplier used to transform the real time of occurrence of an event or a problem into
system time, such as that of a telecommunications system or a computer.
Time Server - The server maintaining and distributing the correct date and time over a computer network.
Note: There is usually a special time-distribution protocol.
Time-Sharing - 1. The interleaving of two or more independent processes on one functional unit. 2.
Pertaining to the interleaved use of computer time that enables two or more users to execute programs
concurrently.
Time Slot - 1. Period of time during which certain activities are governed by specific regulations. [JP1] 2. A
time interval that can be recognized and uniquely defined.
Time Stamp (TS) - 1. A data field in which is recorded (typically with a resolution of 1 millisecond) the
cumulative variable queuing delay experienced by a packet in traversing the network. [After T1.509-1995] 2.
With respect to a recorded network event, a data field in which is recorded the time (time of day or other
instant of elapsed time) at which the event took place.
Time Standard - A stable device that emits signals at equal intervals such that their count may be used as a
clock.
Time Tick - A time mark output of a clock system.
Time-Variant Value - In cryptography, a value that changes with each transaction or with each message
value.
Timing Jitter - The short-term variations of the significant instants of a digital signal from their ideal positions
in time. Here short term implies phase oscillations of frequency greater than or equal to 10 Hz. Timing jitter
may lead to crosstalk and/or distortion of the original analog signal and is a potential source of slips at the
input ports of digital switches. It may also cause slips and resultant errors in asynchronous digital
multiplexes.
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![Tolerance - The permissible range of variation of some characteristic from its nominal value.
Tolerance Field - 1. The region between two curves, such as circles or rectangles, used to specify the
tolerance on component size and geometry. 2. Pertaining to the cross section of an optical fiber, when used
to specify the respective diameters and ovalities of, and concentricity error between, the core and cladding;
two concentric annular regions which define the core-cladding boundary and the cladding outer boundary.
Note: Dimensions are usually expressed in micrometers ( m). The larger annular region is defined by
concentric circles of diameter [D C+ D C] and [D C- D C], where D C is the nominal diameter of the cladding
and D C is the cladding diameter tolerance. The smaller annular region is defined by concentric circles of
diameter [D c+ D c] and [D c- D c], where D c is the nominal diameter of the core and D c is the core
diameter tolerance. When the core and cladding boundaries of the cross section of the fiber in question fall
entirely within their respective defined areas, the fiber meets the specification. 3. Of the cross section of a
given optical fiber, when used to characterize the respective diameters and ovalities of the core and
cladding, and the concentricity error between the core and cladding; two such pairs of concentric circles, the
concentric pairs not necessarily being concentric with one another. Note 1: One pair of concentric circles
characterizes the core, and the other pair, the cladding. The cladding ovality is characterized by the smallest
circle that circumscribes its cross section, and the largest circle that fits within its cross section. (The cross
section is assumed, to a first approximation, to be elliptical in shape, so these defining circles will be
concentric.) The core cross section is characterized by an analogous pair of circles, also concentric with one
another, but not necessarily with those defining the cladding cross section. Note 2: The distance between the
centers of the two concentric pairs (core pair and cladding pair) defines the offset between the core and
cladding (the " core-cladding offset," also called the "concentricity error"). The width of the annulus defined
by the cladding circles determines the ovality of the cladding, and the width of the annulus defined by the
core determines the ovality of the core.
Toll Call - See long-distance call.
Toll Center - An office (or group of offices) within a city which generally handles the originating and incoming
toll traffic for that city to or from other toll center areas and which handles through switched traffic. The toll
center normally handles the inward toll traffic for its tributary exchanges and, in general, either handles the
outward traffic originating at its tributaries or serves as the outlet to interexchange circuits for outward
traffic ticketed and timed at its tributaries. Toll centers are listed as such in the Toll Rate and Route Guide.
Toll Center Area - The areas served by a toll center, including the toll center city and the communities served
by tributaries of the toll center.
Toll Center Toll Office - A toll office (as contrasted to a local office) in a toll center city.
toll circuit - A general term applied to interexchange trunks used primarily for toll traffic.
Toll Connecting Trunk - A general classification of trunks carrying toll traffic and ordinarily extending
between a local office and a toll office, except trunks classified as tributary circuits. Examples of toll
connecting trunks include toll switching trunks, recording trunks, and recording-completing trunks.
toll diversion - A system service feature by which users are denied the ability to place toll calls without the
assistance of an attendant.
Toll Office - A central office used primarily for supervising and switching toll traffic.
Toll Quality - The voice quality resulting from the use of a nominal 4-kHz telephone channel. Note: Toll
quality may be quantized in terms of a specified bit error ratio.
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![Tracking Mode - An operational mode during which a system is operating within specified movement limits
relative to a reference.
Tracking Phase - See tracking mode.
Traffic - 1. The information moved over a communication channel. 2. A quantitative measurement of the
total messages and their length, expressed in CCS or other units, during a specified period of time.
Traffic Analysis - 1. In a communications system, the analysis of traffic rates, volumes, densities, capacities,
and patterns specifically for system performance improvement. 2. [The] study of communications
characteristics external to the text. 3. The analysis of the communications-electronic environment for use in
the design, development, and operation of new communications systems. 4. In cryptology, the inference of
information from observation and analysis of the presence, absence, amount, direction, and frequency of
the traffic flow. 5. [The] Study of communications patterns.
Traffic Capacity - The maximum traffic per unit of time that a given telecommunications system, subsystem,
or device can carry under specified conditions.
Traffic Encryption Key (TEK) - [A] key used to encrypt plain text or to superencrypt previously encrypted text
and/or to decrypt cipher text.
Traffic Engineering - The determination of the numbers and kinds of circuits and quantities of related
terminating and switching equipment required to meet anticipated traffic loads throughout a
communications system.
Traffic-Flow Security - 1. The protection resulting from features, inherent in some crypto-equipment, that
conceal the presence of valid messages on a communications circuit; normally achieved by causing the circuit
to appear busy at all times. 2. Measures used to conceal the presence of valid messages in an on-line
cryptosystem or secure communications system. Note: Encryption of sending and receiving addresses and
causing the circuit to appear busy at all times by sending dummy traffic are two methods of traffic-flow
security. A more common method is to send a continuous encrypted signal, whether or not traffic is being
transmitted.
Traffic Intensity - A measure of the average occupancy of a facility during a specified period of time,
normally a busy hour, measured in traffic units (erlangs) and defined as the ratio of the time during which a
facility is occupied (continuously or cumulatively) to the time this facility is available for occupancy. Note: A
traffic intensity of one traffic unit (one erlang) means continuous occupancy of a facility during the time
period under consideration, regardless of whether or not information is transmitted. Synonym call intensity.
Traffic Load - The total traffic carried by a trunk or trunk group during a specified time interval.
Traffic Monitor - In a communications network, a service feature that provides basic data on the amount and
type of traffic handled by the network.
Traffic Over First Routes - A term applied to the routing of traffic and denoting routing via principal route for
traffic between any two points as distinguished from alternate routes for such traffic.
Traffic Overflow - 1. That condition wherein the traffic offered to a portion of a communication system
exceeds its capacity and the excess may be blocked or may be provided with alternate routing. 2. The excess
traffic itself.
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![Traffic Padding - 1. In COMSEC, a countermeasure that generates spurious data in transmission media to
make traffic analysis or decryption more difficult. 2. In reliability techniques, see pilot-make-busy circuit. 3.
Generation of spurious communications or data units to disguise the amount of real data units being sent.
Traffic Register - See register.
Traffic Service Position System (TSPS) - A stored program electronic system associated with one or more toll
switching systems which provides centralized traffic service position functions for several local offices at one
location.
Traffic Unit - Synonym erlang.
Traffic Usage Recorder - A device for measuring and recording the amount of telephone traffic carried by a
group, or several groups, of switches or trunks.
Trailer - Protocol control information located at the end of a protocol data unit (PDU).
Tranquility - [The] property whereby the security level of an object cannot change while the object is being
processed by an information system (IS).
Transaction Capabilities (TC) - 1. A means based upon the OSI –Reference Model to support applications in
telecommunications networks. 2. Protocol functions and procedures that control non-circuit related
information exchange among signaling points in SS7 networks. It provides a general purpose approach to the
introduction of new services within a network as well as a framework for service architecture for providing
internetwork services. Transaction capabilities includes the application layer protocol called transaction
capabilities application part (TCAP) as well as the supporting Presentation, Session, and Transport layers
called the application service part (ASP).
Transaction Integrity - The degree to which a transaction flowing through a network reaches its intended
destination without impairment of its function, content or meaning.
Transaction-Oriented Application - Applications that exchange messages that are time-critical, bursty, and
often limited in length, to perform an indivisible or elemental unit of work for OAM&P (operations,
administration, maintenance, and provisioning) applications.
Transceiver - 1. A device that performs, within one chassis, both transmitting and receiving functions. 2. In
military communications, the combination of transmitting and receiving equipment that (a) is in a common
housing, (b) usually is designed for portable or mobile use, (c) uses common circuit components for both
transmitting and receiving, and (d) provides half-duplex operation.
Transcoding - The direct digital-to-digital conversion from one encoding scheme, such as voice LPC-10, to a
different encoding scheme without returning the signals to analog form. Note: The transcoded signals, i.e.,
the digital representations of analog signals may be any digital representation of any analog signal, such as
voice, facsimile, or quasi-analog signals.
Transcoding Gain - The factor by which the bit rate of a 64-kb/s channel is reduced when transcoding is used,
e.g., when a transcoder conforming to ANSI T1.303 (i.e., ADPCM 32-kb/s) is used, the transcoding gain will
equal 2. Transcoding gain equals 1 when no transcoding is used.
Transducer - A device for converting energy from one form to another for the purpose of measurement of a
physical quantity or for information transfer.
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![Transmission - 1. The dispatching, for reception elsewhere, of a signal, message, or other form of
information. 2. The propagation of a signal, message, or other form of information by any means, such as by
telegraph, telephone, radio, television, or facsimile via any medium, such as wire, coaxial cable, microwave,
optical fiber, or radio frequency. 3. In communications systems, a series of data units, such as blocks,
messages, or frames. 4. The transfer of electrical power from one location to another via conductors.
Transmission Control Protocol / Internet Protocol - Two interrelated protocols that are part of the Internet
protocol suite. Note 1: TCP operates on the OSI Transport Layer and breaks data into packets. IP operates on
the OSI Network Layer and routes packets. Note 2: TCP/IP was originally developed by the U.S. Department
of Defense.
Transmission Line - The material medium or structure that forms all or part of a path from one place to
another for directing the transmission of energy, such as electric currents, magnetic fields, acoustic waves, or
electromagnetic waves. Note: Examples of transmission lines include wires, optical fibers, coaxial cables,
rectangular closed waveguides, and dielectric slabs.
Transmission Security (TRANSEC) - 1. See communications security. 2. [A] Component of COMSEC resulting
from the application of measures designed to protect transmissions from interception and exploitation by
means other than cryptanalysis.
Transmission Block - 1. A group of bits or characters transmitted as a unit and usually containing an encoding
procedure for error control purposes. 2. In data transmission, a group of records sent, processed, or
recorded as a unit. Note: A transmission block is usually terminated by an end-of-block character (EOB), end-
of-transmission-block character (ETB), or end-of-text character (EOT or ETX).
Transmission Buffer - Storage (viz., buffer storage) in the signaling link control for signal units not yet
transmitted.
Transmission Channel - See channel.
Transmission Coefficient - 1. The ratio of the transmitted field strength to the incident field strength of an
electromagnetic wave when it is incident upon an interface surface between media with two different
refractive indices. 2. In a transmission line, the ratio of the amplitude of the complex transmitted wave to
that of the incident wave at a discontinuity in the line. 3. The probability that a portion of a communications
system, such as a line, circuit, channel or trunk, will meet specified performance criteria. Note: The value of
the transmission coefficient is inversely related to the quality of the line, circuit, channel or trunk.
Transmission Control Character - See control character.
Transmission Control Protocol (TCP) - One of the core protocols of the Internet protocol suite. Using TCP,
applications on networked hosts can create connections to one another, over which they can exchange data.
The protocol guarantees reliable and in-order delivery of sender to receiver data. TCP also distinguishes data
for multiple, concurrent applications (e.g. Web server and email server) running on the same host.
TCP supports many of the Internet's most popular application protocols and resulting applications, including
the World Wide Web, email and Secure Shell.
Transmission Control Protocol/Internet Protocol (TCP/IP) - A set of communications protocols or software
necessary to access the Internet. A network protocol that controls host-to-host transmissions over packet-
switched communication networks.
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![Transmission Frame - A data structure, beginning and ending with delimiters, that consists of fields
predetermined by a protocol for the transmission of user data and control data.
Transmission Level - At a specified point in a telecommunications system, the power that is measured when
a standard test signal, e.g., 0 dBm or -16 dBm at 1000 Hz, is transmitted from a corresponding reference
point. Note: The transmission level is usually expressed in dBm.
Transmission Level Point (TLP) - In a telecommunications system, a test point, i.e., a point where a signal
may be inserted or measured, and for which the nominal power of a test signal is specified. Note 1: In
practice, the abbreviation, TLP, is usually used, and it is modified by the nominal level for the point in
question. For example, where the nominal level is 0 dBm, the expression 0 dBm TLP, or simply, 0TLP, is used.
Where the nominal level is -16 dBm, the expression -16 dBm TLP, or -16TLP, is used. Note 2: The nominal
transmission level at a specified TLP is a function of system design and is an expression of the design gain or
loss. Note 3: Voice-channel transmission levels, i.e., TLPs, are usually specified for a frequency of
approximately 1000 Hz. Note 4: The TLP at a point at which an end instrument, e.g., a telephone set, is
connected is usually specified as 0 dBm.
Transmission Line - The material medium or structure that forms all or part of a path from one place to
another for directing the transmission of energy, such as electric currents, magnetic fields, acoustic waves, or
electromagnetic waves. Note: Examples of transmission lines include wires, optical fibers, coaxial cables,
rectangular closed waveguides, and dielectric slabs.
Transmission Loss - The decrease in power that occurs during transmission from one point to another. Note:
Transmission loss is usually expressed in dB.
Transmission Medium - Any material substance, such as fiber-optic cable, twisted-wire pair, coaxial cable,
dielectric-slab waveguide, water, and air, that can be used for the propagation of signals, usually in the form
of modulated radio, light, or acoustic waves, from one point to another. Note: By extension, free space can
also be considered a transmission medium for electromagnetic waves, although it is not a material medium.
Transmission Security (TRANSEC) - 1. See communications security. 2. [A] Component of COMSEC resulting
from the application of measures designed to protect transmissions from interception and exploitation by
means other than cryptanalysis.
Transmission Security Key (TSK) - [A] key that is used in the control of TRANSEC (transmission security)
processes, such as frequency hopping and spread spectrum.
Transmission Service Channel - In video systems, the one-way transmission path between two designated
points.
Transmission System - Part of a communication system organized to accomplish the transfer of information
from one point to one or more other points by means of signals. Note: Examples of NATO-owned
transmission systems are SATCOM, ACE HIGH and CIP-67.
Transmission Time - In facsimile, the interval between the start of picture signals and the detection of the
end-of-message signal by the receiver for a single document.
Transmission Window - Synonym spectral window. See window.
Transmissivity - Obsolete. See transmittance.
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![Trim Effect - In a crystal oscillator, the degradation of frequency-vs.-temperature stability, and marked
frequency offset, resulting from frequency adjustment which produces a rotation or distortion, or both, of
the inherent frequency-vs.-temperature characteristic.
Triple Data Encryption Algorithm (TDEA) - An encryption algorithm whose key consists of three DES (Data
Encryption Standard) keys, which is also referred to as a key bundle. Note 1: A DES key consists of 64 binary
digits ("0"s or "1"s) of which 56 bits are randomly generated and used directly by the algorithm. (The other 8
bits, which are not used by the algorithm, may be used for error detection.) Note 2: Each TDEA
encryption/decryption operation (as specified in ANSI X9.52) is a compound operation of DES encryption and
decryption operations. Let EK(I) and DK(I) represent the DES encryption and decryption of I using DES key K
respectively. The following operations are TDEA encryption operation: the transformation of a 64-bit block I
into a 64-bit block O that is defined as follows: O = EK3(DK2(EK1(I))).
TDEA Decryption Operation - the transformation of a 64-bit block I into a 64-bit block O that is defined as
follows: O = DK1(EK2(DK3(I))). The standard specifies the following keying options for bundle (K1, K2, K3)
• Keying Option 1 - K1, K2, and K3 are independent keys;
• Keying Option 2 - K1 and K2 are independent keys and K3 = K1;
• Keying Option 3 - K1 = K2 = K3.
Triple Precision - Characterized by the use of three computer words to represent a number in accordance
with required precision.
Triplet - A byte composed of three bits. Synonym three-bit byte.
Tristimulus Values - In a given trichromatic system, the amounts of the three reference color stimuli
required to match the light considered in a given chromatic system.
TRI-TAC - Acronym for tri-services tactical. See tactical communications.
TRI-TAC Equipment - Equipment that (a) accommodates the transition from current manual and analog
systems to fully automated digital systems and (b) provides for message switching, voice communications
circuit switching, and the use of secure voice terminals, digital facsimile systems, and user digital voice
terminals.
Trojan Horse - 1. An apparently harmless program containing malicious logic that allows the unauthorized
collection, falsification, or destruction of data. 2. [A] program containing hidden code allowing the
unauthorized collection, falsification, or destruction of information.
Troposcatter - Synonym tropospheric scatter.
Troposphere - 1. The lower layers of atmosphere, in which the change of temperature with height is
relatively large. It is the region where clouds form, convection is active, and mixing is continuous and more or
less complete. 2. The layer of the Earth's atmosphere, between the surface and the stratosphere, in which
temperature decreases with altitude and which contains approximately 80% of the total air mass. Note: The
thickness of the troposphere varies with season and latitude. It is usually 16 km to 18 km thick over tropical
regions, and less than 10 km thick over the poles.
Tropospheric Duct - See atmospheric duct.
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![Tropospheric Scatter - 1. The propagation of radio waves by scattering as a result of irregularities or
discontinuities in the physical properties of the troposphere. [NTIA] [RR] [JP1] 2. A method of transhorizon
communications using frequencies from approximately 350 MHz to approximately 8400 MHz. Note: The
propagation mechanism is still not fully understood, though it includes several distinguishable but
changeable mechanisms such as propagation by means of random reflections and scattering from
irregularities in the dielectric gradient density of the troposphere, smooth-Earth diffraction, and diffraction
over isolated obstacles (knife-edge diffraction). Synonym troposcatter.
Tropospheric Wave - A radio wave that is propagated by reflection from a place of abrupt change in the
dielectric constant, or its gradient, in the troposphere. Note: In some cases, a ground wave may be so altered
that new components appear to arise from reflection in regions of rapidly changing dielectric constant.
When these components are distinguishable from the other components, they are called "tropospheric
waves."
TRS Cable (Tip, Ring, Sleeve Cable) - An analog cable used to connect audio devices. It typically comes in
1/4" and 1/8" diameters. It is balanced, as opposed to the unbalanced signals of RCA cables.
True Color - The name given to 32-bit, 16.7 million color representation.
True Parity - This term has come about with the advent of logical parity memory. It simply means that the
parity memory actually does something useful instead of just issuing positives over and over.
True Power - Synonym effective power.
TrueType - This is a font standard developed by Apple and used in Mac OS version 7. Later, Apple licensed
the technology to Microsoft, which used it in Windows 3.1 and continues to use it today. However, Apple
and Microsoft TrueType fonts are not compatible.
Truncated Binary Exponential Backoff - In carrier sense multiple access with collision avoidance (CSMA/CA)
networks and in carrier sense multiple access with collision detection (CSMA/CD) networks, the algorithm
used to schedule retransmission after a collision such that the retransmission is delayed by an amount of
time derived from the slot time and the number of attempts to retransmit.
Truncation - The deletion or omission of a leading or a trailing portion of a string in accordance with
specified criteria.
Truncation Error - In the representation of a number, the error introduced when one or more digits are
dropped.
Trunk - A communication line between two switching systems. In other words, a telephone line. A line that
connects to the telephone company CO (central office).
Trunk Circuit Identification Code (TCIC) - A unique identity assigned to each SS7 message trunk
interconnecting two switches.
Trunk Encryption Device (TED) - A bulk encryption device used to provide secure communications over a
wideband digital transmission link. Note: A TED is usually located between the output of a trunk group
multiplexer and a wideband radio or cable facility.
Trunk Group - Two or more trunks of the same type between two given points.
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![Trunk Group Multiplexer (TGM) - A time-division multiplexer that combines individual digital trunk groups
into a higher rate bit stream for transmission over wideband digital communications links.
Trunk Group Serial Number (TGSN) - A unique alphanumeric code used to identify a trunk group.
Trunk Hunting - See hunting.
Trust - In cryptology and cryptosystems, that characteristic allowing one entity to assume that a second
entity will behave exactly as the first entity expects. Note: Trust may apply only for some specific function.
The critical role of trust in the authentication framework is to describe the relationship between an
authenticating entity and a certification authority; an authenticating entity must be certain that it can trust
the certification authority to create only valid and reliable certificates.
Trusted Computer System (TCS) - 1. [An] information system (IS) employing sufficient hardware and
software assurance measures to allow simultaneous processing of a range of classified or sensitive
information. 2. A data processing system that provides sufficient computer security to allow for concurrent
access to data by users with different access rights and to data with different security classification and
security categories.
Trusted Computing Base (TCB) - [The] totality of protection mechanisms within a computer system, including
hardware, firmware, and software, the combination of which is responsible for enforcing a security policy.
Note: The ability of a trusted computing base to enforce correctly a unified security policy depends on the
correctness of the mechanisms within the trusted computing base, the protection of those mechanisms to
ensure their correctness, and the correct input of parameters related to the security policy.
Trusted Distribution - [A] method for distributing trusted computing base (TCB) hardware, software, and
firmware components that protects the TCB from modification during distribution.
Trusted Identification Forwarding - [The] identification method used in information system (IS) networks
whereby the sending host can verify an authorized user on its system is attempting a connection to another
host. The sending host transmits the required user authentication information to the receiving host.
Trusted Path - [The] Mechanism by which a person using a terminal can communicate directly with the
trusted computing base (TCB). Trusted path can only be activated by the person or the TCB and cannot be
imitated by untrusted
Trusted Process - [A] process that has privileges to circumvent the system security policy and has been
tested and verified to operate only as intended.
Trusted Recovery - [The] ability to ensure recovery without compromise after a system failure.
Trusted Software - [The] software portion of a trusted computing base (TCB).
Trusted Third-Party - A security authority trusted by communicating entities with respect to specific security-
related activities (e.g., for the purpose of authentication).
Truth Table - 1. An operation table for a logic operation. 2. A table that describes a logic function by listing all
possible combinations of input values and indicating, for each combination, the output value.
TSEC Nomenclature - [In security, the] system for identifying the type and purpose of certain items of
COMSEC material.
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![TSK - Abbreviation for transmission security key.
TSP - Abbreviation for Telecommunications Service Priority.
TSPS - Abbreviation for traffic service position system.
TSPS Complex - All groups of operator positions, wherever located, associated with the same TSPS stored
program control units.
TSP System - See Telecommunications Service Priority system.
TTTN - Abbreviation for tandem tie trunk network.
TTY - Abbreviation for teletypewriter.
TTY/TDD - Telephone Typewriter and Telephone Device for the Deaf. A telecommunication device for the
hearing impaired using teletypewriter principals. The users call a special operator number and third-party
translation.
Tuning - Adjusting the parameters and components of a circuit so that it resonates at a particular frequency
or so that the current or voltage is either maximized or minimized at a specific point in the circuit. Note:
Tuning is usually accomplished by adjusting the capacitance or the inductance, or both, of elements that are
connected to or in the circuit.
Tunneling - 1. In computer networking, a technique for connecting two networks via a third, while totally
isolating the connected traffic from other traffic in the third network. [After 2382-pt.35] 2. Technology
enabling one network to send its data via another network's connections. Tunneling works by encapsulating
a network protocol within packets carried by the second network.
Tunneling Mode - Synonym leaky mode. In an optical fiber, a mode having a field that decays monotonically
for a finite distance in the transverse direction but becomes oscillatory everywhere beyond that finite
distance. Note: Leaky modes correspond to leaky rays in the terminology of geometric optics. Leaky modes
experience attenuation, even if the waveguide is perfect in every respect.
Tunneling Ray - Synonym leaky ray. In an optical fiber, a ray for which geometric optics would predict total
internal reflection at the boundary between the core and the cladding, but which suffers loss by virtue of the
curved core boundary. Note: Leaky rays correspond to leaky (i.e., tunneling) modes in the terminology of
mode descriptors.
Turing Machine - A mathematical model of a device that changes its internal state and reads from, writes on,
and moves a potentially infinite tape, all in accordance with its present state, thereby constituting a model
for computer-like behavior.
Turnaround Time - In a half-duplex circuit, the time required to reverse the direction of transmission from
transmit to receive or vice versa.
Turnkey - Pertaining to a procurement process that (a) includes contractual actions at least through the
system, subsystem, or equipment installation phase and (b) may include follow-on contractual actions, such
as testing, training, logistical, and operational support. Note: Precise definition of the types of allowable
contractual features are contained in the Federal Acquisition Regulations (FAR).
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![TWAIN (Toolkit Without An Interesting Name) - A set of operations that allow scanners to have a standard
interface to software. This allows the use of your favorite graphics package with your favorite scanner
without worrying if one will support the other. As long as both are TWAIN-complaint they will work together.
Twin Cable - A cable composed of two parallel conductors separated from each other by a ribbon-like
insulator or encased by a foam insulator. Synonym twin-lead.
Twin-Lead - Synonym twin cable. A term that refers to a two-conductor ribbon cable commonly used as a
transmission line for TV signals.
Twin-Lead Adapter - A device for connecting a Twin Lead cable to a coaxial cable.
Twinplex - A frequency-shift-keyed (FSK) carrier telegraphy system in which four unique tones, i.e., two pairs
of tones, are transmitted over a single transmission channel, such as one twisted pair. Note: One tone of
each pair represents a " mark " and the other a "space."
Twin Sideband Transmission - See independent-sideband transmission.
Twist - In telephony, a change, as a function of temperature, in the shape of the frequency-vs.-attenuation
response curve, i.e., characteristic, of a transmission line.
Twisted Pair - A pair of individually insulated conductors (wires) twisted together and treated as an entity in
the transmission of electrical signals or power (e.g., from an electronic power supply to a circuit). Note 1: In
communications cables, the twisted pair is usually if not always composed of two individually insulated solid
conductors (wires). In other applications, e.g., in a power-supply application, each of the insulated
conductors may consist of stranded wire. Note 2: Because the wires are twisted together, interfering signals
tend to create opposing electromagnetic forces at frequent intervals, reducing the effect of the interference
on the signal or power supply voltage being conducted. Note 3: Twisted pairs may be used for bit rates up to
1 Mb/s over short distances (<100 m) and lower bit rates over longer distances. More sophisticated driver
and receiver circuits facilitate similar or higher data rates over longer distances. Note 4: Unshielded twisted
pairs (UTPs) are used extensively in telephone networks and in many data communications applications.
Twisted Pair Cable - See paired cable.
Two-Out-Of-Five Code - A binary-coded decimal notation in which (a) each decimal digit is represented by a
binary numeral consisting of five binary digits of which two are of one kind, called "ones," and three are of
the other kind, called "zeros" and (b) the usual weights assigned to the digit positions are 0-1-2-3-6, except
that "zero" is represented as 01100.
Two-Part Code - Code consisting of an encoding section, in which the vocabulary items (with their associated
code groups) are arranged in alphabetical or other systematic order; and a decoding section, in which the
code groups (with their associated meanings) are arranged in a separate alphabetical or numeric order.
Two-Person Control - Continuous surveillance and control of positive control material at all times by a
minimum of two authorized individuals, each capable of detecting incorrect and unauthorized procedures
with respect to the task being performed, and each familiar with established security and safety
requirements.
Two-Person Integrity (TPI) - [A] system of storage and handling designed to prohibit individual access to
certain COMSEC keying material by requiring the presence of at least two authorized persons, each capable
of detecting incorrect or unauthorized security procedures with respect to the task being performed.
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![Two-Pilot Regulation - In frequency-division multiplexed (FDM) systems, the use of two pilot frequencies
within a band so that the differential change in attenuation with respect to temperature, i.e., twist, can be
detected and compensated by a regulator.
Two-Sample Deviation - The square root of the Allan variance
Two-Sample Variance - Synonym Allan variance.
Two-Source Frequency Keying - Synonym frequency-exchange signaling.
Two-Tone Keying: - In telegraphy systems, keying in which the modulating wave causes the carrier to be
modulated with a single tone for the " mark " and modulated with a different single tone for the "space."
Two-Tone Telegraph - See two-tone keying.
Two-way Alternate Operation - Synonym half-duplex operation.
Two-Way Simultaneous Operation - Synonym duplex operation.
Two-Wire Circuit - Also 2-wire circuit. A full-duplex communications circuit that utilizes only two metallic
conductors, e.g., a single twisted pair.
TWX® - Acronym for teletypewriter exchange service.
TX - Abbreviation for transmitter, transmit.
Type 1 Product - Classified or controlled cryptographic item for securing classified and sensitive U.S.
Government information, when appropriately keyed. The term refers only to products, and not to
information, key, services, or controls. Type 1 products contain classified algorithms. They are available to
U.S. Government users, their contractors, and federally sponsored non-U.S. Government activities subject to
export restrictions in accordance with International Traffic in Arms Regulation.
Type 2 Product - Unclassified cryptographic equipment, assembly, or component, endorsed by the National
Security Agency, for use in national security systems as defined in Title 40 U.S.C. Section 1452. [INFOSEC-99]
Note: The term refers only to products, and not to information, key, services, or controls. Type 2 products
may not be used for classified information, but contain classified National Security Agency algorithms that
distinguish them from products containing the unclassified data algorithm. Type 2 products are subject to
export restrictions in accordance with the International Traffic in Arms Regulation.
Type 3 Algorithm - [A] cryptographic algorithm that has been registered by the National Institute of
Standards and Technology (NIST) and published as a Federal Information Processing Standard (FIPS) for use
in protecting unclassified sensitive, information or commercial information.
Type 4 Algorithm - [An] unclassified cryptographic algorithm that has been registered by the National
Institute of Standards and Technology (NIST), but not published as a Federal Information Processing Standard
(FIPS).
Types of Calls -
• Local — A call within your local calling area covered by your local calling plan.
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![Undetected Error Ratio - The ratio of the number of bits, unit elements, characters, or blocks incorrectly
received and undetected, to the total number of bits, unit elements, characters, or blocks sent. Synonyms
residual error rate, undetected error rate [deprecated] .
Undisturbed Day - A day during which neither sunspot activity nor ionospheric disturbance causes
detectable interfere with radio communications.
Unequipped Indication - A code placed in unequipped channels by originating equipment to indicate to path
terminating equipment that the channel is intentionally unoccupied so that alarms can be inhibited.
Unexpected Frame - A valid frame that cannot be processed. The frame itself is perfectly legitimate. Its
unexpected character is defined by two conditions: the specific type of frame and the state of the receiver.
The layer-2 protocol states define the proper sequence in which frames are expected to occur. The receiver
will compare received frames with its own protocol state to determine whether or not a valid frame is
unexpected.
UNICOM station - Synonym aeronautical advisory station. An aeronautical station used for advisory and civil
defense communications primarily with private aircraft stations.
Unidirectional - The condition where information flow is provided only in one direction.
Unidirectional Channel - Synonym one-way-only channel. A channel capable of transmission in only one
direction, which cannot be reversed.
Unidirectional Operation - Operation in which data are transmitted from a transmitter to a receiver in only
one direction.
Unidirectional Path - A path that logically connects a single path source with the associated path sink.
Uniform Encoding - An analog-to-digital conversion process in which, except for the highest and lowest
quantization steps, all of the quantization subrange values are equal. Synonym uniform quantizing.
Uniform Linear Array - An antenna composed of a relatively large number of usually identical elements
arranged in a single line or in a plane with uniform spacing and usually with a uniform feed system.
Uniform Quantizing - Synonym uniform encoding. An analog-to-digital conversion process in which, except
for the highest and lowest quantization steps, all of the quantization subrange values are equal.
Uniform Resource Locator (URL) - The standard for giving an WWW Internet address (e.g.
http://www.faxswitch.com)
Uniform-Spectrum Random Noise - See white noise. Noise having a frequency spectrum that is continuous
and uniform over a specified frequency band. Note: Uniform-Spectrum Random Noise has equal power per
hertz over the specified frequency band. Synonym additive white gaussian noise.
Uniform Time Scale - A time scale made up of equal intervals.
Uniform Transmission Line - A transmission line that has distributed electrical properties, i.e., resistance,
inductance, and capacitance per unit length, that are constant along the line, and in which the voltage-to-
current ratio does not vary with distance along the line, if the line is terminated in its characteristic
impedance. Note 1: Examples of uniform transmission lines are coaxial cables, twisted pairs, and single wires
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![Upconvert - A process by which a digital, high-definition television takes a lower-definition picture and
converts it into a higher-definition picture. This may be done by doubling each line as it is drawn on the
screen, or by using advanced algorithms to interpolate the data between each lower-resolution line, filling in
the missing image.
Update - The regeneration of a display to show current status, based on changes to the previously displayed
data. Note: An update can be accomplished upon user request or by automatic means.
Upload - To transfer a file or information from your computer to another.
UPT - See Universal Personal Telecommunications Service.
UPT Number - In universal personal telecommunications service, the number that uniquely identifies a UPT
user and that is used to place a call to, or to forward a call to, that user. Note: A user may have multiple UPT
numbers, e.g., a business UPT number for business calls and a private UPT number for private calls. In the
case of multiple numbers, each UPT number is considered, from a network vantage point, to identify a
distinct UPT user, even if all such numbers identify the same person or entity. Synonym universal personal
telecommunications number.
UPT User - In universal personal telecommunications service, a person who (or entity that) has access to
universal personal telecommunications (UPT) services and who has been assigned a UPT number.
URL - See Uniform Resource Locator
Usage - Synonym occupancy. For equipment, such as a circuit or a switch, the ratio of the actual time in use
to the available time during a 1-hour period. Note 1: Usage is usually expressed in percent. Note 2: Usage
may be plotted versus time of day.
User - 1. A person, organization, or other entity (including a computer or computer system), that employs
the services provided by a telecommunication system, or by an information processing system, for transfer
of information. Note: A user functions as a source or final destination of user information, or both. Synonym
subscriber. 2. [In security, a] person or process authorized access to an IS (information system); [an]
individual defined, registered, and bound to a public key structure by certification authority.
User Datagram Protocol (UDP) - In the Internet Protocol suite, a standard, low-overhead, connectionless,
host-to-host protocol that is used over packet-switched computer communications networks, and that
allows an application program on one computer to send a datagram to an application program on another
computer. Note: The main difference between UDP and TCP is that UDP provides connectionless service,
whereas TCP does not.
User Name - Your user name, also called user ID or account name, is the same as your login name. This is the
name by which you and your electronic mailbox are identified online.
User Information - Information transferred across the functional interface between a source user and a
telecommunications system for delivery to a destination user. Note: In telecommunications systems, user
information includes user overhead information.
User Information Bit - A bit transferred from a source user to a telecommunications system for delivery to a
destination user. Note 1: User information bits do not include the overhead bits originated by, or having
their primary functional effect within, the telecommunications system. Note 2: User information bits are
encoded to form channel bits.
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![User Information Block - A block that contains at least one user information bit.
User Overhead Information - See overhead information. - Digital information transferred across the
functional interface between a user and a telecommunications system, or between functional units within a
telecommunications system, for the purpose of directing or controlling the transfer of user information or
the detection and correction of errors. Note: Overhead information originated by the user is not considered
to be system overhead information. Overhead information generated within the communications system
and not delivered to the user is system overhead information. Thus, the user throughput is reduced by both
overheads while system throughput is reduced only by system overhead.
User Part - A functional part of the common channel signaling system that transfers signaling messages via
the message transfer part. Different types of user parts exist (e.g., for telephone and data services), each of
which is specified to a particular use of the signaling system.
USF - Universal Service Fund. The National Exchange Carrier Association administers the USF. This is a
mechanism designed to keep local exchange rates at reasonable levels, especially in high-cost, rural areas.
The fund gets money from a surcharge on phone lines and uses those funds to offset telecommunication
expenses in the high-cost areas.
UseNet Newsfeed - A huge, world wide "Users Network" of discussion groups, or newsgroups, connecting
and sharing information from hundreds of thousands of machines.
Utility Program - A computer program that is in general support of the operations and processes of a
computer. Note: Examples of utility programs include diagnostic programs, trace programs, input routines,
and programs used to perform routine tasks, i.e., perform everyday tasks, such as copying data from one
storage location to another. Synonyms service program, service routine, tool, utility routine.
UUCP Service (UNIX to UNIX Copy Program) - A method of transferring files between UNIX computers that
includes Electronic mail.
UWB - Abbreviation for ultrawideband. 1. Referring to any radio or wireless device where the occupied
bandwidth is greater than 25% of the center frequency or greater than 1.5 GHz. 2. A radio or wireless system
that uses narrow pulses (on the order of 1 to 10 nanoseconds), also called carrierless or impulse systems, for
communications and sensing (short-range radar). 3. A radio or wireless system that uses time-domain
modulation methods (e.g., pulse-position modulation) for communications applications, or time-domain
processing for sensing applications.
V
Validation - 1. Tests to determine whether an implemented system fulfills its requirements. 2. The checking
of data for correctness or for compliance with applicable standards, rules, and conventions. 3. [The] process
of applying specialized security test and evaluation procedures, tools, and equipment needed to establish
acceptance for joint usage of an AIS by one or more departments or agencies and their contractors. Note:
This action will include, as necessary, final development, evaluation, and testing, preparatory to acceptance
by senior security test and evaluation staff specialists. 4. In universal personal telecommunications, the
process of verifying that a user or terminal is authorized to access UPT services.
Value-Added Carrier: - A company that sells the services of a value-added network.
Value-Added Network (VAN) - A network using the communication services of other commercial carriers,
using hardware and software that permit enhanced telecommunication services to be offered.
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![Voice Frequency (VF) - Pertaining to those frequencies within that part of the audio range that is used for
the transmission of speech. (188) Note 1: In telephony, the usable voice-frequency band ranges from
approximately 300 Hz to 3400 Hz. Note 2: In telephony, the bandwidth allocated for a single voice-frequency
transmission channel is usually 4 kHz, including guard bands. Synonym voice band.
Voice Frequency Carrier Telegraph (VFCT) - Synonym voice-frequency telegraph. A method of multiplexing
one or more dc telegraph channels onto a nominal 4-kHz voice frequency channel.
Voice-Frequency (VF) Channel - A channel capable of carrying analog and quasi-analog signals.
Voice Frequency (VF) Primary Patch Bay - A patching facility that provides the first appearance of local-user
VF circuits in the technical control facility (TCF). Note: The VF primary patch bay provides patching,
monitoring, and testing for all VF circuits. Signals will have various levels and signaling schemes depending on
the user terminal equipment.
Voice-Frequency Telegraph (VFTG): A method of multiplexing one or more dc telegraph channels onto a
nominal 4-kHz voice frequency channel. Synonym voice frequency carrier telegraph.
Voice Grade - In the public regulated telecommunications services, a service grade that is described in part
68, Title 47 of the Code of Federal Regulations [CFR] . Note: Voice-grade service does not imply any specific
signaling or supervisory scheme.
Voice Mail - a specific application of an interactive voice response system. In its simplest form it mimics the
functions of an answering machine, but uses a centralised system rather than equipment at the individual
telephone. However it can be far more sophisticated, with the ability to forward messages to another voice
mailbox and send simultaneous messages to multiple voice mailboxes, add voice notes to a message, store
messages for future delivery, make calls to a telephone or paging service when a message is received,
transfer callers to another phone for personal assistance and play different message greetings to different
callers. Voicemail messages are stored in media used by computers to store other forms of data (hard drives,
optical drives, and tape).
Many voicemail systems also offer an automated attendant facility, allowing callers answered by the system
to dial a selected person's mail box or telephone.
Voicemail systems are found associated with many office telephone systems or (PBX). They may also be
associated with public telephone lines as network services. Mobile phones generally have voicemail as a
standard network feature.
The Phone Company Voice Mail feature answers calls and takes messages when you are on the phone, on
the internet, sending a fax, or not at home. This feature also works when the electrical power is out. You can
access your voicemail box through a local access number. You enter your PIN and follow the appropriate
prompts to use the service. There is a maximum capacity for messages, minutes per message, and message
retention length, as outlined in marketing information. Call Forwarding Busy/No Answer must be ordered
but will not be billed when Voice Mail is ordered.
Voice Mail Plus - A phone company feature that includes the same functionality as Voice Mail except it
provides additional mailboxes and recording time. Call Forwarding Busy/No Answer must be ordered but not
billed when Voice Mail is ordered.
Voice-Operated Device Anti-Sing - See vodas. A device used to prevent overall voice-frequency singing in a
two-way telephone circuit by ensuring that transmission can occur in only one direction at any given instant.
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![Volume Unit (VU) - A unit of measurement of the power of an audio-frequency signal, as measured by a vu
meter. Note 1: The vu meter is built and used in accordance with American National Standard C16.5-1942.
Note 2: When using the vu meter to measure sine wave test tone power, 0 vu equals 0 dBm.
VOX - An acoustoelectric transducer and a keying relay connected so that the keying relay is actuated when
sound, or voice, energy above a certain threshold is sensed by the transducer. Note: A vox is used to
eliminate the need for push-to-talk operation of a transmitter by using voice energy to turn on the
transmitter. Synonyms voice operated relay circuit , voice operated transmit.
V Reference Point - The interface point in an ISDN environment between the line termination and the
exchange termination.
VSB - Abbreviation for vestigial sideband. See vestigial sideband transmission. Modified AM transmission in
which one sideband, the carrier, and only a portion of the other sideband are transmitted.
V-series Recommendations - Sets of telecommunications protocols and interfaces defined by CCITT (now
ITU-T) Recommendations. Note: Some of the more common V.-series Recommendations are:
• V.21: A CCITT Recommendation for modem communications over standard commercially available
lines at 300 b/s. This protocol is generally not used in the United States.
• V.22bis: A CCITT Recommendation for modem communications over standard commercially
available voice-grade channels at 2,400 b/s and below.
• V.32: A CCITT Recommendation for modem communications over standard commercially available
voice-grade channels at 9.6 kb/s and below.
• V.32bis: A CCITT Recommendation for modem communication over standard commercially
available voice-grade channels at 14.4 kb/s and below.
• V.34: An ITU-T Recommendation for modem communication over standard commercially available
voice-grade channels at 28.8 kb/s and below.
• V.42: A CCITT Recommendation for error correction on modem communications.
• V.42bis: A CCITT Recommendation for data compression on a modem circuit.
• V.FAST: A new CCITT Recommendation for high-speed modems currently under development.
VSWR - Abbreviation for voltage standing wave ratio. In a transmission line, the ratio of maximum to
minimum voltage in a standing wave pattern. Note: The VSWR is a measure of impedance mismatch
between the transmission line and its load. The higher the VSWR, the greater the mismatch. The minimum
VSWR, i.e., that which corresponds to a perfect impedance match, is unity.
VU - Abbreviation for volume unit. A unit of measurement of the power of an audio-frequency signal, as
measured by a vu meter. (188) Note 1: The vu meter is built and used in accordance with American National
Standard C16.5-1942. Note 2: When using the vu meter to measure sine wave test tone power, 0 vu equals 0
dBm.
Vulnerability - 1. In communications security, see susceptibility. 2. The extent to which a system will degrade
when subjected to a specified set of environmental conditions. 3. In communications interference, see
susceptibility threshold. 4. In cryptology, the point of weakness within the encrypted system where threats
can occur, such as equipment, facilities, hardware, software, operating systems and personnel. 5. [A]
weakness in an information system (IS), [in] system security procedures, [in] internal controls, or [in]
implementation that could be exploited.
W
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![Wafer - A thin slice of semiconducting material, such as a silicon crystal, upon which microcircuits are
constructed by diffusion and deposition of various materials. Note: Millions of individual circuit elements,
constituting hundreds of microcircuits, may be constructed on a single wafer. The individual microcircuits are
separated by scoring and breaking the wafer into individual chips ("dice").
Wallpaper - A graphic image that serves as a background for a Web page or for a computer operating
system's screen.
WAIS - Acronym for Wide Area Information Servers. A distributed text searching system that uses the
protocol standard ANS Z39.50 to search index databases on remote computers. Note 1: WAIS libraries are
most often found on the Internet. Note 2: WAIS allows users to discover and access information resources on
the network without regard to their physical location. Note 3: WAIS software uses the client-server model.
WAN - Wide Area Network. A data communications network which expands a LAN to link up with other LANs
in remote buildings. A physical or logical network that provides data communications to a larger number of
independent users than are usually served by a local area network (LAN) and is usually spread over a larger
geographic area than that of a LAN. Note 1: WANs may include physical networks, such as Integrated
Services Digital Networks (ISDNs), X.25 networks, and T1 networks. Note 2: A metropolitan area network
(MAN) is a WAN that serves all the users in a metropolitan area. WANs may be nationwide or worldwide.
Wander - Relative to jitter and swim, long-term random variations of the significant instants of a digital
signal from their ideal positions. Note 1: Wander variations are those that occur over a period greater than 1
s (second). Note 2: Jitter, swim, wander, and drift have increasing periods of variation in that order.
Warm Boot - Synonym warm restart.
Warm Restart - 1. A sequence of operations that is performed to reset a previously running system, after an
unintentional shutdown. Synonym warm start. 2. In computer operations, the restarting of equipment, after
a sudden shutdown, that allows reuse of previously retained initialized input data, retained programs, and
retained output queues. Note 1: A warm restart may be needed after a program failure. Note 2: A warm start
or restart cannot occur if initial data, programs, and files are not retained after closedown. Synonyms hot
boot, warm boot.
Warm Start - Synonym warm restart.
Warner Exemption - A statutory exemption pertaining to the acquisition of telecommunications systems
that meet the exclusionary criteria of the Warner Amendment, Public Law 97-86, 1 December 1981, which is
also known as the Brooks Bill. Note: Use of FTS2000 by U.S. Government agencies is mandatory when
telecommunications are required. However, the Warner Amendment excludes the mandatory use of
FTS2000 in instances related to maximum security.
Watermark - 1. A copyright-protection method of embedding a code into a digital audio or video file to
attempt to thwart piracy or unlicenced use. 2. In desktop publishing, an inserted (and usually faint) overlay of
an image or text onto pages of a document. Note: The watermark is usually visible on the computer screen in
WYSIWIG fashion and on the printed pages of the final document. The watermark often verifies authenticity
of authorship or release authority.
WATS - Acronym for Wide Area Telephone Service.
.wav - A file extension name for one format [i.e., a wave format] of a sound file.
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![Wide Area Information Servers (WAIS) - A distributed text searching system that uses the protocol standard
ANS Z39.50 to search index databases on remote computers. Note 1: WAIS libraries are most often found on
the Internet. Note 2: WAIS allows users to discover and access information resources on the network
without regard to their physical location. Note 3: WAIS software uses the client-server model.
Wide Area Network (WAN) - A physical or logical network that provides data communications to a larger
number of independent users than are usually served by a local area network (LAN) and is usually spread
over a larger geographic area than that of a LAN. Note 1: WANs may include physical networks, such as
Integrated Services Digital Networks (ISDNs), X.25 networks, and T1 networks. Note 2: A metropolitan area
network (MAN) is a WAN that serves all the users in a metropolitan area. WANs may be nationwide or
worldwide.
Wide Area Telephone Service (WATS) - A toll service offering for customer dial type telecommunications
between a given customer station and stations within specified geographic rate areas employing a single
access line between the customer location and the serving central office. Each access line may be arranged
for either outward (OUT-WATS) or inward (IN-WATS) service or both. [47 CFR Pt.36-A] Note: The offering is
for fixed-rate inter- and intra-LATA services measured by zones and hours.
Wideband - 1. The property of any communications facility, equipment, channel, or system in which the
range of frequencies used for transmission is greater than 0.1 % of the midband frequency. Note:
"Wideband" has many meanings depending upon application. "Wideband" is often used to distinguish it
from "narrowband," where both terms are subjectively defined relative to the implied context. 2. In
communications security systems, a bandwidth exceeding that of a nominal 4-kHz telephone channel. 3. The
property of a circuit that has a bandwidth wider than normal for the type of circuit, frequency of operation,
or type of modulation. 4. In telephony, the property of a circuit that has a bandwidth greater than 4 kHz. 5.
Pertaining to a signal that occupies a broad frequency spectrum. Synonym broadband.
Wideband Channel - A communication channel of a bandwidth equivalent to twelve or more voice-grade
channels.
Wideband Modem - 1. A modem whose modulated output signal can have an essential frequency spectrum
that is broader than that which can be wholly contained within, and faithfully transmitted through, a voice
channel with a nominal 4-kHz bandwidth. (188) 2. A modem whose bandwidth capability is greater than that
of a narrowband modem.
Widescreen - 1. A term used generally to describe an aspect ratio wider than 4:3. For television, this refers to
the 16 x 9 aspect ratio.
Wildcard Character - 1. A character that may be substituted for any of a defined subset of all possible
characters. Note 1: In high-frequency (HF) radio automatic link establishment, the wildcard character "?"
may be substituted for any one of the 36 characters, "A" through "Z" and "0" through "9." Note 2: Whether
the wildcard character represents a single character or a string of characters must be specified. (188) 2. In
computer (software) technology, a character that can be used to substitute for any other character or
characters in a string. Note: The asterisk (*) usually substitutes as a wildcard character for any one or more
of the ASCII characters, and the question mark (?) usually substitutes as a wildcard character for any one
ASCII character.
Wild-Point Detection - A test to determine whether a value conforms to specified criteria. Note: A wild-point
detection can be used to eliminate questionable data points from subsequent processing. Synonym
reasonableness check.
WIN - Abbreviation for WWMCCS Intercomputer Network.
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![Wireless Terminal - Any mobile terminal, mobile station, personal station, or personal terminal using non-
fixed access to the network.
Wireline – A conventional (wired) telephone network versus a wireless network.
Wireline Common Carrier - Common carriers [that] are in the business of providing landline local exchange
telephone service.
Wizard - An intelligent, trainable Web spider. Synonyms droid, smart bot, spider.
Word - A character string or a bit string considered to be an entity for some purpose. Note: In telegraph
communications, six character intervals are defined as a word when computing traffic capacity in words per
minute, which is computed by multiplying the data signaling rate in baud by 10 and dividing the resulting
product by the number of unit intervals per character.
Word Length - The number of characters or bits in a word.
Word Processing: The use of a computer system to manipulate text. Note: Examples of word processing
functions include entering, editing, rearranging, sorting, storing, retrieving, displaying, and printing text.
Synonym text processing.
Work Space - In computers and data processing systems, the portion of main storage that is used by a
computer program for the temporary storage of data.
Work Station - 1. In automated systems, such as computer, communications, and control systems, the input,
output, display, and processing equipment that provides the operator-system interface. 2. A configuration of
input, output, display, and processing equipment that constitutes a stand-alone system not requiring
external access.
Working Loop - A revenue producing pair of wires, or its equivalent, between a customer's station and the
central office from which the station is served.
World Numbering Plan - A plan created by the International Telegraph and Telephone Consultative
Committee (CCITT--now, the ITU-T) that provides each telephone subscriber with a unique number. Each
world telephone number consists of a country code followed by the national number. By international
agreement, the number of digits in the country code plus national number is limited to a total of 15 digits.
World Time - Time scale, based on the second (SI), as defined and recommended by the CCIR, and
maintained by the Bureau International des Poids et Mesures (BIPM). For most practical purposes associated
with the Radio Regulations, UTC is equivalent to mean solar time at the prime meridian (0° longitude),
formerly expressed in GMT. [NTIA] [RR] Note 1: The maintenance by BIPM includes cooperation among
various national laboratories around the world. Note 2: The full definition of UTC is contained in CCIR
Recommendation 460-4. (188) Note 3 : The second was formerly defined in terms of astronomical
phenomena. When this practice was abandoned in order to take advantage of atomic resonance phenomena
("atomic time") to define the second more precisely, it became necessary to make occasional adjustments in
the "atomic" time scale to coordinate it with the workaday mean solar time scale, UT-1, which is based on
the somewhat irregular rotation of the Earth. Rotational irregularities usually result in a net decrease in the
Earth's average rotational velocity, and ensuing lags of UT-1 with respect to UTC. Note 4: Adjustments to the
atomic, i.e., UTC, time scale consist of an occasional addition or deletion of one full second, which is called a
leap second. Twice yearly, during the last minute of the day of June 30 and December 31, Universal Time,
adjustments may be made to ensure that the accumulated difference between UTC and UT-1 will not exceed
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![0.9 s before the next scheduled adjustment. Historically, adjustments, when necessary, have usually
consisted of adding an extra second to the UTC time scale in order to allow the rotation of the Earth to
"catch up." Therefore, the last minute of the UTC time scale, on the day when an adjustment is made, will
have 59 or 61 seconds. Synonyms Coordinated Universal Time , Z Time, Zulu Time.
World Wide Web (WWW) - A HyperText system that allows users to navigate, or look through, linked
documents and resources. Also Web, WWW, W3. A global, virtual-network based hypertext information
system that uses the Internet as its transport mechanism to display computer screens (or Web pages) of
graphical, video, textual, and even audio information. Note: In a hypertext system, one navigates by clicking
hyperlinks, which display another document which also contains hyperlinks. In Web navigation, the next
document seen could be housed on a computer next door or half-way around the world. Created in 1989 at a
research institute in Switzerland, the Web relies upon browsers and the hypertext transport protocol (http),
an Internet standard that specifies how an application can locate and acquire resources stored on another
computer on the Internet. Most Web documents are created using hypertext markup language (html), a
coding system for WWW documents. Incorporating hypermedia (graphics, sounds, animations, video), the
Web has become a popular medium for publishing information on the Internet. With the development of
secured server protocol (https), the Web is now a commercial medium whereby consumers can browse on-
line catalogs and purchase merchandise using secure, encrypted credit card information that is protected
from interception. Synonym Web.
The World Wide Web is an international, virtual-network-based information service composed of Internet
host computers that provide on-line information in a specific hypertext format. Note 1: WWW servers
provide hypertext metalanguage (HTML) formatted documents using the hypertext transfer protocol (HTTP).
Note 2: Information on the WWW is accessed with a hypertext browser such as Mosaic, Viola, or Lynx. Note
3: No hierarchy exists in the WWW, and the same information may be found by many different approaches.
Worm - 1. A computer virus capable of disrupting a computer program. 2. A self-contained program that can
propagate itself through systems or networks. Note: Worms are often designed to use up available resources
such as storage or processing time. 3. [An] independent program that replicates from machine to machine
across network connections, often clogging networks and computer systems as it spreads. 4. Acronym for
write once, read many (times). Note: A worm drive is used in recording data on a disk such that the data can
then be read but not erased.
Worst Hour of the Year - That hour of the year during which the median noise over any radio path is at a
maximum. Note: This hour is considered to coincide with the hour during which the greatest transmission
loss occurs.
W-Profile Fiber - A single-mode fiber that has two claddings. Note 1: Each cladding has a refractive index that
is lower than that of the core. Of the two claddings, inner and outer, the inner cladding has the lower
refractive index. Note 2 : A doubly clad fiber has the advantage of very low macrobending losses. It also has
two zero-dispersion points, and low dispersion over a much wider wavelength range than a singly clad fiber.
(from the fact that a symmetrical plot of its refractive index profile superficially resembles the letter W).
Synonyms depressed-cladding fiber, depressed-inner-cladding fiber, doubly clad fiber.
Wrapping - 1. In a network using dual counter-rotating ring architecture, reconfiguration to circumvent a
failed link or node. 2. In open systems architecture, the use of a network to connect two other networks,
thus providing an increased interaction capability between the two connected networks. Note: Recurring
application of wrapping usually results in a hierarchical structure.
Write - To make a permanent or transient recording of data in a storage device or on a data medium.
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Telecom dictionary
- 1. Telecom Dictionary Definitions of terms ABCDEFGHIJKLMNOPQRSTUVWXYZ A -18 A - A is the abbreviation for atto (10 ). See metric system. A-Condition - An A-Condition, in a start-stop teletypewriter system, the significant condition of the signal element that immediately precedes a character signal or block signal and prepares the receiving equipment for the reception of the code elements. A-D - Abbreviation for analog-to-digital. See analog transmission. - Transmission of a continuously varying signal as opposed to transmission of a discretely varying signal. A-law - See a-law algorithm. - A standard compression algorithm, used in digital communications systems of the European digital hierarchy, to optimize, i.e., modify, the dynamic range of an analog signal for digitizing. Note: The wide dynamic range of speech does not lend itself well to efficient linear digital encoding . A-law encoding effectively reduces the dynamic range of the signal, thereby increasing the coding efficiency and resulting in a signal-to- distortion ratio that is superior to that obtained by linear encoding for a given number of bits. Abandoned Call - A call in which the call originator disconnects or cancels the call after a connection has been made, but before the call is established. Abandonment - Network replacement of a connect signal with an on-hook signal (network) prior to receiving a CI (customer installation) answer signal; abandonment is the only way to end an unanswered call attempt. Abbreviated Address - An abbreviated Address is an address that has fewer characters than the full address, usually for special communications and other services or for certain users. Note: Examples of abbreviated addresses are (a) a four-digit telephone number for a user calling another user connected to the same switching exchange, and (b) message addresses that have only the addressee name and station code or number. Abbreviated Address Calling - Calling that enables a user to employ an address having fewer characters than the full address when initiating a call. Note: Communications network users may be allowed to designate a given number of abbreviated address codes. The allocation of the abbreviated address codes to a destination or group of destinations may be changed as required, by means of a suitable procedure. Abbreviated Dialing - A telephone service feature that (a) permits the user to dial fewer digits to access a network than are required under the nominal numbering plan, and (b) is limited to a subscriber-selected set of frequently dialed numbers. Synonym speed dialing. Abort - 1. In a computer or data transmission system, to terminate, usually in a controlled manner, a processing activity because it is impossible or undesirable for the activity to proceed. 2. In data transmission, 1
- 2. a function invoked by a sending station to cause the recipient to discard or ignore all bit sequences transmitted by the sender since the preceding flag sequence. Abrasive - Any of a number of hard materials, such as aluminum oxide, silicon carbide, and diamond, that are powdered and carefully graded according to particle size, and used to shape and/or finish optical elements, including the end faces of optical fibers and connectors. Note: For finishing the end faces of optical fiber connectors, abrasive particles are adhered to a substrate of plastic film, in a fashion after that of sandpaper. The film is in turn supported by a hard, flat plate. The connector is supported by a fixture that holds it securely in the proper position for finishing. The grinding motion may be performed manually or by a machine. Absolute Address - In communications, computer, and data processing systems, an address that directly identifies a storage location without the use of an intermediate reference, e.g., a base address or a relative address. Absolute Delay - 1. The time interval or phase difference between transmission and reception of a signal. 2. The total time between the instant a bit enters the network and the instant a corresponding bit exists the network. Absolute Gain - 1. Of an antenna, for a given direction and polarization, the ratio of (a) the power that would be required at the input of an ideal isotropic radiator to (b) the power actually supplied to the given antenna, to produce the same radiation intensity in the far-field region. Note 1: If no direction is given, the absolute gain of an antenna corresponds to the direction of maximum effective radiated power. Note 2: Absolute gain is usually expressed in dB. Synonym isotropic gain. 2. Of a device, the ratio of (a) the signal level at the output of the device to (b) that of its input under a specified set of operating conditions. Note 1: Examples of absolute gain are no-load gain, full-load gain, and small-signal gain. Note 2: Absolute gain is usually expressed in dB. Absolute Temperature - See thermodynamic temperature. - A measure, in kelvins (K), proportional to the thermal energy of a given body at equilibrium. Note 1: A temperature of 0 K is called "absolute zero," and coincides with the minimum molecular activity (i.e., thermal energy) of matter. Note 2: Thermodynamic temperature was formerly called "absolute temperature." Note 3: In practice, the International Temperature Scale of 1990 (ITS-90) serves as the basis for high-accuracy temperature measurements in science and technology. Absorptance - The ratio of the luminous flux or absorbed radiant flux to the incident flux. Absorption - In the transmission of electrical, electromagnetic, or acoustic signals, the conversion of the transmitted energy into another form, usually thermal. Note 1: Absorption is one cause of signal attenuation . Note 2: The conversion takes place as a result of interaction between the incident energy and the material medium, at the molecular or atomic level. Absorption Band - A spectral region in which the absorption coefficient reaches a relative maximum, by virtue of the physical properties of the matter in which the absorption process takes place. Absorption Coefficient - A measure of the attenuation caused by absorption of energy that results from its passage through a medium. Note 1: Absorption coefficients are usually expressed in units of reciprocal distance. Note 2: The sum of the absorption coefficient and the scattering coefficient is the attenuation coefficient. 2
- 3. Absorption Index - 1. A measure of the attenuation caused by absorption of energy per unit of distance that occurs in an electromagnetic wave of given wavelength propagating in a material medium of given refractive index. Absorption Loss - That part of the transmission loss caused by the dissipation or conversion of electrical, electromagnetic, or acoustic energy into other forms of energy as a result of its interaction with a material medium. Absorption Modulation - Amplitude modulation of the output of a radio transmitter by means of a variable- impedance circuit that is caused to absorb carrier power in accordance with the modulating wave. Absorption Peak - 1. The wavelength or frequency at which a particular substance absorbs the most power (or, where the attenuation of the propagated signal is the greatest) whenever the substance is bombarded or irradiated with audio, electromagnetic, or light waves. Note: Whenever a material is thus bombarded, there is reflection, transmission through the material, and absorption within the material. In the case of air, O2 has multiple absorption peaks. See figure. 2. In optical communications media, the specific wavelength at which a particular impurity absorbs the most power, i.e., causes a maximum attenuation of propagated lightwaves. Note: Absorption by these impurities at other wavelengths is less than that of the absorption peak. Glass quartz silica, and plastics used in optical fibers, slab dielectric waveguides, optical integrated circuits (OICs), and similar media, usually display absorption peaks. Impurities that cause absorption peaks include copper, iron, nickel, chromium, manganese, and hydroxyl ions. Absorptivity - Of a material propagation medium, absorptance per unit path length. Abstraction - 1. Broadly, the use of specialized software, such as an application programming interface (API), as a means of shielding software from device dependencies or the complexities of underlying software. Note: For instance, hardware abstraction enables programs to focus on a task, such as communications, instead of on individual differences between communications devices. 2. In object-oriented programming, the process of reducing an object to its essence so that only the necessary elements are represented. Abstraction defines an object in terms of its properties (attributes), behaviors (functionality), and interface (means of communicating with other objects). Abstract Syntax - In open systems architecture, the specification of application-layer data or application- protocol control information by using notation rules that are independent of the encoding technique used to represent the information. Abstract Syntax Notation One (ASN.1) - A standard, flexible method that (a) describes data structures for representing, encoding, transmitting, and decoding data, (b) provides a set of formal rules for describing the structure of objects independent of machine-specific encoding techniques, (c) is a formal network- management Transmission Control Protocol / Internet Protocol (TCP/IP) language that uses human-readable notation and a compact, encoded representation of the same information used in communications protocols, and (d) is a precise, formal notation that removes ambiguities. AC - Abbreviation for alternating current. AC Current - In electricity, alternating current (AC) occurs when charge carriers in a conductor or semiconductor periodically reverse their direction of movement. Household utility current in most countries is AC with a frequency of 60 hertz (60 complete cycles per second), although in some countries it is 50 Hz. The radio-frequency (RF) current in antennas and transmission lines is another example of AC. An AC waveform can be sinusoidal, square, or sawtooth-shaped. Some AC waveforms are irregular or complicated. An example of sine-wave AC is common household utility current (in the ideal case). Square or 3
- 4. sawtooth waves are produced by certain types of electronic oscillators, and by a low-end uninterruptible power supply (UPS) when it is operating from its battery. Irregular AC waves are produced by audio amplifiers that deal with analog voice signals and/or music. The voltage of an AC power source can be easily changed by means of a power transformer. This allows the voltage to be stepped up (increased) for transmission and distribution. High-voltage transmission is more efficient than low-voltage transmission over long distances, because the loss caused by conductor resistance decreases as the voltage increases. The voltage of an AC power source changes from instant to instant in time. The effective voltage of an AC utility power source is usually considered to be the DC voltage that would produce the same power dissipation as heat assuming a pure resistance. The effective voltage for a sine wave is not the same as the peak voltage. To obtain effective voltage from peak voltage, multiply by 0.707. To obtain peak voltage from effective voltage, multiply by 1.414. For example, if an AC power source has an effective voltage of 117 V, typical of a household in the United States, the peak voltage is 165 V. Accept -In data transmission, an Accept is the condition assumed by a primary or secondary station upon correct receipt of a frame for processing. Acceptance - The condition that exists when a system or functional unit meets the specified performance and security requirements. Access - 1. The ability and means necessary to store data in, to retrieve data from, to communicate with, or to make use of any resource of a system. 2. To obtain the use of a resource. 3. (COMSEC) [The] capability and opportunity to gain detailed knowledge of or to alter information or material. 4. (AIS) [The] ability and means to communicate with (i.e., input to or receive output from), or otherwise make use of any information, resource, or component in an AIS. Note [for 3 and 4]: An individual does not have "access" if the proper authority or a physical, technical, or procedural measure prevents him/her from obtaining knowledge or having an opportunity to alter information, material, resources, or components. 5. An assigned portion of system resources for one data stream of user communications or signaling. 6. [An] opportunity to make use of an information-system (IS) resource. Access Arrangement - An arrangement to transport access traffic between an end office and an IC POT (interexchange carrier point of termination) and may be either direct routed, tandem routed, or a combination of direct and tandem routed. (In the case of direct routed only, the access arrangement and access connection are synonymous.) Acceptance Angle - In fiber optics, half the vertex angle of that cone within which optical power may be coupled into bound modes of an optical fiber. Note 1: The axis of the cone is collinear with the fiber axis, the vertex of the cone is on the fiber end-face, and the base of the cone faces the optical power source. Note 2: The acceptance angle is measured with respect to the fiber axis. Note 3: Rays entering an optical fiber at angles greater than the acceptance angle are coupled into unbound modes. Acceptance Cone - In fiber optics, the cone within which optical power may be coupled into the bound modes of an optical fiber. Note: The acceptance cone is derived by rotating the acceptance angle about the fiber axis. Acceptance Criterion - See acceptance test. A test of a system or functional unit to ensure that contractual requirements are met. Note: An acceptance test may be performed at the factory or user premises by the user, vendor, or a third party. 4
- 5. Acceptance Limit (AL) - The bound on performance that is allowed at service turnup or interexchange carrier (IC) acceptance of a circuit or connection, or when corrective action is taken to restore a parameter after an immediate action limit (IAL) failure. Performance as measured by a parameter is satisfactory if the value of the parameter is equal to or better than the limit. Acceptance Pattern - 1. Of an antenna, for a given plane, a distribution plot of the off-axis power relative to the on-axis power as a function of angle or position. Note: The acceptance pattern is the equivalent of a horizontal or vertical antenna pattern. 2. Of an optical fiber or fiber bundle, a curve of total transmitted power plotted against the launch angle. Acceptance Test - A test of a system or functional unit to ensure that contractual requirements are met. Note: An acceptance test may be performed at the factory or user premises by the user, vendor, or a third party. Acceptance Testing - Operating and testing of a communication system, subsystem, or component, to ensure that the specified performance characteristics have been met. Acceptance Trial - A trial carried out by nominated representatives of the eventual military users of the weapon or equipment to determine if the specified performance and characteristics have been met. Accepted Interference - Interference at a higher level than that defined as permissible interference and which has been agreed upon between two or more administrations without prejudice to other administrations. Access - 1. The ability and means necessary to store data in, to retrieve data from, to communicate with, or to make use of any resource of a system. 2. To obtain the use of a resource. 3. (COMSEC) [The] capability and opportunity to gain detailed knowledge of or to alter information or material. [NIS] 4. (AIS) [The] ability and means to communicate with (i.e., input to or receive output from), or otherwise make use of any information, resource, or component in an AIS. Note [for 3 and 4]: An individual does not have "access" if the proper authority or a physical, technical, or procedural measure prevents him/her from obtaining knowledge or having an opportunity to alter information, material, resources, or components. [NIS] 5. An assigned portion of system resources for one data stream of user communications or signaling. 6. [An] opportunity to make use of an information-system (IS) resource. Access is commonly defined as the process used for communication between your computer and the Internet. Access is simply being able to get to what you need. Data access is being able to get to (usually having permission to use) particular data on a computer. Web access means having a connection to the World Wide Web through an access provider or an online service provider such as America Online. For data access, access is usually specified as read-only access and read/write access. Access Attempt - The process by which one or more users interact with a telecommunications system to enable initiation of user information transfer. Note: An access attempt begins with an issuance of an access request by an access originator. An access attempt ends either in successful access or in access failure. Access Barred Signal - In a communications system, a signal sent in the backward direction to indicate that a call will not be completed because of a call-originator or a call-receiver facility requirement. Note: An access barred signal may occur for many reasons, such as the failure of a closed user group validation check on an incoming calls-barred facility. 5
- 6. Access Category - A class to which a user, such as a person, program, process, or equipment, of a system may be assigned, based on the resources each user is authorized to use. Access Channel - A designated part of the information transfer capability having specified characteristics, provided at the user-network interface. Access Charge - 1. A fee charged by a local exchange carrier for the use of its local exchange networks. 2. A charge made by a local exchange carrier for use of its local exchange facilities for a purpose such as the origination or termination of traffic that is carried to or from a distant exchange by an interexchange carrier. Access Code - 1. The preliminary digits that a user must dial to be connected to a particular outgoing trunk group or line. 2. A uniform code assigned by the telephone company to an individual customer in the form 101xx and 950-xx. Access Connection - In ISDN technology, a connection (using either the B-Channel or a logical link on the D- Channel) established between the user equipment and a packet-mode handier function, over which packet- mode calls (incoming and outgoing) are established. Access Contention - In ISDN applications, synonym contention. - 1. A condition that arises when two or more data stations attempt to transmit at the same time over a shared channel, or when two data stations attempt to transmit at the same time in two-way alternate communication. Note: A contention can occur in data communications when no station is designated a master station. In contention, each station must monitor the signals and wait for a quiescent condition before initiating a bid for master status. 2. Competition by users of a system for use of the same facility at the same time. Access Control - 1. A service feature or technique used to permit or deny use of the components of a communication system. 2. A technique used to define or restrict the rights of individuals or application programs to obtain data from, or place data onto, a storage device. 3. The definition or restriction of the rights of individuals or application programs to obtain data from, or place data into, a storage device. 4. Limiting access to information system resources only to authorized users, programs, processes, or other systems.5. That function performed by the resource controller that allocates system resources to satisfy user requests. Access Control List - 1. In security, a list of entities, together with their access rights, that are authorized to access a resource. 2. [A] mechanism implementing discretionary and/or mandatory access control between subjects and objects. Access Control Mechanism - 1. In security, a hardware, software, or firmware feature, operating procedure, or management procedure that (a) permits authorized access to a system, such as a communications, computer, and data processing system, (b) prevents unauthorized access to the system, and (c) is considered to have failed when unauthorized access is permitted or when authorized access is prevented. 2. [A] Security safeguard designed to detect and deny unauthorized access and permit authorized access in an information system (IS). Access Control Message - A message that is a user request, a resource controller response, or a request/response between resource controllers. Access Coupler - Deprecated term. See directional coupler. Access Denial - 1. Access failure caused by the issuing of a system blocking signal by a communications system that does not have a call-originator camp-on feature. 2. Access failure caused by exceeding the 6
- 7. maximum access time and nominal system access time fraction during an access attempt. Synonym system blocking. Access-Denial Time - The time between the start of an access attempt and access failure caused by access denial, i.e., system blocking. Note: Access denial times are measured only on access attempts that result in access denial. Access Digit - In automatic direct outward telephone dialing, a digit, often a 1, or a 9, that (a) enables access to an outside facility, e.g., a PBX or local exchange, and (b) is prefixed to the specific number being dialed. Note 1: Throughout the United States, an access digit, usually 1, must be prefixed to an area code before dialing the area code and the specific number to which a connection is desired. Note 2: The access digit 9 is often used to establish a connection between a PBX and a local exchange. Access Failure - In a communications system, an unsuccessful access that results in termination of an access attempt in any manner other than initiation of user information transfer between the intended source and destination (sink) within the specified maximum access time. Note: Access failure can be the result of access denial, access outage, user blocking, or incorrect access. Access Function - A set of processes in a network that provides for interaction between the user and a network. Access Group - A group of one or more stations having identical rights to use the available resources on a PBX, network or host computer. Access Level - 1. In security, the level of authority required from an entity to access a protected resource. Note: An example of access level is the authority to access information at a particular security level. 2. [The] hierarchical portion of the security level used to identify sensitivity of information-system (IS) data and the clearance or authorization of users. Access level, in conjunction with the nonhierarchical categories, forms the sensitivity label of an object. Access Line - 1. A transmission path between end user terminal equipment and a switching center. 2. A channel between an end user's network interface and local end office. Synonym [loosely] loop. 3. A communications facility extending from a customer's premises to a serving central office comprising a subscriber line and, if necessary, a trunk facility, e.g., a WATS access line, TWX access line. Access Lines - A telephone line running from the telephone company’s central office to a point on your property. Access Line Equivalents - A representation of the number of access lines that a system could hold. Access List - 1. In information systems (IS), a compilation of users, programs, or processes and the access levels and types to which each is authorized. 2. In COMSEC, a roster of persons authorized admittance to a controlled area. Access Loop - See attendant access loop. Access Node - In switching systems, the point where user traffic enters and exits a communications network. Note: Access node operations may include various operations, such as protocol conversion and code conversion. 7
- 8. Access Originator - The functional entity responsible for initiating a particular access attempt. Note: An access attempt can be initiated by a source user, a destination user, or the telecommunications system. Access Path - The steps required to obtain the use of a system or device. Note: Examples of access paths are (a) the operations required of a database management system to obtain access to a database and (b) the sequence of steps required to reach a file. Access Period - In security, a segment of time, generally expressed in days or weeks, during which specified access rights prevail. Access Permission - All of a subject's access rights with respect to some object. Access Phase - In an information-transfer transaction, the phase during which an access attempt is made. Note: The access phase is the first phase of an information-transfer transaction. Access Point - 1. A point where connections may be made for testing or using particular communications circuits. 2. In telephony, a junction point in outside plant consisting of a splice at a junction between a branch feeder cable and distribution cables. Access Profile - 1. In security, a profile that associates each user with a list of protected objects that the user may access. 2. [An itemization that] associates each user with a list of protected objects the user may access. Access Provider - 1. An organization that provides users with access to a computer network. Any organization that arranges for an individual or an organization to have access to the Internet. Access providers are generally divided into two classes: Internet access providers (ISPs) and online service providers (OSPs). ISPs can be local businesses that pay for a high-speed connection to one of the companies (such as AT&T, Sprint, or MCI in the U.S.) that are part of the Internet. They can also be national or international companies that have their own networks (such as AT&T's WorldNet or IBM's Global Services). OSPs, sometimes just called "online services," also have their own networks but provide additional information services not available to non-subscribers. America Online is the most successful example of an OSP. 2. A party responsible for traffic originating and terminating in jurisdictional areas defined by regulatory agencies. Access Request - 1. A control message issued by an access originator for the purpose of initiating an access attempt. 2. A signal sent to a network for the purpose of initiating the establishment of a network connection. In this definition, a signal may take the form of a message. Access Right - Permission for a subject to access a particular object for a specific type of operation. Note: An example of an access right is the permission for a process to read a file but not write to it. Access Service Area - A geographic area established for the provisioning and administration of telecommunications service. An access service area encompasses one or more exchanges, which are grouped in access service areas to serve common social, economic, and other purposes. Contrast with LATA. Access System - In communications, computer, and data processing systems, a program that (a) allows an operator to call up different parts of the program package and (b) usually allows functions to be selected from menus in the same way as other commands. Note: An example of an access system is the program supplied with a common spreadsheet program that (a) allows the computer to shift between the spreadsheet program and a graph-printing facility and (b) provides access to various support functions. Access Tandem - 1. A telephone company or centralized equal access provider switching system that provides a concentration and distribution function for originating or terminating traffic between end offices 8
- 9. and a customer-designated premises. 2. An exchange carrier switching system that provides a traffic concentration and distribution function for inter-LATA traffic originating/terminating within a LATA. Access Time - 1. In a telecommunication system, the elapsed time between the start of an access attempt and successful access. Note: Access time values are measured only on access attempts that result in successful access. 2. In a computer, the time interval between the instant at which an instruction control unit initiates a call for data and the instant at which delivery of the data is completed. 3. The time interval between the instant at which storage of data is requested and the instant at which storage is started. 4. In magnetic disk devices, the time for the access arm to reach the desired track and the delay for the rotation of the disk to bring the required sector under the read-write mechanism. Access Type - 1. In computer security, a type of operation specified by an access right. Note: Examples of access type are "read," "write," "execute," "append," "modify," "delete," and "create." [2382-pt.8] 2. [The] privilege to perform action on an object. Read, write, execute, append modify, delete, and create are examples of access types. Access Unit - See medium access unit (MAU). Access Unit Interface - Synonym attachment unit interface. Acceptability - Section 508, an amendment to the United States Workforce Rehabilitation Act of 1973, is a federal law mandating that all electronic and information technology developed, procured, maintained, or used by the federal government be accessible to people with disabilities. Technology is deemed to be "accessible" if it can be used as effectively by people with disabilities as by those without. To demonstrate that a product or Web service is in compliance with Section 508, the creator completes a Voluntary Product Accessibility Template (VPAT), an "informational tool" that describes exactly how the product or service does or does not meet Section 508 standards. The completed VPAT gets posted on the creator's Web site to provide government officials and consumers with access to the information. The scope of Section 508 is limited to the federal sector. It includes binding, enforceable standards, as well as compliance reporting requirements and a complaint procedure. Section 508 doesn't apply to the private sector, nor does it impose requirements on the recipients of federal funding. Because the federal government has so much purchasing power, however, it is hoped that Section 508 will encourage the dev elopement of products and Web-based services that meet accessibility standards. To that end, the United Stated Department of Education now requires states funded by the Assitive Technology Act State Grant program (a grant program that supports consumer-driven state projects to improve access to assistive technology devices and services) to comply with Section 508. Accessibility policies like Section 508 vary from country to country, but most countries, including the European Union (EU), have adopted standards based on the Web Content Accessibility Guidelines of the World Wide Web Consortium. Section 508 is based on W3C Priority 1 checkpoints. Accountability - 1. The property that ensures that the actions of an individual or an institution may be traced uniquely to that individual or institution. 2. In information systems (IS), the process of tracing IS activities to a responsible source.3. In COMSEC, the principle that an individual is entrusted to safeguard and control equipment, keying material, and information and is answerable to proper authority for the loss or misuse of that equipment or information. Accounting Management - In network management, a set of functions that (a) enables network service use to be measured and the costs for such use to be determined and (b) includes all the resources consumed, the facilities used to collect accounting data, the facilities used to set billing parameters for the services used 9
- 10. by customers, maintenance of the data bases used for billing purposes, and the preparation of resource usage and billing reports. Accreditation - 1. In computer security, the authorization and approval--granted by a designated authority to a data processing system, computer network, organization, or individual--to process sensitive information or data. 2. Formal declaration by a designated approving authority that an information system (IS) is approved to operate in a particular security mode using a prescribed set of safeguards at an acceptable level of risk. Accrediting Authority - Synonym designated approving authority. Accumulator - 1. A register in which one operand can be stored and subsequently replaced by the result of an arithmetic or logic operation. 2. A storage register. 3. A storage battery. Accuracy - The degree of conformity of a measured or calculated value to its actual or specified value. AC Current - Alternating Current. ACD - Automatic Call Distributor AC-DC Ringing - Telephone ringing that makes use of both ac and dc voltages and currents. Note: An alternating current may be used to operate a ringer and direct current to aid the relay action that stops the ringing when the called telephone is answered. Achromat - A usually two-element lens that is corrected to bring two specified or distinct wavelengths to a common focal point. Note 1: The term "achromatic" literally means "without color." This is not strictly true, however. Early lenses consisted of only a single element, and therefore could bring only a single wavelength to a given focal point; i.e., they suffered from what is termed "chromatic aberration." The invention of lenses with two elements meant that two distinct wavelengths could be brought to a common focus. This represented a vast improvement over the single-element lens; hence the designation "achromat(ic)." Note 2: The residual chromatic aberration manifested in the image produced by an achromat (and other multi- element lenses) is usually referred to as the "secondary spectrum." Synonyms achromatic doublet, achromatic lens. Achromatic Double - Synonym achromat. Achromatic Doublet - Synonym achromat. Achromatic Lens - Synonym achromat. ACK - Abbreviation for acknowledge character. Acknowledge Character (ACK): A transmission control character transmitted by the receiving station as an affirmative response to the sending station. Note: An acknowledge character may also be used as an accuracy control character. Acknowledgement - 1. A response sent by a receiver to indicate successful receipt of a transmission. Note: An example of an acknowledgement is a protocol data unit, or element thereof, between peer entities, to indicate the status of data units that have been successfully received. 2. A message from the addressee informing the originator that the originator's communication has been received and understood. Acknowledgement Delay Period - Synonym [loosely] sliding window. 10
- 11. A-Condition - In a start-stop teletypewriter system, the significant condition of the signal element that immediately precedes a character signal or block signal and prepares the receiving equipment for the reception of the code elements. Acoustic Coupler - 1. An interface device for coupling electrical signals by acoustical means--usually into and out of a telephone instrument. An acoustic coupler is a hardware device that enables a modem (a device that converts signals from analog to digital and from digital back to analog) to connect to a voice circuit. A handset adapter is used to receive modem tones through the handset's mouthpiece, and the earpiece is used to transmit these tones to the modem. 2. A terminal device used to link data terminals and radio sets with the telephone network. Note: The link is achieved through acoustic (sound) signals rather than through direct electrical connection. Acoustic Delay Line - A device that introduces a delay in the propagation of an electrical signal by (a) employing a transducer to convert the signal into an acoustic wave, (b) propagating the acoustic wave through a medium such as a column of mercury or a carbon or ferrite rod, and (c) by means of another transducer, converting the acoustic wave back to an electrical signal. Note: An acoustic delay line may be used for temporary storage of information, e.g., a digital data stream. Acoustic Noise - 1. An undesired audible disturbance in the audio frequency range. 2. Any undesired acoustic wave or signal, or undesired component of a desired acoustic signal, whether or not audible to the human ear; e.g., interference accompanying a sonar echo. Acoustics - The branch of science and technology that is devoted to the production, transmission, control, processing, transformation, reception, and effects of sound, longitudinal waves, particularly as vibration, pressure, or elastic waves and shock phenomena in material media. Acoustic Wave - (See Sound Wave) A longitudinal wave that (a) consists of a sequence of pressure pulses or elastic displacements of the material, whether gas, liquid, or solid, in which the wave propagates, (b) in gases, consists of a sequence of compressions (dense gas) and rarefactions (less dense gas) that travel through the gas, (c) in liquids, consists of a sequence of combined elastic deformation and compression waves that travel though the liquid, and (d) in solids, consists of a sequence of elastic compression and expansion waves that travel though the solid. Note 1: The speed of an acoustic wave in a material medium is determined by the temperature, pressure, and elastic properties of the medium. In air, acoustic waves propagate at 332 m/s (1087 ft/s) at 0°C, at sea level. In air, sound-wave speed increases approximately 0.6 m/s (2 ft/s) for each kelvin above 0°C. Note 2: Acoustic waves audible to the normal human ear are termed sound waves. Acousto-Optic Effect - A variation of the refractive index of a material caused by interaction with acoustic energy in the form of a wave or pulse. Note: The acousto-optic effect is used in devices that modulate or deflect light. Acousto-Optics - The discipline devoted to the interactions between acoustic waves and light waves in a material medium. Note: Acoustic waves can be made to modulate, deflect, and/or focus light waves by causing a variation in the refractive index of the medium. Acquisition - 1. In satellite communications, the process of locking tracking equipment on a signal from a communications satellite. 2. The process of achieving synchronization. 3. In servo systems, the process of entering the boundary conditions that will allow the loop to capture the signal and achieve lock-on. Acquisition and Tracking Orderwire: See ATOW. 11
- 12. Acquisition Time - 1. In a communications system, the time interval required to attain synchronism. 2. In satellite control communications, the time interval required for locking tracking equipment on a signal from a communications satellite. ACR - Abbreviation for alternate carrier routing and also for anonymous call rejection. Active Device - A device that requires a source of energy for its operation and has an output that is a function of present and past input signals. Note: Examples of active devices include controlled power supplies, transistors, LEDs, amplifiers, and transmitters. Active Key State - A condition of readiness for a key to be used to secure information from the originator, and to process received secure information. Active Laser Medium - Within a laser, the material that emits coherent radiation or exhibits gain as the result of electronic or molecular transitions to a lower energy state or states, from a higher energy state or states to which it had been previously stimulated. Note: Examples of active laser media include certain crystals, gases, glasses, liquids, and semiconductors. Synonym laser medium. Active Satellite - 1. A satellite carrying a station intended to transmit or retransmit radio communication signals. Note: An active satellite may perform signal processing functions such as amplification, regeneration, frequency translation, and link switching, to make the signals suitable for retransmission. 2. An Earth satellite carrying a station intended to transmit or re-transmit radio communication signals. Active Sensor - 1. A detection device that requires input energy from a source other than that which is being sensed. Note: An example of an active sensor is a photoconductive cell. 2. In surveillance, a detection device that emits energy capable of being detected by itself. Note: An example of an active sensor is a measuring instrument that generates a signal, transmits it to a target, and receives a reflected signal from the target. Information concerning the target is obtained by comparison of the received signal with the transmitted signal. 3. A measuring instrument in the Earth exploration-satellite service or in the space research service by means of which information is obtained by transmission and reception of radio waves. Active Signaling Link - A signaling link that has successfully completed the initial alignment procedures and carries (or is ready to carry) signaling traffic. Active Star - See star coupler, multiport repeater. Active Threat - Any threat of a deliberate unauthorized change to the state of a data processing system. Note: For example, an active threat that would result in modification of messages, insertion of spurious messages, masquerade, or denial of service. Active Video Frame Identification - The process of comparing each output video frame with its preceding frame(s) in sequence and quantifying the extent of correspondence between each pair; when there is limited correspondence between a pair of frames (such that the differences measured are distinguishable from the measurement noise), and the corresponding input sequence of frames possesses distinguishable differences, then the current frame is categorized as an active frame. Activity Factor - For a communications channel during a specified time interval, such as the busy hour, the percentage of time that a signal is present in the channel in either direction. 12
- 13. Activity Report - A printed report of a unit's incoming and out-going transactions. It may be printed automatically on demand or manually at a specified interval. Information may include date and time of transmission, the fax number/name, duration, number of pages, and result errors incurred, and comment. ACTS (Automatic Coin Telephone System) - A public coin-operated telephone service that completes a variety of phone calls, times the calls, and collects payment without the aid of an operator. ACU - Abbreviation for automatic calling unit. A-D - Abbreviation for analog-to-digital. See analog transmission. Ad-Hoc Network (or "spontaneous") - A local area network or other small network, especially one with wireless or temporary plug-in connections, in which some of the network devices are part of the network only for the duration of a communications session or, in the case of mobile or portable devices, while in some close proximity to the rest of the network. In Latin, ad hoc literally means "for this," further meaning "for this purpose only," and thus usually temporary. The term has been applied to future office or home networks in which new devices can be quickly added, using, for example, the proposed Bluetooth technology in which devices communicate with the computer and perhaps other devices using wireless transmission. Adapter - A physical device that allows one hardware or electronic interface to be adapted (accommodated without loss of function) to another hardware or electronic interface. In a computer, an adapter is often built into a card that can be inserted into a slot on the computer's motherboard. The card adapts information that is exchanged between the computer's microprocessor and the devices that the card supports. Adaptive Compression - In computer science, a software-oriented compression process based on continuous analysis of the data stream, and depending on the type and content of the data and the storage medium, corresponding compensation of the compression algorithm. Adaptive Prediction - In ADPCM coding, a time-varying process that computes an estimate of the input signal from the quantized difference signal. Adaptive Quantization - In ADPCM (adaptive differential pulse code modulation) coding, a process in which the quantizer step size varies as a function of the quantized input signal's variance. Ada ® - The official, high-level computer language of DOD for embedded-computer, real-time applications as defined in MIL-STD-1815. Note: Ada® is a registered trademark of the U.S. Government (Ada Joint Program Office). Adaptive Communications - Any communications system, or portion thereof, that automatically uses feedback information obtained from the system itself or from the signals carried by the system to modify dynamically one or more of the system operational parameters to improve system performance or to resist degradation. Note: The modification of a system parameter may be discrete, as in hard-switched diversity reception, or may be continuous, as in a predetection combining algorithm Adaptive Channel Allocation - In communications system traffic flow control, channel allocation in which information-handling capacities of channels are not predetermined but are assigned on demand. Note: Adaptive channel allocation is usually accomplished by means of a multiplexing scheme. Adaptive Differential Pulse-Code Modulation (ADPCM) - Differential pulse-code modulation in which the prediction algorithm is adjusted in accordance with specific characteristics of the input signal. 13
- 14. Adaptive Equalization - Equalization (a) that is automatically accomplished while traffic is being transmitted and (b) in which signal characteristics are dynamically adjusted to compensate for changing transmission path characteristics. Adaptive Predictive Coding (APC) - Narrowband analog-to-digital conversion that uses a one-level or multilevel sampling system in which the value of the signal at each sampling instant is predicted according to a linear function of the past values of the quantized signals. Note: APC is related to linear predictive coding (LPC) in that both use adaptive predictors. However, APC uses fewer prediction coefficients, thus requiring a higher sampling rate than LPC. Adaptive Radio - A radio that (a) monitors its own performance, (b) monitors the path quality through sounding or polling, (c) varies operating characteristics, such as frequency, power, or data rate, and (d) uses closed-loop action to optimize its performance by automatically selecting frequencies or channels. Adaptive Routing - Routing that is automatically adjusted to compensate for network changes such as traffic patterns, channel availability, or equipment failures. Note: The experience used for adaptation comes from the traffic being carried. Adaptive System - A system that has a means of monitoring its own performance, a means of varying its own parameters, and uses closed-loop action to improve its performance or to optimize traffic. ADC - Abbreviation for analog-to-digital converter, analog-to-digital conversion. ADCCP - Abbreviation for Advanced Data Communication Control Procedures. - A bit-oriented Data-Link- Layer protocol used to provide point-to-point and point-to-multipoint transmission of data frames that contain error-control information. Note: ADCCP closely resembles high-level data link control (HDLC) and synchronous data link control (SDLC). Ad Clicks - Synonym click-through. - The process of clicking on a Web advertisement and going directly to the advertiser's Web site. Synonyms clicks, requests. Add/drop Multiplexing - A multiplexing function offered in connection with SONET that allows lower level signals to be added or dropped from a high-speed optical carrier channel in a wire center. The connection to the add/ drop multiplexer is via a channel to a central office port at a specific digital speed (i.e., DS3, DS1, etc.). Added Bit - A bit delivered to the intended destination user in addition to intended user information bits and delivered overhead bits. Synonym extra bit. Added Block - Any block, or other delimited bit group, delivered to the intended destination user in addition to intended user information bits and delivered overhead bits. Synonym extra block. Adder - 1. A device whose output data are a representation of the sum of the numbers represented by its input data. Note: An adder may be serial or parallel, digital or analog. 2. A device whose output data are a representation of the sum of the quantities represented by its input data. Note: An adder can add things other than representations of numbers. It can add voltages, etc. Analog adders are not limited to summing representations of numbers. An adder may operate on digital or analog data. Adder-Subtracter - A device that acts as an adder or subtracter depending upon the control signal received; the adder-subtracter may be constructed so as to yield a sum and a difference at the same time. Note: An 14
- 15. arithmetic adder-subtracter yields arithmetic sums and differences, whereas a logical adder-subtracter yields logical sums and differences. Additive White Gaussian Noise (AWGN) - Synonym white noise. Add Mode - In addition and subtraction operations, a mode in which the decimal marker is placed at a predetermined location with respect to the last digit entered. Add-On Conference - A service feature that allows an additional party to be added to an established call without attendant assistance. Note: A common implementation provides a progressive method that allows a call originator or a call receiver to add at least one additional party. Address - 1. In communications, the coded representation of the source or destination of a message. 2. In data processing, a character or group of characters that identifies a register, a particular part of storage, or some other data source or destination. 3. To assign to a device or item of data a label to identify its location. 4. The part of a selection signal that indicates the destination of a call. 5. To refer to a device or data item by its address. Addressability - 1. In computer graphics, the capability of a display surface or storage device to accommodate a specified number of uniquely identifiable points. 2. In micrographics, the capability of a specified field frame to contain a specific number of uniquely identifiable points. Note: The addressability is usually specified as the number of identifiable horizontal points by the number of identifiable vertical points, such as 3000 by 4000. Addressable Point - In computer graphics, any point of a device that can be addressed. Address Field - The portion of a message that contains the source-user address and the destination-user addresses. Note: In a communications network, the address field is usually contained within the message header portion of the message. A message usually consists of the message header, the user data, and a trailer. Address-Indicating Group (AIG) - A station or address designator, used to represent a set of specific and frequently recurring combinations of action or information addresses. Note: The identity of the message originator may also be included in the AIG. An address group is assigned to each AIG for use as an address designator. Address Message - A message sent in the forward direction that contains (a) address information, (b) the signaling information required to route and connect a call to the called line, (c) service-class information, (d) information relating to user and network facilities, and (e) call-originator identity or call-receiver identity. Address Message Sequencing - In common-channel signaling, a procedure for ensuring that address messages are processed in the correct order when the order in which they are received is incorrect. Address Part - A part of an instruction that usually contains only an address or part of an address. Address Pattern - A prescribed structure of data used to represent the destination(s) of a block, message, packet, or other formalized data structure. Address Resolution Protocol (ARP) - A Transmission Control Protocol / Internet Protocol (TCP/IP) protocol that dynamically binds a Network-Layer IP address to a Data-Link-Layer physical hardware address, e.g., Ethernet address. 15
- 16. Address Separator - A character that separates the different addresses in a selection signal. Address Signaling - A process used to convey address information; two address signaling methods, dial pulse (DP) and dual tone multi frequency (DTMF), are used in telephone systems. Addressable Call Endpoint - a device that can originate or receive a call in a telephone network. In voice over IP (VoIP), addressable call endpoints can be categorized as either voice-network dial peers or POTS (plain old telephone service) dial peers. Voice-network dial peers include VoIP-capable computers, routers, and gateways within a network. POTS dial peers include traditional telephone network devices such as phone sets, cell phones, and fax machines. ADH - Abbreviation for automatic data handling. Adiabatic Computer Circuit - A circuit that avoids loss or gain of heat. For example, a computer could clear a "1" in a register by subtracting the "1" instead of erasing it, thereby expending less heat. Adjacent-Channel Interference - Extraneous power from a signal in an adjacent channel. Note 1: Adjacent channel interference may be caused by inadequate filtering, such as incomplete filtering of unwanted modulation products in frequency modulation (FM) systems, improper tuning, or poor frequency control, in either the reference channel or the interfering channel, or both. Note 2: Adjacent-channel interference is distinguished from crosstalk. Adjacent Signaling Points - Two signaling points that are directly interconnected by one or more signaling links. Adjunct Service Point (ASP) - An intelligent-network feature that resides at the intelligent peripheral equipment and responds to service logic interpreter requests for service processing. Administration - 1. Any governmental department or service responsible for discharging the obligations undertaken in the convention of the International Telecommunication Union and the Regulations. 2. Internal management of units. 3. The management and execution of all military matters not included in strategy and tactics. 4. In international telecommunications for a given country, the government agency assigned responsibility for the implementation of telecommunications standards, regulations, recommendations, practices, and procedures. 5. In network management, network support functions that ensure that (a) services are performed, (b) the network is used efficiently, and (c) prescribed service-quality objectives are met. Administrative Management Complex (AMC) - In network management, a complex that is controlled by a network provider, and is responsible for and performs network management functions such as network maintenance. Adobe Acrobat Reader - A software program developed by Adobe Systems, Inc., used to view files in PDF format. The software displays documents with the same layout and design as the original. ADP - Abbreviation for automatic data processing. ADPCM - Abbreviation for adaptive differential pulse-code modulation. ADPE - Abbreviation for automatic data processing equipment. ADP System - Synonym computer system. 16
- 17. ADSL (Asymmetric Digital Subscriber Line) - A new modem technology that allows existing twisted pair telephone lines to access the Internet at T-1 speeds. A technology for transmitting digital information at a high bandwidth on existing phone lines to homes and businesses. Unlike regular dial up phone service, ADSL provides continously-available, "always on" connection. ADSL is asymmetric in that it uses most of the channel to transmit downstream to the user and only a small part to receive information from the user. ADSL simultaneously accommodates analog (voice) information on the same line. ADSL is generally offered at downstream data rates from 512 Kbps to about 6 Mbps. A form of ADSL, known as Universal ADSL or G.lite, has been approved as a standard by the ITU-TS. ADSL was specifically designed to exploit the one-way nature of most multimedia communication in which large amounts of information flow toward the user and only a small amount of interactive control information is returned. Several experiments with ADSL to real users began in 1996. In 1998, wide-scale installations began in several parts of the U.S. In 2000 and beyond, ADSL and other forms of DSL are expected to become generally available in urban areas. With ADSL (and other forms of DSL), telephone companies are competing with cable companies and their cable modem services. ADSL Modem - An ATU-R (ADSL Terminal Unit - Remote) is a hardware unit that is installed in any computer that uses a telephone company connection with Asymmetric Digital Subscriber Line (ADSL) service. The ATU- R connects to an Ethernet network interface card (NIC) in the computer and, on the other side, to a telephone jack in the home or business. Ideally (for less interference), the telephone jack hooks up to a new wire that goes to a signal splitter that the telephone company installs at the telephone company demarcation point (the place where the outside phone company wire or wires connect to the network of phone lines within the customer's building). The splitter divides the signal into low frequencies for voice and high frequencies for data. Advanced Data Communication Control Procedures (ADCCP) - A bit-oriented Data-Link-Layer protocol used to provide point-to-point and point-to-multipoint transmission of data frames that contain error-control information. Note: ADCCP closely resembles high-level data link control (HDLC) and synchronous data link control (SDLC). Advanced Intelligent Network (AIN) - 1. A telecommunications network architecture that uses databases to facilitate call processing, call routing, and network management, allowing carriers to change the routing of both inbound and outbound calls from moment to moment. [FCC-5] 2. A proposed intelligent-network (IN) architecture that includes both IN/1+ and IN/2 concepts. Advanced Mobile Phone Service (AMPS) - A standard system for analog signal cellular telephone service in the United States and is also used in other countries. It is based on the initial electromagnetic radiation spectrum allocation for cellular service by the Federal Communications Commission (FCC) in 1970. Introduced by AT&T in 1983, AMPS became and currently still is the most widely deployed cellular system in the United States. Advanced Television (ATV) - A family of television systems that is intended to be improvements over current commercial-quality television. Note: The ATV family includes improved-definition television (IDTV), extended-definition television (EDTV), and high-definition television (HDTV). AECS - Abbreviation for Aeronautical Emergency Communications System. See Aeronautical Emergency Communications System Plan. Aerial Cable - A communications cable designed for installation on, or suspension from, a pole or other overhead structure. 17
- 18. Aerial Insert - In a direct-buried or underground cable run, a cable rise to a point above ground, followed by an overhead run, e.g., on poles, followed by a drop back into the ground. Note: An aerial insert is used in places where it is not possible or practical to remain underground, such as might be encountered in crossing a deep ditch, canal, river, or subway line. Aeronautical Advisory Station - An aeronautical station used for advisory and civil defense communications primarily with private aircraft stations. Synonym UNICOM station. Aeronautical Broadcast Station - An aeronautical station which makes scheduled broadcasts of meteorological information and notices to airmen. (In certain instances, an aeronautical broadcast station may be placed on board a ship.) Aeronautical Earth Station - An Earth station in the fixed-satellite service, or, in some cases, in the aeronautical mobile-satellite service, located at a specified fixed point on land to provide a feeder link for the aeronautical mobile-satellite service. Aeronautical Emergency Communications System (AECS) Plan - The AECS Plan provides for the operation of aeronautical communications stations, on a voluntary, organized basis, to provide the President and the Federal Government, as well as heads of state and local governments, or their designated representatives, and the aeronautical industry with an expeditious means of communications during an emergency situation. Aeronautical Fixed Service - A radio communication service between specified fixed points provided primarily for the safety of air navigation and for the regular, efficient and economical operation of air transport. Aeronautical Fixed Station - A station in the aeronautical fixed service. Aeronautical Mobile (OR) [off-route] Service - An aeronautical mobile service intended for communications, including those relating to flight coordination, primarily outside national or international civil air routes. Aeronautical Mobile (R) [route] Service - An aeronautical mobile service reserved for communications relating to safety and regularity of flight, primarily along national or international civil air routes. Aeronautical Mobile-Satellite Service - A mobile-satellite service in which mobile Earth stations are located on board aircraft; survival craft stations and emergency position-indicating radio beacon stations may also participate in this service. Aeronautical Mobile-Satellite (OR) [off-route] Service - An aeronautical mobile-satellite service intended for communications, including those relating to flight coordination, primarily outside national and international civil air routes. Aeronautical Mobile-Satellite (R) [route] Service - An aeronautical mobile-satellite service reserved for communications relating to safety and regularity of flight, primarily along national or international civil air routes. Aeronautical Mobile Service - A mobile service between aeronautical stations and aircraft stations, or between aircraft stations, in which survival craft stations may participate; emergency position-indicating radio beacon stations may also participate in this service on designated distress and emergency frequencies. Aeronautical Multicom Service - A mobile service not open to public correspondence, used to provide communications essential to conduct activities being performed by or directed from private aircraft. 18
- 19. Aeronautical Radionavigation-Satellite Service - A radionavigation-satellite service in which Earth stations are located on board aircraft. Aeronautical Radionavigation Service - A radionavigation service intended for the benefit and for the safe operation of aircraft. Aeronautical Station - A land station in the aeronautical mobile service. In certain instances, an aeronautical station may be located, for example, on board ship or on a platform at sea. AF - Abbreviation for audio frequency. AFNOR - Acronym for Association Francaise de Normalisation. France's national standards-setting organization. AGC - Abbreviation for automatic gain control. Agent - Synonym droid. Aggregation - In security, the acquisition of sensitive information by collecting and correlating information of lesser sensitivity. Aggregator - Any entity that, in the ordinary course of its operations, makes telephones available to the public or to transient users of its premises, for interstate telephone calls using a provider of operator services. AI - Abbreviation for artificial intelligence. AIM - Abbreviation for amplitude intensity modulation. See intensity modulation. AIN - Abbreviation for advanced intelligent network. AIOD - Abbreviation for automatic identified outward dialing. AIOD Leads - Terminal equipment leads used solely to transmit automatic identified outward dialing (AIOD) data from a PBX to the public switched telephone network or to switched service networks (e.g., EPSCS), so that a vendor can provide a detailed monthly bill identifying long-distance usage by individual PBX stations, tie trunks, or the attendant. Airborne Radio Relay - 1. Airborne equipment used to relay radio transmission from selected originating transmitters. 2. A technique employing aircraft fitted with radio relay stations for the purpose of increasing the range, flexibility, or physical security of communications systems. Air-Conditioning - The simultaneous controlling of the characteristics of air, such as temperature, humidity, cleanliness, motion, and pollutant concentration, in a space to meet the requirements of the occupants, a process, or equipment. Synonym environmental control. Aircraft Earth Station - A mobile Earth station in the aeronautical mobile-satellite service located on board an aircraft. Aircraft Emergency Frequency - An international aeronautical emergency frequency, such as 121.5 MHz (civil) and 243.0 MHz (military), for aircraft stations and stations concerned with safety and regulation of 19
- 20. flight along national or international civil air routes and maritime mobile service stations authorized to communicate for safety purposes. Aircraft Station - A mobile station in the aeronautical mobile service, other than a survival craft station, located on board an aircraft. Airdrome Control Station - An aeronautical station providing communication between an airdrome control tower and aircraft. Synonym airport control station. Air-Floating Head - Synonym floating head. Air-Ground Radiotelephone Service - A radio service in which common carriers are authorized to offer and provide radio telecommunications service for hire to subscribers in aircraft. Air-Ground Worldwide Communications System - A worldwide military network of ground stations that (a) provides two-way communications links between aircraft and ground stations for navigation and control, including air route traffic control and (b) may also provide support for special functions, such as for civil aircraft providing assistance to military missions and for meeting communications requirements for aircraft flying distinguished visitors. Air Portable - Denotes materiel that is suitable for transport by an aircraft loaded internally or externally, with no more than minor dismantling and reassembling within the capabilities of user units. This term must be qualified to show the extent of air portability. Airport Control Station - Synonym airdrome control station. Air Sounding - Measuring atmospheric phenomena or determining atmospheric conditions, especially by means of apparatus carried by balloons, rockets, or satellites. Air-Spaced Coaxial Cable - A coaxial cable in which air is the primary dielectric (insulator) between the inner and outer conductors. Note: Proper separation between the inner and outer conductors is maintained by a continuous helical insulator or a series of insulating washers spaced at regular intervals. Air Terminal - In grounding systems, the lightning rod or conductor placed on or above a building, structure, or external conductors for the purpose of intercepting lightning. AIS - Abbreviation for alarm indication signal, automated information system. Alarm - An alerting indication to a condition that may have immediate or potential negative impact on the state of the monitored network element. Alarm Center - A location that receives local and remote alarms. Note: An alarm center is usually in a technical control facility. Alarm Event - An instantaneous occurrence that changes at least one of the attributes of the alarm status of an object. This status change may be persistent or temporary, thus allowing for surveillance, monitoring, and performance measurement functionality, etc. Alarm events may or may not generate alarm reports; they may trigger other events or may be triggered by one or more other events. Alarm Indication Signal (AIS) - 1. A signal transmitted in lieu of the normal signal to maintain transmission continuity and to indicate to the receiving equipment that there is a transmission interruption located either 20
- 21. at the equipment originating the AIS signal or upstream of that equipment. 2. A signal transmitted in lieu of the normal signal to maintain transmission continuity and indicate to the receiving terminal that there is a transmission fault located either at the transmitting terminal or upstream of the transmitting terminal. Alarm Indicator - A device that responds to a signal from an alarm sensor. Note: Examples of alarm indicators include bells, lamps, horns, gongs, and buzzers. Alarm Sensor - 1. In communications systems, any device that (a) can sense an abnormal condition within the system and provide a signal indicating the presence or nature of the abnormality to either a local or remote alarm indicator, and (b) may detect events ranging from a simple contact opening or closure to a time-phased automatic shutdown and restart cycle. 2. In a physical security system, an approved device used to indicate a change in the physical environment of a facility or a part thereof. Note: Alarm sensors may also be redundant or chained, such as when one alarm sensor is used to protect the housing, cabling, or power protected by another alarm sensor. Alarm Status - A set of attributes that describes the alarms currently defined for an object, for example, perceived severity, alarm state, etc. The alarm status of an object is a subset of the global status of that object. Alarm Surveillance - A set of functions that enables the monitoring or interrogation (or both) of the telecommunications network concerning alarm-related events or conditions. A-law - See a-law algorithm. A-Law Algorithm - A standard compression algorithm, used in digital communications systems of the European digital hierarchy, to optimize, i.e., modify, the dynamic range of an analog signal for digitizing. Note: The wide dynamic range of speech does not lend itself well to efficient linear digital encoding. A-law encoding effectively reduces the dynamic range of the signal, thereby increasing the coding efficiency and resulting in a signal-to-distortion ratio that is superior to that obtained by linear encoding for a given number of bits. ALE - Abbreviation for automatic link establishment. Alerting Signal - A signal used by the network to indicate the presence of an incoming call. It consists of a ringing signal periodically interrupted by silent (no ringing signal) intervals. Algorithmic Language - An artificial language established for expressing a given class of algorithms. Algorithm Identifier - In encryption, a unique identifier or recognizer for a given encryption or hash algorithm, together with any required parameters. Alias - 1. See aliasing. 2. In networking, one of a set of domain names of an Internet resource. [2382-pt.35] 3. Synonyms personal number, UPT number. Aliasing - In any technology or process involving (a) sampling a signal, e.g., an electrical signal or (a series of images of) a moving subject; (b) processing, storing, or transmitting representations of the samples; and (c) replicating the original signal from the representations: the production of artifacts as a result of sampling at intervals too great to permit faithful replication of the original signal. Note 1: A common example of aliasing in video or motion picture technology is the apparent slowing, freezing, or even reversing of direction of, the motion of spokes in the wheels on a moving vehicle. Note 2: In the sampling and replication of electrical signals, if the sampling interval is too great, high-frequency components may, for example, be replicated as 21
- 22. low-frequency components, distorting the replicated signal. Note 3: Faithful reproduction of a sampled electrical signal requires a theoretical sampling interval not greater than one-half the inverse of the highest Fourier frequency component in the sampled signal (Nyquist interval). In practice, to achieve a given level of fidelity in the replicated signal, the sampling interval must usually be somewhat shorter than the theoretical (Nyquist) interval, because the samples are usually processed, stored, or transmitted in digital form, and quantization errors in the digitizing process will also result in distortion of the (waveform of the) replicated signal. Note 4: The effects of aliasing in the replicated signal may be avoided by filtering the original signal to remove frequency components that are higher than those desired in the replicated signal. Note 5 (from SMPTE): Video images are sampled in two or three dimensions, and computer graphics are sampled in three. In a composite (complex) spectral channel, any cross talk of the information cannot be eliminated by filtering, and will produce aliasing, for example as cross-color and/or cross-luminance. In a rectilinearly sampled system, lines not parallel to a sampling axis will appear stepped unless anti-aliasing processing algorithms have been applied. Alias Point Code - 1. A Signaling System No. 7 (SS7) address that is shared by more than one system supporting the same GTT (global title translation) function (or other SS7 function). It allows other systems to address the function instead of maintaining the status of multiple point codes. [T1.711-1999] 2. A point code that may be assigned to more than one signaling point, each of which is also assigned a "real" point code. Note: Each of the signaling points having the same "alias" point code is capable of providing a predefined functionality (capability) in the network. As an example for management of global translation capability, an STP (signaling transition point) and its mate can be assigned the same "alias" point code. This provides the capability such that if a message that requires global title translation is routed based on "alias" point code, then either STP answering to the "alias" point code can provide the global title translation functionality. Synonym capability code. Aligned Bundle - A bundle of optical fibers in which the relative spatial coordinates of each fiber are the same at the two ends of the bundle. Note: Such a bundle may be used for the transmission of images. Synonym coherent bundle. Alignment Error Rate Monitoring - A procedure by which the error rate of a signaling link is measured during the initial alignment process. Alignment Jitter - The short-term variations between the optimum sampling instants of a digital signal and the sampling clock derived from it. Allan variance - One half of the time average over the sum of the squares of the differences between successive readings of the frequency deviation sampled over the sampling period. Note: The Allan variance is 2 conventionally expressed by y ( ). The samples are taken with no dead-time between them. Synonym two-sample variance. Allcall - In adaptive high-frequency (HF) radio automatic link establishment (ALE), a general broadcast that does not request responses and does not designate any specific addresses. Note: This essential function is required for emergencies ("HELP"), sounding-type data exchanges, and propagation and connectivity tracking. All-Glass Fiber - Synonym all-silica fiber. Allocation (of a frequency band) - 1. Entry in the Table of Frequency Allocations of a given frequency band for the purpose of its use by one or more (terrestrial or space) radio communication services or the radio astronomy service under specified conditions. This term shall also be applied to the frequency band concerned. 2. The process of designating radio-frequency bands for use by specific radio services. 22
- 23. Allotment (of a radio frequency or radio frequency channel) - Entry of a designated frequency channel in an agreed plan, adopted by a component Conference, for use by one or more administrations for a (terrestrial or space) radio communication service in one or more identified countries or geographical areas and under specified conditions. All-Silica Fiber - An optical fiber composed of a silica-based core and cladding. Note: The presence of a protective polymer overcoat does not disqualify a fiber as an all-silica fiber, nor does the presence of a tight buffer. Synonym all-glass fiber. All Trunks Busy (ATB) - An equipment condition in which all trunks (paths) in a given trunk group are busy. Note: All-trunks-busy registers do not indicate subsequent attempts to reach trunk groups. Alphabet - 1. An ordered set of all the letters used in a language, including letters with diacritical signs where appropriate, but not including punctuation marks. 2. An ordered set of all the symbols used in a language, including punctuation marks, numeric digits, nonprinting control characters, and other symbols. Note: Examples of alphabets include the Roman alphabet, the Greek alphabet, the Morse Code, and the 128 characters of the American Standard Code for Information Interchange (ASCII). Alphabetic Character Set - A character set that contains letters and may contain control characters, special characters, and the space character, but not digits. Alphabetic Code - A code according to which data are represented through the use of an alphabetic character set. Alphabetic String: - 1. A string consisting solely of letters from the same alphabet. 2. A character string consisting solely of letters and associated special characters from the same alphabet. Alphabetic Word - 1. A word consisting solely of letters from the same alphabet. 2. A word that consists of letters and associated special characters, but not digits. Alphabet Translation - Deprecated synonym for alphabet transliteration. See alphabet transliteration. Alphabet Transliteration - The substitution of the characters of one alphabet for the corresponding characters of a different alphabet, usually accomplished on a character-by-character basis. Note 1: An example of alphabet transliteration is the substitution of the Roman letters a, b, and p for the Greek letters , , and , respectively. Note 2: Alphabet transliteration is reversible. Note 3: Alphabet transliteration often becomes necessary in telecommunications systems because of the different alphabets and codes used worldwide. Note 4: In alphabet transliteration, no consideration is given to the meaning of the characters or their combinations. Alphanumeric - 1. Pertaining to a character set that contains letters, digits, and sometimes other characters, such as punctuation marks. 2. Pertaining to a set of unique bit patterns that are used to represent letters of an alphabet, decimal digits, punctuation marks, and other special signs and symbols used in grammar, business, and science, such as those displayed on conventional typewriter keyboards. Alphanumeric Character Set - A character set that contains both letters and digits, special characters, and the space character. Alphanumeric Code - 1. A code derived from an alphanumeric character set. 2. A code that, when used, results in a code set that consists of alphanumeric characters. 23
- 24. Alphanumeric Data - Data represented by letters, digits, and sometimes by special characters and the space character. Alpha Profile - See power-law index profile. Altazimuth Mount - A mounting, e.g., for a directional antenna, in which slewing takes place in (a) the plane tangent to the surface of the Earth or other frame of reference and (b) elevation about, i.e., above or below, that plane. Synonym x-y mount. Alteration - In encryption, the process of changing one or more message elements in a message as a means of committing a fraud. Alternate Access Provider - A company that enters a market area as a competitive service provider (CAP) to provide exchange service in competition with one or more existing exchange carrier (s) in the same market area. Alternate Carrier Routing (ACR) - A special advanced intelligent network (AIN) feature supporting Government Emergency Telecommunications Service (GETS) calls. The feature automatically routes GETS calls to selected carriers to provide improved call completion probability during times of network congestion or damage during disasters or crises. Alternate Mark Inversion (AMI) Signal - A pseudoternary signal, representing binary digits, in which (a) successive "marks" are of alternately positive and negative polarity and the absolute values of their amplitudes are normally equal and (b) "spaces" are of zero amplitude. Synonym bipolar signal. Alternate Party - In multilevel precedence and preemption, the call receiver, i.e., the destination user, to which a precedence call will be diverted. Note 1: Diversion will occur when the response timer expires, when the call receiver is busy on a call of equal or higher precedence, or when the call receiver is busy with access resources that are non-preemptable. Note 2: Alternate party diversion is an optional terminating feature that is subscribed to by the call receiver. Thus, the alternate party is specified by the call receiver at the time of subscription. Alternate Route - A second or subsequent choice path between two points. Alternate Routing - 1. The routing of a call or message over a substitute route when a primary route is unavailable for immediate use. 2. In signaling, the process of allocating substitute routes for a given signaling traffic stream in case of failure (s) affecting the signaling links or routes involved in the normal routing of that signaling traffic stream. 3. In signaling, the routing of a given signaling traffic flow in case of failures affecting the signaling link (s), or route(s), involved in the normal routing of that signaling traffic flow. Synonym alternative routing. Alternating Current - (See AC Current) Alternating Mode - Synonym half-duplex (HDX) operation. Alternative Routing - 1. In signaling, the process of allocating substitute routes for a given signaling traffic stream in case of failure (s) affecting the signaling links or routes involved in the normal routing of that signaling traffic stream. 2. In signaling, the routing of a given signaling traffic flow in case of failures affecting the signaling link (s), or route (s), involved in the normal routing of that signaling traffic flow.Synonym alternate routing. 24
- 25. Altitude of the Apogee or of the Perigee - The altitude of the apogee or perigee above a specified reference surface serving to represent the surface of the Earth. Note: In technical usage, the definite article is not used with the term apogee or perigee alone. A body orbiting the Earth is said simply to be "at apogee" or "at perigee." It may, however, properly be said to be "at the point of apogee" or"at the point of perigee." ALU - Abbreviation for arithmetic and logic unit. AM - Abbreviation for amplitude modulation. AMA - Abbreviation for automatic message accounting. Amateur-Satellite Service - A radio communication service using space stations on Earth satellites for the same purposes as those of the amateur service. Amateur Service - A radio communication service for the purpose of self-training, intercommunication and technical investigation carried out by amateurs, that is, by duly authorized persons interested in radio technique solely with a personal aim and without pecuniary interest. Amateur Station - A station in the amateur service. Ambient Noise Level - The level of acoustic noise existing at a given location, such as in a room, in a compartment, or at a place out of doors. Note 1: Ambient noise level is measured with a sound level meter. Note 2: Ambient noise level is usually measured in dB above a reference pressure level of 0.00002 Pa, i.e., 20 Pa (micropascals) in SI units. A pascal is a newton per square meter. Note 3: In the centimeter-gram- 2 second system of units, the reference level for measuring ambient noise level is 0.0002 dyn/cm . Synonym room noise level. Ambient Temperature - The temperature of air or other media in a designated area, particularly the area surrounding equipment. AME - Abbreviation for amplitude modulation equivalent, automatic message exchange. See compatible sideband transmission. American National Standards Institute (ANSI) - The U.S. standards organization that establishes procedures for the development and coordination of voluntary American National Standards. American Standard Code for Information Interchange (ASCII) - See ASCII. AMI - Abbreviation for alternate mark inversion. See alternate mark inversion signal. AMI Violation: - A " mark " that has the same polarity as the previous "mark" in the transmission of alternate mark inversion (AMI) signals. Note: In some transmission protocols, AMI violations are deliberately introduced to facilitate synchronization or to signal a special event. Amplifier - 1. An electronic component that boosts the voltage or power level of a signal that is a linear replica of the input signal, but with greater power or voltage level, and sometimes with an impedance transformation. The output may also be a nonlinear analog function of the input signal, as in a signal compression device. 2. See fiber amplifier, optical repeater. 25
- 26. Amplitude Compression - 1. See signal compression. 2. In video production, the imposition of a nonlinear transfer function on (i.e., the nonlinear processing of, to reduce the dynamic range of) signal amplitude values (e.g., as in gamma correction). Amplitude Distortion - Distortion occurring in a system, subsystem, or device when the output amplitude is not a linear function of the input amplitude under specified conditions. Note: Amplitude distortion is measured with the system operating under steady-state conditions with a sinusoidal input signal. When other frequencies are present, the term "amplitude" refers to that of the fundamental only. Amplitude Equalizer - A corrective network that is designed to modify the amplitude characteristics of a circuit or system over a desired frequency range. Note: Such devices may be fixed, manually adjustable, or automatic. Amplitude hit - See hit. Amplitude Intensity Modulation (AIM) - Deprecated term. See intensity modulation. Amplitude Keying - Keying in which the amplitude of a signal is varied among the members of a set of discrete values. Amplitude Modulation (AM) - Modulation in which the amplitude of a carrier wave is varied in accordance with some characteristic of the modulating signal. Note: Amplitude modulation implies the modulation of a coherent carrier wave by mixing it in a nonlinear device with the modulating signal to produce discrete upper and lower sidebands, which are the sum and difference frequencies of the carrier and signal. The envelope of the resultant modulated wave is an analog of the modulating signal. The instantaneous value of the resultant modulated wave is the vector sum of the corresponding instantaneous values of the carrier wave, upper sideband, and lower sideband. Recovery of the modulating signal may be by direct detection or by heterodyning. Amplitude Modulation Equivalent (AME) - Synonym compatible sideband transmission. Amplitude-vs.-Frequency Distortion - Distortion in a transmission system caused by nonuniform attenuation, or gain, in the system with respect to frequency under specified operating conditions. Synonym frequency distortion. AMPS - allocates frequency ranges within the 800 and 900 Megahertz (MHz) spectrum to cellular telephone. Each service provider can use half of the 824-849 MHz range for receiving signals from cellular phones and half the 869-894 MHz range for transmitting to cellular phones. The bands are divided into 30 kHz sub-bands, called channels. The receiving channels are called reverse channels and the sending channels are called forward channels. The division of the spectrum into sub-band channels is achieved by using frequency division multiple access (FDMA). The signals received from a transmitter cover an area called a cell. As a user moves out of the cell's area into an adjacent cell, the user begins to pick up the new cell's signals without any noticeable transition. The signals in the adjacent cell are sent and received on different channels than the previous cell's signals to so that the signals don't interfere with each other. The analog service of AMPS has been updated with digital cellular service by adding to FDMA a further subdivision of each channel using time division multiple access (TDMA). This service is known as digital AMPS 26
- 27. (D-AMPS). Although AMPS and D-AMPS originated for the North American cellular telephone market, they are now used worldwide with over 74 million subscribers, according to Ericsson, one of the major cellular phone manufacturers. Abbreviation for automatic message processing system. AMTS - Abbreviation for automated maritime telecommunications system. Analog - In telecommunications, an analog signal is one in which a base carrier's alternating current frequency is modified in some way, such as by amplifying the strength of the signal or varying the frequency, in order to add information to the signal. Broadcast and telephone transmission have conventionally used analog technology. An analog signal can be represented as a series of sine waves. The term originated because the modulation of the carrier wave is analogous to the fluctuations of the human voice or other sound that is being transmitted. Analog Channel - A communications path that carries voice or video in analog form — as a varying range of electrical frequencies (See Analog Signal). Analog Component - Synonym CAV. Analog Computer - A device that performs operations on data that are represented within the device by continuous variables having a physical resemblance to the quantities being represented. Note: The earliest analog computers were constructed with purely mechanical components, such as levers, cogs, cams, discs, and gears. These components represented the quantities being manipulated or the operator-inserted values. Modern analog computers usually employ electrical parameters, such as voltages, resistance's, or currents to represent the quantities being manipulated. Analog Data - Data represented by a physical quantity that is considered to be continuously variable and has a magnitude directly proportional to the data or to a suitable function of the data. Analog Decoding - The portion of the digital-to-analog conversion process that generates an analog signal value from the digital signal that resulted from analog encoding. Note: Further action is required to integrate these samples to obtain a continuous approximation of the original signal, because analog decoding does not smooth the signal. Analog Encoding - The portion of the analog-to-digital conversion process that samples an analog signal and creates a digital signal that represents the value of the sample. Note: Multiple samples are needed to digitize a waveform over a time interval. Analog Facsimile Equipment: Facsimile equipment in which (a) analog techniques are used to encode the image detected by the scanner and (b) the output is an analog signal. Note: Examples of analog facsimile equipment are CCITT Group 1 and CCITT Group 2 facsimile equipment. Analog Pass-Through - Digital converter box capability, which allows analog broadcast signals to pass through the converter box to be tuned by your analog TV. Analog Signal - 1. A signal that has a continuous nature rather than a pulsed or discrete nature. Note: Electrical or physical analogies, such as continuously varying voltages, frequencies, or phases, may be used as analog signals. 2. A nominally continuous electrical signal that varies in some direct correlation with another signal impressed on a transducer. Note: For example, an analog signal may vary in frequency, phase, or amplitude in response to changes in physical phenomena, such as sound, light, heat, position, or pressure. 3. 27
- 28. A type of signal that encodes voice, video, or data transmitted over wire or over-the-air that is commonly represented as an oscillating wave. An analog signal may vary in frequency in response to changes in physical phenomena, such as sound, light, heat, position, or pressure. Analog Signaling Data Link - The data link that provides an interface to signaling terminals and is made up of voice-frequency analog transmission channels and modems. Analog Spectrum - A traditional range of frequencies used for radio and television transmission. This is a less-efficient and lower-quality system that uses Radio Frequency (RF) waves to transmit and display pictures and sound. Analog Switch - Switching equipment designed, designated, or used to connect circuits between users for real-time transmission of analog signals Analog-to-Digital (A-D) Coder - Synonym analog-to-digital converter (ADC). Analog-to-Digital Converter (ADC) - A device that converts an analog signal to a digital signal that represents equivalent information. Synonyms analog-to-digital (A-D) coder, analog-to-digital (A-D) encoder. Analog-to-Digital (A-D) Encoder - Synonym analog-to-digital converter (ADC). Analog Transmission - Transmission of a continuously varying signal as opposed to transmission of a discretely varying signal. Analog Transmission Date - In the US, this refers to June 12, 2009, which was the DTV Transition deadline mandated by Congress for the turnoff of analog broadcasting by full-power TV stations. Other countries have also set deadlines for the transition from analog to digital broadcasting. Analog TV- Analog television encodes television picture and sound information and transmits it as an analog signal (one in which the message conveyed by the broadcast signal is a function of deliberate variations in the amplitude and/or frequency of the signal). All systems preceding DTV (e.g. NTSC) are analog television systems. Analog technology has been in use for the past 50 years to transmit conventional TV signals to consumers. Analytical Attack - An attempt to break a code or to find a key using analytical methods. Note: Examples of an analytical attack are: a statistical analysis of patterns; a search for flaws in an encryption algorithm. Synonym cryptanalytical attack. Angle Modulation - Modulation in which the phase or frequency of a sinusoidal carrier is varied. Note: Phase and frequency modulation are particular forms of angle modulation. Angle of Deviation - In optics, the net angular deflection experienced by a light ray after one or more refractions or reflections. Angle of Incidence - The angle between an incident ray and the normal to a reflecting or refracting surface. -10 Angstrom ( ) - A unit of length equal to 10 m. Note 1: The angstrom is not an SI (International System) unit, and it is not accepted for government use.Note 2: The angstrom is, and historically has been, used in the fields of optics, spectroscopy, and microscopy. 28
- 29. Angular Misalignment Loss - Power loss caused by the deviation from optimum angular alignment of the axes of source to wave guide, wave guide to wave guide, or wave guide to detector. Note 1: The wave guide may be dielectric (an optical fiber) or metallic. Note 2: Angular misalignment loss does not include lateral offset loss and longitudinal offset loss. ANI - Abbreviation for automatic number identification. Anisochronous - Pertaining to transmission in which the time interval separating any two significant instants in sequential signals is not necessarily related to the time interval separating any other two significant instants. Note: Isochronous and anisochronous are characteristics, while synchronous and asynchronous are relationships. Anisochronous Transmission - See asynchronous transmission. Anisotropic - Pertaining to a material whose electrical or optical properties vary with (a) the direction of propagation of a traveling wave or with (b) different polarizations of a traveling wave. Note 1: Anisotropy is exhibited by non-cubic crystals, which have different refractive indices for lightwaves propagating in different directions or with different polarizations. Note 2: Anisotropy may be induced in certain materials under mechanical strain. Anomalous Propagation (AP) - Abnormal propagation caused by fluctuations in the properties (such as density and refractive index) of the propagation medium. Note: AP may result in the reception of signals well beyond the distances usually expected. Anonymous Call - A 7- or 10-digit call to the directory number of the public service answering point (PSAP) (where applicable) causing the E911 system (emergency 9-1-1 system) to send to the PSAP a multifrequency (MF) pulse train devoid of the caller's emergency service identification. Anonymous Call Rejection (ACR) - Allows you to automatically reject calls from parties who have activated a privacy feature preventing the delivery of their calling number and/or name to the called party. Once this feature is activated, the call is routed to a denial announcement and subsequently terminated. You will not receive any alerting for a call that is rejected. Anonymous FTP - The name of a file-transfer protocol that allows a user on one host to access and transfer files to and from another host over a network. ANS - Abbreviation for American National Standard. ANSI - Abbreviation for American National Standards Institute. ANSI/EIA/TIA-568 - A U.S. industry standard that specifies a generic telecommunications cabling system, which will support a multiproduct, multivendor environment, for commercial buildings. Note 1: The standard specifies performance characteristics for unshielded twisted pair telecommunications cabling, including categories allowing data communications up to 100 Mb/s. These categories are designated 3, 4, and 5. Categories 1 and 2 have not been defined. Note 2: The standard has been adopted as FIPS PUB 174. Answer Back - A signal sent by receiving equipment to the sending station to indicate that the receiver is ready to accept transmission. Answer Indicator - A signal indicating acceptance of the call by the addressed user. 29
- 30. Answer Machine - Common term in UK and British commonwealth countries for a machine that answers telephone calls and lat you retrieve recorded messages from callers. - A device for automatically answering telephone calls and recording messages left by callers. Unlike voicemail, which is a centralized or networked system that performs a similar function, an answering machine is installed in the customer's premises alongside the telephone. Older answering machines use magnetic tape technology, while current equipment uses solid state memories (memory chips). Magnetic tape is still commonly used in many low cost devices. Also known as an answering machine, answering device, ansafone, ansaphone, answerphone or telephone answering device (TAD). If you want to purchase an answer machine, click here. Answering Device - Also known as an answering machine- A device for answering phone calls and recording callers' messages. - A device for automatically answering telephone calls and recording messages left by callers. Unlike voicemail, which is often a centralized or a networked system that performs a similar function, an answering machine is installed in the customer's premises to augment the telephone. While early answering machines used magnetic tape technology, most modern equipment uses solid state memories. Magnetic tape is still commonly used. Also known as an answer machine, ansafone, ansaphone, answerphone or telephone answering device (TAD), If you are loking for an answering device, click here. Answering Machine - A machine for answering and retrieving your telephone calls by recording callers' messages. - A device for automatically answering telephone calls and recording messages left by callers. Unlike voicemail, which is a centralized or networked system that performs a similar function, an answering machine is installed in the customer's premises alongside the telephone. Early answering machines used magnetic tape technology, while newer equipment uses solid state memories (memory chips). Magnetic tape is still used in many low cost devices. Answering machines answer the phone, play a recorded message and usually give the caller the opportunity to leave a recorded message. Also known as an answer machine (especially in UK and British commonwealth countries), ansafone, ansaphone, answerphone or telephone answering device (TAD). If you are interested in purchasing an answering machine, click here. Answering Machine Accessories - Devices used in conjunction with answering machines or answering devices such as cords, power supplies, prerecorded messages and magnetic tapes. Older answering machines use magnetic tape technology while newer answering machines use solid state memories. Magnetic tapes are still the most common answering machine accessory. Do you need Answering Machine Accessories? Answering Machine Silent Transfer -This feature works like Unanswered Call Silent Transfer except that it is designed for calls of 45 seconds or less. It should only be activated when you are using an answering machine to field after-hours calls. When a manual fax or modem call arrives and the answering machine has answered, the caller will still be able to get to a destination device by staying on the line after the answering machine "times out". If you answer a call and hang up before 45 seconds, The fax switch will transfer the call to the designated device. Factory preset is "off." Answer Signal - 1. A supervisory signal returned from the called telephone to the originating switch when the call receiver answers. Note 1: The answer signal stops the ring back signal from being returned to the caller. Note 2: The answer signal is returned by means of a closed loop. 2. An off-hook signal transmitted towards the network when the called party answers. 3. An off-hook signal transmitted towards the network to indicate when the customer installation (CI) equipment has changed to the communication state. Antenna - 1. Any structure or device used to collect or radiate electromagnetic waves. 2. A device that converts radio frequency electrical energy to radiated electromagnetic energy and vice versa; in a transmitting station, the device from which radio waves are emitted. 3. Device designed to receive the radio waves broadcast by television stations. antenna aperture - See aperture. 30
- 31. Antenna Array - An assembly of antenna elements with dimensions, spacing, and illumination sequence such that the fields for the individual elements combine to produce a maximum intensity in a particular direction and minimum field intensities in other directions. Antenna Blind Cone: The volume of space, usually approximately conical with its vertex at the antenna, that cannot be scanned by an antenna because of limitations of the antenna radiation pattern and mount. Note: An example of an antenna blind cone is that of an air route surveillance radar (ARSR). The horizontal radiation pattern of an ARSR antenna is very narrow. The vertical radiation pattern is fan-shaped, reaching approximately 70° of elevation above the horizontal plane. As the antenna is rotated about a vertical axis, it can illuminate targets only if they are 70° or less from the horizontal plane. Above that elevation, they are in the antenna blind cone. Synonym cone of silence. Antenna Coupler - A device used to match the impedance of a transmitter and/or receiver to an antenna to provide maximum power transfer. Antenna Dissipative Loss - A power loss resulting from changes in the measurable impedance of a practical antenna from a value theoretically calculated for a perfect antenna. Antenna Effective Area - The functionally equivalent area from which an antenna directed toward the source of the received signal gathers or absorbs the energy of an incident electromagnetic wave. Note 1: Antenna effective area is usually expressed in square meters. Note 2: In the case of parabolic and horn-parabolic antennas, the antenna effective area is about 0.35 to 0.55 of the geometric area of the antenna aperture. Antenna Efficiency - The ratio of the total radiated power to the total input power. Note: The total radiated power is the total input power less antenna dissipative losses. Antenna Electrical Beam Tilt - The shaping of the radiation pattern in the vertical plane of a transmitting antenna by electrical means so that maximum radiation occurs at an angle below the horizontal plane. Antenna Gain - The ratio of the power required at the input of a loss-free reference antenna to the power supplied to the input of the given antenna to produce, in a given direction, the same field strength at the same distance. Note 1: Antenna gain is usually expressed in dB. Note 2: Unless otherwise specified, the gain refers to the direction of maximum radiation. The gain may be considered for a specified polarization. Depending on the choice of the reference antenna, a distinction is made between: • absolute or isotropic gain (Gi), when the reference antenna is an isotropic antenna isolated in space; • gain relative to a half-wave dipole (Gd) when the reference antenna is a half-wave dipole isolated in space and with an equatorial plane that contains the given direction; • gain relative to a short vertical antenna (Gr), when the reference antenna is a linear conductor, much shorter than one quarter of the wavelength, normal to the surface of a perfectly conducting plane which contains the given direction. Synonyms gain of an antenna, power gain of an antenna. Antenna Gain-to-Noise-Temperature (G/T) - In the characterization of antenna performance, a figure of merit, where G is the antenna gain in decibels at the receive frequency, and T is the equivalent noise temperature of the receiving system in kelvins. Antenna Height Above Average Terrain - The antenna height above the average terrain elevations from 3.2 to 16 kilometers (2 to 10 miles) from the antenna for the eight directions spaced evenly for each 45° of azimuth starting with true north. Note: In general, a different antenna height above average terrain will be determined in each direction from the antenna. The average of these eight heights is the antenna height above average terrain. In some cases, such as seashore, fewer than eight directions may be used. 31
- 32. Antenna Lobe - A three-dimensional section of the radiation pattern of a directional antenna, bounded by one or more cones of nulls or by regions of diminished irradiance. Antenna Matching - The process of adjusting impedance so that the input impedance of an antenna equals or approximates the characteristic impedance of its transmission line over a specified range of frequencies. Note: The impedance of either the transmission line, or the antenna, or both, may be adjusted to effect the match. Antenna Noise Temperature - The temperature of a hypothetical resistor at the input of an ideal noise-free receiver that would generate the same output noise power per unit bandwidth as that at the antenna output at a specified frequency. Note 1: The antenna noise temperature depends on antenna coupling to all noise sources in its environment as well as on noise generated within the antenna. Note 2: The antenna noise temperature is a measure of noise whose value is equal to the actual temperature of a passive device. Anti-Clockwise Polarized Wave - Synonym left-hand polarized wave. Anti-Interference - Pertaining to equipment, processes, or techniques used to reduce the effect of natural and man-made noise on radio communications. Anti-Jam - Measures ensuring that intended transmitted information can be received despite deliberate jamming attempts. Anti-Node - A point in a standing wave at which the amplitude is a maximum. Antireflection Coating - A thin, dielectric or metallic film, or several such films, applied to an optical surface to reduce its reflectance and thereby increase its transmittance.Note: For minimum reflection of a normal incident wave of a single wavelength, the antireflection coating may consist of a single layer and must have (a) a refractive index equal to the square root of the refractive indices of the materials bounding the coating, and (b) a thickness equal to one-quarter the wavelength in question (i.e., the wavelength within the material of which the coating consists). For minimum reflection of multiple wavelengths, additional layers must be added. Anti-Spoof - 1. Measures taken to prevent an unauthorized person/entity from impersonating an authorized person/entity to gain access to a data system. [DoJ] 2. Measures preventing an opponent's participation in an information system (IS). Anti-Virus Program - A computer program designed to detect computer-file viruses and possibly to suggest or take corrective action. Synonym vaccine program. Anycall - In adaptive high-frequency (HF) radio automatic link establishment, a broadcast in which (a) the called stations are unspecified, (b) stations receiving the call stop scanning, and (c) each station automatically responds in pseudorandom time slots. AP - Abbreviation for anomalous propagation. APC - Abbreviation for adaptive predictive coding. APD - Abbreviation for avalanche photodiode. Note: apd and a.p.d. are also used. 32
- 33. Aperiodic Antenna - An antenna designed to have an approximately constant input impedance over a wide range of frequencies. Note: Examples of aperiodic antennas include terminated rhombic antennas and wave antennas. Synonym nonresonant antenna. Aperture - 1. In a directional antenna, the portion of a plane surface very near the antenna normal to the direction of maximum radiant intensity, through which the major part of the radiation passes. 2. In an acoustic device that launches a sound wave, the passageway, determined by the size of a hole in the inelastic material and the wavelength. Aperture Correction - 1. In a scanned image system, electrical compensation for the distortion introduced by the limiting size of a scanning aperture. 2. In television technology, restoration of the depth of modulation to the higher (i.e., higher Fourier) frequency components of the video signal, with the objective of achieving a subjective improvement in image quality. Note: Aperture correction is required to compensate for the properties of the camera lens, optical beam-splitting installation, and camera tube, all of which contribute to a reduced signal at higher spatial frequencies. Problems requiring aperture correction arise in a scanning system when the frequency response falls off as the effective wavelength of the detail to be resolved in the image approaches the dimension of the scanning aperture and becomes zero when that effective wavelength equals the dimension of the scanning aperture. Aperture Distortion - In facsimile, the distortion of the recorded image caused by the shape and finite size of the scanning and recording apertures. Note: The distortion may occur in one or more attributes of the recorded image, such as in resolution, density, or shape. Aperture Illumination - 1. The field distribution, in amplitude and phase, over the antenna physical aperture. 2. The phase and amplitude of the element feed voltages or the distribution of the currents in an array of elements. Aperture-to-Medium Coupling Loss - The difference between the theoretical gain of a very large antenna, such as the antennas in beyond-the-horizon microwave links, and the gain that can be realized in operation. Note 1: Aperture-to-medium coupling loss is related to the ratio of the scatter angle to the antenna beam width. Note 2: The "very large antennas" are referred to in wavelengths; thus, this loss can apply to line-of- sight systems also. Apogee - In an orbit of a satellite orbiting the Earth, the point that is farthest from the gravitational center of the Earth. Apogee Altitude - See altitude of the apogee or of the perigee. App - Abbreviation for application, application software. Apparent Power - In alternating-current power transmission and distribution, the product of the rms voltage and amperage. Note 1: When the applied voltage and the current are in phase with one another, the apparent power is equal to the effective power, i.e., the real power delivered to or consumed by the load. If the current lags or leads the applied voltage, the apparent power is greater than the effective power. Note 2: Only effective power, i.e., the real power delivered to or consumed by the load, is expressed in watts. Apparent power is properly expressed only in volt-amperes, never watts. See diagram under effective power. Applet - A small, self-contained computer program that usually performs a task as part of, or under the control of, a larger software application. For example, most modern World Wide Web browsers are capable of making use of applets written in the Java programming language to perform simple tasks such as display animations or more complex tasks such as spreadsheet and database operations. 33
- 34. Application - Software that performs a specific task or function, such as word-processing, creation of spreadsheets, generation of graphics, facilitating electronic mail, etc. Synonym application software. Application Association - A cooperative relationship between two application entities, formed by their exchange of application protocol control information through their use of presentation services. Application Compatibility Toolkit (ACT) - A set of freely downloadable program utilities and related documents from Microsoft for ensuring compatibility among application programs in Windows operating systems, especially in a large network environment. The Toolkit can also be used to diagnose and fix problems that may be related to compatibility. The Toolkit can be used for applications running in Windows 2000 with Service Pack 3 or later, Windows XP, and Windows Server 2003. Microsoft says that the tools can be used to resolve over 200 symptoms of problems. The Toolkit can be downloaded from Microsoft's Web site or ordered for delivery on a CD. The Analyzer and the Verifier can also be downloaded or ordered separately. Application Entity (AE) - The system-independent application activities that are made available as application services to the application agent, e.g., a set of application service elements that together perform all or part of the communication aspects of an application process. Application Layer - Layer 7 of the Open Systems Interconnection--Reference Model. The highest layer. This layer interfaces directly to and performs common application services for the application processes; it also issues requests to the Presentation Layer. The common application services provide semantic conversion between associated application processes. Note: Examples of common application services of general interest include the virtual file, virtual terminal, and job transfer and manipulation protocols. See Open Systems Interconnection--Reference Model. Application Platform - Synonym platform. Application Program - See application. Software that performs a specific task or function, such as word- processing, creation of spreadsheets, generation of graphics, facilitating electronic mail, etc. Application Program Interface (API) - A formalized set of software calls and routines that can be referenced by an application program in order to access supporting network services. Application Protocol - A set of rules and formats (semantic and syntactic) that determines the communication behavior of application entities in the performance of application functions. Application Service Element (ASE) - A coherent set of integrated functions to help accomplish application communication, e.g., within an application entity. Application Software - Synonym application. Applique - Circuit components added to an existing system to provide additional or alternate functions. Note: Applique may be used to modify carrier telephone equipment designed for ringdown manual operation to allow for use between points having dial equipment. Appointment Book - A small (pocket-size or smaller), specialized, portable computing device, with a self- contained power source, designed to (a) accept as inputs; (b) store; and (c) read out, user-designated information, usually appointments, telephone numbers, etc. Approved Circuit - Deprecated synonym for protected distribution system. 34
- 35. Aramid Yarn - Generic name for a tough synthetic yarn that is often used in optical cable construction for the strength member, protective braid, and/or rip cord for jacket removal. Architecture - See computer architecture, network architecture. Archive File - A software file that has been set aside, often in a redundant storage medium, as a security measure or for later retrieval, e.g., for research or verification. Archiving - The storing of files, records, and other data for reference and alternative backup. Area Broadcast Shift - The changing from listening to transmissions intended for one broadcast area to listening to transmissions intended for another broadcast area. Note 1: An area broadcast shift may occur when a ship or aircraft crosses the boundary between listening areas. Note 2: Shift times, on the date a ship or aircraft is expected to pass into another area, must be strictly observed or the ship or aircraft will miss messages intended for it. Synonym radio watch shift. Area Code - In the North American telephone system, an area code is a three-digit code delineating a "toll" area in the United States, Canada, and Mexico. Area codes are distributed according to the North American Number Plan (NANP). The area code is also referred to as a Number Plan Area or NPA. See access code, code, country code, NXX code. Also See Telephone Area Codes of North America. Area Loss - When optical fibers are joined by a splice or a pair of mated connectors, a power loss that is caused by any mismatch in size or shape of the cross section of the cores of the mating fibers. Note 1: Any of the above conditions may allow light from the core of the "transmitting" fiber to enter the cladding of the "receiving" fiber, where it is quickly lost. Note 2: Area loss may be dependent on the direction of propagation. For example, in coupling a signal from an optical fiber having a smaller core to an otherwise identical one having a larger core, there will be no area loss, but in the opposite direction, there will be area loss. Argument - 1. An independent variable. 2. Any value of an independent variable. Note: Examples of arguments include search keys, numbers that identify the location of a data item in a table, and the in sin . Arithmetic and Logic Unit (ALU) - A part of a computer that performs arithmetic, logic, and related operations. Arithmetic Overflow - 1. In a digital computer, the condition that occurs when a calculation produces a result that is greater than a given register or storage location can store or represent. 2. In a digital computer, the amount that a calculated value is greater than a given register or storage location can store or represent. Note: The overflow may be placed at another location. Synonym [loosely] overflow. Arithmetic Register - A register that holds the operands or the results of operations such as arithmetic operations, logic operations, and shifts. Arithmetic Shift - A shift, applied to the representation of a number in a fixed radix numeration system and in a fixed-point representation system, and in which only the characters representing the fixed-point part of the number are moved. An arithmetic shift is usually equivalent to multiplying the number by a positive or a negative integral power of the radix, except for the effect of any rounding; compare the logical shift with the arithmetic shift, especially in the case of floating-point representation. 35
- 36. Arithmetic Underflow - In a digital computer, the condition that occurs when a calculation produces a non- zero result that is less than the smallest non-zero quantity that a given register or storage location can store or represent. Arithmetic Unit - In a processor, the part that performs arithmetic operations; sometimes the unit performs both arithmetic and logic operations. Armed Forces Radio Service (AFRS) - A radio broadcasting service that is operated by and for the personnel of the armed services in the area covered by the broadcast. Note: An example of an AFRS is the radio service operated by the U.S. Army for U.S. and allied military personnel on duty in overseas areas. Armor - Of a communications cable, a component intended to protect the critical internal components, e.g., buffer tubes or fibers, or electrical conductors, from damage from external mechanical attack, e.g., rodent attack or abrasion. Note: Armor usually takes the form of a steel or aluminum tape wrapped about an inner jacket that covers the critical internal components. An outer jacket usually covers the armor. ARP - Abbreviation for address resolution protocol. ARPANET - Abbreviation for Advanced Research Projects Agency Network. A packet-switching network used by the Department of Defense, later evolved into the Internet. ARQ - Abbreviation for automatic repeat-request. Error control for data transmission in which the receiver detects transmission errors in a message and automatically requests a retransmission from the transmitter. Note: Usually, when the transmitter receives the ARQ, the transmitter retransmits the message until it is either correctly received or the error persists beyond a predetermined number of retransmissions. Synonyms error-detecting-and-feedback system, repeat-request system. Array - 1. An arrangement of elements in one or more dimensions. 2. In a programming language, an aggregate that consists of data objects with identical attributes, each of which may be uniquely referenced by subscription. Array Processor - A processor capable of executing instructions in which the operands may be arrays rather than data elements. Synonym vector processor. Arrester - A device that protects hardware, such as systems, subsystems, circuits, and equipment, from voltage or current surges produced by lightning or electromagnetic pulses. Note: If the hardware is adequately protected, associated software may also be adequately protected. Synonyms surge protective device, surge suppressor. ARS - Abbreviation for automatic route selection. Article - Synonym posting. Articulation Index - A measure of the intelligibility of voice signals, expressed as a percentage of speech units that are understood by the listener when heard out of context. Note: The articulation index is affected by noise, interference, and distortion. Articulation Score (AS) - A subjective measure of the intelligibility of a voice system in terms of the percentage of words correctly understood over a channel perturbed by interference. Note: Articulation scores have been experimentally obtained as functions of varying word content, bandwidth, audio signal-to- noise ratio and the experience of the talkers and listeners involved. 36
- 37. Artifact - In facsimile or television, a defect or distortion of the image, introduced along the sequence from origination and image capture to final display. Note 1: Artifacts may arise from the overload of channel capacity by excess signal bandwidth. Note 2: In general, artifacts may result from (a) sampling effects in temporal, spatial, or frequency domains, (b) processing by the transfer functions, (c) compromises and inadequacies in the system employed, (d) cascading of minor defects, or (e) any other departure of the total system from "complete transparency." Artificial Intelligence (AI) - The capability of a device to perform functions that are normally associated with human intelligence, such as reasoning and optimization through experience. Note: AI is the branch of computer science that attempts to approximate the results of human reasoning by organizing and manipulating factual and heuristic knowledge. Areas of AI activity include expert systems, natural language understanding, speech recognition, vision, and robotics. Artificial Transmission Line - A four-terminal electrical network, i.e. an electrical circuit, that has the characteristic impedance, transmission time delay, phase shift, and/or other parameter(s) of a real transmission line and therefore can be used to simulate a real transmission line in one or more of these respects. Synonym [loosely] art line. Art Line - Synonym [loosely] artificial transmission line. ARU - Abbreviation for audio response unit. ASCII (pronounced: ask-ee) - ASCII is an acronym for American Standard Code for Information Interchange, a code that represents the most basic letters of the Roman alphabet, numbers, and other characters used in computing. ASCII characters allow us to communicate with computers, which use their own language called binary made up of 0s and 1s. ASCII files are also called text files. ASCII is the standard code used for information interchange among data processing systems, data communications systems, and associated equipment in the United States. Note 1: The ASCII character set contains 128 coded characters. Note 2: Each ASCII character is a 7-bit coded unique character; 8 bits when a parity check bit is included. Note 3: The ASCII character set consists of control characters and graphic characters. Note 4: When considered simply as a set of 128 unique bit patterns, or 256 with a parity bit, disassociated from the character equivalences in national implementations, the ASCII may be considered as an alphabet used in machine languages. Note 5: The ASCII is the U.S. version of International Reference Alphabet (IRA) No. 5 (formerly International Alphabet No. 5, or "IA5") as specified in ITU-T Recommendation T.50. ASP - Abbreviation for adjunct service point. Aspect Ratio - 1. In facsimile or television, the ratio of the width to the height of a scanning field or image. Note: For example, the classical NTSC television standard specifies an aspect ratio of 4:3, and the new high- definition television standard specifies 16:9. - For 4:3, the traditional TV aspect ratio, a 32-inch TV would be 25½ inches wide and 19 inches tall. A 16:9 widescreen 32-inch TV is closer to a movie screen than a traditional TV, and would be 28 inches wide and 16 inches tall. 2. The ratio of the width to the height of any video or scanned image display. ASR ( Automated Speech Recognition) - Is a technology that allows users of information systems to speak entries rather than punching numbers on a keypad. ASR is used primarily to provide information and to forward telephone calls. In recent years, ASR has become popular in the customer service departments of large corporations. It is also used by some government agencies and other organizations. Basic ASR systems recognize single-word 37
- 38. entries such as yes-or-no responses and spoken numerals. This makes it possible for people to work their way through automated menus without having to enter dozens of numerals manually with no tolerance for error. In a manual-entry situation, a customer might hit the wrong key after having entered 20 or 30 numerals at intervals previously in the menu, and give up rather than call again and start over. ASR virtually eliminates this problem. Sophisticated ASR systems allow the user to enter direct queries or responses, such as a request for driving directions or the telephone number of a hotel in a particular town. This shortens the menu navigation process by reducing the number of decision points. It also reduces the number of instructions that the user must receive and comprehend. For institutions that rely heavily on customer service, such as airlines and insurance companies, ASR makes it possible to reduce the number of human call-center employees. Those people can then be trained for other jobs that are more profitable and interesting, such as complaint resolution, customer retention, or sales. The technology of speech recognition has been around for some time. It is improving, but problems still exist. An ASR system cannot always correctly recognize the input from a person who speaks with a heavy accent or dialect, and it has major problems with people who combine words from two languages by force of habit. Marginal cell-phone connections can cause the system to misinterpret the input. And, although the cost is gradually diminishing, ASR systems are still too expensive for some organizations. Assemble - To translate a computer program expressed in an assembly language into a machine language. Assembler: A computer program that is used to assemble. Synonym assembly program. Assembly - In logistics, an item forming a portion of an equipment that can be provisioned and replaced as an entity and which normally incorporates replaceable parts or groups of parts. Assembly Language - A computer-oriented language (a) in which instructions are symbolic and usually in one-to-one correspondence with sets of machine language instructions and (b) that may provide other facilities, such as the use of macro instructions. Synonym computer-dependent language. Assembly Program - Synonym assembler. Assembly Time - The elapsed time taken for the execution of an assembler. Asset - 1. In security, a resource or information that is to be protected. 2. Any system or component (e.g., subsystem, hardware, firmware, software, database, or interconnection communications network or facility) that is part of a communications system or an information system. Assigned Frequency - 1. The center of the assigned frequency band assigned to a station. [RR] 2. The frequency of the center of the radiated bandwidth. Note: The frequency of the rf carrier, whether suppressed or radiated, is usually given in parentheses following the assigned frequency, and is the frequency appearing in the dial settings of rf equipment intended for single-sideband or independent- sideband transmission. 3. The frequency coinciding with the center of an authorized bandwidth of emission. [47CFR] 4. The center of the frequency band assigned to a station. Assigned Frequency Band - The frequency band within which the emission of a station is authorized; the width of the band equals the necessary bandwidth plus twice the absolute value of the frequency tolerance. Where space stations are concerned, the assigned frequency band includes twice the maximum Doppler shift that may occur in relation to any point of the Earth's surface. 38
- 39. Assignment - For NS/EP, the designation of priority level (s). Assignment (of a radio frequency or radio frequency channel) - Authorization given by an administration for a radio station to use a radio frequency or radio frequency channel under specified conditions. Assistive Technology - According to the United States Assistive Technology Act of 1998, assistive technology (also called adaptive technology) refers to any "product, device, or equipment, whether acquired commercially, modified or customized, that is used to maintain, increase, or improve the functional capabilities of individuals with disabilities." Common computer-related assistive technology products include screen magnifiers, large-key keyboards, alternative input devices such as touch screen displays, over-sized trackballs and joysticks, speech recognition programs, and text readers. Associated Common-Channel Signaling - Common-channel signaling in which the signal channel is associated with a specific trunk group and terminates at the same pair of switches as the trunk group. Note: In associated common-channel signaling, the signaling is usually accomplished by using the same facilities as the associated trunk group. Associated Mode of Signaling - The mode in which messages for a signaling relation involving two adjacent signaling points are conveyed over a directly interconnecting signaling link. Associative Storage - 1. A storage device whose storage locations are identified by their contents, or by a part of their contents, rather than by their names or positions. Note: Associative storage can also refer to this process as well as to the device. Synonym content-addressable storage. 2. Storage that supplements another storage. Assurance - 1. Grounds for confidence that an information-technology (IT) product or system meets its security objectives. 2. In INFOSEC, see information assurance. Asymmetrical Modulator - Synonym unbalanced modulator. A modulator in which the modulation factor is different for the alternate half-cycles of the carrier. Asymmetric Compression - A data compression technique that requires more processing capability to compress than to decompress. Note: Asymmetric compression is typically used for the mass distribution of programs on media such as CD ROM, where significant expense can be incurred for the production and compression of data but the retrieval (or the playback) system must be low in cost. Asymmetric Cryptographic Algorithm - A cryptographic formula that uses two related keys—a public key and a private key —each of which has the characteristic algorithm that, given the public key, it is computationally infeasible to derive the private key. Asymmetric Digital Subscriber Line (ADSL): 1. An access technology that allows voice and high-speed data to be sent simultaneously over local exchange service copper facilities; the technology supports data rates of up to 1.544 Mb/s when receiving data (downstream rate) and up to 256 kb/s when sending data (upstream rate). 2. A modem technology that provides enhanced and affordable access to the Internet, live video, and a wide variety of other multimedia broadband services over existing copper twisted-pair wirelines; usually the ADSL operates with different data rates in the two directions. Asymmetric Encryption - An encryption system that utilizes two keys, one called a public key (which is known to both the sender and the recipient of encrypted data), and the other, called a private key (known only to the individual sending the data). Note: Data are encrypted with the private key and decrypted with the public key. Asymmetric encryption allows for the secure transfer of data. 39
- 40. Asynchronous Communications System - A data communications system that uses asynchronous operation. Note: The time spacing between successive data characters or blocks may be of arbitrary duration. Synonym start-stop system. Asynchronous Multiplexed Transmission System - A multiplexed transmission system in which the rates of the carrier and its tributaries are not traceable to the same master clocking source. Note: In this type of system, extra signal elements are usually appended to the individual tributary signals for the purpose of interleaving them at a rate consistent with the carrier rate. Asynchronous Network - A network in which the clocks do not need to be synchronous or mesochronous. Synonym nonsynchronous network. Asynchronous Operation - 1. A sequence of operations in which operations are executed out of time coincidence with any event. 2. An operation that occurs without a regular or predictable time relationship to a specified event; e.g., the calling of an error diagnostic routine that may receive control at any time during the execution of a computer program. Synonym asynchronous working. Asynchronous Time-Division Multiplexing (ATDM) - Time-division multiplexing in which asynchronous transmission is used. Asynchronous Transfer Mode (ATM) - A high-speed multiplexing and switching method utilizing fixed-length cells of 53 octets to support multiple types of traffic. Note: ATM, specified in international standards, is asynchronous in the sense that cells carrying user data need not be periodic. Asynchronous Transmission - Data transmission in which the instant that each character, or block of characters, starts is arbitrary; once started, the time of occurrence of each signal representing a bit within the character, or block, has the same relationship to significant instants of a fixed time frame. Asynchronous Working - Synonym asynchronous operation. ATB - Abbreviation for all trunks busy. AT Commands - A de facto standard for modem commands from an attached CPU, used in most 1,200 and 2,400 b/s modems. ATDM - Abbreviation for asynchronous time-division multiplexing. ATM - Abbreviation for Asynchronous Transfer Mode. Asynchronous transfer mode (ATM) is the international standard implementation of cell relay. It is defined to work over different physical media and at speeds ranging from 45-622 Mbps, with extensions to lower and higher speeds possible. Vendors are beginning to produce ATM network equipment and carriers are beginning to assemble ATM networks. Current service offerings are developmental in nature, however, and it is expected to take several years for the technology to mature. Significant infrastructure investments by carriers will be required to make ATM widely available. ATM, sometimes called cell relay, is a high speed multiplexing and switching technology for data. An advanced packet switching scheme, ATM makes all its packets one length. These uniformly small packets or cells let data flow smoothly, like a collection of images on movie film, all moving through the projector at a constant frame rate. ATM also boasts improved error control compared to conventional packet switching, as well as numerous other features that now make it a core technology of data networks world wide. ATM can run over SONET or T-Carrier. 40
- 41. ATM (asynchronous transfer mode) Connection - A virtual channel connection (VCC) or a virtual path connection (VPC). ATM (asynchronous transfer mode) Layer Connection - An association established by the ATM Layer to support communication between two or more ATM service users (i.e., two or more next higher layer entities or two or more ATM Management entities). The communication over an ATM Layer connection may be either bidirectional or unidirectional. When bidirectional, two virtual channel connections (VCCS) are used. When unidirectional, only one VCC is used. Note: In the case where there is ATM Layer connection associated ATM Layer Management (e.g., F5 Flow), the ATM Layer connection is bidirectional even if the user communication is unidirectional. ATM (asynchronous transfer mode) Transport System - A transport system composed of a carrier system terminated by an ATM multiplexer at each end. The relationship between input and output, i.e., virtual circuits, cannot change on a per call basis, i.e., permanent virtual circuits only are supported. This device does not allow blocking or signal compression. ATM Link (asynchronous transfer mode link) - A virtual path link (VPL) or a virtual channel link (VCL). Atmospheric Duct - A horizontal layer in the lower atmosphere in which the vertical refractive index gradients are such that radio signals (a) are guided or focused within the duct, (b) tend to follow the curvature of the Earth, and (c) experience less attenuation in the ducts than they would if the ducts were not present. Note: The reduced refractive index at the higher altitudes bends the signals back toward the Earth. Signals in a higher refractive index layer, i.e., duct, tend to remain in that layer because of the reflection and refraction encountered at the boundary with a lower refractive index material. Atmospheric Noise - Radio noise caused by natural atmospheric processes, primarily lightning discharges in thunderstorms. ATM Switch (asynchronous transfer mode switch) - 1. With reference to both analog and digital interfaces, the ATM functional unit and technology that operates with analog 2-wire interfaces and standard digital line rates on both the inputs and the outputs, e.g., DS1 on the input and DS3 on the output, and which passes the cells received on the input to the output. The relationship between input and output, can change on a per call basis, i.e., switched virtual circuits must be supported and permanent virtual circuits may be supported. (For the purposes of this document it is assumed that the cell formation function associated with an analog input is performed before the switch function occurs. However, this definition is not intended to constrain technical implementations.) This device allows blocking and concentration. The switch function is also required to perform 2-wire to 4-wire conversion as well as A/D conversion. 2. With reference to digital interfaces only, the ATM functional unit and technology that operates with cell-based signals and over standard line rates on both the inputs and the outputs, e.g., DS1 on the input and DS3 on the output, and which passes the cells received on the input to the output. The relationship between input and output, can change on a per-call basis, i.e., switched virtual circuits must be supported and permanent virtual circuits may be supported. This device allows blocking and performs concentration. Atomic Time - See International Atomic Time. ATOW - Acronym for acquisition and tracking orderwire. A downlink circuit that provides a terminal with information regarding uplink acquisition and synchronization status. ATSC - Advanced Television Systems Committee. This is the name of the DTV system used by broadcasters in the U.S. 41
- 42. ATSC Tuner - Often called an ATSC receiver or HDTV tuner, allows reception of DTV signals broadcast over- the-air by TV stations. May be integrated into a television set, VCR, DVR, or set-top box. Attachment - In e-mail, a computer file that is transmitted with an e-mail message. Note: Attachments are converted by an e-mail manager program, or by an add-on, to a MIME (multipurpose Internet mail extension) or binary format. The files are recovered by the recipient's e-mail manager program or by an add- on into their original, usually application-specific, format. Attachment Unit Interface (AUI) - In a local area network, the interface between the medium access unit (MAU) and the data terminal equipment within a data station. Attack - 1. An attempt to violate computer security. Note: An example of an attack is malicious logic. 2. [An] intentional act of attempting to bypass one or more of the following security controls of an information system (IS): nonrepudiation, authentication, integrity, availability, or confidentiality. Attack Time - The time between (a) the instant that a signal at the input of a device or circuit exceeds the activation threshold of the device or circuit and (b) the instant that the device or circuit reacts in a specified manner, or to a specified degree, to the input. Note: Attack time occurs in devices such as clippers, peak limiters, compressors, and voxes. Attendant Access Loop - A switched circuit that provides an attendant with a manual means for call completion and control. Note: An attendant access loop might be given a specific telephone number. Synonym access loop. Attendant Conference - A network-provided service feature that allows an attendant to establish a conference connection of three or more users. Attendant Position - The part of a switching system used by an attendant, i.e., an operator, to assist users in call completion and use of special services. Attention Character - In [a] trusted-computing-base (TCB) design, a character entered from a terminal that tells the TCB the user wants a secure communications path from the terminal to some trusted node to provide a secure service for the user. Attention Signal - The attention signal to be used by AM, FM, and TV broadcast stations to actuate muted receivers for inter-station receipt of emergency cuing announcements and broadcasts involving a range of emergency contingencies posing a threat to the safety of life or property. Attenuation - The decrease in intensity of a signal, beam, or wave as a result of absorption of energy and of scattering out of the path to the detector, but not including the reduction due to geometric spreading. Note 1: Attenuation is usually expressed in dB. Note 2: "Attenuation" is often used as a misnomer for " attenuation coefficient," which is expressed in dB per kilometer. Note 3: A distinction must be made as to whether the attenuation is that of signal power or signal electric field strength. Attenuation Coefficient - The rate of diminution of average power with respect to distance along a transmission path. Note: The attenuation coefficient is often calculated as the sum of the absorption coefficient and the scattering coefficient. Synonym attenuation rate. Attenuation Constant - 1. The real part of the propagation constant in any electromagnetic propagation medium. Note 1: The attenuation constant is usually expressed as a numerical value per unit length. Note 2: 42
- 43. The attenuation constant may be calculated or experimentally determined for each medium. 2. For a particular propagation mode in an optical fiber, the real part of the axial propagation constant. Attenuation Distortion - The difference in loss at specified frequencies relative to the loss at 1004 Hz, unless otherwise specified. Attenuation-Limited Operation - The condition that prevails when attenuation, rather than bandwidth, limits the performance of a communications link. Attenuation Rate - Synonym attenuation coefficient. Attenuator - 1. In electrical systems, a network that reduces the amplitude of a signal without appreciably distorting its waveform. Note 1: Electrical attenuators are usually passive devices. Note 2: The degree of attenuation may be fixed, continuously adjustable, or incrementally adjustable. Fixed attenuators are often called pads, especially in telephony. Note 3: The input and output impedances of an attenuator are usually matched to the impedances of the signal source and load, respectively. 2. In optical systems, a device that reduces the amplitude of a signal without appreciably distorting its waveform. Note 1: Optical attenuators are usually passive devices. Note 2: The degree of attenuation may be fixed, continuously adjustable, or incrementally adjustable. Attribute - 1. In database management, a property inherent in an entity or associated with that entity for database purposes. 2. In network management, a property of a managed object that has a value. Note 1: Mandatory initial values for attributes can be specified as part of the managed object class definition. Note 2: Attributes may be either mandatory or conditional. Attribute Authority: In computer security, an entity that is trusted by at least two entities to create and assign attribute certificates. Attribute Certificate - A set of attributes and a public key certificate identifier that are made unforgeable by use of the digital signature created with a private key. ATV - Abbreviation for advanced television. Audible - Synonym for audible ringing tone. Audible Ringing - An audible signal (information tone) transmitted to the calling party when the called party is alerted. Audible Ringing Tone - In telephony, a signal, usually consisting of an audio tone interrupted at a slow repetition rate, provided to a caller to indicate that the called-party instrument is being sent a ringing signal. Note: The audible ringing tone may be generated by the called-party servicing switch or by the calling-party servicing switch, but it is not generated by the called telephone instrument. Synonyms audible ringing, ringback tone. Audio Channel - A means for delivering audio signals from one point to another. An audio waveform submitted to the channel input results in a similar (not necessarily identical) waveform at the channel output. The audio channel may be comprised of the following components: encoders (compressors) and decoders (decompressors), buffers, multiplexors and demultiplexors, modulators and demodulators, transmission facilities, switches, multipoint conference units, and other components necessary to achieve the desired channel characteristics. 43
- 44. Audio Dubbing - 1. In videotape editing, a process or technique employed to (a) enhance (e.g., remove noise from, or introduce some kind of special effect into), (b) add to, or (c) replace totally, the originally recorded audio (if any), without modifying the originally recorded video signal. 2. In audiotape editing or mixing, a process analogous to any of the above, performed (a) on a single audio channel, or (b) on one or more audio channels of a multi-track recording without modifying the other channel(s). 3. The copying of one or more audio signals from one storage medium, location, or format to another with or without modification or enhancement. Audio-Follow-Video - A video recording, mixing or switching technique or process in which the audio signal associated with any given video signal is recorded, switched, or mixed with that video signal. Audio Frame - A presentation unit of the audio channel; a group of consecutive audio samples. The preferred number of samples in an audio frame depends on the audio sample rate. These audio frames have no relationship to the frames designated by certain audio/speech codecs. Audio Frequency (AF) - The band of frequencies (approximately 20 Hz to 20 kHz) that, when transmitted as acoustic waves, can be heard by the normal human ear. Audio Response Unit (ARU) - A device that provides synthesized voice responses to dual-tone multifrequency signaling input by processing calls based on (a) the call-originator input, (b) information received from a host data base, and (c) information in the incoming call, such as the time of day. Note: ARUs are used to increase the number of information calls handled and to provide consistent quality in information retrieval. Audit - 1. To conduct an independent review and examination of system records and activities in order to test the adequacy and effectiveness of data security and data integrity procedures, to ensure compliance with established policy and operational procedures, and to recommend any necessary changes. 2. Independent review and examination of records and activities to assess the adequacy of system controls, to ensure compliance with established policies and operational procedures, and to recommend necessary changes in controls, policies, or procedures. Audit Record Field - A field containing information regarding all entities in a transaction, and indicators of the types of processing performed by those entities. Audit Review File - A file created by executing statements included in a computer program for the explicit purpose of providing data for auditing. Audit Trail - 1. A record of both completed and attempted accesses and service. 2. Data in the form of a logical path linking a sequence of events, used to trace the transactions that have affected the contents of a record. 3. [In INFOSEC, a] chronological record of system activities to enable the reconstruction and examination of the sequence of events and/or changes in an event. Note: Audit trail may apply to information in an information system (IS), to message routing in a communications system, or to the transfer of COMSEC material. AUI - Abbreviation for attachment unit interface. Aurora - Sporadic radiant emission from the upper atmosphere that usually occurs about the North and South magnetic poles of the Earth. Note 1: Auroras are most intense at times of intense magnetic storms caused by sunspot activity. The distribution of auroral intensity with altitude shows a pronounced maximum near 100 km above the Earth. Auroras may occasionally be observed within 40° or less of the equator. Note 2: Auroras interfere with radio communications. Note 3: In the Northern hemisphere, the aurora is called the 44
- 45. Aurora Borealis (Northern Lights). In the Southern hemisphere, the aurora is called the Aurora Australis (Southern Lights). Authenticate - 1. To establish, usually by challenge and response, that a transmission attempt is authorized and valid. 2. [To] verify the identity of a user, user device, or other entity, or the integrity of data stored, transmitted, or otherwise exposed to unauthorized modification in an information system (IS), or establish the validity of a transmission. 3. A challenge given by voice or electrical means to attest to the authenticity of a message or transmission. Authentication - 1. [Any] Security measure designed to establish the validity of a transmission, message, or originator, or a means of verifying an individual's authorization to receive specific categories of information. 2. A security measure designed to protect a communications system against acceptance of a fraudulent transmission or simulation by establishing the validity of a transmission, message, or originator. 3. Evidence by proper signature or seal that a document is genuine and official. Authentication Algorithm: An encryption process or tool in which the results of text encryption depend on all relevant authentication elements. Authentication Element - A contiguous group of characters or bits that are corruption-protected by being processed by the authentication algorithm. Authentication Exchange - A mechanism intended to ensure the identity of an entity by means of an information exchange. Authentication Information - Information used to establish the validity of a claimed identity of an entity. Authentication Key - A (data-encryption algorithm) key used to authenticate data in accordance with specific encryption standards. Authentication System - [A] cryptosystem or process used for authentication. Authenticator - 1. A symbol or group of symbols, or a series of bits, selected or derived in a prearranged manner and usually inserted at a predetermined point within a message or transmission for the purpose of attesting to the validity of the message or transmission. 2. A letter, numeral, group of letters or numerals, or any combinations of these, attesting to the authenticity of a message or transmission. 3. a means used to confirm the identity of a station, originator, or individual. Authorization - 1. The rights granted to a user to access, read, modify, insert, or delete certain data, or to execute certain programs. 2. Access privileges granted to a user, program, or process. Authorization Certificate - Any of several types of attribute certificates containing information used in the authorization process. Note: Authorization information may also be contained in a public key certificate, in which case that public key certificate also serves as an authorization certification Authorized Bandwidth - 1. Authorized bandwidth is, for purposes of this Manual, the necessary bandwidth (bandwidth required for transmission and reception of intelligence) and does not include allowance for transmitter drift or Doppler shift. 2. The maximum bandwidth authorized to be used by a station as specified in the station license. This shall be occupied bandwidth or necessary bandwidth, whichever is greater. 3. The maximum width of the band of frequencies permitted to be used by a station. This is normally considered to be the necessary or occupied bandwidth, whichever is greater. 45
- 46. Authorized Frequency - 1. A frequency that is allocated and assigned by a competent authority to a specific user for a specific purpose. 2. The frequency, or frequency range, assigned to a station by the Commission [FCC] and specified in the instrument of authorization. See assigned frequency. Authorized Signatory - The highest level issuer of authorization certificates in an organization. Note: Authorized signatories are designated in a signatory certificate, which is issued to an organization by an agreed signatory authority. Authorized User - In security, a user who may, according to an organization's security policy, perform an operation. AUTODIN - Acronym for automatic digital network. See Defense Data Network. Auto Fax Tone (CNG ) - This tone is produced by virtually all FAX machines when it dials the receiving FAX machine’s number from memory. Older FAX machines and some current models that do not have speed-dial memory will not produce CNG. CNG is a medium-pitch tone (1100 Hz) that last 1/2 second and repeats every 3-1/2 seconds. A FAX machine will produce CNG for about 45 seconds after it dials the receiving FAX number. Automated Attendant - An automated attendant system allows the caller to be automatically be transferred to a user's extension without the intervention of a receptionist. A receptionist can be reached by pressing 0 on most systems. There is a dial-by-name directory like 411 to find user on a system. The dial-by-name directory is usually set up last name followed by first name. Once the user ID is announced you can press # or it will automatically ring the extension. Express messaging is used when you don't want to disturb the user or are calling a guest mailbox without a phone. A phone can be set to "Do Not Disturb" to forward all calls directly to voicemail without ringing the extension. On some systems there is a message-only information so that a company can give directions to their office, job offerings etc. Theese mailboxes are forwarded to the receptionist after each message plays or the user can return to the main menu. Some colleges have telephone registration where the user uses the key pad or voice response to register for courses, check for grades, etc. Other features of automated attendant systems include transferring to another outside line, connecting two companies via wide area networking, incorporating Outlook Express to have Unified Messaging. Automated Data Medium - Synonym machine-readable medium. - A medium capable of storing data in a form that can be accessed by an automated sensing device. Note: Examples of machine-readable media include (a) magnetic disks, cards, tapes, and drums, (b) punched cards and paper tapes, (c) optical disks, and (d) magnetic ink characters. Automated Information System (AIS) - 1. An assembly of computer hardware, software, firmware, or any combination of these, configured to accomplish specific information-handling operations, such as communication, computation, dissemination, processing, and storage of information. 2. any equipment or interconnected system or subsystems of equipment that is used in the automatic acquisition, storage, manipulation, management, movement, control, display, switching, interchange, transmission or reception of data and includes computer software, firmware, and hardware. Note: Included are computers, word processing systems, networks, or other electronic information handling systems, and associated equipment. 3. See information systems security. 46
- 47. Automated Information Systems Security - 1. Measures and controls that ensure confidentiality, integrity, and availability of the information processed and stored by automated information systems. Note 1: The unauthorized disclosure, modification, or destruction may be accidental or intentional. Note 2: Automated information systems security includes consideration of all hardware and software functions, characteristics and features; operational procedures; accountability procedures; and access controls at the central computer facility, remote computer, and terminal facilities; management constraints; physical structures and devices, such as computers, transmission lines, and power sources; and personnel and communications controls needed to provide an acceptable level of risk for the automated information system and for the data and information contained in the system. Automated information systems security also includes the totality of security safeguards needed to provide an acceptable protection level for an automated information system and for the data handled by an automated information system. 2. Synonym computer security. Automated Maritime Telecommunications System (AMTS) - An automatic, integrated and interconnected maritime communications system serving ship stations on specified inland and coastal waters of the United States. Automated Radio - A radio that can be automatically controlled by electronic devices and that requires little or no human intervention. Automated Security Monitoring - Use of automated procedures to ensure security controls are not circumvented or the use of these tools to track actions taken by subjects suspected of misusing the information system (IS). Automated Tactical Command and Control System - A command and control system, or part thereof, that manipulates the movement of information from source to user without human intervention. Note: In an automated tactical command and control system, automated execution of a decision without human intervention is not mandatory. Automatic Answering - A service feature in which the called terminal automatically responds to the calling signal and the call may be established whether or not the called terminal is attended by an operator. Automatic Callback - A service feature that permits a user, when encountering a busy condition, to instruct the system to retain the called and calling numbers and to establish the call when there is an available line. Note 1: Automatic callback may be implemented in the terminal, in the switching system, or shared between them. Note 2: Automatic callback is not the same as camp-on. Automatic Call Distributor (ACD) - A device that distributes incoming calls to a specific group of terminals. Note: If the number of active calls is less than the number of terminals, the next call will be routed to the terminal that has been in the idle state the longest. If all terminals are busy, the incoming calls are held in a first-in-first-out queue until a terminal becomes available. An ACD is a telephone facility that manages incoming calls and handles them based on the number called and an associated database of handling instructions. Many companies offering sales and service support use ACDs to validate callers, make outgoing responses or calls, forward calls to the right party, allow callers to record messages, gather usage statistics, balance the use of phone lines, and provide other services. ACDs often provide some form of Automatic Customer/Caller Identification (ACIS) such as that provided by Direct Inward Dialing (DID), Dialed Number Identification Service (DNIS), or Automatic Number Identification (ANI). Automatic Call Processor - A device that distributes incoming calls to a specific devices. Note: If the number of active calls is more than the number of lines, the next will receive a busy signal. 47
- 48. Automatic Calling - Calling in which the elements of the selection signal are entered into the data network contiguously at the full data signaling rate. The selection signal is generated by the data terminal equipment. Note: A limit may be imposed by the design criteria of the network to prevent more than a permitted number of unsuccessful call attempts to the same address within a specified period. Automatic Calling Unit (ACU) - A device that enables equipment, such as computers and card dialers, to originate calls automatically over a telecommunications network. Automatic Coin Telephone System (ACTS) - is a public coin-operated telephone service that completes a variety of phone calls, times the calls, and collects payment without the aid of an operator. Automatic Data Handling (ADH): 1. A generalization of automatic data processing to include the aspect of data transfer. 2. Combining data processing and data transfer. Automatic Data Processing (ADP) - 1. An interacting assembly of procedures, processes, methods, personnel, and equipment to perform automatically a series of data processing operations on data. Note: The data processing operations may result in a change in the semantic content of the data. 2. Data processing by means of one or more devices that use common storage for all or part of a computer program, and also for all or part of the data necessary for execution of the program; that execute user-written or user- designated programs; that perform user-designated symbol manipulation, such as arithmetic operations, logic operation, or character-string manipulations; and that can execute programs that modify themselves during their execution. Note: Automatic data processing may be performed by a stand-alone unit or by several connected units. 3. Data processing largely performed by automatic means. 4. That branch of science and technology concerned with methods and techniques relating to data processing largely performed by automatic means. Automatic Data Processing Equipment (ADPE) - Any equipment or interconnected system or subsystems of equipment that is used in the automatic acquisition, storage, manipulation, management, movement, control, display, switching, interchange, transmission, or reception, of data or information (i) by a Federal agency, or (ii) under a contract with a Federal agency which (i) requires the use of such equipment, or (ii) requires the performance of a service or the furnishing of a product which is performed or produced making significant use of such equipment. Such term includes (i) computer, (ii) ancillary equipment, (iii) software, firmware, and similar procedures, (iv) services, including support services, and (v) related resources as defined by regulations issued by the Administrator for General Services. . . . [Public Law 99-500, Title VII, Sec. 822 (a) Section 111(a) of the Federal Property and Administrative Services Act of 1949 (40 U.S.C. 759(a)) revised.] Automatic Dialing - See automatic calling unit. Automatic Digital Network (AUTODIN) - Formerly, a worldwide data communications network of the Defense Communications System, now replaced by the Defense Switched Network (DSN). Automatic Error Correction - See error-correcting code. Automatic Exchange - In a telephone system, an exchange in which communications among users are effected by means of switches set in operation by the originating user equipment without human intervention at the central office or branch exchange. Automatic Fax Switch - A device that allows a single phone line to be shared for multiple devices. Common applications include any variation of voice, a fax machine, fax/modem and/or modem(s). Incoming calls are automatically routed to the proper device(s). If the call comes in and it is a fax call, the call is automatically routed to the fax machine or fax.modem. If the call is a modem call, it is routed to the correct modem. Voice 48
- 49. calls are routes to phone(s) and/pr answering machine. May require a security access code (SAC) in the dialing string to automatically switch to the modem. Synonym Automatic Line Sharing Device . Fax Switch , Phone Fax Switch , Automatic Frequency Control (AFC) - A device or circuit that maintains the frequency of an oscillator within the specified limits with respect to a reference frequency. Automatic Function - A machine function or series of machine functions controlled by a program and carried out without assistance of an operator. Automatic Gain Control (AGC) - A process or means by which gain is automatically adjusted in a specified manner as a function of a specified parameter, such as received signal level. Automatic Identified Outward Dialing (AIOD) - A service feature of some switching or terminal devices that provides the user with an itemized statement of usage on directly dialed calls. Note: AIOD is facilitated by automatic number identification (ANI) equipment to provide automatic message accounting (AMA). Automatic Line Sharing Device - A device that allows a single phone line to be shared for multiple devices. Common applications include any variation of voice, a fax machine, fax/modem and/or modem(s). Incoming calls are automatically routed to the proper device(s). If the call comes in and it is a fax call, the call is automatically routed to the fax machine or fax .modem. If the call is a modem call, it is routed to the correct modem. Voice calls are routes to phone(s) and/pr answering machine. May require a security access code (SAC) in the dialing string to automatically switch to the modem. Synonyms Automatic Fax Switch , Fax Switch , Phone Fax Switch , Automatic Link Establishment (ALE) - 1. In high-frequency (HF) radio, the capability of a station to make contact, or initiate a circuit, between itself and another specified radio station, without human intervention and usually under processor control. Note: ALE techniques include automatic signaling, selective calling, and automatic handshaking. Other automatic techniques that are related to ALE are channel scanning and selection, link quality analysis (LQA), polling, sounding, message store-and-forward, address protection, and anti-spoofing. 2. In HF radio, a link control system that includes automatic scanning, selective calling, sounding, and transmit channel selection using link quality analysis data. Note: Optional ALE functions include polling and the exchange of orderwire commands and messages. Automatic Link Transfer - Automatic rerouting of the radio portion of a call for signal quality, traffic management, or other reasons. Automatic Message Accounting (AMA) - A service feature that automatically records data regarding user- dialed calls. Automatic Message Exchange (AME) - In an adaptive high-frequency (HF) radio network, an automated process allowing the transfer of a message from message injection to addressee reception, without human intervention. Note: Through the use of machine-addressable transport guidance information, i.e., the message header, the message is automatically routed through an on-line direct connection through single or multiple transmission media. Automatic Message Processing System (AMPS) - Any organized assembly of resources and methods used to collect, process, and distribute messages largely by automatic means. Automatic Number Identification (ANI) - 1. A service feature in which the directory number or equipment number of a calling station is automatically obtained. Note: ANI is used in message accounting. 2. The code 49
- 50. that provides the billing number of the line or trunk that originated a call. 3. A system that identifies the billing account for a call. For 911 systems, the ANI identifies the calling party and may be used as a call back number. Automatic Operation - The functioning of systems, equipment, or processes in a desired manner at the proper time under control of mechanical or electronic devices that operate without human intervention. Automatic Personal Deregistration - The process by which a user's location registration is automatically canceled without any explicit action from the user. Automatic Personal Registration - The process by which a user's location registration is automatically updated without any explicit action from the user. Automatic Redial - A service feature that allows the user to dial, by depressing a single key or a few keys, the most recent telephone number dialed at that instrument. Note: Automatic redial is often associated with the telephone instrument, but may be provided by a PBX, or by the central office. Synonym last number redial. Automatic Reload - See bootstrap. Automatic Remote Rekeying - [In INFOSEC, a] procedure to rekey a distant crypto-equipment electronically without specific actions by the receiving terminal operator. [INFOSEC-99] Note: Automatic remote rekeying may also apply to non-crypto devices. Automatic Remote Reprogramming and Rekeying - The procedure by which distant equipment is reprogrammed or rekeyed electronically without specific actions by the receiving terminal. Automatic Repeat-Request (ARQ) - See ARQ. Automatic Ringdown Circuit - A circuit providing priority telephone service, typically for key personnel; the circuit is activated when the telephone handset is removed from the cradle causing a ringing signal to be sent to the distant unit(s). See verified off-hook. Automatic Route Selection (ARS) - Electronic or mechanical selection and routing of outgoing calls without human intervention. Automatic Secure Voice Communications Network (AUTOSEVOCOM) - A worldwide, switched, secure voice network developed to fulfill DOD long-haul, secure voice requirements. Automatic Sequential Connection - A service feature in which the terminals at each of a set of specified addresses are automatically connected, in a predetermined sequence, to a single terminal at a specified address. Automatic Signaling Service - Synonym hotline. Automatic Sounding - The testing of selected channels or paths by providing a very brief beacon-like identifying broadcast that may be used by other stations to evaluate connectivity, propagation, and availability, and to identify known working channels for possible later use for communications or calling. Note 1: Automatic soundings are primarily intended to increase the efficiency of the automatic link establishment (ALE) function, thereby increasing system throughput. Note 2: Sounding information is used for identifying the specific channel to be used for a particular ALE connectivity attempt. 50
- 51. Automatic Switching System - 1. In data communications, a switching system in which all the operations required to execute the three phases of information-transfer transactions are automatically executed in response to signals from a user end-instrument. Note: In an automatic switching system, the information- transfer transaction is performed without human intervention, except for initiation of the access phase and the disengagement phase by a user. 2. In telephony, a system in which all the operations required to set up, supervise, and release connections required for calls are automatically performed in response to signals from a calling device. Automatic Voice Network (AUTOVON) - Formerly, the principal long-haul, unsecure voice communications network within the Defense Communications System, now replaced by the Defense Switched Network (DSN). Automation - 1. The implementation of processes by automatic means. 2. The investigation, design, development, and application of methods of rendering processes automatic, self-moving, or self-controlling. 3. The conversion of a procedure, a process, or equipment to automatic operation. Autonomous System - Internet (TCP/IP) terminology for a collection of gateways (routers) that fall under one administrative entity and that cooperate using a common interior gateway protocol (IGP). [Bahorsky] Note: Routers pertaining to different autonomous systems must agree on a common exterior gateway protocol in order to communicate with each other effectively. Auto-Reply - In e-mail systems, a message sent automatically upon receipt of incoming e-mail. Note: Auto- replies are used to acknowledge delivery of e-mail and to provide receipts for e-mail messages. AUTOSEVOCOM - Acronym for Automatic Secure Voice Communications Network. AUTOVON - Acronym for Automatic Voice Network. Superseded by Defense Switched Network. Auxiliary Operation - An offline operation performed by equipment not under control of the processing unit. Auxiliary Power - Electric power that is provided by an alternate source and that serves as backup for the primary power source at the station main bus or prescribed sub-bus. Note 1: An offline unit provides electrical isolation between the primary power source and the critical technical load whereas an online unit does not. Note 2: A Class A power source is a primary power source, i.e., a source that assures an essentially continuous supply of power. Note 3: Types of auxiliary power services include Class B, a standby power plant to cover extended outages of the order of days; Class C, a 10-to-60-second quick-start unit to cover short- term outages of the order of hours; and Class D, an uninterruptible non-break unit using stored energy to provide continuous power within specified voltage and frequency tolerances. Auxiliary Storage - 1. Storage that is available to a processor only through its input / output channels. 2. In a computer, any storage that is not internal memory, i.e., is not random access memory (RAM). Note: Examples of auxiliary storage media are magnetic diskettes, optical disks including CD ROM, and magnetic tape cassettes. Availability - 1. The degree to which a system, subsystem, or equipment is operable and in a committable state at the start of a mission, when the mission is called for at an unknown, i.e., a random, time. Note 1: The conditions determining operability and committability must be specified. Note 2: Expressed mathematically, availability is 1 minus the unavailability. 2. The ratio of (a) the total time a functional unit is capable of being used during a given interval to (b) the length of the interval. Note 1: An example of availability is 100/168 if the unit is capable of being used for 100 hours in a week. Note 2: Typical availability objectives are specified in decimal fractions, such as 0.9998. 3. Timely, reliable access to data and information services for authorized users. 51
- 52. Available Line - 1. In voice, video, or data communications, a circuit between two points that is ready for service, but is in the idle state. 2. In facsimile transmission, the portion of the scanning line that can be specifically used for image signals. Synonym useful line. Available State - A state where a (bidirectional or unidirectional) service is usable. Note: Each direction of a service is assumed to be in the available state unless a transition to the unavailable state is observed without a subsequent transition to the available state. In this standard the transitions between the available and unavailable states are: (a) transition to the unavailable state occurs at the beginning of 10 consecutive severely errored seconds (SES); (b) transition to the available state occurs at the beginning of 10 consecutive seconds none of which is an SES. Available Time - From the point of view of a user, the time during which a functional unit can be used. Note: From the point of view of operating and maintenance personnel, the available time is the same as the uptime, i.e., the time during which a functional unit is fully operational. Avalanche Multiplication - A current-multiplying phenomenon that occurs in a semiconductor photodiode that is reverse-biased just below its breakdown voltage. Note: Under such a condition, photocurrent carriers, i.e., electrons, are swept across the junction with sufficient energy to ionize additional bonds, creating additional electron-hole pairs in a regenerative action. Avalanche Photodiode (APD) - A photodiode that operates with a reverse-bias voltage that causes the primary photocurrent to undergo amplification by cumulative multiplication of charge carriers. Note: As the reverse-bias voltage increases toward the breakdown, hole-electron pairs are created by absorbed photons. An avalanche effect occurs when the hole-electron pairs acquire sufficient energy to create additional pairs when the incident photons collide with the ions, i.e., the holes and electrons. Thus, a signal gain is achieved. Avatar - An interactive representation of a human in a virtual reality environment. Average Picture Level (APL) - In video systems, the average level of the picture signal during active scanning time integrated over a frame period; defined as a percentage of the range between blanking and reference white level. Average Rate of Transmission - Synonym effective transmission rate. AVI (.avi) - Abbreviation for audio video interleaved. A file-name extension used to indicate a compressed video file in the AVI standard for a common operating system. Note: This file format for digital video and audio compression indicates that (a) the audio and video data are stored in alternate blocks, and (b) the file format is cross-platform compatible, allowing .avi video files to be played under various operating systems. AVK - Abbreviation for audio video kernel. Digital video interface (. dvi) software designed for playing motion video and audio across several different varieties of hardware and operating systems. Avoidance Routing - The assignment of a circuit path to avoid certain critical or trouble-prone circuit nodes. AVSS - Abbreviation for audio-video support system. A digital video interface system software (for DOS) that plays motion video and audio. AWG - Abbreviation for American wire gauge. A standard system for measuring and classifying the thickness of wire conductors; also referred to as the "Brown and Sharpe (B & S)" wire gauge. AWGN - Abbreviation for additive white gaussian noise. See white noise. 52
- 53. Axial Propagation Constant - In an optical fiber, the propagation constant evaluated along the optical axis of the fiber in the direction of transmission. Note: The real part of the axial propagation constant is the attenuation constant. The imaginary part is the phase constant. Axial Ratio - Of an electromagnetic wave having elliptical polarization, the ratio of the magnitudes of the major axis and the minor axis of the ellipse described by the electric field vector. Axial Ray - A light ray that travels along the optical axis. B b - Abbreviation for bit. (binary digit) The smallest unit of computer information. B - Abbreviation for bel, byte. A byte is combination of bits that represents a single character (approximately 8 bits equal one byte). B8ZS (bipolar 8-zero substitution, also called binary 8-zero substitution, clear channel, and clear 64) - is an encoding method used on T1 circuits that inserts two successive ones of the same voltage - referred to as a bipolar violation - into a signal whenever eight consecutive zeros are transmitted. The device receiving the signal interprets the bipolar violation as a timing mark, which keeps the transmitting and receiving devices synchronized. Ordinarily, when successive ones are transmitted, one has a positive voltage and the other has a negative voltage. B8ZS is based on an older encoding method called alternate mark inversion (AMI). AMI is used with Dataphone Digital Service, the oldest data service still in use that uses 64 Kbps channels. AMI, however, requires the use of 8 Kbps of the 64 Kbps of each channel to maintain synchronization. In a T1 circuit, there are 24 channels. This loss adds up to 192 Kbps, which means that in reality only 56 Kbps is available for data transmission. B8ZS uses bipolar violations to synchronize devices, a solution that does not require the use of extra bits, which means a T1 circuit using B8ZS can use the full 64 Kbps for each channel for data. B8ZS is not compatible with older AMI equipment. T1 technology is used in the United States and Japan. In Europe, a comparable technology called E1 provides 32 channels instead of 24 and uses an encoding scheme called high-density bipolar 3 (HDB3) instead of B8ZS. Babble - In transmission systems, the aggregate of crosstalk induced in a given line by all other lines. Backbone - 1. The high-traffic-density connectivity portion of any communications network. 2. In packet- switched networks, a primary forward-direction path traced sequentially through two or more major relay or switching stations. Note: In packet-switched networks, a backbone consists primarily of switches and interswitch trunks. Backbone - A series of high-speed network connections through which other networks connect. Back Door - Synonym trapdoor. A hidden software or hardware mechanism, usually created for testing and troubleshooting, that may be used to circumvent computer security. Background - 1. In Web pages, an image or color, usually defined in HTML, that serves as the underlying color or imagery for a Web page. Note: Browsers may also be configured to dictate backgrounds. 2. In computer display systems, the underlying color or imagery for the main screen or for the fundamental window of a computer's operating system. 53
- 54. Background Noise - The total system noise in the absence of information transmission. Background Processing - The execution of lower priority computer programs when higher priority programs are not using the system resources. Note: Priorities may be assigned by system software, application software, or the operator. Backhaul - 1. The practice of routing telecommunications traffic beyond its intended destination, and then back to the intended destination, usually for the purpose of taking advantage of tariffs or prices that are lower than those afforded by direct routing. 2. In security, to bring a call that has been routed along a particular path (usually via satellite) to some earlier position in the switching sequence (also using satellites). Note: The technique supports CALEA, the Communications Assistance to Law Enforcement Act and LAES, Lawfully Authorized Electronic Surveillance. 3. In commercial telephone networks, referring to a trunk or line between two central offices that may not share the same facilities or geographic location, and which trunk is used to support special services, e.g., orderwires, off-premises extensions, common exchange number routing, or least-cost routing of customer centrex services. 4. In mission programs requiring contingency networking, referring to a link that provides feedback to the mission control center to verify that the transmission via a primary communications has been successful. Note: In cases where the primary path fails to deliver the transmission, the communications may occur over the backhaul connection or an alternative network connection. 5. In contingency networking, an alternative connection that is routed via a diversified path, e.g., an alternative frequency, satellite facility, cable, trunk, or time slot. Backscattering - 1. Radio wave propagation in which the direction of the incident and scattered waves, resolved along a reference direction (usually horizontal) are oppositely directed. A signal received by backscattering is often referred to as "backscatter." 2. In optics, the scattering of light into a direction generally opposite to the original one. Back-to-Back Connection - 1. A direct connection between the output of a transmitting device and the input of an associated receiving device. Note: When used for equipment measurements or testing purposes, such a back-to-back connection eliminates the effects of the transmission channel or medium. 2. A direct connection between the output of a receiving device and the input to a transmitting device. Note: The term "direct," as used in both definitions, may be construed as permitting a passive device such as a pad (attenuator) to accommodate power level constraints. Backup - 1. [A] copy of files and programs made to facilitate recovery, if necessary. 2. See backup file. Backup File - A copy of a file made for purposes of later reconstruction of the file, if necessary. Note: A backup file may be used for preserving the integrity of the original file and may be recorded on any suitable medium. Synonym job-recovery control file. Backward Channel - 1. In data transmission, a secondary channel in which the direction of transmission is constrained to be opposite to that of the primary, i.e., the forward (user-information) channel. Note: The direction of transmission in the backward channel is restricted by the control interchange circuit that controls the direction of transmission in the primary channel. 2. In a data circuit, the channel that passes data in a direction opposite to that of its associated forward channel. Note 1: The backward channel is usually used for transmission of supervisory, acknowledgement, or error-control signals. The direction of flow of these signals is opposite to that in which user information is being transferred. Note 2: The backward- channel bandwidth is usually less than that of the primary channel, i.e., the forward (user information) channel. Backward Indicator Bit (BIB) - A signal unit (or sequence of bits) that (by changing its status) is used to request retransmission by the remote end whenever it receives a signal unit that is out of sequence. 54
- 55. Backward Recovery - The reconstruction of an earlier version of a file by using a newer version of data recorded in a journal. Backward Sequence Number (BSN) - A field in a signal unit that contains the forward sequence number of a correctly received signal unit being acknowledged in the signal unit that is being returned to the sender. Backward Signal - A signal sent from the called to the calling station, i.e., from the original data sink to the original data source. Note: Backward signals are usually sent via a backward channel and may consist of supervisory, acknowledgment, or control signals. Backward Supervision - The use of supervisory signal sequences from a secondary to a primary station. Bacterium - A program that attempts to propagate itself by e-mailing a copy of itself to e-mail addresses found on a recipient's hard drive. This is done without the consent or knowledge of the recipient. Note: In many cases, this type of program does not attempt to cause any direct damage to user's system, but rather attempts to overload the e-mail distribution system, much as a successful chain letter would do to the postal system. Synonym [in cryptosystems] chain letter. Bad Sectoring - A technique for copy protection in which bad sectors are intentionally written on a diskette. Balance - In electrical circuits and networks, to adjust the impedance to achieve specific objectives, such as to reach specified return loss objectives at a hybrid junction of two-wire and four-wire circuits. Balanced - Pertaining to electrical symmetry. Balanced Code - 1. In PCM systems, a code constructed so that the frequency spectrum resulting from the transmission of any code word has no dc component. 2. In PCM, a code that has a finite digital sum variation. Balanced Line - A transmission line consisting of two conductors in the presence of ground, capable of being operated in such a way that when the voltages of the two conductors at all transverse planes are equal in magnitude and opposite in polarity with respect to ground, the currents in the two conductors are equal in magnitude and opposite in direction. Note: A balanced line may be operated in an unbalanced condition. Synonym balanced signal pair. Balanced Modulator - A modulator constructed so that the carrier is suppressed and any associated carrier noise is balanced out. Note 1: The balanced modulator output contains only the sidebands. Note 2: Balanced modulators are used in AM transmission systems. Balanced Signal Pair - Synonym balanced line. A transmission line consisting of two conductors in the presence of ground, capable of being operated in such a way that when the voltages of the two conductors at all transverse planes are equal in magnitude and opposite in polarity with respect to ground, the currents in the two conductors are equal in magnitude and opposite in direction. Note: A balanced line may be operated in an unbalanced condition. Balance Return Loss - 1. A measure of the degree of balance between two impedances connected to two conjugate sides of a hybrid set, coil, network, or junction. 2. A measure of the effectiveness with which a balancing network simulates the impedance of a two-wire circuit at a hybrid coil. Balancing Network - 1. In a hybrid set, hybrid coil, or resistance hybrid, a circuit used to match, i.e., to balance, the impedance of a uniform transmission line, i.e., twisted metallic pair, over a selected range of frequencies. Note: A balancing network is required to ensure isolation between the two ports of the four- 55
- 56. wire side of the hybrid. 2. A device used between a balanced device or line and an unbalanced device or line for the purpose of transforming from balanced to unbalanced or from unbalanced to balanced. Balun - Abbreviation for balanced to unbalanced. In radio frequency usage, a device used to couple a balanced device or line to an unbalanced device or line. Band - 1. In communications, the frequency spectrum between two defined limits. 2. A group of tracks on a magnetic drum or on one side of a magnetic disk. 3. A set of frequencies authorized for use in a geographical area defined for common carriers for purposes of communications system management. Band-Elimination Filter - Synonym band-stop filter. A filter that attenuates, usually to very low levels, all frequencies between two non-zero, finite limits and passes all frequencies not within the limits. Note: A band-stop filter may be designed to stop the specified band of frequencies but usually only attenuates them below some specified level. Bandpass Filter - A filter that ideally passes all frequencies between two non-zero finite limits and bars all frequencies not within the limits. Note: The cutoff frequencies are usually taken to be the 3-dB points. Band-Rejection Filter - Synonym band-stop filter. A filter that attenuates, usually to very low levels, all frequencies between two non-zero, finite limits and passes all frequencies not within the limits. Note: A band-stop filter may be designed to stop the specified band of frequencies but usually only attenuates them below some specified level. Band-Stop Filter - A filter that attenuates, usually to very low levels, all frequencies between two non-zero, finite limits and passes all frequencies not within the limits. Note: A band-stop filter may be designed to stop the specified band of frequencies but usually only attenuates them below some specified level. Synonyms band-elimination filter, band-rejection filter, band-suppression filter, notched filter. Band-Suppression Filter - Synonym band-stop filter. A filter that attenuates, usually to very low levels, all frequencies between two non-zero, finite limits and passes all frequencies not within the limits. Note: A band-stop filter may be designed to stop the specified band of frequencies but usually only attenuates them below some specified level. Bandwidth - According to Webster's: a range within a band of wavelengths, frequencies, or energies; esp: a range of radio frequencies which is occupied by a modulated carrier wave, which is assigned to a service, or over which a device can operate. In Internet terms, bandwidth commonly refers to the amount of information that can be sent through a connection. In computer networks, bandwidth is often used as a synonym for data transfer rate - the amount of data that can be carried from one point to another in a given time period (usually a second). This kind of bandwidth is usually expressed in bits (of data) per second (bps). Occasionally, it's expressed as bytes per second (Bps). A modem that works at 57,600 bps has twice the bandwidth of a modem that works at 28,800 bps. In general, a link with a high bandwidth is one that may be able to carry enough information to sustain the succession of images in a video presentation. It should be remembered that a real communications path usually consists of a succession of links, each with its own bandwidth. If one of these is much slower than the rest, it is said to be a bandwidth bottleneck. Bandwidth Balancing Mechanism - In a distributed-queue dual-bus network, a procedure in which a node occasionally skips the use of empty queued arbitrated slots, and which procedure effects sharing of the bandwidth mechanisms. 56
- 57. Bandwidth Compression - 1. The reduction of the bandwidth needed to transmit a given amount of data in a given time. 2. The reduction of the time needed to transmit a given amount of data in a given bandwidth. Note: Bandwidth compression implies a reduction in normal bandwidth of an information-carrying signal without reducing the information content of the signal. Bandwidth•Distance Product - Of an optical fiber, under specified launching and cabling conditions, at a specified wavelength, a figure of merit equal to the product of the fiber's length and the 3-dB bandwidth of the optical signal. Note 1: The bandwidth•distance product is usually stated in megahertz • kilometer (MHz •km) or gigahertz •kilometer (GHz•km). Note 2: The bandwidth•distance product, which is normalized to 1 km, is a useful figure of merit for predicting the effective fiber bandwidth for other lengths, and for concatenated fibers. Synonym bandwidth•length product. Bandwidth•Length Product - Synonym for bandwidth•distance product. - Of an optical fiber, under specified launching and cabling conditions, at a specified wavelength, a figure of merit equal to the product of the fiber's length and the 3-dB bandwidth of the optical signal. Note 1: The bandwidth•length product is usually stated in megahertz • kilometer (MHz •km) or gigahertz •kilometer (GHz•km). Note 2: The bandwidth•length product, which is normalized to 1 km, is a useful figure of merit for predicting the effective fiber bandwidth for other lengths, and for concatenated fibers. Bandwidth-Limited Operation - The condition prevailing when the system bandwidth limits performance. Note: Bandwidth-limited operation occurs when the system distorts the signal waveform beyond specified limits. For linear systems, bandwidth-limited operation is equivalent to distortion-limited operation. Bandwidth (of an optical fiber) - 1. The lowest modulation frequency at which the RMS peak-to-valley amplitude (optical power) difference of an intensity-modulated monochromatic signal decreases, at the output of the fiber, to a specified fraction (usually one-half) of the RMS peak-to-valley amplitude (optical power) difference of a nearly-zero (arbitrarily low) modulation frequency, both modulation frequencies having the same RMS peak-to-valley amplitude (optical power) difference at the fiber input. Note 1: In multimode fibers, multimode distortion is usually the most significant parameter limiting fiber bandwidth, although material dispersion may also play a significant role, especially in the first (850-nm) window. Note 2: In multimode fibers, the bandwidth•distance product (loosely, "fiber bandwidth") is customarily specified by vendors for the bandwidth as limited by multimode distortion only. The spectral width of the optical source is assumed to be extremely narrow. In practice, the effective fiber bandwidth will also be limited by dispersion, especially in the first (850-nm) window, where material dispersion is relatively high, because optical sources have a finite spectral width. Laser diodes typically have a spectral width of several nanometers, FWHM. LEDs typically have a spectral width of 35 to 100 nm, FWHM. Note 3: The effective risetime of multimode fibers may be estimated fairly accurately as the square root of the sum of the squares of the material-dispersion-limited risetime and the multimode-distortion-limited risetime. Note 4: In single- mode fibers, the most important parameters affecting fiber bandwidth are material dispersion and waveguide dispersion. Practical fibers are designed so that material dispersion and waveguide dispersion cancel one another at the wavelength of interest. Note 5: Regarding effective fiber bandwidth as it affects overall system performance, it should be recognized that optical detectors such as PIN diodes are square-law devices. Their photocurrent is proportional to the optical power of the detected signal. Because electrical power is a function of the square of the current, when the optical power decreases by one-half (a 3-dB decrease), the electrical power decreases by three-fourths (a 6-dB decrease). 2. Loosely, synonym bandwidth•distance product. Bang - The exclamation point character (!) used in early addressing schemes to separate the names of individual machines. Note: Bang-style addressing is no longer common. Synonym scream. Banner - 1. An HTML tag that creates scrolling text on a Web page. 2. Scrolling or fixed text used as an advertisement on a Web page, e.g., banner advertising. 3. In computer networking, a page that is 57
- 58. automatically prefixed to, and printed out as part of, a printing job, as a means of identifying uniquely the output belonging to a given user of a shared printer. Note: A banner may, in addition to identifying the owner of the printout, also identify the file name, queue, and server involved. Synonym banner page. 4. [A] display on an information system (IS) that sets parameters for system or data use. Banner Page - Synonym banner. In computer networking, a page that is automatically prefixed to, and printed out as part of, a printing job, as a means of identifying uniquely the output belonging to a given user of a shared printer. Note: A banner may, in addition to identifying the owner of the printout, also identify the file name, queue, and server involved. Bar Code - A code representing characters by sets of parallel bars of varying thickness and separation that are read optically by transverse scanning. Note: Bar code uses include identifying merchandise, sorting mail, and inventorying supplies. Barge-In Protection- When installed on an incoming telephone line before ALL telephone equipment (extension wall jacks or multi-line phone systems), The Barge-In Protection feature will protect any voice or data call from being accessed by other telephone equipment on the same line. Any phone device that goes "off-hook" during a conversation or data transmission will receive a silent line or a busy signal depending on the product. Barn Doors - This term is used in television production to describe the effect that occurs when a 4:3 image is viewed on a 16:9 screen. When this happens, viewers see black bars, or, "barn doors," on the sides of the screen. Barrage Jamming - Jamming accomplished by transmitting a band of frequencies that is large with respect to the bandwidth of a single emitter. Note: Barrage jamming may be accomplished by presetting multiple jammers on adjacent frequencies or by using a single wideband transmitter. Barrage jamming makes it possible to jam emitters on different frequencies simultaneously and reduces the need for operator assistance or complex control equipment. These advantages are gained at the expense of reduced jamming power at any given frequency. Base - 1. In the numeration system commonly used in scientific notation, the real number that is raised to a power denoted by the exponent and then multiplied by the coefficient to determine the value of the number represented without the use of exponents. Note: An example of a base is the number 6.25 in the expression 1.5 2.70 × 6.25 42.19. The 2.70 is the coefficient and the 1.5 is the exponent. In the decimal numeration system, the base is 10 and in the binary numeration system, the base is 2. The value e 2.718 is the natural base. 2. A reference value. 3. A number that is multiplied by itself as many times as indicated by an exponent. Base Address - 1. An address that is used as the origin in the calculation of addresses in the execution of a computer program. 2. A given address from which an absolute address is derived by combination with a relative address. Note: Base addresses are primarily used by computer programmers rather than by computer users. Baseband - 1. The original band of frequencies produced by a transducer, such as a microphone, telegraph key, or other signal-initiating device, prior to initial modulation. Note 1: In transmission systems, the baseband signal is usually used to modulate a carrier. Note 2: Demodulation re-creates the baseband signal. Note 3: Baseband describes the signal state prior to modulation, prior to multiplexing, following demultiplexing, and following demodulation. Note 4: Baseband frequencies are usually characterized by being much lower in frequency than the frequencies that result when the baseband signal is used to modulate a carrier or subcarrier. 2. In facsimile, the frequency of a signal equal in bandwidth to that between zero frequency and maximum keying frequency. 58
- 59. Baseband Local Area Network - A local area network in which information is encoded, multiplexed, and transmitted without modulation of carriers. Baseband Modulation - Intensity modulation of an optical source, e.g., LED or ILD, directly, without first modulating the signal of interest onto an electrical carrier wave. Baseband Signaling - Transmission of a digital or analog signal at its original frequencies; i.e., a signal in its original form, not changed by modulation. Basecom - Abbreviation for base communications. - Communications services, such as the installation, operation, maintenance, augmentation, modification, and rehabilitation of communications networks, systems, facilities, and equipment, including off-post extensions, provided for the operation of a military post, camp, installation, station, or activity. Base Communications (basecom) - Communications services, such as the installation, operation, maintenance, augmentation, modification, and rehabilitation of communications networks, systems, facilities, and equipment, including off-post extensions, provided for the operation of a military post, camp, installation, station, or activity. Synonym communications base station. Base Earth Station - An Earth station in the fixed-satellite service or, in some cases, in the land mobile- satellite service, located at a specified fixed point or within a specified area on land to provide a feeder link for the land mobile-satellite service. Base Key - A key used to derive (to compute cryptographically) or to decrypt transaction keys. Base Station - 1. A land station in the land mobile service. 2. In personal communication service, the common name for all the radio equipment located at one fixed location, and that is used for serving one or several cells. Basic Access - A characterization of a simple standardized combination of access channels that constitute the access arrangements for the majority of ISDN users; specifically, any of the following combinations of access channels: (1) one D-channel, (2) one B-channel plus one D-channel, (3) two B-channels plus one D-channel. Basic Call - A call between two users that does not include additional features (e.g., a plain telephone call). Basic Call Process (BCP) - The sequence of activities used in processing a basic call attempt. Basic Exchange Telecommunications Radio Service (BETRS) - A commercial service that can extend telephone service to rural areas by replacing the local loop with radio communications. Note: In the BETRS, non-government ultra high frequency (UHF) and very high frequency (VHF) common carrier and the private radio service frequencies are shared. Basic Group - See group. Basic Mode Link Control - Control of data links by use of the control characters of the 7-bit character set for information processing interchange as given in ISO Standard 646-1983 and CCITT (ITU-T) Recommendation Basic Rate Interface (BRI) - An ITU-T Integrated Services Digital Network (ISDN) multipurpose user interface standard that denotes the capability of simultaneous voice and data services provided over two clear 64-kb/s channels and one clear 16-kb/s channel (2B+D) access arrangement to each user location. - In the Integrated Services Digital Network (ISDN), there are two levels of service: the Basic Rate Interface (BRI), intended for 59
- 60. the home and small enterprise, and the Primary Rate Interface (PRI), for larger users. Both rates include a number of B-channels and a D-channel. Each B-channel carries data, voice, and other services. The D-channel carries control and signaling information. The Basic Rate Interface consists of two 64 Kbps B-channels and one 16 Kbps D-channel. Thus, a Basic Rate Interface user can have up to 128 Kbps service. The Primary Rate Interface consists of 23 B-channels and one 64 Kpbs D-channel in the United States or 30 B-channels and 1 D-channel in Europe. Basic Service - 1. A pure transmission capability over a communication path that is virtually transparent in terms of its interaction with customer-supplied information. 2. The offering of transmission capacity between two or more points suitable for a user's transmission needs and subject only to the technical parameters of fidelity and distortion criteria, or other conditioning. Basic Service Element (BSE) - 1. An optional unbundled feature, generally associated with the basic serving arrangement (BSA), that an enhanced-service provider (ESP) may require or find useful in configuring an enhanced service. 2. A fundamental (basic) communication network service; an optional network capability associated with a BSA. Note: BSEs constitute optional capabilities to which the customer may subscribe or decline to subscribe. Basic Serving Arrangement (BSA) - 1. The fundamental tariffed switching and transmission (and other) services that an operating company must provide to an enhanced service provider (ESP) to connect with its customers through the company network. 2. In an open-network-architecture context, the fundamental underlying connection of an enhanced service provider (ESP) to and through the operating company's network including an ESP access link, the features and functions associated with that access link at the central office serving the ESP and/or other offices, and the transport (dedicated or switched) within the network that completes the connection from the ESP to the central office serving its customers or to capabilities associated with the customer's complementary network services. Note: Each component may have a number of categories of network characteristics. Within these categories of network characteristics are alternatives from among which the customer must choose. Examples of BSA components are ESP access link, transport and/or usage. Basic Status - In data transmission, the status of the capability of a secondary station to send or receive a frame containing an information field. Bastion Host - A host computer that, in a screened subnetwork, performs the functions of a firewall. Synonym screened-host gateway. Batched Communications - Synonym batched transmission. - The transmission of two or more messages from one station to another without intervening responses from the receiving station. Batched Transmission - The transmission of two or more messages from one station to another without intervening responses from the receiving station. Synonym batched communications. Batch Processing - 1. The processing of data or the accomplishment of jobs accumulated in advance in such a manner that the user cannot further influence the processing while it is in progress. 2. The processing of data accumulated over a period of time. 3. Loosely, the execution of computer programs serially. 4. Pertaining to the technique of executing a set of computer programs such that each is completed before the next program of the set is started. 5. Pertaining to the sequential input of computer programs or data. Baud (Bd) - 1. A unit of modulation rate. Note: One baud corresponds to a rate of one unit interval per second, where the modulation rate is expressed as the reciprocal of the duration in seconds of the shortest unit interval. 2. A unit of signaling speed equal to the number of discrete signal conditions, variations, or 60
- 61. events per second. Note 1: If the duration of the unit interval is 20 milliseconds, the signaling speed is 50 bauds. If the signal transmitted during each unit interval can take on any one of n discrete states, the bit rate is equal to the rate in bauds times log 2 n. . The technique used to encode the allowable signal states may be any combination of amplitude, frequency, or phase modulation, but it cannot use a further time-division multiplexing technique to subdivide the unit intervals into multiple subintervals. In some signaling systems, non-information-carrying signals may be inserted to facilitate synchronization; e.g., in certain forms of binary modulation coding, there is a forced inversion of the signal state at the center of the bit interval. In these cases, the synchronization signals are included in the calculation of the rate in bauds but not in the computation of bit rate. Note 2: Baud is sometimes used as a synonym for bit-per-second. This usage is deprecated. Baudot Code - A synchronous code in which five equal-length bits represent one character. Note 1: The Baudot code, which was developed circa 1880, has been replaced by the start-stop asynchronous International Alphabet No. 2 (IA No. 2). Note 2: IA No. 2 is not, and should not be identified as, the Baudot code. Note 3: The Baudot code has been widely used in teletypewriter systems. BCC - Abbreviation for block check character. - A character added to a transmission block to facilitate error detection. Note: In longitudinal redundancy checking and cyclic redundancy checking, block check characters are computed for, and added to, each message block transmitted. This block check character is compared with a second block check character computed by the receiver to determine whether the transmission is error free. BCD - Abbreviation for binary-coded decimal code. See binary-coded decimal notation. B-channel - In the Integrated Services Digital Network (ISDN), the B-channel is the channel that carries the main data. (The "B" stands for "bearer" channel.) In ISDN, there are two levels of service: the Basic Rate Interface, intended for the home and small enterprise, and the Primary Rate Interface, for larger users. Both rates include a number of B- (bearer) channels and a D- channel. The B-channels carry data, voice, and other services. The D-channel carries control and signaling information. The Basic Rate Interface consists of two 64 Kbps B-channels and one 16 Kbps D-channel. Thus, a Basic Rate Interface user can have up to 128 Kbps service. The Primary Rate Interface consists of 23 B-channels and one 64 Kpbs D-channel in the United States or 30 B-channels and 1 D-channel in Europe. B channel - 1. A communications channel used for the transmission of an aggregate signal generated by multichannel transmitting equipment. 2. The CCITT (now, ITU-T) designation for a clear channel, 64-kb/s service capability provided to a subscriber under the Integrated Services Digital Network offering. Note: The B channel, also called the bearer channel, is intended for transport of user information, as opposed to signaling information. BCH code - Abbreviation for Bose-Chaudhuri-Hochquenghem code . A multilevel, cyclic, error-correcting, variable-length digital code used to correct errors up to approximately 25% of the total number of digits. Note: BCH codes are not limited to binary codes, but may be used with multilevel phase-shift keying whenever the number of levels is a prime number or a power of a prime number, such as 2, 3, 4, 5, 7, 8, 11, and 13. A BCH code in 11 levels has been used to represent the 10 decimal digits plus a sign digit. BCI - Abbreviation for bit-count integrity. - 1. In message communications, the preservation of the exact number of bits that are in the original message. 2. In connection-oriented services, preservation of the number of bits per unit time. Note: Bit-count integrity is not the same as bit integrity, which requires that the delivered bits correspond exactly with the original bits. 61
- 62. Beacon - See radiobeacon station. - A station in the radionavigation service the emissions of which are intended to enable a mobile station to determine its bearing or direction in relation to the radiobeacon station. Beam - 1. The main lobe of an antenna radiation pattern. 2. A column of light. Note: A beam may be parallel, divergent, or convergent. Beam Diameter - Of an electromagnetic beam, along any specified line that (a) intersects the beam axis and (b) lies in any specified plane normal to the beam axis, the distance between the two diametrically opposite points at which the irradiance is a specified fraction, e.g., ½ or 1/ , of the beam's peak irradiance. Note 1: Beam diameter is usually used to characterize electromagnetic beams in the optical regime, and occasionally in the microwave regime, i.e., cases in which the aperture from which the beam emerges is very large with respect to the wavelength. Note 2: Beam diameter usually refers to a beam of circular cross section, but not necessarily so. A beam may, for example, have an elliptical cross section, in which case the orientation of the beam diameter must be specified, e.g., with respect to the major or minor axis of the elliptical cross section. Beam Divergence - Of an electromagnetic beam, in any plane that intersects the beam axis, the increase in beam diameter with distance from the aperture from which the beam emerges. Note 1: Beam divergence is usually used to characterize electromagnetic beams in the optical regime, i.e., cases in which the aperture from which the beam emerges is very large with respect to the wavelength. Note 2: Beam divergence usually refers to a beam of circular cross section, but not necessarily so. A beam may, for example, have an elliptical cross section, in which case the orientation of the beam divergence must be specified, e.g., with respect to the major or minor axis of the elliptical Beamsplitter - A device for dividing an optical beam into two or more separate beams. Note: An example of a beamsplitter is a partially reflecting mirror. Beam Steering - Changing the direction of the main lobe of a radiation pattern. Note: In radio systems, beam steering may be accomplished by switching antenna elements or by changing the relative phases of the rf signals driving the elements. In optical systems, beam steering may be accomplished by changing the refractive index of the medium through which the beam is transmitted or by the use of mirrors or lenses. Beamwidth - 1. In the radio regime, of an antenna pattern, the angle between the half-power (3-dB) points of the main lobe, when referenced to the peak effective radiated power of the main lobe. Note: Beamwidth is usually expressed in degrees. It is usually expressed for the horizontal plane, but may also be expressed for the vertical plane. 2. For the optical regime, see beam divergence. Bearer Channel - See B channel. - In the Integrated Services Digital Network (ISDN), the B-channel is the channel that carries the main data. (The "B" stands for "bearer" channel.) In ISDN, there are two levels of service: the Basic Rate Interface, intended for the home and small enterprise, and the Primary Rate Interface, for larger users. Both rates include a number of B- (bearer) channels and a D- channel. The B-channels carry data, voice, and other services. The D-channel carries control and signaling information. Bearer Service - A telecommunications service that allows transmission of user-information signals between user-network interfaces. See B channel, service access. Beating - See heterodyne. - 1. To generate new frequencies by mixing two or more signals in a nonlinear device such as a vacuum tube, transistor, or diode mixer. Note: A superheterodyne receiver converts any selected incoming frequency by heterodyne action to a common intermediate frequency where 62
- 63. amplification and selectivity (filtering) are provided. 2. A frequency produced by mixing two or more signals in a nonlinear device. Beeping - Synonym paging, radio paging. - The use of a pocket-size radio receiver capable of alerting its wearer that there is a phone call, either from a displayed phone number or to a predesignated number. Note: Beeping (Radio paging) may be considered a subset of paging. B8ZS (bipolar 8-zero substitution, also called binary 8-zero substitution, clear channel, and clear 64) - is an encoding method used on T1 circuits that inserts two successive ones of the same voltage - referred to as a bipolar violation - into a signal whenever eight consecutive zeros are transmitted. The device receiving the signal interprets the bipolar violation as a timing mark, which keeps the transmitting and receiving devices synchronized. Ordinarily, when successive ones are transmitted, one has a positive voltage and the other has a negative voltage. B8ZS is based on an older encoding method called alternate mark inversion (AMI). AMI is used with Dataphone Digital Service, the oldest data service still in use that uses 64 Kbps channels. AMI, however, requires the use of 8 Kbps of the 64 Kbps of each channel to maintain synchronization. In a T1 circuit, there are 24 channels. This loss adds up to 192 Kbps, which means that in reality only 56 Kbps is available for data transmission. B8ZS uses bipolar violations to synchronize devices, a solution that does not require the use of extra bits, which means a T1 circuit using B8ZS can use the full 64 Kbps for each channel for data. B8ZS is not compatible with older AMI equipment. T1 technology is used in the United States and Japan. In Europe, a comparable technology called E1 provides 32 channels instead of 24 and uses an encoding scheme called high-density bipolar 3 (HDB3) instead of B8ZS. A T-carrier line code in which bipolar violations are deliberately inserted if user data contains a string of 8 or more consecutive zeros. Note 1: B8ZS is used to ensure a sufficient number of transitions to maintain system synchronization when the user data stream contains an insufficient number of "ones" to do so. Note 2: B8ZS is used in the European hierarchy at the T1 rate. bel (B): A unit of measure of ratios of power levels, i.e., relative power levels. Note 1: The number of bels for a given ratio of power levels is calculated by taking the logarithm, to the base 10, of the ratio. Mathematically, the number of bels is calculated as B = log10(P 1/P 2) where P 1 and P 2 are power levels. Note 2: The dB, equal to 0.1 B, is a more commonly used unit. Bell (BEL) Character - A transmission control character that is used when there is a need to call for user or operator attention in a communications system, and that usually activates an audio or visual alarm or other attention-getting device. Bell-La Padula Security Model - [A] formal state-transition model of a computer security policy that describes a formal set of access controls based on information sensitivity and subject authorizations. Bell Operating Company - (see BOC). Historically, any of the 22 operating companies that were divested from AT&T by court order. Note: Cincinnati Bell Telephone Co. and Southern New England Bell Telephone Co. were not included. Bell Operating Company is a term for any of the 22 original companies (or their successors) that were created when AT&T was broken up in 1983 and given the right to provide local telephone service in a given geographic area. The companies had previously existed as subsidiaries of AT&T and were called the "Bell System." The purpose of the breakup was to create competition at both the local and long-distance service levels. BOCs compete with other, independent companies to sell local phone service. In certain areas, long- 63
- 64. distance companies, including AT&T, can now compete for local service. Collectively, companies offering local phone service are referred to legally as local exchange carriers (local exchange carrier). BOCs are not allowed to manufacture equipment and were initially not allowed to provide long-distance service. The Telecommunications Act of 1996 now permits them to engage in long-distance business under certain circumstances. As of 1996, the BOCs consisted of original and successor companies to: Bell Telephone Company of Nevada, Illinois Bell, Indiana Bell, Michigan Bell, New England Telephone and Telegraph Company, New Jersey Bell, New York Telephone Company, U S West Communications Company, South Central Bell, Southern Bell, Southwestern Bell, Bell Telephone of Pennsylvania, The Chesapeake and Potomac Telephone Company, The Chesapeake and Potomac Telephone Company of Maryland, The Chesapeake and Potomac Telephone Company of Virginia, The Diamond State Telephone Company, The Ohio Bell Telephone Company, The Pacific Telephone and Telegraph Company, and the Wisconsin Telephone Company. Bend Loss - See macrobend loss, microbend loss. In an optical fiber, that loss attributable to macrobending. Synonym curvature loss. Benign - A condition of cryptographic data that cannot be compromised by human access. Benign Environment - [In security, a] nonhostile environment that may be protected from external hostile elements by physical, personnel, and procedural security countermeasures. BER (bit error rate) - In telecommunication transmission, the BER is the percentage of bits that have errors relative to the total number of bits received in a transmission, usually expressed as ten to a negative power. For example, a transmission might have a BER of 10 to the minus 6, meaning that, out of 1,000,000 bits transmitted, one bit was in error. The BER is an indication of how often a packet or other data unit has to be retransmitted because of an error. Too high a BER may indicate that a slower data rate would actually improve overall transmission time for a given amount of transmitted data since the BER might be reduced, lowering the number of packets that had to be resent. BER - Abbreviation for bit error ratio. BERT - Acronym for bit error ratio tester. - A testing device that compares a received data pattern with a known transmitted pattern to determine the level of transmission quality. Beta Test - A secondary software product test involving select or voluntary participants before the product is marketed to the general public. Note: Participants agree to provide detailed feedback to the product's manufacturer in return for their being allowed to preview, use, and contribute to the final form of the product. BETRS - Abbreviation for basic exchange telecommunications radio service. - A commercial service that can extend telephone service to rural areas by replacing the local loop with radio communications. Note: In the BETRS, non-government ultra high frequency (UHF) and very high frequency (VHF) common carrier and the private radio service frequencies are shared. Between-the-lines Entry - Unauthorized access to a momentarily inactive terminal, of a legitimate user, assigned to a communications channel. BEX - Abbreviation for broadband exchange. A communications switch capable of interconnecting channels having bandwidths greater than voice bandwidth. 64
- 65. B Frame - An MPEG video frame type that provides bidirectional interframe compression. Note: A b frame derives its content from the closest 1 or P frame, one in the past and one in the future. Generating b frames requires greater computing power than does generating 1 or P frames. The use of b frames enables compression ratios of 200:1. Robust MPEG encoders employ a combination of b, 1, and P frame encoding. Bias - 1. A systematic deviation of a value from a reference value. 2. The amount by which the average of a set of values departs from a reference value. 3. Electrical, mechanical, magnetic, or other force (field) applied to a device to establish a reference level to operate the device. 4. In telegraph signaling systems, the development of a positive or negative dc voltage at a point on a line that should remain at a specified reference level, such as zero. Note: A bias may be applied or produced by (i) the electrical characteristics of the line, (ii) the terminal equipment, and (iii) the signaling scheme. Bias Distortion - 1. Signal distortion resulting from a shift in the bias. 2. In binary signaling, distortion of the signal in which all the significant intervals have uniformly longer or shorter durations than their theoretical durations. Note: Bias distortion is expressed in percent of the system-specified unit interval. Biased - In the generation of pseudorandom or random numbers, pertaining to or describing a condition that renders the more likely occurrence of some numbers or patterns than others. Biconical Antenna - An antenna consisting of two conical conductors, having a common axis and vertex, and extending in opposite directions. Note 1: In a biconical antenna, excitation is applied at the common vertex. Note 2: If one of the cones is reduced to a plane, the antenna is called a discone. Bidirectional Asymmetry - In data transmission, the condition that exists when information flow characteristics are different in each direction. Bidirectional Connection - Association established between two higher layer entities for which information is transmitted between both entities. Bidirectional Coupler - See directional coupler. A transmission coupling device for separately sampling (through a known coupling loss) either the forward (incident) or the backward (reflected) wave in a transmission line. Note: A directional coupler may be used to sample either a forward or backward wave in a transmission line. A unidirectional coupler has available terminals or connections for sampling only one direction of transmission; a bidirectional coupler has available terminals for sampling both directions. Bidirectional Symmetry - The condition that exists when information flow characteristics are the same in each direction. Big-Endian - A format for transmission or storage of binary data in which the most significant byte (bit) appears first. BIH - French abbreviation for International Time Bureau. See International Atomic Time. The time scale established by the Bureau International des Poids et Mesures (BIPM--International Bureau of Weights and Measures in Sevres, France) on the basis of atomic clock data supplied by cooperating institutions. Bilateral Control - Synonym bilateral synchronization. - A synchronization control system between exchanges A and B in which the clock at exchange A controls the data received at exchange B and the clock at exchange B controls the data received at exchange A. Note: Bilateral control is usually implemented by deriving the timing from the incoming bit stream. 65
- 66. Bilateral Synchronization - A synchronization control system between exchanges A and B in which the clock at exchange A controls the data received at exchange B and the clock at exchange B controls the data received at exchange A. Note: Bilateral synchronization is usually implemented by deriving the timing from the incoming bit stream. Synonym bilateral control. Billboard Antenna - An array of parallel dipole antennas with flat reflectors, usually positioned in a line or plane. Note 1: The spacing and dimensions of the dipoles depend on the wavelength. Note 2: The main lobe of a fixed billboard antenna may, within limits, be steered by appropriate phasing of the respective signals to individual elements of the array. Synonym broadside antenna. Billed Number Screening - Allows you to restrict billing of Collect and/or Third Number Billing calls to your residential or business telephone account. Binary - 1. Pertaining to a selection, choice, or condition that has two possible different values or states. 2. Pertaining to a fixed radix numeration system that has a radix of 2. Binary Code - A code, the elements of which can assume either one of two possible states. Binary-Coded Decimal Code - Synonym binary-coded decimal notation. - A binary notation in which each of the decimal digits is represented by a binary numeral. Binary-Coded Decimal Interchange Code - See binary-coded decimal notation. Binary-Coded Decimal (BCD) Notation - A binary notation in which each of the decimal digits is represented by a binary numeral. Synonyms binary-coded decimal code, binary-coded decimal representation. Binary-Coded Decimal Representation - Synonym binary-coded decimal notation. A binary notation in which each of the decimal digits is represented by a binary numeral. Binary Digit (bit) - See bit. The smallest unit of computer information. Binary Element - A constituent element of data that takes either of two values or states. Note: Binary element should not be confused with binary digit. Binary Exponential Backoff - See truncated binary exponential backoff. - In carrier sense multiple access with collision avoidance (CSMA/CA) networks and in carrier sense multiple access with collision detection (CSMA/CD) networks, the algorithm used to schedule retransmission after a collision such that the retransmission is delayed by an amount of time derived from the slot time and the number of attempts to retransmit. Binary Modulation - The process of varying a parameter of a carrier as a function of two finite, discrete states. Binary Notation - 1. Any notation that uses two different characters, usually the digits 0 and 1. Note: Data encoded in binary notation need not be in the form of a pure binary numeration system; e.g., they may be represented by a Gray code. 2. A scheme for representing numbers, which scheme is characterized by the arrangements of digits in sequence, with the understanding that successive digits are interpreted as coefficients of successive powers of base 2. 66
- 67. Binary Number - A number that is expressed in binary notation and is usually characterized by the arrangement of bits in sequence, with the understanding that successive bits are interpreted as coefficients of successive powers of the base 2. Binary String - Synonym bit string. - A sequence of bits. Note: In a bit stream, individual bit strings may be separated by data delimiters. Binary Synchronous (bi-sync) Communication - A character-oriented, data-link-layer protocol. Note: The bi- sync protocol is being phased out of most computer communication networks in favor of bit-oriented protocols such as SDLC, HDLC, and ADCCP. Binding - 1. In computer, communications, and automatic data processing systems, assigning a value or referent to an identifier. Note: Examples of binding include assigning a value to a parameter, assigning an absolute address to a virtual or relative address, and assigning a device identifier to a symbolic address or label. 2. [In security, the] process of associating a specific communications terminal with a specific cryptographic key or associating two related elements of information. Biometric - Any specific and uniquely identifiable physical human characteristic, e.g., of the retina, iris, acoustic spectrum of the voice (i.e., voiceprint), fingerprint(s), handwriting, pattern of finger lengths, etc., that may be used to validate the identity of an individual. Note: Biometrics provide a highly secure means of identification, for purposes of security involving, e.g., Internet communications and cryptosystems. Biometrics - Automated methods of authenticating or verifying an individual based upon a physical or behavioral characteristic. Biphase Modulation - Synonym phase-shift keying. - 1. In digital transmission, angle modulation in which the phase of the carrier is discretely varied in relation either to a reference phase or to the phase of the immediately preceding signal element, in accordance with data being transmitted. 2. In a communications system, the representing of characters, such as bits or quaternary digits, by a shift in the phase of an electromagnetic carrier wave with respect to a reference, by an amount corresponding to the symbol being encoded. Note 1: For example, when encoding bits, the phase shift could be 0° for encoding a "0," and 180° for encoding a "1," or the phase shift could be -90 for "0" and +90° for a "1," thus making the representations for "0" and "1" a total of 180° apart. Note 2: In PSK systems designed so that the carrier can assume only two different phase angles, each change of phase carries one bit of information, i.e., the bit rate equals the modulation rate. If the number of recognizable phase angles is increased to 4, then 2 bits of information can be encoded into each signal element; likewise, 8 phase angles can encode 3 bits in each signal element. Bipolar 8-Zero Substitution (B8ZS, binary 8-zero substitution, clear channel, and clear 64) - is an encoding method used on T1 circuits that inserts two successive ones of the same voltage - referred to as a bipolar violation - into a signal whenever eight consecutive zeros are transmitted. The device receiving the signal interprets the bipolar violation as a timing mark, which keeps the transmitting and receiving devices synchronized. Ordinarily, when successive ones are transmitted, one has a positive voltage and the other has a negative voltage (see B8ZS). Bipolar Signal - 1. A signal that may assume either of two polarities, neither of which is zero. Note 1: A bipolar signal may have a two-state non-return-to-zero (NRZ) or a three-state return-to-zero (RZ) binary coding scheme. Note 2: A bipolar signal is usually symmetrical with respect to zero amplitude, i.e., the absolute values of the positive and negative signal states are nominally equal. 2. A pseudoternary signal, conveying binary digits, in which successive "ones" (marks, pulses) are of alternating, positive (+) and 67
- 68. negative (-) polarity, equal in amplitude, and in which a "zero" (space, no pulse) is of zero amplitude.Synonym alternate mark inversion signal. Bipolar Violation - In a bipolar alternate mark inversion (AMI) signal, a "one" condition (mark, pulse) having the same polarity as its predecessor. Birefringence - In a transparent material, anisotropism of the refractive index, which varies as a function of polarization as well as orientation with respect to the incident ray. Note 1: The term "birefringence" means, literally, " double refraction." Note 2: All crystals except those of cubic lattice structure exhibit some degree of anisotropy with regard to their physical properties, including refractive index. Other materials, such as glasses or plastics, become birefringent when subjected to mechanical strain. Note 3: Birefringent materials, including crystals, have the ability to refract an unpolarized incident ray into two separate, orthogonally polarized rays, which in the general case take different paths, depending on orientation of the material with respect to the incident ray. The refracted rays are referred to as the "ordinary," or "O" ray, which obeys Snell's Law, and the "extraordinary," or "E" ray, which does not. Synonym double refraction. Birefringent Medium - See birefringence. Birthday Phenomenon - The phenomenon stating that, for a category size of 365 (the number of days in a year), after only 23 people are gathered, the probability is greater than 0.5 that at least two people have a common birthday (month and day). Note: The birthday phenomenon applied to DES encryption means that where category size is 264, this same probability of a repeat (match) occurs at approximately r=232. The theory behind this principle applies that for a 64-bit block encryption operation with a fixed key, if one has a text dictionary of 232 plaintext/ciphertext pairs and 232 blocks of ciphertext produced from random input, then it should be expected that one block of unknown ciphertext will be found in the dictionary. B-ISDN - Abbreviation for broadband ISDN. Bistable - Pertaining to a device capable of assuming either one of two stable states. Bistable Circuit - Synonym flip-flop. - A device that may assume either one of two reversible, stable states. Note 1: The bistable circuit is used as a basic control element in computer and communications systems. Note 2: In a bistable circuit, the transition from one stable state to the other is unstable, i.e., for the very short period during which the transition takes place, both outputs may assume the same state, which state may be unpredictable. Bistable Multivibrator - Synonym flip-flop. - A device that may assume either one of two reversible, stable states. Note 1: The bistable multivibrator is used as a basic control element in computer and communications systems. Note 2: In a bistable multivibrator, the transition from one stable state to the other is unstable, i.e., for the very short period during which the transition takes place, both outputs may assume the same state, which state may be unpredictable. Bistable Trigger Circuit - Synonym flip-flop. - A device that may assume either one of two reversible, stable states. Note 1: The bistable trigger circuit is used as a basic control element in computer and communications systems. Note 2: In a bistable trigger circuit, the transition from one stable state to the other is unstable, i.e., for the very short period during which the transition takes place, both outputs may assume the same state, which state may be unpredictable. Bi-Sync - Abbreviation for binary synchronous (bi-sync) communication. - A character-oriented, data-link- layer protocol. Note: The bi-sync protocol is being phased out of most computer communication networks in favor of bit-oriented protocols such as SDLC, HDLC, and ADCCP. 68
- 69. Bit - (binary digit) The smallest unit of computer information. Bit-by-Bit Asynchronous Operation - In data transmission, an operation in which manual, semiautomatic, or automatic shifts in the data modulation rate are accomplished by gating or slewing the clock modulation rate. Note: For example, bit-by-bit asynchronous operation may be at 50 b/s one moment and at 1200 b/s the next moment. Bit Configuration - The sequence of bits used to encode a character. Bit-Count Integrity (BCI) - 1. In message communications, the preservation of the exact number of bits that are in the original message. 2. In connection-oriented services, preservation of the number of bits per unit time. Note: Bit-count integrity is not the same as bit integrity, which requires that the delivered bits correspond exactly with the original bits. Bit Density - The number of bits recorded per unit length, area, or volume. Note: Bit density is the reciprocal of bit pitch. Synonym recording density. Bit Depth - Synonym bits per pixel. - In a digitized image, the number of bits used to represent the luminance (brightness, gray scale) and chroma (color) information contained in each pixel. Biternary Transmission - Digital transmission in which two binary pulse trains are combined for transmission over a channel in which the available bandwidth is sufficient for transmission of only one of the two pulse trains at a time if they remain in binary form. Bit Error - A bit that is transferred from the source to the destination within the assigned time slot, but that, when delivered, is of a different value from that sent from the source. Bit Error Rate - (See BER) Bit Error Ratio (BER) - The number of erroneous bits divided by the total number of bits transmitted, received, or processed over some stipulated period. Note 1: Examples of bit error ratio are (a) transmission BER, i.e., the number of erroneous bits received divided by the total number of bits transmitted; and (b) information BER, i.e., the number of erroneous decoded (corrected) bits divided by the total number of decoded (corrected) bits. Note 2: The BER is usually expressed as a coefficient and a power of 10; for 5 -5 example, 2.5 erroneous bits out of 100,000 bits transmitted would be 2.5 out of 10 or 2.5 × 10 . Bit Error Ratio Tester (BERT) - A testing device that compares a received data pattern with a known transmitted pattern to determine the level of transmission quality. Bit Interleaved Parity N (BIP-N): A method of error monitoring. If even parity is used, an N bit code is generated by the transmitting equipment over a specified portion of the signal in such a manner that the first bit of the code provides even parity over the first bit of all N-bit sequences in the covered portion of the signal, the second bit provides even parity over the second bits of all N-bit sequences within the specified portion, and so on. Even parity is generated by setting the BIP-N bits so that there are an even number of 1s in each of all N-bit sequences including the BIP-N. Bit Interval - See bit, character interval, unit interval. Bit Inversion - 1. The changing of the state of a bit to the opposite state. 2. The changing of the state that represents a given bit, i.e., a 0 or a 1, to the opposite state. Note: For example, if a 1 is represented by a 69
- 70. given polarity or phase at one stage in a circuit, the 1 is represented by the opposite polarity or phase at the next stage. Bitmap - In computer graphics, a representation of an image (which category includes characters) by code or a coding scheme that defines (a) the position of pixels by row (horizontal position) and column (vertical position), and (b) individual pixel characteristics such as gray scale and color. Loosely synonymous with raster. Bitmapped Graphics - In computer graphics, an image created with, or represented by, a matrix of pixels. Synonym [loosely] raster graphics. Bit Masking - In embedded ADPCM (adaptive differential pulse-code modulation), the process of discarding the enhancement bits. BITNET - Abbreviation for Because It's Time NETwork. An early (ca. 1981) store-and-forward digital communications network interconnecting universities and research institutions worldwide. Note: BITNET, which is now obsolete, had a purpose akin to that of the present Internet, but was not nearly so robust, and at a speed of only 9600 b/s, it could not support the data rates presently attainable via the Internet. Bit Padding - is the addition of one or more extra bits to a transmission or storage unit to make it conform to a standard size. Some sources identify bit padding as a type of bit stuffing. Bit Pairing - The practice of establishing, within a code set, a number of subsets that have an identical bit representation except for the state of a specified bit. Note: An example of bit pairing occurs in the International Alphabet No. 5 and the American Standard Code for Information Interchange (ASCII), where the upper case letters are related to their respective lower case letters by the state of bit six. Bit Period (T) - The amount of time required to transmit a logical one or a logical zero Bit Position - A character position in a word in a binary notation. Bit Rate (BR) - 1. In a bit stream, the number of bits occurring per unit time, usually expressed in bits per second. Note: For n-ary operation, the bit rate is equal to log 2 n times the rate (in bauds), where n is the number of significant conditions in the signal. 2. The rate of transmission of information in binary (two state) form in bits per unit time. Bit-Rate•Distance Product - See bandwidth•distance product. - Of an optical fiber, under specified launching and cabling conditions, at a specified wavelength, a figure of merit equal to the product of the fiber's length and the 3-dB bandwidth of the optical signal. Note 1: The bit-rate•distance product is usually stated in megahertz • kilometer (MHz •km) or gigahertz •kilometer (GHz•km). Note 2: The bit-rate•distance product, which is normalized to 1 km, is a useful figure of merit for predicting the effective fiber bandwidth for other lengths, and for concatenated fibers. Bit Robbing - In digital carrier systems, the practice or technique of preempting, at regular intervals and for the purpose of transmitting signaling information, one digit time slot that (a) is associated with the given user channel for which signaling is required, and (b) is used primarily for transporting encoded speech via that channel. Note 1: Bit robbing is an option in networks compatible with T-carrier, e.g., an ISDN. Note 2: In conventional T-carrier systems, bit robbing uses, in every sixth frame, the time slot associated with the least significant bit. Synonym speech digit signaling. 70
- 71. Bit Robbing - is a technique used in signaling on the T-carrier system, the widely-used system for transmitting both voice and data in digital form in the public switched telephone network (PSTN) and in private networks. In the basic T-1 system, a 193 bit frame, serving 24 channels, is transmitted in a sequence of 12 frames that are referred to as a superframe. Special signaling information, such as whether a voice channel is on-hook or off-hook, is included within the superframe by using a bit (called the a bit) that is "robbed" from the sixth frame as a signaling bit and another bit (the b bit) that is robbed from the 12th frame. Bit robbing is acceptable for voice conversations or data transmissions that are received by a modem but not for "pure" data transmission (where every bit is significant). Bit robbing is the reason that a 64 Kbps channel only carries 56 Kbps of usable data. Bit robbing is a form of in-band signalling. Bit-Sequence Independence - A characteristic of some digital data transmission systems that impose no restrictions on, or modification of, the transmitted bit sequence. Note: Bit-sequence-independent protocols are in contrast to protocols that reserve certain bit sequences for special meanings, such as the flag sequence, 01111110, for HDLC, SDLC, and ADCCP protocols. Bit Slip - In digital transmission, the loss of a bit or bits, caused by variations in the respective clock rates of the transmitting and receiving devices. Note: One cause of bit slippage is overflow of a receive buffer that occurs when the transmitter's clock rate exceeds that of the receiver. This causes one or more bits to be dropped for lack of storage capacity. Bits Per Inch (b/in) - A unit used to express the linear bit density of data in storage. Note: The abbreviation " bpi" is not in accordance with international standards, and is therefore deprecated. Bits Per Pixel (BPP) - In a digitized image, the number of bits used to represent the luminance (brightness, gray scale) and chroma (color) information contained in each pixel. Synonym bit depth. Bits Per Second (bps or bit/sec) - In data communications, bits per second is a common measure of data speed for computer modems and transmission carriers. As the term implies, the speed in bps is equal to the number of bits transmitted or received each second. Larger units are sometimes used to denote high data speeds. One kilobit per second (abbreviated Kbps in the U.S.; kbps elsewhere) is equal to 1,000 bps. One megabit per second (Mbps) is equal to 1,000,000 bps or 1,000 Kbps. Bit-Stepped - Pertaining to the control of digital equipment in which operations are performed one step at a time at the applicable bit rate. Bit-Stream Transmission - 1. In bit-oriented systems, the transmission of bit strings. 2. In character-oriented systems, the transmission of bit streams that represent characters. Note: In bit-stream transmission, the bits usually occur at fixed time intervals, start and stop signals are not used, and the bit patterns follow each other in sequence without interruption. Bit String - A sequence of bits. Note: In a bit stream, individual bit strings may be separated by data delimiters. Synonym binary string. Bit Stuffing - is the insertion of one or more bits into a transmission unit as a way to provide signaling information to a receiver. The receiver knows how to detect and remove or disregard the stuffed bits. Bit stuffing is the insertion of noninformation bits into data. 71
- 72. For example, the timing or bit rate of T-carrier system signals is constantly synchronized between any terminal device and an adjacent repeater or between any two repeaters. The synchronization is achieved by detecting the transition in polarity for 1 bits in the data stream. (T-1 signalling uses bipolar signaling, where each successive bit with a value of 1 is represented by voltage with a reverse polarity from the previous bit. Bits with a value of 0 are represented by a no-voltage time slot.) If more than 15 bits in a row are sent with a 0 value, this "lull" in 1 bits that the system depends on for synchronization may be long enough for two end points to become out of synchronization. To handle this situation (the sequence of more than 15 0 bits), the signal is "stuffed" with a short, unique bit pattern (which includes some 1 bits) that is recognized as a synchronization pattern. The receiving end removes the stuffed bits and restores the bit stream to its original sequence. In another example of bit stuffing, a standard HDLC packet begins and ends with 01111110. To make sure this sequence doesn't appear again before the end of the packet, a 0 is inserted after every five consecutive 1s. Bit stuffing is defined by some to include bit padding or the addition of bits to a tranmission to make the tranmission unit conform to a standard size. Note 1: Stuffed bits should not be confused with overhead bits. Note 2: In data transmission, bit stuffing is used for various purposes, such as for synchronizing bit streams that do not necessarily have the same or rationally related bit rates, or to fill buffers or frames. The location of the stuffing bits is communicated to the receiving end of the data link, where these extra bits are removed to return the bit streams to their original bit rates or form. Bit stuffing may be used to synchronize several channels before multiplexing or to rate-match two single channels to each other. Synonym positive justification. Bit Stuffing Rate - See nominal bit stuffing rate. - The rate at which stuffing bits are inserted when both the input and output bit rates are at their nominal values. Bit Synchronization - Synchronization in which the decision instant is brought into alignment with the received bit, i.e., the basic signaling element. Bit Synchronous Operation - Operation in which data circuit terminating equipment (DCE), data terminal equipment (DTE), and transmitting circuits are all operated in bit synchronism with a clock. Note 1: In bit synchronous operation, clock timing is usually delivered at twice the modulation rate, and one bit is transmitted or received during each clock cycle. Note 2: Bit synchronous operation is sometimes erroneously referred to as digital synchronization. BIU - Abbreviation for bus interface unit. See network interface device. BLACK - 1. [A] designation applied to telecommunications and automated information systems, and to associated areas, circuits, components, and equipment, in which only unclassified signals are processed. Note: Encrypted signals are unclassified. 2. Designation applied to information systems, and to associated areas, circuits, components, and equipment, in which national security information is not processed. Blackbody - A totally absorbing body that does not reflect radiation. Note: In thermal equilibrium, a blackbody absorbs and radiates at the same rate; the radiation will just equal absorption when thermal equilibrium is maintained. Black Box - is any device, sometimes highly important, whose workings are not understood by or accessible to its user. According to Edward Tenner, writing in The Washington Post, the first black box was a gun sight carried on World War II Flying Fortresses, with hidden components that corrected for environmental variables, such as wind speed. The crew probably didn't know how the device worked, but they knew it 72
- 73. might be crucial to their survival. Nowadays, there are two types of black box carried on aircraft, which may be combined into a single device: a flight data recorder (FDR), which logs information such as speed and altitude, and a cockpit voice recorder (CVR), which logs all voice communication in the cockpit. These black boxes also carry beacons to help find the aircraft in a rescue situation. Black box is a generic term for a single-purpose device having limited functionality. Note: A black box is usually represented in schematic drawings as a geometric figure, possibly with defined connector (s), but no details with respect to the type or number of internal components that enable it to perform its defined task. Black Burst - A composite color video signal comprised of sync, color burst, and black video. Note: Black burst is used to synchronize (genlock) other video sources to the same sync and color information. Black burst generators are used in video studios to "lock" the entire facility to a common signal ("house sync" or "house black"). Black Facsimile Transmission - 1. In facsimile systems using amplitude modulation, that form of transmission in which the maximum transmitted power corresponds to the maximum density of the subject. 2. In facsimile systems using frequency modulation, that form of transmission in which the lowest transmitted frequency corresponds to the maximum density of the subject. Black Level - Of a television baseband signal (e.g., NTSC composite video), the voltage level corresponding to black or to the maximum limit of black peaks. Black Noise - Noise that has a frequency spectrum of predominately zero power level over all frequencies except for a few narrow bands or spikes. Note: An example of black noise in a facsimile transmission system is the spectrum that might be obtained when scanning a black area in which there are a few random white spots. Thus, in the time domain, a few random pulses occur while scanning. Black Recording - 1. In facsimile systems using amplitude modulation, recording in which the maximum received power corresponds to the maximum density of the record medium. 2. In a facsimile system using frequency modulation, recording in which the lowest received frequency corresponds to the maximum density of the record medium. Black Signal - In facsimile, the signal resulting from scanning a maximum-density area of the object. BLACK signal - A signal that represents only unclassified or encrypted information, usually in cryptographic systems. Blanketing - The interference that is caused by the presence of an AM broadcast signal of one volt per meter (V/m) or greater strengths in the area adjacent to the antenna of the transmitting station. The 1 V/m contour is referred to as the blanket contour and the area within this contour is referred to as the "blanket area." Blanketing Area - In the vicinity of a transmitting antenna, the area in which the signal from that antenna interferes with the reception of other signals. Note: The blanketing area around a given transmitting antenna depends on the selectivity and sensitivity of the receiver, and on the respective levels of the other signals in question. Blanking - 1. The period of time in which no video image is displayed. 2. In graphic display, the suppression of the display of one or more display elements or display segments. Blanking Interval - In raster-scanned television technology, the period between (a) the end of one horizontal scanning line and the beginning of the next (the horizontal blanking interval), or (b) the end of one field and 73
- 74. the beginning of the next (the vertical blanking interval), during which the display of picture information is suppressed. Note 1: Blanking intervals were a necessary part of the original NTSC and other, similar, television signal structures, which were based on the state of the art of electronics in the 1930s and even earlier. Both the camera and display (television receiver) were dependent upon specialized electron tubes that employed an electron beam that was swept (scanned) across the photosensitive or photoemissive area, respectively, of the tube in question. It was necessary that the beam be turned off during its return sweep (trace), to avoid marring the image (trace). While television cameras based on charge-coupled devices (CCDs), which have no such constraint, have supplanted cameras based on electron beams, most receivers still depend upon beam-based tubes. Note 2: To support a smooth transition (avoid obsolescence of older receivers) as the state of the art improved, the basic original signal structure was retained, with modifications (e.g., the superposition of signals necessary to support color). Blanking Level - In a baseband television signal, the DC level (nominally 0 volts) from which the amplitudes of the various components of the signal are measured. Conventionally, the viewable parts of the signal (except subcarriers) are positive with respect to blanking, while the synchronizing pulses are negative with respect to blanking. In North American NTSC signals, the darkest portions of the image (black level) are offset positively with respect to blanking level. This offset is called either pedestal or setup, depending on how it is generated. In almost all other television signals, including component RGB, there is no setup, so black level is the same voltage as blanking level. Synonym pedestal. Blind Transmission - Transmission without obtaining a receipt, i.e., acknowledgement of reception, from the intended receiving station. Note: Blind transmission may occur or be necessary when security constraints, such as radio silence, are imposed, when technical difficulties with a sender's receiver or receiver's transmitter occur, or when lack of time precludes the delay caused by waiting for receipts. Blinking - In graphic display devices, an intentional periodic change in the intensity of one or more display elements or display segments. Block - 1. A group of bits or digits that is transmitted as a unit and that may be encoded for error-control purposes. 2. A string of records, words, or characters, that for technical or logical purposes are treated as a unit. Note 1: Blocks (a) are separated by interblock gaps, (b) are delimited by an end-of-block signal, and (c) may contain one or more records. Note 2: A block is usually subjected to some type of block processing, such as multidimensional parity checking, associated with it. 3. In programming languages, a subdivision of a program that serves to group related statements, delimit routines, specify storage allocation, delineate the applicability of labels, or segment parts of the program for other purposes. Block Character - See end-of-transmission-block character. - A transmission control character used to indicate the end of a transmission block of data when data are divided into such blocks for transmission purposes. Block Check - In the processing or transmission of digital data, an error-control procedure that is used to determine whether a block of data is structured according to given rules. Block Check Character (BCC) - A character added to a transmission block to facilitate error detection. Note: In longitudinal redundancy checking and cyclic redundancy checking, block check characters are computed for, and added to, each message block transmitted. This block check character is compared with a second block check character computed by the receiver to determine whether the transmission is error free. Block Code - An error detection and/or correction code in which the encoded block consists of N symbols, containing K information symbols (K <N) and N-K redundant check symbols, such that most naturally occurring errors can be detected and/or corrected. 74
- 75. Block Diagram - A diagram of a system, a computer, or a device in which the principal parts are represented by suitably annotated geometrical figures to show both the basic functions of the parts and their functional relationships. Block Distortion - In the received image in video systems, distortion characterized by the appearance of an underlying block encoding structure. Block Dropping - A process by which one or more of the less significant bits of all the samples stored in a packet are dropped to alleviate congestion. Block Efficiency - In a block, the ratio of the number of user information bits to the total number of bits. Note: For a given block scheme, block efficiency represents the maximum possible efficiency for a given block scheme transmitted over a perfect transmission link. Block Error - A block within which at least one bit error occurs when the block is transferred from the source to the destination within the time slot assigned. Block-Error Probability - The expected block-error ratio. Block-Error Ratio - 1. The ratio of the number of incorrectly received blocks to the total number of blocks transferred. Note: The block-error ratio is calculated using empirical measurements. Multiple block-error ratios may be used to predict block-error probability. 2. The ratio of the number of blocks that contain at least one bit in error to the total number of blocks transmitted in a given time interval. Blocking - 1. The formatting of data into blocks for purposes of transmission, storage, checking, or other functions. 2. Denying access to, or use of, a facility, system, or component. 3. The failure of a telecommunications network to meet a user service demand, because of the lack of an available communications path. Blocking Criterion - In telephone traffic engineering, a criterion that specifies the maximum number of calls or service demands that fail to receive immediate service. Note: The blocking criterion is usually expressed in probabilistic notation, such as P.001. Blocking Factor - The number of records in a block. Note: The blocking factor is calculated by dividing the block length by the length of each record contained in the block. If the records are not of the same length, the average record length may be used to compute the blocking factor. Synonym grouping factor. Blocking Formula - A specific probability distribution function intended to model calling patterns of users who fail to find available facilities. Note: There are several blocking formulas. The applicability of each to a given situation depends on its underlying assumptions regarding caller behavior. Blocking Network - In telecommunications, a network that has fewer transmission paths than would be required if all users were to communicate simultaneously. Note: Blocking networks are used because not all users require service simultaneously. Certain statistical distributions apply to the patterns of user demand. Blocking Options - Local phone companys may offer several blocking options that you may subscribe to such as Anonymous Call Rejection, Billed Number Screening, Call Block 900/976 Restriction, Call Block Full Restriction, Call Block International Restriction, Call Block Long Distance Toll Restriction, Caller ID - Block Per Line, Caller ID - Block Per Call, and Pay Per Use Feature Blocking. Monthly Recurring Charges may apply. Most phone companies must provide and cannot charge local customers for Caller ID Per-Call Blocking of their number. 75
- 76. Block Length - The number of data units, such as bits, bytes, characters, or records, in a block. Block-Loss Probability - The ratio of the number of lost blocks to the total number of block transfer attempts during a specified period. Block-Misdelivery Probability - The ratio of the number of misdelivered blocks to the total number of block transfer attempts during a specified period. Block Parity - The designation of one or more bits in a block as parity bits used to force the block into a selected parity, either odd or even. Note: Block parity is used to assist in error detection or correction. Block Transfer - The process, initiated by a single action, of transferring one or more blocks of data. Block Transfer Attempt - A coordinated sequence of user and telecommunication system activities undertaken to effect transfer of an individual block from a source user to a destination user. Note: A block transfer attempt begins when the first bit of the block crosses the functional interface between the source user and the telecommunication system. A block transfer attempt ends either in successful block transfer or in block transfer failure. Block Transfer Efficiency - The average ratio of user information bits to total bits in successfully transferred blocks. Block Transfer Failure - Failure to deliver a block successfully. Note: The principal block transfer failure outcomes are: lost block, misdelivered block, and added block. Block Transfer Rate - The number of successful block transfers during a performance measurement period divided by the duration of the period. Block Transfer Time - The average value of the duration of a successful block transfer attempt. Note: A block transfer attempt is successful if (a) the transmitted block is delivered to the intended destination user within the maximum allowable performance period and (b) the contents of the delivered block are correct. Blue Noise - In a spectrum of frequencies, a region in which the spectral density, i.e., power per hertz, is proportional to the frequency. Blue-Screening - See chroma keying. - . Note 1: Chroma keying is used to create an overlay effect in the final picture, e.g., to insert a false background, such as a weather map or scenic view, behind the principal subject being photographed. Note 2: The principal subject is photographed against a background having a single color or a relatively narrow range of colors, usually in the blue or green. When the phase of the chroma signal corresponds to the preprogrammed state or states associated with the background color, or range of colors, behind the principal subject, the signal from the alternate, i.e., false, background is inserted in the composite signal and presented at the output. When the phase of the chroma signal deviates from that associated with the background color(s) behind the principal subject, video associated with the principal subject is presented at the output. Bluetooth - A low-power, short-range, rf technology that allows the connection of intelligent communications devices or appliances in a household or an office in a short-range wireless network. Examples of Bluetooth applications are transferring data between cell phones, radios, pagers, personal digital assistants, notebook computers, video and still cameras, audio players, and local area networks. 76
- 77. Blurring - In television and video systems, a global distortion over the entire image, characterized by reduced sharpness of edges and limited spatial detail. BNC connector - A type of bayonet (twist-lock) coaxial connector commonly used in applications involving small (e.g., RG-59, RG-62) coaxial cables. Board - In computers, a board, depending on usage, can be short for motherboard, the physical arrangement of a computer's basic components and circuitry, or it can refer to an expansion board (or card or adapter), which fits into one of the computer's expansion slots and provides expanded capability. BOC (Bell operating company) Abbreviation for Bell Operating Company. - is a term for any of the 22 original companies (or their successors) that were created when AT&T was broken up in 1983 and given the right to provide local telephone service in a given geographic area. The companies had previously existed as subsidiaries of AT&T and were called the "Bell System." The purpose of the breakup was to create competition at both the local and long-distance service levels. BOCs compete with other, independent companies to sell local phone service. In certain areas, long-distance companies, including AT&T, can now compete for local service. Collectively, companies offering local phone service are referred to legally as local exchange carriers (local exchange carrier). BOCs are not allowed to manufacture equipment and were initially not allowed to provide long-distance service. The Telecommunications Act of 1996 now permits them to engage in long-distance business under certain circumstances. As of 1996, the BOCs consisted of original and successor companies to: Bell Telephone Company of Nevada, Illinois Bell, Indiana Bell, Michigan Bell, New England Telephone and Telegraph Company, New Jersey Bell, New York Telephone Company, U S West Communications Company, South Central Bell, Southern Bell, Southwestern Bell, Bell Telephone of Pennsylvania, The Chesapeake and Potomac Telephone Company, The Chesapeake and Potomac Telephone Company of Maryland, The Chesapeake and Potomac Telephone Company of Virginia, The Diamond State Telephone Company, The Ohio Bell Telephone Company, The Pacific Telephone and Telegraph Company, and the Wisconsin Telephone Company. Historically, a BOC is any of the 22 operating companies that were divested from AT&T by court order. Note: Cincinnati Bell Telephone Co. and Southern New England Bell Telephone Co. were not included. Boltzmann's Constant (k): The number that relates the average energy of a molecule to its absolute -23 temperature. Note: Boltzmann's constant is approximately 1.38 × 10 J/K (joules/ kelvin). Bond - An electrical connection that provides a low-resistance path between two conducting surfaces. Bonding - 1. In electrical engineering, the process of connecting together metal parts so that they make low resistance electrical contact for direct current and lower frequency alternating currents. [JP1] 2. The process of establishing the required degree of electrical continuity between two or more conductive surfaces that are to be joined. Bookmark - A name or address of an Internet resource, stored in a software file at a user's site, e.g., in a desktop computer, for convenient future use. Note: An example of a bookmark is an entry in a bookmark file (or bookmark list) such as maintained within or by a Web browser for the convenience of the user in revisiting a previously visited Web site. 77
- 78. Bookmark List - Synonym hotlist. - A list of frequently used web locations and URLs (Uniform Resource Locators). Note: Hotlists may consist of a) lists of bookmarks accessed by a browser or b) lists of URLs at a web site for linking to other relevant web sites. Synonyms hotlist, go list, history list. Boolean function - 1. A mathematical function that describes Boolean operations. 2. A switching function in which the number of possible values of the function and each of its independent variables is two. Boolean operation - 1. Any operation in which each of the operands and the result take one of two values. Note: Typical states are "0 or 1," "on or off," "open or closed," or "present or absent." 2. An operation that follows the rules of Boolean Algebra. Bootstrap - 1. A technique or device designed to bring about a desired state by means of its own action. 2. That part of a computer program that may be used to establish another version of the computer program. 3. The automatic procedure whereby the basic operating system of a processor is reloaded following a complete shutdown or loss of memory. 4. A set of instructions that cause additional instructions to be loaded until the complete computer program is in storage. 5. To initialize a system by means of a bootstrap. Bootup - In computer science, the initial sequence of events (usually preprogrammed in firmware present in the computer) that are necessary to start a computer; i.e., to initialize its operating system, load programs into memory, etc., when (a) it is first powered up, or (b) when already powered up, upon some kind of assenting action by the user. Boot Up - To take some kind of assenting action to initiate computer bootup, e.g., to turn on the primary power (often referred to as initiating a cold bootup) or restart a powered-up computer (often referred to as initiating a hot bootup or hot reboot). Bose-Chaudhuri-Hochquenghem code - See BCH code. A multilevel, cyclic, error-correcting, variable-length digital code used to correct errors up to approximately 25% of the total number of digits. Note: BCH codes are not limited to binary codes, but may be used with multilevel phase-shift keying whenever the number of levels is a prime number or a power of a prime number, such as 2, 3, 4, 5, 7, 8, 11, and 13. A BCH code in 11 levels has been used to represent the 10 decimal digits plus a sign digit. Bot - Abbreviation for robot. A relatively small and focused computer application that (a) runs continuously, in the background (i.e., simultaneously), as other programs are being run, and (b) responds automatically to a user's activity. Synonyms agent, droid, infobot. Note 1: Many bots are created for the benefit of the user, e.g., those that send information upon request, perform automated searches, or monitor messages in a network forum. Other robots (e.g., a computer virus) are intended to harm the user or to spam the user (e.g., with advertising). Note 2: Many bots have nicknames that loosely describe their function. Some examples of bots are: adbot A bot that searches newsgroups and other on-line documents for email addresses. When one is found, an advertisement is automatically sent to that address. The address is usually saved in a database for sale to other advertisers. Alternatively, an adbot can be one that automatically posts advertisements to newsgroups and other network forums. crawler Synonym web crawler. knowbot Abbreviation for knowledge robot. A bot that automatically searches on-line information for data relevant to a user's previous search criteria. knowledge See knowbot. robot list server A bot that accepts messages from users and then sends a copy of that messages to all members of the related mailing list. The list server will also allow list members to customize the way 78
- 79. messages are sent to them (e.g., the messages can be sent as they are received by the list server or saved, compiled, and then sent). pokerbot A bot that automatically plays the game of poker in various on-line forums. Note: Many on-line games have had bots designed to play them, e.g., a chessbot or a bridgebot. portal A bot that serves as a starting point for browsers. A portal will often include a search engine. robot See bot. robotic Synonym search engine. librarian search bot Synonym search engine. search A bot that accepts words or phrases from an Internet user via a browser, searches a database engine for matching web pages, and displays a list of those pages that match the search criteria. spambot A bot that sends unwanted, unrequested, and usually repetitive e-mail or messages directly to a user or to a message forum. In most cases, this unwanted information is commercial advertisements, although the message can be propaganda supporting a cause or nonsense messages designed to fill up a user's mailbox. spider Synonym web crawler. web crawler A bot that searches the world wide web for new and updated web pages. Found pages are categorized by subject and placed in a database. Typically, an associated search engine will access that database. wizard A bot that has some ability to make informed decisions. For example, a wizard might determine the city from which you are accessing the network and provide to you the current weather report for your area. Bounce - To return, to the sender, e-mail that is, for whatever reason, undeliverable to its intended destination. Note 1: There are various reasons why e-mail may be bounced. Examples are an incorrect address, problems with local network facilities, and problems with telecommunications links. Note 2: Bounced e-mail is often accompanied by an error message describing the reason that it was not delivered. Bouncing Busy Hour (BBH) - The hour in which the highest usage is measured for any day. The readings are on the hour or half hour. The selected clock hour will vary from day to day, depending on the measured usage. Boundary - 1. [In security,] Software, hardware, or a physical barrier that limits access to a system or part of a system.2. Synonym [in networking] section boundary. Bound Mode - In an optical fiber, a mode that (a) has a field intensity that decays monotonically in the transverse direction everywhere external to the core and (b) does not lose power to radiation. Note: Except for single-mode fibers, the power in bound modes is predominantly contained in the core of the fiber.Synonyms guided mode, trapped mode. Bound Ray - In an optical fiber, a ray that is confined primarily to the core. BPI ( bpi) - See bits per inch. - A unit used to express the linear bit density of data in storage. Note: The abbreviation " bpi" is not in accordance with international standards, and is therefore deprecated. BPS - (See bits per second). - In data communications, bits per second is a common measure of data speed for computer modems and transmission carriers. As the term implies, the speed in bps is equal to the number of bits transmitted or received each second. 79
- 80. Braid - 1. An essential part of many fiber-optic cable designs, consisting of a layer of woven yarn. Note: In the case of single-fiber loose-buffered or two-fiber "zip-cord" loose-buffered fiber-optic cables, the braid is situated between the buffer tube and jacket. In the case of cables having multiple buffer tubes, the braid is usually situated between the inner jacket and outer jacket. 2. Loosely, an unwoven parallel bundle of yarn situated around the tight buffer of a single-fiber or two-fiber "zip-cord" fiber-optic cable. Note 1: The braid serves to add tensile strength to the cable. The braid may also be anchored to an optical connector or splice organizer assembly to secure the end of the cable. Note 2: The braid is often of an aramid yarn. Branch - 1. In a computer program, a conditional jump or departure from the implicit or declared order in which instructions are being executed. 2. To select a branch, as in definition #1. 3. A direct path joining two nodes of a network or graph. 4. In a power distribution system, a circuit from a distribution device (power panel) of a lower power handling capability than that of the input circuits to the device. Branching Network - A network used for transmission or reception of signals over two or more channels. Branching Repeater - A repeater with two or more outputs for each input. Branch Point - A network point where two or more possible routes through different intermediate networks from the origination network to destination network physically diverge. A branch point may occur in any network except the destination network. Breach - The circumvention or disablement of some element of computer security, with or without detection, which could result in a penetration of (a) the affected computer's software or data base (s), or (b) another device or network to which the affected computer may also be connected. Breadboard - 1. An assembly of circuits or parts used to prove the feasibility of a device, circuit, system, or principle with little or no regard to the final configuration or packaging of the parts. 2. To prepare a breadboard. Break Interval - 1. In dial-pulse signaling, that portion of the dial pulse in which the pulsing circuit is in its high-impedance condition. 2. In dial-pulse signaling, that portion of the dial pulse in which the pulsing circuit is on-hook. Break Out - To separate the individual fibers or buffer tubes of a fiber-optic cable for the purpose of splicing or installing optical connectors. Synonyms fan out, furcate. Break-Out Box - A testing device that permits a user to access individual leads of an interface cable, using jumper wires, in order to monitor, switch, or patch the electrical output of the cable. Breakout Cable - A multifiber fiber-optic cable design in which individual fibers, usually tight-buffered, are surrounded by separate strength members and jackets, which are in turn enveloped by a common jacket. Note 1: The breakout cable facilitates easy installation of fiber-optic connectors. All that need be done to prepare the ends of the cable to receive connectors is to remove the outer jacket, exposing what are essentially individual single-fiber cables. Note 2: Because it tends to induce bends in the fibers, the breakout cable design usually results in slightly higher transmission losses, for a given fiber, than loose-buffer designs. Synonym fanout cable. Breakout Kit - A kit of materials, composed of an outer jacket in which is contained a strength member consisting of a bundle of usually aramid yarn, which jacket and yarn may be slipped over a loose buffer tube containing a single fiber, to convert the buffer tube and fiber to a complete single-fiber cable to which a fiber-optic connector may be directly attached. Note 1: A heat-shrinkable plastic boot may also be used for 80
- 81. cosmetic purposes, strain relief, and to seal the point where the individual cables so created, merge. Note 2: Use of a breakout kit enables a fiber-optic cable containing multiple loose buffer tubes to receive connectors without the splicing of pigtails. Brewster's angle - For a plane electromagnetic wavefront incident on a plane boundary between two dielectric media having different refractive indices, the angle of incidence at which transmittance from one medium to the other is unity when the wavefront is linearly polarized with its electric vector parallel to the plane of incidence. Brewster's law - See Brewster's angle. BRI - Abbreviation for basic rate interface. Brick - An informal name for a hand-held radiotelephone unit. Synonyms personal terminal, radio personal terminal. Brick Wall Filter - A low-pass filter with a steep cut-off (such as 20 dB /octave or greater), such that a negligible amount of higher frequency information passes. Note: A brick wall filter typically has uniform group delay. Bridge - 1. In communications networks, a device that (a) links or routes signals from one ring or bus to another or from one network to another, (b) may extend the distance span and capacity of a single LAN system, (c) performs no modification to packets or messages, (d) operates at the data-link layer of the OSI-- Reference Model (Layer 2), (e) reads packets, and (f) passes only those with addresses on the same segment of the network as the originating user. 2. A functional unit that interconnects two local area networks that use the same logical link control procedure, but may use different medium access control procedures. 3. A balanced electrical network, e.g., a Wheatstone bridge. Note: A bridge may be used for electrical measurements, especially resistances or impedances. 4. See hybrid coil. Bridged Ringing - The part of a signaling system in which ringers associated with a particular line are connected across that line. Bridged Tap - Any portion of a loop that is not in the direct talking path between the central office and the service user's terminating equipment. A bridged tap may be an unused cable pair connected at an intermediate point or an extension of the circuit beyond the service user's location. Note: A bridged tap creates an impedance mismatch within the transmission line, which creates signal reflections. These reflections are generally not noticed in standard (POTS) voicegrade service, but become significant with high frequency (x DSL--which can be A DSL, asynchronous DSL, or S DSL, synchronous DSL, etc.) and digital transmission (DDS and DS1) services. Bridge Lifter - A device that electrically or physically removes bridged telephone pairs. Note: Relays, saturable inductors, and semiconductors are used as bridge lifters. Bridge-to-Bridge Station - A ship station operating in the port operations service in which messages are restricted to navigational communications and which is capable of operation from the ship's navigational bridge or, in the case of a dredge, from its main control station, operating on a frequency or frequencies in the 156-162 MHz band. Bridge Transformer - Synonym hybrid coil. - A single transformer that effectively has three windings, and which is designed to be configured as a circuit having four branches, i.e., ports, that are conjugate in pairs. Note: The primary use of a hybrid coil is to convert between 2-wire and 4-wire operation in concatenated 81
- 82. sections of a communications circuit. Such conversion is necessary when repeaters are introduced in a 2-wire circuit. Bridging Connection - A parallel connection used to extract some of the signal energy from a circuit, usually with negligible effect on the normal operation of the circuit. Bridging Loss - At a given frequency, the loss that results when an impedance is connected across a transmission line. Note: Bridging loss is expressed as the ratio, in dB, of the signal power delivered, prior to bridging, to a given point in a system downstream from the bridging point, to the signal power delivered to the given point after bridging. Brightness - An attribute of visual perception in which a source appears to emit a given amount of light. Note 1: "Brightness" should be used only for nonquantitative references to physiological sensations and perceptions of light. Note 2: "Brightness" was formerly used as a synonym for the photometric term "luminance" and (incorrectly) for the radiometric term " radiance." Brillouin Diagram - See Brillouin scattering. - In a physical medium, scattering of lightwaves, caused by thermally driven density fluctuations. Note: Brillouin scattering may cause frequency shifts of several gigahertz at room temperature. Brillouin Scattering - In a physical medium, scattering of lightwaves, caused by thermally driven density fluctuations. Note: Brillouin scattering may cause frequency shifts of several gigahertz at room temperature. Broadband - 1. Synonym [in analog technology] wideband. 2. A descriptive term for evolving digital technologies that provide consumers a signal-switched facility offering integrated access to voice, high-speed data service, video-demand services, and interactive delivery services. Broadband Exchange (BEX) - A communications switch capable of interconnecting channels having bandwidths greater than voice bandwidth. Broadband Internet Connection - A connection capable of carrying high quality VoIP conversations, and is much more cheap and efficient than a traditional telephone line. Broadband ISDN (B-ISDN) - An Integrated Services Digital Network (ISDN) offering broadband capabilities. Note 1: B-ISDN is an ITU-T proposed (originally a CCITT-proposed) service that may (a) include interfaces operating at data rates from 150 to 600 Mb/s, (b) use asynchronous transfer mode (ATM) to carry all services over a single, integrated, high-speed packet-switched network, (c) have LAN interconnection capability, (d) provide access to a remote, shared disk server, (e) provide voice/ video /data teleconferencing, (f) provide transport for programming services, such as cable TV, (g) provide single-user controlled access to remote video sources, (h) handle voice/video telephone calls, and (i) access shop-at-home and other information services. Note 2: Techniques used in the B-ISDN include code conversion, information compression, multipoint connections, and multiple-connection calls. Current proposals use a service-independent call structure that allows flexible arrangement and modular control of access and transport edges. The service components of a connection can provide each user with independent control of access features and can serve as the basis of a simplified control structure for multipoint and multiconnection calls. Such a network might be expected to offer a variety of ancillary information processing functions. Broadband Phone - is a type of voice based communications system, which can be created using a regular touch tone telephone, a broadband connection, and a connecting adapter. Broadband System - See [in analog technology] wideband. 82
- 83. Broadcasting-Satellite Service - A radiocommunication service in which signals transmitted or retransmitted by space stations are intended for direct reception by the general public. In the broadcasting-satellite service, the term "direct reception" shall encompass both individual reception and community reception. Broadcasting Satellite Space Station - A space station in the broadcasting-satellite service (sound broadcasting). Broadcasting Service - A radiocommunication service in which the transmissions are intended for direct reception by the general public. This service may include sound transmissions, television transmissions or other types of transmissions. Broadcasting Station - A station in the broadcasting service. Broadcast Operation - The transmission of signals that may be simultaneously received by stations that usually make no acknowledgement. Broadcast Spectrum - An entire range of frequencies used for radio and television transmission. Broadcasting - Using radio waves to distribute radio or TV programs, which are available for reception by the general public. Broadside Antenna - Synonym billboard antenna. - An array of parallel dipole antennas with flat reflectors, usually positioned in a line or plane. Note 1: The spacing and dimensions of the dipoles depend on the wavelength. Note 2: The main lobe of a fixed billboard antenna may, within limits, be steered by appropriate phasing of the respective signals to individual elements of the array. Brouter - A combined bridge and router that operates without protocol restrictions, routes data using a protocol it supports, and bridges data it cannot route. Browser - A software program that allows you to view HTML documents and navigate on the WWW. Any computer software program for reading hypertext. Note 1: Browsers are usually associated with the Internet and the World Wide Web (WWW). Note 2: A browser may be able to access information in many formats, and through different services including HTTP and FTP. Browsing - [The] act of searching through information-system (IS) storage to locate or acquire information without necessarily knowing of the existence or the format of the information being sought. Brute-Force Attack - In security, an attack that requires trying all (or a large fraction of all) possible values until the right value is found. Synonym [loosely] exhaustive attack. b/s - Abbreviation for bits per second. BSA - Abbreviation for basic serving arrangement. BSE - Abbreviation for basic service element. BSI - Abbreviation for British Standards Institution. B6ZS - Abbreviation for bipolar with six-zero substitution. A T-carrier line code in which bipolar violations are deliberately inserted if user data contain a string of 6 or more consecutive zeros. Note 1: B6ZS is used to ensure a sufficient number of transitions to maintain system synchronization when the user data stream 83
- 84. contains an insufficient number of "ones" to do so. Note 2: B6ZS is used in the North American hierarchy at the T2 rate. B3ZS - Abbreviation for bipolar with three-zero substitution. A T-carrier line code in which bipolar violations are deliberately inserted if user data contain a string of 3 or more consecutive zeros. Note 1: B3ZS is used to ensure a sufficient number of transitions to maintain system synchronization when the user data stream contains an insufficient number of "ones" to do so. Note 2: B3ZS is used in the North American hierarchy at the T3 rate. Budgeting - Synonym proration. The proportional distribution or allocation of parameters, such as noise power and transmission losses, among a number of tandem-connected items, such as equipment, cables, links, or trunks, in order to balance the performance of communications circuits. Buffer - 1. A routine or storage medium used to compensate for a difference in rate of flow of data, or time of occurrence of events, when transferring data from one device to another. Note: Buffers are used for many purposes, such as (a) interconnecting two digital circuits operating at different rates, (b) holding data for use at a later time, (c) allowing timing corrections to be made on a data stream, (d) collecting binary data bits into groups that can then be operated on as a unit, (e) delaying the transit time of a signal in order to allow other operations to occur. 2. To use a buffer or buffers. 3. An isolating circuit, often an amplifier, used to minimize the influence of a driven circuit on the driving circuit. Synonym buffer amplifier. 4. In a fiber optic communication cable, one type of component used to encapsulate one or more optical fibers for the purpose of providing such functions as mechanical isolation, protection from physical damage and fiber identification. Note: The buffer may take the form of a miniature conduit, contained within the cable and called a loose buffer, or loose buffer tube, in which one or more fibers may be enclosed, often with a lubricating gel. A tight buffer consists of a polymer coating in intimate contact with the primary coating applied to the fiber during manufacture. Buffer Amplifier - Synonym buffer. Bug - 1. A concealed microphone or listening device or other audiosurveillance device.2. A mistake in a computer program. 3. To install means for audiosurveillance. 4. A semiautomatic telegraph key. 5. A mistake or malfunction. Building Out - The process of adding a combination of inductance, capacitance, and resistance to a cable pair so that its electrical length may be increased by a desired amount to control impedance and loss characteristics. Synonym line buildout. Build-Out Delay - The maximum variable transmission and processing delay that is permitted in a wideband network. Each PVP (packetized voice protocol) node records the delay that it adds and updates accordingly the TS (time stamp) value in the packet header. When the terminating endpoint of a PVP node receives a voice packet, the provisioned build-out and the time stamp value are compared. If the TS value is larger than the build-out, the PVP node drops the packet. If the delay is less than the provisioned build-out, the packet is delayed by the difference between the two values. Bulk Encryption - Simultaneous encryption of all channels of a multichannel telecommunications link. Note: A single encryption device can be used to encrypt the output signal from a multiplexer. Bulletin Board - A form of electronic messaging in which addressed messages or files are entered by users into a computer or network of computers. Note: Other users may obtain, at their convenience and request, messages or files available to them. Synonym electronic bulletin board. 84
- 85. Bunched Frame-Alignment Signal - A frame-alignment signal in which the signal elements occupy consecutive digit positions. Bundle - 1. A group of optical fibers or electrical conductors, such as wires and coaxial cables, usually in a single jacket. Note: Multiple bundles of optical fibers or electrical conductors may be placed in the same cable. 2. In cryptography, the three cryptographic keys (K1, K2, K3) used with a TDEA mode. Buried Cable - See direct-buried cable. Buried Plant - See direct-buried cable. Burst - 1. In data communications, a sequence of signals, noise, or interference counted as a unit in accordance with some specific criterion or measure. 2. To separate continuous-form or multipart paper into discrete sheets. Burst Isochronous - Deprecated synonym for isochronous burst transmission. Burst Switching - In a packet-switched network, a switching capability in which each network switch extracts routing instructions from an incoming packet header to establish and maintain the appropriate switch connection for the duration of the packet, following which the connection is automatically released. Note: In concept, burst switching is similar to connectionless mode transmission, but it differs from the latter in that burst switching implies an intent to establish the switch connection in near real time so that only minimum buffering is required at the node switch. Burst Transmission - 1. Transmission that combines a very high data signaling rate with very short transmission times. 2. Operation of a data network in which data transmission is interrupted at intervals. Note: Burst transmission enables communications between data terminal equipment (DTEs) and a data network operating at dissimilar data signaling rates. Synonym data burst. Bus - One or more conductors or optical fibers that serve as a common connection for a group of related devices. Business Systems - The set of voice, data, and Internet products that provide communication solutions and services to business customers. The products usually reside within the customer's place of business. Bus Interface Unit (BIU): See network interface device. - 1. A device that performs interface functions, such as code conversion, protocol conversion, and buffering, required for communications to and from a network. 2. A device used primarily within a local area network (LAN) to allow a number of independent devices, with varying protocols, to communicate with each other. Note 1: An NID converts each device protocol into a common transmission protocol. Note 2: The transmission protocol may be chosen to accommodate directly a number of the devices used within the network without the need for protocol conversion for those devices by the NID. Synonym network interface unit. Bus Network - See network topology. A network topology in which all nodes, i.e., stations, are connected together by a single bus. Bus Topology - See network topology. A network topology in which all nodes, i.e., stations, are connected together by a single bus. Busy Back - Deprecated term. See busy signal. 85
- 86. Busy Hour - In a communications system, the sliding 60-minute period during which occurs the maximum total traffic load in a given 24-hour period. Note 1: The busy hour is determined by fitting a horizontal line segment equivalent to one hour under the traffic load curve about the peak load point. Note 2: If the service time interval is less than 60 minutes, the busy hour is the 60-minute interval that contains the service timer interval. Note 3: In cases where more than one busy hour occurs in a 24-hour period, i.e., when saturation occurs, the busy hour or hours most applicable to the particular situation are used. Synonym peak busy hour. Busy Verification - In a public switched telephone network, a network-provided service feature that permits an attendant to verify the busy or idle state of station lines and to break into the conversation. Note: A 440- Hz tone is applied to the line for 2 seconds, followed by a 0.5-second burst every 10 seconds, to alert both parties that the attendant is connected to the circuit. Busy Season - During a 1-year cycle, the period of 3 consecutive months having the highest busy hour traffic. Busy Signal - 1. In telephony, an audible or visual signal that indicates that no transmission path to the called number is available. Synonym busy tone. 2. In telephony, an audible or visual signal that indicates that the called number is occupied or otherwise unavailable. Synonym reorder tone. Busy Test - In telephony, a test made to determine whether certain facilities, such as a subscriber line or a central office trunk, are available for use. Busy Tone - Synonym busy signal. In telephony, an audible or visual signal that indicates that no transmission path to the called number is available. BW - Abbreviation for bandwidth. Bypass - 1. The use of any telecommunications facilities or services that circumvents those of the local exchange common carrier. Note: Bypass facilities or services may be either customer-provided or vendor- supplied. 2. An alternate circuit that is routed around equipment or system component. Note: Bypasses are often used to allow system operation to continue when the bypassed equipment or a system component is inoperable or unavailable. Byte - A combination of bits that represents a single character (approximately 8 bits equal one byte). A sequence of contiguous bits (usually 8) considered as a unit. Note: In pre-1970 literature, "byte" referred to a variable-length bit string. Since that time, the usage has changed so that now it almost always refers to an 8- bit string. This usage predominates in computer and data transmission literature; when so used, the term is synonymous with " octet." C Cable - 1. An assembly of one or more insulated conductors, or optical fibers, or a combination of both, within an enveloping jacket. Note 1: A cable is constructed so that the conductors or fibers may be used singly or in groups. Note 2: Certain types of communications cables, especially long submarine cables but also terrestrial cables, whether the communications media are metallic or optical fiber, may contain metallic conductors that supply power to repeaters (amplifiers). 2. A message sent by cable, or by any means of telegraphy (including wireless means). CableCARD - Security card that Digital Cable Ready (DCR) TV owners must obtain from their cable company in order to view scrambled programming, such as premium services. 86
- 87. Cable Head-Rnd (or headend) - is the facility at a local cable TV office that originates and communicates cable TV services and cable modem services to subscribers. In distributing cable television services, the head- end includes a satellite dish antenna for receiving incoming programming. This programming is then passed on to the subscriber. (Cable TV companies may also play videotapes and originate live programming.) Normally, all signals are those that are sent downstream to the subscriber, but some are received upstream such as when a customer requests a pay-per-view program. When a cable company provides Internet access to subscribers, the head-end includes the computer system and databases needed to provide Internet access. The most important component located at the head-end is the cable modem termination system (CMTS), which sends and receives digital cable modem signals on a cable network and is necessary for providing Internet services to cable subscribers. Cable TV (CATV) - A broadband communications technology in which multiple television channels, as well as audio and data signals, may be transmitted either one way or bidirectionally through an often hybrid (fiber and coaxial) distribution system to a single or to multiple specific locations. CATV originated in areas where good reception of direct broadcast TV was not possible. Now CATV also consists of a cable distribution system to large metropolitan areas in competition with direct broadcasting. The abbreviation CATV originally meant community antenna television. However, CATV is now usually understood to mean cable TV. CALEA (Communications Assistance for Law Enforcement Act) - A 1994 act that requires telecommunications services to provide wiretapping access. The act specifically excludes information services, so the question is whether VoIP is a telecommunications service, and thus covered by the act, or an information service, and thus exempted. VoIP providers are receiving pressure to comply with the act. Call - 1. In communications, any demand to set up a connection. 2. A unit of traffic measurement. 3. The actions performed by a call originator. 4. The operations required to establish, maintain, and release a connection. 5. To use a connection between two stations. 6. The action of bringing a computer program, a routine, or a subroutine into effect, usually by specifying the entry conditions and the entry point. 7. A customer attempt for which complete address information (e.g., 0-, 911, or 10 digits) is provided to the serving dial tone office. Call Attempt - In a telecommunications system, a demand by a user for a connection to another user. Note: In telephone traffic analysis, call attempts are counted during a specific time frame. The call-attempt count includes all completed, overflowed, abandoned, and lost calls. Callback ( international callback) - is a system for avoiding regular phone company long-distance charges by having a call initiated from within the United States with the orginating caller joining in a conference call. Here's how the procedure works: • A call originator (for example, someone in South America) calls a predesignated number in the United States, waits until it rings once, and then hangs up. • A machine in the office where the phone rang recognizes that the phone number was called and knows the phone number of the party that called it (because it was the only party that knew the number). • The machine places a call (which may be a local or a long-distance call) that originates from the U.S. location and also calls the party who initiated this procedure, thus arranging a conference call but at the U.S. long-distance rate. • In another variation, the automatically-generated call from the U.S. may call the originator and ask the originator to dial their desired number or provide a U.S. dial tone. • The originator (who subscribes to this callback service) is billed by the U.S.-based service at its own rates. 87
- 88. In localities where portable phone (cellphone) companies do not charge for incoming calls, callback is also sometimes used to avoid airtime charges for outgoing calls. Call Block - Allows you to block up to six pre-selected phone numbers. To block a designated phone number, press *60 , press #, wait for the dial tone, and dial the first designated phone number you wish to block, followed by the #. Repeat this process to add more phone numbers. To deactivate, press *80. Calls from cellular phones and calls placed with operator assistance cannot be blocked. Call Block 900/976 Restriction - Restricts all outgoing calls to 900 and 976 telephone numbers. Due to many phone companies’ inability to bill 900 and 976 calls, most will automatically block all 900 and 976 calls originating from your residential telephone line. Call Block Full Restriction - Allows you to restrict all outgoing calls to 1+, 0-, 0+, 00-, 211, 311, 411, 511, 900 telephone numbers, 976 telephone numbers, International 01+, International 011, 101XXXX. Call Blocking Options - Local phone companys may offer several call blocking options that you may subscribe to such as Anonymous Call Rejection, Billed Number Screening, Call Block 900/976 Restriction, Call Block Full Restriction, Call Block International Restriction, Call Block Long Distance Toll Restriction, Caller ID - Block Per Line, Caller ID - Block Per Call, and Pay Per Use Feature Blocking. Monthly Recurring Charges may apply. Most phone companies must provide and cannot charge local customers for Caller ID Per-Call Blocking of their number. Call Block International Restriction – Restricts you from placing outgoing 011+ and 101XXXX011+ International direct dialed calls. Call Block Long Distance Toll Restriction - Restricts you from placing 1+ and 0+ outgoing calls (including access to 900/976 pay per call services). Call Collision - 1. The contention that occurs when a terminal and data circuit-terminating equipment (DCE) specify the same channel at the same time to transfer a call request and handle an incoming call. Note: When call collision occurs, the DCE proceeds with the call request and cancels the incoming call. 2. The condition that occurs when a trunk or channel is seized at both ends simultaneously, thereby blocking a call. Synonym dual seizure. Deprecated synonym glare. Caller ID -Allows you to view the telephone number, date and time on your caller ID display before the call is answered. The calling information is delivered between the first and second ringing cycle of the call. See Caller ID with Number and Caller ID with Number, Name and ACR for more information Caller ID Blocking (Calling Number Delivery Block) - Prevents your name and number from appearing on the Caller ID unit of the person you’re calling. You may subscribe to Caller ID Complete Blocking at no charge for continuous call blocking. To activate Caller ID Blocking on a per-use basis, press *67 before each call. If you subscribe to continuous Caller ID Complete Blocking, press *82 before each call to deactivate the service. Caller ID - Block Per Line - Allows you to prevent delivery of your telephone number on all outgoing calls. Once you subscribe to this feature, it will be in operation on a continuous basis unless you dial *82 to unblock before a call is placed. This feature is also known as “Caller ID – Complete Blocking per Line.” 88
- 89. Caller ID - Block Per Call - Allows you to prevent delivery, on a per call basis, of your telephone number on an outgoing call to another party who subscribes to Caller ID. You can access this service by dialing *67. This feature is also known as “Caller ID - Selective Block per Call.” Caller ID – Complete Blocking per Line - - Allows you to prevent delivery of your telephone number on all outgoing calls. Once you subscribe to this feature, it will be in operation on a continuous basis unless you dial *82 to unblock before a call is placed. This feature is also known as “Caller ID – Block per Line.” Caller ID - Selective Block per Call - - Allows you to prevent delivery, on a per call basis, of your telephone number on an outgoing call to another party who subscribes to Caller ID. You can access this service by dialing *67. This feature is also known as “Caller ID - Block per Call.” Caller ID with Number - Allows you to view the telephone number, date and time on your caller ID display before the call is answered. The calling information is delivered between the first and second ringing cycle of the call. System will default to this if Caller ID with Number, Name and ACR is not available. Caller ID with Number, Name and ACR – Displays the listed name associated with the incoming telephone number. The name will be delivered to your caller ID display device attached to your telephone line, telephone, or answering machine with a built-in display screen. Call Failure Rate (CFR)- is a statistical measure commonly used in assessing Internet service providers (ISPs) or any network provider. The call failure rate is the percentage of calls to an ISP or network provider that fail to get through. Companies can measure the CFR for their own employees who dial in for access to the company's network. Rating companies report on the CFRs for major ISPs like AOL, Ameritech, and Mindspring. Visual Networks, formerly Inverse Network Technology, is probably the best known benchmarking company of ISPs. Call Forwarding - A telephone service that enables a customer to have an incoming call automatically rerouted rerouted to another, designated number or extension. Notice that the fee charging structure for a calling party to place a call to the called party which has their number forwarded can be subtle: if the called party has forwarded their number to a mobile telephone, the caller could incur higher rates due to the subsequent use of the mobile telephone network. However, the line which is being forwarded usually incurs all related charges, including long distance. Special types of call forwarding can be activated only if the line is busy, or if there is no answer, or even only for calls from selected numbers. In North America, the NANP uses the following vertical service codes to control call forwarding: • forward all calls: *72, activation; *73, deactivation • on busy or no answer: *68, activation; *88, deactivation • from select callers: *63, activation; *83, deactivation • on ISDN: *56, change forward-to number Customer-programmable features (where available): • busy line: *90, activation; *91, deactivation; *40, change number • no answer: *92, activation; *93, deactivation; *42, change number 89
- 90. Call Forwarding Busy – Allows you to activate this feature, via dialed access voice prompt menus, to automatically transfer all incoming calls that reach a busy response from your telephone number to another telephone number until you deactivate this feature. Call Forwarding Busy/No Answer - Allows you to activate this feature, via dialed access voice prompt menus, to automatically transfer all incoming calls that reach a busy or no answer response from your telephone number to another telephone number until you deactivate this feature. Call Forward Busy- Call Alert for AOL - supports a new s ervice AOL is offering to its customers. It will provide you with an alert that a call has come in over the same line you are utilizing to access the Internet. Call Forwarding No Answer - Allows you to activate this feature, via dialed access voice prompt menus, to automatically transfer all incoming calls that reach a no answer response from your telephone number to another telephone number until you deactivate this feature. Call Forwarding - Preferred - Allows you to transfer up to six telephone numbers on a screening list to another number. Only the calls on the screening list are forwarded. You can activate this feature by dialing *63, and deactivate by dialing *83. Call Forwarding Remote Access – Allows you to remotely activate the call forwarding feature at your home, or change the call forwarded telephone number that was previously set. This feature includes the basic Call Forwarding Variable feature. It allows you to forward calls from your home telephone number or from another telephone number when away from home using a touchtone phone. Call Forwarding Ring No Answer - Allows you to control the number of seconds or ring cycles that occur prior to forwarding an unanswered call to voice mail or to another telephone number. Call Forwarding Variable - Allows you to forward your calls to a number of your choosing. Allows you to activate this feature, via dialed access voice prompt menus, to automatically transfer all incoming calls from your telephone number to another telephone number until you deactivate this feature. Press 72# and enter the number to which you want your incoming calls forwarded. When that call is answered, Call Forward - Variable is in effect. If the call is not answered or if the number is busy, your calls will not be forwarded. You must then repeat the process for your calls to be forwarded. To deactivate, press73* . Two short tones, followed by a normal tone, will indicate the feature is deactivated. Repeat these steps each time you wish to forward calls. Call Grab - If the Call Override feature does not perform due to any line problems with your local phone service provider, this standard feature will allow you to override the fax switch's tone detect and call routing operation. Call Grab can be initiated from any touch tone or pulse extension phone by dialing "9" on the telephone key pad. When "9" is dialed, the fax switch will immediately cease its call routing function. This feature is standard and will work regardless of the status of the "Call Override" feature. Note: YOU must enable the "Pulse Detect" feature if you want to grab a call from a pulse dial phone. Call Management - 1. In telegraphy, route selection, signaling, and circuit usage and availability for a call. 2. In universal personal telecommunications, the ability of a user to inform the network how to handle incoming calls in accord with certain parameters, such as the call originator, the time of day, and the nature of the call. Note: Call management is accomplished by means of information in the user's service profile. Call Originator - An entity, such as a person, equipment, or program that originates a call. Synonym calling party. 90
- 91. Calling Party - Synonym call originator. - An entity, such as a person, equipment, or program that originates a call. Call Processing - 1. The sequence of operations performed by a switching system from the acceptance of an incoming call through the final disposition of the call. 2. The end-to-end sequence of operations performed by a network from the instant a call attempt is initiated until the instant the call release is completed. 3. In data transmission, the operations required to complete all three phases of an information transfer transaction. Call Processor - A device that manages telephone traffic and routes incoming calls to the proper equipment. A call processor analyzes and routes incoming calls to your telephones or data equipment. Multi-Link call processors are dependable and reliable. See faxswitch for more information.. Call Return - Allows you to automatically redial the last incoming telephone number, which is done by using a code. The last telephone number does not have to be known or have been answered by you. Activation must occur before another incoming call, or before a call waiting indication is received. Allows you to dial the last number called whether you answered the call or not. Press *69 to hear a recording of the phone number of the last incoming call. If the line is busy or there is no answer, Call Return will continue trying to reach the calling party for 30 minutes. Press *89 to deactivate Call Return before the 30 minutes have elapsed. Call Screening - Allows you to prevent calls from an unwanted caller whose number may or may not be known. When the unwanted call is received, you will need to hang up and immediately dial the Call Screening access code, which will deny the caller the ability to ring your telephone number. Also, you have the ability to create a list of telephone numbers from which you do not wish to receive calls. Calls from these telephone numbers will be sent to an announcement indicating that the call cannot be completed because you have activated Call Screening. Most phone comnpanies can block up to six numbers from calling your residential telephone line. Call Screening allows you to block phone numbers from a list you’ve designated and route them to a message indicating you’re not receiving calls at this time. Dial *60 to activate and follow the instructions. Dial *80 and follow the prompts to deactivate. Call-Second - A unit used to measure communications traffic. Note 1: A call-second is equivalent to 1 call 1 second long. Note 2: One user making two 75-second calls is equivalent to two users each making one 75- second call. Each case produces 150 call-seconds of traffic. Note 3: The CCS, equivalent to 100 call-seconds, is often used. Note 4: 3600 call-seconds = 36 CCS = 1 call-hour. Note 5: 3600 call-seconds per hour = 36 CCS per hour = 1 call-hour per hour = 1 erlang = 1 traffic unit. Call Sign - A station or address designator represented by a combination of characters or pronounceable words that is used to identify such entities as a communications facility, station, command, authority, activity, or unit. Call Sign Station - In broadcasting and radio communications, a Call Sign is a unique designation that identifies a transmitting station. In some cases, they are used as names for broadcasting stations. A Call Sign can be formally assigned by a government agency or informally adopted by individuals or organizations, and it can be cryptographically encoded to disguise a station's identity. Call Trace - Allows you to initiate an automatic trace of the last call received. You need to dial *57 to have your local telephone carrier Annoyance Call Center trace annoying calls. After two confirmed traces of the same number, your local phone company's Annoyance Call Center will work with law enforcement 91
- 92. authorities to take the appropriate action to end the annoying calls. The trace must begin prior to another call being received. If you receive a harassing or threatening call, you can have the number traced. To activate this feature, hang up immediately from an offensive phone call. Wait 10 seconds, pick up the handset, and press *57 to trace the call. If the trace is successful, a confirmation announcement will be given and further instructions will be provided. If the trace is unsuccessful, you will hear an error message. Call Trace is a feature, not an emergency number. Call Waiting - Provides a tone signal when a second call is coming in on a busy line. Allows you to answer the second call without disconnecting from the existing call, switch between the calls, and end either call at any time. This feature enables you to know when someone else is calling and allows the call to be received without having two lines. This feature is provided by many telephone companies so that two calls to be managed at the same time on one line. Your automatic call processor will work fine with "Call Waiting." A special tone signals you when there’s an incoming call while you’re on the phone. At the tone briefly press and release the telephone switch hook or “flash” button. This places the first call on hold while you answer the incoming call. To return to the first call (and to switch back and forth), press and release the switch hook or flash button again. To temporarily deactivate Call Waiting, press *70 and wait for a second dial tone before placing your call. Call Waiting will be automatically reactivated for new incoming calls when you hang up. Call Waiting Deluxe - Provides a tone signal when a second call is coming in on a busy line, and see caller information for the waiting call on your caller ID display. You must subscribe to Caller ID with Number, Name and ACR feature. Allows you the benefits of Caller ID with Name and Call Waiting. The Caller ID unit displays both the names and phone numbers of incoming Call Waiting calls when you are on the phone. A special tone signals you when there’s an incoming call while you’re on the phone. At the tone briefly press and release the telephone switch hook or “flash” button. This places the first call on hold while you answer the incoming call. To return to the first call (and to switch back and forth), press and release the switch hook or flash button again. To temporarily deactivate Call Waiting, press *70 and wait for a second dial tone before placing your call. Call Waiting will be automatically reactivated for new incoming calls when you hang up. This feature is not compatible with Call Waiting or Call Waiting Deluxe with Call Forward No Answer. Call Waiting Deluxe with Call Forward No Answer - Allows you to forward a waiting call to another number. You to control the treatment applied to incoming calls while you are on a call. This feature includes the functionality of forwarding unanswered incoming calls to another telephone number or voicemail. This feature is not compatible with Call Waiting or Call Waiting Deluxe. You must have Caller ID with Number, Name and ACR. Call Waiting Speaking – Gives you the name of the person calling. First, you hear the Call Waiting "beep" and then you hear the name of the caller. Once you've heard the name, you decide if you want to "click over" and take the call. Candela - The luminous intensity in a specified direction, of a monochromatic source which has a frequency 12 of 540 x 10 Hz and which has a radiant intensity, in the specified direction, of (1/683) watt per steradian. 92
- 93. Capacity - See channel capacity, traffic capacity. The maximum possible information transfer rate through a channel, subject to specified constraints. Card - A card (or expansion card, board, or adapter) is circuitry designed to provide expanded capability to a computer. It is provided on the surface of a standard-size rigid material (fiberboard or something similar) and then plugged into one of the computer's expansion slots in its motherboard (or backplane). Cards may come in one of two sizes designed to match standard slot dimensions. A card can actually contain the capability within its circuitry (as a video card does) or it can control (through an extended connection) a device (such as a hard disk drive). Carrier - In the telecommunications industry, a carrier is a telephone or other company that sells or rents telecommunication transmission services. A local exchange carrier (LEC) is a local phone company and an inter-exchange carrier (IEC or IXC) carries long-distance calls. Carrier and Data Tone - very loud screech that is produced when the FAX machines or MODEMs are actually transferring data. Unlike CNG or DTMF, carrier and data will be constantly changing. Carrier Power (of a radio transmitter) - 1. The average power supplied to the antenna transmission line by a transmitter during one radio frequency cycle taken under the condition of no modulation. Note: The concept does not apply to pulse modulation or frequency-shift keying. 2. The average unmodulated power supplied to a transmission line. Carrier Frequency - 1. The nominal frequency of a carrier wave. 2. In frequency modulation, synonym center frequency. 3. The frequency of the unmodulated electrical wave at the output of an amplitude modulated (AM), frequency modulated (FM), or phase modulated (PM) transmitter. 4. The output of a transmitter when the modulating wave is made zero. Carrier System - A multichannel telecommunications system in which a number of individual circuits (data, voice, or combination thereof) are multiplexed for transmission between nodes of a network. Note 1: In carrier systems, many different forms of multiplexing may be used, such as time-division multiplexing and frequency-division multiplexing. Note 2: Multiple layers of multiplexing may ultimately be performed upon a given input signal; i.e., the output resulting from one stage of modulation may in turn be modulated. Note 3: At a given node, specified channels, groups, supergroups, etc., may be demultiplexed without demultiplexing the others. Synonym [loosely] carrier. Carrier Wave - Synonym carrier (cxr). CATV - Abbreviation for cable TV. CCIR - Abbreviation for International Radio Consultative Committee, a predecessor organization of the ITU-R. CCITT - Abbreviation for International Telegraph and Telephone Consultative Committee; a predecessor organization of the ITU-T. CCS (centum call second) - also known as the hundred call second -- is a unit of telecommunications traffic density that is the equivalent of one call (including call attempts and holding time) in a specific channel for 100 seconds in an hour. The 100 seconds need not be, and generally are not, in a contiguous block. In digital telecommunications, the voice signals are compressed. This makes it possible for one channel to carry numerous calls simultaneously by means of multiplexing. In theory, there are many ways in which a 93
- 94. channel can carry a particular number of CCS. Here are three specific examples for a traffic density of 360 CCS: • 10 calls, each consuming the full hour during an hour • 20 calls, each of which consume 1/2 hour during an hour • 600 calls, each of which consume one minute during an hour The CCS is a more convenient unit in some applications than the erlang, which is the equivalent of one call occupying a channel for an hour. In some instances, a smaller unit than the CCS, known as the call-second, is used. One call-second is equivalent to one call occupying a channel for one second. Thus, 1 CCS = 100 call- seconds = 1/36 erlang. CDMA - Abbreviation for code-division multiple access. - A coding scheme, used as a modulation technique, in which multiple channels are independently coded for transmission over a single wideband channel. Note 1: In some communication systems, CDMA is used as an access method that permits carriers from different stations to use the same transmission equipment by using a wider bandwidth than the individual carriers. On reception, each carrier can be distinguished from the others by means of a specific modulation code, thereby allowing for the reception of signals that were originally overlapping in frequency and time. Thus, several transmissions can occur simultaneously within the same bandwidth, with the mutual interference reduced by the degree of orthogonality of the unique codes used in each transmission. Note 2: CDMA permits a more uniform distribution of energy in the emitted bandwidth. CD-ROM - Pronounced see-dee-rom. Short for Compact Disc-Read-Only Memory, a type of optical disk capable of storing large amounts of data -- up to 1GB, although the most common size is 650MB (megabytes). A single CD-ROM has the storage capacity of 700 floppy disks, enough memory to store about 300,000 text pages. CD-ROMs are stamped by the vendor, and once stamped, they cannot be erased and filled with new data. To read a CD, you need a CD-ROM player. All CD-ROMs conform to a standard size and format, so you can load any type of CD-ROM into any CD-ROM player. In addition, CD-ROM players are capable of playing audio CDs, which share the same technology. CD-ROMs are particularly well-suited to information that requires large storage capacity. This includes large software applications that support color, graphics, sound, and especially video. Cell - In wireless telephony, a cell is the geographical area covered by a cellular telephone transmitter. The transmitter facility itself is called the cell site. The cell provided by a cell site can be from one mile to twenty miles in diameter, depending on terrain and transmission power. Several coordinated cell sites are called a cell system. When you sign up with a cellular telephone service provider, you generally are given access to their cell system, which is essentially local. When travelling out of the range of this cell system, the cell system can enable you to be transferred to a neighboring company's cell system without your being aware of it. This is called roaming service. The cell sites in a system connect to a Mobile Telephone Switching Office (MTSO), which in turn connects to the standard landline telephone system. Cell Relay - A high-bandwidth, low-delay, switching and multiplexing packet technology. Its combination of simplified error and flow control, fixed-length cells which allow high-speed switching, and procedures for allocating network bandwidth enable it to support voice, data, image, and video traffic. 94
- 95. Cellular Phone - Synonym cellular mobile, cellular telephone. A mobile communications system that uses a combination of radio transmission and conventional telephone switching to permit telephone communication to and from mobile users within a specified area. Note: In cellular mobile systems, large geographical areas are segmented into many smaller areas, i.e., cells, each of which has its own radio transmitters and receivers and a single controller interconnected with the public switched telephone network. Cellular Mobile - A mobile communications system that uses a combination of radio transmission and conventional telephone switching to permit telephone communication to and from mobile users within a specified area. Note: In cellular mobile systems, large geographical areas are segmented into many smaller areas, i.e., cells, each of which has its own radio transmitters and receivers and a single controller interconnected with the public switched telephone network. Synonyms cellular phone, cellular radio, cellular telephone. Cellular Radio - Synonym cellular mobile, cellular phone, cellular telephone. A mobile communications system that uses a combination of radio transmission and conventional telephone switching to permit telephone communication to and from mobile users within a specified area. Note: In cellular mobile systems, large geographical areas are segmented into many smaller areas, i.e., cells, each of which has its own radio transmitters and receivers and a single controller interconnected with the public switched telephone network. Cellular Telephone - A type of short-wave analog or digital telecommunication in which a subscriber has a wireless connection from a mobile telephone to a relatively nearby transmitter. The transmitter's span of coverage is called a cell. Generally, cellular telephone service is available in urban areas and along major highways. As the cellular telephone user moves from one cell or area of coverage to another, the telephone is effectively passed on to the local cell transmitter. A cellular telephone is not to be confused with a cordless telephone (which is simply a phone with a very short wireless connection to a local phone outlet). A newer service similar to cellular is personal communications services (PCS). Center Frequency - 1. In frequency modulation, the rest frequency, i.e., the frequency of the unmodulated carrier. Synonym carrier frequency. 2. The frequency of the middle of the bandwidth of a channel. 3. In facsimile systems, the frequency midway between the picture-black and picture-white frequencies. Central Office (CO) - In telephone communication in the United States, a central office (CO) is an office in a locality to which subscriber home and business lines are connected on what is called a local loop. The central office has switching equipment that can switch calls locally or to long-distance carrier phone offices. CGI -1. Abbreviation for common gateway interface. A means for allowing programs or scripts (usually written in C++ or Perl) to add functionality to the World Wide Web. Note: Examples are search engines, feedback forms, and guestbooks. 2. Abbreviation for computer graphics interface. Changeover - The procedure of transferring signaling traffic from one signaling link to one or more different signaling links, when the link in use fails or is required to be cleared of traffic. Channel - 1. A connection between initiating and terminating nodes of a circuit. 2. A single path provided by a transmission medium via either (a) physical separation, such as by multipair cable or (b) electrical separation, such as by frequency- or time-division multiplexing. 3. A path for conveying electrical or electromagnetic signals, usually distinguished from other parallel paths. 4. Used in conjunction with a predetermined letter, number, or codeword to reference a specific radio frequency. 5. The portion of a storage medium, such as a track or a band, that is accessible to a given reading or writing station or head. 6. 95
- 96. In a communications system, the part that connects a data source to a data sink. 7. A virtual area where Internet Relay Chat (IRC) users communicate (exchanging text messages) in real time. Note: There are thousands of channels located on the Internet. 8. An IRC conduit designated for the real-time exchange of text messages. 9. An electrical path suitable for the transmission of communications between two or more points, ordinarily between two or more stations or between channel terminations in Telecommunication Company central offices. A channel may be furnished by wire, fiber optics, radio or a combination thereof. 10. The portion of the electromagnetic spectrum assigned by the FCC for one emission. In certain circumstances, however, more than one emission may be transmitted on a channel. Channel-Associated Signaling - Signaling in which the signals necessary to switch a given circuit are transmitted via the circuit itself or via a signaling channel permanently associated with it. Channel Bank - A device at a telephone company central office (public exchange) that converts analog signals from home and business users into digital signals to be carried over higher-speed lines between the central office and other exchanges. The analog signal is converted into a digital signal that transmits at a rate of 64 thousand bits per second (Kbps). This 64 Kbps signal is a standard known as a DS0 signal. The signal is multiplexed with other DS0 signals on the same line using time-division multiplexing (TDM) . Usually, the digital information is put on each DS0 signal using pulse code modulation (PCM). Channel Capacity - The maximum possible information transfer rate through a channel, subject to specified constraints. Channel Scan - Channel Scan will search for digital broadcast channels that are available in your area; once the scan is completed, you will be able to tune to the digital channels received by your antenna. Character - 1. A letter, digit, or other symbol that is used as part of the organization, control, or representation of data. 2. One of the units of an alphabet. Character Interval - In a communications system, the total number of unit intervals required to transmit any given character, including synchronizing, information, error checking, or control characters, but not including signals that are not associated with individual characters. Note: An example of a time interval that is excluded when determining character interval is any time added between the end of a stop signal and the beginning of the next start signal to accommodate changing transmission conditions, such as a change in data signaling rate or buffering requirements. This added time is defined as a part of the intercharacter interval. Chroma Keying - In television, nearly instantaneous switching between multiple video signals, based on the state, i.e., phase, of the color (chroma) signal of one, to form a single composite video signal. Note 1: Chroma keying is used to create an overlay effect in the final picture, e.g., to insert a false background, such as a weather map or scenic view, behind the principal subject being photographed. Note 2: The principal subject is photographed against a background having a single color or a relatively narrow range of colors, usually in the blue or green. When the phase of the chroma signal corresponds to the preprogrammed state or states associated with the background color, or range of colors, behind the principal subject, the signal from the alternate, i.e., false, background is inserted in the composite signal and presented at the output. When the phase of the chroma signal deviates from that associated with the background color(s) behind the principal subject, video associated with the principal subject is presented at the output. Synonyms color keying, [loosely] blue-screening, [in security] keying. Chromatic Dispersion - A commonly used (but redundant) synonym for material dispersion. See dispersion. 96
- 97. Cipher - 1. Any cryptographic system in which arbitrary symbols, or groups of symbols, represent units of plain text or in which units of plain text are rearranged, or both. 2. The result of using a cipher. Note: An example of a cipher is an enciphered message or text. Cipher Text - Enciphered information. Note: Cipher text is the result obtained from enciphering plain or encoded text. Circuit - 1. The complete path between two terminals over which one-way or two-way communications may be provided. 2. An electronic path between two or more points, capable of providing a number of channels. 3. A number of conductors connected together for the purpose of carrying an electrical current. 4. An electronic closed-loop path among two or more points used for signal transfer. 5. A number of electrical components, such as resistors, inductances, capacitors, transistors, and power sources connected together in one or more closed loops. 6. A fully operative communications path established in the normal circuit layout and currently used for message, WATS access, TWX, or private line services. Circuit-Switched - Communication system that establishes a dedicated channel for each transmission. The copper-wire telephone system (POTS) uses circuit-switching, as do PBX systems. Dedicated channels mean strong reliability and low latency, but the downside is that only one type of communication can use the channel at any given time. Cladding - 1. Of an optical fiber, one or more layers of material of lower refractive index, in intimate contact with a core material of higher refractive index. 2. A process of covering one metal with another (usually achieved by pressure rolling, extruding, drawing, or swaging) until a bond is achieved. Class of Emission - The set of characteristics of an emission, designated by standard symbols, e.g., type of modulation of the main carrier, modulating signal, type of information to be transmitted, and also, if appropriate, any additional signal characteristics. Click-Through - The process of clicking on a Web advertisement and going directly to the advertiser's Web site. Synonyms ad clicks, clicks, requests. Client - A program or computer that is used to contact and obtain data from another program or computer, referred to as the server. Client-Server - Any hardware / software combination that generally adheres to a client-server architecture, regardless of the type of application. Client-Server Architecture: Any network-based software system that uses client software to request a specific service, and corresponding server software to provide the service from another computer on the network. Clip - 1. In moving picture or television technology, a relatively short, continuous set of frames (often including the associated audio, if any), stored on a recording medium. Synonyms take, scene. 2. In audio, a short, uninterrupted sound track. Note: Both audio and video clips may be part of a digitized information package, e.g., on a Web page. 3. To limit to a predetermined level (e.g., at the output of an otherwise linear amplifier) the amplitude of an otherwise linear signal. Note: In contrast with an analog compression circuit, which reduces the dynamic range of a signal but retains its basic waveform, a clipping circuit treats (processes, amplifies) a signal in a linear fashion unless the output level reaches a certain threshold, which it may not exceed, and at which it remains unless the input decreases to a level at which the processed output level is lower than the clipping level. 97
- 98. Clipping - 1. In telephony, the loss of the initial or final parts of a word, words, or syllable, usually caused by the nonideal operation of voice-actuated devices. 2. The limiting of instantaneous signal amplitudes to a predetermined maximum value. 3. In a display device, the removal of those parts of display elements that lie outside of a given boundary. CLEC - Competitive Local Exchange Carrier. Deregulated local telephone companies resulting from the Telecommunications Act of 1996 that are competing for local exchange service, as well as for long distance and Internet service. In the United States, a CLEC (competitive local exchange carrier) is a telephone company that competes with the already established local telephone business by providing its own network and switching. The term distinguishes new or potential competitors from established local exchange carriers (LECs) and arises from the Telecommunications Act of 1996, which was intended to promote competition among both long-distance and local phone service providers. Clock - 1. A reference source of timing information. 2. A device providing signals used in a transmission system to control the timing of certain functions such as the duration of signal elements or the sampling rate. 3. A device that generates periodic, accurately spaced signals used for such purposes as timing, regulation of the operations of a processor, or generation of interrupts. Clock Normal Mode - An operating condition of a clock in which the output signals are controlled by an external input reference. It is the expected mode. In normal mode, each clock in a chain has the same long- term average frequency, and the time error between the input and output of each clock is bounded. Only stratum 1 sources of timing require no input and therefore have a unique status of "normal" operation being equivalent to "freerun". Synonym locked mode. Closed Captioning - Service allowing persons with hearing disabilities to read dialogue or the audio portion of a video, film, or other presentation, on the TV screen. Closed Circuit - 1. In radio and television transmission, pertaining to an arrangement in which programs are directly transmitted to specific users and not broadcast to the general public. 2. In telecommunications, a circuit dedicated to specific users. 3. A completed electrical circuit. CNG - See CNG Tone. C-Message Weighting - A noise spectral weighting used in a noise power measuring set to measure noise power on a line that is terminated by a 500-type set or similar instrument. Note: The instrument is calibrated in dBrnC. CNG Tone (AUTO FAX TONE) (CNG ) - This tone is produced by virtually all FAX machines when it dials the receiving FAX machine’s number from memory. Older FAX machines and some current models that do not have speed-dial memory will not produce CNG. CNG is a medium-pitch tone (1100 Hz) that last 1/2 second and repeats every 3-1/2 seconds. A FAX machine will produce CNG for about 45 seconds after it dials the receiving FAX number. An 1100Hz tone transmitted by a fax machine when it calls another fax machine. The half-second tone is repeated every 3.5 seconds for approximately 45 seconds. See fax switch. CO - Central Office. – Your telephone company. Your CO is the building where your telephone line is electronically managed. A telephone company’s building where subscribers’ lines are joined to the switching equipment to connect calls. Coast Station - A land station in the maritime mobile service. 98
- 99. Coating - See primary coating. - The plastic overcoat in intimate contact with the cladding of an optical fiber, applied during the manufacturing process. Note 1: The primary coating typically has an outside diameter of approximately 250 to 750 m, and serves to protect the fiber from mechanical damage and chemical attack. It also enhances optical fiber properties by stripping off cladding modes, and in the case where multiple fibers are used inside a single buffer tube, it suppresses cross-coupling of optical signals from one fiber to another. Note 2: The primary coating should not be confused with a tight buffer, or the plastic cladding of a plastic- clad-silica (PCS) fiber. Note 3: The primary coating, which typically consists of many layers, may be color- coded to distinguish fibers from one another, e.g., in a buffer tube containing multiple fibers. Synonyms primary polymer coating, primary polymer overcoat. Coaxial - Coaxial inputs (sometimes just called "cable") provide a simple and common way to transmit video. Now coaxial inputs are mostly used for connecting a TV set to an antenna or cable system. Coaxial Adapter - Device for connecting a coaxial cable to a TV with a Twin Lead cable connection port. Coaxial Cable (coax) - 1. A cable consisting of a center conductor surrounded by an insulating material and a concentric outer conductor and optional protective covering, all of circular cross-section. Synonym (when combined with others under a common sheath) coaxial tube. 2. A cable consisting of multiple coaxial tubes under a single protective sheath. Note: Coaxial cables are used primarily for CATV and other wideband, video, or rf applications. COBOL - Acronym for common business oriented language. A programming language designed for business data processing. Code - 1. A set of unambiguous rules specifying the manner in which data may be represented in a discrete form. Note 1: Codes may be used for brevity or security. Note 2: Use of a code provides a means of converting information into a form suitable for communications, processing, or encryption. 2. [In COMSEC, any] system of communication in which arbitrary groups of letters, numbers, or symbols represent units of plain text of varying length. Note: Codes may or may not provide security. Common uses include: (a) converting information into a form suitable for communications or encryption, (b) reducing the length of time required to transmit information, (c) describing the instructions which control the operation of a computer, and (d) converting plain text to meaningless combinations of letters or numbers and vice versa. 3. A cryptosystem in which the cryptographic equivalents, (usually called "code groups") typically consisting of letters or digits (or both) in otherwise meaningless combinations, are substituted for plain text elements which are primarily words, phrases, or sentences. 4. A set of rules that maps the elements of one set, the coded set, onto the elements of another set, the code element set. Synonym coding scheme. 5. A set of items, such as abbreviations, that represents corresponding members of another set. Synonym encode. 6. To represent data or a computer program in a symbolic form that can be accepted by a processor. 7. To write a routine. Codec - Term is short for "Coder-decoder." A codec is a device that converts analog video and audio signals into a digital format for transmission. It also converts received digital signals back into an analog format. Code-Division Multiple Access (CDMA) - A coding scheme, used as a modulation technique, in which multiple channels are independently coded for transmission over a single wideband channel. Note 1: In some communication systems, CDMA is used as an access method that permits carriers from different stations to use the same transmission equipment by using a wider bandwidth than the individual carriers. On reception, each carrier can be distinguished from the others by means of a specific modulation code, thereby allowing for the reception of signals that were originally overlapping in frequency and time. Thus, several transmissions can occur simultaneously within the same bandwidth, with the mutual interference reduced by the degree of orthogonality of the unique codes used in each transmission. Note 2: CDMA permits a more uniform distribution of energy in the emitted bandwidth. 99
- 100. Code Word - 1. In a code, a word that consists of a sequence of symbols assembled in accordance with the specific rules of the code and assigned a unique meaning. Note: Examples of code words are error-detecting- or-correcting code words and communication code words, such as SOS, MAYDAY, ROGER, TEN-FOUR, and OUT. 2. A cryptonym used to identify sensitive intelligence data. 3. A word that has been assigned a classification and a classified meaning to safeguard intentions and information regarding a classified plan or operation. Coding - 1. In communications systems, the altering of the characteristics of a signal to make the signal more suitable for an intended application, such as optimizing the signal for transmission, improving transmission quality and fidelity, modifying the signal spectrum, increasing the information content, providing error detection and/or correction, and providing data security. Note: A single coding scheme usually does not provide more than one or two specific capabilities. Different codes have different advantages and disadvantages. 2. In communications and computer systems, implementing rules that are used to map the elements of one set onto the elements of another set, usually on a one-to-one basis. 3. The digital encoding of an analog signal and, conversely, decoding to an analog signal. Coding Scheme - Synonym code. A set of rules that maps the elements of one set, the coded set, onto the elements of another set, the code element set Coherent - Pertaining to a fixed phase relationship between corresponding points on an electromagnetic wave. Note: A truly coherent wave would be perfectly coherent at all points in space. In practice, however, the region of high coherence may extend over only a finite distance. Collective Address - Synonym group address. In a communications network, a predefined address used to address only a specified set of users. Collocation - is moving or placing things together, sometimes implying a proper order. On the Internet, this term (often spelled "colocation" or "co-location") is used to mean the provision of space for a customer's telecommunications equipment on the service provider's premises. For example, a Web site owner could place the site's own computer servers on the premises of the Internet service provider (ISP). Or an ISP could place its network routers on the premises of the company offering switching services with other ISPs. The alternative to collocation is to have the equipment and the demarcation point located at the customer's premises. Collocation is sometimes provided by companies that specialize in Web site hosting. Color Burst - In analog color television technology, a signal consisting of several (8 to 10 in NTSC) cycles of unmodulated color subcarrier, superimposed at a specified location within the composite signal. Note: The color burst (a) enables the color-decoding circuits in the receiver, and (b) serves as an amplitude, frequency, and phase reference to which the local color (subcarrier frequency) oscillator in the receiver is phase-locked to ensure color fidelity and stability in the displayed picture. Color Coordinate Transformation - Computation of the tristimulus values of colors in terms of one set of primaries. Note: This computation may be performed electrically in a color television system. Color Keying - Synonym chroma keying. - In television, nearly instantaneous switching between multiple video signals, based on the state, i.e., phase, of the color (chroma) signal of one, to form a single composite video signal. Note 1: Chroma keying is used to create an overlay effect in the final picture, e.g., to insert a false background, such as a weather map or scenic view, behind the principal subject being photographed. Note 2: The principal subject is photographed against a background having a single color or a relatively narrow range of colors, usually in the blue or green. When the phase of the chroma signal corresponds to the preprogrammed state or states associated with the background color, or range of colors, behind the 100
- 101. principal subject, the signal from the alternate, i.e., false, background is inserted in the composite signal and presented at the output. When the phase of the chroma signal deviates from that associated with the background color(s) behind the principal subject, video associated with the principal subject is presented at the output. Color Subcarrier - In analog color television technology, a signal superimposed upon the picture (gray scale) information for the purpose of conveying the associated color information. Note: The color information is conveyed by the instantaneous phase of the color subcarrier with respect to that of the color burst. .com - 1. A top-level domain name-suffix originally intended to designate commercial entities such as corporations and companies. 2. A filename suffix indicating an executable file. Note: Usually, ".com" programs are smaller and simpler than programs with the ".exe" suffix. Combinational Logic Element - A device having at least one output channel and one or more input channels, all characterized by discrete states, such that at any instant the state of each output channel is completely determined by the states of the input channels at the same instant. Command - 1. An order for an action to take place. 2. In data transmission, an instruction sent by the primary station instructing a secondary station to perform some specific function. 3. In signaling systems, a control signal. 4. In computer programming, that part of a computer instruction word that specifies the operation to be performed. 5. Loosely, a mathematical or logic operator. Command and Control (C2): The exercise of authority and direction by a properly designated commander over assigned forces in the accomplishment of the mission. Command and control functions are performed through an arrangement of personnel, equipment, communications, facilities, and procedures employed by a commander in planning, coordinating, and controlling forces and operations in the accomplishment of the mission. Command, Control and Communications (C3) - The capabilities required by commanders to exercise command and control of their forces. Common Carrier - In a telecommunications context, a telecommunications company that holds itself out to the public for hire to provide communications transmission services. Note: In the United States, such companies are usually subject to regulation by Federal and state regulatory commissions. Synonyms carrier, commercial carrier, communications common carrier, [and, loosely] interexchange carrier. Common-Channel Signaling - 1. In a multichannel communications system, signaling in which one channel in each link is used for signaling to control, account for, and manage traffic on all channels of the link. Note: The channel used for common-channel signaling does not carry user information. 2. A signaling method in which a single channel conveys, by means of labeled messages, signaling information relating to a multiplicity of circuits or calls and other information, such as that used for network management. Common Control - An automatic switching arrangement in which the control equipment necessary for the establishment of connections is shared by being associated with a given call only during the period required to accomplish the control function for the given call. Note: In common control, the channels that are used for signaling, whether frequency bands or time slots, are not used for message traffic. Common Gateway Interface - See CGI. A means for allowing programs or scripts (usually written in C++ or Perl) to add functionality to the World Wide Web. Note: Examples are search engines, feedback forms, and guestbooks. 101
- 102. Common User Network - A system of circuits or channels allocated to furnish communication paths between switching centers to provide communication service on a common basis to all connected stations or subscribers. It is sometimes described as a general purpose network. Communications - 1. Information transfer, among users or processes, according to agreed conventions. 2. The branch of technology concerned with the representation, transfer, interpretation, and processing of data among persons, places, and machines. Note: The meaning assigned to the data must be preserved during these operations. Communications Center - 1. An agency charged with the responsibility for handling and controlling communications traffic. The center normally includes message center, transmitting, and receiving facilities. 2. A facility that (a) serves as a node for a communications network, (b) is equipped for technical control and maintenance of the circuits originating, transiting, or terminating at the node, (c) may contain message- center facilities, and (d) may serve as a gateway. Synonyms comm center, message center. Communications Channel - See channel. - 1. A connection between initiating and terminating nodes of a circuit. 2. A single path provided by a transmission medium via either (a) physical separation, such as by multipair cable or (b) electrical separation, such as by frequency- or time-division multiplexing. 3. A path for conveying electrical or electromagnetic signals, usually distinguished from other parallel paths. 4. Used in conjunction with a predetermined letter, number, or codeword to reference a specific radio frequency. 5. The portion of a storage medium, such as a track or a band, that is accessible to a given reading or writing station or head. 6. In a communications system, the part that connects a data source to a data sink. 7. A virtual area where Internet Relay Chat (IRC) users communicate (exchanging text messages) in real time. Note: There are thousands of channels located on the Internet. 8. An IRC conduit designated for the real- time exchange of text messages. 9. An electrical path suitable for the transmission of communications between two or more points, ordinarily between two or more stations or between channel terminations in Telecommunication Company central offices. A channel may be furnished by wire, fiber optics, radio or a combination thereof. 10. The portion of the electromagnetic spectrum assigned by the FCC for one emission. In certain circumstances, however, more than one emission may be transmitted on a channel. Communications Common Carrier - 1. The term "communications common carrier" as used in this part means any person (individual, partnership, association, joint-stock company, trust, corporation, or other entity) engaged as a common carrier for hire, in interstate or foreign communication by wire or radio or in interstate or foreign radio transmission of energy, including such carriers as are described in subsection 2(b) (2) and (3) of the Communications Act of 1934, as amended, and, in addition, for purposes of subpart H of this part, includes any individual, partnership, association, joint-stock company, trust, corporation, or other entity which owns or controls, directly or indirectly, or is under direct or indirect common control with, any such carrier. 2. Any person engaged in rendering communication service for hire to the public. Synonym common carrier. Communications Intelligence (COMINT) - Technical and intelligence information derived from foreign communications by other than the intended recipients. Communications Net - An organization of stations capable of direct communication on a common channel or frequency. Synonym net. Communications Network - An organization of stations capable of intercommunications, but not necessarily on the same channel. Communications Security (COMSEC) - Measures and controls taken to deny unauthorized persons information derived from telecommunications and to ensure the authenticity of such telecommunications. 102
- 103. Note: Communications security includes cryptosecurity, transmission security, emission security, and physical security of COMSEC material. [INFOSEC] • (a) cryptosecurity: [The] component of communications security that results from the provision of technically sound cryptosystems and their proper use. [NIS] • (b) emission security: Protection resulting from all measures taken to deny unauthorized persons information of value which might be derived from intercept and analysis of compromising emanations from crypto-equipment, AIS, and telecommunications systems. [NIS] • (c) physical security: The component of communications security that results from all physical measures necessary to safeguard classified equipment, material, and documents from access thereto or observation thereof by unauthorized persons. [JP 1-02] • (d) transmission security: [The] component of communications security that results from the application of measures designed to protect transmissions from interception and exploitation by means other than cryptanalysis. Communications System - A collection of individual communications networks, transmission systems, relay stations, tributary stations, and data terminal equipment (DTE) usually capable of interconnection and interoperation to form an integrated whole. Note: The components of a communications system serve a common purpose, are technically compatible, use common procedures, respond to controls, and operate in unison. Compact - See data compaction. Compact Disc - Known by its abbreviation, CD, a compact disc is a polycarbonate with one or more metal layers capable of storing digital information. The most prevalent types of compact discs are those used by the music industry to store digital recordings and CD-ROMs used to store computer data. Both of these types of compact disc are read-only, which means that once the data has been recorded onto them, they can only be read, or played. Competitive Local Exchange Carrier - A telephone company that competes with the larger incumbent carriers (ILECs) through reselling the ILEC services and/or creating services that use the ILEC's infrastructure. The Regional Bells are ILECs; local phone companies are frequently CLECs. Compile - 1. To translate a computer program expressed in a high-level language into a program expressed in a lower level language, such as an intermediate language, assembly language, or a machine language. 2. To prepare a machine language program from a computer program written in another programming language by making use of the overall logic structure of the program or by generating more than one computer instruction for each symbolic statement as well as performing the function of an assembler. Component - 1. An assembly, or part thereof, that is essential to the operation of some larger assembly and is an immediate subdivision of the assembly to which it belongs. Note: For example, a radio receiver may be a component of a complete radio set consisting of a combined transmitter-receiver, i.e., a transceiver. The same radio receiver could also be a subsystem of the combined transmitter-receiver, in which case the IF amplifier section would be a component of the receiver but not of the radio set. Similarly, within the IF amplifier section, items, such as resistors, capacitors, vacuum tubes, and transistors, are components of that section. 2. In logistics, a part, or combination of parts having a specified function, that can only be installed or replaced as an entity. 3. In material, an assembly or any combination of parts, subassemblies, and assemblies mounted together in manufacture, assembly, maintenance, or rebuild. Component Video - Also known as "Y Pb Pr," this connector splits the video signal into three parts. With two audio connections, this five-wire solution is the most common way to connect an EDTV to DVD player and most HDTV monitors to their receivers or other set-top boxes. 103
- 104. Composite Color - The structure of a video signal wherein the luminance and two bandlimited color- difference signals are simultaneously present in the channel. Note: The format may be achieved by frequency-division multiplexing, quadrature modulation, etc. It is common to strive for integrity by suitable separation of the frequencies, or since scanned video signals are highly periodic, by choosing frequencies such that the chrominance information is interleaved within spectral regions of the luminance signal wherein a minimum of luminance information resides. Composite Video - 1. See composite video signal. - The electrical signal that represents complete color picture information and all synchronization signals, including blanking and the deflection synchronization signals to which the color synchronization signal is added in the appropriate time relationship. 2. Also called "RCA" connectors, it is the most common way to connect peripherals and other components. It consists of one yellow connector for video and two audio connectors for "right" and "left." Composite connectors cannot transmit high-definition pictures. This means that, for HDTV, another connector option — such as HDMI or Component Video — must be employed. Composite Video Signal - The electrical signal that represents complete color picture information and all synchronization signals, including blanking and the deflection synchronization signals to which the color synchronization signal is added in the appropriate time relationship. Synonym composite video. Compression - 1. See data compression, signal compression. VoIP uses various compression ratios, the highest approximately 12:1. Compression varies according to available bandwidth. 2. Term that refers to the reduction of the size of digital data files by removing redundant and/or non-critical information ("data" being the elements of video, audio and other "information"). DTV in the U.S. would not be possible without compression. Compromise - 1. The known or suspected exposure of clandestine personnel, installations, or other assets or of classified information or material, to an unauthorized person. 2. The disclosure of cryptographic information to unauthorized persons. 3. The recovery of plain text of encrypted messages by unauthorized persons through cryptanalysis methods. 4. Disclosure of information to unauthorized persons or a violation of the security policy of a system in which unauthorized intentional or unintentional disclosure, modification, destruction, or loss of an object may have occurred. Compromising Emanations - Unintentional signals that, if intercepted and analyzed, would disclose the information transmitted, received, handled, or otherwise processed by information systems equipment. Computer - 1. A device that accepts data, processes the data in accordance with a stored program, generates results, and usually consists of input, output, storage, arithmetic, logic, and control units. 2. A functional unit that can perform substantial computation, including numerous arithmetic operations or logic operations, without human intervention during a run. Note 1: This definition, approved by the Customs Council, distinguishes a computer from similar devices, such as hand-held calculators and certain types of control devices. Note 2: Computers have been loosely classified into microcomputers, minicomputers, and main- frame computers, based on their size. These distinctions are rapidly disappearing as the capabilities of even the smaller units have increased. Microcomputers now are usually more powerful and versatile than the minicomputers and the main-frame computers were a few years ago. Computer Conferencing - 1. Teleconferencing supported by one or more computers. 2. An arrangement in which access, by multiple users, to a common database is mediated by a controlling computer. 3. The interconnection of two or more computers working in a distributed manner on a common application process. 104
- 105. Computer Graphics - 1. Graphics implemented through the use of computers. 2. Methods and techniques for converting data to or from graphic displays via computers. 3. The branch of science and technology concerned with methods and techniques for converting data to or from visual presentation using computers. Computer Input - This term refers to an input feature on some HDTV sets (like SVGA or VGA) that allows TV sets to be connected to computers. Computer Network - 1. A network of data processing nodes that are interconnected for the purpose of data communication. 2. A communications network in which the end instruments are computers. Computer-Oriented Language - A programming language in which words and syntax are designed for use on a specific computer or class of computers. Synonyms low-level language, machine-oriented language. Computer Program - See program. - 1. A plan or routine for solving a problem on a computer. Note: Processing may include the use of an assembler, a compiler, an interpreter, or a translator to prepare the program for execution, as well as the execution of the program. The sequence of instructions may include statements and necessary declarations. 2. A sequence of instructions used by a computer to do a particular job or solve a given problem. 3. To design, write, and test programs. Computer Security (COMPUSEC) - 1. Measures and controls that ensure confidentiality, integrity, and availability of information-system (IS) assets including hardware, software, firmware, and information being processed, stored, and communicated. Synonym automated information systems security. 2. The application of hardware, firmware and software security features to a computer system in order to protect against, or prevent, the unauthorized disclosure, manipulation, deletion of information or denial of service. 3. The protection resulting from all measures to deny unauthorized access and exploitation of friendly computer systems. Computer Science - The study of computers, including both hardware and software design. Computer science is composed of many broad disciplines, including artificial intelligence and software engineering. Most universities now offer bachelor, master, and doctorate degrees in computer science. Computer Word - In computing, a group of bits or characters that occupies one or more storage locations and is treated by computers as a unit. Synonym machine word. Compression - The reduction in size of data in order to save space or transmission time. For data transmission, compression can be performed on just the data content or on the entire transmission unit (including header data) depending on a number of factors. Content compression can be as simple as removing all extra space characters, inserting a single repeat character to indicate a string of repeated characters, and substituting smaller bit strings for frequently occurring characters. This kind of compression can reduce a text file to 50% of its original size. Compression is performed by a program that uses a formula or algorithm to determine how to compress or decompress data. Graphic image file formats are usually designed to compress information as much as possible (since these can tend to become very large files). Graphic image compression can be either lossy (some information is permanently lost) or lossless (all information can be restored). When you send or receive information on the Internet, larger text files, either singly or with others as part of an archive file, may be transmitted in a zip, gzip, or other compressed format. WinZip is a popular Windows program that compresses files when it packages them in an archive. 105
- 106. COMSEC - Acronym for communications security. COMSEC material: [An] item designed to secure or authenticate telecommunications. Note: COMSEC material includes, but is not limited to, key, equipment, devices, documents, firmware or software that embodies or describes cryptographic logic and other items that perform COMSEC functions. Conference Controller - In audio and video teleconferences, the user in charge of the conference when the service is invoked and the conference reaches the active state. Note: The conference controller may perform any or all of the following actions: drop, floating, isolate, reattach, and split. Configuration Management - 1. [The] management of security features and assurances through control of changes made to hardware, software, firmware, documentation, test, test fixtures, and test documentation throughout the life cycle of an information system (IS). 2. The control of changes--including the recording thereof--that are made to the hardware, software, firmware, and documentation throughout the system life cycle. Congestion - 1. In a communications switch, a state or condition that occurs when more subscribers attempt simultaneously to access the switch than it is able to handle, even if unsaturated. 2. In a saturated communications system, the condition that occurs when an additional demand for service occurs. Connection - In telecommunication and computing in general, a connection is the successful completion of necessary arrangements so that two or more parties (for example, people or programs) can communicate at a long distance. In this usage, the term has a strong physical (hardware) connotation although logical (software) elements are usually involved as well. A dialup (sometimes called a switched) connection is a telephonic arrangement that is set up only when needed, using shared, circuit-switched communication lines (as in "plain old telephone service"). A dedicated (sometimes called a nonswitched) connection is a continuous, always available connection (familiar to users of Digital Subscriber Line or DSL service). A leased line is a line rented from a telephone company that provides dedicated connection between two points (such as a headquarters office and a manufacturing plant). Connection - 1. A provision for a signal to propagate from one point to another, such as from one circuit, line, subassembly, or component to another. 2. An association established between functional units for conveying information. 3. A temporary concatenation of transmission channels or telecommunication circuits, switching and other functional units set up to provide a route for a transfer of information between two or more points in a telecommunication network. Connectionless Data Transfer - See connectionless mode transmission. Connectionless Mode Transmission - 1. In a packet-switched network, transmission in which each packet is encoded with a header containing a destination address sufficient to permit the independent delivery of the packet without the aid of additional instructions. Note 1: A packet transmitted in a connectionless mode is frequently called a datagram. Note 2: In connectionless mode transmission of a packet, the service provider usually cannot guarantee there will be no loss, error insertion, misdelivery, duplication, or out-of-sequence delivery of the packet. However, the risk of these hazards' occurring may be reduced by providing a reliable transmission service at a higher protocol layer, such as the Transport Layer of the Open Systems Interconnection--Reference Model. 2. The transmission of a unit of data in a single self-contained operation without establishing, maintaining, and releasing a connection. Connectivity - The technical communications link between a computer system and the Internet. 106
- 107. Connector - A device for mating and demating electrical power connections or communications media. Note: A connector is distinguished from a splice, which is a permanent joint. Connect Signal - An off-hook condition applied to the network interface (NI) by the network that indicated the network intends to complete a call attempt to the customer installation (CI) or intends to continue an established connection . Contamination - The introduction of data of one security [classification or] security category into data of a lower security classification or different security category. Content Hosting (hosting) - Storage and management of databases by a content provider. Content Provider - An organization that creates and maintains databases containing information from an information provider. Note: The content provider and the information provider may be the same organization. Control Character - A character that initiates, modifies, or stops a function, event, operation, or control operation. Note: Control characters may be recorded for use in subsequent actions. They are not graphic characters but may have a graphic representation in some circumstances. Control Function - Synonym control operation. - An operation that affects the recording, processing, transmission, or interpretation of data. Note: Examples of control operations include starting and stopping a process; executing a carriage return, a font change, or a rewind; and transmitting an end-of-transmission (EOT) control character. Control Operation - An operation that affects the recording, processing, transmission, or interpretation of data. Note: Examples of control operations include starting and stopping a process; executing a carriage return, a font change, or a rewind; and transmitting an end-of-transmission (EOT) control character. Synonym control function. Controller - In an automated radio, the device that commands the radio transmitter and receiver, and that performs processes, such as automatic link establishment, channel scanning and selection, link quality analysis, polling, sounding, message store and forward, address protection, and anti-spoofing. Converter Box - Also referred to as a “digital-to-analog converter box,” this is a stand-alone device that receives, decodes, and converts over-the-air digital programming into analog. When connected to an analog television, it permits digital programming to be displayed in analog. Cookie -1. A small piece of information that is automatically stored on a client computer by a Web browser and referenced to identify repeat visitors to a Web site and to tailor information in anticipation of the visitor's interests. Note: Some privacy advocates have objected to the use of cookies without a user's consent. 2. A general mechanism that server side connections (such as CGI scripts) can use both to store and to retrieve information on the client side of the connection. Note 1: A server, when returning an HTTP object to a client, may also send a piece of state information that the client will store. Included in that state object is a description of the range of URLs for which that state is valid. Any future HTTP requests made by the client that fall in that range will include a transmittal of the current value of the state object from the client back to the server. The state object is called a cookie. This simple mechanism provides a tool that enables new types of applications to be written for Web-based environments. Shopping applications can now store information about the currently selected items, for-fee services can send back registration information and free the client from retyping a user ID on subsequent connections, sites can store per-user preferences on the client, and have the client supply those preferences every time that site is accessed. Note 2: Session cookies are volatile 107
- 108. in that they disappear at the end of a session, whereas persistent cookies are retained from one session to the next. Synonym magic cookie. Coordinated Universal Time (UTC) - Time scale based on the second (SI), as defined and recommended by the CCIR, and maintained by the Bureau International des Poids et Mesures (BIPM). For most practical purposes associated with the Radio Regulations, UTC is equivalent to mean solar time at the prime meridian (0° longitude), formerly expressed in GMT. Note 1: The maintenance by BIPM includes coordinating inputs from time standards belonging to various national laboratories around the world, which inputs are averaged to create the international time standard (second). Note 2: The full definition of UTC is contained in CCIR Recommendation 460-4. Note 3: The second was formerly defined in terms of astronomical phenomena. When this practice was abandoned in order to take advantage of atomic resonance phenomena (" atomic time ") to define the second more precisely, it became necessary to make occasional adjustments in the "atomic" time scale to coordinate it with the workaday mean solar time scale, UT-1, which is based on the somewhat irregular rotation of the Earth. Rotational irregularities usually result in a net decrease in the Earth's average rotational velocity, and ensuing lags of UT-1 with respect to UTC. Note 4: Adjustments to the atomic, i.e., UTC, time scale consist of an occasional addition or deletion of one full second, which is called a leap second. Twice yearly, during the last minute of the day of June 30 and December 31, Universal Time, adjustments may be made to ensure that the accumulated difference between UTC and UT-1 will not exceed 0.9 s before the next scheduled adjustment. Historically, adjustments, when necessary, have usually consisted of adding an extra second to the UTC time scale in order to allow the rotation of the Earth to "catch up." Therefore, the last minute of the UTC time scale, on the day when an adjustment is made, will have 61 seconds. Synonyms World Time, Z Time, Zulu Time. Copy - 1. To receive a message. 2. A recorded message or a duplicate of it. 3. To read data from a source, leaving the source data unchanged at the source, and to write the same data elsewhere, though they may be in a physical form that differs from that of the source. 4. To understand a transmitted message. Core - 1. The central region about the longitudinal axis of an optical fiber, which region supports guiding of the optical signal. Note 1: For the fiber to guide the optical signal, the refractive index of the core must be slightly higher than that of the cladding. Note 2: In different types of fibers, the core and core-cladding boundary function slightly differently in guiding the signal. Especially in single-mode fibers, a significant fraction of the energy in the bound mode travels in the cladding. 2. A piece of ferromagnetic material, usually toroidal in shape, used as a component in a computer memory device. Note: The type of memory referred to has very limited application in today's computer environment. It has been largely replaced by semiconductor and other technologies. 3. The material at the center of an electromechanical relay or solenoid, about which the coil is wound. Core Diameter - In the cross section of a realizable optical fiber, ideally circular, but assumed to a first approximation to be elliptical, the average of the diameters of the smallest circle that can be circumscribed about the core-cladding boundary, and the largest circle that can be inscribed within the core-cladding boundary. Corrective Maintenance - 1. Maintenance actions carried out to restore a defective item to a specified condition. 2. Tests, measurements, and adjustments made to remove or correct a fault. Corresponding Entities - Peer entities with a lower layer connection among them. Cosmic Noise - Random noise that originates outside the Earth's atmosphere. Note: Cosmic noise characteristics are similar to those of thermal noise. Cosmic noise is experienced at frequencies above about 15 MHz when highly directional antennas are pointed toward the Sun or to certain other regions of the sky such as the center of the Milky Way Galaxy. Synonym galactic radio noise. 108
- 109. Contention - 1. A condition that arises when two or more data stations attempt to transmit at the same time over a shared channel, or when two data stations attempt to transmit at the same time in two-way alternate communication. Note: A contention can occur in data communications when no station is designated a master station. In contention, each station must monitor the signals and wait for a quiescent condition before initiating a bid for master status. 2. Competition by users of a system for use of the same facility at the same time. Synonym access contention. Coupling - The desirable or undesirable transfer of energy from one medium, such as a metallic wire or an optical fiber, to another like medium, including fortuitous transfer. Note: Examples of coupling include capacitive (electrostatic) coupling, inductive (magnetic) coupling, conducted (resistive or hard-wire) coupling, and fiber-optic coupling. Coupling Loss - 1. The loss that occurs when energy is transferred from one circuit, circuit element, or medium to another. Note: Coupling loss is usually expressed in the same units--such as watts or dB--as in the originating circuit element or medium. 2. In fiber optics, the power loss that occurs when coupling light from one optical device or medium to another. CPE - (see Customer Premises Equipment) CPNI (Customer Proprietary Network Information)- Information that telecommunications services such as local, long distance, and wireless telephone companies acquire about their subscribers. It includes not only what services they use but their amount and type of usage. The Telecommunications Act of 1996 together with clarifications from the Federal Communications Commission (FCC) generally prohibits the use of that information without customer permission, even for the purpose of marketing the customers other services . In the case of customers who switch to other service providers, the original service provider is prohibited from using the information to try to get the customer back. CPNI includes such information as optional services subscribed to, current charges, directory assistance charges, usage data, and calling patterns. The CPNI rules do not prohibit the gathering and publishing of aggregate customer information nor the use of customer information for the purpose of creating directories. Cramming – An illegal practice in which customers are billed for additional telephone features they didn't’t order. Crawler - Synonyms droid, Web crawler, Web spider. Critical Frequency - 1. In radio propagation by way of the ionosphere, the limiting frequency at or below which a wave component is reflected by, and above which it penetrates through, an ionospheric layer. 2. At vertical incidence, the limiting frequency at or below which incidence, the wave component is reflected by, and above which it penetrates through, an ionospheric layer. Note: The existence of the critical frequency is the result of electron limitation, i.e., the inadequacy of the existing number of free electrons to support reflection at higher frequencies. Cropping - When viewing widescreen format on an analog TV, the picture is cropped — i.e., black bars appear above, below, and on either side of the picture. This is done to maintain the original aspect ratio of the original picture source. Cross-Connect: Synonym cross-connection. 109
- 110. Cross-Connection: Connections between terminal blocks on the two sides of a distribution frame, or between terminals on a terminal block. Note: Connections between terminals on the same block are also called straps. Synonyms cross-connect, jumper. Cross Coupling - The coupling of a signal from one channel, circuit, or conductor to another, where it is usually considered to be an undesired signal. Crosstalk (XT) - 1. Undesired coupling of a signal from one circuit, part of a circuit, or channel, to another. 2. Any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel. Note 1: In telephony, crosstalk is usually distinguishable as speech or signaling tones. Note 2: In video, "ghost" images from one source appear in addition to the signals of interest transmitted from another. CRT- Cathode Ray Tube. Display screens used in TV sets and computer monitors that use a Cathode Ray Tube, which is also called a "picture tube." Cathode Ray Tubes were found in all electronic television sets up until the invention of the less bulky LCD screens. Cryptanalysis - 1. Operations performed in converting encrypted messages to plain text without initial knowledge of the crypto-algorithm and/or key employed in the encryption. 2. The study of encrypted texts. CRYPTO - The marking or designator identifying COMSEC keying material used to secure or authenticate telecommunications carrying classified or sensitive U.S. Government or U.S. Government-derived information. Note: When written in all upper case letters, CRYPTO has the meaning stated above. When written in lower case as a prefix, crypto and crypt are abbreviations for cryptographic. Crypto-Algorithm - [A] well-defined procedure or sequence of rules or steps, or a series of mathematical equations used to describe cryptographic processes such as encryption/decryption, key generation, authentication, signatures, etc. Crypto-Equipment - See cryptographic equipment. - Any device that embodies cryptographic logic or performs one or more cryptographic functions (e.g., key generation, encryption, and authentication). Cryptology - 1. The science that deals with hidden, disguised, or encrypted communications. It includes communications security and communications intelligence. 2. [The] field encompassing both cryptography and cryptanalysis. Cryptographic - Pertaining to, or concerned with, cryptography. Cryptographic Equipment (crypto-equipment) - Any device that embodies cryptographic logic or performs one or more cryptographic functions (e.g., key generation, encryption, and authentication). Cryptographic Logic - The embodiment of one (or more) crypto-algorithm (s) along with alarms, checks, and other processes essential to effective and secure performance of the cryptographic process(es). Cryptography - 1. [The] art or science concerning the principles, means, and methods for rendering plain information unintelligible, and for restoring encrypted information to intelligible form. 2. The branch of cryptology that treats of the principles, means, and methods of designing and using cryptosystems. Cryptosecurity - See communications security. [The] component of communications security that results from the provision of technically sound cryptosystems and their proper use. 110
- 111. CSSR – Customer Sales and Service Representative. These TDS Telecom employees work in the sales and service offices of our local operating companies. They answer customer questions, market services, and handle payments. CST – Customer Service Technician. These TDS Telecom employees work in our local operating companies and provide installation and repair service for our customers. CTI ( computer-telephony integration, or sometimes simply "computer telephony") - is the use of computers to manage telephone calls. The term is used in describing the computerized services of call centers, such as those that direct your phone call to the right department at a business you're calling. It's also sometimes used to describe the ability to use your personal computer to initiate and manage phone calls (in which case you can think of your computer as your personal call center). CTI applications provide the ability to do one or more of the following: • Authenticate callers. Using one of several standard methods, the telephone number of the caller can be screened against a database. • Recognize a voice, either for authentication or for message forwarding • Using live, recorded voice, or touch-tone entered input, determine how to process a call (for example, by forwarding it to the appropriate person or department) • Provide interactive voice response (IVR) to callers • Match the number of a caller with a customer record and display it for reference when talking to the caller • Manage voice or video conferences • Collect and display pending live calls or messages that have been left by callers • Receive fax messages and route them to appropriate fax machines • For outbound calling such as telemarketing, predial callers • Based on call input, initiate a smart agent application to provide help with the caller's request The Advanced Intelligent Network (AIN) is a telephone service architecture that separates CTI services from call switching and will make it easier to add new services. The Windows Telephony Application Program Interface (TAPI) and Novell's TSAPI are programming interfaces intended to make it easier to create applications that enable telephone services on a personal computer or in a local area network. Current - A flow of electrical charge carriers, usually electrons or electron-deficient atoms. The common symbol for current is the uppercase letter I. The standard unit is the ampere, symbolized by A. One ampere 18 of current represents one coulomb of electrical charge (6.24 x 10 charge carriers) moving past a specific point in one second. Physicists consider current to flow from relatively positive points to relatively negative points; this is called conventional current or Franklin current. Electrons, the most common charge carriers, are negatively charged. They flow from relatively negative points to relatively positive points. Electric current can be either direct or alternating. Direct current (DC) flows in the same direction at all points in time, although the instantaneous magnitude of the current might vary. In an alternating current (AC), the flow of charge carriers reverses direction periodically. The number of complete AC cycles per second is the frequency, which is measured in hertz. An example of pure DC is the current produced by an electrochemical cell. The output of a power-supply rectifier, prior to filtering, is an example of pulsating DC. The output of common utility outlets is AC. Current per unit cross-sectional area is known as current density. It is expressed in amperes per square meter, amperes per square centimeter, or amperes per square millimeter. Current density can also be expressed in amperes per circular mil. In general, the greater the current in a conductor, the higher the 111
- 112. current density. However, in some situations, current density varies in different parts of an electrical conductor. A classic example is the so-called skin effect, in which current density is high near the outer surface of a conductor, and low near the center. This effect occurs with alternating currents at high frequencies. Another example is the current inside an active electronic component such as a field-effect transistor (FET). An electric current always produces a magnetic field. The stronger the current, the more intense the magnetic field. A pulsating DC, or an AC, characteristically produces an electromagnetic field. This is the principle by which wireless signal propagation occurs. Curvature Loss - In an optical fiber, that loss attributable to macrobending. - Synonym macrobend loss. Customer Controlled Call Forwarding Busy - Allows you the capability to activate and deactivate call forwarding busy from your home telephone number using dial codes. Forwards calls to the number you have pre-selected. To activate, press 82#. To deactivate, press 83#. Customer Controlled Call Forwarding No Answer - Allows you the capability to automatically forward unanswered incoming calls to another telephone number after a pre-selected number (2-7) of rings. Forwards calls to the number you have pre-selected. Activate this feature by pressing 77#. To deactivate, press 78#. Customer Installation (CI) - All telecommunication equipment and wiring on the customer side of the network interface. Customer Premises Equipment (CPE) - Telephone or other service provider equipment that is located on the customer's premises (physical location) rather than on the provider's premises or in between. Telephone handsets, cable TV set-top boxes, and Digital Subscriber Line routers are examples. Historically, this term referred to equipment placed at the customer's end of the telephone line and usually owned by the telephone company. Today, almost any end-user equipment can be called customer premise equipment and it can be owned by the customer or by the provider. Custom Ring Service 1 - Allows you to receive calls dialed to two different telephone numbers without having a second access line. Distinctive ringing will be provided for the second telephone number to facilitate identification of incoming calls. One directory listing is provided for each Custom Ring number. Custom Ring Service 2 - Allows you to receive calls dialed to three separate telephone numbers without having a second or third access line. Distinctive ringing will be provided for each of the additional telephone numbers to facilitate identification of incoming calls. One directory listing is provided for each Custom Ring number. You must have Custom Ring Service 1 to have Custom Ring Service 2. Cutoff Wavelength - 1. The wavelength corresponding to the cutoff frequency. 2. In an uncabled single- mode optical fiber, the wavelength greater than which a particular waveguide mode ceases to be a bound mode. Note 1: The cutoff wavelength is usually taken to be the wavelength at which the normalized frequency is equal to 2.405. Note 2: The cabled cutoff wavelength is usually considered to be a more functional parameter because it takes into consideration the effects of cabling the fiber. CXR ( cxr) - Abbreviation for carrier. Cybermall - An electronic site shared by a number of commercial interests, and at which users can browse, shop, and place orders for the products listed at that site. [Bahorsky] Synonym Internet mall. 112
- 113. Cyberspace - The impression of space and community formed by computers, computer networks, and their users; the virtual "world" that Internet users inhabit when they are online. D - Telecom Dictionary for the Letter D D-channel - In the Integrated Services Digital Network (ISDN), the D-channel is the channel that carries control and signalling information. (The "D" stands for "delta" channel.) The B-channel ("B" for "bearer") carries the main data. In ISDN, there are two levels of service: the Basic Rate Interface, intended for the home and small enterprise, and the Primary Rate Interface, for larger users. Both rates include a number of B- (bearer) channels and a D- (delta) channel. The B-channels carry data, voice, and other services. The D-channel carries control and signaling information. The Basic Rate Interface consists of two 64 Kbps B-channels and one 16 Kbps D-channel. Thus, a Basic Rate Interface user can have up to 128 Kbps service. The Primary Rate Interface consists of 23 B-channels and one 64- Kpbs D channel in the United States or 30 B-channels and 1 D-channel in Europe. D-A - Abbreviation for digital-to-analog. See digital transmission system. Daemon - Abbreviation for disk and execution monitor. A procedure that is invoked without being called explicitly whenever an alteration, an addition, or a deletion or other event occurs. Pronounced dee' mun. Also spelled demon. Damping - 1. The progressive diminution with time of certain quantities characteristic of a phenomenon. 2. The progressive decay with time in the amplitude of the free oscillations in a circuit. 3. Energy dissipation mechanisms that reduce the amplification and broaden the vibratory response in the region of a resonance. Damping Ratio: In studies of network survivability in an earthquake, the ratio of actual damping to critical damping. Dangling Threat - Set of properties about the external environment for which there is no corresponding vulnerability and therefore no implied risk Data - In telecommunications, data sometimes means digital-encoded information to distinguish it from analog-encoded information such as conventional telephone voice calls. In general, "analog" or voice transmission requires a dedicated continual connection for the duration of a related series of transmissions. Data transmission can often be sent with intermittent connections in packets that arrive in piecemeal fashion. In computing, data is information that has been translated into a form that is more convenient to move or process. Generally and in science, data is a gathered body of facts. Data Authentication - A process used to verify data integrity, e.g., verification that data received are identical to data sent, or verification that a program is not infected by a virus. Database - 1. A set of data that is required for a specific purpose or is fundamental to a system, project, enterprise, or business. Note: A database may consist of one or more data banks and be geographically distributed among several repositories. 2. A formally structured collection of data. Note: In automated information systems, the database is manipulated using a database management system. Database Management System (DBMS): A software system that facilitates (a) the creation and maintenance of a database or databases, and (b) the execution of computer programs using the database or databases. 113
- 114. Datacasting -Also known as "enhanced TV," this is digital programming that provides additional features to viewers (with program material or non-program-related resources) such as the ability to download data (video, audio, text, graphics, maps, services, etc.) to specially equipped computers, cache boxes, set-top boxes, or DTV receivers. Data Communication - The transfer of information between functional units by means of data transmission according to a protocol. Note: Data are transferred from one or more sources to one or more sinks over one or more data links. Data Compaction - The reduction of the number of data elements, bandwidth, cost, and time for the generation, transmission, and storage of data without loss of information by eliminating unnecessary redundancy, removing irrelevancy, or using special coding. Note 1: Examples of data compaction methods are the use of fixed-tolerance bands, variable-tolerance bands, slope-keypoints, sample changes, curve patterns, curve fitting, variable-precision coding, frequency analysis, and probability analysis. Note 2: Simply squeezing noncompacted data into a smaller space, for example by increasing packing density or by transferring data on punched cards onto magnetic tape, is not data compaction. Note 3: Whereas data compaction reduces the amount of data used to represent a given amount of information, data compression does not. Data Compression - 1. Increasing the amount of data that can be stored in a given domain, such as space, time, or frequency, or contained in a given message length. 2. Reducing the amount of storage space required to store a given amount of data, or reducing the length of message required to transfer a given amount of information. Note 1: Data compression may be accomplished by simply squeezing a given amount of data into a smaller space, for example, by increasing packing density or by transferring data on punched cards onto magnetic tape. Note 2: Data compression does not reduce the amount of data used to represent a given amount of information, whereas data compaction does. Both data compression and data compaction result in the use of fewer data elements for a given amount of information. Data Conferencing Repeater - A device that enables any one user of a group of users to transmit a message to all other users in that group. Synonym technical control hubbing repeater. Datagram - In packet switching, a self-contained packet, independent of other packets, that contains information sufficient for routing from the originating data terminal equipment (DTE) to the destination DTE without relying on prior exchanges between the equipment and the network. Note: Unlike virtual call service, when datagrams are sent there are no call establishment or clearing procedures. Thus, the network may not be able to provide protection against loss, duplication, or misdelivery. Data Integrity - 1. The condition existing when data is unchanged from its source and has not been accidentally or maliciously modified, altered, or destroyed. 2. The condition in which data are identically maintained during any operation, such as transfer, storage, and retrieval. 3. The preservation of data for their intended use. 4. Relative to specified operations, the a priori expectation of data quality. Data Link - 1. The means of connecting one location to another for the purpose of transmitting and receiving data. 2. An assembly, consisting of parts of two data terminal equipments (DTEs) and the interconnecting data circuit, that is controlled by a link protocol enabling data to be transferred from a data source to a data sink. Data Link Layer - See Open Systems Interconnection--Reference Model. Layer 2. This layer responds to service requests from the Network Layer and issues service requests to the Physical Layer. The Data Link Layer provides the functional and procedural means to transfer data between network entities and to detect and possibly correct errors that may occur in the Physical Layer. Note: Examples of data link protocols are HDLC and ADCCP for point-to-point or packet-switched networks and LLC for local area networks. 114
- 115. Data Processing - The systematic performance of operations upon data such as handling, merging, sorting, and computing. Note: The semantic content of the original data should not be changed. The semantic content of the processed data may be changed. Synonym information processing. Data Signaling Rate (DSR) - The aggregate rate at which data pass a point in the transmission path of a data transmission system. Note 1: The DSR is usually expressed in bits per second. Data Stream - A sequence of digitally encoded signals used to represent information in transmission. Data Transfer Rate (or often just data rate) - The amount of digital data that is moved from one place to another in a given time, usually in a second's time. The data transfer rate can be viewed as the speed of travel of a given amount of data from one place to another. In general, the greater the bandwidth of a given path, the higher the data transfer rate. In telecommunications, data transfer is usually measured in bits per second. For example, a typical low- speed connection to the Internet may be 33.6 kilobits per second (Kbps). On Ethernet local area networks, data transfer can be as fast as 10 megabits per second. Network switches are planned that will transfer data in the terabit range. In earlier telecommunication systems, data transfer was sometimes measured in characters or blocks (of a certain size) per second. Data Transmission - The sending of data from one place to another by means of signals over a channel. dB - Abbreviation for decibel (s). One tenth of the common logarithm of the ratio of relative powers, equal to 0.1 B (bel). Note 1: The decibel is the conventional relative power ratio, rather than the bel, for expressing relative powers because the decibel is smaller and therefore more convenient than the bel. Note 2: The dB is used rather than arithmetic ratios or percentages because when circuits are connected in tandem, expressions of power level, in dB, may be arithmetically added and subtracted. For example, in an optical link, if a known amount of optical power, in dBm, is launched into a fiber, and the losses, in dB, of each component (e.g., connectors, splices, and lengths of fiber) are known, the overall link loss may be quickly calculated with simple addition and subtraction. dBa - Abbreviation for decibels adjusted. Weighted absolute noise power, calculated in dB referenced to 3.16 picowatts (-85 dBm), which is 0 dBa. Note: The use of F1A-line or HA1-receiver weighting must be indicated in parentheses as required. A one-milliwatt, 1000-Hz tone will read +85 dBa, but the same power as white noise, randomly distributed over a 3-kHz band (nominally 300 to 3300 Hz), will read +82 dBa, due to the frequency weighting. Synonym dBrn adjusted. dBm - Abbreviation. dB referenced to one milliwatt. Note 1: dBm is used in communication work as a measure of absolute power values. Zero dBm equals one milliwatt. Note 2: In DOD practice, unweighted measurement is normally understood, applicable to a certain bandwidth, which must be stated or implied. Note 3: In European practice, psophometric weighting may be implied, as indicated by context; equivalent to dBm0p, which is preferred. dBm0 - Power in dBm referred to or measured at a zero transmission level point (0TLP). Note 1: A 0TLP is also called a point of zero relative transmission level (0 dBr0). Note 2: Some international documents use dBm0 to mean noise power in dBm0p (psophometrically weighted dBm0). In the United States, dBm0 is not so used. dBm0p - Noise power in dBm0, measured by a psophometer or noise measuring set having psophometric weighting. 115
- 116. dBrnC - Weighted noise power in dBrn, measured by a noise measuring set with C-message weighting. DBS -Digital Broadcast Satellite. TV programming delivered via high-powered satellite. Signals are transmitted to a small dish (usually 18-24 inches across) mounted outdoors. DCR -Digital Cable Ready TV. Also referred to as "Plug-and-Play," this is a DTV or other device for digital cable customers that plugs directly into the cable jack and does not require a separate set-top box to view analog and unscrambled digital cable. Used with a CableCARD, it can receive scrambled programming such as premium services. Decibel - See dB. Decision Circuit - A circuit that measures the probable value of a signal element and makes an output signal decision based on the value of the input signal and a predetermined criterion or criteria. Decision Instant - In the reception of a digital signal, the instant at which a decision is made by a receiving device as to the probable value of a signal condition. Synonym selection position. Decoder - A device or program that translates encoded data into its original format — i.e., it decodes the data. Decrypt - 1. A generic term encompassing decode and decypher. 2. To convert encrypted text into its equivalent plain text by means of a cryptosystem. (This does not include solution by cryptanalysis.) Note: The term "decrypt" covers the meanings of " decipher " and "decode." Dedicated Line - A telecommunications path between two points that is available 24 hours a day for use by a designated user (individual or company). It is not shared in common among multiple users as dial-up lines are. A dedicated line can be a physical path owned by the user or rented from a telephone company, in which case it is called a leased line. A synonym is nonswitched line (as opposed to a switched or dial-up line). Dedicated Service - A connection to the Internet using a leased line that provides for very fast, high bandwidth connections. Also called permanent direct service. Defense Communications System (DCS) - Department of Defense long-haul voice, data, and record traffic system which includes the Defense Data Network, Defense Satellite Communications Systems, and Defense Switched Network. Defense Data Network (DDN): A component of the Defense Communications System used for switching Department of Defense automated data processing systems. Degradation - 1. The deterioration in quality, level, or standard of performance of a functional unit. 2. In communications, a condition in which one or more of the required performance parameters fall outside predetermined limits, resulting in a lower quality of service. Note: Degradation is usually categorized as either "graceful" or "catastrophic." Degree of Coherence - A dimensionless unit, expressed as a ratio, used to indicate the extent of coherence of an electromagnetic wave such as a lightwave. Delay - 1. The amount of time by which an event is retarded. 2. The time between the instant at which a given event occurs and the instant at which a related aspect of that event occurs. Note 1: The events, relationships, and aspects of the entity being delayed must be precisely specified. Note 2: Total delay may be 116
- 117. demonstrated by the impulse response of a device or system. Note 3: In analog systems, total delay is described in terms of the transfer functions in the frequency domain. Synonym delay time. 3. In radar, the electronic delay of the start of the time base used to select a particular segment of the total. Delay Time: Synonym delay. Delivered Block - A successfully transferred block. Demon - A procedure that is invoked without being called explicitly whenever an alteration, an addition, or a deletion or other event occurs. Pronounced dee' mun. Also spelled daemon. Demarc (an abbreviation for demarcation point) - Marks the point where communications facilities owned by one organization interface with that of another organization. In telephone terminology, this is the interface between customer-premises equipment and network service provider equipment. Demultiplexing - The separation of two or more channels previously multiplexed; i.e., the reverse of multiplexing. Denial of Service - 1. The prevention of authorized access to resources or the delaying of time-critical operations. 2. The result of any action or series of actions that prevents any part of an information system (IS) from functioning. Density - 1. In a facsimile system, a measure of the light transmission or reflection properties of an area of an object. Note 1: Density is usually expressed as the logarithm to the base 10 of the ratio of incident to transmitted or reflected irradiance. Note 2: There are many types of density, such as diffuse, double diffuse, and specular density, each of which will usually have different numerical values for different materials. The relevant type of density depends on the type of optical system, the component materials of the object, and the surface characteristics of the object. 2. In video, the degree of darkness of an image, or the percent of the screen used in an image. 3. In optics, a figure of merit that describes the degree of attenuation introduced by a filter. Departure Angle - The angle between the axis of the main lobe of an antenna pattern and the horizontal plane at the transmitting antenna. Synonym takeoff angle. De-Stuffing - The controlled deletion of stuffing bits from a stuffed digital signal, to recover the original signal. Synonyms negative justification, negative pulse stuffing. Destination User - In an information transfer transaction, the user that receives information from the source, i.e., from the originating user. Detection - 1. The recovery of information from an electrical or electromagnetic signal. Note: Conventional radio waves are usually detected by heterodyning, i.e., coherent reception/detection. In this method of reception/detection, the received signal is mixed, in some type of nonlinear device, with a signal from a local oscillator, to produce an intermediate frequency, i.e., beat frequency, from which the modulating signal is recovered, i.e., detected. The inherent instabilities of available optical sources have, until relatively recently, prevented practical use of coherent reception/detection in optical communication receivers. At present, coherent optical receivers, using sophisticated technology, are just beginning to emerge from the laboratory into the field. Virtually all existing optical receivers employ direct detection; that is, the received optical signal impinges directly onto a detector. Direct detection is less sensitive than coherent detection. 2. In tactical operations, the perception of an object of possible military interest but unconfirmed by recognition. 3. In surveillance, the determination and transmission by a surveillance system that an event has occurred. 117
- 118. Detector - 1. A device that is responsive to the presence or absence of a stimulus. 2. In an AM radio receiver, a circuit or device that recovers the signal of interest from the modulated wave. Note: In FM reception, a circuit called a discriminator is used to convert frequency variations to amplitude variations. 3. In an optical communications receiver, a device that converts the received optical signal to another form. Note: Currently, this conversion is from optical to electrical power; however, optical-to-optical techniques are under development. Device Driver - Software that interfaces a computer with a specific peripheral device, e.g. a videodisk player or a printer. Dial Pulse - A dc pulse produced by an end instrument that interrupts a steady current at a sequence and rate determined by the selected digit and the operating characteristics of the instrument. Dial-Pulse Signaling - A method of transmitting a telephone address over a direct-current path. The dc current is interrupted at the transmitting end in a defined pattern representing a particular digit in a telephone number. The number of interruptions in the dc current specifies the address digit. Dielectric - 1. A substance in which an electric field may be maintained with zero or near-zero power dissipation, i.e., the electrical conductivity is zero or near zero. Note 1: A dielectric material is an electrical insulator. Note 2: In a dielectric, electrons are bound to atoms and molecules, hence there are few free electrons. 2. Pertaining to a substance that has a zero or near zero electrical conductivity. Digest - 1. In e-mail, a periodic mailing of a collection of messages compiled from a mailing list or interest group. 2. A command issued to a list server or to a list processor requesting that postings be delivered to a subscriber in summary form. Digit - A symbol, numeral, or graphic character that represents an integer. Note 1: Examples of digits include any one of the decimal characters "0" through "9" and either of the binary characters "0" or "1." Note 2: In a given numeration system, the number of allowable different digits, including zero, is always equal to the base (radix). Digital - 1. An advanced type of radio transmission that broadcasts voice or data intact via radio waves, which allows for greater call clarity, advanced wireless features and improved voice capacity. The industry uses three types of digital technology: TDMA, CDMA and GSM. Digital describes electronic technology that generates, stores, and processes data in terms of two states: positive and non-positive. Positive is expressed or represented by the number 1 and non-positive by the number 0. Thus, data transmitted or stored with digital technology is expressed as a string of 0's and 1's. Each of these state digits is referred to as a bit (and a string of bits that a computer can address individually as a group is a byte). Prior to digital technology, electronic transmission was limited to analog technology, which conveys data as electronic signals of varying frequency or amplitude that are added to carrier waves of a given frequency. Broadcast and phone transmission has conventionally used analog technology. Digital technology is primarily used with new physical communications media, such as satellite and fiber optic transmission. A modem is used to convert the digital information in your computer to analog signals for your phone line and to convert analog phone signals to digital information for your computer. 118
- 119. 2. Describes a new, more efficient method of storing, processing and transmitting information through the use of computer code. Digital can also refer to the circuitry in which data-carrying signals are restricted to one of two voltage levels, corresponding to logic 1 or 0. Digital Cable - A service provided by many cable providers, digital cable offers viewers more channels. Contrary to what many consumers believe, digital cable is not the same thing as HDTV or DTV; rather, digital cable simply offers cable subscribers the option of paying for more services. Digital Channel (Pre-Transition) - A communications path that handles only digital signals. All voice and video signals have to be converted from analog to digital in order to be carried over a digital channel. In regard to the DTV Transition, this is the digital channel number used before the transition was completed. Digital Channel (Post -Transition) - A communications path that handles only digital signals. All voice and video signals have to be converted from analog to digital in order to be carried over a digital channel. In regard to the DTV Transition, this is the corresponding digital channel number used after the channel has transitioned. Digital Data - 1. Data represented by discrete values or conditions, as opposed to analog data. 2. Discrete representations of quantized values of variables, e.g., the representation of numbers by digits, perhaps with special characters and the "space" character. Digital Loop Carrier (DLC) - Equipment that bundles a number of individual phone line signals into a single multiplexed digital signal for local traffic between a telephone company central office and a business complex or other outlying service area. Typically, up to 24 analog voice calls are combined into a single signal and transmitted over a single copper T-carrier system or E-carrier line, an optical fiber cable, or a wireless connection. In a home, business, or other installation using digital loop carrier, the analog phone lines of individual users are connected to a local DLC box which then converts the analog signals into digital and combines (multiplexes) them into one signal that it sent to the phone company's central office on the single line. At the central office, the combined signal is separated back into the original signals. An estimated 20% of today's telephone users are being served by digital loop carriers. Digital loop carrier can carry traffic for regular phone calls (plain old telephone service) and Integrated Services Digital Network (ISDN) service. More recently, approaches have been developed for using DLC to handle the higher bandwidth of Digital Subscriber Line (DSL) service. Digital loop carrier is typically used as an efficient way to provide service to an office building or complex and to extend service to new areas outside the current local loop. DLC is also used to set up telephone service in emergency situations. Customers can easily migrate from a T-1 or E-1 line to fiber optic when it becomes needed and is available. Digital Monitor - Digital monitors are TV sets that can display a digital signal, but lack an integrated tuner (unlike an integrated digital TV set), and thus cannot receive a digital broadcast signal without an additional set-top box. Digital Signal (DS) - 1. A signal in which discrete steps are used to represent information. Note 1: In a digital signal, the discrete steps may be further characterized by signal elements, such as significant conditions, significant instants, and transitions. Note 2: Digital signals contain m-ary significant conditions. 2. A signal that takes on only two values — off or on — typically represented by "0" or "1." Digital signals require less power but typically more bandwidth than analog, and copies of digital signals can be made exactly like the original. 119
- 120. Digital Signal Processors - All digital audio systems use DSP technology in order to differentiate between signal and noise. In telephone communication, too, much noise creates problems in maintaining connections, and in VoIP systems the DSP component provides features such as tone generation, echo cancellation, and buffering Digital Speech Interpolation (DSI) - 1. In digital speech transmission, the use of periods of inactivity or constant signal level to increase the transmission efficiency by insertion of additional signals. 2. A process that takes advantage of inactive periods of a conversation to insert speech from other conversations and to remove silent periods. Digital Subscriber Line (DSL) – A DSL line transmits simultaneous voice and high-speed data over existing copper telephone wires without the need of additional phone lines. DSL provides an Internet connection over regular telephone lines, but much faster. Speed may vary from 128 kilobit per second, up to 9 megabit per second. A Digital Subscriber Line is a popular alternative to Leased Lines and ISDN, being faster than ISDN and less costly than traditional Leased Lines. Digital Subscriber Line or Digital Subscriber Loop is often referred to as xDSL. DSL is an always-on connection to the Internet that allows for simultaneous PC and telephone use. Digital Subscriber Line Access Multiplexer - (see DSLAM) Digital -to-Analog Converter Box - Also referred to as a "converter box" or a "digital converter box," this is a stand-alone device that receives, decodes, and converts over-the-air digital programming into analog. When connected to an analog television, it permits digital programming to be displayed in analog. Digital -to-Analog Converter Coupon Program - To help defray some of the cost for consumers who are transitioning to DTV, the Government established the Digital-to-Analog Converter Box Coupon Program. The NTIA, a part of the Department of Commerce, administers this program. Digital Transmission System - A transmission system in which (a) all circuits carry digital signals and (b) the signals are combined into one or more serial bit streams that include all framing and supervisory signals. Note: A-D / D-A conversion, if required, is accomplished external to the system. Digital Tuner - A digital tuner serves as the decoder required to receive and display digital broadcasts. It can be included inside a TV set or in a set-top box. Dialup Service - A connection that allows you to access the Internet by dialing into a computer through a modem and telephone line. Direct Detection - See detection. The recovery of information from an electrical or electromagnetic signal. Note: Conventional radio waves are usually detected by heterodyning, i.e., coherent reception/detection. In this method of reception/detection, the received signal is mixed, in some type of nonlinear device, with a signal from a local oscillator, to produce an intermediate frequency, i.e., beat frequency, from which the modulating signal is recovered, i.e., detected. The inherent instabilities of available optical sources have, until relatively recently, prevented practical use of coherent reception/detection in optical communication receivers. At present, coherent optical receivers, using sophisticated technology, are just beginning to emerge from the laboratory into the field. Virtually all existing optical receivers employ direct detection; that is, the received optical signal impinges directly onto a detector. Direct detection is less sensitive than coherent detection. Direct Inward Dialing (DID) - A service of a local phone company (or local exchange carrier) that provides a block of telephone numbers for calling into a company's private branch exchange (PBX) system. Using DID, a 120
- 121. company can offer its customers individual phone numbers for each person or workstation within the company without requiring a physical line into the PBX for each possible connection. For example, a company might rent 100 phone numbers from the phone company that could be called over eight physical telephone lines (these are called "trunk lines"). This would allow up to eight ongoing calls at a time; additional inbound calls would get a busy signal until one of the calls completed or be able to leave a voice mail message. The PBX automatically switches a call for a given phone number to the appropriate workstation in the company. A PBX switchboard operator is not involved. A DID system can be used for fax and voice mail as well as for live voice connections. Compared to regular PBX service, DID saves the cost of a switchboard operator, calls go through faster, and callers feel they are calling a person rather than a company. Direct Orbit - For a satellite orbiting the Earth, an orbit in which the projection of the satellite on the equatorial plane revolves about the Earth in the same direction as the rotation of the Earth. Directory - While there is no single source or official Internet directory, there are several search vehicles available to research or access information on the WWW. Directories categorize and list information in specific headings or categories. Directory Access Protocol (DAP) - A directory protocol that defines the exchange of requests and outcomes between user and system. Directory number - A network (sub) address (from a telephone user perspective) such as the telephone number in the telecommunication network. For the purpose of this configuration management model, the directory number is described in a managed object that contains references to other objects or attributes related to the services of subscribers. For service providers, the directory number is the key element used to manage subscriber services. Direct Outward Dialing (DOD) - A service of a local phone company (or local exchange carrier) that allows subscribers within a company's private branch exchange (PBX) system to connect to outside lines directly. Using DOD, a company can offer each person or workstation within the company the ability to dial numbers direct, without the need to go through an operator or dial other numbers first. DOD is often used together with Direct Inward Dialing (DID). When DOD is used in a company with 100 workstations, for example, eight physical telephone lines (called trunk lines) might be rented from the telephone copmany. This would allow up to eight ongoing calls at a time; additional outbound call attempts would produce a busy signal until one of the calls completed. A DOD system can be used for fax, dial-up Internet, and voice mail, as well as for live voice connections. Compared to regular PBX service, DOD saves the cost of a switchboard operator, and calls go through faster. Directional Coupler - A transmission coupling device for separately sampling (through a known coupling loss) either the forward (incident) or the backward (reflected) wave in a transmission line. Note: A directional coupler may be used to sample either a forward or backward wave in a transmission line. A unidirectional coupler has available terminals or connections for sampling only one direction of transmission; a bidirectional coupler has available terminals for sampling both directions. Synonyms splitter, T-coupler, tee coupler. Disclosure - A violation of computer security whereby data have been made available to unauthorized entities. Discone Antenna - See biconical antenna. 121
- 122. Disconnect - In telephony, the disassociation or release of a switched circuit between two stations. Discriminator - The part of an FM receiver that extracts the desired signal from an incoming FM wave by changing frequency variations into amplitude variations. Disengagement Attempt - An attempt to terminate a telecommunications system access. Note: Disengagement attempts may be initiated by a user or the telecommunications system. Disengagement Originator - The user or functional unit that initiates a disengagement attempt. Note 1: A disengagement originator may be the originating user, the destination user, or the communications system. Note 2: The communications system may deliberately originate the disengagement because of preemption or inadvertently because of system malfunction. Disengagement Request - A control or overhead signal issued by a disengagement originator for the purpose of initiating a disengagement attempt. Disk and Execution Monitor (daemon) - See daemon. A procedure that is invoked without being called explicitly whenever an alteration, an addition, or a deletion or other event occurs. Pronounced dee' mun. Also spelled demon. Diskette - In computer technology, a small disk of flexible plastic, coated with a magnetizable material and enclosed in a protective jacket, used to store digital data. Note: A diskette is distinguished from a hard disk by virtue of the fact that it is flexible, and unlike most hard disks, is removable from its drive. Synonyms flexible disk, floppy disk. Dispersion - Any phenomenon in which the velocity of propagation of an electromagnetic wave is wavelength dependent. Note 1: In communication technology, "dispersion" is used to describe any process by which an electromagnetic signal propagating in a physical medium is degraded because the various wave components (i.e., frequencies) of the signal have different propagation velocities within the physical medium. Note 2: In an optical fiber, there are several significant dispersion effects, such as material dispersion, profile dispersion, and waveguide dispersion, that degrade the signal. Note 3: In optical fiber communications, the incorrect terms " multimode dispersion " and " intermodal dispersion " should not be used as synonyms for the correct term " multimode distortion." Note 4: In classical optics, "dispersion" is used to denote the wavelength dependence of refractive index in matter, (dn/d , where n is the refractive index and is the wavelength) caused by interaction between the matter and light. "Dispersion," as used in fiber optic communications, should not be confused with "dispersion" as used by optical lens designers. Note 5: Three types of dispersion, relating to optical fibers, are defined as follows: • material dispersion: In optical fiber communication, the wavelength dependence of the velocity of propagation (of the optical signal) on the bulk material of which the fiber is made. Note 1: Because every optical signal has a finite spectral width, material dispersion results in spreading of the signal. Note 2: Use of the redundant term " chromatic dispersion " is discouraged. Note 3: In pure silica, the basic material from which the most common telecommunication-grade fibers are made, material dispersion is minimum at wavelengths in the vicinity of 1.27 m (slightly longer in practical fibers). • profile dispersion: In an optical fiber, that dispersion attributable to the variation of refractive index contrast with wavelength. Profile dispersion is a function of the profile dispersion parameter. • waveguide dispersion: Dispersion, of importance only in single-mode fibers, caused by the dependence of the phase and group velocities on core radius, numerical aperture, and wavelength. Note 1: For circular waveguides, the dependence is on the ratio, a / , where a is the core radius and is the wavelength. Note 2: Practical single-mode fibers are designed so that material dispersion and waveguide dispersion cancel one another at the wavelength of interest. 122
- 123. Display Device - An output unit that gives a visual representation of data. Distinctive Ring - An inexpensive service that lets businesses and homes to have two or three different phone numbers on one phone line. What distinguishes the different telephone numbers coming in on the same line is their signature ring, a pattern of long and/or short rings. Each number has its own special ring. Most telephone companies throughout the US and Canada offer distinctive ring. These "Distinctive Ring" services go by different names depending on your phone company -custom Ringing by US West, SmartRing by GTE, RingMaster by Bell South, RingMate by NYNEX, Personalized Ringing by Southwestern Bell and SBC, Multi-Ring by Ameritech, Distinctive Ring by ATT and SBC and IdentaRing by Bell Atlantic. Note: Without distinctive ringing, all the instruments on the party line will ring at the same time, selection being made by the number of rings. Two popular Distinctive Ring Devices are the SR-Series Call Processors and The Line Hunter. For deteailed info see Distinctive Ring Definition and Use. Distinctive Ring Device - A device that tests a phone line for a distinctive ring signal and routes the call to a specific device (example: phone, phone system, answering machine, fax machine. fax modem). For more info see Fax Switch. For more info see Distinctive Ring Definition and Use. Distinctive Ring Service - Provides a distinctive ringing pattern for up to six different telephone numbers on a screening list. The telephone numbers on the screening list may be changed or reprogrammed at any time. See Distinctive Ring. For more info see Distinctive Ring Definition and Use. Distortion - 1. In a system or device, any departure of the output signal waveform from that which should result from the input signal waveform's being operated on by the system's specified, i.e., ideal, transfer function. Note: Distortion may result from many mechanisms. Examples include nonlinearities in the transfer function of an active device, such as a vacuum tube, transistor, or operational amplifier. Distortion may also be caused by a passive component such as a coaxial cable or optical fiber, or by inhomogeneities, reflections, etc., in the propagation path. 2. In start-stop teletypewriter signaling, the shifting of the significant instants of the signal pulses from their proper positions relative to the beginning of the start pulse. Note: The magnitude of the distortion is expressed in percent of an ideal unit pulse length. Distributed-Queue Dual-Bus (DQDB) [network] - A distributed multi-access network that (a) supports integrated communications using a dual bus and distributed queuing, (b) provides access to local or metropolitan area networks, and (c) supports connectionless data transfer, connection-oriented data transfer, and isochronous communications, such as voice communications. Distribution Frame - In communications, a structure with terminations for connecting the permanent wiring of a facility in such a manner that interconnection by cross-connections may readily be made. Distribution List Server - Synonym list server. - A functional unit (hardware and software) for operating a computer conferencing system by acting as a repository for electronic messages and redistributing those messages automatically or on-demand. Diversity Combiner - A circuit or device for combining two or more signals carrying the same information received via separate paths or channels with the objective of providing a single resultant signal that is superior in quality to any of the contributing signals. Divestiture - The court-ordered separation of the Bell Operating Telephone Companies from AT&T. 123
- 124. DMA - Designated Market Area. A term used by Nielsen Media Research to identify an exclusive geographic area of counties in which the home market television stations hold a dominance of total hours viewed. There are 210 DMA in the U.S. DNS - See Domain Name System DOD - Abbreviation for Department of Defense, direct outward dialing. Dolby® Digital - A form of multi-channel digital sound, it provides efficient encoding and noise reduction for high-quality surround sound — technology used in movie theaters and upscale home theater systems that enhances audio. Home theater components with this technology work in conjunction with a "5.1-speaker" system (five speakers plus a low-frequency subwoofer) to produce true-to-life audio that draws the listener into the onscreen action. Domain - 1. The independent variable used to express a function. Note: Examples of domains are time, frequency, and space. 2. In distributed networks, all the hardware and software under the control of a specified set of one or more host processors. [From Weik '89] 3. [A] unique context (e.g., access control parameters) in which a program is operating; in effect, the set of objects a subject has the privilege to access. Domain Name - A unique name that identifies an Internet site; the Domain Name will always have at least two parts separated by dots (for example: tds.net or tdsnet.com). These names are granted and controlled by a centralized Internet Network Information Center (InterNIC), administered by the National Science Foundation. Domain Name System (DNS) - A system by which one Internet host can find another. DNS translates words (Domain Names) into numbers that Internet computers can understand. Double Refraction - Synonym birefringence. - In a transparent material, anisotropism of the refractive index, which varies as a function of polarization as well as orientation with respect to the incident ray. Note 1: The term "birefringence" means, literally, " double refraction." Note 2: All crystals except those of cubic lattice structure exhibit some degree of anisotropy with regard to their physical properties, including refractive index. Other materials, such as glasses or plastics, become birefringent when subjected to mechanical strain. Note 3: Birefringent materials, including crystals, have the ability to refract an unpolarized incident ray into two separate, orthogonally polarized rays, which in the general case take different paths, depending on orientation of the material with respect to the incident ray. The refracted rays are referred to as the "ordinary," or "O" ray, which obeys Snell's Law, and the "extraordinary," or "E" ray, which does not. Downconvert - A process by which a high-resolution signal is reduced to a lower resolution for display. Usually, extra lines are simply ignored when drawing the lower resolution image; however, more sophisticated methods are sometimes used. Download - To transfer of a file or information from another computer to yours. Downstream - 1. In communications, the direction of transmission flow from the source toward the sink. 2. With respect to the flow of data in a communications path: at a specified point, the direction toward which data are received later than at the specified point. DQDB - Abbreviation for distributed-queue dual-bus. - A distributed multi-access network that (a) supports integrated communications using a dual bus and distributed queuing, (b) provides access to local or metropolitan area networks, and (c) supports connectionless data transfer, connection-oriented data transfer, and isochronous communications, such as voice communications. 124
- 125. Drift - A comparatively long-term change in an attribute or value of a system or equipment operational parameter. Note 1: The drift should be characterized, such as "diurnal frequency drift" and "output level drift." Note 2: Drift is usually undesirable and unidirectional, but may be bidirectional, cyclic, or of such long- term duration and low excursion rate as to be negligible. Driver - See device driver. - Software that interfaces a computer with a specific peripheral device, e.g. a videodisk player or a printer. Droid - 1. In the Internet, an intelligent search tool that automatically seeks out relevant online information based on the user's specifications. Synonyms agent, bot, crawler, hotbot, infobot, information agent, intelligent agent, Internet search engine, knowbot, knowledge robot, personal agent, robotic librarian, search robot, spider, Web crawler, Web spider, wizard. 2. In artificial intelligence, an entity with the ability to sense its environment and to act in such a way or to affect that environment; typically knowledge-based entities that can communicate with each other through some message-passing scheme. DS-1 - See T-1 DS-3 - See T-3 DSL - Stands for Digital Subscriber Line, a recently developed (late 1990s) digital communications technology that can provide high-speed transmissions over standard copper telephone wiring. It uses a twisted-pair copper wire connection with a special modem at either end that filters out background noise and interference and allows high-speed data transfer. It is limited to a transmission distance of 18 000 feet. DSL offers speeds in excess of dial-up. Speed may vary from 128 kilobit per second, up to 9 megabit per second.. DSL is a broadband technology that enables high-speed Internet access to a home or business. DSL is an always-on connection to the Internet that allows for simultaneous PC and telephone use. This is a method of transmitting data over telephone lines prevalent in the United States. The UK uses a variant called ADSL for providing broadband to users. DSLAM (Digital Subscriber Line Access Multiplexer) - A network device, usually at a telephone company central office, that receives signals from multiple customer Digital Subscriber Line (DSL) connections and puts the signals on a high-speed backbone line using multiplexing techniques. Depending on the product, DSLAM multiplexers connect DSL lines with some combination of asynchronous transfer mode (ATM), frame relay, or Internet Protocol networks. DSLAM enables a phone company to offer business or homes users the fastest phone line technology (DSL) with the fastest backbone network technology (ATM). DSP (Digital Signal Processors) - All digital audio systems use DSP technology in order to differentiate between signal and noise. In telephone communication, too, much noise creates problems in maintaining connections, and in VoIP systems the DSP component provides features such as tone generation, echo cancellation, and buffering DSR - Abbreviation for data signaling rate. DTMF (DUAL TONE , MULTIFREQUENCY) - This tone is commonly called "touch-tone". Not all push-button phones are capable of producing the DTMF tones. Abbreviation for Dual Tone Multi Frequency DTTV (digital terrestrial television, sometimes also abbreviated DTT) - Digital television (DTV) broadcast entirely over earthbound circuits. A satellite is not used for any part of the link between the broadcaster and the end user. DTTV signals are broadcast over essentially the same media as the older analog terrestrial TV signals. The most common circuits use coaxial cable at the subscriber end to connect the network to the TV receiver. 125
- 126. fiber optic and/or microwave links may be used between the studio and the broadcast station, or between the broadcast station and local community networks. DTTV provides a clearer picture and superior sound quality when compared to analog TV, with less interference. DTTV offers far more channels, thus providing the viewer with a greater variety of programs to choose from. DTTV can be viewed on personal computers. Using a split-screen format, a computer user can surf the Web while watching TV. In regions not served by cable, DTTV is generally impractical. For this reason, digital satellite TV (DSTV) has become popular, especially in rural areas and in some small towns. A few city dwellers prefer DSTV even when they have the option of subscribing to DTTV. DTV - Digital Television. An advanced broadcasting technology that uses radio frequency (RF) to transmit computer code and display it as pictures and sound. DTV is the umbrella term encompassing HDTV and several other applications, including SDTV, datacasting, multicasting and interactivity. Dual Bus - A pair of parallel buses arranged such that the direction of data flow in one bus is opposite to the direction of data flow in the other bus. Dual Seizure - The condition that occurs when, in both-way operation, two exchanges attempt to seize the same circuit at approximately the same time. Synonyms call collision, glare [deprecated]. Dual Tone Multifrequency (DTMF)- This tone is commonly called "touch-tone". Not all push-button phones are capable of producing the DTMF tones. Duct - 1. In interfacility cabling, a conduit, which may be direct-earth buried or encased in concrete, used to enclose communications or power cables. Note: For maximum resistance to rodent attack, direct-earth- buried conduit should have an outside diameter equal to or greater than 6 cm (2.25 in.). 2. See atmospheric duct. Ducting - The propagation of radio waves within an atmospheric duct. Duplex Communication - means that both ends of the communication can send and receive signals at the same time. full-duplex communication is the same thing. half-duplex is also bidirectional communication but signals can only flow in one direction at a time. Simplex communication means that communication can only flow in one direction and never flow back the other way. An ordinary telephone conversation is a duplex communication. Most inexpensive speakerphones in conference rooms are half-duplex communication. (If you're speaking, you can't hear anyone else interrupt. You have to pause to let others speak.) DVI - Digital Video Interface. A high-quality digital connector. Similar to HDMI and sometimes with HDCP, DVI can digitally transmit uncompressed, high-definition video, preserving perfect picture quality. Unlike HDMI or Firewire, DVI requires a separate audio connection. DVR - Digital Video Recorder. A device that records video in a digital format to a disk drive or other memory medium within a device. The term includes stand-alone set-top boxes, Portable Media Players (PMP) and software for personal computers, which enables video capture and playback to and from disk. Dynamic Range - 1. In a system or device, the ratio of (a) a specified maximum level of a parameter, such as power, current, voltage, or frequency to (b) the minimum detectable value of that parameter. Note: The 126
- 127. dynamic range is usually expressed in dB. 2. In a transmission system, the ratio of (a) the overload level, i.e., the maximum signal power that the system can tolerate without distortion of the signal, to (b) the noise level of the system. Note: The dynamic range of transmission systems is usually expressed in dB. 3. In digital systems or devices, the ratio of maximum and minimum signal levels required to maintain a specified bit error ratio. E E-1 - The European equivalent of a T-1. E1 (or E-1) - A European digital transmission format devised by the ITU-TS and given the name by the Conference of European Postal and Telecommunication Administration (CEPT). It's the equivalent of the North American T-carrier system format. E2 through E5 are carriers in increasing multiples of the E1 format. The E1 signal format carries data at a rate of 2.048 million bits per second and can carry 32 channels of 64 Kbps* each. E1 carries at a somewhat higher data rate than T-1 (which carries 1.544 million bits per second) because, unlike T-1, it does not do bit-robbing and all eight bits per channel are used to code the signal. E1 and T-1 can be interconnected for international use. E2 (E-2) - A line that carries four multiplexed E1 signals with a data rate of 8.448 million bits per second. E3 (E-3) - A line that carries 16 E1 signals with a data rate of 34.368 million bits per second. E4 (E-4) - A line that carries four E3 channels with a data rate of 139.264 million bits per second. E5 (E-5) - A line that carries four E4 channels with a data rate of 565.148 million bits per second. E911 - Technology allowing 911 calls from cellular phones to be routed to the geographically correct emergency station (a.k.a. PSAP: Public Safety Answering Point). VoIP users currently have limited access to 911 services, and with some providers none, because VoIP is not geographically based. In the United States, E911 (Enhanced 911) is support for wireless phone users who dial 911, the standard number for requesting help in an emergency. Since wireless users are often mobile, some sort of enhancement is needed to 911 service that allows the location of the user to be known to the call receiver. E911 support is mandated by the U.S. Federal Communications Commission (FCC) for traditional mobile phone service and, since May 19, 2005, for certain VoIP service. Phase 1 of the E911 program required a service provider to provide the telephone number of a 911 caller and the location of the antenna receiving the call to a local Public Safety Answering Point (PSAP). Phase 2 requires the provider to furnish more precise information about the caller's location, usually to within 50 to 300 meters. Phase 2, which requires new technology, is to be completed by the end of 2005. On May 19, 2005, the FCC also required that Internet service providers who interconnect VoIP calls with the public switched telephone network (PSTN) must provide E911 service for these callers and call dispatchers. Providers are required to inform users of the capabilities and any limitations of their 911 service. Providers were given 120 days to comply. Previously, as a general policy, the FCC had taken a "hands-off" position about regulating Internet traffic on the argument that the Internet is an information service rather than a communications service. Providers do not have to furnish E911 service for VoIP callers who do not interconnect with the PSTN such as those using instant messaging and Internet gaming. E911 Taxes/Surcharges - This tax is set and imposed by local governments to help pay for the cost of an emergency response communications system that identifies both the caller and the location of the call. 127
- 128. Ear and mouth (E&M) - A technology in voice over IP (VoIP) that uses a traditional telephone handset with an earphone (or earpiece) for listening to incoming audio and a microphone (or mouthpiece) for transmitting audio. Calls using an E&M interface can be made from, received from, or disconnected by a private branch exchange (PBX) as well as from a VoIP-capable computer. The main advantage of E&M is the fact that it allows a PBX to reliably detect disconnect (hang-up) signals. This eliminates problems that can otherwise occur with locked computer ports at the terminations of calls, and thus minimizes the risk of needlessly consuming network resources. The term ear and mouth interface is sometimes used as a synonym for a telephone handset itself, or for a headset-and-microphone combination that allows hands-free operation. Earth Electrode Subsystem - A network of electrically interconnected rods, plates, mats, or grids, installed and connected, for the purpose of establishing a low-resistance contact with earth. Earth Ground - See ground. - 1. An electrical connection to earth through an earth-electrode subsystem. 2. In an electrical circuit, a common return path that usually (a) is connected to an earth-electrode subsystem and (b) is extended throughout a facility via a facility ground system consisting of the signal reference subsystem, the fault protection subsystem, and the lightning protection subsystem. 3. In an electrical circuit, a common return path that (a) may not necessarily be connected to earth and (b) is the zero voltage reference level for the equipment or system. EAS - 1. Extended Area Service. Customers usually pay a larger flat rate to increase their local calling area if an area gets EAS. It can decrease a customer’s monthly bill if the customer makes a certain number of calls to the expanded area. 2. Emergency Alert System. This is designed to provide the President with a means to address the American people in the event of a national emergency. E-carrier - System, where 'E' stands for European, is incompatible with the T-carrier and is used just about everywhere else in the world besides North America and Japan. It typically uses the E1 line rate and the E3 line rate. The E2 line rate is less commonly used. A European digital transmission format devised by the ITU- TS and given the name by the Conference of European Postal and Telecommunication Administration (CEPT). It's the equivalent of the North American T-carrier system format. E2 through E5 are carriers in increasing multiples of the E1 format. Echo - 1. A wave that has been reflected by a discontinuity in the propagation medium. 2. A wave that has been reflected or otherwise returned with sufficient magnitude and delay to be perceived. Note 1: Echoes are frequently measured in dB relative to the directly transmitted wave. Note 2: Echoes may be desirable (as in radar ) or undesirable (as in telephone systems). 3. In computing, to print or display characters (a) as they are entered from an input device, (b) as instructions are executed, or (c) as retransmitted characters received from a remote terminal. 4. In computer graphics, the immediate notification of the current values provided by an input device to the operator at the display console. Echo Check - A check to determine the integrity of transmission of data, whereby the received data are returned to the source for comparison with the originally transmitted data. Synonym loop check. EDI - (Electronic Data Interchange) - The electronic communication of business transactions, such as orders, confirmations and invoices, between organizations. Third parties provide EDI services that enable organizations with different equipment to connect. Although interactive access may be a part of it, EDI implies direct computer to computer transactions into vendors' databases and ordering systems. The Internet has given EDI quite a boost, but not by using private networks and the traditional EDI data 128
- 129. formats (X12, EDIFACT and TRADACOMS). Rather, XML has been the glue that connects businesses together using the Web as the communications vehicle. Edge-Emitting LED - An LED that has a physical structure superficially resembling that of an injection laser diode, operated below the lasing threshold and emitting incoherent light. Note: Edge-emitting LEDs have a relatively small beam divergence, and thus are capable of launching more optical power into a given fiber than are the conventional surface-emitting LEDs. EDTV - Enhanced Definition TV. A better digital television transmission than SDTV with at least 480p (progressive), in a 16:9 or 4:3 display and Dolby® digital surround sound. The quality of most progressive scan DVDs and players is 480p. Effective Radiated Power (e.r.p.) (in a given direction) - 1. The power supplied to an antenna multiplied by the antenna gain in a given direction. Note 1: If the direction is not specified, the direction of maximum gain is assumed. Note 2: The type of reference antenna must be specified. 2. The product of the power supplied to the antenna and its gain relative to a half-wave dipole in a given direction. Note: If the direction is not specified, the direction of maximum gain is assumed. 3. The effective radiated power of a transmitter (with antenna, transmission line, duplexers, etc.,) is the power that would be necessary at the input terminals of a reference half-wave dipole antenna in order to produce the same maximum field intensity. ERP is usually calculated by multiplying the measured transmitter output power by the specified antenna system gain, relative to a half-wave dipole, in the direction of interest. Electrical Plugs and Sockets - When electricity was first introduced into the domestic environment it was primarily for lighting. However, as it became a viable alternative to other means of heating and also the development of labour saving appliances, a means of connection to the supply other than via a light socket was required. In the 1920s, the two-prong plug made its appearance. At that time, some electricity companies operated a split tariff system where the cost of electricity for lighting was lower than that for other purposes, which led to low wattage appliances (e.g. vacuum cleaners, hair dryers, etc.) being connected to the light fitting. The picture below shows a 1909 electric toaster with a lightbulb socket plug. As the need for safer installations grew, three-pin outlets were developed. The third pin on the outlet was an earth pin, which was effectively connected to earth, this being at the same potential as the neutral supply line. The idea behind it was that in the event of a short circuit to earth, a fuse would blow, thus disconnecting the supply. The reason why we are now stuck with no less than 13 different styles of plugs and wall outlets, is because many countries preferred to develop a plug of their own, instead of adopting the US standard. Moreover, the plugs and sockets are only very rarely compatible, which makes it often necessary to replace the plug when you buy appliances abroad. Below is a brief outline of the plugs and sockets used around the world in domestical environment. TYPE A (used in, among others, North and Central America and Japan) 129
- 130. This class II ungrounded plug with two flat parallel prongs is pretty much standard in most of North and Central America. At first glance, the Japanese plug and socket seem to be identical to this standard. However, the Japanese plug has two identical flat prongs, whereas the US plug has one prong which is slightly larger. Therefore it is no problem to use Japanese plugs in the US, but the opposite does not work often. Furthermore, Japanese standard wire sizes and the resulting current ratings are different than those used on the American continent. Type A and B plugs have two flat prongs with a hole near the tip. These holes aren't there without a reason. If you were to take apart a type A or B socket and look at the contact wipers that the prongs slide into, you would find that in some cases they have have bumps on them. These bumps fit into the holes so that the outlet can grip the plug’s prongs more firmly. This prevents the plug from slipping out of the socket due to the weight of the plug and cord. It also improves the contact between the plug and the outlet. Some sockets, however, don't have those bumps but just two spring-action blades that grip the sides of the plug pin, in which case the holes aren't necessary. There are also some special outlets which allow you to lock the cord into the socket, by putting rods through the holes. This way, for example vending machines cannot be unplugged. Moreover, electrical devices can be "factory-sealed" by the manufacturer using a plastic tie or a small padlock through one or both of the plug prong holes. For example, a manufacturer might apply a plastic band through the hole and attach it to a tag that says: "You must do X or Y before plugging in this device". The user cannot plug in the device without removing the tag, so the user is sure to see the tag. TYPE B (used in, among others, North and Central America and Japan) 130
- 131. This is a class I plug with two flat parallel prongs and a grounding pin (American standard NEMA 5- 15/Canadian standard CS22.2, n°42). It is rated at 15 amps and although this plug is also standard in Japan, it is less frequently used than in North America. Consequently, most appliances sold in Japan use a class II ungrounded plug. As is the case with the type A standard, the Japanese type B plugs and sockets are slightly different from their American counterparts. An ungrounded version of the North American NEMA 5-15 plug is commonly used in Central America and parts of South America. It is therefore common for equipment users to simply cut off the grounding pin that the plug can be mated with a two-pole ungrounded socket. TYPE C (used in all countries of Europe except the United Kingdom, Ireland, Cyprus and Malta) This two-wire plug is ungrounded and has two round prongs. It is popularly known as the europlug which is described in CEE 7/16. This is probably the single most widely used international plug. It will mate with any socket that accepts 4.0-4.8 mm round contacts on 19 mm centres. It is commonly used in all countries of Europe except the United Kingdom and Ireland. It is also used in various parts of the developing world. This plug is generally limited for use in class II applications that require 2.5 amps or less. It is, of course, unpolarised. TYPE D (used almost exclusively in India, Sri Lanka, Nepal and Namibia) 131
- 132. India has standardised on a plug which was originally defined in British Standard 546 (the standard in Great Britain before 1962). This plug has three large round pins in a triangular pattern. It is rated at 5 amps. Type M, which has larger pins and is rated at 15 amps, is used alongside type D for larger appliances in India, Sri Lanka, Nepal and Namibia. Some sockets can take both type M and type D plugs. Although type D is now almost exclusively used in India, Sri Lanka, Nepal and Namibia, it can still occasionally be found in hotels and theatres in the UK and Ireland. It should be noted that tourists should not attempt to connect anything to a BS546 round-pin outlet found in the UK or Ireland as it is likely to be on a circuit that has a special purpose: e.g. for providing direct current (DC) or for plugging in lamps that are controlled by a light switch or a dimmer. TYPE E (primarily used in France, Belgium, Poland, Slovakia, the Czech Republic, Tunisia and Morocco) France, Belgium and some other countries have standardised on a socket which is different from the CEE 7/4 socket (type F) that is standard in Germany and other continental European countries. The reason for incompatibility is that grounding in the E socket is accomplished with a round male pin permanently mounted in the socket. The plug itself is similar to C except that it is round and has the addition of a female contact to accept the grounding pin in the socket. In order to bridge the differences between sockets E and F, the CEE 7/7 plug was developed: it has grounding clips on both sides to mate with the type F socket and a female contact to accept the grounding pin of the type E socket. The original type E plug, which does not have grounding clips, is no longer used, although very rarely it can still be found on some older appliances. Note that the CEE 7/7 plug is polarised when used with a type E outlet. The plug is rated at 16 amps. Above that, equipment must either be wired permanently to the mains or connected via another higher power connector such as the IEC 309 system. A type C plug fits perfectly into a type E socket. TYPE F (used in, among others, Germany, Austria, the Netherlands, Sweden, Norway, Finland, Portugal, Spain and Eastern Europe) 132
- 133. Plug F, known as CEE 7/4 and commonly called "Schuko plug", is similar to C except that it is round and has the addition of two grounding clips on the side of the plug. It has two 4.8 mm round contacts on 19 mm centres. Because the CEE 7/4 plug can be inserted in either direction into the receptacle, the Schuko connection system is unpolarised (i.e. line and neutral are connected at random). It is used in applications up to 16 amps. Above that, equipment must either be wired permanently to the mains or connected via another higher power connector such as the IEC 309 system. In order to bridge the differences between sockets E and F, the CEE 7/7 plug was developed. This plug, which is shown above, has grounding clips on both sides to mate with the type F socket and a female contact to accept the grounding pin of the type E socket. The original type F plug, which does not have this female contact, is still available at the DIY shops but only in a rewireable version. A type C plug fits perfectly into a type F socket. The Soviet Republics use a standard plug and socket defined in Russian Standard Gost 7396 which is similar to the Schuko standard. Contacts are also on 19 mm centres, but the diameter of this contact is 4.0 mm compared to 4.8 mm which is standard in Continental Europe. It is possible to mate Russian plugs with Schuko outlets, but Russian sockets will not allow to connect type E and F plugs as the outlets have smaller hole diameters than the pins of those two plugs mentioned. Many official standards in Eastern Europe are virtually identical to the Schuko standard. Furthermore, one of the protocols governing the reunification of Germany provided that the DIN and VDE standards would prevail without exception. The former East Germany was required to confirm to the Schuko standard. It appears that most if not all of the Eastern European countries generally use the Schuko standard internally but, until recently, they exported appliances to the Soviet Union with the Soviet standard plug installed. Because the volumes of appliance exports to the Soviet Union were large, the Soviet plug has found its way into use in Eastern Europe as well. TYPE G (mainly used in the United Kingdom, Ireland, Cyprus, Malta, Malaysia and Singapore) This plug has three rectangular prongs that form a triangle. British Standard BS 1363 requires use of a 133
- 134. three-wire grounded and fused plug for all connections to the power mains (including class II, two-wire appliances). British power outlets incorporate shutters on line and neutral contacts to prevent someone from pushing a foreign object into the socket. The British domestic electrical system uses a ring circuit in the building which is rated for 32 amps (6 amps for lighting circuits). Moreover, there is also a fusing in the plug; a cartridge fuse, usually of 3 amps for small appliances like radios etc. and 13 amps for heavy duty appliances such as heaters. Almost everywhere else in the world a spur main system is used. In this system each wall socket, or group of sockets, has a fuse at the main switchboard whereas the plug has none. So if you take some foreign appliance to the UK, you can use an adaptor, but technically it must incorporate the correct value fuse. Most would have a 13 amps one, too big for the computer for example. BS 1363 was published in 1962 and since that time it has gradually replaced the earlier standard plugs and sockets (type D) (BS 546). TYPE H (used exclusively in Israel) This plug, defined in SI 32, is unique to Israel. It has two flat prongs like the type B plug, but they form a V- shape rather than being parallel like B plugs. Type H plugs have got a grounding pin as well and are rated at 16 amps. Type H sockets are so shaped as to accommodate type C plugs as well. The slots for the non- grounded prongs have widenings in the middle specifically to allow type C prongs to fit in. TYPE I (mainly used in Australia, New Zealand, Papua New Guinea and Argentina) 134
- 135. This plug has also a grounding pin and two flat prongs forming a V-shape. There is an ungrounded version of this plug as well, with only two flat V-shaped prongs. Although the above plug looks very similar to the one used in Israel (type H), both plugs are not compatible. Australia’s standard plug/socket system is described in SAA document AS 3112 and is used in applications up to 10 amps. A plug/socket configuration with rating at 15 amps (ground pin is wider: 8 mm instead of 6.35 mm) is also available. A standard 10 amp plug will fit into a 15 amp outlet, but a 15 amp plug only fits this special 15 amp socket. There is also a 20 amp plug whose earth blade is wider still. A lower-amperage plug will always fit into a higher-amperage outlet but not vice versa. Although there are slight differences, the Australian plug mates with the socket used in the People's Republic of China (mainland China). TYPE J (used almost exclusively in Switzerland, Liechtenstein and Brazil) Switzerland has its own standard which is described in SEC 1011. This plug is similar to C, except that it has the addition of a grounding pin. This connector system is rated for use in applications up to 10 amps. Above 10 amps, equipment must be either wired permanently to the electrical supply system with appropriate branch circuit protection or connected to the mains with an appropriate high power industrial connector. Type J is also the official grounded standard in Brazil, as described in NBR 14136. A type C plug fits perfectly into a type J socket. TYPE K (used almost exclusively in Denmark and Greenland) The Danish standard is described in Afsnit 107-2-D1. The plug is similar to F except that it has a grounding pin instead of grounding clips. The Danish socket will also accept either the CEE 7/4 or CEE 7/7 plugs: however, 135
- 136. there is no grounding connection with these plugs because a male ground pin is required on the plug. The correct plug must be used in Denmark for safety reasons. A variation of this plug intended for use only on surge protected computer circuits has been introduced. The current rating on both plugs is 10 amps. A type C plug fits perfectly into a type K socket. TYPE L (used almost exclusively in Italy and randomly found throughout North Africa) The Italian grounded plug/socket standard, CEI 23-16/VII, includes two styles rated at 10 and 16 amps. They differ in terms of contact diameter and spacing, and are therefore incompatible with each other. The plugs are similar to C except that they are earthed by means of a centre grounding pin. Because they can be inserted in either direction at random, they are unpolarised. A type C plug fits perfectly into a type L socket. TYPE M (used almost exclusively in South Africa, Swaziland and Lesotho) This plug resembles the Indian type D plug, but its pins are much larger. Type M is rated at 15 amps. Although type D is standard in India, Sri Lanka, Nepal and Namibia, type M is also used for larger appliances. Some sockets over there can take both type M and type D plugs. COUNTRY PLUG & SOCKET Afghanistan C/F 136
- 137. Albania C/F Algeria C/F American Samoa A/B/F/I Andorra C/F Angola C Anguilla A Antigua A/B Argentina C / I* Armenia C/F Aruba A/B/F Australia I Austria C/F Azerbaijan C Azores B/C/F Bahamas A/B Bahrain G Balearic Islands C/F Bangladesh A/C/D/G/K Barbados A/B Belarus C Belgium E Belize B/G Benin E Bermuda A/B Bhutan D/F/G Bolivia A/C Bosnia & Herzegovina C/F Botswana D/G Brazil A / B / C / I / J** Brunei G Bulgaria C/F Burkina Faso C/E Burundi C/E Cambodia A/C/G Cameroon C/E Canada A/B Canary Islands C/E/L Cape Verde C/F Cayman Islands A/B 137
- 138. Central African Republic C/E Chad D/E/F Channel Islands C/G Chile C/L China, People's Republic of A/I/G Colombia A/B Comoros C/E Congo, People's Rep. of C/E Congo, Dem. Rep. of (formerly C/D Zaire) Cook Islands I Costa Rica A/B Côte d'Ivoire C/E (Ivory Coast) Croatia C/F Cuba A/B/C/L Cyprus G / F*** Czech Republic E Denmark C/K Djibouti C/E Dominica D/G Dominican Republic A/B East Timor C/E/F/I Ecuador A/B Egypt C El Salvador A/B/C/D/E/F/G/I/J/L Equatorial Guinea C/E Eritrea C Estonia F Ethiopia C/F Faeroe Islands C/K Falkland Islands G Fiji I Finland C/F France E French Guyana C/D/E Gabon C Gambia G Gaza H 138
- 139. Georgia C Germany C/F Ghana D/G Gibraltar C/G Greece C/F Greenland C/K Grenada (Windward Islands) G Guadeloupe C/D/E Guam A/B Guatemala A/B/G/I Guinea C/F/K Guinea-Bissau C Guyana A/B/D/G Haiti A/B Honduras A/B Hong Kong D/M/G Hungary C/F Iceland C/F India C/D/M Indonesia C/F/G Iran C/F Iraq C/D/G Ireland (Eire) G Isle of Man C/G Israel H/C Italy F/L Jamaica A/B Japan A/B Jordan B/C/D/F/G/J Kenya G Kazakhstan C Kiribati I Korea, South C/F Kuwait C/G Kyrgyzstan C Laos A/B/C/E/F Latvia C/F Lebanon A/B/C/D/G Lesotho M 139
- 140. Liberia A/B Libya D Liechtenstein J Lithuania C/E Luxembourg C/F Macau D/G Macedonia C/F Madagascar C/D/E/J/K Madeira C/F Malawi G Malaysia G Maldives A/D/G/J/K/L Mali C/E Malta G Martinique C/D/E Mauritania C Mauritius C/G Mexico A Micronesia, Federal States of A / B Moldova C Monaco C/D/E/F Mongolia C/E Montserrat (Leeward Islands) A / B Morocco C/E Mozambique C/F/M Myanmar (formerly Burma) C/D/F/G Namibia D/M Nauru I Nepal C/D/M Netherlands C/F Netherlands Antilles A/B/F New Caledonia F New Zealand I Nicaragua A Niger A/B/C/D/E/F Nigeria D/G Norway C/F Oman C/G Pakistan C/D 140
- 141. Palau A/B Panama A/B Papua New Guinea I Paraguay C Peru A/B/C Philippines A/B/C Poland C/E Portugal C/F Puerto Rico A/B Qatar D/G Réunion Island E Romania C/F Russian Federation C/F Rwanda C/J St. Kitts and Nevis (Leeward D/G Islands) St. Lucia (Windward Islands) G St. Vincent (Windward A/C/E/G/I/K Islands) San Marino F/L Saudi Arabia A/B/C/G Senegal C/D/E/K Serbia & Montenegro C/F Seychelles G Sierra Leone D/G Singapore G Slovakia E Slovenia C/F Somalia C South Africa M**** Spain C/F Sri Lanka D/M Sudan C/D Suriname C/F Swaziland M Sweden C/F Switzerland J Syria C/E/L Tahiti A/B/E 141
- 142. Tajikistan C/I Taiwan A/B Tanzania D/G Thailand A/C Togo C Tonga I Trinidad & Tobago A/B Tunisia C/E Turkey C/F Turkmenistan B/F Uganda G Ukraine C/F United Arab Emirates G United Kingdom G United States of America A/B Uruguay C/F/I/L Uzbekistan C/I Venezuela A/B Vietnam A/C/G Virgin Islands (British and A/B U.S.) Western Samoa I Yemen, Rep. of A/D/G Zambia C/D/G Zimbabwe D/G * Argentina has standardised on type I sockets and plugs. Type C plugs and power points are still commonly found in older buildings. ** Although many types of plugs and receptacles are used all over Brazil, only type J plugs and sockets are allowed. Type C plugs (NOT type C sockets !) are authorised as well. *** Type G plugs and sockets are used in the north as well as the south of Cyprus, whereas type F plugs and receptacles are only found in the north of the island. **** The official South African socket and plug standard is type M. Nevertheless, appliances with a type C plug are still very commonly found and used with a plug adapter. The outline map below visualises the spread of the different plug types used around the world. For easy reference, compatible plug types are represented with the same colour. 142
- 143. What do I need to use my appliances abroad ? Plug Adapters They do not convert electricity. They simply allow a dual-voltage appliance, a transformer or a converter from one country to be plugged into the wall outlet of another country. The plug of a Continental European appliance will not fit into an outlet in a foreign country without an adapter. Converters Converters and transformers both step up or down the voltage, but there is a difference in use between them. Converters should be used only with "electric" products. Electric products are simple heating devices or have mechanical motors. Examples are hair dryers, steam irons, shavers, toothbrushes or small fans. Converters are not designed for "continuous duty" and should only be used for short periods of time (1 to 2 hours). Additionally, most converters can only be used for ungrounded appliances (2 pins on the plug). Converters must be unplugged from the wall when not in use. Transformers Transformers also step up or down the voltage, but they are more expensive than converters and are used with "electronic" products. Electronic products have a chip or circuit. Examples are radios, CD or DVD players, shavers, camcorder battery rechargers, computers, computer printers, fax machines, televisions and answering machines. Transformers can also be used with electric appliances and may be operated continually for many days. The advantage of converters, however, is that they are lighter and less expensive. 143
- 144. Computers are electronic devices and therefore they must be used with a transformer, unless they are dual voltage. Fortunately, most laptop battery chargers and AC adapters are dual voltage, so they can be used with only a plug adapter for the country you will be visiting. Transformers are sold in various sizes based on how much wattage they can support. Therefore one must pay careful attention to the wattage ratings of the appliances to be plugged into a transformer. The wattage rating of the transformer must always be larger than the wattage rating of the appliance to be plugged into it (plus a 25% buffer to allow for heat build-up in the transformer or converter). When plugging multiple items into a power strip, then into the transformer, you must calculate the combined wattage of all appliances and the power strip, then add an additional 25% to that total. The appliance’s voltage and wattage requirements are listed on the manufacturer's label located on the back or at the bottom of the appliance. In some cases, the voltage and amperage will be listed, but not the wattage. If this is the case, simply multiply the voltage by the amperage rating to find the wattage rating (e.g. 230 V * 1 A = 230 W). Below is a list that gives an idea what the wattage of common appliances is. Use this as a guide only. Always check your appliance first ! • 75 watts: small, low-wattage appliances such as radios, CD players, heating pads, and some televisions. • 300 watts: larger radios, stereo consoles, electric blankets, sewing machines, hand mixers, small fans and most TV sets. • 500 watts: refrigerators, hair dryers, stand mixers, blenders and some stereo equipment. • 750 watts: projectors, some sewing machines and small electric broom type vacuums. • 1000 watts: washing machines, small heaters, some coffee makers and vacuums. • 1600 – 2000 watts: dishwashers, most appliances that have heating elements such as toasters, electric deep-frying pans, irons, and grills. • 3000 watts: heaters and air conditioners. Transformers and converters only convert the voltage, not the frequency. The difference in cycles may cause the motor in a 50 Hz appliance to operate slightly faster when used on 60 Hz electricity. This cycle difference will cause electric clocks and timing circuits to keep incorrect time: European alarm clocks will run faster on 60 Hz electricity and American clocks will lose some 10 minutes every hour when used in Europe. However, most modern electronic equipment like battery chargers, computers, printers, stereos, DVD players, etc. are usually not affected by the difference in cycles and adjust themselves accordingly the slower cycles. Why can only “electric” appliances be used with a converter, and not “electronic” ones ? The difference between a converter and a transformer lies in how the device converts voltage current. Alternating current power is supplied in alternating bursts that are in a shape called a "sine wave". To reduce 230 V to 110 V, for example, a converter chops off the sine waves in half, whereas a transformer alters the amplitude of the waves. This is a critical difference because electronic devices require a full sine wave for operation. This is why they can only operate with a transformer. Electric appliances function with either a full or a half sine wave, so they can be used with either a converter or a transformer. 144
- 145. The converter's "chopping" off of sine waves is a relatively simple and compact function. The transformer's alteration of sine waves is a relatively sophisticated function and requires more space. As a result, transformers are generally larger, heavier and much more expensive than converters. Trick to know the local voltage In case you forget to check what the local voltage is in the country you’re going to: here’s a small trick. Just take a look at the glass of an ordinary light bulb or stop at a supermarket and note what is printed on a light bulb packet ! Electrical Length - 1. Of a transmission medium, its length expressed as a multiple or submultiple of the wavelength of a periodic electromagnetic or electrical signal propagating within the medium. Note 1: The wavelength may be expressed in radians or in artificial units of angular measure, such as degrees. Note 2: In both coaxial cables and optical fibers, the velocity of propagation is approximately two-thirds that of free space. Consequently, the wavelength will be approximately two-thirds that in free space, and the electrical length, approximately 1.5 times the physical length. 2. Of a transmission medium, its physical length multiplied by the ratio of (a) the propagation time of an electrical or electromagnetic signal through the medium to (b) the propagation time of an electromagnetic wave in free space over a distance equal to the physical length of the medium in question. Note: The electrical length of a physical medium will always be greater than its physical length. For example, in coaxial cables, distributed resistances, capacitances and inductances impede the propagation of the signal. In an optical fiber, interaction of the lightwave with the materials of which the fiber is made, and fiber geometry, affect the velocity of propagation of the signal. 3. Of an antenna, the effective length of an element, usually expressed in wavelengths. Note 1: The electrical length is in general different from the physical length. Note 2: By the addition of an appropriate reactive element (capacitive or inductive), the electrical length may be made significantly shorter or longer than the physical length. Electric Field - The effect produced by the existence of an electric charge, such as an electron, ion, or proton, in the volume of space or medium that surrounds it. Note: Each of a distribution of charges contributes to the whole field at a point on the basis of superposition. A charge placed in the volume of space or in the surrounding medium has a force exerted on it. Electricity around the globe - There is no standard mains voltage throughout the world and also the frequency, i.e. the number of times the current changes direction per second, is not everywhere the same. Moreover, plug shapes, plug holes, plug sizes and sockets are also different in many countries. Those seemingly unimportant differences, however, have some unpleasant consequences. Most appliances bought overseas simply cannot be connected to the wall outlets at home. There are only two ways to solve this problem: you just cut off the original plug and replace it with the one that is standard in your country, or you buy an unhandy and ugly adapter. While it is easy to buy a plug adapter or a new "local" plug for your "foreign" appliances, in many cases this only solves half the problem, because it doesn't help with the possible voltage disparity. A 110-volt electrical appliance designed for use in North America or Japan will provide a nice fireworks display - complete with sparks and smoke - if plugged into a European socket. It goes without saying that the lack of a single voltage, frequency and globally standardised plugs entail many extra costs for manufacturers and increase the burden on the environment. For more information, see: Single-phase voltage and frequency, Electrical plugs and sockets 145
- 146. Electromagnetic Radiation (EMR) - Radiation made up of oscillating electric and magnetic fields and propagated with the speed of light. Includes gamma radiation, X-rays, ultraviolet, visible, and infrared radiation, and radar and radio waves. Electromagnetic Spectrum - The range of frequencies of electromagnetic radiation from zero to infinity. Note: The electromagnetic spectrum was, by custom and practice, formerly divided into 26 alphabetically designated bands. This usage still prevails to some degree. However, the ITU formally recognizes 12 bands, from 30 Hz to 3000 GHz. New bands, from 3 THz to 3000 THz, are under active consideration for recognition. Electromagnetic Wave (EMW) - A wave produced by the interaction of time-varying electric and magnetic fields. Electronic Mail - See e-mail. - A system that allows the sending and receiving of messages through a computer. The transmission of text messages and optional file attachments over a network. Within an enterprise, users can send mail to a single recipient or broadcast it to multiple users. Mail is sent to a simulated mailbox in the network mail server or host computer until it is examined and deleted. The mail program (e-mail client) in your computer queries the mail server every so many minutes and alerts you if new mail has arrived. Electro-Optical Intelligence (ELECTRO-OPTINT): Intelligence information other than signals intelligence derived from the optical monitoring of the electromagnetic spectrum from ultraviolet (0.01 m) through the far infrared (1000 m). E-mail - Electronic mail - A system that allows the sending and receiving of messages through a computer. The transmission of text messages and optional file attachments over a network. Within an enterprise, users can send mail to a single recipient or broadcast it to multiple users. Mail is sent to a simulated mailbox in the 146
- 147. network mail server or host computer until it is examined and deleted. The mail program (e-mail client) in your computer queries the mail server every so many minutes and alerts you if new mail has arrived. E-mail Address - A computer mailing address to which electronic mail is sent. E-mail Exploder - Synonym mail exploder, exploder. - Part of an e-mail delivery system that allows a message to be automatically and efficiently delivered to a list of addresses, thus implementing mailing lists. Emergency Video Description - Video descriptions are a way to inform people who are blind or have other vision disabilities of what is happening on the television screen. Video description is the insertion of verbal descriptions about the setting and/or action in a program when information about these visual elements is not contained in the audio portion of the program. These descriptions supplement the regular audio track of the program. Emission - 1. Electromagnetic energy propagated from a source by radiation or conduction. Note: The emission may be either desired or undesired and may occur anywhere in the electromagnetic spectrum. 2. Radiation produced, or the production of radiation, by a radio transmitting station. For example, the energy radiated by the local oscillator of a radio receiver would not be an emission but a radiation. 3. The electromagnetic energy radiated from an antenna. Emission Security - Protection resulting from measures taken to deny unauthorized persons information derived from intercept and analysis of compromising emanations from crypto-equipment or an information system (IS). [INFOSEC-99] Synonym [in INFOSEC] emissions security. Encoding - See analog encoding. The portion of the analog-to-digital conversion process that samples an analog signal and creates a digital signal that represents the value of the sample. Note: Multiple samples are needed to digitize a waveform over a time interval. Encryption - A way of making transmitted data, such as e-mails, unreadable to everyone except the receiver. If the data is intercepted by anyone as it travels over a network, it cannot be read. Only those persons that have the right type of decoding software can unscramble the message. Encryption is used to protect e- commerce and financial transactions. End Distortion - In start-stop teletypewriter operation, the shifting of the end of all marking pulses, except the stop pulse, from their proper positions in relation to the beginning of the next start pulse. Note 1: Shifting of the end of the stop pulse is a deviation in character time and rate rather than an end distortion. Note 2: Spacing end distortion is the termination of marking pulses before the proper time. Note 3: Marking end distortion is the continuation of marking pulses past the proper time. Note 4: The magnitude of the distortion is expressed as a percentage of an ideal pulse length. End Exchange - Synonym end office. - A central office at which user lines and trunks are interconnected. Synonym end exchange. End Instrument - A communication device that is connected to the terminals of a circuit. End Office (EO) - A central office at which user lines and trunks are interconnected. Synonym end exchange. End-of-Transmission-Block Character (ETB) - A transmission control character used to indicate the end of a transmission block of data when data are divided into such blocks for transmission purposes. 147
- 148. End-of-Transmission Character (EOT) - A transmission control character used to indicate the conclusion of a transmission that may have included one or more texts and any associated message headings. Note: An EOT is often used to initiate other functions, such as releasing circuits, disconnecting terminals, or placing receive terminals in a standby condition. End-to-End Signaling - The capability changeover procedure to be used whenever the normal one cannot be accomplished (i.e., in case of some failure in the signaling terminal equipment or in case of inaccessibility between the two involved signaling points). Enhanced 911 (E911) - Technology allowing 911 calls from cellular phones to be routed to the geographically correct emergency station (a.k.a. PSAP: Public Safety Answering Point). VoIP users currently have limited access to 911 services, and with some providers none, because VoIP is not geographically based. Envelope - The boundary of the family of curves obtained by varying a parameter of a wave. See figure under amplitude modulation. EO - Abbreviation for End Office - A central office at which user lines and trunks are interconnected. Synonym end exchange. EOT - Abbreviation for end-of-transmission character. EPG - Electronic Program Guide. An interactive list of upcoming TV programming that can be transmitted along with a DTV program Equilibrium Mode Distribution (EMD) - That condition in a multimode fiber wherein after propagation has taken place for a certain distance, called the " equilibrium length," the relative power distribution among modes becomes statistically constant and remains so for the course of further propagation down the fiber. Note 1: In practice, the equilibrium length may vary from a fraction of a kilometer to more than a kilometer. Note 2: After the equilibrium length has been traversed, the numerical aperture of the fiber's output is independent of the numerical aperture of the optical source, i.e., beam, that drives the fiber. This is because of mode coupling and stripping, primarily by small perturbations in the fiber's geometry which result from the manufacturing and cabling processes. Note 3: In the ray-optics analogy, the equilibrium mode distribution may be loosely thought of as a condition in which the "outermost rays" in the fiber core are stripped off by such phenomena as microbends, and only the "innermost rays" continue to propagate. In a typical 50-m core multimode graded-index fiber, light propagating under equilibrium conditions occupies essentially the middle seven-tenths of the core and has a numerical aperture approximately seven-tenths that of the full numerical aperture of the fiber. This is why in-line optical attenuators based on the principle of gap loss may be ineffective or induce a lower-than-rated loss if they are inserted near the optical receiver. To be fully effective, gap-loss attenuators should be inserted near the optical transmitter, where the core is fully filled. Synonyms equilibrium mode power distribution, steady-state condition. Erasure - [A] process intended to render magnetically stored information irretrievable by normal means. Erlang - A unit of traffic density in a telecommunications system. One erlang is the equivalent of one call (including call attempts and holding time) in a specific channel for 3600 seconds in an hour. The 3600 seconds need not be, and generally are not, in a contiguous block. In digital telecommunications, the voice signals are compressed. This makes it possible for one channel to carry numerous calls simultaneously by means of multiplexing. In theory, there are many ways in which a channel can carry a certain number of erlangs. For example, a traffic density of 3 erlangs can consist of three simultaneous calls, each lasting for an hour (a total of 10,800 seconds); it can consist of six calls, each of which are allocated 30 minutes (1800 seconds) of time during the hour; it might consist of 180 calls, each of which occupy one minute (60 seconds) of time during an hour. Smaller units of traffic density are sometimes used. The hundred or centum call 148
- 149. second or CCS is the equivalent of one call for 100 seconds out of an hour. A traffic density of 1 CCS is equal to 1/36 erlang. An erlang can be applied to the group of lines in a telephone trunk line or to the traffic in a telephone call center. The term is named after the Danish telephone engineer, A. K. Erlang, the originator of queueing theory. Error - 1. The difference between a computed, estimated, or measured value and the true, specified, or theoretically correct value. 2. A deviation from a correct value caused by a malfunction in a system or a functional unit. Note: An example of an error is the occurrence of a wrong bit caused by an equipment malfunction. Error Control - Any technique that will detect or correct errors. Error Message - In a computer or communications system, a message that indicates that an error has been made and, sometimes, the nature or type of error. Error Ratio - The ratio of the number of bits, elements, characters, or blocks incorrectly received to the total number of bits, elements, characters, or blocks sent during a specified time interval. Note: For a given communication system, the bit error ratio will be affected by both the data transmission rate and the signal power margin. Ethernet - A network link that can transmit approximately 10,000,000 bits per second. Ethernet is the most widely-installed local area network ( LAN) technology. Specified in a standard, IEEE 802.3, Ethernet was originally developed by Xerox from an earlier specification called Alohanet (for the Palo Alto Research Center Aloha network) and then developed further by Xerox, DEC, and Intel. An Ethernet LAN typically uses coaxial cable or special grades of twisted pair wires. Ethernet is also used in wireless LANs. The most commonly installed Ethernet systems are called 10BASE-T and provide transmission speeds up to 10 Mbps. Devices are connected to the cable and compete for access using a Carrier Sense Multiple Access with Collision Detection (CSMA/CD ) protocol. Fast Ethernet or 100BASE-T provides transmission speeds up to 100 megabits per second and is typically used for LAN backbone systems, supporting workstations with 10BASE-T cards. Gigabit Ethernet provides an even higher level of backbone support at 1000 megabits per second (1 gigabit or 1 billion bits per second). 10-Gigabit Ethernet provides up to 10 billion bits per second. Ethernet was named by Robert Metcalfe, one of its developers, for the passive substance called "luminiferous (light-transmitting) ether" that was once thought to pervade the universe, carrying light throughout. Ethernet was so- named to describe the way that cabling, also a passive medium, could similarly carry data everywhere throughout the network. Evaluation - Assessment of an information technology (IT) product or system against defined security-related functional and assurance criteria, performed by a combination of testing and analytic techniques. Even Parity - See parity, parity check. - A test that determines whether the number of ones or zeros in an array of binary digits is odd or even. Note: Odd parity is standard for synchronous transmission and even parity for asynchronous transmission. EWSD (Electronic Worldwide Switch Digital, or, in German, Elektronisches WaehlSystem [Digital]) - A widely-installed telephonic switch system developed by Siemens. Siemens says that EWSD performs switching for over 160 million lines in more than 100 countries. EWSD is a modular system in which some switches in the system can be installed in a telephone company's centrex facility and other switches can be located at the customer. 149
- 150. Important features of EWSD include the following: • Advanced Intelligent Network (AIN) 0.1 and 0.2 capabilities allow switching services to be added at Service Control Points, meaning that new services can be added and performed by the switching system without the customer having to buy new equipment. • In addition to AIN capabilities, EWSD provides ISDN, CLASS, SS7, and centrex services. • digital and analog lines can be combined in the same line groups, allowing full interoperability between digital and analog terminals. • Carriers using EWSD can provide Automatic Call Distributor services for customers with call centers. • EWSD provides both Bellcore AIN 0.2 and Global System for Mobile (GSM) communications for personal communications services. Line types supported include single or two-party analog, coin, TR08, and ISDN Basic Rate Interface. Unidirectional Digital Subscriber Line (DSL) support is planned. Any line type can be added by simply changing the line card. Exchange - A geographic area established by a telephone company for specifying the local telephone service area. Exchange Access - In telephone networks, access in which exchange services are provided for originating or terminating interexchange telecommunications within the exchange area. Exchange Area - A geographic area served by one or more central offices within which local telephone service is furnished under regulation. Exchange Transmission Plant - This is a combination of (a) exchange cable and wire facilities (b) exchange central office circuit equipment, including associated land and buildings and (c) information origination/termination equipment which forms a complete channel. Expander - A device that restores the dynamic range of a compressed signal to its original dynamic range. Exploder - Synonym mail exploder. - Part of an e-mail delivery system that allows a message to be automatically and efficiently delivered to a list of addresses, thus implementing mailing lists. Exposure - In INFOSEC, the potential compromise associated with an attack exploiting a corresponding vulnerability. Extension - A catch-all term that describes additional phones attached to a single line (as in a residence or small office) or a station of a Key system or PBX. F Facet Erosion - In laser diodes, a phenomenon in which a high field intensity of stimulated optical radiation causes degradation of the facets, i.e., those forming the cavity mirrors, decreasing reflectivity and resulting in a decrease of the internal quantum efficiency and an increase in the threshold current. Facility - 1. A fixed, mobile, or transportable structure, including (a) all installed electrical and electronic wiring, cabling, and equipment and (b) all supporting structures, such as utility, ground network, and electrical supporting structures. 2. A network-provided service to users or the network operating administration. 3. A transmission pathway and associated equipment. 4. In a protocol applicable to a data unit, such as a block or frame, an additional item of information or a constraint encoded within the protocol 150
- 151. to provide the required control. 5. A real property entity consisting of one or more of the following: a building, a structure, a utility system, pavement, and underlying land. Facility Assembly - A group of interconnected equipment and transmission media uniquely identified and dedicated to a specific type of service. Facility Code - A two- digit code (FC) used in the exchange - carrier -to- interexchange carrier (EC-to- IC ) facility / service selective signaling protocol and the IC-to-EC facility/service selective signaling protocol that identifies the type of facility requested. Facility Grounding System - The electrically interconnected system of conductors and conductive elements that (a) provides multiple current paths to the earth electrode subsystem, and (b) consists of the earth electrode subsystem, the lightning protection subsystem, and the fault protection subsystem. Facility Group - The particular group of facilities to route the call. Facility Group Member - The specific member of a trunk group or a multi-line hunt group. Facsimile - (FACSimile) Originally called "telecopying," it is the communication of a printed page between remote locations. Fax machines scan a paper form and transmit a coded image over the telephone system. The receiving machine prints a facsimile of the original. A fax machine is made up of a scanner, printer and modem with fax signaling. (see Fax) Fax standards were developed starting in 1968 and are classified by Groups. Groups 1 and 2, used until the late 1980s, transmitted a page in six and three minutes respectively. Group 3 transmits at less than one minute per page and uses data compression at 9,600 bps. The Group 3 speed increase led to the extraordinary rise in usage in the late 1980s. Group 3 resolution is 203x98 dpi in standard mode, 203x196 in fine mode and 203x392 in super fine mode. Group 3 is still the standard today, but Group 4 machines can transmit a page in just a few seconds and provide up to 400x400 resolution. Group 4 requires 56 to 64 Kbps bandwidth and needs ISDN or Switched 56 circuits. See fax/modem and e-mail. Facsimile Converter - 1. In a facsimile receiver, a device that changes the signal modulation from frequency- shift keying (FSK) to amplitude modulation (AM). 2. In a facsimile transmitter, a device that changes the signal modulation from amplitude modulation (AM) to frequency-shift keying (FSK). Facsimile Frequency Shift - At any point in a frequency-shift facsimile system, the numerical difference between the frequency that corresponds to a white signal and the frequency that corresponds to a black signal. Facsimile Picture Signal - In facsimile systems, the baseband signal that results from the scanning process. Facsimile Receiver - In a facsimile system, the equipment that converts the facsimile picture signal into a recorded copy. Facsimile Recorder - In a facsimile receiver, the device that performs the final conversion of the facsimile picture signal to an image of the object, i.e., makes the recorded copy. 151
- 152. Facsimile Signal Level - In a facsimile system, the signal level at any point in the system. Note 1: The facsimile signal level is used to establish the operating levels. Note 2: The facsimile signal level is usually expressed in dB with respect to some standard value, such as 1 mW (milliwatt), i.e., 0 dBm. Facsimile Transceiver - In a facsimile system, the equipment that sends and receives facsimile signals. Note: Full-duplex facsimile transceivers can send and receive at the same time; half-duplex facsimile transceivers cannot. Facsimile Transmitter - In a facsimile system, the equipment that converts the baseband picture signals, i.e., the baseband signals resulting from scanning the object, into signals suitable for transmission by a communications system. Fade - 1. In signal propagation, see fading. 2. In video, the act of dissolving a video picture to either a color, pattern, or titles. Note: Fading a video image is often used as an artistic tool in video productions, usually seen as a fade to black. 3. In audio, a decrease in the sound level until it is no longer audible. Fade Margin - 1. A design allowance that provides for sufficient system gain or sensitivity to accommodate expected fading, for the purpose of ensuring that the required quality of service is maintained. 2. The amount by which a received signal level may be reduced without causing system performance to fall below a specified threshold value. Synonym fading margin. Fading - In a received signal, the variation (with time ) of the amplitude or relative phase, or both, of one or more of the frequency components of the signal. Note: Fading is caused by changes in the characteristics of the propagation path with time. Fading Distribution - The probability distribution that signal fading will exceed a given value relative to a specified reference level. Note 1: In the case of phase interference fading, the time distribution of the instantaneous field strength usually approximates a Rayleigh distribution when several signal components of equal amplitude are present. Note 2: The field strength is usually measured in volts per meter. Note 3: The fading distribution may also be measured in terms of power level, where the unit of measure is usually watts per square meter and the expression is in dB. Fading Margin - Synonym fade margin. 1. A design allowance that provides for sufficient system gain or sensitivity to accommodate expected fading, for the purpose of ensuring that the required quality of service is maintained. 2. The amount by which a received signal level may be reduced without causing system performance to fall below a specified threshold value. Fail - See failure, graceful degradation. The temporary or permanent termination of the ability of an entity to perform its required function. Fail Safe - 1. Of a device, the capability to fail without detriment to other devices or danger to personnel. 2. Pertaining to the automatic protection of programs and/or processing systems to maintain safety when a hardware or software failure is detected in a system. 3. The automatic protection of programs and/or processing systems when hardware or software failure is detected. 4. Pertaining to the structuring of a system such that either it cannot fail to accomplish its assigned mission regardless of environmental factors or that the probability of such failure is extremely low Fail-Safe Operation - 1. Operation that ensures that a failure of equipment, process, or system does not propagate beyond the immediate environs of the failing entity. 2. A control operation or function that prevents improper system functioning or catastrophic degradation in the event of circuit malfunction or operator error. 152
- 153. Fail Soft - The selective termination of affected nonessential processing, when hardware or software failure is determined to be imminent. Failure - The temporary or permanent termination of the ability of an entity to perform its required function. Failure Access - An Unauthorized access to data resulting from a hardware or software failure. Failure Control - The methods used to detect imminent hardware or software failure and provide fail safe or fail soft recovery. Fair Queuing - The controlling of congestion in gateways by restricting every host to an equal share of gateway bandwidth. Note: Fair queuing does not distinguish between small and large hosts or between hosts with few active connections and those with many. Fake Sector - In information assurance, a sector consisting of a header but no data, used in large numbers on a diskette to cause an unauthorized copying program to fail to copy the diskette. Fall Time - The time required for the amplitude of a pulse to decrease (fall) from a specified value (usually 90 percent of the peak value exclusive of overshoot or undershoot ) to another specified value (usually 10 percent of the peak value exclusive of overshoot or undershoot). Note: Limits on undershoot and oscillation, i.e., hunting, may need to be specified when specifying fall time limits. Synonym pulse decay time. False Character - See illegal character. A character, or a combination of bits, that is not valid in a given system according to specified criteria, such as with respect to a specified alphabet, a particular pattern of bits, a rule of formation, or a check code. False Clock - A condition where a phase-locked loop controlling a clock locks on a frequency other than the correct frequency. Note 1: False clock can occur when there is excessive phase shift, as a function of frequency, in the loop. Note 2: False clock often occurs where the false frequency is a harmonic of the correct frequency. False Lock - A condition where a phase-locked loop locks to a frequency other than the correct one, or to an improper phase. Fan-Beam Antenna - A directional antenna producing a main beam having a large ratio of major to minor dimension at any transverse cross section. Fan Out - Synonym break out. To separate the individual fibers or buffer tubes of a fiber-optic cable for the purpose of splicing or installing optical connectors. Fanout Cable - Synonym breakout cable. A multifiber fiber -optic cable design in which individual fibers, usually tight-buffered, are surrounded by separate strength members and jackets, which are in turn enveloped by a common jacket. Note 1: The breakout cable facilitates easy installation of fiber-optic connectors. All that need be done to prepare the ends of the cable to receive connectors is to remove the outer jacket, exposing what are essentially individual single-fiber cables. Note 2: Because it tends to induce bends in the fibers, the breakout cable design usually results in slightly higher transmission losses, for a given fiber, than loose- buffer designs. FAQ - An acronym for Frequently Asked Questions. FAQs are online documents that list and answer the most common questions on a particular subject. 153
- 154. FAQ File - Abbreviation for Frequently Asked Questions file. An online file that contains frequently asked questions with answers provided to assist new users and avoid repetitive offline inquiries. Note: An FAQ file is usually created for Internet news groups, but is also used in other applications. Faraday Effect - A magneto-optic effect in which the polarization plane of an electromagnetic wave is rotated under the influence of a magnetic field parallel to the direction of propagation. Note: The Faraday effect may be used to modulate a lightwave. Far-End Block Error (FEBE) - An indication returned to a transmitting node (source) that an errored block has been detected at the receiving node (sink). Far-End Crosstalk - Crosstalk that is propagated in a disturbed channel in the same direction as the propagation of a signal in the disturbing channel. Note: The terminals of the disturbed channel, at which the far-end crosstalk is present, and the energized terminals of the disturbing channel, are usually remote from each other. Far-End Customer Interface - An associated, loop signaling, customer installation located at the far end of the network transmission path from the network interface (NI) described in the designated document. Far-End receive Failure (FERF) - An indication returned to a transmitting link terminating equipment (LTE) upon receipt of a line AIS ( alarm indication signal ) code or detection of an incoming line failure at the receiving LTE. Far Field - Synonym far-field region. The region where the angular field distribution is essentially independent of distance from the source. Note 1: If the source has a maximum overall dimension D that is large compared to the wavelength, the far-field region is commonly taken to exist at distances greater than 2 2D / from the source, being the wavelength. Note 2: For a beam focused at infinity, the far-field region is sometimes referred to as the Fraunhofer region. Synonyms far field, far zone, Fraunhofer region, radiation field. Far-Field Region - The region where the angular field distribution is essentially independent of distance from the source. Note 1: If the source has a maximum overall dimension D that is large compared to the 2 wavelength, the far-field region is commonly taken to exist at distances greater than 2D / from the source, being the wavelength. Note 2: For a beam focused at infinity, the far-field region is sometimes referred to as the Fraunhofer region. Synonyms far field, far zone, Fraunhofer region, radiation field. Far-Field Diffraction Pattern - The diffraction pattern of a source (such as an LED, ILD, or the output end of an optical fiber ) observed at an infinite distance from the source. Note 1: A far- field pattern exists at distances that are large compared with s 2 / , where s is a characteristic dimension of the source and is the wavelength. For example, if the source is a uniformly illuminated circle, then s is the radius of the circle. Note 2: The far-field diffraction pattern of a source may be observed at infinity or (except for scale) in the focal plane of a well-corrected lens. The far-field pattern of a diffracting screen illuminated by a point source may be observed in the image plane of the source. Synonym Fraunhofer diffraction pattern. Far-Field Radiation Pattern - A radiation pattern measured at the far field of an antenna or other emitter. Far-Field Region - The region where the angular field distribution is essentially independent of distance from the source. Note 1: If the source has a maximum overall dimension D that is large compared to the 2 wavelength, the far-field region is commonly taken to exist at distances greater than 2D / from the source, being the wavelength. Note 2: For a beam focused at infinity, the far-field region is sometimes referred to as the Fraunhofer region. Synonyms far field, far zone, Fraunhofer region, radiation field. 154
- 155. Far Zone - Synonym far-field region. - The region where the angular field distribution is essentially independent of distance from the source. Note 1: If the source has a maximum overall dimension D that is large compared to the wavelength, the far-field region is commonly taken to exist at distances greater than 2 2D / from the source, being the wavelength. Note 2: For a beam focused at infinity, the far-field region is sometimes referred to as the Fraunhofer region. Synonyms far field, far zone, Fraunhofer region, radiation field. Fast Packet Switching - A packet switching technique that increases the throughput by eliminating overhead. Note 1: Overhead reduction is accomplished by allocating flow control and error correction functions to either the user applications or the network nodes that interface with the user. Note 2: Cell relay and frame relay are two implementations of fast packet switching. Fast Select - An optional user facility in the virtual call service of CCITT X.25 protocol (now, ITU-T X.25 protocol) that allows the inclusion of user data in the call request/connected and clear indication packets. Note: Fast select is an essential feature of the CCITT X.25 (1984) protocol. Fat Client - A client -centric computing model where software must be installed on each client in a network . This often requires that each client computer be upgraded to the same level. Fault - 1. An accidental condition that causes a functional unit to fail to perform its required function. 2. A defect that causes a reproducible or catastrophic malfunction. Note: A malfunction is considered reproducible if it occurs consistently under the same circumstances. 3. In power systems, an unintentional short-circuit, or partial short-circuit, between energized conductors or between an energized conductor and ground. Fault Management - In network management, the set of functions that (a) detect, isolate, and correct malfunctions in a telecommunications network, (b) compensate for environmental changes, and (c) include maintaining and examining error logs, accepting and acting on error detection notifications, tracing and identifying faults, carrying out sequences of diagnostics tests, correcting faults, reporting error conditions, and localizing and tracing faults by examining and manipulating database information. Fault Protection Subsystem - In a facility power distribution system, the subsystem that provides a direct path from each power sink to the earth electrode subsystem . Note: The fault protection subsystem is usually referred to as a "green wire." Fault Tolerance - The extent to which a functional unit will continue to operate at a defined performance level even though one or more of its components are malfunctioning. Fax Tone Detection -This feature, when activated, tells fax switch to detect the presence of CNG/fax tones which may be transmitted by a calling fax machine or PC Fax card. All calls accompanied by CNG tones, whether they be from a fax machine or PC Fax card, are routed through to equipment connected to the device port labeled FAX. If no fax-type equipment is used on fax switch, simply deactivate this feature. Fax (Telecopying) - The telephonic transmission of scanned-in printed material (text or images), usually to a telephone number associated with a printer or other output device. The original document is scanned with a fax machine, which treats the contents (text or images) as a single fixed graphic image, converting it into a bitmap. In this digital form, the information is transmitted as electrical signals through the telephone system. The receiving fax machine reconverts the coded image and prints a paper copy of the document. Almost all modems manufactured today are capable of sending and receiving fax data. Fax/modem software generates fax signals directly from disk files or the screen. Even if a document is text only, it is treated by the 155
- 156. computer as a scanned image and is transmitted to the receiver as a bitmap. Faxing a message online works well if the recipient wants only to read the message. However, if the document requires editing, it must be converted into ASCII text by an OCR (optical character recognition) program, or it must be retyped manually into the computer. A more efficient method of sending documents that require modification is through the e-mail system. E-mail files are already ASCII text so they can be edited immediately in any text editor or word processing program. The Internet now provides a new and cheaper way to send faxes in some cases. A number of free and commercial companies provide arrangements for using the Internet rather than the public telephone system for most or part of the path to the fax point. Some services also provide the ability to broadcast a fax to multiple addresses. Acronym for facsimile. Fax Board - Fax capability built onto a printed circuit board. Today, most fax boards are fax/modems, which also provide data transmission. See fax/modem. Fax Group - An encoding format used for fax transmission. There are two types: Fax Group 3, also known as G3, and Fax Group 4, also known as G4. Fax Group 3 and 4 are two of the encoding formats for Tagged Image File Format (TIFF) files. The more commonly used format, Fax Group 3, is Recommendation T.4 of the CCIT, now known as the ITU-T (for Telecommunication Standardization Sector of the International Telecommunications Union). Fax Group 3 supports one-dimensional image compression of black and white images, On a standard fax machine, Fax Group 3 uses redundancy reduction to enhance speed and is able to transmit a page in one minute or less. Fax Group 3 can achieve compression ratios of 10:1 for office documents and 15:1 for engineering drawings with a resolution of 200 dots per inch (dpi). Less frequently used, Fax Group 4 (G4) is ITU-T Recommendation T.6 and supports two-dimensional image compression, compressing the line width as well as the line length. Fax Group 4 can achieve compression ratios of 15:1 for office documents and 20:1 for engineering drawings with a resolution of 400 dpi. Unlike Fax Group 3, Fax Group 4 can use Integrated Services Digital Network (ISDN) for transmission. Fax Logger - Automatically storing copies of incoming and outgoing faxes onto some storage medium. Fax Machine (Facsimile) - A device that attaches to your telephone line and is capable of scanning a document, electronically transmitting and receiving the image, and printing the image(sometimes called "TELEFAX" or "TELECOPIER") Fax/Modem - A combination fax board and data modem available as an external unit that plugs into the serial port of the computer or as an expansion board for internal installation. It includes a switch that routes the call to the fax or data modem. Incoming faxes are printed on the computer's printer. Most all modems today are fax/modems. A fax/modem requires software that generates the fax transmission from typed-in text, a disk file or from a screen image. Fax/modems often transmit a sharper image than a fax machine, which obtains its source material by scanning the page. Group 3 fax/modems provide various levels of processing based upon their service class. Class 1 devices perform basic handshaking and data conversion and are the most flexible, because much of the work is done by the computer's CPU. Class 2 devices establish and end the call and perform error checking. There are a variety of de facto Class 2 implementations and one Class 2.0 standard. As PCs have become more powerful, future service classes with more features are unlikely. Fax Modem Switch - A device that allows a single phone line to be shared for a fax machine and a modem. When a call comes in and it is a fax call, the call is automatically routed to the fax machine or fax.modem. If 156
- 157. the call is a modem call, it is routed to the correct modem.. Some devices handle voice, fax and data modem switching. May require a security access code (SAC) in the dialing string to automatically switch to the modem. Fax over Internet Protocol (FoIP) - The fax counterpart to VoIP, available from some providers either free or at additional cost. FoIP is actually more reliable than VoIP because of its tolerance for poor latency. Fax Phone Switch - A device that tests a phone line for a fax signal and routes the call to the fax machine. When a fax machine dials a number and the line answers, it emits an 1100Hz signal (CNG tone) to identify itself. Tone Detection Fax Phone Switches listen for this signal and if present, automatically routes the call to a fax machine, fax modem or fax printer. Calls without the fax tones are automatically routes to phones or phone system. Some devices handle voice, fax and data modem switching and may require keying in a security access code (SAC) to switch to the modem. Distinctive Ring Fax Phone Switches use a phone company feature called distinctive ring to route the calls instead of using tones. See CNG tone. Synonyms Automatic Fax Switch , Fax Switch , Phone Fax Switch , Fax Modem Switch. For more info see Fax Switch. Fax Server - A computer in a network that provides a bank of fax/modems, allowing users to fax out and remote users to fax in over the next available modem. The fax server may be a dedicated machine or implemented on a file server that is providing other services. A fax server (or faxserver) is a system installed in a local area network (LAN) server that allows computer users who are attached to the LAN to send and receive fax messages. Fax messages can be stored as printable word processing, graphics, database, or spreadsheet files. Scanned documents can be sent as fax messages, allowing a computer and scanner to effectively emulate a dedicated fax machine. A fax server is composed of a computer with a fax program, a fax modem (a modem capable of sending and receiving fax signals as well as conventional Internet data), a connection to the Internet or a telephone line, and connections to the LAN users. There are several advantages to a fax server when compared with an ordinary fax machine. A single fax server can emulate multiple fax machines (one for each network user), thereby reducing overhead. Some functions can be automated. For example, a business fax server can automatically send invoices and purchase orders to customers and suppliers at specified times. Received faxes can be automatically stored as files on the server, and retrieved later by network users. In addition, a fax server can function without paper, reducing clutter and eliminating the need to continually check paper trays. The term "fax server" is sometimes used to describe a program that enables a computer to send and receive fax messages. Fax Switch - A device that analyses incoming phone calls for a fax signal and routes the call to the fax machine. When a fax machine dials a number and the line answers, it emits an 1100Hz signal (CNG tone) to identify itself. A tone detection fax switch listens for these CNG tones and if present, routes the call to the fax device. Another type of fax switch is a distinctive ring fax switch, which is a device that tests a phone line for a distinctive ring signal and routes the call to a specific device (example: phone, phone system, answering machine, fax machine. fax modem). For more info see Distinctive Ring Definition and Use. Some devices handle voice, fax and data modem switching and may require keying in a security access code (SAC) to switch to the modem. See CNG tone. For more info see Fax Switch. Fax Switches - Fax Switches test a phone line for a fax signal and routes the call to the fax machine. When a fax machine dials a number and the line answers, it emits an 1100Hz signal (CNG tone) to identify itself. Some devices handle voice, fax and data modem switching and may require keying in a security access code (SAC) to switch to the modem. See CNG tone. For more info see Fax Switches. 157
- 158. Fax Tone Detection-This feature, when activated, tells automatic call processors and fax switches to detect the presence of CNG/fax tones which may be transmitted by a calling fax machine or PC Fax card. All calls accompanied by CNG tones, whether they be from a fax machine or PC Fax card, are routed through to equipment connected to the device port labeled FAX. If no fax-type equipment is used on the line sharing device, simply deactivate this feature. Typically with most line sharing equipment the factory preset is "on". FC - Abbreviation for functional component. - In intelligent networks, an elemental call -processing component that directs internal network resources to perform specific actions, such as collecting dialed digits. Note: An FC is unique to the intelligent-network-IN/2 architecture. FCC - Federal Communications Commission. The U.S. Government board made up of five presidential appointees that has the authority to regulate all non-Federal Government interstate telecommunications (including radio and television broadcasting) as well as all international communications that originate or terminate in the United States. Note: Similar authority for regulation of Federal Government telecommunications is vested in the National Telecommunications and Information Administration (NTIA). The FCC is the regulator of telephone and telecommunications services in the United States. It's not yet known the full extent to which the FCC will regulate VoIP communications. Part of the complication lies with determining the regulation of communications that begin or end on an FCC-regulated system, such as the standard telephone service. FCC Registration Program - The Federal Communications Commission program and associated directives intended to assure that all connected terminal equipment and protective circuitry will not harm the public switched telephone network or certain private line services. Note 1: The FCC registration program requires the registering of terminal equipment and protective circuitry in accordance with Subpart C of part 68, Title 47 of the Code of Federal Regulations. This includes the assignment of identification numbers to the equipment and the testing of the equipment. Note 2: The FCC registration program contains no requirement that accepted terminal equipment be compatible with, or function with, the network. FCS - Abbreviation for frame check sequence. See cyclic redundancy check. 1. An error - detection scheme that (a) uses parity bits generated by polynomial encoding of digital signals, (b) appends those parity bits to the digital signal, and (c) uses decoding algorithms that detect errors in the received digital signal. Note: Error correction, if required, may be accomplished through the use of an automatic repeat-request ( ARQ ) system. 2. An error checking mechanism that checks data integrity by computing a polynomial algorithm based checksum. FDDI - Abbreviation for fiber distributed data interface. A concept, defined in ANSI standards, for an optical- fiber -based token-ring network, featuring (a) dual counter-rotating logical rings, each with a data transmission capacity of 100 Mb/s, (b) reliable data transfer , (c) active link monitoring, (d) station management, and (e) survivability features. Note 1: The four standards are (a) ANSI X3T9.5, containing Physical Media Dependent (PMD) specifications, (b) ANSI X3T9.5, containing the Physical (PHY) specifications, (c) ANSI X3.139, containing Media Access Control ( MAC ) specifications, and (d) ANSI X39.5, containing the Station Management (SMT) specifications. Note 2: The data rate of an FDDI ring may be doubled to 200 Mb/s, with loss of redundancy. Note 3: FDDI-2 , a second- generation FDDI network standard, is under development. FDDI-2: See fiber distributed data interface. FDDI-2, a second-generation FDDI network standard, is under development. FDHM - See full width at half maximum. An expression of the extent of a function, given by the difference between the two extreme values of the independent variable at which the dependent variable is equal to half of its maximum value. Note 1: FWHM is applied to such phenomena as the duration of pulse waveforms 158
- 159. and the spectral width of sources used for optical communications . Note 2: The term full duration at half maximum ( FDHM ) is preferred when the independent variable is time. FDM - Abbreviation for frequency-division multiplexing. The deriving of two or more simultaneous, continuous channels from a transmission medium by assigning a separate portion of the available frequency spectrum to each of the individual channels. FDMA - Abbreviation for frequency-division multiple access. The use of frequency division to provide multiple and simultaneous transmissions to a single transponder. FDX - Abbreviation for full duplex. See full-duplex (FDX) circuit, full-duplex (FDX) operation. A circuit that permits simultaneous transmission in both directions. Feature Code - A code (or codes) used to select/activate a service feature (e.g., forwarding, using two- or three-digit codes preceded by * or 1 1 or #, and which may precede subsequent digit selection). FEC - Abbreviation for forward error correction. A system of error control for data transmission wherein the receiving device has the capability to detect and correct any character or code block that contains fewer than a predetermined number of symbols in error. Note: FEC is accomplished by adding bits to each transmitted character or code block, using a predetermined algorithm. Federal Communications Commission - See FCC. The U.S. Government board made up of five presidential appointees that has the authority to regulate all non-Federal Government interstate telecommunications (including radio and television broadcasting) as well as all international communications that originate or terminate in the United States. Note: Similar authority for regulation of Federal Government telecommunications is vested in the National Telecommunications and Information Administration (NTIA). Federal Excise Tax - A 3% tax mandated by the federal government imposed on all telecommunications services including local, long distance and wireless bills. Federal Networking Council (FNC) - The body responsible for coordinating networking needs among U.S. Federal agencies. Federal Subscriber Line Charge - This is a charge paid by consumers implemented by the Federal Communications Commission (FCC). It is intended to recover some of the costs associated with a customer's local telephone line to access the interstate long distance network. It helps keep interstate long distance rates low. You pay this charge whether or not you actually make long distance calls. Federal Telecommunications System (FTS) - A switched long-distance telecommunications service formerly provided for official Federal Government use. Note: FTS has been replaced by Federal Telecommunications Service 2000 (FTS2000). Federal Telecommunications System 2000 Service - See FTS2000. The designation for a defunct Federal telecommunications contract replaced by the contract designated by the title "FTS2001." Federal Universal Service Charge – See "Universal Service Fund Surcharge" Feed - 1. To supply a signal to the input of a system, subsystem, equipment, or component, such as a transmission line or antenna. 2. A coupling device between an antenna and its transmission line. Note: A feed may consist of a distribution network or a primary radiator. 3. A transmission facility between (a) the point of origin of a signal, such as is generated in a radio or television studio, and (b) the head-end of a 159
- 160. distribution facility, such as a broadcasting station in a network. 4. Pertaining to the function of inserting one thing into another, such as in a feed horn, paper feed, card feed, and line feed. Feedback - 1. The return of a portion of the output, or processed portion of the output, of a (usually active) device to the input. Note 1: The feedback signal will have a certain magnitude and phase relationship relative to the output signal or the input signal. This relationship can be used to influence the behavior, such as the gain and stability, of the overall circuit. Note 2: If the feedback is regenerative (additive), it is called "positive feedback," which increases gain and distortion, and decreases linearity and stability. Note 3: If the feedback is degenerative (subtractive), it is called "negative feedback," which reduces the gain and distortion, and increases linearity and stability. Note 4: Feedback may occur inadvertently, and be detrimental. 2. Information returned as a response to an originating source. Feedback Path - The signal path from the input of the bit-masking block to the output of the adaptive predictor. Feeder Echo Noise - Signal distortion resulting from reflected waves in a transmission line that is many wavelengths long and mismatched at both the generator and the load ends. Feeder Link - A radio link from an Earth station at a given location to a space station, or vice versa, conveying information for a space radiocommunication service other than for the fixed-satellite service. The given location may be at a specified fixed point, or at any fixed point within specified areas. Feed-Forward Path - In the encoder, the signal path from the input of the PCM-to-uniform-PCM converter to the output of the adaptive quantizer. In the decoder, the feed-forward path is the signal path from the input of the feed-forward inverse adaptive quantizer to the output of the synchronous coding adjustment block. FEP - Abbreviation for front-end processor. A programmed-logic or stored-program device that interfaces data communication equipment with an input / output bus or memory of a data processing computer. Fermat's Principle - A principle stating that a ray of light follows the path that requires the least time to travel from one point to another, including reflections and refractions that may occur. Synonym least-time principle. Fetch Protection - 1. [An] AIS-provided restriction to prevent a program from accessing data in another user's segment of storage. 2. [An] information-system (IS) hardware-provided restriction to prevent a program from accessing data in another user's segment of storage. FET photodetector: A photodetector using photogeneration of carriers in the channel region of a field-effect transistor structure to provide photodetection with current gain. Fiber - See optical fiber. A filament of transparent dielectric material, usually glass or plastic, and usually circular in cross section, that guides light. Note 1: An optical fiber usually has a cylindrical core surrounded by, and in intimate contact with, a cladding of similar geometry. Note 2: The refractive index of the core must be slightly higher than that of the cladding for the light to be guided by the fiber. Fiber Amplifier - A device that amplifies an optical signal directly, without the need to convert it to an electrical signal, amplify it electrically, and reconvert it to an optical signal. Note 1: One type of fiber amplifier uses a doped fiber (e.g., a fiber doped with erbium), which bears the communication signal, and which is optically pumped with a laser having a high-powered continuous output at an optical frequency slightly higher than that of the communication signal. The signal is intensified by Raman amplification. Note 2: Because neither optical-electrical conversion nor electrical amplification takes place, this type of amplifier 160
- 161. is well suited for a wide variety of applications, both digital and analog. Note 3: Because this type of amplifier does not require extraordinary frequency (wavelength) control of the pumping laser, it is relatively simple. Fiber Axis - The longitudinal center of symmetry of an optical fiber, i.e., the locus of points that are determined by the centers of mechanical symmetry of the outside diameters of fiber cross sections sampled continuously along the length of the fiber. Fiber Bandwidth - See bandwidth (of an optical fiber). Fiber Buffer - See buffer. In a fiber optic communication cable, one type of component used to encapsulate one or more optical fibers for the purpose of providing such functions as mechanical isolation, protection from physical damage and fiber identification. Note: The buffer may take the form of a miniature conduit, contained within the cable and called a loose buffer, or loose buffer tube, in which one or more fibers may be enclosed, often with a lubricating gel. A tight buffer consists of a polymer coating in intimate contact with the primary coating applied to the fiber during manufacture. Fiber Cable - See fiber optic cable. A telecommunications cable in which one or more optical fibers are used as the propagation medium. Note 1: The optical fibers are surrounded by buffers, strength members, and jackets for protection, stiffness, and strength. Note 2: A fiber-optic cable may be an all-fiber cable, or contain both optical fibers and metallic conductors. One possible use for the metallic conductors is the transmission of electric power for repeaters. Synonyms optical cable, optical fiber cable. Fiber Cutoff Wavelength ( cf): See cutoff wavelength. 1. The wavelength corresponding to the cutoff frequency. 2. In an uncabled single-mode optical fiber, the wavelength greater than which a particular waveguide mode ceases to be a bound mode. Note 1: The cutoff wavelength is usually taken to be the wavelength at which the normalized frequency is equal to 2.405. Note 2: The cabled cutoff wavelength is usually considered to be a more functional parameter because it takes into consideration the effects of cabling the fiber. Fiber Dispersion - See dispersion. In optical fiber communications, the incorrect terms " multimode dispersion " and " intermodal dispersion " should not be used as synonyms for the correct term " multimode distortion." Note: In classical optics, "dispersion" is used to denote the wavelength dependence of refractive index in matter, (dn/d , where n is the refractive index and is the wavelength) caused by interaction between the matter and light. "Dispersion," as used in fiber optic communications, should not be confused with "dispersion" as used by optical lens designers. Note 5: Three types of dispersion, relating to optical fibers, are defined as follows: • material dispersion: In optical fiber communication, the wavelength dependence of the velocity of propagation (of the optical signal) on the bulk material of which the fiber is made. Note 1: Because every optical signal has a finite spectral width, material dispersion results in spreading of the signal. Note 2: Use of the redundant term " chromatic dispersion " is discouraged. Note 3: In pure silica, the basic material from which the most common telecommunication-grade fibers are made, material dispersion is minimum at wavelengths in the vicinity of 1.27 m (slightly longer in practical fibers). • profile dispersion: In an optical fiber, that dispersion attributable to the variation of refractive index contrast with wavelength. Profile dispersion is a function of the profile dispersion parameter. • waveguide dispersion: Dispersion, of importance only in single-mode fibers, caused by the dependence of the phase and group velocities on core radius, numerical aperture, and wavelength. Note 1: For circular waveguides, the dependence is on the ratio, a / , where a is the core radius and is the wavelength. Note 2: Practical single-mode fibers are designed so that material dispersion and waveguide dispersion cancel one another at the wavelength of interest. 161
- 162. Fiber Distributed Data Interface (FDDI) - A concept, defined in ANSI standards, for an optical-fiber-based token-ring network, featuring (a) dual counter-rotating logical rings, each with a data transmission capacity of 100 Mb/s, (b) reliable data transfer, (c) active link monitoring, (d) station management, and (e) survivability features. Note 1: The four standards are (a) ANSI X3T9.5, containing Physical Media Dependent (PMD) specifications, (b) ANSI X3T9.5, containing the Physical (PHY) specifications, (c) ANSI X3.139, containing Media Access Control (MAC) specifications, and (d) ANSI X39.5, containing the Station Management (SMT) specifications. Note 2: The data rate of an FDDI ring may be doubled to 200 Mb/s, with loss of redundancy. Note 3: FDDI-2, a second-generation FDDI network standard, is under development. Fiber Optic (or "optical fiber") - Refers to the medium and the technology associated with the transmission of information as light impulses along a glass or plastic wire or fiber. Fiber optic wire carries much more information than conventional copper wire and is far less subject to electromagnetic interference. Most telephone company long-distance lines are now fiber optic. Transmission on fiber optic wire requires repeating at distance intervals. The glass fiber requires more protection within an outer cable than copper. For these reasons and because the installation of any new wiring is labor-intensive, few communities yet have fiber optic wires or cables from the phone company's branch office to local customers (known as local loop). Fiber Optic Bus - See bus. One or more optical fibers that serve as a common connection for a group of related devices. Fiber Optic Cable - A telecommunications cable in which one or more optical fibers are used as the propagation medium. Note 1: The optical fibers are surrounded by buffers, strength members, and jackets for protection, stiffness, and strength. Note 2: A fiber-optic cable may be an all-fiber cable, or contain both optical fibers and metallic conductors. One possible use for the metallic conductors is the transmission of electric power for repeaters. Synonyms optical cable, optical fiber cable. Fiber Optic Isolator - See optical isolator. A device that uses a short optical transmission path to accomplish electrical isolation between elements of a circuit. Note 1: The optical path may be air or a dielectric waveguide. Note 2: The transmitting and receiving elements of a fiber optic isolator may be contained within a single compact module, for mounting, e.g., on a circuit board. Fiber Optic Link - A communications link that transmits signals by means of modulated light propagated in an optical fiber. Fiber Optics (FO): The branch of optical technology concerned with the transmission of light through fibers made of transparent materials such as glasses and plastics. Note 1: Telecommunications applications of fiber optics use flexible low-loss fibers, using a single fiber per optical path. Present-day plastic fibers have losses that are too high for telecommunications applications. Note 2: Various industrial and medical applications of fiber optics, such as endoscopes, use flexible fiber bundles in which individual fibers are spatially aligned, permitting optical relay of an image. Note 3: Some specialized industrial applications use rigid (fused) aligned fiber bundles for image transfer; such as in the fiber optics faceplates used on some cathode ray rubes (CRTs) to "flatten" the image. Fiber Pigtail - See pigtail. A short length of optical fiber that is permanently affixed to an active device, e.g., LED or laser diode, and is used to couple the device, using a splice or connector, to a longer fiber. 2. A short length of single-fiber cable, usually tight-buffered, that has an optical connector on one end and a length of exposed fiber at the other end. Note: The exposed fiber of the pigtail is then spliced to one fiber of a multifiber trunk, i.e., arterial, cable, to enable the multifiber cable to be "broken out" into individual single- fiber cables that may be connected to a patch panel or an input or output port of an optical receiver or 162
- 163. transmitter. 3. A short length of electrical conductor permanently affixed to a component, used to connect the component to another conductor. Fidelity - The degree to which a system, or a portion of a system, accurately reproduces, at its output, the essential characteristics of the signal impressed upon its input or the result of a prescribed operation on the signal impressed upon its input. FidoNet - A network designed for e-mail distribution through individual bulletin board systems rather than through Internet servers. Field - 1. The volume of influence of a physical phenomenon, expressed vectorially. 2. On a data medium or in storage, a specified area used for a particular class of data, e.g. , a group of character positions used to enter or display wage rates on a screen. 3. Defined logical data that are part of a record. 4. The elementary unit of a record that may contain a data item, a data aggregate, a pointer, or a link. 5. In an interlaced, raster -scanned video display, a partial frame, consisting of every nth scanning line of a complete frame, where n is an integer equal to the number of fields (usually two) in a complete frame. Note 1: For example, in the National Television Standards Committee (NTSC) television specification used in the United States, a single frame is composed of two fields, each of which has half the number of scanning lines in a complete frame. The scanning lines of a field are separated by twice the space between the scanning lines in the full frame. The two fields are interlaced, i.e. , a complete frame consists of the following traces, which are listed in the order of their appearance in the complete frame, but not the order in which scanning occurs: the first line of the first field, the first line of the second field, the second line of the first field, the second line of the second field, the third line of the first field, the third line of the second field, etc. , until completion of the full frame. The fields are scanned alternately, one complete field at a time. Thus, the flicker rate of the display is perceived by the eye to be twice as fast as that which would result if the complete frame were to be scanned in line-by-line order. Note 2: Not all scanning lines are necessarily applied to user information, i.e. , the graphic display. Certain scanning lines, not seen under ordinary viewing conditions, are often used for transmitting test signals that indicate the quality of the displayed video. Field-Disturbance Sensor - A restricted radiation device which establishes a radio frequency field in its vicinity and detects changes in that field resulting from the movement of persons or objects within the radio frequency field. Examples: microwave intrusion sensors; devices that use rf energy for production line counting and sensing. Field Intensity - The irradiance of an electromagnetic wave under specified conditions. Note: Field intensity is usually expressed in watts per square meter Field Strength - 1. The magnitude of an electric, magnetic, or electromagnetic field at a given point. Note: The field strength of an electromagnetic wave is usually expressed as the rms value of the electric field, in volts per meter. The field strength of a magnetic field is usually expressed in amperes per meter Synonym radio field intensity. 2. The electric field strength in the horizontal plane. Field Tag - Synonym flag. In data transmission or processing, an indicator, such as a signal, symbol, character, or digit, used for identification. Note: A flag may be a byte, word, mark, group mark, or letter that signals the occurrence of some condition or event, such as the end of a word, block, or message. Field Wire - A flexible insulated wire used in field telephone and telegraph systems. Note 1: WD-1 and WF-16 are types of field wire. Note 2: Field wire usually contains conductors and high-tensile-strength strands serving as strength members. 163
- 164. FIFO - Abbreviation for first-in first-out. A queuing discipline in which entities in a queue leave the queue in the same order in which they arrive. Note 1: Service, when available, is offered to the entity that has been in the FIFO queue the longest. Note 2: FIFO techniques are used in message switching. File - 1. The largest unit of storage structure that consists of a named collection of all occurrences in a database of records of a particular record type. 2. A set of related records treated as a unit, for example, in stock control, a file could consist of a set of invoices. File Archive - Synonym FTP archive. A collection of files that are available by using file transfer protocol (FTP). Synonym file site. File Name Extension - 1. A suffix that is preceded by a decimal (".") and that is appended to a computer file name. Note: Common filename extensions with their meanings are: .wpd = a type of word-processing document .doc = a type of word-processing document .exe = executable code or a self-extracting archive file. .gif = a graphical interchange format (graphics file) .txt = a text file. 2. Proprietary HTML tags that are recognized by a single Web browser or by those Web browsers developed by a single company. File-Oriented Applications - Applications concerned with the storage, manipulation, and exchange of information between application processes in the form of files. File Protection - 1. The execution of appropriate administrative, technical, or physical means to guard against the unauthorized access to, modification of, or deletion of a file. [After 2382-8] 2. [The] aggregate of processes and procedures designed to inhibit unauthorized access, contamination, elimination, modification, or destruction of a file or any of its contents. File Security - [A] means by which access to computer files is limited to authorized users only. File Server - 1. A high-capacity disk storage device or a computer that each computer on a network can use or access and retrieve files that can be shared among attached computers. 2. A program, running on a computer, that allows different programs, running on other computers, to access the files of that computer. File Site - Synonym FTP archive. A collection of files that are available by using file transfer protocol (FTP). File Transfer - In networking, a service to move a part or the whole of a file's content over a computer network. File Transfer, Access, and Management (FTAM) - An application's service and protocol based on the concept of virtual file store. Note: FTAM allows remote access to various levels in a file structure and provides a comprehensive set of file management capabilities. 164
- 165. File Transfer Protocol (FTP) - A common method for sending and/or receiving files between Internet sites using a login system. Publicly accessed FTP sites are often called anonymous FTPs. Fill - See bit stuffing. The insertion of noninformation bits into data. Note 1: Stuffed bits should not be confused with overhead bits. Note 2: In data transmission, bit stuffing is used for various purposes, such as for synchronizing bit streams that do not necessarily have the same or rationally related bit rates, or to fill buffers or frames. The location of the stuffing bits is communicated to the receiving end of the data link, where these extra bits are removed to return the bit streams to their original bit rates or form. Bit stuffing may be used to synchronize several channels before multiplexing or to rate-match two single channels to each other. Synonym positive justification. Fill Bit - See bit stuffing. The insertion of noninformation bits into data. Note 1: Stuffed bits should not be confused with overhead bits. Note 2: In data transmission, bit stuffing is used for various purposes, such as for synchronizing bit streams that do not necessarily have the same or rationally related bit rates, or to fill buffers or frames. The location of the stuffing bits is communicated to the receiving end of the data link, where these extra bits are removed to return the bit streams to their original bit rates or form. Bit stuffing may be used to synchronize several channels before multiplexing or to rate-match two single channels to each other. Fill Device - [A] COMSEC item used to transfer or store key in electronic form or to insert key into a crypto- equipment. Filled Cable - A cable that has a nonhygroscopic material, usually a gel, inside the jacket or sheath. Note 1: The nonhygroscopic material fills the spaces between the interior parts of the cable, preventing moisture from entering minor leaks in the sheath and migrating inside the cable. Note 2: A metallic cable, such as a coaxial cable or a metal waveguide, filled with a dielectric material, is not considered as a filled cable. Fill-in Area - The area where the coverage contour of an FM translator or booster station is within the protected contour of the associated primary station (i.e., predicted 0.5 mV/m contour for commercial Class B stations, predicted 0.7 mV/m contour for commercial Class B1 stations, and predicted 1 mV/m contour for all other classes of stations). Fill-in Signal Unit (FISU) - A signal unit that is transmitted when there are no message signal units or link status signal units to be transmitted. It contains only error control and delimitation information. FILO - Abbreviation for first-in last-out. A queuing discipline in which entities in a queue leave the queue in the reverse order from that in which they arrived. Note: An understanding of FILO techniques is important in the understanding of store-and-forward capabilities in packing switching. Filter - In electronics, a device which transmits only part of the incident energy and may thereby change the spectral distribution of energy: • (a) high pass filters transmit energy above a certain frequency; • (b) low pass filters transmit energy below a certain frequency; • (c) band pass filters transmit energy of a certain bandwidth; • (d) band stop filters transmit energy outside a specific frequency band Filtered Symmetric Differential Phase-Shift Keying (FSDPSK) - A method of encoding information for digital transmission in which (a) a binary 0 is encoded as a +90° change in the carrier phase and a binary 1 is encoded as a -90° change in the carrier phase, and (b) abrupt phase transitions are smoothed by filtering or other functionally equivalent pulse shaping techniques. 165
- 166. Final Trunk Group - A last-choice trunk group that receives overflow traffic, may receive first-route traffic and for which there is no alternate route. There are various types of final trunk groups, differentiated by the type of traffic that they carry. Finger - A computer-operating-system command for accessing limited network-user-account information. Note: Finger is limited to providing information such as the full name of the account holder and address information, intentionally made public by the account holder. Finger is also used to establish the existence of an address and to discover whether or not the account is currently logged on. Finished Call - 1. In an information transaction, a call in which the call originator or call receiver terminates the communication and goes on hook, i.e., hangs up. 2. In an information transfer transaction, the termination of the information transfer phase. FIP - Acronym for Federal Information Processing. FIP Equipment - In the Federal government, any equipment or interconnected system or subsystems of equipment (as defined in 41CFR) used in the automatic acquisition, storage, manipulation, management, movement, control, display, switching, interchange, transmission, or reception of data or information. FIP System - In the Federal government, any organized combination of FIP equipment, software, services, support services, or related supplies. FIREFLY - [A] key management protocol based on public key cryptography. Firewall - 1. A computer that (a) acts as an interface between two networks ( e.g., the Internet and an private network, respectively), and (b) regulates traffic between those networks for the purpose of protecting the internal network from electronic attacks originating from the external network. The firewall is capable of handling the following tasks: (a) isolating internal and external traffic (a bridge service ); (b) making internal addresses invisible and directly unaccessible from outside and passing through authorized traffic after proper checking (a proxy service); (c) facilitating protected (encrypted) connections to cooperative parties over public networks (a tunneling service); (d) filtering outgoing traffic for security and network usage rules (filtering or monitoring service); (e) filtering incoming traffic for rogue data (viruses, spam, inappropriate data (filtering), or improper actions ( port scanning, overload prevention, etc. ; (f) blocking forbidden external services or addresses (blocking, "network nanny"-functions); (g) providing log -in services for authorized outside users and simulating the approved outside user as an inside user (proxy, log- in server ); (h) caching network traffic (cache service); (i) converting between different network protocols on different protocol levels (bridge when handling lower level protocols, gateway when handling higher level protocols); (j) traffic diverting ( e.g., for cost optimizing, accounting, network planning, monitoring); (k)providing consistent, open entry to the internal network ( portal service) and facilitating public network address and connection sharing (proxy service). 2. A system designed to defend against unauthorized access to or from a private network. Firewalls can be implemented in both hardware and software, or a combination of both. Firmware - 1. Software that is embedded in a hardware device that allows reading and executing the software, but does not allow modification, e.g., writing or deleting data by an end user. Note 1: An example of firmware is a computer program in a read-only memory ( ROM ) integrated circuit chip. A hardware configuration is usually used to represent the software. Note 2: Another example of firmware is a program embedded in an erasable programmable read-only memory (EPROM) chip, which program may be modified by special external hardware, but not by an application program. 2. A program recorded in permanent or semipermanent computer memory. 166
- 167. First-In First-Out (FIFO) - A queuing discipline in which entities in a queue leave the queue in the same order in which they arrive. Note 1: Service, when available, is offered to the entity that has been in the FIFO queue the longest. Note 2: FIFO techniques are used in message switching. First-In Last-Out (FILO) - A queuing discipline in which entities in a queue leave the queue in the reverse order from that in which they arrived. Note: An understanding of FILO techniques is important in the understanding of store-and-forward capabilities in packing switching. First-Route Traffic - Traffic that has not been route-advanced at any switching system. First Window - Of silica-based optical fibers, the transmission window at approximately 830 to 850 nm. FISINT - Acronym for foreign instrumentation signals intelligence. - 1. Intelligence information derived from electromagnetic emissions associated with the testing and operational deployment of foreign aerospace, surface, and subsurface systems. 2. Technical information and intelligence information derived from the intercept of foreign instrumentation signals by other than the intended recipients. Foreign instrumentation signals intelligence is a category of signals intelligence. Note: Foreign instrumentation signals include but are not limited to signals from telemetry, beaconry, electronic interrogators, tracking/fusing/ arming/firing command systems, and video data links. Five-Hundred (500) Service - A telephone service that allows individuals to receive, via a single number, telephone calls in various locations (e.g., home, office, or car phone) from call originators not necessarily using the same common carrier. Fixed Access - In personal communications service ( PCS ), terminal access to a network in which there is a set relationship between a terminal and the access interface. Note: A single " identifier " serves for both the access interface and the terminal. If the terminal moves to another access interface, that terminal assumes the identity of the new interface. Fixed Attenuator - See pad. A network, of fixed resistors, that attenuates signals by a fixed amount with negligible distortion. Note: The resistive network is called an attenuator if the resistance is adjustable. Fixed Loop - A service feature that permits an attendant on an assisted call to retain connection through the attendant position for the duration of the call. Note: The attendant will usually receive a disconnect signal when the call is terminated. Fixed Microwave Auxiliary Station - A fixed station used in connection with (a) the alignment of microwave transmitting and receiving antenna systems and equipment, (b) coordination of microwave radio survey operations, and (c) cue and contact control of television pickup station operations. Fixed-Reference Modulation - Modulation in which the significant condition for any signal element is based on a fixed reference. Fixed-Satellite Service -1. A radiocommunication service between Earth stations at given positions when one or more satellites are used; the given position may be a specified fixed point or any fixed point within specified areas; in some cases this service includes satellite -to-satellite links, which may also be effected in the inter-satellite service, the fixed-satellite service may also include feeder links for other space radiocommunication services. 2. A radiocommunication service between Earth stations at given positions when one or more satellites are used; the given position may be a specified fixed point or any fixed point within specified areas; in some cases this service includes satellite-to-satellite links, which may also be 167
- 168. operated in the inter-satellite service; the fixed-satellite service may also include feeder links of other space radiocommunication services. Fixed Service (FX) - A radiocommunication service between specified fixed points. Fixed Station 1. A station in the fixed service. 2. The term "fixed station" in the fixed public or fixed public press service includes all apparatus used in rendering the authorized service at a particular location under a single instrument of authorization. Fixed Storage - Synonym read-only storage. A storage device in which the contents cannot be modified, except by a particular user, or when operating under particular conditions, e.g. , a storage device in which writing is prevented by a lockout. Fixed-Tolerance-Band Compaction - Data compaction accomplished by storing or transmitting data only when the data fall outside prescribed limits. Note: An example of fixed- tolerance - band compaction in a telemetering system is the transmission of the temperature only when the temperature is above or below preestablished threshold limits. Thus, the recipient of the transmission is to assume that the value is in the prescribed range unless a signal to the contrary occurs. Flag: In data transmission or processing, an indicator, such as a signal, symbol, character, or digit, used for identification. Note: A flag may be a byte, word, mark, group mark, or letter that signals the occurrence of some condition or event, such as the end of a word, block, or message. Synonym field tag. Flag Sequence - In data transmission or processing, a sequence of bits used to delimit, i.e. mark, the beginning and end of a frame. Note 1: An 8-bit sequence is usually used as the flag sequence; for example, the 8-bit flag sequence 01111110. Note 2: Flag sequences are used in bit-oriented protocols, such as Advanced Data Communication Control Procedures ( ADCCP ), Synchronous Data Link Control ( SDLC ), and High-Level Data Link Control ( HDLC ). Flame - To send nasty or insulting messages, usually in response to someone's having broken the rules of Internet etiquette (called netiquette ). Flash -1. A signal generated by the momentary depression of the telephone switchhook or other device. Note: A flash may be used to request additional services. 2. An on-hook signal of a defined duration, used to activate network features. Flash Card - In computer -based equipment (such as MP3 players, digital cameras, and palm-held computers), a type of memory storage device approximately the size of a matchbook, capable of recording several megabytes of (usually compressed) digitized audio files or data files. Synonym flash memory card. Flash Feature - A supplementary calling feature provided by the near-end customer interface (CI) that is activated or controlled through the use of one or more flash signals. Flash Memory Card - Synonym flash card. In computer -based equipment (such as MP3 players, digital cameras, and palm-held computers), a type of memory storage device approximately the size of a matchbook, capable of recording several megabytes of (usually compressed) digitized audio files or data files. FLASH Message - A category of precedence reserved for initial enemy contact messages or operational combat messages of extreme urgency. Brevity is mandatory. 168
- 169. Flash Signal: A loop -open signal of 300 to 1000 ms at the network interface (NI) that is generated by the network, typically under the control of the far-end customer interface (CI), to control supplementary calling features when such features are provided by the near-end CI. Flat Fading - Fading in which all frequency components of a received radio signal vary in the same proportion simultaneously. Flat Panel TV Sets - Thin, lightweight TV sets that can be hung on a wall. Current flat panels (also called “flat screens”) use LCD or Plasma screen technology. Flat Rate Service - Telephone service in which a single payment permits an unlimited number of local calls to be made without further charge for a specified period of time. Flat Weighting - In a noise-measuring set, a noise weighting based on an amplitude-frequency characteristic that is flat over a frequency range that must be stated. Note 1: Flat noise power is expressed in dBrn (f1- f2) or in dBm (f1- f2). Note 2: "3-kHz flat weighting" and "15-kHz flat weighting" are based on amplitude- frequency characteristics that are flat between 30 Hz and the frequency indicated. Flaw - 1. In computer security, an error of commission, an omission, or an oversight that allows protection mechanisms to be bypassed or disabled. 2. An error of commission, omission, or oversight in an information system (IS) that may allow protection mechanisms to be bypassed. Synonym loophole. Flaw Hypothesis Methodology - System analysis and penetration technique in which the specification and documentation for an information system (IS) are analyzed to produce a list of hypothetical flaws. This list is prioritized on the basis of the estimated probability that a flaw exists, on the ease of exploiting it, and on the extent of control or compromise it would provide. The prioritized list is used to perform penetration testing of a system. F layer - See F region. That portion of the ionosphere existing between approximately 160 and 400 km above the surface of the Earth, consisting of layers of increased free-electron density caused by the ionizing effect of solar radiation. Note 1: The F region reflects normal- incident frequencies at or below the critical frequency (approximately 10 MHz ) and partially absorbs waves of higher frequency. Note 2: The F 1 layer exists from about 160 to 250 km above the surface of the Earth and only during daylight hours. Though fairly regular in its characteristics, it is not observable everywhere or on all days. The principal reflecting layer during the summer for paths of 2,000 to 3,500 km is the F 1 layer. The F 1 layer has approximately 5 × 10 5 e/cm 3 (free electrons per cubic centimeter) at noontime and minimum sunspot activity, and increases to roughly 2 × 10 6 e/cm 3 during maximum sunspot activity. The density falls off to below 10 4 e/cm 3 at night. Note 3: The F 1 layer merges into the F 2 layer at night. Note 4: The F 2 layer exists from about 250 to 400 km above the surface of the Earth. The F 2 layer is the principal reflecting layer for HF communications during both day and night. The horizon-limited distance for one- hop F 2 propagation is usually around 4,000 km. The F 2 layer has about 10 6 e/cm 3 . However, variations are usually large, irregular, and particularly pronounced during magnetic storms. Fleming's Rule - A rule stating that if the thumb of the right hand points in the direction of an electric current, then the curled fingers point in the direction of the magnetic field that encircles the current; and further, if the curled fingers of the right hand describe the electric current in a solenoid, then the thumb points in the direction of the magnetic field inside the solenoid. Synonym right-hand rule. Flexible Disk - Synonym diskette. In computer technology, a small disk of flexible plastic, coated with a magnetizable material and enclosed in a protective jacket, used to store digital data. Note: A diskette is distinguished from a hard disk by virtue of the fact that it is flexible, and unlike most hard disks, is removable from its drive. 169
- 170. Flicker - In video, any of several visual artifacts similar to ( i.e., manifested as) a stroboscopic effect ( jerkiness ), sometimes caused by or related to vertical synchronization characteristics or video field display rates. Flip-Flop - A device that may assume either one of two reversible, stable states. Note 1: The flip-flop is used as a basic control element in computer and communications systems. Note 2: In a flip-flop, the transition from one stable state to the other is unstable, i.e., for the very short period during which the transition takes place, both outputs may assume the same state, which state may be unpredictable. Synonyms bistable circuit, bistable multivibrator, bistable trigger circuit. Floating - See conference floating. In conference calling, the state in which the conference is active but without a controller. This state is possible when two or more conferees exist on an active conference and the controller successfully disconnects himself/herself. Floating Head - A magnetic head floating on a layer of air away from the recording surface. Synonyms air- floating head, flying head. Floating-Point Coding Compaction - Data compaction accomplished by using coefficients, a base, and exponents to specify the scale, range, or magnitude of numbers. Note: An example of floating -point coding compaction is using 119.8 × 10 6 , 119.8(6), or 119.86 to represent 119,800,000. If the number is rounded to 120,000,000, it might be written as 1206 or 127 in which the last digit is the number of zeros to be appended to the preceding digits. Thus, only three positions are required instead of nine to represent the number in storage or in a message, which is only 33% of the original space and time requirement. Float Operation - Operation of a dc system with the battery, rectifier, and load all connected in parallel. The battery charger supplies the normal dc load plus any battery self-discharge current or recharge current required after a discharge. Flooding - Insertion of a large volume of data resulting in denial of service. Synonyms [in e-mail and forum postings] mail bombing, spamming; [in radio and wireline communications] flood-search routing, pilot- make-busy. Flooding Compound - A substance surrounding the buffer tubes of a fiber -optic cable, to prevent water intrusion into the interstices in the event of a breach of the jacket. Flood Projection - In facsimile , the optical method of scanning in which the object is floodlighted and the scanning spot is defined by a masked portion of the illuminated area. Flood Search Routing - In a telephone network, nondeterministic routing in which a dialed number received at a switch is transmitted to all switches, i.e., flooded, in the area code directly connected to that switch; if the dialed number is not an affiliated subscriber at that switch, the number is then retransmitted to all directly connected switches, and then routed through the switch that has the dialed number corresponding to the particular user end instrument affiliated with it. Note 1: All digits of the numbering plan are used to identify a particular subscriber. Note 2: Flood search routing allows subscribers to have telephone numbers independent of switch codes. Note 3: Flood search routing provides the highest probability that a call will go through even though a number of switches and links fail. floppy disk - Synonym diskette. In computer technology, a small disk of flexible plastic, coated with a magnetizable material and enclosed in a protective jacket, used to store digital data. Note: A diskette is distinguished from a hard disk by virtue of the fact that it is flexible, and unlike most hard disks, is removable from its drive. 170
- 171. flops - Acronym for floating -point operations per second. Note: For example, 15 Mflops equals 15 million floating-point arithmetic operations per second. Flowchart - A graphical representation in which symbols are used to represent such things as operations, data , flow direction, and equipment, for the definition, analysis, or solution of a problem. Synonym flow diagram. Flow Control - See transmit flow control. In data communications systems, control of the rate at which data are transmitted from a terminal so that the data can be received by another terminal. Note 1: Transmit flow control may occur between data terminal equipment ( DTE ) and a switching center, via data circuit- terminating equipment ( DCE ), or between two DTEs. The transmission rate may be controlled because of network or DTE requirements. Note 2: Transmit flow control can occur independently in the two directions of data transfer, thus permitting the transfer rates in one direction to be different from the transfer rates in the other direction. Flow Control Procedure - A procedure for controlling the rate of transfer of data among elements of a network, e.g. , between a DTE ( data terminal equipment ) and a data switching exchange network, to prevent overload. Flow Diagram - Synonym flowchart. A graphical representation in which symbols are used to represent such things as operations, data , flow direction, and equipment, for the definition, analysis, or solution of a problem. Flowline - On a flowchart, a line that (a) has an indicated direction, (b) represents a connection between other symbols, and (c) indicates the sequence of operations or the transfer of control. Flutter - Rapid variation of signal parameters, such as amplitude, phase, and frequency. Note: Examples of flutter are (a) rapid variations in received signal levels, such as variations that may be caused by atmospheric disturbances, antenna movements in a high wind, or interaction with other signals, (b) in radio propagation, a phenomenon in which nearly all radio signals that are usually reflected by ionospheric layers in or above the E-region experience partial or complete absorption, (c) in radio transmission, rapidly changing signal levels, together with variable multipath time delays, caused by reflection and possible partial absorption of the signal by aircraft flying through the radio beam or common scatter volume, (d) the variation in the transmission characteristics of a loaded telephone circuit caused by the action of telegraph direct currents on the loading coils, (e) in recording and reproducing equipment, the deviation of frequency caused by irregular mechanical motion, e.g., that of capstan angular velocity in a tape transport mechanism, during operation. Synonym [loosely] frequency flutter . Flux - 1. The lines of force of a magnetic field. 2. Obsolete synonym for radiant power. Flying Head - Synonym floating head. A magnetic head floating on a layer of air away from the recording surface. Flywheel Effect - In an oscillator, the continuation of oscillations after removal of the control stimulus. Note 1: The flywheel effect is usually caused by interacting inductive and capacitive circuits in the oscillator. Note 2: The flywheel effect may be desirable, such as in phase -locked loops used in synchronous systems, or undesirable, such as in voltage-controlled oscillators. Synonym flywheeling. Flywheeling - Synonym flywheel effect. In an oscillator, the continuation of oscillations after removal of the control stimulus. Note 1: The flywheel effect is usually caused by interacting inductive and capacitive circuits in the oscillator. Note 2: The flywheel effect may be desirable, such as in phase -locked loops used in synchronous systems, or undesirable, such as in voltage-controlled oscillators. 171
- 172. FM - Abbreviation for frequency modulation. Modulation in which the instantaneous frequency of a sine wave carrier is caused to depart from the center frequency by an amount proportional to the instantaneous value of the modulating signal. Note 1: In FM, the carrier frequency is called the center frequency. Note 2: FM is a form of angle modulation. Note 3: In optical communications, even if the electrical baseband signal is used to frequency-modulate an electrical carrier (an "FM" optical communications system), it is still the intensity of the lightwave that is varied (modulated) by the electrical FM carrier. In this case, the "information," as far as the lightwave is concerned, is the electrical FM carrier. The lightwave is varied in intensity at an instantaneous rate corresponding to the instantaneous frequency of the electrical FM carrier. FM Blanketing - That form of interference to the reception of other broadcast stations, which is caused by the presence of an FM broadcast signal of 115 dB (562 mV/m) or greater signal strength in the area adjacent to the antenna of the transmitting station. The 115-dB contour is referred to as the " blanketing area." FM Broadcast Translator - See translator. A device that converts information from one system of representation into equivalent information in another system of representation. Note: An example of a translator in telephony is the device that converts dialed digits into call - routing information. 2. A computer program that translates from one languag into another language and in particular from one programming language into another programming language. 3. In FM and TV broadcasting, a repeater station that receives a primary station 's signal , amplifies it, shifts it in frequency, and rebroadcasts it. 4. A device that converts one frequency to another. FM Capture Effect - Synonym capture effect. A phenomenon, associated with FM reception, in which only the stronger of two signals at or near the same frequency will be demodulated. Note 1: The complete suppression of the weaker signal occurs at the receiver limiter, where it is treated as noise and rejected. Note 2: When both signals are nearly equal in strength, or are fading independently, the receiver may switch from one to the other. FM Capture Ratio - See capture effect. A phenomenon, associated with FM reception, in which only the stronger of two signals at or near the same frequency will be demodulated. Note 1: The complete suppression of the weaker signal occurs at the receiver limiter, where it is treated as noise and rejected. Note 2: When both signals are nearly equal in strength, or are fading independently, the receiver may switch from one to the other. FM Improvement Factor - The quotient obtained by dividing the signal-to-noise ratio ( SNR ) at the output of an FM receiver by the carrier-to-noise ratio ( CNR ) at the input of the receiver. Note: When the FM improvement factor is greater than unity, the improvement in the SNR is always obtained at the expense of an increased bandwidth in the receiver and the transmission path. FM Improvement Threshold - The point in an FM receiver at which the peaks in the rf signal equal the peaks of the thermal noise generated in the receiver. Note: A baseband signal-to-noise ratio of about 30 dB is typical at the improvement threshold, and this ratio improves 1 dB for each decibel of increase in the signal above the threshold. FM Threshold Effect - In an FM receiver, the effect produced when the desired- signal gain begins to limit the desired signal, and thus noise limiting (suppression). Note: FM threshold effect occurs at (and above) the point at which the FM signal-to-noise improvement is measured. FM Threshold Extension - A change in the value of the FM threshold of a receiver. Note: FM threshold extension may be obtained by decreasing the operational bandwidth, thus decreasing the received noise power and allowing the threshold of the desired signal to occur at a lower signal input level. 172
- 173. FO - Abbreviation for fiber optics. The branch of optical technology concerned with the transmission of light through fibers made of transparent materials such as glasses and plastics. Note 1: Telecommunications applications of fiber optics use flexible low- loss fibers, using a single fiber per optical path. Present-day plastic fibers have losses that are too high for telecommunications applications. Note 2: Various industrial and medical applications of fiber optics, such as endoscopes, use flexible fiber bundles in which individual fibers are spatially aligned, permitting optical relay of an image. Note 3: Some specialized industrial applications use rigid (fused) aligned fiber bundles for image transfer; such as in the fiber optics faceplates used on some cathode ray rubes (CRTs) to "flatten" the image. FoIP (Fax over Internet Protocol) - The fax counterpart to VoIP, available from some providers either free or at additional cost. FoIP is actually more reliable than VoIP because of its tolerance for poor latency. Followup - Synonym thread. In computer conferencing, a set of sequential messages containing closely related information. Footprint - In satellite communications, that portion of the Earth's surface over which a satellite antenna delivers a specified amount of signal power under specified conditions. Note: The limiting case of footprint area is somewhat less than one-half the Earth's surface, and depends on the altitude of the satellite. Forbidden Character - Synonym illegal character. A character, or a combination of bits, that is not valid in a given system according to specified criteria, such as with respect to a specified alphabet, a particular pattern of bits, a rule of formation, or a check code. Forced Rerouting - A procedure of transferring signaling traffic from one signaling route to another, when the signaling route in use fails or is required to be cleared of traffic. Foreign Exchange (FX) Service - A network -provided service in which a telephone in a given local exchange area is connected, via a private line, to a central office in another, i.e., "foreign", exchange, rather than the local exchange area 's central office. Note: To call originators, it appears that the subscriber having the FX service is located in the foreign exchange area. Foreign Instrumentation Signals Intelligence (FISINT) - 1. Intelligence information derived from electromagnetic emissions associated with the testing and operational deployment of foreign aerospace, surface, and subsurface systems. 2. Technical information and intelligence information derived from the intercept of foreign instrumentation signals by other than the intended recipients. Foreign instrumentation signals intelligence is a category of signals intelligence. Note: Foreign instrumentation signals include but are not limited to signals from telemetry, beaconry, electronic interrogators, tracking/fusing/ arming/firing command systems, and video data links. Form - An HTML-based, interactive, ease-of-use Web site feature, containing checkboxes, option lists, text boxes, and buttons that allow users to submit pre-formatted requests or queries or to respond to pre- formatted questions. Format - 1. The arrangement of bits or characters within a group, such as a word, message, or language. 2. The shape, size, and general makeup of a document. Format Converter -1. In video and television technology, a device that allows the reformatting of a digital data stream originating from one sampling structure (lines per frame, pixels per line) into a digital data stream of another sampling structure for the purposes of recording or passing the original data stream through distribution devices designed to accommodate the latter structure. Note: Since, in format conversion, the data still represent the original sampling structure, this process is not the same as standards conversion (from PAL to NTSC, for instance). A format converter can, for instance, accept a signal introduced 173
- 174. in a proposed format, and convert it for recording on, and subsequent reproduction from, a high-definition television digital recorder designed for the 1125/60/2:1 format. 2. In television technology, a system that converts display information from the familiar 3 x 4 aspect ratio to the newer 9 x 16 aspect ratio. Format Structure - A combination of two or more data elements grouped in a prescribed sequence. Fortran - See language processor. A program that performs tasks, such as translating and interpreting, required for processing a specified programming language. Note: Examples of language processors include a Fortran processor and a COBOL processor. Fortuitous Conductor - Any conductor that may provide an unintended path for signals. Note: Examples of fortuitous conductors are water pipes, wires, cables, and metal building and equipment structural members. Fortuitous Distortion - Distortion resulting from causes generally subject to laws concerning random occurrences. Forum - A computer conference devoted to a specific subject, having an initiator, members, readers, and possibly moderators. Synonyms chat group, discussion group, discussion list, discussion thread, follow up, interest group, library, newsgroup, thread. Forward Busying - In a telecommunications system, a feature in which supervisory signals are forwarded in advance of address signals in order to seize assets of the system before attempting to establish a connection. Forward Channel - The channel of a data circuit that transmits data from the originating user to the destination user. Note: The forward channel carries message traffic and some control information. Forward Echo - In a transmission line, an echo propagating in the same direction as the original wave and consisting of energy reflected back by one discontinuity and then forward again by another discontinuity. Note: Forward echoes can be supported by reflections caused by splices or other discontinuities in the transmission medium ( e.g. , optical fiber, twisted pair, or coaxial tube). In metallic lines, they may be supported by impedance mismatches between the source or load and the characteristic impedance of the transmission medium. Forward Error Correction (FEC) - A system of error control for data transmission wherein the receiving device has the capability to detect and correct any character or code block that contains fewer than a predetermined number of symbols in error. Note: FEC is accomplished by adding bits to each transmitted character or code block, using a predetermined algorithm. Forward Indicator Bit (FIB) - A bit in a signal unit which indicates the start of a retransmission cycle. Forward Propagation Ionospheric Scatter (FPIS) - Synonym ionospheric scatter. The propagation of radio waves by scattering as a result of irregularities or discontinuities in the ionization of the ionosphere. Forward Recovery - The data reconstitution of a later version of data by using an earlier version and data recorded in a journal. Forward Scatter - The deflection --by diffraction, nonhomogeneous refraction, or nonspecular reflection by particulate matter of dimensions that are large with respect to the wavelength in question but small with respect to the beam diameter --of a portion of an incident electromagnetic wave, in such a manner that the energy so deflected propagates in a direction that is within 90° of the direction of propagation of the incident 174
- 175. wave. Note: The scattering process may be polarization -sensitive, i.e. , incident waves that are identical in every respect but their polarization may be scattered differently. Forward Secrecy - The confidence that the compromise of a long-term private key does not compromise any earlier session keys. Forward Sequence Number (FSN) - A field in a signal unit used to identify the transmitted message signal units. Forward Signal: A signal sent in the direction from the calling to the called station, i.e. , from the original data source to the original data sink. Note: The forward signal is transmitted in the forward channel. FOT - Abbreviation for frequency of optimum transmission. In the transmission of radio waves via ionospheric reflection, the highest effective, i.e., working, frequency that is predicted to be usable for a specified path and time for 90% of the days of the month. Note 1: The FOT is normally just below the value of the maximum usable frequency (MUF). In the prediction of usable frequencies, the FOT is commonly taken as 15% below the monthly median value of the MUF for the specified time and path. Note 2: The FOT is usually the most effective frequency for ionospheric reflection of radio waves between two specified points on Earth. Synonyms frequency of optimum traffic, optimum traffic frequency, optimum transmission frequency, optimum working frequency. Fourier Analysis - The definition of a periodic waveform of arbitrary shape as a summation of sine waves having specific amplitudes and phases, and having frequencies corresponding to the harmonics of the waveform being defined. Note: A Fourier analysis is particularly well suited for communications equipment design and for predicting the performance of a given design. Four-Wire Circuit - A two-way circuit using two paths so arranged that the respective signals are transmitted in one direction only by one path and in the other direction by the other path. Note: The four-wire circuit gets its name from the fact that, historically, two conductors were used in each of two directions for full- duplex operation. The name may still be applied, e.g., to a communications link supported by optical fibers, even though only one fiber is required for transmission in each direction. Four-Wire Repeater - A repeater, consisting of two amplifiers, one associated with each direction, used in a four-wire circuit. Four-Wire Terminating Set - A balanced transformer used to perform a conversion between 4-wire and 2- wire operation. Note 1: For example, a 4-wire circuit may, by means of a 4-wire terminating set, be connected to a 2-wire telephone set. Also, a pair of 4-wire terminating sets may be used to introduce an intermediate 4-wire loop into a 2-wire circuit, in which loop repeaters may be situated to amplify signals in each direction without positive feedback and oscillation. Note 2: Four-wire terminating sets have been largely supplanted by resistance hybrids. Fox Message - A standard test message that includes all the alphanumerics on a teletypewriter and also function characteristics ( space, figures shift, letters shift). Note: An example of a fox message is "THE QUICK BROWN FOX JUMPED OVER THE LAZY DOG'S BACK 1234567890." FPIS - Abbreviation for forward propagation ionospheric scatter. See ionospheric scatter. FPS - Abbreviation for frames per second. In video and television, the number of images contained in a single second of a moving picture. Note: Thirty fps is considered full- motion video in NTSC systems, while 25 fps is 175
- 176. considered full-motion in PAL and SECAM systems. Many proprietary video technologies produce 15 fps video; 24 fps is considered full-motion in motion-picture technology. Fractal - A mathematical formula or algorithm that constitutes or defines an efficient way of formulating computer graphics. Fractal graphics translate the natural curves of an object into mathematical formulas, from which the entire image can later be constructed. Fractals are self-similar in that any piece of the fractal design contains a miniature of the entire design. A fractal is completely described by (a) one piece ( layer ) of the design, and (b) a sublayer of the design, which sublayer shows how contiguous pieces (layers) fit together. For this reason, fractal patterns (designs) require very little computer storage space. An example of a fractal is a fern leaf design. Fractional Frequency Deviation - Synonym fractional frequency offset . A measure of the deviation of the frequency of a signal from a reference, expressed as a ratio. The ratio is dimensionless but typically expressed as parts per million, ppm. For example, 4.6 ppm = 4.6/106. Fractional frequency offset = [(f-fr) / fr] where: f = the actual frequency output of the signal in question, and fr = the reference frequency. Fractional Frequency Fluctuation - The deviation of the frequency of an oscillator from its nominal constant frequency, normalized to the nominal frequency. Fractional Frequency Offset - A measure of the deviation of the frequency of a signal from a reference, expressed as a ratio. The ratio is dimensionless but typically expressed as parts per million, ppm. For example, 4.6 ppm = 4.6/106. Fractional frequency offset = [(f-fr) / fr] where: f = the actual frequency output of the signal in question, and fr = the reference frequency. Synonym fractional frequency deviation. Fractional T1 - A fractional T1 or T3 line is a T1 or T3 digital phone line in the North American T-carrier system that is leased to a customer at a fraction of its data-carrying capacity and at a correspondingly lower cost. A T1 line contains 24 channels, each with a data transfer capacity of 64 Kbps. The customer can rent some number of the 24 channels. The transmission method and speed of transfer remain the same. Overhead bits and framing are still used, but the unrented channels simply contain no data. In telecommunications a fractional T1 is a portion of the 1.544 Mb/s (T1-aggregate) bit stream; the available fractions being determined by the type of multiplexer used to achieve the T1 aggregate bit stream. T3 lines (which offer 672 64 Kbps channels) are also sometimes offered as a fractional service. T1 and fractional T1 service are sometimes advertised as "point-to-point" service (from the customer to the service provider). Fragmentation -1. The process in which an IP ( Internet protocol ) datagram is broken into smaller pieces to fit the requirements of a given physical network; the reverse process of reassembly. 2. The physical separation of portions of a file on a computer disk. Frame -1. In data transmission, the sequence of contiguous bits delimited by, and including, beginning and ending flag sequences. Note 1: A frame usually consists of a specified number of bits between flag sequences and usually includes an address field, a control field, and a frame check sequence. Note 2: Frames usually consist of a representation of the original data to be transmitted, together with other bits which may be used for error detection or control. Additional bits may be used for routing, synchronization, or overhead information not directly associated with the original data. 2. In the multiplex structure of pulse-code modulation ( PCM ) systems, a set of consecutive time slots in which the position of each digit can be identified by reference to a frame-alignment signal. Note: The frame-alignment signal does not necessarily occur, in whole or in part, in each frame. 3. In a time-division multiplexing ( TDM ) system, a repetitive group of signals resulting from a single sampling of all channels, including any required system information, such as additional synchronizing signals. Note: "In-frame" is the condition that exists when there is a channel -to- 176
- 177. channel and bit-to-bit correspondence, exclusive of transmission errors, between all inputs of a time-division multiplexer and the output of its associated demultiplexer. 4. In ISDN, a block of variable length, labeled at the Data Link Layer of the Open Systems Interconnection--Reference Model. 5. In video display, the set of all picture elements that represent one complete image. Note: In NTSC and other television standards used throughout the world, a frame consists of two interlaced fields, each of which has half the number of scanning lines, and consequently, half the number of pixels, of one frame. 6. In video display, one complete scanned image from a series of video images. Note: A video frame is usually composed of two interlaced fields. 7. In computer screen displays of HTML documents, a portion (usually rectangular) of the screen where one usually finds the same types of fields/information displayed, in the same manner as one usually finds the same or similar information displayed in the same segment of different copies of a printed form. 8. An HTML feature that allows multiple Web pages to be viewed simultaneously (by means of scrolling or re- sizing) through a browser window. Frame Alignment - 1. In the reception of framed digital data, the extent to which a received frame is correctly aligned with respect to the clock at the receiver. 2. The state in which the frame of the receiving equipment is synchronized with that of the received signal. Frame-Alignment Recovery Time - Synonym reframing time. The time interval between the instant at which a valid frame-alignment signal is available at the receiving data terminal equipment and the instant at which frame alignment is established. Note: The reframing time includes the time required for replicated verification of the validity of the frame-alignment signal. Frame-Alignment Signal - In the transmission of data frames, a distinctive sequence of bits used to accomplish frame alignment. Note: A frame-alignment signal may also contain additional bits for status, control, and error detection. Frame-Alignment Time Slot - A time slot occupying the same relative position in every frame and used to transmit the frame alignment signal. Frame Check Sequence (FCS) - 1. An error-detection scheme that (a) uses parity bits generated by polynomial encoding of digital signals, (b) appends those parity bits to the digital signal, and (c) uses decoding algorithms that detect errors in the received digital signal. Note: Error correction, if required, may be accomplished through the use of an automatic repeat-request (ARQ) system. 2. [An] error checking mechanism that checks data integrity by computing a polynomial algorithm based checksum. Framed Interface - An interface through which information flow is partitioned into physical, periodic frames consisting of overhead information and an information payload. Frame Duration - The time between the beginning of a frame and the end of that frame. Note: For fixed- length frames, at a fixed data rate, frame duration is constant. Frame Frequency - Synonym frame rate. The number of frames transmitted or received per unit time. Note 1: The frame rate is usually expressed in frames per second. Note 2: In television transmission, the frame rate must be distinguished from the field rate, which in the NTSC and other systems, is twice the frame rate. Frame Grabber - A device that can seize and record a single frame of video information out of a sequence of many frames. Frame Matching - The process of comparing one sequence of frames with another sequence of frames in order to determine the correspondence between frames in each sequence and the correspondence of individual frames. Note: One means to test the correspondence between two video frames is to compare 177
- 178. their digital representations on a pixel by pixel basis, and summarizing over all pixels as the mean-square of the differences (usually called "mean square error "). Frame Overhead - Bits ( binary digits) that are added at regular intervals to a digital signal at the sending end of a digital link and used to provide network functions such as framing, operations, administration, and maintenance. Frame Pitch - The distance, time, or number of bits between corresponding points, i.e., significant instants, in two consecutive frames. Frame Rate - The number of frames transmitted or received per unit time. Note 1: The frame rate is usually expressed in frames per second. Note 2: In television transmission, the frame rate must be distinguished from the field rate, which in the NTSC and other systems, is twice the frame rate.Synonym frame frequency. Frame-Rate Conversion - With respect to television or other video display technologies, the process of transforming from one standard frame rate to another, using an algorithm. Note: Standard display rates of 24, 25, 29.97, 30, and 60 fps (frames per second) presently exist. Frame Relay - An interface protocol for statistically multiplexed packet -switched data communications in which (a) variable-sized packets (frames) are used that completely enclose the user packets they transport, and (b) transmission rates are usually between 56 kb/s and 1.544 Mb/s (the T-1 rate). Note 1: In frame relay, (a) there is neither flow-control nor an error -correction capability, (b) there is information -content independence, (c) there is a correspondence only to the ISO Open systems Interconnection--Reference Model Layers 1 and 2, (d) variable-sized user packets are enclosed in larger packets (frames) that add addressing and verification information, (e) frames may vary in length up to a design limit, usually 1 kilobyte or more, (f) one frame relay packet transports one user packet, (g) implementation of fast-packet technology is used for connection -oriented frame relay services, and (h) there is a capability to handle time - delay insensitive traffic, such as LAN interworking and image transfer. Note 2: Frame relay is referred to as the local management interface (LMI) standard and is specified in ANSI T1.617. Frame Relaying Protocol Data Unit (FPDU) - A data unit exchanged at the user-network interface and having a format based on that defined in CCITT Recommendation Q.921 (1988) ( ANSI T1.602). Frame Relaying Service Data Unit (FSDU) - The data unit exchanged at the functional boundary between the core function of Q.921 and the end-to-end protocol implemented above the core functions of Q.921. Frame Size - The number of octets after the address field and before the frame check sequence ( FCS ) field in a frame. The octet count is done either before zero-bit insertion or after zero-bit extraction. Frame Slip - In the reception of framed data, the loss of synchronization between a received frame and the receiver clock, causing a frame misalignment event, and resulting in the loss of the data contained in the received frame. Note: A frame slip should not be confused with a dropped frame where synchronization is not lost, e.g. , in the case of buffer overflow. Frame Synchronization - Of a received stream of framed data, the process by which incoming frame alignment signals, i.e. , distinctive bit sequences, are identified, i.e. , distinguished from data bits, permitting the data bits within the frame to be extracted for decoding or retransmission. Note: The usual practice is to insert, in a dedicated time slot within the frame, a noninformation bit that is used for the actual synchronization of the incoming data with the receiver. Synonym framing. 178
- 179. Frame Synchronization Pattern - In digital communications, a prescribed recurring pattern of bits transmitted to enable the receiver to achieve frame synchronization. Framing -1. In time-division multiplexing reception, synonym frame synchronization. 2. In video reception, the process of adjusting the timing of the receiver to coincide with the received video synchronization pulse. 3. In facsimile, the adjustment of the facsimile picture to a desired position in the direction of line progression. Framing Bit -1. A bit used for frame synchronization. 2. In a bit stream, a bit used in determining the beginning or end of a frame. Note 1: The framing bit occurs at a specific position in the frame. Note 2: In a bit stream, framing bits are noninformation bits. Note 3: Framing in a digital signal is usually repetitive. Framing Signal - See frame-alignment signal, framing bit. In the transmission of data frames, a distinctive sequence of bits used to accomplish frame alignment. Note: A frame-alignment signal may also contain additional bits for status, control, and error detection. Fraunhofer Diffraction Pattern - Synonym far-field diffraction pattern. The diffraction pattern of a source (such as an LED, ILD, or the output end of an optical fiber ) observed at an infinite distance from the source. Note 1: A far- field pattern exists at distances that are large compared with s 2 / , where s is a characteristic dimension of the source and is the wavelength. For example, if the source is a uniformly illuminated circle, then s is the radius of the circle. Note 2: The far-field diffraction pattern of a source may be observed at infinity or (except for scale) in the focal plane of a well-corrected lens. The far-field pattern of a diffracting screen illuminated by a point source may be observed in the image plane of the source. Synonym Fraunhofer diffraction pattern. Fraunhofer Region - Synonym far-field region. The region where the angular field distribution is essentially independent of distance from the source. Note 1: If the source has a maximum overall dimension D that is large compared to the wavelength, the far-field region is commonly taken to exist at distances greater than 2 2D / from the source, being the wavelength. Note 2: For a beam focused at infinity, the far-field region is sometimes referred to as the Fraunhofer region. Free Net - A radio net in which any station may communicate with any other station in the net without first obtaining the permission of the net- control station. Note: Permission to operate as a free net is granted by the net-control station until such time as a directed net is established by the net-control station. See [for Internet systems] freenet. Freenet - A system of computer networks (usually funded by individuals or organizations) consisting of community-based bulletin board systems with, e.g., e-mail, information services, interactive communications, and conferencing, and that are available to the user free of charge, or for a small membership fee. See [for radio communications] free net. Freephone - In the U.K., Freephone is a type of Number Translation Service (NTS) that allows a phone user to call a non-geographic number beginning with 0800 or 0500 without incurring a charge. All charges and associated costs are charged to the organization that receives the call. Businesses and non-profit help lines often offer Freephone numbers. Freephone is similar to 1-800 numbers used in the U.S. Free Routing - The routing of messages in such a manner that they are forwarded toward their destination or addressee over any available channel without dependence upon predetermined routing. Free-Running Capability - In a synchronized oscillator, the capability to operate in the absence of a synchronizing signal. 179
- 180. Free Space - A theoretical concept of space devoid of all matter. Note: Free space also implies remoteness from material objects that could influence the propagation of electromagnetic waves. Free-Space Coupling - Coupling of magnetic, electric, or electromagnetic fields that are not confined to a conductor. Note: Coupling by the deliberate introduction of capacitors and inductors is not considered free- space coupling. Free-Space Loss - The signal attenuation that would result if all absorbing, diffracting, obstructing, refracting, scattering, and reflecting influences were sufficiently removed so as to have no effect on propagation. Note: Free-space loss is primarily caused by beam divergence, i.e. , signal energy spreading over larger areas at increased distances from the source. Freeware - Software that is developed usually by individuals or small companies and distributed, usually via FTP, at essentially no cost to the recipient. Note: Often the developer or another party retains the copyright to the software product; therefore, freeware is not necessarily in the public domain, and its distribution may be controlled by the copyright owner. Freeze Frame - A frame of visual information that is selected from a set of motion video frames, and is held in a buffer. Freeze Frame Television - Television in which fixed ("still") images are transmitted sequentially at a rate far too slow to be perceived as continuous motion by human vision. Note: Transmission of an image is usually performed periodically by a processing unit that contains memory in which data representing the image are stored. For an image of specified quality, e.g., resolution and color fidelity, freeze- frame television has a lower bandwidth requirement than that of full-motion operation. Freeze-Out - The condition that occurs when an earlier nonactive speaker on an input transmission trunk channel becomes active and cannot immediately be assigned to a bearer channel, due to lack of free instantaneous transmission capacity. Freeze-Out Fraction - The ratio of the total time that the individual channels experience the freeze-out condition to the total time of the active intervals, and their corresponding hangover times and front end delays, for all transmission trunks over a fixed interval of time, e.g., 1 minute. F region - That portion of the ionosphere existing between approximately 160 and 400 km above the surface of the Earth, consisting of layers of increased free-electron density caused by the ionizing effect of solar radiation. Note 1: The F region reflects normal-incident frequencies at or below the critical frequency (approximately 10 MHz) and partially absorbs waves of higher frequency. Note 2: The F1 layer exists from about 160 to 250 km above the surface of the Earth and only during daylight hours. Though fairly regular in its characteristics, it is not observable everywhere or on all days. The principal reflecting layer during the 5 3 summer for paths of 2,000 to 3,500 km is the F1 layer. The F1 layer has approximately 5 × 10 e/cm (free 6 electrons per cubic centimeter) at noontime and minimum sunspot activity, and increases to roughly 2 × 10 3 4 3 e/cm during maximum sunspot activity. The density falls off to below 10 e/cm at night. Note 3: The F1 layer merges into the F2 layer at night. Note 4: The F2 layer exists from about 250 to 400 km above the surface of the Earth. The F2 layer is the principal reflecting layer for HF communications during both day and night. The horizon-limited distance for one-hop F2 propagation is usually around 4,000 km. The F2 layer has 6 3 about 10 e/cm . However, variations are usually large, irregular, and particularly pronounced during magnetic storms. French Telephone Jack - Below is an image of a typical telephone jack in France. You will notice that a French telephone jack is much bigger than what you would find in the US. The adapter is type F-010 as is the jack. 180
- 181. Interestingly enough the telephone connector pin is the same as in the US. That is RJ11, but there is a large adapter that the phone connector pin plugs into and then the adapter is plugged into the phone jack. This all means that if you have a DSL line you will have two adapters sticking out of your wall. The first will be for your DSL modem and the second will be for your telephone. Your French ISP will send you the adapter (sometimes two) that the modem will plug into. Normally you will get the adapters when you receive your modem, but if need be you can buy DSL adapters in most supermarkets. French Telephone Adaptor - Adapter This is a typical French adapter (type F-010) that plugs into the phone wall jack. At the bottom of the adapter is the plug for a RJ11 phone line. French F-010 - F-010 is a type of telephone plug and matching socket. The F-010 standard originated in France and is used there and in other countries, including Algeria, Andorra, Bhutan, Burkina Faso, Chad, Comoros, Republic of the Congo, Djibouti, Equatorial Guinea, French Guiana, Gabon, Grenadines, Guadeloupe, Ivory Coast, Madagascar, Mali, Martinique, Mauritania, Mauritius, Monaco, Morocco, New Caledonia, Niger, Polynesia, Rwanda, St. Martin, Somalia, Tahiti, Togo and Tunisia. French Adapters Plugged into each other This is an example of two French telephone adapters sticking out of a wall. The first adapter is for the DSL modem and the second is for the telephone. Frequency - A certain "size" of radio wave: The rate at which the electric and magnetic fields of a radio wave vibrate per second. 1. For a periodic function, the number of cycles or events per unit time. 2. The number of cycles occurring per second of an electrical or electromagnetic wave; a number representing a specific point in the electromagnetic spectrum. Frequency Accuracy - The degree of conformity to a specified value of a frequency. Frequency Aging - Of an oscillator, the change in frequency, over time, caused by internal changes in oscillator parameters even when external factors, such as environment and power supply characteristics, are constant. Frequency Allocation - See allocation (of a frequency band). Frequency Allotment - See allotment (of a radio frequency or radio frequency channel ). Frequency-Analysis Compaction - Data compaction accomplished by using an expression composed of a number of different frequencies of different magnitudes to represent a particular curve. Note: An example of frequency -analysis compaction is the use of a Fourier analysis to represent an arbitrary curve, a periodic function, an aperiodic function, or a wave shape. Thus, the fundamental frequency, the amplitude of the fundamental frequency, and the amplitudes and frequencies of the harmonics are all that are needed to reconstitute the function or wave shape. The shape can thus be readily stored and transmitted in this compacted form. Frequency Assignment -1. Authorization, given by an Administration, for a radio station to use a radio frequency or radio frequency channel under specified conditions 2. The process of authorizing a specific frequency, group of frequencies, or frequency band to be used at a certain location under specified 181
- 182. conditions, such as bandwidth, power, azimuth, duty cycle, or modulation. Synonym radio frequency channel assignment. Frequency Assignment Authority - The power granted an Administration, or its designated or delegated leader or agency via treaty or law, to specify frequencies, or frequency bands, in the electromagnetic spectrum for use in systems or equipment. Note: Primary frequency assignment authority for the United States is exercised by the National Telecommunications and Information Administration (NTIA) for the Federal Government and by the Federal Communications Commission ( FCC ) for non-Federal Government organizations. International frequency assignment authority is vested in the International Frequency Registration Board of the International Telecommunication Union. Frequency Averaging -1. The process by which the relative phases of precision clocks are compared for the purpose of defining a single time standard. 2. A process in which network synchronization is achieved by use, at all nodes, of oscillators that adjust their frequencies to the average frequency of the digital bit streams received from connected nodes. Note: In frequency averaging, all oscillators are assigned equal weight in determining the ultimate network frequency. Frequency Band - See electromagnetic spectrum. The range of frequencies of electromagnetic radiation from zero to infinity. Note: The electromagnetic spectrum was, by custom and practice, formerly divided into 26 alphabetically designated bands. This usage still prevails to some degree. However, the ITU formally recognizes 12 bands, from 30 Hz to 3000 GHz. New bands, from 3 THz to 3000 THz, are under active consideration for recognition. Frequency Band Allocation - See allocation (of a frequency band ). 1. Entry in the Table of Frequency Allocations of a given frequency band for the purpose of its use by one or more (terrestrial or space) radiocommunication services or the radio astronomy service under specified conditions. This term shall also be applied to the frequency band concerned. 2. The process of designating radio-frequency bands for use by specific radio services. Frequency-Change Signaling - A signaling method in which one or more discrete frequencies correspond to each desired significant condition of a code. Note 1: The transition from one set of frequencies to the other may be a continuous or a discontinuous change in frequency or in phase. Note 2: Frequency-change signaling may be used in both supervisory signaling and data transmission. Frequency Coherence - See phase coherence. The state in which two signals maintain a fixed phase relationship with each other or with a third signal that can serve as a reference for each. Frequency Compatibility -1. Of an electronic device, the extent to which it will operate at its designed performance level in its intended operational environment (including the presence of interference ) without causing interference to other devices. 2. The degree to which an electrical or electronic device or devices operating on or responding to a specified frequency or frequencies is capable of functioning with other such devices. Frequency Departure -1. The difference between the instantaneous frequency of a digital signal and the long-term average frequency of that signal. 2. An unintentional deviation from the nominal frequency value. Frequency-Derived Channel - A channel derived by dividing an allocated or available bandwidth over a medium into two or more portions, each usable separately. Note: A frequency -derived channel is continuously available and may be further divided on either a frequency or time basis. Frequency Deviation -1. The amount by which a frequency differs from a prescribed value, such as the amount an oscillator frequency drifts from its nominal frequency. 2. In frequency modulation, the absolute 182
- 183. difference between (a) the maximum permissible instantaneous frequency of the modulated wave or the minimum permissible instantaneous frequency of the modulated wave and (b) the carrier frequency. 3. In frequency modulation, the maximum absolute difference, during a specified period, between the instantaneous frequency of the modulated wave and the carrier frequency. Frequency Dispersal - An electronic counter- countermeasure ( ECCM ) in which communications nets ' operating frequencies are widely separated from each other, causing a requirement to spread jamming power over wider frequency bands and thus compelling a reduction of available jamming power on any single channel or frequency, or causing a requirement for more jamming power or more jamming equipment. Frequency Displacement - The end-to-end shift in frequency that may result from independent frequency translation errors in a circuit. Frequency Distortion - Synonym amplitude-vs.-frequency distortion. Distortion in a transmission system caused by nonuniform attenuation, or gain, in the system with respect to frequency under specified operating conditions. Frequency Diversity - Transmission and reception in which the same information signal is transmitted and received simultaneously on two or more independently fading carrier frequencies. Frequency-Division Multiple Access (FDMA) - The use of frequency division to provide multiple and simultaneous transmissions to a single transponder. Frequency-Division Multiplexing (FDM) - A scheme in which numerous signals are combined for transmission on a single communications line or channel. Each signal is assigned a different frequency (subchannel) within the main channel. A typical analog Internet connection via a twisted pair telephone line requires approximately three kilohertz (3 kHz) of bandwidth for accurate and reliable data transfer. Twisted-pair lines are common in households and small businesses. But major telephone cables, operating between large businesses, government agencies, and municipalities, are capable of much larger bandwidths. Suppose a long-distance cable is available with a bandwidth allotment of three megahertz (3 MHz). This is 3,000 kHz, so in theory, it is possible to place 1,000 signals, each 3 kHz wide, into the long-distance channel. The circuit that does this is known as a multiplexer. It accepts the input from each individual end user, and generates a signal on a different frequency for each of the inputs. This results in a high-bandwidth, complex signal containing data from all the end users. At the other end of the long-distance cable, the individual signals are separated out by means of a circuit called a demultiplexer, and routed to the proper end users. A two-way communications circuit requires a multiplexer/demultiplexer at each end of the long-distance, high- bandwidth cable. When FDM is used in a communications network, each input signal is sent and received at maximum speed at all times. This is its chief asset. However, if many signals must be sent along a single long-distance line, the necessary bandwidth is large, and careful engineering is required to ensure that the system will perform properly. In some systems, a different scheme, known as time-division multiplexing, is used instead. Frequency Drift - An undesired progressive change in frequency with time. Note 1: Causes of frequency drift include component aging and environmental changes. Note 2: Frequency drift may be in either direction and is not necessarily linear. 183
- 184. Frequency-Exchange Signaling - Frequency-change signaling in which the change from one significant condition to another is accompanied by decay in amplitude of one or more frequencies and by buildup in amplitude of one or more other frequencies. Note: Frequency-exchange signaling applies to supervisory signaling and user - information transmission. Synonym two-source frequency keying. Frequency Fluctuation - A short-term variation, with respect to time, of the frequency of an oscillator. Frequency Flutter - A deviation of frequency that generally results from irregular motion of the recording medium during the recording, duplication, or reproduction. Synonym [loosely] flutter. Frequency Frogging -1. The interchanging of the frequencies of carrier channels to accomplish specific purposes, such as to prevent feedback and oscillation, to reduce crosstalk, and to correct for a high frequency-response slope in the transmission line. Note: Frequency frogging is accomplished by having modulators, which are integrated into specially designed repeaters, translate a low-frequency group to a high-frequency group, and vice versa. A channel will appear in the low group for one repeater section and will then be translated to the high group for the next section because of frequency frogging. This results in nearly constant attenuation with frequency over two successive repeater sections, and eliminates the need for large slope equalization and adjustments. Singing and crosstalk are minimized because the high- level output of a repeater is at a different frequency than the low-level input to other repeaters. 2. In microwave systems, the alternate use of two frequencies at repeater sites to prevent feedback and oscillation. Frequency Guard Band - A frequency band deliberately left vacant between two channels to provide a margin of safety against mutual interference. Frequency Hopping - The repeated switching of frequencies during radio transmission according to a specified algorithm, to minimize unauthorized interception or jamming of telecommunications. Note: The overall bandwidth required for frequency hopping is much wider than that required to transmit the same information using only one carrier frequency. Frequency-Hopping Spread Spectrum - A signal structuring technique employing automatic switching of the transmitted frequency. Selection of the frequency to be transmitted is typically made in a pseudo-random manner from a set of frequencies covering a band wider than the information bandwidth. The intended receiver would frequency- hop in synchronization with the code of the transmitter in order to retrieve the desired information. Note: In many cases, used as an electronic counter- countermeasure ( ECCM ) technique. Frequency Hour - One frequency used for one hour regardless of the number of transmitters over which it is simultaneously broadcast by a station during that hour. Frequency Instability - See frequency stability. The degree to which variations of the frequency of an oscillator deviate from the mean frequency over a specified period of time. Frequency Lock - The condition in which a frequency -correcting feedback loop maintains control of an oscillator within the limits of one cycle. Note: Frequency lock does not imply phase lock, but phase lock does imply frequency lock. Frequency Modulation (FM) - Modulation in which the instantaneous frequency of a sine wave carrier is caused to depart from the center frequency by an amount proportional to the instantaneous value of the modulating signal. Note 1: In FM, the carrier frequency is called the center frequency. Note 2: FM is a form of angle modulation. Note 3: In optical communications, even if the electrical baseband signal is used to frequency-modulate an electrical carrier (an "FM" optical communications system), it is still the intensity of the lightwave that is varied (modulated) by the electrical FM carrier. In this case, the "information," as far as 184
- 185. the lightwave is concerned, is the electrical FM carrier. The lightwave is varied in intensity at an instantaneous rate corresponding to the instantaneous frequency of the electrical FM carrier. Frequency Offset - The difference between the frequency of a source and a reference frequency. Frequency of Optimum Traffic - Synonym FOT. In the transmission of radio waves via ionospheric reflection, the highest effective, i.e., working, frequency that is predicted to be usable for a specified path and time for 90% of the days of the month. Note 1: The FOT is normally just below the value of the maximum usable frequency (MUF). In the prediction of usable frequencies, the FOT is commonly taken as 15% below the monthly median value of the MUF for the specified time and path. Note 2: The FOT is usually the most effective frequency for ionospheric reflection of radio waves between two specified points on Earth. Synonyms frequency of optimum transmission, optimum traffic frequency, optimum transmission frequency, optimum working frequency. Frequency of Optimum Transmission (FOT) - Abbreviation for FOT. In the transmission of radio waves via ionospheric reflection, the highest effective, i.e., working, frequency that is predicted to be usable for a specified path and time for 90% of the days of the month. Note 1: The FOT is normally just below the value of the maximum usable frequency (MUF). In the prediction of usable frequencies, the FOT is commonly taken as 15% below the monthly median value of the MUF for the specified time and path. Note 2: The FOT is usually the most effective frequency for ionospheric reflection of radio waves between two specified points on Earth. Synonyms frequency of optimum traffic, optimum traffic frequency, optimum transmission frequency, optimum working frequency. Frequency Prediction - A prediction of the maximum usable frequency ( MUF ), the optimum traffic frequency, and the lowest usable frequency ( LUF ) for transmission between two specific locations or geographical areas during various times throughout a 24-hour period. Note: The prediction is usually indicated by means of a graph for each frequency plotted as a function of time. Frequency Range - A continuous range or spectrum of frequencies that extends from one limiting frequency to another. Note 1: The frequency range for given equipment specifies the frequencies at which the equipment is operable. For example, filters pass or stop certain bands of frequencies. The frequency range for propagation indicates the frequencies at which electromagnetic wave propagation in certain modes or paths is possible over given distances. Frequency allocation, however, is made in terms of bands of frequencies. There is little, if any, conceptual difference between a range of frequencies and a band of frequencies. Note 2: " Frequency band " usually identifies a specific band of frequencies in the Tables of Frequency Allocations. Frequency Response - See insertion-loss-vs.-frequency characteristic. Of a system or device, a plot of the amplitude as a function of frequency. Note: The insertion-loss-vs.-frequency characteristic may be expressed as absolute gain or loss, or it may be normalized with respect to gain or loss at a specified reference frequency. Frequency Response Curve - A plot of the gain or attenuation of a device, such as an amplifier or a filter, as a function of frequency. Note: A flat curve indicates a uniform gain or attenuation over the range of frequencies for which the curve is flat. Most amplifiers have a flat frequency response over a certain band, above and below which the gain is reduced. The frequency response curve of a filter has one or more peaks or troughs. Frequency Scanning - Conducting a search for signals over a band or range of frequencies by means of a manually or automatically tuned receiver. Note: The tuning rate, i.e., the frequency change rate, may be fixed or variable, or it may be performed mechanically at low speed or electronically at high speed. 185
- 186. Frequency scanning may be used to enable a radar to transmit on a clear frequency, i.e., a no- interference frequency, by searching a frequency band and then tuning the system to a clear portion of that band. Frequency Sharing - The assignment to or use of the same radio frequency by two or more stations that are separated geographically or that use the frequency at different times. Note 1: Frequency sharing reduces the potential for mutual interference where the assignment of different frequencies to each user is not practical or possible. Note 2: In a communications net, frequency sharing does not pertain to stations that use the same frequency. Frequency Spectrum - See electromagnetic spectrum. The range of frequencies of electromagnetic radiation from zero to infinity. Note: The electromagnetic spectrum was, by custom and practice, formerly divided into 26 alphabetically designated bands. This usage still prevails to some degree. However, the ITU formally recognizes 12 bands, from 30 Hz to 3000 GHz. New bands, from 3 THz to 3000 THz, are under active consideration for recognition. Fresnel Reflection - In optics, the reflection of a portion of incident light at a discrete interface between two media having different refractive indices. Note 1: Fresnel reflection occurs at the air-glass interfaces at the entrance and exit ends of an optical fiber. Resultant transmission losses, on the order of 4% per interface, can be reduced considerably by the use of index-matching materials. Note 2: The coefficient of reflection depends upon the refractive index difference, the angle of incidence, and the polarization of the incident radiation. In general, the greater the angle of incidence with respect to the normal, the greater the Fresnel reflection coefficient, but for radiation that is linearly polarized in the plane of incidence, there is zero reflection at Brewster's angle. Note 3: Macroscopic optical elements may be given antireflection coatings consisting of one or more dielectric thin-film layers having specific refractive indices and thicknesses. Antireflection coatings reduce overall Fresnel reflection by mutual interference of individual Fresnel reflections at the boundaries of the individual layers. Front-End Processor (FEP) - A programmed-logic or stored-program device that interfaces data communication equipment with an input / output bus or memory of a data processing computer. Front Projectors - These are TV sets that create the image on a small display, and then enlarge it by projecting it onto a wall or stand-alone screen (much like a movie theater). Front projectors tend to be dimmer than direct flat panels or CRTs, and often require the room to be dark to be able to see the image clearly. FTAM - Abbreviation for file transfer, access, and management. An application's service and protocol based on the concept of virtual file store. Note: FTAM allows remote access to various levels in a file structure and provides a comprehensive set of file management capabilities. FTS2000 - Abbreviation for Federal Telecommunications System 2000. The designation for a defunct Federal telecommunications contract replaced by the contract designated by the title "FTS2001." FTP is the abbreviation for File Transfer Protocol. The Transmission Control Protocol / Internet Protocol (TCP/IP) protocol that is (a) a standard high-level protocol for transferring files from one computer to another, (b) usually implemented as an application level program, and (c) uses the Telnet and TCP protocols. Note: In conjunction with the proper local software, FTP allows computers connected to the Internet to exchange files, regardless of the computer platform. See File Transfer Protocol FTP Archive - A collection of files that are available by using file transfer protocol (FTP). Synonyms file archive, file site. 186
- 187. FTTP (Fiber to the Premises) - A fiber-optic network that connects directly from the carrier network to the user premises. Another fiber-optic network is FTTC (Fiber to the Curb) that connects from the carrier network to the curb, and from there to the premises by copper wire or coaxial cable. Full-Duplex (FDX) Circuit - A circuit that permits simultaneous transmission in both directions. Full-Duplex (FDX) Operation - Synonym duplex operation. Operating method in which transmission is possible simultaneously, in both directions of a telecommunication channel. [NTIA] [RR] Note 1: This definition is not limited to radio transmission. Note 2: In general, duplex operation and semi-duplex operation require two frequencies in radiocommunication; simplex operation may use either one or two. Synonym two-way simultaneous operation. Full Width at Half Maximum (FWHM) - An expression of the extent of a function, given by the difference between the two extreme values of the independent variable at which the dependent variable is equal to half of its maximum value. Note 1: FWHM is applied to such phenomena as the duration of pulse waveforms and the spectral width of sources used for optical communications. Note 2: The term full duration at half maximum (FDHM) is preferred when the independent variable is time. Fully Connected Mesh Network - See network topology. Fully Connected Topology - See network topology. Functionality - The ability of equipment to operate as expected during actual service conditions in a central office. Functional Component (FC) - In intelligent networks, an elemental call-processing component that directs internal network resources to perform specific actions, such as collecting dialed digits. Note: An FC is unique to the intelligent-network-IN/2 architecture. Functional Unit - An entity of hardware, software, or both, capable of accomplishing a specified purpose. Fundamental - Of a periodic wave, the sinusoidal component, i.e., Fourier component, having the lowest frequency. Note: Every periodic waveform may be expressed as the summation of the fundamental and its harmonics. For example, a square wave may be expressed as the summation of sine waves equal in frequency to the fundamental and all odd harmonics, each frequency having an appropriate amplitude and phase. A pure sinusoidal wave has only one component, i.e., the fundamental. Fundamental Mode - The lowest order mode of a waveguide. Note: In optical fibers, the fundamental mode is designated LP01 or HE11. Fusion - Synonym (in cryptosystems) linkage. - In computer security, the purposeful combining of data or information from one data processing system with data or information from another system to derive protected information. Fusion Splice - In fiber optics, a splice created by localized heating of the ends of the two fibers to be joined. Note: A properly made fusion splice results in a continuous length of material with minimal discontinuities at the splice. G 187
- 188. Gain - The ratio of output current, voltage, or power to input current, voltage, or power, respectively. Note 1: Gain is usually expressed in dB. Note 2: If the ratio is less than unity, the gain, expressed in dB, will be negative, in which case there is a loss between input and output. Gain Hit - See hit. A transient disturbance to, or momentary interruption of, a communication channel, power supply (especially that provided via a commercial electric power distribution network or grid, but not limited to same), etc. Gain Medium - An active medium, device, or system in which amplification of input occurs with or without feedback. Note: Gain media include amplifiers, lasers, and avalanche photodiodes (APDs). Gain of an Antenna - Synonym antenna gain. - The ratio of the power required at the input of a loss-free reference antenna to the power supplied to the input of the given antenna to produce, in a given direction, the same field strength at the same distance. Note 1: Antenna gain is usually expressed in dB. Note 2: Unless otherwise specified, the gain refers to the direction of maximum radiation. The gain may be considered for a specified polarization. Depending on the choice of the reference antenna, a distinction is made between: • absolute or isotropic gain (Gi), when the reference antenna is an isotropic antenna isolated in space; • gain relative to a half-wave dipole (Gd) when the reference antenna is a half-wave dipole isolated in space and with an equatorial plane that contains the given direction; • gain relative to a short vertical antenna (Gr), when the reference antenna is a linear conductor, much shorter than one quarter of the wavelength, normal to the surface of a perfectly conducting plane which contains the given direction. Synonyms antenna gain, power gain of an antenna. Galactic Radio Noise - Synonym cosmic noise. - Random noise that originates outside the Earth's atmosphere. Note: Cosmic noise characteristics are similar to those of thermal noise. Cosmic noise is experienced at frequencies above about 15 MHz when highly directional antennas are pointed toward the Sun or to certain other regions of the sky such as the center of the Milky Way Galaxy. Gamma Correction - In video, the insertion of a nonlinear output-input characteristic for the purpose of changing the system transfer characteristic. Note: Historically, gamma correction was a precompensation applied to the video signal at the camera to correct for the nonlinearities of the CRT (i.e., the power function of the electron gun) and, as such, it was the inverse of the electron gun function. It is now widely used, however, to describe "the total of all transfer function manipulations" (i.e., including departures from a true power-law function), whether inherent or intentionally introduced to act upon the video signal for the purpose of reducing the bandwidth for signal processing, making the image on the final display conform to preconceived artistic objectives, or providing noise suppression, or even bit-rate reduction. GAN (global area network) - A network that (a) is composed of different interconnected computer networks and (b) covers an unlimited geographical area. Note: Loosely synonymous with an internet (as opposed to the Internet (with an uppercase "I"), which designates one specific network). Gap - A period of low energy content signals present of a digital speech interpolation device. Gap Loss - 1. The power loss that occurs when an optical signal is transferred from one fiber to another that is axially aligned with it, but longitudinally separated from it. Note: The gap allows light from the "transmitting" fiber to spread out as it leaves the fiber endface. When it strikes the "receiving" fiber, some of the light will enter the cladding, where it is quickly lost. 2. An analogous form of coupling loss that occurs between an optical source, e.g., an LED, and an optical fiber. Note: Gap loss is not usually significant at the optical detector, because the sensitive area of the detector is normally somewhat larger than the cross section of the fiber core. Unless the separation is substantial, all light emerging from the fiber, even though it diverges, will still strike the detector. Synonym longitudinal offset loss. 188
- 189. Gap-Loss Attenuator - An optical attenuator that exploits the principle of gap loss to reduce the optical power level when inserted in-line in the fiber path; e.g., to prevent saturation of the receiver. Note: Gap-loss attenuators should be used in-line near the optical transmitter. Gaps - Periods of no speech activity or low-energy content signals present in the access channel of a wideband packet network. Garble - 1. An error in transmission, reception, encryption, or decryption that changes the text of a message or any portion thereof in such a manner that it is incorrect or undecryptable. 2. In a telephone circuit or channel, readily audible but unintelligible interference from another circuit or channel. Note: Garble may, for example, take place in an FDM telephone carrier system in which an interfering signal from another channel or system is demodulated in such a fashion that it has an objectionable audio power level but is nonetheless unintelligible. Gate - 1. A device having one output channel and one or more input channels, such that the output channel state is completely determined by the input channel states, except during switching transients. 2. One of many types of combinational logic elements having at least two inputs; e.g., AND, OR, NAND, and NOR. Gateway - A system that translates incompatible networks or applications. Gateway is also commonly used to refer to any system that provides access to another system. A gateway is a network point that acts as an entrance to another network. On the Internet, a node or stopping point can be either a gateway node or a host (end-point) node. Both the computers of Internet users and the computers that serve pages to users are host nodes. The computers that control traffic within your company's network or at your local Internet service provider (ISP) are gateway nodes. In the network for an enterprise, a computer server acting as a gateway node is often also acting as a proxy server and a firewall server. A gateway is often associated with both a router, which knows where to direct a given packet of data that arrives at the gateway, and a switch, which furnishes the actual path in and out of the gateway for a given packet. 1. In a communications network, a network node equipped for interfacing with another network that uses different protocols. Note 1: A gateway may contain devices such as protocol translators, impedance matching devices, rate converters, fault isolators, or signal translators as necessary to provide system interoperability. It also requires that mutually acceptable administrative procedures be established between the two networks. Note 2: A protocol translation/mapping gateway interconnects networks with different network protocol technologies by performing the required protocol conversions. 2. [An] interface providing a compatibility between networks by converting transmission speeds, protocols, codes, or security measures. 3. Loosely, a computer configured to perform the tasks of a gateway. Gating - 1. The process of selecting only those portions of a wave between specified time intervals or between specified amplitude limits. 2. The controlling of signals by means of combinational logic elements. 3. A process in which a predetermined set of conditions, when established, permits a second process to occur. Gaussian Beam - A beam of light whose electric field intensity distribution is gaussian. Gaussian Filter - A filter having a response curve (magnitude versus frequency) that approximates an ideal gaussian curve. Gaussian Pulse - A pulse that has a waveform described by the gaussian distribution. 189
- 190. GBH - Abbreviation for group busy hour. The busy hour for a given trunk group. Gb/s - Abbreviation for gigabytes per second. See International System of Units. GCT - Abbreviation for Greenwich Civil Time. See Coordinated Universal Time. GDF - Abbreviation for group distribution frame. Gel - 1. A substance, resembling petroleum jelly in viscosity, that surrounds a fiber, or multiple fibers, enclosed in a loose buffer tube. Note: This gel serves to lubricate and support the fibers in the buffer tube. It also prevents water intrusion in the event the buffer tube is breached. 2. Index-matching material in the form of a gel. Synonyms index-matching gel, matching gel. General Purpose Computer - A computer designed to perform, or that is capable of performing, in a reasonably efficient manner, the functions required by both scientific and business applications. Note: A general purpose computer is often understood to be a large system, capable of supporting remote terminal operations, but it may also be a smaller computer, e.g., a desktop workstation. General Purpose Interface (GPI) - An equipment-interface device (usually computer equipment) with some number of digital lines, usually a multiple of eight, which may be used for input, output, or both, depending on the function. Note: The digital lines may be individually controlled, although nothing precludes using them in combination. General Purpose Network - See common user network. - A system of circuits or channels allocated to furnish communication paths between switching centers to provide communication service on a common basis to all connected stations or subscribers. Generation - In audio and video analog recording, pertaining to the number of duplication steps between an original recording and a given copy. Note 1: A second generation duplicate is a copy of the original master and a third generation duplicate is a copy of a copy of the original master, etc. Note 2: Relative to digital duplication, the copy is almost always identical to the original, so the term generation is irrelevant. Generation Loss - In analog recording, cumulative deterioration of signal quality introduced as a consequence of limitations of the recording electronics and storage medium, when successive copies of an original recording are made, each from the preceding copy. Note 1: Examples of signal deterioration attributable to generation loss are increased distortion, increased noise, change in frequency response, and change in the relative phase of one frequency component with respect to another. Note 2: As a specific example, in the recording of television baseband signals, generation loss may manifest itself in the loss of fine detail, color distortion, erratic synchronization, etc. In audio recording, generation loss may manifest itself as audible distortion or loss of frequency response. Note 3: Generation loss is limited to analog recording because digital recording and reproduction may be performed in a manner that is essentially free from generation loss. Digital signals may be reshaped before being rerecorded, so successive generations are extremely faithful to one another, with possible exceptions attributable primarily to occasional uncompensated flaws that may be present in the recording medium. The degree to which this affects the outcome (signal quality) depends on the specific recording technique involved, but it is usually negligible. In digital recording, essentially all of the distortion introduced in the recording and playback process takes place in (a) the analog-to-digital conversion that occurs during the initial recording, and (b) the digital-to-analog process that occurs during playback. Note 4: Generation loss in digital recordings can quickly become non- negligible unless all transfers of the recording take place solely in the digital domain and lossless compression / decompression is used. 190
- 191. Genlock - The synchronization of two television signals at the vertical, horizontal, and chroma phase levels such that the signals may be cut, mixed, or cross-faded without noticeable roll, jump, or chroma shift. Note: Modern usage accomplishes this with a frame synchronizer/ time base corrector, but it may also be accomplished by a closed loop method or an open loop method, the latter using a pair of rubidium clocks and a video delay line to maintain chroma lock. Geometric Optics - The branch of optics that describes light propagation in terms of rays. Note 1: Rays are bent at the interface between two dissimilar media, and may be curved in a medium in which the refractive index is a function of position. Note 2: The ray in geometric optics is perpendicular to the wavefront in physical optics. Synonym ray optics. Geometric Spreading - See inverse-square law , which is the physical law stating that irradiance, i.e., the power per unit area in the direction of propagation, of a spherical wavefront varies inversely as the square of the distance from the source, assuming there are no losses caused by absorption or scattering. Note: For example, the power radiated from a point source, e.g., an omnidirectional isotropic antenna, or from any source at very large distances from the source compared to the size of the source, must spread itself over larger and larger spherical surfaces as the distance from the source increases. Diffuse and incoherent radiation are similarly affected. Geostationary Orbit - A circular orbit in the equatorial plane, any point on which revolves about the Earth in the same direction and with the same period as the Earth's rotation. Note: An object in a geostationary orbit will remain directly above a fixed point on the equator at a distance of approximately 42,164 km from the center of the Earth, i.e., approximately 35,786 km above mean sea level. Classification Orbital Altitude (km above the earth) LEO 500-2,000 MEO 8,000-20,000 Geostationary Orbit 35,786 Geostationary Satellite - A geosynchronous satellite whose circular and direct orbit lies in the plane of the Earth's equator and which thus remains fixed relative to the Earth; by extension, a satellite that remains approximately fixed relative to the Earth. Geostationary Satellite Orbit - The orbit in which a satellite must be placed to be a geostationary satellite. Geosynchronous Orbit - Any orbit about the Earth, which orbit has a period equal to the period of rotation of the Earth about its axis, and in the same sense, i.e., direction, as the rotation of the Earth. Germanium Photodiode - A germanium-based PN- or PIN-junction photodiode. Note 1: Germanium photodiodes are useful for direct detection of optical wavelengths from approximately 1 m to several tens of m. Note 2: Germanium-based detectors are noisier than silicon-based detectors. Silicon-based detectors are therefore usually preferred for wavelengths shorter than 1 m. GETS - Abbreviation for Government Emergency Telecommunications Service (GETS). - A special federal government telecommunications service that provides National Security and Emergency Preparedness (NS/EP) users with priority switched voice and voiceband data communications during periods of emergency or crisis. GETS uses existing features and services of the Public Switched Network (PSN) with selected NS/EP augmentations and enhancements. Access to GETS requires a telephone calling card with personal identification number. GETS is maintained in a constant state of readiness to make maximum use of all available PSN telephone resources should network congestion or damage occur during an emergency or 191
- 192. crisis. GETS calls receive priority over other traffic through special features such as trunk queuing, exemption from restrictive network management controls and Alternate Carrier Routing (ACR) on approximately 85% of all local carrier access lines. Comparable features provide priority treatment and enhanced routing in the interexchange networks. While GETS calls receive priority for next available path, they do not preempt other traffic. The Signaling System No. 7 (SS7) -High Probability of Completion (HPC) Network Capability standard is applied to provide NS/EP call identification and priority signaling. GFP (global functional plane) - The plane in the intelligent network conceptual model that defines service independent building blocks (SIBs) used in providing service features. Ghost - In the transmission or recording of raster-scanned analog television signals, an artifact manifested as a weak, ghost-like secondary image, offset (in the direction of the scan) with respect to the position of the primary image. Note: Ghosting is probably most familiar as a consequence of multipath rf reception of a broadcast television signal. The slight delay in the arrival time of the reflected signal results in the display of a secondary image that follows the primary. In the playback of a tape-recorded program, ghosting may also be introduced by print-through in the magnetic tape medium. Ghosting - See ghost. 9 GHz (Gigahertz) - A unit of frequency denoting 10 Hz. gif - (or .gif) Abbreviation for graphical interchange format. A file-name extension indicating a certain digital image file format suitable for efficiently importing image data into computer files or for transmitting or displaying the formatted image on a computer monitor or printing it out. 9 Gigaflop - A billion, i.e., 10 , floating point operations per second. 9 Gigahertz (GHz) - A unit of frequency denoting 10 Hz. GII - Abbreviation for global information infrastructure. The totality of worldwide infrastructure elements that combine the three industry sectors of (a) telecommunications, (b) computer (information) technology, and (c) consumer electronics to extend the capabilities of the NII (national information infrastructure) worldwide. Glare - Deprecated synonym for call collision. See also dual seizure. - 1. The contention that occurs when a terminal and data circuit-terminating equipment (DCE) specify the same channel at the same time to transfer a call request and handle an incoming call. Note: When call collision occurs, the DCE proceeds with the call request and cancels the incoming call. 2. The condition that occurs when a trunk or channel is seized at both ends simultaneously, thereby blocking a call. Synonym dual seizure. Glare Master - The Signaling System No. 7 (SS7) switch designated as control switch for circuits in the both- way circuit group. For the same circuits, the other switch is referred to as the slave. On detecting glare, the control switch proceeds to complete the call for which it has already sent an initial address message (IAM). The IAM received from the slave is discarded. The call being processed by the slave is backed off and the switch path released. A release message is not sent. Glass - 1. In the strict sense, a state of matter. 2. In fiber-optic communication, any of a number of noncrystalline, amorphous inorganic substances, formed, by heating, from metallic or semiconductor oxides or halides, and used as the material for fibers. Note: The most common glasses are based on silicon dioxide (SiO2). 192
- 193. Glide Slope Facility - In aeronautical navigation, an instrument approach landing facility that furnishes vertical guidance information to an aircraft from its approach altitude down to the surface of the runway. Global - 1. Pertaining to, or involving, the entire world. 2. Pertaining to that which is defined in one subsection of an entity and used in at least one other subsection of the same entity. 3. In computer, data processing, and communications systems, pertaining to what is applicable to an area beyond the immediate area of consideration. Note: Examples of global entities are (a) in computer programming, an entity that is defined in one subdivision of a computer program and used in at least one other subdivision of that program and (b) in personal computer systems and their software packages, a setting, definition, or condition that applies to the entire software system. Global Address - In a communications network, the predefined address that is used as an address for all users of that network, and that may not be the address of an individual user, or subgroup of users, of the network. Global Area Network (GAN) - A network that (a) is composed of different interconnected computer networks and (b) covers an unlimited geographical area. Note: Loosely synonymous with an internet (as opposed to the Internet (with an uppercase "I"), which designates one specific network). Global Functional Plane (GFP) - The plane in the intelligent network conceptual model that defines service independent building blocks (SIBs) used in providing service features. Global Information Infrastructure - See GII. The totality of worldwide infrastructure elements that combine the three industry sectors of (a) telecommunications, (b) computer (information) technology, and (c) consumer electronics to extend the capabilities of the NII (national information infrastructure) worldwide. Global Positioning System (GPS): See GPS. A satellite-based global navigation system that consists of (a) a constellation of 24 satellites in orbit 11,000 nmi above the Earth, (b) several on-station (i.e., in-orbit) spares, and (c) a ground-based control segment. The satellites transmit signals that are used for extremely accurate three-dimensional (latitude, longitude, and elevation) global navigation (position determination), and for the dissemination of precise time. GPS-derived position determination is based on the arrival times, at an appropriate receiver, of precisely timed signals from the satellites that are above the user's radio horizon. Global Status - 1. The set of attributes of an entity, described at a particular time, when that set is extended to every occurrence of that entity within a prescribed boundary. 2. The complete set of attributes necessary to describe an entity at a particular time. Global System for Mobile Communications (GSM) - A public, all-digital cellular network that is standardized worldwide and that uses (a) TDMA techniques for multiplexing at approximately 900 MHz, (b) compressed voice at about 13 kb/s, (c) 16 kb/s circuit-switching technology, and (d) error-correcting algorithms. Global Title (GT): A "logical" or "virtual" address used for routing Signaling System No. 7 (SS7) messages using signaling connection control part (SCCP) capabilities. To complete message routing, a GT must be translated to a SS7 point code and subsystem number. Glyph - Any graphic symbol not in the ASCII character set. GMT - Abbreviation for Greenwich Mean Time. Obsolete term. See Coordinated Universal Time. - Mean solar time at the meridian of Greenwich, England, formerly used as a basis for standard time throughout the world. 193
- 194. Go-Ahead Message - Synonym go-ahead notice. - In a tape-relay communications system, a service message, usually sent to a relay station or to a tributary station, that contains a request to the operator to resume transmitting over a specified channel or channels. Synonyms start notice. Go-Ahead Notice - In a tape-relay communications system, a service message, usually sent to a relay station or to a tributary station, that contains a request to the operator to resume transmitting over a specified channel or channels. Synonyms go-ahead message, start message, start notice. Go-Ahead Tone - In communications systems, an audible signal transmitted by a system indicating that the system is ready to receive a message or signal. Gold Code - In spread-spectrum systems, a code that is generated by summing, using modulo-two addition, the outputs of two spread-spectrum code-sequence generators. Go List - Synonyms bookmark list, history list, hotlist. Gopher - A system of clients and servers, in menu format, that allows for navigation on the Internet. A menu- based information searching tool that allows users to access various types of databases, such as FTP archives and white pages databases. Note 1: Gopher is most often used as an Internet browser. Note 2: Gopher software uses the client-server model. Gopherspace - That part of the cyberspace to which the user has access by means of gopher software. Note: The use of gopher software has declined rapidly in recent years as the use of Web software has increased. GOS - Abbreviation for grade of service. - 1. The probability of a call's being blocked or delayed more than a specified interval, expressed as a decimal fraction. Note: Grade of service may be applied to the busy hour or to some other specified period or set of traffic conditions. Grade of service may be viewed independently from the perspective of incoming versus outgoing calls, and is not necessarily equal in each direction. 2. In telephony, the quality of service for which a circuit is designed or conditioned to provide, e.g., voice grade or program grade. Note: Criteria for different grades of service may include equalization for amplitude over a specified band of frequencies, or in the case of digital data transported via analog circuits, equalization for phase also. GOSIP - Acronym for Government Open Systems Interconnection Profile. A definition of Federal Government functional requirements for open systems computer network products, including a common set of Open System Interconnection (OSI) data communication protocols that enables systems developed by different vendors to interoperate and enable the users of different applications on these systems to exchange information. Note 1: The OSI protocols were developed primarily by ISO and CCITT (now, ITU-T). Note 2: The GOSIP is a subset of the OSI protocols and is based on agreements reached by vendors and users of computer networks participating in the National Institute of Standards and Technology (NIST) Implementors Workshop. Government Emergency Telecommunications Service (GETS) - A special federal government telecommunications service that provides National Security and Emergency Preparedness (NS/EP) users with priority switched voice and voiceband data communications during periods of emergency or crisis. GETS uses existing features and services of the Public Switched Network (PSN) with selected NS/EP augmentations and enhancements. Access to GETS requires a telephone calling card with personal identification number. GETS is maintained in a constant state of readiness to make maximum use of all available PSN telephone resources should network congestion or damage occur during an emergency or crisis. GETS calls receive priority over other traffic through special features such as trunk queuing, exemption from restrictive network management controls and Alternate Carrier Routing (ACR) on approximately 85% of all local carrier access lines. Comparable features provide priority treatment and enhanced routing in the interexchange networks. 194
- 195. While GETS calls receive priority for next available path, they do not preempt other traffic. The Signaling System No. 7 (SS7) -High Probability of Completion (HPC) Network Capability standard (ANSI T1.631-1993) is applied to provide NS/EP call identification and priority signaling. Government Open Systems Interconnection Profile - See GOSIP. A definition of Federal Government functional requirements for open systems computer network products, including a common set of Open System Interconnection (OSI) data communication protocols that enables systems developed by different vendors to interoperate and enable the users of different applications on these systems to exchange information. Note 1: The OSI protocols were developed primarily by ISO and CCITT (now, ITU-T). Note 2: The GOSIP is a subset of the OSI protocols and is based on agreements reached by vendors and users of computer networks participating in the National Institute of Standards and Technology (NIST) Implementors Workshop. GPI - Abbreviation for general purpose interface. An equipment-interface device (usually computer equipment) with some number of digital lines, usually a multiple of eight, which may be used for input, output, or both, depending on the function. Note: The digital lines may be individually controlled, although nothing precludes using them in combination. See general purpose interface. GPS - Abbreviation for global positioning system. A satellite-based global navigation system that consists of (a) a constellation of 24 satellites in orbit 11,000 nmi above the Earth, (b) several on-station (i.e., in-orbit) spares, and (c) a ground-based control segment. The satellites transmit signals that are used for extremely accurate three-dimensional (latitude, longitude, and elevation) global navigation (position determination), and for the dissemination of precise time. GPS-derived position determination is based on the arrival times, at an appropriate receiver, of precisely timed signals from the satellites that are above the user's radio horizon. Graceful Degradation - Degradation of a system in such a manner that it continues to operate, but provides a reduced level of service rather than failing completely. Graded-Index Fiber - An optical fiber with a core having a refractive index that decreases with increasing radial distance from the fiber axis. Note: The most common refractive index profile for a graded-index fiber is very nearly parabolic. The parabolic profile results in continual refocusing of the rays in the core, and compensates for multimode distortion. Graded-Index Profile - In the core of an optical fiber, a plot of the variation of refractive index such that the refractive index decreases with increasing radial distance from the fiber axis. Grade of Service (GOS) - 1. The probability of a call's being blocked or delayed more than a specified interval, expressed as a decimal fraction. Note: Grade of service may be applied to the busy hour or to some other specified period or set of traffic conditions. Grade of service may be viewed independently from the perspective of incoming versus outgoing calls, and is not necessarily equal in each direction. 2. In telephony, the quality of service for which a circuit is designed or conditioned to provide, e.g., voice grade or program grade. Note: Criteria for different grades of service may include equalization for amplitude over a specified band of frequencies, or in the case of digital data transported via analog circuits, equalization for phase also. Gradient - In graphics, especially computer graphics, that which characterizes an area in which a smooth transition between one color and another, or between black and white (i.e., contrast), takes place. Grandfathered Systems - Systems, including but not limited to: (a) PBX and key telephone systems, directly connected to the public switched telephone network on June 1, 1978, that may remain permanently connected thereto without registration unless subsequently modified, and (b) systems that are of the same type as those connected to the public switched telephone network on July 1, 1978, that were added before 195
- 196. January 1, 1980, and that may remain permanently connected thereto without registration unless subsequently modified. Grandfathered Terminal Equipment - Terminal equipment (other than PBX and key telephone systems) and protective circuitry connected to the public switched telephone network before July 1, 1978, that may remain connected thereto for life without registration unless subsequently modified. Graphical User Interface - See gui. A computer environment or program that displays, or facilitates the display of, on-screen options, usually in the form of icons (pictorial symbols) or menus (lists of alphanumeric characters) by means of which users may enter commands. Note 1: Options are selected by using the appropriate hardware (e.g., mouse, designated keyboard keys, or touchpad) to move a display cursor to, or on top of, the icon or menu item of interest. The application or function so represented may then be selected (e.g., by clicking a mouse button, pressing the "enter" key, or by touching the touchpad). Note 2: Pronounced "gooey." Graphic Character - 1. A visual representation of a character, other than a control character. 2. In the ASCII code, a character other than an alphanumeric character, intended to be written, printed, or otherwise displayed in a form that can be read by humans. Note 1: Graphic characters are contained in rows 2 through 7 of the ASCII code table. Note 2: The space and delete characters are considered to be graphic characters. Graphics - The art or science of conveying information through the use of display media, such as graphs, letters, lines, drawings, and pictures. Note: Graphics includes the transmission of coded images such as facsimile. Graphics Pipe - In computer science and technology, the special hardware within the computer optimized for the display of real-time 3D graphics. Gray Code - A binary code in which consecutive decimal numbers are represented by binary expressions that differ in the state of one, and only one, one bit. Synonym reflected code. Gray Scale - An optical pattern consisting of discrete steps or shades of gray between black and white. Great Circle - A circle defined by the intersection of the surface of the Earth and any plane that passes through the center of the Earth. Note: On the idealized surface of the Earth, the shortest distance between two points lies along a great circle. Greenwich Civil Time (GCT) - Synonym Greenwich Mean Time (GMT). Obsolete term. See Coordinated Universal Time. - Mean solar time at the meridian of Greenwich, England, formerly used as a basis for standard time throughout the world. Greenwich Mean Time (GMT) - Mean solar time at the meridian of Greenwich, England, formerly used as a basis for standard time throughout the world. Obsolete term. Synonym Greenwich Civil Time. See Coordinated Universal Time. Ground - 1. An electrical connection to earth through an earth-electrode subsystem. 2. In an electrical circuit, a common return path that usually (a) is connected to an earth-electrode subsystem and (b) is extended throughout a facility via a facility ground system consisting of the signal reference subsystem, the fault protection subsystem, and the lightning protection subsystem. 3. In an electrical circuit, a common return path that (a) may not necessarily be connected to earth and (b) is the zero voltage reference level for the equipment or system. 196
- 197. Ground Absorption - The dissipation of rf energy by the earth. Ground Constants - The electrical parameters of earth, such as conductivity, permittivity, and magnetic permeability. Note 1: The values of these parameters vary with the local chemical composition and density of the earth. Note 2: For a propagating electromagnetic wave, such as a surface wave propagating along the surface of the Earth, these parameters vary with frequency and direction. Ground Current - In the presence of an electrical fault, the current that flows in the protective ground wire of a power distribution system. Ground Loop - In an electrical system, an unwanted current that flows in a conductor connecting two points that are nominally at the same potential, i.e., ground, but are actually at different potentials. Note 1: For example, the electrical potential at different points on the surface of the Earth can vary by hundreds of volts, primarily from the influence of the solar wind. Such an occurrence can be hazardous, e.g., to personnel working on long grounded conductors such as metallic telecommunications cable pairs. Note 2: A ground loop can also exist in a floating ground system, i.e., one not connected to an Earth ground, if the conductors that constitute the ground system have a relatively high resistance, or have, flowing through them, high currents that produce a significant voltage ("I•R") drop. Note 3: Ground loops can be detrimental to the operation of the electrical system. Ground Plane - An electrically conductive surface that serves as the near-field reflection point for an antenna. Note: A ground plane may consist of a natural (e.g., Earth or sea) surface, an artificial surface of opportunity (e.g., the roof of a motor vehicle), or a specially designed artificial surface (e.g., the disc of a discone antenna). Ground Potential - The zero reference level used to apply and measure voltages in a system. Note: A potential difference may exist between this reference level and the ground potential of the Earth, which varies with locality, soil conditions, and meteorological phenomena. Ground-Return Circuit - 1. A circuit using a common return path that is at ground potential. Note: Earth may serve as a portion of the ground-return circuit. 2. A circuit in which there is a common return path, whether or not connected to earth. Ground Start - A line or equipment that establishes a dial tone by completing a circuit between one of the wires of the line and earth ground. Ground start circuits are used mainly for PBX applications. Loop start equipment will not operate if connected directly to a ground start line. A method of signaling from a terminal or subscriber loop to a switch, in which method one side of a cable pair is temporarily grounded. Ground-Start Signaling - A type of analog voicegrade access line signaling that requires the customer interface (CI) to provide a ground on the ring conductor at the network interface (NI) to initiate service requests. Ground Wave - In radio transmission, a surface wave that propagates close to the surface of the Earth. Note 1: The Earth has one refractive index and the atmosphere has another, thus constituting an interface that supports surface wave transmission. These refractive indices are subject to spatial and temporal changes. Note 2: Ground waves do not include ionospheric and tropospheric waves. Ground Window - The interface or transition point between the isolated and integrated ground planes. The ground window can be a dimensional area around a bus bar or the bus bar itself. After passing through the ground window, there shall be no additional paths to ground, intentional or unintentional, inside the isolated ground plane. 197
- 198. Group - 1. In frequency-division multiplexing, a specific number of associated voice channels, either within a supergroup or as an independent entity. Note 1: In wideband systems, a group usually consists of 12 voice channels and occupies the frequency band from 60 kHz to 108 kHz. Note 2: this is ITU-T group B (formerly CCITT group B). Note 3: ITU-T Basic Group A, for carrier telephone systems, consists of 12 channels occupying upper sidebands in the 12-kHz to 60-kHz band. Basic Group A is no longer mentioned in ITU-T Recommendations. Note 4: A supergroup usually consists of 60 voice channels, i.e., 5 groups of 12 voice channels each, occupying the frequency band from 312 kHz to 552 kHz. Note 5: A mastergroup consists of 10 supergroups or 600 voice channels. Note 6: The ITU-T standard mastergroup consists of 5 supergroups. The U.S. commercial carrier standard mastergroup consists of 10 supergroups. Note 7: The terms "supermaster group" or "jumbo group" are sometimes used to refer to 6 mastergroups. 2. A set of characters forming a unit for transmission or cryptographic treatment. Group Address - In a communications network, a predefined address used to address only a specified set of users. Synonym collective address. Group Alerting and Dispatching System - A service feature that (a) enables a controlling telephone to place a call to a specified number of telephones simultaneously, (b) enables the call to be recorded, (c) if any of the called lines is busy, enables the equipment to camp on until the busy line is free, and (d) rings the free line and plays the recorded message. Group Busy Hour (GBH): The busy hour for a given trunk group. Group Delay - 1. The rate of change of the total phase shift with respect to angular frequency, d /d , through a device or transmission medium, where is the total phase shift, and is the angular frequency equal to 2 f, where f is the frequency. 2. In an optical fiber, the transit time required for optical power, traveling at a given mode's group velocity, to travel a given distance. Note: For optical fiber dispersion measurement purposes, the quantity of interest is group delay per unit length, which is the reciprocal of the group velocity of a particular mode. The measured group delay of a signal through an optical fiber exhibits a wavelength dependence due to the various dispersion mechanisms present in the fiber. Group Delay Time - In a group of waves that have slightly different individual frequencies, the time required for any defined point on the envelope (i.e., the envelope determined by the additive resultant of the group of waves) to travel through a device or transmission facility. Group Distribution Frame (GDF) - In frequency-division multiplexing, a distribution frame that provides terminating and interconnecting facilities at the group level, i.e., group modulator output and group demodulator input circuits of FDM carrier equipment. Note: The basic spectrum of the FDM group is 60 kHz to 108 kHz. Group Index (N): In fiber optics, for a given mode propagating in a medium of refractive index , the velocity of light in vacuum, c, divided by the group velocity of the mode. Grouping Factor - Synonym blocking factor. - The number of records in a block. Note: The blocking factor is calculated by dividing the block length by the length of each record contained in the block. If the records are not of the same length, the average record length may be used to compute the blocking factor. Group 1. . . 4 facsimile - See facsimile. Group Patch Bay - See patch bay. 198
- 199. Group Velocity - 1. The velocity of propagation of an envelope produced when an electromagnetic wave is modulated by, or mixed with, other waves of different frequencies. Note: The group velocity is the velocity of information propagation and, loosely, of energy propagation. 2. In optical fiber transmission, for a particular mode, the reciprocal of the rate of change of the phase constant with respect to angular frequency. Note: The group velocity equals the phase velocity if the phase constant is a linear function of the angular frequency, = 2 f, where f is the frequency. 3. In optical-fiber transmission, the velocity of the modulated optical power. Groupware - Network-compatible software applications that facilitate shared work on information and documents. GSM (Global System for Mobile communication) - A digital mobile telephone system that is widely used in Europe and other parts of the world. GSM uses a variation of time division multiple access (TDMA) and is the most widely used of the three digital wireless telephone technologies (TDMA, GSM, and CDMA). GSM digitizes and compresses data, then sends it down a channel with two other streams of user data, each in its own time slot. It operates at either the 900 MHz or 1800 MHz frequency band. GSM is the de facto wireless telephone standard in Europe. GSM has over 120 million users worldwide and is available in 120 countries, according to the GSM MoU Association. Since many GSM network operators have roaming agreements with foreign operators, users can often continue to use their mobile phones when they travel to other countries. American Personal Communications (APC), a subsidiary of Sprint, is using GSM as the technology for a broadband personal communications service (PCS). The service will ultimately have more than 400 base stations for the palm-sized handsets that are being made by Ericsson, Motorola, and Nokia. The handsets include a phone, a text pager, and an answering machine. GSM together with other technologies is part of an evolution of wireless mobile telemmunication that includes High-Speed Circuit-Switched Data (HCSD), General Packet Radio System (GPRS), Enhanced Data GSM Environment (EDGE), and Universal Mobile Telecommunications Service (UMTS). G /T - Abbreviation for antenna gain-to-noise-temperature. Guard - In computer security, a functional unit that provides a security filter between two data processing systems operating at different security levels or between a user terminal and a database to filter out data that the user is not authorized to access. Guard Band - See frequency guard band, time guard band. Guarded Frequency - A transmission frequency that is not to be jammed or interfered with because of the value of the information being derived from it. Note: For example, a guarded frequency will not be jammed when the tactical, strategic, and technical information that can be obtained from the transmissions outweighs the potential operational gain achieved by jamming. Gui - Acronym for graphical user interface. A computer environment or program that displays, or facilitates the display of, on-screen options, usually in the form of icons (pictorial symbols) or menus (lists of alphanumeric characters) by means of which users may enter commands. Note 1: Options are selected by using the appropriate hardware (e.g., mouse, designated keyboard keys, or touchpad) to move a display cursor to, or on top of, the icon or menu item of interest. The application or function so represented may then be selected (e.g., by clicking a mouse button, pressing the "enter" key, or by touching the touchpad). Note 2: Pronounced "gooey." 199
- 200. Guided Mode - Synonym bound mode. In an optical fiber, a mode that (a) has a field intensity that decays monotonically in the transverse direction everywhere external to the core and (b) does not lose power to radiation. Note: Except for single-mode fibers, the power in bound modes is predominantly contained in the core of the fiber. Guided Ray - In an optical fiber, a ray that is confined primarily to the core. Synonyms bound ray, trapped ray. Guided Wave - A wave having (a) energy concentrated near a boundary, or between substantially parallel boundaries, separating materials of different properties and (b) a direction of propagation effectively parallel to these boundaries. H H.323 - The standard call protocol for voice and videoconferencing over LANs, WANs, and the Internet, allowing these activities on a real-time basis as opposed to a packet-switched network. Initially designed to allow multimedia to function over unreliable networks, it's the oldest and most established of the VoIP protocols. See also SIP and MGCP. Hack - 1. To break into or use a computer network or use a system without authorization, as a hacker might do. 2. Referring to a track used to bypass a flaw or a bug in an application program or application. Hacker - 1. A person who breaks into, or attempts to break into, or use, a computer network or system without authorization, often at random, for personal amusement or gratification, and not necessarily with malicious intent. 2. [An] unauthorized user who attempts to or gains access to an information system. 3. A technically sophisticated computer expert who intentionally gains unauthorized access to targeted protected resources. 4. Loosely, a computer enthusiast. 5. A person who uses a computer resource in a manner for which it is not intended or which is in conflict with the terms of an acceptable-use policy, but (unlike the work of a cracker) is not necessarily malicious in intent. hack: 1. To break into or use a computer network or use a system without authorization, as a hacker might do. 2. Referring to a track used to bypass a flaw or a bug in an application program or application. Hagelbarger Code - A convolutional code that enables error bursts to be corrected provided that there are relatively long error-free intervals between the error bursts. Note: In the Hagelbarger code, inserted parity check bits are spread out in time so that an error burst is not likely to affect more than one of the groups in which parity is checked. Half-Duplex (HDX) Operation - Operation in which communication between two terminals occurs in either direction, but in only one direction at a time. Note: Half-duplex operation may occur on a half-duplex circuit or on a duplex circuit, but it may not occur on a simplex circuit. Synonyms one-way reversible operation, two-way alternate operation. Halftone - Any photomechanical printing surface or the impression therefrom in which detail and tone values are represented by a series of evenly spaced dots in varying size and shape, varying in direct proportion to the intensity of tones they represent Halftone Characteristic - 1. In facsimile systems, the relationship between the density of the recorded copy and the density of the object, i.e., the original. 2. In facsimile systems, the relationship between the amplitude of the facsimile signal to either the density of the object or the density of the recorded copy when only a portion of the system is under consideration. Note: In an FM facsimile system, an appropriate parameter other than the amplitude is used. 200
- 201. Hamming code: An error-detecting and error-correcting binary code, used in data transmission, that can (a) detect all single- and double-bit errors and (b) correct all single-bit errors. Note: A Hamming code satisfies m the relation 2 n +1, where n is the total number of bits in the block, k is the number of information bits in the block, and m is the number of check bits in the block, where m = n-k. Hamming Distance - The number of digit positions in which the corresponding digits of two binary words of the same length are different. Note 1: The Hamming distance between 1011101 and 1001001 is two. Note 2: The concept can be extended to other notation systems. For example, the Hamming distance between 2143896 and 2233796 is three, and between "toned" and "roses" it is also three. Synonym signal distance. Hamming Weight - The number of non-zero symbols in a symbol sequence. Note: For binary signaling, Hamming weight is the number of "1" bits in the binary sequence. Handoff - 1. In cellular mobile systems, the process of transferring a phone call in progress from one cell transmitter and receiver and frequency pair to another cell transmitter and receiver using a different frequency pair without interruption of the call. Synonym handover. 2. In satellite communications, the process of transferring ground-station control responsibility from one ground station to another without loss or interruption of service. Handover - 1. In telephony, synonym handoff. 2. The transfer (permanent or temporary) of a component or series of components to another application process. 3. The automatic rerouting of the radio portion of a call for signal quality, traffic management, or other reasons. Handshaking - 1. In data communications, a sequence of events governed by hardware or software, requiring mutual agreement of the state of the operational modes prior to information exchange. 2. The process used to establish communications parameters between two stations. Note: Handshaking follows the establishment of a circuit between the stations and precedes information transfer. It is used to agree upon such parameters as information transfer rate, alphabet, parity, interrupt procedure, and other protocol features. Handshaking Procedures - [The] dialogue between two information systems for synchronizing, identifying, and authenticating themselves to one another. Hangover - Synonym tailing. In facsimile systems, the excessive prolongation of the decay of the signal. Hang-Up - Calling- or called-user placement of a telephone set or other unit of telecommunications equipment in the quiescent state. Hang-Up Signal - An on-hook signal sent from an end office toward the disconnect-control office indicating either calling or called user hang-up and requesting the connection be disconnected. The interface remains dedicated to the call until the disconnect-control office responds to the hang-up signal. HA1-Receiver Weighting - A noise weighting used in a noise measuring set to measure noise across the HA1- receiver of a 302-type or similar instrument. Note 1: The meter scale readings of an HA1 test set are in dBa (HA1). Note 2: HA1 noise weighting is obsolete for new DOD applications. Hard Copy - In computer graphics and in telecommunications, a permanent reproduction, on any media suitable for direct use by a person, of displayed or transmitted data. Note 1: Examples of hard copy include teletypewriter pages, continuous printed tapes, facsimile pages, computer printouts, and radiophoto prints. Note 2: Magnetic tapes, diskettes, and nonprinted punched paper tapes are not hard copy. 201
- 202. Hard-Copy Key - [A] physical keying material, such as printed key lists, punched or printed key tapes, or programmable, read-only memories (pROM). Hard Disk - A flat, circular, rigid plate with a magnetizable surface on one or both sides of which data can be stored. Note: A hard disk is distinguished from a diskette by virtue of the fact that it is rigid. Early in the development of computer technology, hard disks, often multiple disks mounted on a common spindle, were interchangeable and removable from their drives, which were separate from the processor chassis. This technology is still in use, especially in conjunction with large mainframe computers, but physically smaller computers use hard disks that are in sealed units, along with their control electronics and read /write heads. The sealed units are usually installed permanently in the same chassis that contains the processor. Hard-Drawn Copper Wire - Copper wire that has not been annealed after being drawn. Hardened - Pertaining to the condition of a facility with protective features that enable it to withstand destructive forces, such as explosions, natural disasters, or ionizing radiation. Hard Limiting - See limiting. Any process by which a specified characteristic (usually amplitude) of the output of a device is prevented from exceeding a predetermined value. Note 1: Hard limiting (" clipping ") is a limiting action in which there is (a) over the permitted dynamic range, negligible variation in the expected characteristic of the output signal, and (b) a steady-state signal, at the maximum permitted level, for the duration of each period when the output would otherwise be required to exceed the permitted dynamic range in order to correspond to the transfer function of the device. Note 2: Soft limiting is limiting in which the transfer function of a device is a function of its instantaneous or integrated output level. The output waveform is therefore distorted, but not clipped. Hard Sectoring - In magnetic or optical disk storage, sectoring that uses a physical mark on the disk, from which mark sector locations are referenced. Note: Hard sectoring may be done, for example, by punching an index hole in a floppy diskette. When the presence of the index hole is recognized by an optical reader, a reference signal is generated. All sector locations can be referenced from this signal. Hardware - 1. Physical equipment as opposed to programs, procedures, rules, and associated documentation. 2. The generic term dealing with physical items as distinguished from its capability or function such as equipment, tools, implements, instruments, devices, sets, fittings, trimmings, assemblies, subassemblies, components, and parts. The term is often used in regard to the stage of development, as in the passage of a device or component from the design stage into the hardware stage as the finished object. 3. In data automation, the physical equipment or devices forming a computer and peripheral components. Hardware Platform - Synonym platform. 1. The type of computer on which a given operating system or application runs. Synonym hardware platform. 2. The operating system in use on a given computer. Synonym operating system platform. 3. The application program in use on a given computer and operating system. Synonym application platform. Note 1: The term platform, usually with some kind of accompanying qualifying verbiage, may also be applied to any combination of the foregoing. Note 2: The term cross- platform may be used to characterize an application program or operating system that may be run on more than one platform. Hardwire - 1. To connect equipment or components permanently in contrast to using switches, plugs, or connectors. 2. To wire in fixed logic or read-only storage that cannot be altered by program changes. Hardwired Key - [A] permanently installed key. Information (usually a sequence of random or pseudorandom binary digits) used initially to set up and permanently installed for the operations performed in crypto- equipment for the purpose of encrypting or decrypting electronic signals, for determining electronic counter- 202
- 203. countermeasures patterns (e.g., frequency hopping or spread spectrum), or for producing other key. Note: "Key" has replaced the terms "variable," "key(ing) variable," and "cryptovariable." Harmful Interference - 1. Any emission, radiation, or induction interference that endangers the functioning or seriously degrades, obstructs, or repeatedly interrupts a communications system, such as a radio navigation service, telecommunications service, radio communications service, search and rescue service, or weather service, operating in accordance with approved standards, regulations, and procedures. Note: To be considered harmful interference, the interference must cause serious detrimental effects, such as circuit outages and message losses, as opposed to interference that is merely a nuisance or annoyance that can be overcome by appropriate measures. 2. Interference which endangers the functioning of a radionavigation service or of other safety services or seriously degrades, obstructs, or repeatedly interrupts a radiocommunication service operating in accordance with these [Radio] Regulations. Harmonic - 1. Of a sinusoidal wave, an integral multiple of the frequency of the wave. Note: The frequency of the sine wave is called the fundamental frequency or the first harmonic, the second harmonic is twice the fundamental frequency, the third harmonic is thrice the fundamental frequency, etc. 2. Of a periodic signal or other periodic phenomenon, such as an electromagnetic wave or a sound wave, a component frequency of the signal that is an integral multiple of the fundamental frequency. Note: The fundamental frequency is the reciprocal of the period of the periodic phenomenon. Harmonic Distortion - In the output signal of a device, distortion caused by the presence of frequencies that are not present in the input signal. Note: Harmonic distortion is caused by nonlinearities within the device. Hash Function - A mathematical function that maps values from a large (or very large) domain into a smaller range, and that reduces a potentially long message into a "message digest" or "hash value" or that is sufficiently compact to be input into a digital signature algorithm. Note: A "good" hash function is one that results from applying the function to a (large) set of values that are evenly (and randomly) distributed over the range. Hashing - Computation of a hash total, which is: 1. The result obtained by subjecting a set of data to an algorithm for purposes of checking the data at the time the algorithm is applied or for use at a later time such as after transmission or retrieval from storage. 2. [A] value computed on data to detect error or manipulation. Hash Total - 1. The result obtained by subjecting a set of data to an algorithm for purposes of checking the data at the time the algorithm is applied or for use at a later time such as after transmission or retrieval from storage. 2. [A] value computed on data to detect error or manipulation. See checksum. Hash Value - In cryptography, the result of applying a cryptologic hash function to a message. Hashword - [The] memory address containing [a] hash total. Hazards of Electromagnetic Radiation to Fuel (HERF) - The potential for electromagnetic radiation to cause ignition or detonation of volatile combustibles, such as aircraft fuels. Hazards of Electromagnetic Radiation to Ordnance (HERO) - The potential for electromagnetic radiation to affect adversely munitions or electroexplosive devices. Hazards of Electromagnetic Radiation to Personnel (HERP) - The potential for electromagnetic radiation to produce harmful biological effects in humans. 203
- 204. H-bend - A smooth change in the direction of the axis of a waveguide, throughout which the axis remains in a plane parallel to the direction of magnetic H-field (transverse) polarization. Synonym H-plane bend. H-channel - In Integrated Services Digital Networks (ISDN), a 384-kb/s, 1472-kb/s, or 1536-kb/s channel, designated as "H0", "H10", and "H11", respectively, accompanied by timing signals used to carry a wide variety of user information. Note: Examples of types of user information representation forms include fast facsimile, video, high-speed data, high-quality audio, packet-switched data, bit streams at rates less than the respective H-channel bit rate that have been rate-adapted or multiplexed together, and packet-switched information. HDCP - Abbreviation for High Definition Content Protection. Technology used to prevent piracy of high- quality uncompressed video, primarily over DVI connections. HDLC - Abbreviation for high-level data link control. A Link-Level protocol used to facilitate reliable point-to- point transmission of a data packet. Note: A subset of HDLC, known as " LAP-B," is the Layer-two protocol for ITU-T Recommendation X.25. HDMI - Abbreviation for High Definition Multimedia Interface. A high-quality digital connector. Similar to DVI and sometimes with HDCP, HDMI can digitally transmit uncompressed high-definition video and audio on the same cable, preserving picture and sound quality. HDTV - Abbreviation for high-definition television. Television that has approximately twice the horizontal and twice the vertical emitted resolution specified by the NTSC standard. The highest quality digital television, generally widescreen 16:9. It consists of either 1080 interlaced or 720 progressively scanned lines of resolution and includes the ability to transmit digital surround sound. Note that HDTV and DTV are not the same thing — HDTV is one format of DTV. Note 1: In HDTV, the total number of pixels is therefore approximately four times that of the NTSC standard. Note 2: HDTV may include any or all improved- definition television (IDTV) and extended-television (EDTV) improvements. Note 3: HDTV employs a wide aspect ratio. HDTV Monitor (also HDTV-Ready) - A TV set with the inputs and capability to become an HDTV with the addition of an HDTV tuner, HD cable set-top box, or HD satellite receiver. HDTV Tuner (also known as Decoder or Receiver) - A device capable of receiving and decoding HDTV signals. HDTV tuners can either be built into a TV set (called an Integrated Digital TV Set) or be a stand-alone device, such as a set-top box. HDX - Abbreviation for half-duplex (HDX) operation. Operation in which communication between two terminals occurs in either direction, but in only one direction at a time. Note: Half-duplex operation may occur on a half-duplex circuit or on a duplex circuit, but it may not occur on a simplex circuit. Synonyms one- way reversible operation, two-way alternate operation. Head - A device that reads, writes, and/or erases data on a storage medium. Head End - See cable headend, headend. 1. A central control device required by some networks (e.g., LANs or MANs) to provide such centralized functions as remodulation, retiming, message accountability, contention control, diagnostic control, and access to a gateway. 2. A control center of a CATV system, where incoming signals are amplified, converted, processed, and combined into a common cable for transmission to customers. The headend usually includes antennas, preamplifiers, frequency converters, demodulators, modulators, processors, and other related equipment. Synonym [in this sense] cable headend. 204
- 205. Headend - 1. A central control device required by some networks (e.g., LANs or MANs) to provide such centralized functions as remodulation, retiming, message accountability, contention control, diagnostic control, and access to a gateway. 2. A control center of a CATV system, where incoming signals are amplified, converted, processed, and combined into a common cable for transmission to customers. The headend usually includes antennas, preamplifiers, frequency converters, demodulators, modulators, processors, and other related equipment. Header - The portion of a message that contains information used to guide the message to the correct destination. Note: Examples of items that may be in a header are the addresses of the sender and receiver, precedence level, routing instructions, and synchronizing bits. Header Check Sequence (HCS) - A 16-bit cyclic redundancy check (CRC) check sequence (CS) that is derived from bits from the first 8 octets (excluding flags) of a UIH format packet. Head-of-Bus Function - The function that generates management information and empty bus slots at the point on each bus where data flow begins. Head-on Collision - A collision that occurs on a communications channel when two or more users begin to transmit on the channel at approximately the same instant. Heaviside Layer -That portion of the ionosphere existing between approximately 95 and 130 km above the surface of the Earth. Note: The Heaviside Layer ( E Region) lies between the D and F regions. Synonym E region, Kennelly-Heaviside layer. Height Gain - For a given propagation mode of an electromagnetic wave, the ratio of the field strength at a specified height to the field strength at the surface of the Earth. Helical Antenna - An antenna that has the form of a helix. Note: When the helix circumference is much smaller than one wavelength, the antenna radiates at right angles to the axis of the helix. When the helix circumference is one wavelength, maximum radiation is along the helix axis. Helical Scan - A method of recording video information diagonally on a tape, used in home and professional video cassette recorders (VCRs). Note: High-speed rotating video heads scan these diagonal video tracks, giving an effective tape speed much higher than the actual tape speed, allowing more information to be recorded on a given length of magnetic tape. HEMP - Abbreviation for high-altitude electromagnetic pulse. An electromagnetic pulse produced at an altitude effectively above the sensible atmosphere, i.e., above about 120 km. HE11 Mode - Designation for the fundamental hybrid mode of an optical fiber. HERF - Abbreviation for hazards of electromagnetic radiation to fuel. The potential for electromagnetic radiation to cause ignition or detonation of volatile combustibles, such as aircraft fuels. HERO - Abbreviation for hazards of electromagnetic radiation to ordnance. The potential for electromagnetic radiation to affect adversely munitions or electroexplosive devices. HERP - Abbreviation for hazards of electromagnetic radiation to personnel. - The potential for electromagnetic radiation to produce harmful biological effects in humans. 205
- 206. Hertz (Hz) - 1. The SI unit of frequency, equal to one cycle per second. Note: A periodic phenomenon that has a period of one second has a frequency of one hertz. 2. A unit of frequency which is equivalent to one cycle per second. Hertzian Wave - Synonym radio wave. An electromagnetic wave of a frequency arbitrarily lower than 3000 GHz. Heterochronous - A relationship between two signals such that their corresponding significant instants do not necessarily occur at the same time. Note: Two signals having different nominal signaling rates and not stemming from the same clock or from homochronous clocks are usually heterochronous. Heterodyne - 1. To generate new frequencies by mixing two or more signals in a nonlinear device such as a vacuum tube, transistor, or diode mixer. Note: A superheterodyne receiver converts any selected incoming frequency by heterodyne action to a common intermediate frequency where amplification and selectivity (filtering) are provided. 2. A frequency produced by mixing two or more signals in a nonlinear device. Heterodyne Repeater - In radio reception and retransmission, a repeater that converts the original band of frequencies of the received signal to a different frequency band for retransmission after amplification. Note: Heterodyne repeaters are used, for example, in microwave systems, to avoid undesired feedback between the receiving and transmitting antennas. Synonym IF repeater. Heterogeneous Multiplexing - Multiplexing in which not all the information-bearer channels operate at the same data signaling rate. Heuristic Routing - Routing in which data, such as time delay, extracted from incoming messages, during specified periods and over different routes, are used to determine the optimum routing for transmitting data back to the sources. Note: Heuristic routing allows a measure of route optimization based on recent empirical knowledge of the state of the network. Hexadecimal - 1. Characterized by a selection, choice or condition that has sixteen possible different values or states. Synonym sexadecimal. 2. Pertaining to a fixed-radix numeration system in which the radix is sixteen. HF - Abbreviation for high frequency. Frequencies from 3 MHz to 30 MHz. HFDF - Abbreviation for high-frequency distribution frame (HFDF): A distribution frame that provides terminating and interconnecting facilities for those combined supergroup modulator output circuits and combined supergroup demodulator input circuits that contain signals occupying the baseband spectrum. Hierarchical Computer Network - A computer network in which processing and control functions are performed at several levels by computers specially suited for the functions performed, such as industrial process control, inventory control, database control, or hospital automation. Hierarchically Synchronized Network - A mutually synchronized network in which some clocks exert more control than others, the network operating frequency being a weighted mean of the natural frequencies of the population of clocks. Hierarchical Routing - Routing that is based on hierarchical addressing. Note: Most Transmission Control Protocol / Internet Protocol (TCP/IP) routing is based on a two-level hierarchical routing in which an IP address is divided into a network portion and a host portion. Gateways use only the network portion until an 206
- 207. IP datagram reaches a gateway that can deliver it directly. Additional levels of hierarchical routing are introduced by the addition of subnetworks. High-Altitude Electromagnetic Pulse (HEMP) - An electromagnetic pulse produced at an altitude effectively above the sensible atmosphere, i.e., above about 120 km. High-Definition Television (HDTV) - Television that has approximately twice the horizontal and twice the vertical emitted resolution specified by the NTSC standard. Note 1: In HDTV, the total number of pixels is therefore approximately four times that of the NTSC standard. Note 2: HDTV may include any or all improved-definition television (IDTV) and extended-television (EDTV) improvements. Note 3: HDTV employs a wide aspect ratio. Higher Frequency Ground - Deprecated name for facility grounding system. The electrically interconnected system of conductors and conductive elements that (a) provides multiple current paths to the earth electrode subsystem, and (b) consists of the earth electrode subsystem, the lightning protection subsystem, and the fault protection subsystem. High Frequency (HF): Frequencies from 3 MHz to 30 MHz. See electromagnetic spectrum. High-Frequency Distribution Frame (HFDF) - A distribution frame that provides terminating and interconnecting facilities for those combined supergroup modulator output circuits and combined supergroup demodulator input circuits that contain signals occupying the baseband spectrum. High-Level Control - In the hierarchical structure of a primary or secondary data transmission station, the conceptual level of control or processing logic that (a) is above the Link Level and (b) controls Link Level functions, such as device control, buffer allocation, and station management. High-Level Data Link Control (HDLC) - A Link-Level protocol used to facilitate reliable point-to-point transmission of a data packet. Note: A subset of HDLC, known as " LAP-B," is the Layer-two protocol for ITU-T Recommendation X.25. High-Level Language (HLL) - A computer programming language that is primarily designed for, and syntactically oriented to, particular classes of problems and that is essentially independent of the structure of a specific computer or class of computers; for example, Ada ®, COBOL, Fortran, Pascal. Synonym high- order language. High-Order Language - Synonym high-level language. High-Pass Filter - A filter that passes frequencies above a given frequency and attenuates all others. High-Performance Equipment - Equipment that (a) has the performance characteristics required for use in trunks or links, (b) is designed primarily for use in global and tactical systems, and (c) sufficiently withstands electromagnetic interference when operating in a variety of network or point-to-point circuits. Note: Requirements for global and tactical high-performance equipment may differ. High-Priority Emergency Service Call - A call identified as receiving emergency service treatment, which has been marked as requiring special treatment by the emergency service administration. The call has an associated CESID and transfer numbers. 207
- 208. High Probability of Completion (HPC) - With reference to American National Standard ANSI T1.631-1993, an aspect of National Security and Emergency Preparedness (NS/EP) telephone calls, as implemented in the public switched network (PSN) for the Government Emergency Telecommunications Service (GETS). High Sierra Format - A standard format for placing fields and directories on CD ROM, revised and adopted by the International Organization for Standardization as ISO 9660. High-Usage Trunk Group - A group of trunks for which an alternate route has been provided to absorb the relatively high rate of overflow traffic. Highway - 1. A digital serial-coded bit stream with time slots allotted to each call on a sequential basis. 2. A common path or a set of parallel paths over which signals from more than one channel pass with separation achieved by time division. Hiss - Noise in the audio frequency range, having subjective characteristics analogous to prolonged sibilant sounds. Note: Noise in which there are no pronounced low-frequency components may be considered as hiss. History List - A record of the documents visited during a Web session, which list allows users to access previously visited pages more quickly or to generate a record of a user's progress. Synonym bookmark list, go list, hotlist. Hit - 1. A transient disturbance to, or momentary interruption of, a communication channel, power supply (especially that provided via a commercial electric power distribution network or grid, but not limited to same), etc. 2. A match of a data item to a prescribed criterion or criteria. Note: For example, each of the matches from a search engine is called a "hit." 3. The access of any item, such as a page or a graphic image, from a Web server. Note 1: Hits are recorded for the purpose of assessing traffic /interest in a web site; many web sites have a commercial sponsor who pays a small amount per hit for displaying the commercial advertisement on that site. Note 2: The number of hits on a web site is not synonymous with the number of distinct visitors. 4. The number of document requests being answered by a server. Hit Counter - An indicator on a Web page that graphically displays the number of previous users that have accessed the page. HLL: Abbreviation for high-level language. A computer programming language that is primarily designed for, and syntactically oriented to, particular classes of problems and that is essentially independent of the structure of a specific computer or class of computers; for example, Ada ®, COBOL, Fortran, Pascal. Hockey Puck - A polishing fixture used to facilitate the manual finishing of the endfaces of certain types of optical fiber connectors. Note 1: The hockey puck consists of the appropriate mating sleeve for the connector in question, mounted at right angles to, and in the center of, a disk of stainless steel or other hard material. When the unfinished connector, secured to the fiber-optic cable, is mounted in the hockey puck, excess material (e.g., fiber end, bead of adhesive material, and excess connector length, if present) protrudes from the opposite side of the disk. The excess is then ground away as the fixture is manually swept to and fro, usually in a figure-8 pattern, in contact with a piece of microfinishing film which is in turn supported by a rigid flat substrate. Two to four grades of microfinishing film, with abrasive particles ranging in size from 15 m to 0.3 m, are commonly used. Note 2: Various manufacturers use proprietary names to identify this device; however "hockey puck" has become ubiquitous. Hold-in Frequency Range - The range of frequencies over which a phase-locked loop can vary and still maintain frequency lock. 208
- 209. Holding Time - 1. The total length of time that a call makes use of a trunk or channel. Note: Holding time is usually measured in seconds. 2. The time in which an item of telephone plant is in actual use either by a customer or an operator. For example, on a completed telephone call, holding time includes conversation time as well as other time in use. At local dial offices any measured minutes which result from other than customer attempts to place calls (as evidenced by the dialing of at least one digit) are not treated as holding time. Hold-in Range - See hold-in frequency range. The range of frequencies over which a phase-locked loop can vary and still maintain frequency lock. Home Network - The carrier's own Signaling System No. 7 (SS7) network. Home Page - The Web document that your browser displays when you access a site - typically the main page of a Web site. 1. The document that is configured to be displayed first when a Web browser is opened. 2. The document designed to be the user's point of entry into a Web site, or the page that the user first sees when he or she first visits a company's Web site. Homing - 1. A process in which a mobile station is directed, or directs itself, toward an electromagnetic, thermal, sonic, or other source of energy, whether primary or reflected, or follows a vector force field or a gradient of a scalar force field. 2. In radio direction-finding, the locating of a moving signal source by a moving direction-finding station that has a mobile advantage. 3. The act of approaching a source of electromagnetic radiation in which the approaching vehicle is guided by a receiver with a directional antenna. 4. Seeking, finding, intercepting, and engaging an object, i.e., a target (fixed or mobile) that may contain a signal source. Homochronous - The relationship between two signals such that their corresponding significant instants are displaced by a constant interval of time. Homogeneous Cladding - In an optical fiber, a cladding in which the nominal refractive index is constant throughout. Note: An optical fiber may have several homogeneous claddings, each having a different refractive index. Homogeneous Multiplexing - Multiplexing in which all of the information-bearer channels operate at the same data signaling rate. Hop - 1. The excursion of a radio wave from the Earth to the ionosphere and back to the Earth. Note: The number of hops is synonymous with the number of reflections from the ionosphere. 2. A waveform transmitted for the duration of each relocation of the carrier frequency of a frequency-hopped system. 3. To modify a modulated waveform with constant center frequency so that it frequency hops. 4. An intermediate network connection consisting of a leg from one router to another router and over which a packet travels to reach its destination. Note: Hops can be traced using ping or other trace utilities. Hop Count - 1. In a data communications network, the number of legs traversed by a packet between its source and destination. Note: Hop count may be used to determine the time-to-live for some packets. 2. The number of signal regenerating devices (such as repeaters, bridges, routers, and gateways) through which data must pass to reach their destination. Horizon Angle - Of a directional antenna, the angle, in a vertical plane, subtended by the lines extending (a) from the antenna to the radio horizon and (b) from the antenna in its direction of maximum radiation. 209
- 210. Horizontal Redundancy Check - Synonym longitudinal redundancy check. - A system of error control based on the formation of a block check following preset rules. Note 1: The block check formation rules are applied in the same manner to each character. Note 2: A combination of longitudinal and vertical redundancy check allows the detection and correction of single bit errors. Horizontal Resolution - 1. In facsimile, the number of pixels per unit distance in the direction of scanning or recording. 2. In digital telegraphy, the number of pixels in the horizontal direction. 3. In raster-scanned television, the number of picture elements in a scan line. 4. In a computer monitor, the number of pixels per unit distance in the horizontal direction. Note: This value is inversely proportional to the dot pitch of the monitor. Horn - 1. In radio transmission, an open-ended waveguide, of increasing cross-sectional area, which radiates directly in a desired direction or feeds a reflector that forms a desired beam. Note 1: Horns may have one or more expansion curves, i.e., longitudinal cross sections, such as elliptical, conical, hyperbolic, or parabolic curves, and not necessarily the same expansion curve in each (E-plane and H-plane) cross section. Note 2: A very wide range of beam patterns may be formed by controlling horn dimensions and shapes, placement of the reflector, and reflector shape and dimensions. 2. A portion of a waveguide in which the cross section is smoothly increased along the axial direction. 3. In audio systems, a tube, usually having a rectangular transverse cross section and a linearly or exponentially increasing cross-sectional area, used for radiating or receiving acoustic waves. Horn Gap Switch - A switch provided with arcing horns, ordinarily used for disconnecting or breaking the charging current of overhead transmission and distribution lines. Host - A computer directly connected to the Internet. Also refers to a computer on a network that provides services to other computers on the network. 1. In packet- and message-switching communications networks, the collection of hardware and software that makes use of packet or message switching to support user-to- user, i.e., end-to-end, communications, interprocess communications, and distributed data processing. 2. Synonym host computer. Host Address - A fully qualified domain name (usually alphabetic) identifying the address of one specific host computer on the Internet. Note: The host address is a subset of the IP address. Host Central Office - An electronic analog or digital base switching unit containing the central call processing functions which service the host office and its remote locations. Host Computer - 1. In a computer network, a computer that provides end users with services such as computation and database access and that usually performs network control functions. Synonym host. 2. A computer on which is developed software intended to be used on another computer. Host-Host Protocol - End-to-end (transport) protocol. Hosting - Synonym (in Internet usage) content hosting. Storage and management of databases by a content provider. Host Name - A fully qualified domain name identifying one specific host computer within the Internet. Hot Boot - Synonym warm restart. 1. A sequence of operations that is performed to reset a previously running system, after an unintentional shutdown. Synonym warm start. 2. In computer operations, the restarting of equipment, after a sudden shutdown, that allows reuse of previously retained initialized input data, retained programs, and retained output queues. Note 1: A warm restart may be needed after a 210
- 211. program failure. Note 2: A warm start or restart cannot occur if initial data, programs, and files are not retained after closedown. Hotbot - Synonym droid. 1. In the Internet, an intelligent search tool that automatically seeks out relevant online information based on the user's specifications. Synonyms agent, bot, crawler, hotbot, infobot, information agent, intelligent agent, Internet search engine, knowbot, knowledge robot, personal agent, robotic librarian, search robot, spider, Web crawler, Web spider, wizard. 2. In artificial intelligence, an entity with the ability to sense its environment and to act in such a way or to affect that environment; typically knowledge-based entities that can communicate with each other through some message-passing scheme. Hotline - A point-to-point communications link in which a call is automatically originated to the preselected destination without any additional action by the user when the end instrument goes off-hook. Note 1: Hotlines cannot be used to originate calls other than to preselected destinations. Note 2: Various priority services that require dialing are not properly termed "hotlines." Synonyms automatic signaling service, off- hook service. Hotlink - See hyperlink. 1. A software function that (a) is manifest to the user as displayed, selectable words or icons, and (b) allows viewers of an HTML document to navigate thereby to another HTML document or file. 2. The link created, as in 1. Hotlist - A list of frequently used web locations and URLs (Uniform Resource Locators). Note: Hotlists may consist of a) lists of bookmarks accessed by a browser or b) lists of URLs at a web site for linking to other relevant web sites. Synonyms bookmark list, go list, history list. Hot Site - In computer security, synonym for hot standby. See standby. 1. In computer and communications systems operations, pertaining to a power-saving condition or status of operation of equipment that is ready for use but not in use. Note: An example of a standby condition is a radio station operating condition in which the operator can receive but is not transmitting. 2. Pertaining to a dormant operating condition or state of a system or equipment that permits complete resumption of operation in a stable state within a short time. 3. Pertaining to spare equipment that is placed in operation only when other, in-use equipment becomes inoperative. Note: Standby equipment is usually classified as (a) hot standby equipment, which is warmed up, i.e., powered and ready for immediate service, and which may be switched into service automatically upon detection of a failure in the regular equipment, or (b) cold standby equipment, which is turned off or not connected to a primary power source, and which must be placed into service manually. Hot Standby - 1. In computer and communications systems operations, pertaining to a power-saving condition or status of operation of equipment that is ready for use but not in use. Note: An example of a standby condition is a radio station operating condition in which the operator can receive but is not transmitting. 2. Pertaining to a dormant operating condition or state of a system or equipment that permits complete resumption of operation in a stable state within a short time. 3. Pertaining to spare equipment that is placed in operation only when other, in-use equipment becomes inoperative. Note: Standby equipment is usually classified as (a) hot standby equipment, which is warmed up, i.e., powered and ready for immediate service, and which may be switched into service automatically upon detection of a failure in the regular equipment, or (b) cold standby equipment, which is turned off or not connected to a primary power source, and which must be placed into service manually. See standby. Hot Swap - In an electronic device, of a subassembly or component therein (e.g. circuit card), the act or process of removing and replacing the subassembly or component without first powering down the device. Note: Hot swapping of components in devices or environments not designed to support such practice may result in damage to the component or device, or may pose a spark hazard even if the primary power has been removed. And, in some computing devices, hot swapping may not be appropriate because new components may be recognized only during boot-up. 211
- 212. House Cable - Deprecated term. Communication cable within a building or a complex of buildings. Note: House cable owned before divestiture by the Bell System and after divestiture by the Regional Bell Operating Companies will eventually be fully depreciated and will then belong to the customer. See on-premises wiring. Housekeeping Signals - Synonym service signals. Signals that enable data systems equipment to function correctly, and possibly to provide ancillary facilities. HPC - Abbreviation for high probability of completion. H-Plane Bend - Synonym H-bend. A smooth change in the direction of the axis of a waveguide, throughout which the axis remains in a plane parallel to the direction of magnetic H-field (transverse) polarization. Synonym H-plane bend. HTML - See HyperText Markup Language Abbreviation for Hypertext Markup Language. An application of SGML (Standard Generalized Markup Language) implemented in conjunction with the World Wide Web to facilitate the electronic exchange and display of simple documents using the Internet. HTTP - Abbreviation for Hypertext Transfer Protocol. In the World Wide Web, a protocol that facilitates the transfer of hypertext-based files between local and remote systems. Hub - 1. A distribution point in a network. 2. A device that accepts a signal from one point and redistributes it to one or more points. Huffman Coding - A coding technique used to compact data by representing the more common events with short codes and the less common events with longer codes. Note: Huffman coding is used in Group 3 facsimile. Human-Machine Interface (HMI) - Human-machine interface between user and terminal / system that consists of a physical section (electro-acoustic, electro-optic transducer, keys, etc.) and a logical section dealing with functional operation states. Hundred Call-Seconds (CCS): See call-second. The CCS, equivalent to 100 call-seconds, is often used. Note 4: 3600 call-seconds = 36 CCS = 1 call-hour. Note 5: 3600 call-seconds per hour = 36 CCS per hour = 1 call-hour per hour = 1 erlang = 1 traffic unit. Hunt Group -A service provided by most phone companies that allows several lines to be tied together. A single number is generally dialed by all callers. If that line is busy, the phone company will "roll-over" the call to another line in that group. Also called "rollover" and more recently "busy-line transfer". Hunting - 1. In telephony, pertaining to the operation of a selector or other similar device to find and establish a connection with an idle circuit of a chosen group. 2. Pertaining to the failure of a device to achieve a state of equilibrium, usually by alternately overshooting and undershooting the point of equilibrium. Hybrid - 1. A functional unit in which two or more different technologies are combined to satisfy a given requirement. Note: Examples of hybrids include (a) an electronic circuit having both vacuum tubes and transistors, (b) a mixture of thin-film and discrete integrated circuits, and (c) a computer that has both analog and digital capability. 2. A resistance hybrid. 3. A hybrid coil. Hybrid Balance - An expression of the degree of electrical symmetry between two impedances connected to two conjugate sides of a hybrid set or resistance hybrid. Note 1: Hybrid balance is usually expressed in dB. 212
- 213. Note 2: If the respective impedances of the branches of the hybrid that are connected to the conjugate sides of the hybrid are known, hybrid balance may be computed by the formula for return loss. Hybrid Cable - An optical communications cable having two or more different types of optical fibers, e.g., single-mode and multimode fibers. Hybrid Coil - A single transformer that effectively has three windings, and which is designed to be configured as a circuit having four branches, i.e., ports, that are conjugate in pairs. Note: The primary use of a hybrid coil is to convert between 2-wire and 4-wire operation in concatenated sections of a communications circuit. Such conversion is necessary when repeaters are introduced in a 2-wire circuit. Synonym bridge transformer. Hybrid Communications Network - A communications network that uses a combination of line facilities, i.e., trunks, loops, or links, some of which use only analog or quasi-analog signals and some of which use only digital signals. Synonyms hybrid network, hybrid system. Hybrid Computer - A computer that processes both analog and digital data. Hybrid Connector - A connector that contains contacts for more than one type of service. Note: Examples of hybrid connectors are those that have contacts for both optical fibers and twisted pairs, electric power and twisted pairs, or shielded and unshielded twisted pairs. Hybrid Coupler - In an antenna system, a hybrid junction used as a directional coupler. Note: The loss through a hybrid coupler is usually 3 dB. Hybrid Fiber Coaxial Cable (HFC) - A telecommunications cable in which optical fiber cable and coaxial cable constitute different portions of a network carrying broadband content (such as video, data, and voice). Typically, a local CATV company might use fiber optic cable from the cable headend (distribution center) to the serving node located near business and residential users, and then use coaxial cable from these nodes to individual businesses and homes. An advantage of HFC is that some of the characteristics of fiber optic cable (high bandwidth and low noise /low interference susceptibility) can be brought close to the user without having to replace the entire existing coaxial cable that is installed. Hybrid Interface Structure - In integrated services digital networks (ISDN), an interface structure that uses both labeled and positioned channels. Hybrid Junction - A waveguide or transmission line arranged such that (a) there are four ports, (b) each port is terminated in its characteristic impedance, and (c) energy entering any one port is transferred, usually equally, to two of the three remaining ports. Note: Hybrid junctions are used as mixing or dividing devices. Hybrid Mode - A mode consisting of components of both electrical and magnetic field vectors in the direction of propagation. Note: In fiber optics, such modes correspond to skew (nonmeridional) rays. Hybrid Network - See hybrid communications network. A communications network that uses a combination of line facilities, i.e., trunks, loops, or links, some of which use only analog or quasi-analog signals and some of which use only digital signals. Synonyms hybrid network, hybrid system. Hybrid Routing - Routing in which numbering plans and routing tables are used to permit the collocation, in the same area code, of switches using a deterministic routing scheme with switches using a nondeterministic routing scheme, such as flood search routing. Note: Routing tables are constructed with no duplicate numbers, so that direct dial service can be provided to all network subscribers. This may require the use of 10-digit numbers. 213
- 214. Hybrid Set - Two or more transformers interconnected to form a network having four ports that are conjugate in pairs. Note: The primary use of a hybrid set is to convert between 2-wire and 4-wire operation in concatenated sections of a communications circuit. Such conversion is necessary when repeaters are introduced in a 2-wire circuit. Hybrid Spread Spectrum - A combination of frequency hopping spread spectrum and direct-sequence spread spectrum. Hybrid System - Synonym hybrid communications network. A communications network that uses a combination of line facilities, i.e., trunks, loops, or links, some of which use only analog or quasi-analog signals and some of which use only digital signals. Synonyms hybrid network, hybrid system. Hybrid Topology - See network topology. A combination of any two or more network topologies. Note 1: Instances can occur where two basic network topologies, when connected together, can still retain the basic network character, and therefore not be a hybrid network. For example, a tree network connected to a tree network is still a tree network. Therefore, a hybrid network accrues only when two basic networks are connected and the resulting network topology fails to meet one of the basic topology definitions. For example, two star networks connected together exhibit hybrid network topologies. Note 2: A hybrid topology always accrues when two different basic network topologies are connected. Hydroxyl ion Absorption - In optical fibers, the absorption of electromagnetic waves, including the near- infrared, due to the presence of trapped hydroxyl ions remaining from water as a contaminant. Note: The - hydroxyl (OH ) ion can penetrate glass during or after product fabrication, resulting in significant attenuation of discrete optical wavelengths, e.g., approximately 1.3 m, used for communications via optical fibers. Hyperlink - 1. A software function that (a) is manifest to the user as displayed, selectable words or icons, and (b) allows viewers of an HTML document to navigate thereby to another HTML document or file. 2. The link created, as in 1. Hypermedia - Computer-addressable files that contain pointers for linking to multimedia information, such as text, graphics, video, or audio in the same or other documents. Note: The use of hypertext links is known as navigating. Hypertext - The system of coding that is used to create or navigate hypermedia in a nonsequential manner HyperText Link - A connection between two Web documents; usually underlined text or a graphic that you click on to display another Web document. HyperText Markup Language (HTML) - The basic coding language used to create WWW documents. Hypertext Transfer Protocol - See HTTP. HyperText Transport Protocol (HTTP) - The protocol for moving HyperText files across the Internet HTTP - See HyperText Transport Protocol Hz - : Abbreviation for hertz. 1. The SI unit of frequency, equal to one cycle per second. Note: A periodic phenomenon that has a period of one second has a frequency of one hertz. 2. A unit of frequency which is equivalent to one cycle per second. I 214
- 215. I2 - Abbreviation for Internet second generation. A proposed high-speed Internet for use exclusively by government researchers and academic institutions. IAL - Abbreviation for Immediate Action Limit. The bound on performance allowed for a circuit or connection that is in service. When any parameter value exceeds the IAL, the circuit or connection is considered defective and corrective action is necessary. IANA - Abbreviation for Internet Assigned Numbers Authority. An organization directed by the Internet Architecture Board (IAB) and which assigns IP numbers and protocol parameters such as port, protocol, and enterprise numbers, and options, codes, and types. Ia - The 4-wire (2-pair) bidirectional primary rate interface point on the network side of the termination equipment (i.e., NT1, NT2), including the equipment connecting cord, or equivalent, on the user side of the interface cable. Ib - The 4-wire (2-pair) bidirectional primary rate (PR) interface point on the user side of the termination equipment (i.e., NT1 and NT2), including the equipment connecting cord or equivalent on the network side of the interface cable. IC - Abbreviation for integrated circuit (IC): An electronic circuit that consists of many individual circuit elements, such as transistors, diodes, resistors, capacitors, inductors, and other active and passive semiconductor devices, formed on a single chip of semiconducting material and mounted on a single piece of substrate material. Synonyms chip, microcircuit. ICA - Abbreviation for International Communications Association. ICI - Abbreviation for incoming call identification. A switching system feature that allows an attendant to identify visually the type of service or trunk group associated with a call directed to the attendant's position. ICMP - Abbreviation for Internet Control Message Protocol. An Internet protocol that reports datagram delivery errors. Note 1: ICMP is a key part of the TCP/IP protocol suite. Note 2: The packet internet gopher (ping) application is based on ICMP. Icon - In computer systems, a small, pictorial representation of an application software package, idea, or concept used in a window or a menu to represent commands, files, or options. ICW - Abbreviation for interrupted continuous wave. Modulation in which there is on-off keying of a continuous wave. Identification - [The] process an information system (IS) uses to recognize an entity. Identification, Friend or Foe (IFF) - A system using electromagnetic transmissions to which equipment carried by friendly forces automatically responds, for example, by emitting pulses, thereby distinguishing themselves from enemy forces. Note: The secondary surveillance radar (SSR) system used in modern air traffic control systems is an outgrowth of the military IFF system used during World War II. The IFF equipment carried by modern military aircraft is compatible with the transponder system used for civilian air traffic control. Identification Friend or Foe Personal Identifier - The discrete identification, friend or foe code assigned to a particular aircraft, ship, or other vehicle for identification by electronic means. 215
- 216. Identification Information -A form of notification information that consists of the documentation of the actual sequence of intermediate networks traversed by a signaling message. The documentation of the sequence of networks traversed may also include the origination and destination networks. The documentation that the message traversed a given network is performed by that network itself. Intermediate networks that are not ISNI-capable are not identified. ISNI identification information can be used to force a return error message, destined for the originating SEP, to transit the same intermediate network(s) as the original message. Identifier (ID) - 1. In telecommunications and data processing systems, one or more characters used to identify, name, or characterize the nature, properties, or contents of a set of data elements. 2. A string of bits or characters that names an entity, such as a program, device, or system, in order that other entities can call that entity. 3. In programming languages, a lexical unit that names a language object, such as a variable, array, record, label, or procedure. Note: An identifier is placed in a label. The label is attached to, is a part of, or remains associated with, the information it identifies. If the label becomes disassociated from the information it identifies, the information may not be accessible. Identity Authentication - The performance of tests to enable a data processing system to recognize entities. Note: An example of identity authentication is the checking of a password or identity token. Identity Token - 1. A device, such as a metal key or smart card, used for identity authentication.2. [A] Smart card, metal key, or other physical object used to authenticate identity. Identity Validation - Tests enabling an information system to authenticate users or resources. IDF - Abbreviation for intermediate distribution frame. In a central office or customer premises, a frame that (a) cross-connects the user cable media to individual user line circuits and (b) may serve as a distribution point for multipair cables from the main distribution frame (MDF) or combined distribution frame (CDF) to individual cables connected to equipment in areas remote from these frames. Idle-Channel Noise - Noise that is present in a communications channel when no signals are applied. Note: The channel conditions and terminations must be stated for idle-channel noise measurements to be meaningful. Idle Character - A control character that is transmitted when no useful information is being transmitted. Idle Code - A special sequence that indicates that no data are being sent on the channelized side. Idle-Line Termination - A switch-controlled electrical network that maintains a desired impedance at a trunk or line terminal that is in the idle state. Idle State - The telecommunications service condition that exists whenever user messages are not being transmitted but the service is immediately available for use. Idle Time - A period during which a system, circuit, or component is not in use, but is available. IDN - Abbreviation for integrated digital network. A network that uses both digital transmission and digital switching. IDTV - Abbreviation for improved-definition television. - Television transmitters and receivers that (a) are built to satisfy performance requirements over and above those required by the NTSC standard and (b) remain within the general parameters of NTSC standard emissions. Note 1: IDTV improvements may be 216
- 217. made at the TV transmitter or the receiver. Note 2: Examples of improvements include enhancements in encoding, digital filtering, scan interpolation, interlaced line scanning, and ghost cancellation. Note 3: IDTV improvements must allow the TV signal to be transmitted and received in the standard 4:3 aspect ratio. Synonym enhanced-quality television. IETF - Abbreviation for Internet Engineering Task force. One of the task forces (with more than 40 working groups) of the Internet Architecture Board, responsible for solving short-term engineering needs of the Internet. IF - Abbreviation for intermediate frequency. A frequency to which a carrier frequency is shifted as an intermediate step in transmission or reception. I/F - I/F: Abbreviation for interface.- 1. In a system, a shared boundary, i.e., the boundary between two subsystems or two devices. 2. A shared boundary between two functional units, defined by specific attributes, such as functional characteristics, common physical interconnection characteristics, and signal characteristics. 3. A point of communication between two or more processes, persons, or other physical entities. 4. A point of interconnection between user terminal equipment and commercial communications facilities. 5. To interconnect two or more entities at a common point or shared boundary. 6. [A] common boundary between independent systems or modules where interactions take place. 7. The point of interconnection between two distinct but adjacent communications systems having different functions. The interface in the communication-satellite service is that point where communications terminal equipment of the terrestrial common carriers or other authorized entities interconnects with the terminal equipment of the communication-satellite earth station complex. The interface in the communication-satellite service shall be located at the earth station site, or if this is impracticable, as close thereto as possible. IFF - Abbreviation for identification, friend or foe.- A system using electromagnetic transmissions to which equipment carried by friendly forces automatically responds, for example, by emitting pulses, thereby distinguishing themselves from enemy forces. Note: The secondary surveillance radar (SSR) system used in modern air traffic control systems is an outgrowth of the military IFF system used during World War II. The IFF equipment carried by modern military aircraft is compatible with the transponder system used for civilian air traffic control. IF4 (Interface 4) - An interface suitable for multipoint concentration by polling. IF1 (Interface 1) - An interface suitable for star concentration. IFRB - Abbreviation for International Frequency Registration Board. See Radio Regulations Board. The Radio Regulations Board was formerly called International Frequency Registration Board (IFRB). A permanent organization of the International Telecommunication Union (ITU) that implements frequency assignment policy and maintains the Master International Frequency Register (MIFR). IF Repeater - See heterodyne repeater. In radio reception and retransmission, a repeater that converts the original band of frequencies of the received signal to a different frequency band for retransmission after amplification. Note: IF repeaters are used, for example, in microwave systems, to avoid undesired feedback between the receiving and transmitting antennas. IFS - Abbreviation for ionospheric forward scatter. See ionospheric scatter. ionospheric scatter: The propagation of radio waves by scattering as a result of irregularities or discontinuities in the ionization of the ionosphere. Synonym forward propagation ionospheric scatter. 217
- 218. IF6 (Interface 6) - An interface between a network element (NE) to one or more network elements (NEs) in other locations using star configuration embedded operations channel (EOCs) or conventional communications services. IF2 (Interface 2) - An interface suitable for communication between a network element (NE) location and operations systems (OSs) over packet switched networks, dedicated lines, or circuit switched connections. ILD - Abbreviation for injection laser diode. ILEC - Incumbent Local Exchange Carrier. The existing local exchange carrier in any given area, as opposed to CLECs. Illegal Character - A character, or a combination of bits, that is not valid in a given system according to specified criteria, such as with respect to a specified alphabet, a particular pattern of bits, a rule of formation, or a check code. Synonyms false character, forbidden character, improper character, unallowable character, unused character. ILS - Abbreviation for instrument landing system. - 1. A radio-navigation system which provides aircraft with horizontal and vertical guidance just before and during landing and, at certain fixed points, indicates the distance to the reference point of landing. 2. A system of radio navigation intended to assist aircraft in landing which provides lateral and vertical guidance, which may include indications of distance from the optimum point of landing. IM - Abbreviation for intensity modulation, intermodulation. The production, in a nonlinear element of a system, of frequencies corresponding to the sum and difference frequencies of the fundamentals and harmonics thereof that are transmitted through the element. Image - In the field of image processing, a two-dimensional representation of a scene. Synonym picture. Image Antenna - A hypothetical mirror-image, i.e., virtual-image, of an antenna, i.e., antenna element, considered to extend as far below ground, i.e., the ground plane, as the actual antenna is above the ground plane. Note 1: The image antenna is helpful in calculating electric field vectors, magnetic field vectors, and electromagnetic fields emanating from the real antenna, particularly in the vicinity of the antenna and along the ground. Each charge and current in the real antenna has its image that may also be considered as a source of radiation equal to, but differently directed from, its real counterpart. Note 2: An image antenna may also be considered to be on the opposite side of any equipotential plane surface, such as a metal plate acting as a ground plane, analogous to the position of a virtual optical image in a plane mirror. Note 3: The ground plane need not be grounded to the Earth. Image Capture - The transducing of the information in a real image into the photographic or electronic medium. Note: Normally in motion-reproducing systems, synchronous audio information is simultaneously transduced. Image Compression - 1. Application of an appropriate transfer function to an image signal so as to limit dynamic range. 2. Application of bandwidth limiting or bit-rate reduction to an image signal in order to bring it within the limitations of a lower capacity channel. Image Enhancement - In video technology, a technique used to improve contrast and picture clarity by flattening the camera response to 400 lines (by aperture correction) and applying an additional correction to increase the depth of modulation in the range of 250 to 300 lines (in an NTSC system), both vertically and 218
- 219. horizontally. Note: Image enhancement produces a correction signal with symmetrical overshoots around transitions in the picture, but it must be used sparingly if natural appearance is to be maintained. Image File Architecture - The formalization of a multidisciplinary agreement—regarding digital image characteristics, such as the structure of digital image files, the organization of the image data itself, and the definition of fully flexible, interoperable, scalable, and extensible systems—which agreement facilitates the exchange of such files across various technology interfaces. Image File Descriptor - A block of data that (a) may contain, in standardized format, data concerning production, ownership, access, previous processing, etc., relevant to the basic interpretation of the data, and (b) enhances the utility of the main data for the user. Image File Header - A compact label for image files, created using a universally accepted algorithm, that (a) identifies the encoding standard, (b) specifies the length of the file, (c) indicates whether a readable descriptor is included, (d) permits random interception of data stream, and (d) offers optional error protection. Image File Motion-Picture Format - The defining file format for exchange of digital motion-picture information on a variety of media between computer-based systems. Note: This flexible file format describes pixel-based (raster) images with attributes defined in the binary file descriptor—which identifies (a) generic file information, image information, data format, and image orientation information; (b) motion-picture and television industry-specific information; and (c) user defined information. The format assumes non real-time application, with accommodation for real-time to be considered as the developing technology permits. Image File Video Index - A recommended practice intended to provide a method of coding video index information in which various picture- and program-related source data can be carried in conjunction with the video signal. Note: There are three classes of video index data based on type and use of the data. Class 1 contains information that is required to know how to use the signal. Class 2 contains heritage information for better usage of the signal. Class 3 contains other information not required to know how to use the signal. Image Frequency - In radio reception using heterodyning in the tuning process, an undesired input frequency that is capable of producing the same intermediate frequency (IF) that the desired input frequency produces. Note: The term image arises from the mirror-like symmetry of signal and image frequencies about the beating-oscillator frequency. Image Frequency Rejection Ratio - In reception using heterodyning in the tuning process, the ratio of (a) the intermediate-frequency (IF) signal level produced by the desired input frequency to (b) that produced by the image frequency. Note 1: The image rejection ratio is usually expressed in dB. Note 2: When the image rejection ratio is measured, the input signal levels of the desired and image frequencies must be equal for the measurement to be meaningful. Synonym image rejection ratio. Image Generation - The creation of an image from an image concept. Note: The image can be created with computer-graphics software or photography, for example. Image Map - A Web page feature in which hyperlinks are assigned ("mapped") to different portions of a graphic image, thereby allowing users to access links by clicking with a mouse on the mapped areas. Note: Image map requests are processed by CGI scripts on the server. Image Rejection Ratio - In reception using heterodyning in the tuning process, the ratio of (a) the intermediate-frequency (IF) signal level produced by the desired input frequency to (b) that produced by the image frequency. Note 1: The image rejection ratio is usually expressed in dB. Note 2: When the image 219
- 220. rejection ratio is measured, the input signal levels of the desired and image frequencies must be equal for the measurement to be meaningful. Synonym image frequency rejection ratio. Imagery - Collectively, the representations of objects reproduced electronically or by optical means on film, electronic display devices, or other media. IMD - Abbreviation for intermodulation distortion. - Nonlinear distortion characterized by the appearance, in the output of a device, of frequencies that are linear combinations of the fundamental frequencies and all harmonics present in the input signals. Note: Harmonic components themselves are not usually considered to characterize intermodulation distortion. When the harmonics are included as part of the distortion, a statement to that effect should be made. Imitative Communications - See communications deception. 1. Deliberate transmission, retransmission, or alteration of communications to mislead an adversary's interpretation of the communications. 2. Use of devices, operations, and techniques with the intent of confusing or misleading the user of a communications link or a navigation system. Immediate Action Limit (IAL) - The bound on performance allowed for a circuit or connection that is in service. When any parameter value exceeds the IAL, the circuit or connection is considered defective and corrective action is necessary. Immediate Activation - In cryptology, a condition of readiness associated with a key having no effective date. Note: A key is immediately activated (a) by the receiver when the RSM is sent in response to the KSM that carried that key, and (b) by the sender when the RSM is received in response to the KSM that carried the key. Immediate Message - A category of precedence reserved for messages relating to situations that gravely affect the security of national/allied forces or populace and that require immediate delivery to the addressee(s). Immunity - The ability of an assembly, equipment, or a system to perform without degradation in the presence of an electromagnetic disturbance. IMP - Abbreviation for interface message processor. - A processor-controlled switch used in packet-switched networks to route packets to their proper destination. Impedance - The total passive opposition offered to the flow of electric current. Note 1: Impedance is determined by the particular combination of resistance, inductive reactance, and capacitive reactance in a given circuit. Note 2: Impedance is a function of frequency, except in the case of purely resistive networks. Impedance Matching - The connection of an additional impedance to an existing one in order to accomplish a specific effect, such as to balance a circuit or to reduce reflection in a transmission line. Impersonating - [A] form of spoofing. Spoofing is the interception, alteration, and retransmission of a cipher signal or data in such a way as to mislead the recipient. 2. (AIS) [An] attempt to gain access to an AIS by posing as an authorized user. [NIS] 3. Unauthorized use of legitimate Identification and Authentication (I&A) data, however it was obtained, to mimic a subject different from the attacker. Impersonating, masquerading, piggybacking, and mimicking are forms of spoofing. Implant - [In security, an] electronic device or electronic equipment modification designed to gain unauthorized interception of information-bearing emanations. 220
- 221. Implicit Congestion Control - A scheme under which user terminals first detect a possible congestion condition by means other than explicit congestion messages, and then take appropriate action to reduce their throughput. Improper Character - Synonym illegal character. A character, or a combination of bits, that is not valid in a given system according to specified criteria, such as with respect to a specified alphabet, a particular pattern of bits, a rule of formation, or a check code. Improved-Definition Television (IDTV) - Television transmitters and receivers that (a) are built to satisfy performance requirements over and above those required by the NTSC standard and (b) remain within the general parameters of NTSC standard emissions. Note 1: IDTV improvements may be made at the TV transmitter or the receiver. Note 2: Examples of improvements include enhancements in encoding, digital filtering, scan interpolation, interlaced line scanning, and ghost cancellation. Note 3: IDTV improvements must allow the TV signal to be transmitted and received in the standard 4:3 aspect ratio. Synonym enhanced- quality television. Improvement Threshold - See FM improvement threshold. The point in an FM receiver at which the peaks in the rf signal equal the peaks of the thermal noise generated in the receiver. Note: A baseband signal-to-noise ratio of about 30 dB is typical at the improvement threshold, and this ratio improves 1 dB for each decibel of increase in the signal above the threshold. Impulse - A short surge of electrical, magnetic, or electromagnetic energy. Synonym surge. Impulse Excitation - The production of oscillation in a circuit or device by impressing a stimulus (signal) for a period that is extremely short compared to the duration of the oscillation that it produces. Synonym shock excitation. Impulse Noise - Noise consisting of random occurrences of energy spikes having random amplitude and spectral content. Note: Impulse noise in a data channel can be a definitive cause of data transmission errors. Impulse Response - 1. Of a device, the mathematical function that describes the output waveform that results when the input is excited by a unit impulse. 2. The waveform that results at the output of a device when the input is excited by a unit impulse. IN - Abbreviation for intelligent network. - 1. A network that allows functionality to be distributed flexibly at a variety of nodes on and off the network and allows the architecture to be modified to control the services. 2. In North America, an advanced network concept that is envisioned to offer such things as (a) distributed call-processing capabilities across multiple network modules, (b) real-time authorization code verification, (c) one-number services, and (d) flexible private network services [including (1) reconfiguration by subscriber, (2) traffic analyses, (3) service restrictions, (4) routing control, and (5) data on call histories]. Levels of IN development are identified below: • IN/1 A proposed intelligent network targeted toward services that allow increased customer control and that can be provided by centralized switching vehicles serving a large customer base. • IN/1+ A proposed intelligent network targeted toward services that can be provided by centralized switching vehicles, e.g., access tandems, serving a large customer base. • IN/2 A proposed, advanced intelligent-network concept that extends the distributed IN/1 architecture to accommodate the concept called " service independence." Note: Traditionally, service logic has been localized at individual switching systems. The IN/2 architecture provides flexibility in the placement of service logic, requiring the use of advanced techniques to manage the distribution of both network data and service logic across multiple IN/2 modules. 221
- 222. Inactive Signaling Link - A signaling link that has been deactivated and cannot therefore carry signaling traffic. In-band - Using or involving the information digit time slots of a DS1 frame; i.e., bit assignments of a frame exclusive of the framing bit. In-band Control - Control effected by sending control information over the same channel as the one used to send data. In-band Noise Power Ratio - For multichannel equipment, the ratio of (a) the mean noise power measured in any channel, with all channels loaded with white noise, to (b) the mean noise power measured in the same channel, with all channels but the measured channel loaded with white noise. In-band Signaling - Signaling that uses frequencies or time slots within the bandwidth or data stream occupied by the information channel. In Call - A UPT (Universal Personal Telecommunications) call type which permits a UPT user to have calls to his/her UPT number routed to the terminal specified by the user. In call Delivery - A feature by which incoming calls are presented at the terminal address registered previously by in-call registration. This feature is invoked when originating parties or others call the UPT (Universal Personal Telecommunications service) user. In-call Registration - A feature that enables the UPT (Universal Personal Telecommunications service) user to register from the current terminal address for incoming calls to be presented to that terminal address. When registered, all incoming calls to the UPT number of the UPT user will be presented to the registered terminal address, for the duration specified by the UPT user (duration may also be specified in terms of number of incoming UPT calls), or until a specified deregistration time. A UPT user's in-call registration will cancel the previous in-call registration of that UPT user's UPT number. Several UPT users may register for incoming calls to the same terminal address simultaneously. The UPT user may also explicitly de-register for incoming calls. Incident - 1. In information systems (IS), [an] assessed occurrence having actual or potentially adverse effects on an IS. 2. In COMSEC, the occurrence that potentially jeopardizes the security of COMSEC material or the secure electrical transmission of national security information or information governed by 10 U.S.C. Section 2315. Incidental-Radiation Device - A device that radiates radio frequency energy during the course of its operation although the device is not intentionally designed to generate radio frequency energy. Inclination of an Orbit (of an Earth satellite) - The angle determined by the plane containing the orbit and the plane of the Earth's equator. Inclined Orbit - Any nonequatorial orbit of a satellite. Note: Inclined orbits may be circular or elliptical, synchronous or asynchronous, and direct or retrograde. Inclusion - A foreign object present within, for example, an optical fiber or a crystal. Incoherent - In optics, characterized by a degree of coherence significantly less than 0.88. Incoming Access - The ability of a user to terminate data calls via an ISDN. 222
- 223. Incoming Call Identification (ICI) - A switching system feature that allows an attendant to identify visually the type of service or trunk group associated with a call directed to the attendant's position. Incorrect Block - A block successfully delivered to the intended destination user, but having one or more incorrect bits, additions, or deletions, in the delivered block. Incremental Compaction - Data compaction accomplished by specifying only the initial value and all subsequent changes. Note: An example of incremental compaction is the storing or transmitting of a line voltage followed only by the deviations from the initial value. Thus, instead of transmitting the values 102, 104, 105, 103, 100, 104 and 106, only the values 102, +2, +1, -2, -3, +4, and +2, or only the values 100, +2, +4, +5, +3, 0, +4, and +6 need be sent, depending on the system used. At a given data rate, transmitting only the initial and incremental values require much less time and space than transmitting the absolute values. Incremental Phase Modulation (IPM) - In spread-spectrum systems, phase modulation in which one binary code sequence is shifted with respect to another, usually to conduct a synchronizing search, i.e., a search to discover if the two sequences are the same, and perhaps thereby enabling two data streams to be synchronized. Indefinite Call Sign - 1. A call sign that represents a group of facilities, commands, authorities, activities, or units rather than one of these. 2. In radio communications, a call sign that does not identify a station and that is used in the call-up signal or in a message that has the station call sign encrypted in the text. Independent Clocks - In communication network timing subsystems, free-running precision clocks used, for synchronization purposes, at the nodes. Note: Variable storage buffers, installed to accommodate variations in transmission delay between nodes, are made large enough to accommodate small time (phase) departures among the nodal clocks that control transmission. Traffic may occasionally be interrupted to allow the buffers to be emptied of some or all of their stored data. Independent-Sideband (ISB) Transmission - Double-sideband transmission in which the information carried by each sideband is different. Note: The carrier may be suppressed. Independent Telephone Company - A telephone company not affiliated with any of the original Bell telephone companies. See RBOC. Index Dip - In an optical fiber, an undesired decrease in the refractive index at the center of the core. Note: An index dip is an artifact of certain manufacturing processes. Synonym profile dip. Indexing - See interaction crosstalk. Crosstalk caused by coupling between carrier and noncarrier circuits. Note: If the interaction crosstalk is, in turn, coupled to another carrier circuit, that crosstalk is called "indexing." Index-Matching Gel - Synonym gel. 1. A substance, resembling petroleum jelly in viscosity, that surrounds a fiber, or multiple fibers, enclosed in a loose buffer tube. Note: This gel serves to lubricate and support the fibers in the buffer tube. It also prevents water intrusion in the event the buffer tube is breached. 2. Index- matching material in the form of a gel. Synonym matching gel. Index-Matching Material - A substance, usually a liquid, cement (adhesive), or gel, which has an index of refraction that closely approximates that of an optical fiber, and is used to reduce Fresnel reflection at the fiber endface. (FAA) Note 1: An index-matching material may be used in conjunction with pairs of mated connectors, with mechanical splices, or at the ends of fibers. Note 2: Without the use of an index-matching material, Fresnel reflections will occur at the smooth endfaces of a fiber. These reflections may be as high as 223
- 224. -14 dB (i.e., 14 dB below the level of the incident signal). When the reflected signal returns to the transmitting end, it is reflected again and returns to the receiving end at a level that is (28 plus twice the fiber loss) dB below the direct signal. The reflected signal will also be delayed by twice the delay time introduced by the fiber. The reflected signal will have no practical effect on digital systems because of its low level relative to the direct signal; i.e., it will have no practical effect on the detected signal seen at the decision point of the digital optical receiver. It may be noticeable in an analog baseband intensity-modulated video signal. Index of Cooperation - 1. In facsimile, the product of the total line length and the number of lines per unit length, divided by . 2. For rotating devices, the product of the drum diameter and the number of lines per unit length. Synonyms: diametral index of cooperation, international index of cooperation. Index of Refraction - Synonym refractive index. ( , n): Of a medium, the ratio of the velocity of propagation of an electromagnetic wave in vacuum to its velocity in the medium. Note: When the Greek character eta is unavailable, the letter n is used to represent the refractive index. Index Profile - Synonym refractive index profile. Of the cross section of an optical fiber, the description, i.e., plot, of the value of the refractive index as a function of distance from the fiber axis along a diameter. n Indirect Control - In digital data transmission, the use of a clock rate of 2 times the modulation rate, where n is an integer greater than one. Indirect Wave - A wave, such as a radio wave or sound wave, that arrives at a given point by reflection or scattering from surrounding objects, rather than directly from the source. Individual Line - A line that connects a single user to a switching center. Individual Reception (in the broadcasting-satellite service) - The reception of emissions from a space station in the broadcasting-satellite service by simple domestic installations and in particular those possessing small antennae. Inductive Coupling - The transfer of energy from one circuit to another by virtue of the mutual inductance between the circuits. Note 1: Inductive coupling may be deliberate and desired (as in an antenna coupler) or may be undesired (as in power line inductive coupling into telephone lines). Note 2: Capacitive coupling favors transfer of higher frequency components, whereas inductive coupling favors transfer of lower frequency components. Industrial, Scientific, and Medical (ISM) Applications (of radio frequency energy) - Operation of equipment or appliances designed to generate and use locally radio-frequency energy for industrial, scientific, medical, domestic or similar purposes, excluding applications in the field of telecommunications. Industry Standard - A voluntary, industry-developed document that establishes requirements for products, practices, or operations. Infobahn - A slang term for The Internet or NII. See National Information Infrastructure. A proposed, advanced, seamless web of public and private communications networks, interactive services, interoperable hardware and software, computers, databases, and consumer electronics to put vast amounts of information at users' fingertips. Note: NII includes more than just the physical facilities (more than the cameras, scanners, keyboards, telephones, fax machines, computers, switches, compact disks, video and audio tape, cable, wire, satellites, optical fiber transmission lines, microwave nets, switches, televisions, monitors, and printers) used to transmit, store, process, and display voice, data, and images; it encompasses a wide range of interactive 224
- 225. functions, user-tailored services, and multimedia databases that are interconnected in a technology-neutral manner that will favor no one industry over any other. Synonym information superhighway. Infobot - Synonym droid. 1. In the Internet, an intelligent search tool that automatically seeks out relevant online information based on the user's specifications. Synonyms agent, bot, crawler, hotbot, infobot, information agent, intelligent agent, Internet search engine, knowbot, knowledge robot, personal agent, robotic librarian, search robot, spider, Web crawler, Web spider, wizard. 2. In artificial intelligence, an entity with the ability to sense its environment and to act in such a way or to affect that environment; typically knowledge-based entities that can communicate with each other through some message-passing scheme. Information - 1. Facts, data, or instructions in any medium or form. 2. The meaning that a human assigns to data by means of the known conventions used in their representation. Information agent - Synonym droid. 1. In the Internet, an intelligent search tool that automatically seeks out relevant online information based on the user's specifications. Synonyms agent, bot, crawler, hotbot, infobot, information agent, intelligent agent, Internet search engine, knowbot, knowledge robot, personal agent, robotic librarian, search robot, spider, Web crawler, Web spider, wizard. 2. In artificial intelligence, an entity with the ability to sense its environment and to act in such a way or to affect that environment; typically knowledge-based entities that can communicate with each other through some message-passing scheme. Information Assurance - Information operations (IO) that protect and defend information and information systems (IS) by ensuring their availability, integrity, authentication, confidentiality, and nonrepudiation. This includes providing for restoration of information systems by incorporating protection, detection, and reaction capabilities. Information-Bearer Channel - 1. A channel capable of transmitting all the information required for communication, such as user data, synchronizing sequences, and control signals. Note: The information- bearer channel may operate at a higher data rate than that required for user data alone. 2. A basic communications channel with the necessary bandwidth but without enhanced or value-added services. Information Bit - See user information bit. A bit transferred from a source user to a telecommunications system for delivery to a destination user. Note 1: User information bits do not include the overhead bits originated by, or having their primary functional effect within, the telecommunications system. Note 2: User information bits are encoded to form channel bits. Information Digit(s) - A single-digit data element in the 7-digit format that is outpulsed by the network to indicate the numbering plan digit (NPD) and CESID (caller's emergency service ID) display status. In the 10- digit format, two information digits used to indicate the CESID display status. The information digit or digits can also indicate a maintenance test call. Information Feedback - The return of received data to the source, usually for the purpose of checking the accuracy of transmission by comparison with the original data. Information Field - In data transmission, a field assigned to contain user information. Note: The contents of the information field are not interpreted at the link level. Information Flow Control - A procedure to ensure that information transfers within an information system (IS) are not made from a higher security level object to an object of a lower security level. 225
- 226. Information Integrity - In a frame-relaying network, the condition when all frames relayed by the network satisfy the frame check sequence check. Information Origination/Termination Equipment - Equipment used to input into or receive output from the telecommunications network. Information processing - Synonym data processing.The systematic performance of operations upon data such as handling, merging, sorting, and computing. Note: The semantic content of the original data should not be changed. The semantic content of the processed data may be changed. Information processing center (IPC): A facility staffed and equipped for processing and distributing information. Note: An IPC may be geographically distributed. Information Provider - An entity that collects information and makes it available to Internet users. Note: The information can be provided directly to users, or provided via an Internet access provider or a content provider. Information Rate - For a frame relay logical connection, the average number of end user bits transferred per second, in one direction, across a user-network interface as measured over an interval of duration 't'. The measurement interval 't' is network dependent. Information Security - The protection of information against unauthorized disclosure, transfer, modification, or destruction, whether accidental or intentional. Information Source - Synonym source user. The user providing the information to be transferred to a destination user during a particular information transfer transaction. Information Superhighway - Synonym National Information Infrastructure. A proposed, advanced, seamless web of public and private communications networks, interactive services, interoperable hardware and software, computers, databases, and consumer electronics to put vast amounts of information at users' fingertips. Note: NII includes more than just the physical facilities (more than the cameras, scanners, keyboards, telephones, fax machines, computers, switches, compact disks, video and audio tape, cable, wire, satellites, optical fiber transmission lines, microwave nets, switches, televisions, monitors, and printers) used to transmit, store, process, and display voice, data, and images; it encompasses a wide range of interactive functions, user-tailored services, and multimedia databases that are interconnected in a technology-neutral manner that will favor no one industry over any other. Information System - 1. A system, whether automated or manual, that comprises people, machines, and/or methods organized to collect, process, transmit, and disseminate data that represent user information. 2. Any telecommunications and/or computer related equipment or interconnected system or subsystems of equipment that is used in the acquisition, storage, manipulation, management, movement, control, display, switching, interchange, transmission, or reception of voice and/or data, and includes software, firmware, and hardware. 3. The entire infrastructure, organization, personnel, and components for the collection, processing, storage, transmission, display, dissemination, and disposition of information. Information Systems Security (INFOSEC and/or ISS) - [The] protection of information systems against unauthorized access to or modification of information, whether in storage, processing or transit, and against the denial of service to authorized users, including those measures necessary to detect, document, and counter such threats. 226
- 227. Information Technology (IT) - The branch of technology devoted to (a) the study and application of data and the processing thereof; i.e., the automatic acquisition, storage, manipulation (including transformation), management, movement, control, display, switching, interchange, transmission or reception of data, and (b) the development and use of the hardware, software, firmware, and procedures associated with this processing. Information Transfer - The process of moving messages containing user information from a source to a sink. Note: The information transfer rate may or may not be equal to the transmission modulation rate. Information Transfer Capability - The capability associated with the transfer of different types of information through the ISDN. It can be used to characterize a telecommunication service or connection. Values associated with this attribute are unrestricted digital, speech, 3.1-kHz audio, 7- kHz audio, 15-kHz audio, and video. Information Transfer Interface - Establishment of a communication (signaling) path and any required bearer path between the RPT/RT and the radio port. For example, in TDMA and FDMA, time slots and frequencies are identified, and in CDMA, sequence codes are identified. Information Transfer Mode - The operational mode for transferring (transportation and switching) user information through the ISDN. It can be used to characterize a telecommunication service or a connection in the network. Values associated with the attribute are circuit mode and packet mode. Information-Transfer Phase - In an information-transfer transaction, the phase during which user information blocks are transferred from the source user to a destination user. Information Transfer Rate - The transfer of digital information between two access points or reference points. Values associated with this attribute are appropriate bit rate (in circuit mode) and throughput rate (in packet mode). Information-Transfer Transaction - A coordinated sequence of user and telecommunications system actions that cause information present at a source user to become present at a destination user. Note: An information-transfer transaction usually consists of three consecutive phases called the access phase, the information-transfer phase, and the disengagement phase. INFOSEC - Acronym for information systems security. [The] protection of information systems against unauthorized access to or modification of information, whether in storage, processing or transit, and against the denial of service to authorized users, including those measures necessary to detect, document, and counter such threats. Infrared (IR) - The region of the electromagnetic spectrum bounded by the long-wavelength extreme of the visible spectrum (approximately 0.7 m) and the shortest microwaves (approximately 0.1 mm). See electromagnetic spectrum. Ink Vapor Recording - Recording in which vaporized ink particles are deposited directly upon the record medium. Infrastructure Assurance - Preemptive or reactive risk-management techniques designed to increase confidence that disruption of a system will be minimized if its critical infrastructure is attacked. Infrastructure Protection - Preemptive or reactive risk-management techniques designed to prevent disruption of a system after its critical infrastructure is attacked. 227
- 228. Inhibiting Signal - A signal that prevents the occurrence of an event. Note: An inhibiting signal may be used, for example, to disable an AND gate, thus preventing any signals from passing through it as long as the inhibiting signal is present. Initial Alignment - A procedure used to qualify a signaling link for carriage of signaling traffic, either for the first time orinitial alignment: A procedure used to qualify a signaling link for carriage of signaling traffic, either for the first time or after failure has occurred. after failure has occurred. Iinitialization Vector - In encryption, a nonsecret binary vector used as the initializing input algorithm for the encryption of a plaintext block sequence to increase security by introducing additional cryptographic variance and to synchronize cryptographic equipment. Initialize - Setting the state of a cryptographic logic prior to key generation, encryption, or other operating mode. Initial Text Sequence - In cryptography, a 64-bit binary sector that may be attached to the beginning of a message. Initiating MSC - The mobile switching center (MSC) (switch) that obtains routing information (i.e., LRN). Injection Fiber - Synonym launching fiber. An optical fiber used in conjunction with a source to excite the modes of another fiber in a particular fashion. Note: Launching fibers are most often used in test systems to improve the precision of measurements. Injection Laser Diode (ILD) - A laser that uses a forward-biased semiconductor junction as the active medium. Note: Stimulated emission of coherent light occurs at a p-n junction where electrons and holes are driven into the junction. Synonyms diode laser, laser diode, semiconductor laser. Ink Vapor Recording - Recording in which vaporized ink particles are deposited directly upon the record medium. Inline - An image on a web page that is displayed directly to the viewer rather than being made available only as a hot link. Input - 1. In a device, process, or channel, a point that accepts data. 2. A state, or a sequence of states, of a point that accepts data. 3. A stimulus, such as a signal or interference, that enters a functional unit, such as a telecommunications system, a computer, or a computer program. Input Data - 1. Data being received or to be received by a device or a computer program. 2. Data to be processed. Input Focus - The attribute of a user interface component, such as a window, that enables it to receive input from a particular input device, such as the keyboard. Input-Output Channel - For a computer, a device that handles the transfer of data between internal memory and peripheral equipment. Input-Output Controller (IOC) - A functional unit that controls one or more input-output channels. Synonym I/O controller. Input/Output (I/O) Device - A device that introduces data into or extracts data from a system. 228
- 229. Input Protection - For analog input channels, protection against overvoltages that may be applied between any two input connectors or between any input connector and ground. Insertion Gain - The gain resulting from the insertion of a device in a transmission line, expressed as the ratio of the signal power delivered to that part of the line following the device to the signal power delivered to that same part before insertion. Note 1: If the resulting number is less than unity, an " insertion loss " is indicated. Note 2: Insertion gain is usually expressed in dB. Insertion Loss - 1. The loss resulting from the insertion of a device in a transmission line, expressed as the reciprocal of the ratio of the signal power delivered to that part of the line following the device to the signal power delivered to that same part before insertion. Note: Insertion loss is usually expressed in dB. 2. In an optical fiber system, the total optical power loss caused by insertion of an optical component, such as a connector, splice, or coupler. Insertion-Loss-vs.-Frequency Characteristic - Of a system or device, a plot of the amplitude as a function of frequency. Note: The insertion-loss-vs.-frequency characteristic may be expressed as absolute gain or loss, or it may be normalized with respect to gain or loss at a specified reference frequency. Inside Call - Synonym internal call. A call placed within a private branch exchange (PBX) or local switchboard, i.e., not through a central office in a public switched network. Inside Plant - 1. All the cabling and equipment installed in a telecommunications facility, including the main distribution frame (MDF) and all the equipment extending inward therefrom, such as PABX or central office equipment, MDF protectors, and grounding systems. 2. In radio and radar systems, all communications- electronics (C-E) equipment that is installed in buildings. Inside Wire - See on-premises wiring. Customer-owned metallic or optical-fiber communications transmission lines, installed within or between buildings. Note: On-premises wiring may consist of horizontal wiring, vertical wiring, and backbone wiring, and may extend from the external network interface to the user work station areas. It includes the total communications wiring to transport current or future data, voice, LAN, and image information. In-Slot Signaling - Signaling performed in the associated channel time slot. Inspection Lot - A collection of produced units from which a statistically valid sample is to be drawn and inspected to determine conformance with acceptability criteria. Note: The inspection lot may differ from a collection of units designated as a lot for other purposes, such as for production, storage, packaging, and shipment. Instantiation - the process of creating a managed object according to a managed object class definition. Instruction - In a programming language, an expression that specifies one operation and identifies its operands, if any. Instructional Television Fixed Station - A fixed station operated by an educational organization and used primarily for the transmission of visual and aural instructional, cultural, and other types of educational material to one or more fixed receiving locations. Instrument Landing System (ILS) - 1. A radio-navigation system which provides aircraft with horizontal and vertical guidance just before and during landing and, at certain fixed points, indicates the distance to the reference point of landing. 2. A system of radio navigation intended to assist aircraft in landing which 229
- 230. provides lateral and vertical guidance, which may include indications of distance from the optimum point of landing. Instrument Landing System Glide Path - A system of vertical guidance embodied in the instrument landing system which indicates the vertical deviation of the aircraft from its optimum path of descent. Instrument Landing System Localizer - A system of horizontal guidance embodied in the instrument landing system which indicates the horizontal deviation of the aircraft from its optimum path of descent along the axis of the runway. Insulated Wire - Telecommunications plant containing from one to six paired conductors, and possibly a shield. Wire may be found in either aerial or buried installations. Integrated Circuit (IC) - An electronic circuit that consists of many individual circuit elements, such as transistors, diodes, resistors, capacitors, inductors, and other active and passive semiconductor devices, formed on a single chip of semiconducting material and mounted on a single piece of substrate material. Synonyms chip, microcircuit. Integrated Digital Network (IDN) - A network that uses both digital transmission and digital switching. Integrated Ground Plane - A set of interconnected frames that is intentionally grounded via multiple connections to a ground reference. Multiple connections are intended to keep voltage drops (due to power faults in the ac or dc power systems or from lightning) to acceptable levels. The following are examples of an integrated ground plane: building steel, water pipes, ground rod systems, counterpoises, vertical and horizontal ground reference conductors, grounding (earthing) wires, and metallic raceways form an integrated ground plane when bonded together by a multiplicity of both deliberate and incidental connections. Synonym common bonding network (CBN). Integrated Optical Circuit (IOC) - A circuit, or group of interconnected circuits, consisting of miniature solid- state optical components on semiconductor or dielectric substrates. Note: IOC components include light sources, optical filters, photodetectors, and thin-film optical waveguides. Integrated Services Digital Network (ISDN) - A high performance, digital phone circuit available from most regional telephone companies that allows for voice and data to be transmitted on the same line, producing fast, noise-free connections. - See ISDN. An integrated digital network in which the same time-division switches and digital transmission paths are used to establish connections for different services. Note 1: ISDN services include telephone, data, electronic mail, and facsimile. Note 2: The method used to accomplish a connection is often specified: for example, switched connection, nonswitched connection, exchange connection, ISDN connection. Integrated Station - A terminal device in which a telephone and one or more other devices, such as a video display unit, keyboard, or printer, are integrated and used over a single circuit. Integrated System - A telecommunication system that transfers analog and digital traffic over the same switched network. Integrated Voice and Data Terminal (IVDT) - See integrated station. A terminal device in which a telephone and one or more other devices, such as a video display unit, keyboard, or printer, are integrated and used over a single circuit. 230
- 231. Integrating Network - A network (circuit) that produces an output waveform that is the time integral of the input waveform. Note: Integrating networks are used in signal processing, such as for producing sawtooth waves from square waves. Integrity - The quality of an information system (IS) reflecting the logical correctness and reliability of the operating system; the logical completeness of the hardware and software implementing the protection mechanisms; and the consistency of the data structures and occurrence of the stored data. Note that, in a formal security mode, integrity is interpreted more narrowly to mean protection against unauthorized modification or destruction of information. Integrity Check Value - A checksum capable of detecting modification of an information system (IS). Intelligent Agent - Synonym droid. 1. In the Internet, an intelligent search tool that automatically seeks out relevant online information based on the user's specifications. Synonyms agent, bot, crawler, hotbot, infobot, information agent, intelligent agent, Internet search engine, knowbot, knowledge robot, personal agent, robotic librarian, search robot, spider, Web crawler, Web spider, wizard. 2. In artificial intelligence, an entity with the ability to sense its environment and to act in such a way or to affect that environment; typically knowledge-based entities that can communicate with each other through some message-passing scheme. Intelligent Network (IN) - 1. A network that allows functionality to be distributed flexibly at a variety of nodes on and off the network and allows the architecture to be modified to control the services. 2. In North America, an advanced network concept that is envisioned to offer such things as (a) distributed call- processing capabilities across multiple network modules, (b) real-time authorization code verification, (c) one-number services, and (d) flexible private network services [including (1) reconfiguration by subscriber, (2) traffic analyses, (3) service restrictions, (4) routing control, and (5) data on call histories]. Levels of IN development are identified below: • IN/1 A proposed intelligent network targeted toward services that allow increased customer control and that can be provided by centralized switching vehicles serving a large customer base. • IN/1+ A proposed intelligent network targeted toward services that can be provided by centralized switching vehicles, e.g., access tandems, serving a large customer base. • IN/2 A proposed, advanced intelligent-network concept that extends the distributed IN/1 architecture to accommodate the concept called " service independence." Note: Traditionally, service logic has been localized at individual switching systems. The IN/2 architecture provides flexibility in the placement of service logic, requiring the use of advanced techniques to manage the distribution of both network data and service logic across multiple IN/2 modules. Intelligent Network Application Protocol (INAP) - A protocol for intelligent network applications contained in Layer 7 (the Application Layer of the OSI model). Intelligent Network (IN) Supported Service - A service provided using the capabilities of the intelligent network. Intelligent Peripheral (IP) - 1. A functional component that may be used most efficiently when accessed locally. 2. An intelligent-network feature that provides specialized telecommunication capabilities required by IN/2 service logic programs. Intelligibility - For voice communications, the capability of being understood. Note: Intelligibility does not imply the recognition of a particular voice. 231
- 232. Intelligible Crosstalk - Crosstalk from which information can be derived. INTELSAT - Abbreviation for International Telecommunications Satellite Organization. Intensity - The square of the electric field strength of an electromagnetic wave. Note: Intensity is proportional to irradiance and may be used in place of the term "irradiance" when only relative values are important. Intensity Modulation (IM) - In optical communications, a form of modulation in which the optical power output of a source is varied in accordance with some characteristic of the modulating signal. Note: In intensity modulation, there are no discrete upper and lower sidebands in the usually understood sense of these terms, because present optical sources lack sufficient coherence to produce them. The envelope of the modulated optical signal is an analog of the modulating signal in the sense that the instantaneous power of the envelope is an analog of the characteristic of interest in the modulating signal. Recovery of the modulating signal is by direct detection, not heterodyning. Interaction Crosstalk - Crosstalk caused by coupling between carrier and noncarrier circuits. Note: If the interaction crosstalk is, in turn, coupled to another carrier circuit, that crosstalk is called "indexing." Interactive - Pertaining to a communications environment in which more than one party is equipped and ready to participate actively in a session or a protocol. [After X9.42] Note: Common usage of the term refers to a session where at least one of the parties is human and another of the parties is a software application. Interactive Data Transaction - A unidirectional message, transmitted via a data channel, that requires a response in order for work to proceed logically. Interactive Service - In an integrated services digital network (ISDN), a telecommunications service that facilitates a bidirectional exchange of information among users or among users and hosts. Note: Interactive services are grouped into conversational services, messaging services, and retrieval services. Interactive Voice Response - In telephony, interactive voice response, or IVR, is a computerised system that allows a person, typically a telephone caller, to select an option from a voice menu and otherwise interface with a computer system. Generally the system plays pre-recorded voice prompts to which the person presses a number on a telephone keypad to select the option chosen, or speaks simple answers such as "yes", "no", or numbers in answer to the voice prompts. The latest systems use natural language speech recognition to interpret the questions that the person wants answered. Other innovations include the ability to speak complex and dynamic information such as an e-mail, news report or weather information using Text-To-Speech (TTS). TTS is computer generated synthesised speech and is no longer the robotic voice people associate with computers. Real voices are used to create the speech in tiny fragments that are glued together before being played to the caller. IVR systems are found operating telephone banking services, voicemail systems are similar to IVR systems but offer limited functionality. IVR systems can be used to create services from telephone banking, order placement, caller identification and airline ticket booking. ACD systems are often the first point of contact when calling many larger businesses. IVR systems are generally used at the front end of call centers to identify what service the caller wants and to extract numeric information such as account numbers as well as provide answers to simple questions such as account balances or allow pre-recorded information to be heard. 232
- 233. IVR systems are often criticised as being unhelpful and difficult to use due to poor design and lack of appreciation of the callers' needs. A properly designed IVR system should connect callers to their desired service promptly and with a minimum of fuss. IVR call flows are created in a variety of ways: while older systems depended upon proprietary programming or scripting languages, modern systems are structured similar to WWW pages, using the VoiceXML or SALT (http://www.saltforum.org/speechtek05/) language. This allows any Web server to act as an application server, freeing the developer to focus on the call flow. Developers then also no longer require specialized programming skills, as any Web developer already has all the tools needed to create an IVR call flow. Interblock Gap - On a data recording medium, an area used to indicate the end of a block or physical record. Note: Examples of interblock gaps are the gaps between blocks on magnetic tape and disks. Intercept - 1. To stop a telephone call directed to an improper, disconnected, or restricted telephone number, and to redirect that call to an operator or a recording. 2. To gain possession of communications intended for others without their consent, and, ordinarily, without delaying or preventing the transmission. Note: An intercept may be an authorized or unauthorized action. 3. The acquisition of a transmitted signal with the intent of delaying or eliminating receipt of that signal by the intended destination user. 4. A call disposition category for a call attempt to a non-operating number. Intercept Call Request - An operator services call request initiated by the network because of the service condition of the line of the called party (e.g., line out of service, etc.). Interchange - Mutual acceptance and exchange of messages between entities. Interchangeability - 1. The ability to exchange hardware components having the same form, fit, and function, across platforms, without affecting the functionality of the system. 2. A condition which exists when two or more items possess such functional and physical characteristics as to be equivalent in performance and durability, and are capable of being exchanged one for the other without alteration of the items themselves, or of adjoining items, except for adjustment, and without selection for fit and performance. Interchangeable Connectors - Connectors that share common installation geometry and have the same transmission performance. Interchange Circuit - A circuit that facilitates the exchange of data and signaling information between data terminal equipment (DTE) and data circuit-terminating equipment (DCE). Note: An interchange circuit can carry many types of signals and provide many types of service features, such as control signals, timing signals, and common return functions. Intercharacter Interval - In asynchronous transmission, the time interval between the end of the stop signal of one character and the beginning of the start signal of the next character. Note: The intercharacter interval may be of any duration. The signal sense of the intercharacter interval is always the same as the sense of the stop element, i.e., "1" or "mark." Intercom - 1. A telephone apparatus by means of which personnel can talk to each other within an aircraft, tank, ship, or activity. [JP 1-02] 2. A dedicated voice service within a specified user environment. Interconnect Facility - In a communications network, one or more communications links that (a) are used to provide local area communications service among several locations and (b) collectively form a node in the network. Note 1: An interconnect facility may include network control and administrative circuits as well as 233
- 234. the primary traffic circuits. Note 2: An interconnect facility may use any medium available and may be redundant. Interconnecting Networks (ICNs) - Two or more networks connected for purposes of call processing. Interconnection - 1. The linking together of interoperable systems. 2. The linkage used to join two or more communications units, such as systems, networks, links, nodes, equipment, circuits, and devices. Interconnectivity - See interconnection. - 1. The linking together of interoperable systems. 2. The linkage used to join two or more communications units, such as systems, networks, links, nodes, equipment, circuits, and devices. Interdigit Interval - A multifrequency (MF) and dual tone multifrequency (DTMF) signal timing interval that is equal to the sum of the fall time, signal-off time, and rise time. The interdigit interval starts when the MF or DTMF signal duration ends. The interdigit interval ends when the next MF or DTMF signal duration begins. Interest Group - A gathering or category of network users who have a similar interest in a particular topic and who share their opinions with each other via email or an internet forum. Interexchange Carrier (IXC or IC) - 1. A communications common carrier authorized to provide interexchange telecommunications services within world zone 1 using the North American numbering plan. 2. A telecommunications common carrier authorized to provide telecommunications services between LATAs. Note: The term "interexchange carrier" is also used to refer to any other entity that connects to the exchange access network at a point of termination (POT).3. A carrier that provides connections between LATAs, where the calling or called customer is located in the United States. Note: This definition has no Canadian equivalent. However, the term "interexchange carrier" is used in the context of a carrier that provides connections extending across borders to carriers in the United States. Synonyms [loosely] carrier, common carrier, commercial carrier, communications carrier. Interexchange Channel - A circuit which is included in the interexchange transmission equipment. Interexchange Transmission Equipment - The combination of (a) interexchange cable and wire facilities, (b) interexchange circuit equipment and, (c) associated land and buildings. Interface (I/F) - 1. In a system, a shared boundary, i.e., the boundary between two subsystems or two devices. 2. A shared boundary between two functional units, defined by specific attributes, such as functional characteristics, common physical interconnection characteristics, and signal characteristics. 3. A point of communication between two or more processes, persons, or other physical entities. 4. A point of interconnection between user terminal equipment and commercial communications facilities. 5. To interconnect two or more entities at a common point or shared boundary. 6. [A] common boundary between independent systems or modules where interactions take place. 7. The point of interconnection between two distinct but adjacent communications systems having different functions. The interface in the communication-satellite service is that point where communications terminal equipment of the terrestrial common carriers or other authorized entities interconnects with the terminal equipment of the communication-satellite earth station complex. The interface in the communication-satellite service shall be located at the earth station site, or if this is impracticable, as close thereto as possible. Interface Data - The parameter within a primitive that is the unit of information transferred to/from the upper layer or sublayer in a single interaction. 234
- 235. Interface Functionality - In telephony, the characteristic of interfaces that allows them to support transmission, switching, and signaling functions identical to those used in the enhanced services provided by the carrier. Note: As part of its comparably efficient interconnection (CEI) offering, the carrier must make available standardized hardware and software interfaces that are able to support transmission, switching, and signaling functions identical to those used in the enhanced services provided by the carrier. Interface Message Processor (IMP) - A processor-controlled switch used in packet-switched networks to route packets to their proper destination. Interface Payload - In integrated services digital networks (ISDN), the part of the bit stream through a framed interface used for telecommunications services and signaling. Interface Point - Synonym point of interface. In a telecommunications system, the physical interface between the local access and transport area (LATA) access and inter-LATA functions. Note: The interface point is used to establish the technical interface, the test points, and the points of operational responsibility. Interface Rate - The gross bit rate of the signal at the boundary between the physical layer and the physical medium. Interface Standard - A standard that describes one or more functional characteristics (such as code conversion, line assignments, or protocol compliance) or physical characteristics (such as electrical, mechanical, or optical characteristics) necessary to allow the exchange of information between two or more (usually different) systems or equipment. Note 1: An interface standard may include operational characteristics and acceptable levels of performance. Note 2: In the military community, interface standards permit command and control functions to be performed using communication and computer systems. Interference - 1. In general, extraneous energy, from natural or man-made sources, that impedes the reception of desired signals. 2. A coherent emission having a relatively narrow spectral content, e.g., a radio emission from another transmitter at approximately the same frequency, or having a harmonic frequency approximately the same as, another emission of interest to a given recipient, and which impedes reception of the desired signal by the intended recipient. Note: In the context of this definition, interference is distinguished from noise in that the latter is an incoherent emission from a natural source (e.g., lightning) or a man-made source, of a character unlike that of the desired signal (e.g., commutator noise from rotating machinery) and which usually has a broad spectral content. 3. The effect of unwanted energy due to one or a combination of emissions, radiation, or inductions upon reception in a radiocommunication system, manifested by any performance degradation, misinterpretation, or loss of information which could be extracted in the absence of such unwanted energy. 4. The interaction of two or more coherent or partially coherent waves, which interaction produces a resultant wave that differs from the original waves in phase, amplitude, or both. Note: Interference may be constructive or destructive, i.e., it may result in increased amplitude or decreased amplitude, respectively. Two waves equal in frequency and amplitude, and out of phase by 180°, will completely cancel one another. In phase, they create a resultant wave having twice the amplitude of either interfering beam. Interference Emission - Emission that results in an electrical signal's being propagated into, and interfering with the proper operation of, electronic or electrical equipment. Note: The frequency range of interference emissions may include the entire electromagnetic spectrum. Interference Filter - An optical filter that reflects one or more spectral bands or lines and transmits others, while maintaining a nearly zero coefficient of absorption for all wavelengths of interest. Note 1: An interference filter may be high-pass, low-pass, bandpass, or band-rejection. Note 2: An interference filter consists of multiple thin layers of dielectric material having different refractive indices. There also may be 235
- 236. metallic layers. Interference filters are wavelength-selective by virtue of the interference effects that take place between the incident and reflected waves at the thin-film boundaries. Interfering Contour - The locus of points surrounding a transmitter where the predicted median field strength of the signal from that transmitter is the maximum field strength that is not considered to cause interference at the service contour of another transmitter. Interferometer - An instrument that uses the principle of interference of electromagnetic waves for purposes of measurement. Note: Interferometers may be used to measure a variety of physical variables, such as displacement (distance), temperature, pressure, and strain. Interferometry - The branch of science devoted to the study and measurement of the interaction of waves, such as electromagnetic waves and acoustic waves. Note 1: The interaction of the waves can produce various spatial-, time-, and frequency-domain energy distribution patterns. Note 2: Interferometric techniques are used to measure refractive index profiles, e.g., those of the preforms from which optical fibers are drawn, and to sense and measure physical variables, such as displacement (distance), temperature, pressure, and magnetic fields. Interframe Time Fill - In digital data transmission, a sequence of bits transmitted between consecutive frames. Note: Interframe time fill does not include bits stuffed within a frame. Interlaced Scanning - In raster-scanned video displays, a scanning technique in which all odd-numbered scanning lines are first traced in succession, followed by the tracing of the even-numbered scanning lines in succession, each of which is traced between a pair of odd-numbered scanning lines. Note 1: The pattern created by tracing the odd-numbered scanning lines is called the odd field , and the pattern created by tracing the even-numbered scanning lines is called the even field. Each field contains half the information content, i.e., pixels, of the complete video frame. Note 2: Image flicker is less apparent in an interlaced display than in a noninterlaced display, because the rate at which successive fields occur in an interlaced display is twice that at which successive frames would occur in a noninterlaced display containing the same number of scanning lines and having the same frame refresh rate. Synonym interlacing. Interlacing - Synonym interlaced scanning. In raster-scanned video displays, a scanning technique in which all odd-numbered scanning lines are first traced in succession, followed by the tracing of the even-numbered scanning lines in succession, each of which is traced between a pair of odd-numbered scanning lines. Note 1: The pattern created by tracing the odd-numbered scanning lines is called the odd field , and the pattern created by tracing the even-numbered scanning lines is called the even field. Each field contains half the information content, i.e., pixels, of the complete video frame. Note 2: Image flicker is less apparent in an interlaced display than in a noninterlaced display, because the rate at which successive fields occur in an interlaced display is twice that at which successive frames would occur in a noninterlaced display containing the same number of scanning lines and having the same frame refresh rate. Inter-LATA - 1. Between local access and transport areas (LATAs). 2. Services, revenues, and functions associated with telecommunications that originate in one LATA and that terminate in another one or that terminate outside of that LATA. InterLata Carrier - The carrier that provides your telecommunications service between your LATA and another LATA. Generally called "Long Distance Carriers." Interleaving - The transmission of pulses from two or more digital sources in time-division sequence over a single path. 236
- 237. Interlocal Trunk - A circuit between two local central office units, either manual or dial. Interlocal trunks may be used for either exchange or toll traffic or both. Intermediate Certificates - In cryptology, certificates in a certificate chain other than the first or end certificate. Intermediate Distribution Frame (IDF) - In a central office or customer premises, a frame that (a) cross- connects the user cable media to individual user line circuits and (b) may serve as a distribution point for multipair cables from the main distribution frame (MDF) or combined distribution frame (CDF) to individual cables connected to equipment in areas remote from these frames. Intermediate Element - In a network, a line-unit-line termination (LULT) or a line-unit-network termination (LUNT). Intermediate Field - Synonym intermediate-field region. Intermediate-Field Region - For an antenna, the transition region--lying between the near-field region and the far-field region--in which the field strength of an electromagnetic wave is dependent upon the inverse distance, inverse square of the distance, and the inverse cube of the distance from the antenna. Note: For an antenna that is small compared to the wavelength in question, the intermediate-field region is considered to exist at all distances between 0.1 wavelength and 1.0 wavelength from the antenna. Synonyms intermediate field, intermediate zone, transition zone. Intermediate Frequency (IF) - A frequency to which a carrier frequency is shifted as an intermediate step in transmission or reception. Intermediate Language - In computer programming, a target language into which all or part of a single statement or a source program--in a source language--is translated before it is further translated or interpreted. Note: For a subsequent translation, an intermediate language may serve as a source language. Intermediate-Level Language - In computer, communications, and data processing systems, a programming language that (a) is less machine-oriented than a machine language, (b) is not so machine-independent as a common language, such as Ada ®, COBOL, or Fortran, (c) contains macros that are less powerful than common-language macros, and (d) usually is the object language of a root compiler. Examples of intermediate-level languages include assembly languages, such as PL/I. Intermediate Operating System - In some operating system (OS) architectures, the OS functions that may be implemented through a central element and one or more remote elements that may do such work as area resource control or area reports. Intermediate System - A system that provides an Open Systems Interconnection--Reference Model (OSI-- RM) Network Layer relay function in which data received from one corresponding network entity are forwarded to another corresponding network entity. Intermediate Translation Signaling Point (ITSP) - A translation signaling point (TSP) that translates the global title (as received or after changing to another global title) to identify the next TSP in succession to which the switched control center system (SCCP) message is then routed. The next TSP may be another ITSP or a final TSP Intermediate Trunk (IT) - A channel mapping designation that ranges between 1 and 216 and relates the digital circuit multiplication equipment (DCME) transmission trunk to an internal numbering designation 237
- 238. used within the DCME for conveying trunk-channel-to-bearer-channel connectivity via the DCME assignment channel. Intermediate Zone - Synonym intermediate-field region. For an antenna, the transition region--lying between the near-field region and the far-field region--in which the field strength of an electromagnetic wave is dependent upon the inverse distance, inverse square of the distance, and the inverse cube of the distance from the antenna. Note: For an antenna that is small compared to the wavelength in question, the intermediate-field region is considered to exist at all distances between 0.1 wavelength and 1.0 wavelength from the antenna. Intermittent Service Area - The area receiving service from the groundwave of a broadcast station but beyond the primary service area and subject to some interference and fading. Intermodal Delay Distortion - Synonym multimode distortion. A distortion mechanism, occurring in multimode fibers, in which the signal is spread in time because the velocity of propagation of the optical signal is not the same for all modes. Note 1: In the ray-optics analogy, multimode distortion in a step-index optical fiber may be compared to multipath propagation of a radio signal. The direct signal is distorted by the arrival of the reflected signal a short time later. In a step-index optical fiber, rays taking more direct paths through the fiber core, i.e., those which undergo the fewest reflections at the core-cladding boundary, will traverse the length of the fiber sooner than those rays which undergo more reflections. This results in distortion of the signal. Note 2: Multimode distortion limits the bandwidth of multimode fibers. For example, a typical step-index fiber with a 50- m core would be limited to approximately 20 MHz for a one-kilometer length, i.e., a bandwidth of 20 MHz•km. Note 3: Multimode distortion may be considerably reduced, but never completely eliminated, by the use of a core having a graded refractive index. The bandwidth of a typical off-the-shelf graded-index multimode fiber, having a 50- m core, may approach 1 GHz•km or more. Multimode graded-index fibers having bandwidths approaching 3 GHz•km have been produced. Note 4: Because of its similarity to dispersion in its effect on the optical signal, multimode distortion is sometimes incorrectly referred to as " intermodal dispersion," " modal dispersion," or " multimode dispersion." Such usage is incorrect because multimode distortion is not a truly dispersive effect. Dispersion is a wavelength- dependant phenomenon, whereas multimode distortion may occur at a single wavelength. Intermodal Dispersion - Incorrect synonym for multimode distortion. Intermodal Distortion - Synonym multimode distortion. Intermodulation (IM) - The production, in a nonlinear element of a system, of frequencies corresponding to the sum and difference frequencies of the fundamentals and harmonics thereof that are transmitted through the element. Intermodulation Distortion (IMD) - Nonlinear distortion characterized by the appearance, in the output of a device, of frequencies that are linear combinations of the fundamental frequencies and all harmonics present in the input signals. Note: Harmonic components themselves are not usually considered to characterize intermodulation distortion. When the harmonics are included as part of the distortion, a statement to that effect should be made. Intermodulation Noise - In a transmission path or device, noise, generated during modulation and demodulation, that results from nonlinear characteristics in the path or device. Intermodulation Product - In the output of a nonlinear system, a frequency produced by intermodulation of harmonics of the frequencies present in the input signal. 238
- 239. Internal Bias - In a start-stop teletypewriter receiving mechanism, bias generated locally by the mechanism, and which has the same effect on the operating margin as bias external to the receiver, i.e., applied bias. Note: Internal bias may be a marking bias or a spacing bias. Internal Call - A call placed within a private branch exchange (PBX) or local switchboard, i.e., not through a central office in a public switched network. Synonym inside call. Internal Memory - In a computer, all of the storage spaces that are accessible by a processor without the use of the computer input-output channels. Note: Internal memory usually includes several types of storage, such as main storage, cache memory, and special registers, all of which can be directly accessed by the processor. Synonym internal storage. Internal Photoelectric Effect - A photoconductive or photovoltaic effect. Internal Storage - Synonym internal memory. In a computer, all of the storage spaces that are accessible by a processor without the use of the computer input-output channels. Note: Internal memory usually includes several types of storage, such as main storage, cache memory, and special registers, all of which can be directly accessed by the processor. Internal VoIP - In a medium or large office, the internal phone system can be Internet based. In this case, calls between extensions, and possibly between office buildings, run over a private data network. To reach the outside world, the company's Internet phone system can connect to the Internet, the regular phone system, or both. International Atomic Time (TAI) - The time scale established by the Bureau International des Poids et Mesures (BIPM--International Bureau of Weights and Measures in Sevres, France) on the basis of atomic clock data supplied by cooperating institutions. International Carrier (INC) - A carrier authorized to provide telecommunications services outside World Zone 1 using the international dialing plan; however, the carrier has the option of providing service to World Zone 1 points outside the forty-eight contiguous states of the United States. International Fixed Public Control Service - A fixed service carried on for the purpose of communicating between transmitting stations, receiving stations, message centers or control points in the international fixed public radiocommunication service. International Fixed Public Radiocommunication Service - A fixed service, the stations of which are open to public correspondence and which, in general, is intended to provide radiocommunication between any one of the contiguous 48 states (including the District of Columbia) and the state of Alaska, or the State of Hawaii, or any U.S. possession or any foreign point; or between any U.S. possession and any other point; or between the state of Alaska and any other point; or between the state of Hawaii and any other point. In addition, radiocommunications within the contiguous 48 states (including the District of Columbia) in 239
- 240. connection with the relaying of international traffic between stations which provide the above service, are also deemed to be the international fixed public radiocommunications service; provided, however, that communications solely between Alaska, or any one of the contiguous 48 states (including the District of Columbia), and either Canada or Mexico are not deemed to be in the international fixed public radiocommunication service when such radiocommunications are transmitted on frequencies above 72 MHz. International Index Of Cooperation - Synonym index of cooperation. 1. In facsimile, the product of the total line length and the number of lines per unit length, divided by . 2. For rotating devices, the product of the drum diameter and the number of lines per unit length. Synonyms: diametral index of cooperation, international index of cooperation. International Frequency Registration Board- See Radio Regulations Board. The Radio Regulations Board was formerly called International Frequency Registration Board (IFRB). A permanent organization of the International Telecommunication Union (ITU) that implements frequency assignment policy and maintains the Master International Frequency Register (MIFR). (IFRB). International Organization for Standardization - See ISO. An international organization that (a) consists of member bodies that are the national standards bodies of most of the countries of the world, (b) is responsible for the development and publication of international standards in various technical fields, after developing a suitable consensus, (c) is affiliated with the United Nations, and (d) has its headquarters at 1, rue de Varembé, Geneva, Switzerland. Note: Member bodies of ISO include, among others, the American National Standards Institute (ANSI), the Association Française de Normalisation (AFNOR), the British Standards Institution (BSI), and the Deutsche Institut für Normung (DIN). International Prefix - The combination of digits to be dialed by a calling subscriber making a call to a subscriber in another country to obtain access to the automatic outgoing international equipment. International Radio Consultative Committee (CCIR) - See ITU-R. The Radiocommunications Sector of the ITU; responsible for studying technical issues related to radiocommunications, and having some regulatory powers. Note: A predecessor organization was the CCIR. International Reference Alphabet (IRA) No. 5 - See ASCII. ASCII is an acronym for American Standard Code for Information Interchange, a code that represents the most basic letters of the Roman alphabet, numbers, and other characters used in computing. ASCII characters allow us to communicate with computers, which use their own language called binary made up of 0s and 1s. ASCII files are also called text files. ASCII is the standard code used for information interchange among data processing systems, data communications systems, and associated equipment in the United States. Note 1: The ASCII character set contains 128 coded characters. Note 2: Each ASCII character is a 7-bit coded unique character; 8 bits when a parity check bit is included. Note 3: The ASCII character set consists of control characters and graphic characters. Note 4: When considered simply as a set of 128 unique bit patterns, or 256 with a parity bit, disassociated from the character equivalences in national implementations, the ASCII may be considered as an alphabet used in machine languages. Note 5: The ASCII is the U.S. version of International Reference Alphabet (IRA) No. 5 (formerly International Alphabet No. 5, or "IA5") as specified in ITU-T Recommendation T.50. International Routing Code - A 3-digit code within the North American numbering plan, beginning with 1, that classifies international calls as requiring either regular or special handling. International System of Units (SI) - The modern form of the metric system, which has been adopted by the United States and most other nations. Note: The SI is constructed from seven base units for independent physical quantities. 240
- 241. International Telecommunication Union (ITU) - A civil international organization established to promote standardized telecommunications on a worldwide basis. Note: The ITU-R and ITU-T are committees under the ITU. The ITU headquarters is located in Geneva, Switzerland. While older than the United Nations, it is recognized by the U.N. as the specialized agency for telecommunications. International Telegraph Alphabet Number 5 (ITA-5) - An alphabet in which (a) 128 unique 7-bit strings are used to encode upper- and lower-case letters, 10 decimal numerals, special signs and symbols, diacritical marks, data delimiters, and transmission control characters, (b) 12 of the 7-bit strings are not assigned to any letter, numeral, or control character, and (c) the unassigned bit strings are open for use in a given country that may have unique requirements, such as monetary symbols; diacritical marks, such as the tilde, umlaut, circumflex, and dieresis, and (d) a two-condition 8-bit pattern may be used that consists of seven information bits and a parity check bit. Note: ITA-5 is used for effecting information interchange. It is a result of a joint agreement between the International Telegraph and Telephone Consultative Committee (CCITT), now ITU-T, of the International Telecommunication Union (ITU) and the International Organization for Standardization (ISO). It is published as CCITT (ITU-T) Recommendation V.3 and as ISO 646. It has also been adopted by NATO for military use. The United States adaptation of ITA-5 is ASCII (American Standard Code for Information Interchange) published by the American National Standards Institute (ANSI). Synonym International Reference Alphabet (IRA). International Telegraph and Telephone Consultative Committee (CCITT) - See ITU-T. Abbreviation for International Telecommunication Union--Telecommunication Standardization Sector. The Telecommunication Standardization Sector of the International Telecommunication Union (ITU). Note 1: ITU- T is responsible for studying technical, operating, and tariff Questions and issuing Recommendations on them, with the goal of standardizing telecommunications worldwide. Note 2: In principle, the ITU-T combines the standards-setting activities of the predecessor organizations formerly called the International Telegraph and Telephone Consultative Committee (CCITT) and the International Radio Consultative Committee (CCIR). International Time Bureau (BIH) - See International Atomic Time. The time scale established by the Bureau International des Poids et Mesures (BIPM--International Bureau of Weights and Measures in Sevres, France) on the basis of atomic clock data supplied by cooperating institutions. Internaut - Slang term for a user of the Internet. Synonym cybernaut. Internet - A collection and interconnection of tens of thousands of independent global networks. internet - Any interconnection among or between private, industrial or governmental computer (digital communication) networks. Note: The term internet (spelled with a lower case "i") is distinguished from the Internet (spelled with the "I" capitalized). "The Internet" refers to a specific, historic, ubiquitous worldwide digital communications network. Internet [the] - 1. A worldwide interconnection of individual networks a) with an agreement on how to talk to each other, and b) operated by government, industry, academia, and private parties. Note: The Internet originally served to interconnect laboratories engaged in government research, and has now been expanded to serve millions of users and a multitude of purposes, such as interpersonal messaging, computer conferences, file transfer, and consulting of files containing documents. 2. The international computer network of both federal and nonfederal interoperable packet switched data networks. Internet2 - See I2. Abbreviation for Internet second generation. A proposed high-speed Internet for use exclusively by government researchers and academic institutions. Internet 2 - A proposed high-speed Internet for use exclusively by government researchers and academic institutions. See I2. Abbreviation for Internet second generation. 241
- 242. Internet Address - In The Internet protocol, the decimal-numeric, fixed-length address that identifies the hosts of data sources, and, specifically, a communication port. Note: A single Internet address can have multiple URLs. Synonyms IP address, Internet protocol address. Internet Appliance - Synonym thin client. A server-centric computing model in which the application software, data, and CPU power resides on a network server rather than on the client computer (s). Note 1: This computing philosophy allows administrators to purchase one relatively powerful and expensive server and be confident that any external terminal, regardless of its power or sophistication, can run applications on the server. Most "shopping" Web pages, for example, are thin-client applications (i.e., the client needs nothing more than a browser and a connection to the network to be able to search the "shopping" page and to order products). Local area networks can use thin-client modeling to install only one copy of necessary programs onto the main server for many clients on the network to use. Note 2: Server software is required to interface clients with the software on the server. Synonyms Internet appliance (computing), Internet box (computing), network computer. Internet Architecture Board (IAB) - The technical body that oversees the development of the Internet suite of protocols (commonly referred to as "TCP/IP "), and that has two task forces (the Internet Research Task Force and the Internet Engineering Task Force), each charged with investigating a particular field. Internet Assigned Numbers Authority (IANA) - An organization, directed by the Internet Architecture Board, that assigns IP numbers and protocol parameters such as port, protocol, and enterprise numbers, and opinions, codes, and types. Internet Control Message Protocol - See ICMP. An Internet protocol that reports datagram delivery errors. Note 1: ICMP is a key part of the TCP/IP protocol suite. Note 2: The packet internet gopher (ping) application is based on ICMP. Internet Information Center - See InterNIC. The centralized organization run by the National Science Foundation that provides various administrative services for the Internet, including Domain Name registration. Internet Mail Agent - Synonym message transfer agent. An OSI application process used to store and forward messages as described in the X.400 message handling system. Internet Mall - Synonym cybermall. An electronic site shared by a number of commercial interests, and at which users can browse, shop, and place orders for the products listed at that site. Internet Network Information Center - See InterNIC. The centralized organization run by the National Science Foundation that provides various administrative services for the Internet, including Domain Name registration. Internet Phone - A combination of software and hardware that allows a user to approximate a telephone conversation over an Internet connection instead of using a traditional telephone system. Note 1: The required hardware generally consists of a microphone and headphones. Note 2: The sound quality of current Internet-phone systems is much less than that of traditional telephone systems. Synonym Web phone. Internet Phone Service - In the most flexible form of VoIP, Internet technology replaces the connection between the telephone and the phone company. You plug an ordinary telephone into an adapter that connects to your broadband setup. Your call is routed over the Web to a VoIP service provider. This provider connects your calls to the telephone system. If the person you are calling is also a user of the same Internet calling system, the call will never touch the phone system at all. 242
- 243. Internet Presence Provider - See IPP. An organization or commercial enterprise that provides storage space for the Web resources of an individual or other entity and enables those resources to be accessed by Internet users. Note: An IPP may not offer basic Internet connections as an ISP usually does. Internet Protocol Address - Synonym Internet address. See IP address. A 32 bit address (four bytes separated by periods) that defines the location of a host on the Internet. Internet Protocol (IP) - A DOD standard protocol designed for use in interconnected systems of packet- switched computer communication networks. Note: The internet protocol provides for transmitting blocks of data called datagrams from sources to destinations, where sources and destinations are hosts identified by fixed-length addresses. The internet protocol also provides for fragmentation and reassembly of long datagrams, if necessary, for transmission through small-packet networks. Internet Protocol (IP) Spoofing - 1. The creation of IP packets with counterfeit (spoofed) IP source addresses. 2. A method of attack used by network intruders to defeat network security measures such as authentication based on IP addresses. Note 1: An attack using IP spoofing may lead to unauthorized user access, and possibly root access, on the targeted system. Note 2: A packet-filtering-router firewall may not provide adequate protection against IP spoofing attacks. It is possible to route packets through this type of firewall if the router is not configured to filter incoming packets having source addresses on the local domain. Note 3: IP spoofing is possible even if no reply packets can reach the attacker. Note 4: A method for preventing IP spoofing problems is to install a filtering router that does not allow incoming packets to have a source address different from the local domain. In addition, outgoing packets should not be allowed to contain a source address different from the local domain, in order to prevent an IP spoofing attack from originating from the local network. Internet Relay Chat (IRC) - A popular program that allows users all around the world to communicate live, or chat, with other users. A service for conducting a chat on the Internet, i.e., an application that allows a number of individual users to exchange text messages simultaneously in real time over The Internet. Internet Research Task Force - See IRTF. A task force of the Internet Architecture Board (IAB), and which is responsible for research and development of the Internet protocol suite. Internet Resource - Within the Internet, an accessible facility or entity that contains information or provides data-processing capabilities. Note: An example of an Internet resource is a Web server. Internet Search Engine - Synonym droid. - 1. In the Internet, an intelligent search tool that automatically seeks out relevant online information based on the user's specifications. Synonyms agent, bot, crawler, hotbot, infobot, information agent, intelligent agent, Internet search engine, knowbot, knowledge robot, personal agent, robotic librarian, search robot, spider, Web crawler, Web spider, wizard. 2. In artificial intelligence, an entity with the ability to sense its environment and to act in such a way or to affect that environment; typically knowledge-based entities that can communicate with each other through some message-passing scheme. 243
- 244. Internet Service Provider - See ISP. A company or organization that provides connections to the Internet to companies or individuals via dial-up, ISDN, T1, or other connection. Internet Society - See ISOC. A nongovernmental, international organization for global cooperation and coordination for The Internet and its internetworking technologies and applications. Internet Telephone - See Internet phone. A combination of software and hardware that allows a user to approximate a telephone conversation over an Internet connection instead of using a traditional telephone system. Note 1: The required hardware generally consists of a microphone and headphones. Note 2: The sound quality of current Internet-phone systems is much less than that of traditional telephone systems. Internet Telephony - See Internet phone. See Internet phone. A combination of software and hardware that allows a user to approximate a telephone conversation over an Internet connection instead of using a traditional telephone system. Note 1: The required hardware generally consists of a microphone and headphones. Note 2: The sound quality of current Internet-phone systems is much less than that of traditional telephone systems. Internetwork - Synonym internet. 1. A worldwide interconnection of individual networks a) with an agreement on how to talk to each other, and b) operated by government, industry, academia, and private parties. Note: The Internet originally served to interconnect laboratories engaged in government research, and has now been expanded to serve millions of users and a multitude of purposes, such as interpersonal messaging, computer conferences, file transfer, and consulting of files containing documents. 2. The international computer network of both federal and nonfederal interoperable packet switched data networks. Internetwork Connection - See gateway. 1. In a communications network, a network node equipped for interfacing with another network that uses different protocols. Note 1: A gateway may contain devices such as protocol translators, impedance matching devices, rate converters, fault isolators, or signal translators as necessary to provide system interoperability. It also requires that mutually acceptable administrative procedures be established between the two networks. Note 2: A protocol translation/mapping gateway interconnects networks with different network protocol technologies by performing the required protocol conversions. 2. [An] interface providing a compatibility between networks by converting transmission speeds, protocols, codes, or security measures. 3. Loosely, a computer configured to perform the tasks of a gateway. Internetworking - The process of interconnecting two or more individual networks to facilitate communications among their respective nodes. Note: The interconnected networks may be different types. Each network is distinct, with its own addresses, internal protocols, access methods, and administration. Iinternetwork Interface (INI) - The point of demarcation between networks when service is provided across multiple networks. Internetwork Packet Exchange - See IPX. A proprietary (LAN) protocol. InterNIC (Internet Network Information Center) - The centralized organization run by the National Science Foundation that provides various administrative services for the Internet, including Domain Name registration. The association of providers of domain-name registration, information, and database services to the Internet. Interoffice Trunk - A single direct transmission channel, e.g., voice-frequency circuit, between central offices. 244
- 245. Interoperability - 1. The ability of systems, units or forces to provide services to and accept services from other systems, units, or forces and to use the services so exchanged to enable them to operate effectively together. 2. The condition achieved among communications-electronics systems or items of communications-electronics equipment when information or services can be exchanged directly and satisfactorily between them and/or their users. The degree of interoperability should be defined when referring to specific cases. 3. Allows applications executing on separate hardware platforms, or in multi- processing environments on the same platform, to share data and cooperate in processing it through communications mechanisms such as remote procedure calls, transparent file access, etc. 4. The ability of a set of modeling and simulation to provide services to and accept services from other modeling and simulation, and to use the services for exchange enabling them to operate effectively together. 5. The capability to provide useful and cost-effective interchange of electronic data among, e.g., different signal formats, transmission media, applications, industries, or performance levels. Interoperability Standard - A document that establishes engineering and technical requirements that are necessary to be employed in the design of systems, units, or forces and to use the services so exchanged to enable them to operate effectively together. Interoperation - The use of interoperable systems, units, or forces. Interpolation Gain - The input trunk channel multiplication ratio that is achieved through DSI. The interpolation gain is the ratio of the number of input transmission trunks to the number of DCME bearer channels where the same signal encoding rate is used for both trunk and bearer channels. Interposition Trunk - 1. A single direct transmission channel, e.g., voice-frequency circuit, between two positions of a large switchboard to facilitate the interconnection of other circuits appearing at the respective switchboard positions. 2. Within a technical control facility, a single direct transmission circuit, between positions in a testboard or patch bay, which circuit facilitates testing or patching between the respective positions. Interpret - To translate and to execute each source language statement of a computer program before translating and executing the next statement. Interrogation - 1. The transmission of a signal or combination of signals intended to trigger a response. 2. The process whereby a station or device requests another station or device to identify itself or to give its status. Interrupt - A suspension of a process, such as the execution of a computer program, caused by an event external to that process, and performed in such a way that the process can be resumed. Synonym interruption. Interrupted Continuous Wave (ICW) - Modulation in which there is on-off keying of a continuous wave. Interrupted Isochronous Transmission - Synonym isochronous burst transmission. In a data network where the information-bearer channel rate is higher than the input data signaling rate, transmission performed by interrupting, at controlled intervals, the data stream being transmitted. Note 1: Isochronous burst transmission enables communication between data terminal equipment (DTE) and data networks that operate at dissimilar data signaling rates, such as when the information-bearer channel rate is higher than the DTE output data signaling rate. Note 2: The binary digits are transferred at the information-bearer channel rate. The transfer is interrupted at intervals in order to produce the required average data signaling rate. Note 3: The interruption is always for an integral number of unit intervals. Note 4: Isochronous burst transmission has particular application where envelopes are being transferred between data circuit- 245
- 246. terminating equipment (DCE) and only the bytes contained within the envelopes are being transferred between the DCE and the DTE. Interruption - Synonym interrupt. A suspension of a process, such as the execution of a computer program, caused by an event external to that process, and performed in such a way that the process can be resumed. Interruption Control - A system that monitors a pilot for interruptions on frequency division multiplexing (FDM) systems and that transmits an indication to the switching equipment. Inter-Satellite Service - A radiocommunication service providing links between artificial Earth satellites. Interswitch Trunk - A single direct transmission channel, e.g., voice-frequency circuit, between switching nodes. Intersymbol Interference - 1. In a digital transmission system, distortion of the received signal, which distortion is manifested in the temporal spreading and consequent overlap of individual pulses to the degree that the receiver cannot reliably distinguish between changes of state, i.e., between individual signal elements. Note 1: At a certain threshold, intersymbol interference will compromise the integrity of the received data. Note 2: Intersymbol interference attributable to the statistical nature of quantum mechanisms sets the fundamental limit to receiver sensitivity. Note 3: Intersymbol interference may be measured by eye patterns. 2. Extraneous energy from the signal in one or more keying intervals that interferes with the reception of the signal in another keying interval. 3. The disturbance caused by extraneous energy from the signal in one or more keying intervals that interferes with the reception of the signal in another keying interval. Intertoll Circuits - Circuits between toll centers and circuits between a toll center and a tandem system in a different toll center area. Intertoll Trunk - A single direct transmission channel, e.g., voice-frequency circuit, between two toll offices. Interworking Functions - Mechanisms that mask differences in physical, link, and network technologies by converting (or mapping) states and protocols into consistent network and user services. IntraLATA - Telephone services within the boundaries of a local access area. See LATA. Generally known as "Local Telephone Companies." Intra-LATA - Within the boundaries of a local access and transport area (LATA). Intramodal Distortion - In an optical fiber, distortion caused by dispersion, such as material or profile dispersion, of a given propagating mode. Intranet - Any private network that uses some or all of the protocols of The Internet. Note: In an intranet, nodes interact in a client-server relationship, nodes are identified by using Internet protocol (IP) addresses, and files are identified by universal resource locators (URLs). The data being exchanged are typically formatted using the HTML language, and is controlled and displayed using a browser. The intranet may be connected to The Internet via firewalls, or it may be totally separate. Intraoffice Trunk - A single direct transmission channel, e.g., voice-frequency circuit, within a given switching center. 246
- 247. Intrinsic Joint Loss - Of nonidentical optical fibers joined by a splice or a mated pair of connectors, the power loss attributable to manufacturing variations, in such parameters as physical dimensions, differences in refractive index (including profile parameter), numerical aperture, and mode field diameter. Intrinsic Noise - In a transmission path or device, that noise inherent to the path or device and not contingent upon modulation. Intrusive Measurements - Measurements that require that the facility be taken out of service and made unavailable to the user. Invalid Frame - A frame for which one or more of the following conditions apply: the frame is not properly bounded by flags; the frame does not consist of an integral number of octets prior to zero-bit insertion or following zero-bit extraction; the frame contains a frame-check sequence error (note that this condition is not recorded in the protocol abnormality log); the frame contains an incorrect address field. Inverse Adaptive Quantizer - In the encoder and the feedback path of the decoder, the process that maps the core bits into a quantized difference signal. In the feed-forward path of the decoder, the process that maps the core bits and the received enhancement bits into a quantized difference signal Inverse Multiplexer - A functional unit capable of accessing and combining two or more low-speed circuits into a virtual broadband circuit, up to and including an aggregate equal to a T1 rate. Inverse-Square Law - The physical law stating that irradiance, i.e., the power per unit area in the direction of propagation, of a spherical wavefront varies inversely as the square of the distance from the source, assuming there are no losses caused by absorption or scattering. Note: For example, the power radiated from a point source, e.g., an omnidirectional isotropic antenna, or from any source at very large distances from the source compared to the size of the source, must spread itself over larger and larger spherical surfaces as the distance from the source increases. Diffuse and incoherent radiation are similarly affected. Inverted Position - In frequency-division multiplexing, a position of a translated channel in which an increasing signal frequency in the untranslated channel causes a decreasing signal frequency in the translated channel. Inverter - 1. In electrical engineering, a device for converting direct current into alternating current. 2. In computers, a device or circuit that inverts the polarity of a signal or pulse. Deprecated synonym negation circuit. Inward Wide-Area Telephone Service (INWATS) - Synonym eight-hundred (800) service. A service that allows call originators to place toll telephone calls to 800-service subscribers, from within specified rate areas, without a charge to the call originator. Note: The 800 series denotes the service access codes of 800, 888, 877, 866, 855, 844, 833, and 822. INWATS - Acronym for Inward Wide-Area Telephone Service. Synonym eight-hundred (800) service. A service that allows call originators to place toll telephone calls to 800-service subscribers, from within specified rate areas, without a charge to the call originator. Note: The 800 series denotes the service access codes of 800, 888, 877, 866, 855, 844, 833, and 822. I/O - Abbreviation for input / output. IONL - Abbreviation for Internal Organization of the Network Layer. The OSI standard for the detailed architecture of the Network Layer. Note: Basically, it partitions the Network layer into subnetworks 247
- 248. interconnected by convergence protocols (equivalent to internetworking protocols), creating what is called a catenet or internet. Ionosphere - That part of the atmosphere, extending from about 70 to 500 kilometers, in which ions and free electrons exist in sufficient quantities to reflect and/or refract electromagnetic waves. Ionosphere Sounder - A device that transmits signals for the purpose of determining ionospheric conditions. Ionospheric Absorption - Absorption occurring as a result of interaction between an electromagnetic wave and free electrons in the ionosphere. Ionospheric Disturbance - An increase in the ionization of the ionosphere, caused by solar activity, which results in greatly increased radio wave absorption. Ionospheric Forward Scatter (IFS): Synonym ionospheric scatter. The propagation of radio waves by scattering as a result of irregularities or discontinuities in the ionization of the ionosphere. Ionospheric Reflection - Of electromagnetic waves propagating in the ionosphere, a redirection, i.e., bending--by a complex processing involving reflection and refraction--of the waves back toward the Earth. Note: The amount of bending depends on the extent of penetration (which is a function of frequency), the angle of incidence, polarization of the wave, and ionospheric conditions, such as the ionization density. Ionospheric Scatter - The propagation of radio waves by scattering as a result of irregularities or discontinuities in the ionization of the ionosphere. Synonym forward propagation ionospheric scatter Ionospheric Sounding - A technique that provides real-time data on high-frequency ionospheric-dependent radio propagation, using a basic system consisting of a synchronized transmitter and receiver. Note: The time delay between transmission and reception is translated into effective ionospheric layer altitude. Vertical incident sounding uses a collocated transmitter and receiver and involves directing a range of frequencies vertically to the ionosphere and measuring the values of the reflected returned signals to determine the effective ionosphere layer altitude. This technique is also used to determine the critical frequency. Oblique sounders use a transmitter at one end of a given propagation path, and a synchronized receiver, usually with an oscilloscope-type display (ionogram), at the other end. The transmitter emits a stepped- or swept- frequency signal which is displayed or measured at the receiver. The measurement converts time delay to effective altitude of the ionospheric layer. The ionogram display shows the effective altitude of the ionospheric layer as a function of frequency. Ionospheric Turbulence - Ongoing disturbances of the ionosphere that scatter incident electromagnetic waves. Note: Ionospheric turbulence results in irregularities in the composition of the ionosphere that change with time. This causes changes in reflection properties. These, in turn, cause changes in skip distance, fading, local intensification, and distortion of the incident waves. IP - Abbreviation for intelligent peripheral, Internet protocol. A DOD standard protocol designed for use in interconnected systems of packet-switched computer communication networks. Note: The internet protocol provides for transmitting blocks of data called datagrams from sources to destinations, where sources and destinations are hosts identified by fixed-length addresses. The internet protocol also provides for fragmentation and reassembly of long datagrams, if necessary, for transmission through small-packet networks. IP Address - A 32 bit address (four bytes separated by periods) that defines the location of a host on the Internet. A device's or resource's numerical address as expressed in the format specified in the Internet Protocol. Note 1: In the current addressing format, IP version 4 (IPv4), an IP address is a 32-bit sequence 248
- 249. divided into four groups of decimal numbers separated by periods ("dots"), commonly referred to as "dotted decimals." The IP address of a device is made up of two parts: the number of the network to which it is connected, and a sequence representing the specific device within that network. An IP address may be used on private intranets, as well as The Internet. Note 2: Due to inefficiencies that have arisen in address assignment, available IPv4 addresses are nearly exhausted. A newer version of IP addressing (IP version 6, consisting of a 128-bit numerical sequence) is currently being developed. Synonyms Internet address, IP number. IPC - Abbreviation for information processing center. A facility staffed and equipped for processing and distributing information. Note: An IPC may be geographically distributed. IP Datagram - The fundamental unit of information passed across any network utilizing Internet protocol. Note: An IP datagram contains source and destination addresses along with data and a number of fields that define such things as the length of the datagram, the header checksum, and flags that indicate whether the datagram can be (or has been) fragmented. IP Dialup Access - Nonpermanent access, by means of a switched network (e.g., the public switched telephone network), to any network utilizing The Internet Protocol, especially The Internet. Note: Two well- known protocols for dialup access are PPP (point-to-point) and SLIP (serial line internet protocol). IP Multicast - A technique that allows packets to be simultaneously transmitted over the Mbone (multicast backbone on The Internet) to a selected set of destinations. Note: Standard Internet traffic requires a separate set of packets for each destination. IP multicast allows for one set of packets to be sent to multiple destinations. IPng - Abbreviation for IP next generation, IP version 6. IP number - Synonym IP address. A device's or resource's numerical address as expressed in the format specified in the Internet Protocol. Note 1: In the current addressing format, IP version 4 (IPv4), an IP address is a 32-bit sequence divided into four groups of decimal numbers separated by periods ("dots"), commonly referred to as "dotted decimals." The IP address of a device is made up of two parts: the number of the network to which it is connected, and a sequence representing the specific device within that network. An IP address may be used on private intranets, as well as The Internet. Note 2: Due to inefficiencies that have arisen in address assignment, available IPv4 addresses are nearly exhausted. A newer version of IP addressing (IP version 6, consisting of a 128-bit numerical sequence) is currently being developed. IPP - Abbreviation for Internet presence provider. An organization or commercial enterprise that provides storage space for the Web resources of an individual or other entity and enables those resources to be accessed by Internet users. Note: An IPP may not offer basic Internet connections as an ISP usually does. IP Spoofing - 1. A technique used by hackers to access computer systems by modifying packet headers to make them appear to have originated from a trusted port. 2. The practice of falsifying an e-mail header to make it appear as though it originated from a different address. IP Switching - A method of routing developed to use asynchronous transfer mode (ATM) hardware to route packets through networks more rapidly. IPTF - Abbreviation for Infrastructure Protection Task Force. Preemptive or reactive risk-management techniques designed to prevent disruption of a system after its critical infrastructure is attacked. IPX - Abbreviation for Internetwork Packet Exchange. A proprietary (LAN) protocol. 249
- 250. IR - Abbreviation for infrared. The region of the electromagnetic spectrum bounded by the long-wavelength extreme of the visible spectrum (approximately 0.7 m) and the shortest microwaves (approximately 0.1 mm). IRC - See Internet Relay Chat. - A popular program that allows users all around the world to communicate live, or chat, with other users. A service for conducting a chat on the Internet, i.e., an application that allows a number of individual users to exchange text messages simultaneously in real time over The Internet. Irradiance - Radiant power incident per unit area upon a surface. Note: Irradiance is usually expressed in watts per square meter, but may also be expressed in joules per square meter. Deprecated synonym power density. Irradiation - The product of irradiance and time, i.e., the time integral of irradiance. Note: For example, an 2 2 irradiation of 100 J/m (joules per square meter) is obtained when an irradiance of 25 W/m (watts per square meter) is continuously incident for 4 seconds. Irreversible Encryption - Encryption that produces ciphertext from which the original data cannot be reproduced. Note: Irreversible encryption is useful in authentication. For example, a password might be irreversibly encrypted and the resulting ciphertext stored. A password presented later would be irreversibly encrypted identically and the two strings of ciphertext compared. If they are identical, the presented password is correct. Synonyms irreversible encipherment, one-way encryption. IRTF - Abbreviation for Internet Research Task Force. A task force of the Internet Architecture Board (IAB), and which is responsible for research and development of the Internet protocol suite. ISB - Abbreviation for independent sideband. See independent-sideband transmission. Double-sideband transmission in which the information carried by each sideband is different. Note: The carrier may be suppressed. ISDN - See Integrated Services Digital Network - ISBDN usually refers to Broadband Integrated Services Digital Network or B-ISDN. The main aspect of BISDN that has been developed and published as a standard is the use of ATM multiplexing and routing for high bit-rate data services; BISDN refers to use of ATM. BISDN appears to have very little relationship to ordinary (circuit-switched 64 kb/s channel) ISDN systems, although there are some so-called "broadband" or "wideband" ISDN circuit switched services such as 384 kbit/s (sometimes called a "six-pack" because it uses six channels of 64 kb/s each). An integrated digital network in which the same time-division switches and digital transmission paths are used to establish connections for different services. Note 1: ISDN services include telephone, data, electronic mail, and facsimile. Note 2: The method used to accomplish a connection is often specified: for example, switched connection, nonswitched connection, exchange connection, ISDN connection. ISDN User Part (ISUP) - The functional part of the Signaling System No. 7 (SS7) protocol, i.e., the part that specifies the interexchange signaling procedures for the set up and tear down of trunk calls between networks. The ISDN User Part is one of the specified users of the Message Transfer Part (MTP) transport capability of the SS7 interconnections. The user part identification is encoded in the service indicator (SI) portion of the service information octet (SIO). ISM - Abbreviation for industrial, scientific, and medical applications (of radio frequency energy). ISMAP - A Web page feature in which hyperlinks are assigned or "mapped" to different portions of a graphic image. Note: Users access links by using a mouse to click on mapped areas. ISMAP requests are processed by common gateway interface (CGI) scripts on the server. 250
- 251. ISO - Abbreviation for International Organization for Standardization. An international organization that (a) consists of member bodies that are the national standards bodies of most of the countries of the world, (b) is responsible for the development and publication of international standards in various technical fields, after developing a suitable consensus, (c) is affiliated with the United Nations, and (d) has its headquarters at 1, rue de Varembé, Geneva, Switzerland. Note: Member bodies of ISO include, among others, the American National Standards Institute (ANSI), the Association Française de Normalisation (AFNOR), the British Standards Institution (BSI), and the Deutsche Institut für Normung (DIN). ISOC - Abbreviation for Internet Society. A nongovernmental, international organization for global cooperation and coordination for The Internet and its internetworking technologies and applications. Isochrone - A line on a map or chart joining points associated with a constant time difference from the transmitter to receiver of electromagnetic waves, such as radio waves, at all points along the line. Isochronous - 1. Of a periodic signal, pertaining to transmission in which the time interval separating any two corresponding transitions is equal to the unit interval or to a multiple of the unit interval. 2. Pertaining to data transmission in which corresponding significant instants of two or more sequential signals have a constant phase relationship. Note: "Isochronous" and "anisochronous" are characteristics, while "synchronous" and "asynchronous" are relationships. Isochronous Burst Transmission - In a data network where the information-bearer channel rate is higher than the input data signaling rate, transmission performed by interrupting, at controlled intervals, the data stream being transmitted. Note 1: Isochronous burst transmission enables communication between data terminal equipment (DTE) and data networks that operate at dissimilar data signaling rates, such as when the information-bearer channel rate is higher than the DTE output data signaling rate. Note 2: The binary digits are transferred at the information-bearer channel rate. The transfer is interrupted at intervals in order to produce the required average data signaling rate. Note 3: The interruption is always for an integral number of unit intervals. Note 4: Isochronous burst transmission has particular application where envelopes are being transferred between data circuit-terminating equipment (DCE) and only the bytes contained within the envelopes are being transferred between the DCE and the DTE. Synonyms burst isochronous (deprecated), interrupted isochronous transmission. Isochronous Demodulation - Demodulation in which the time interval separating any two significant instants is equal to the unit interval or a multiple of the unit interval. Isochronous Distortion - The difference between the measured modulation rate and the theoretical modulation rate in a digital system. Isochronous Modulation - Modulation in which the time interval separating any two significant instants is equal to the unit interval or a multiple of the unit interval. Isochronous Signal - A signal in which the time interval separating any two significant instants is equal to the unit interval or a multiple of the unit interval. Note 1: Variations in the time intervals are constrained within specified limits. Note 2: "Isochronous" is a characteristic, while "synchronous" indicates a relationship. Isolate - To restrict communication in both directions with a participant of the conference. Isolated Bonding Network - Synonym isolated ground plane. A set of interconnected frames that is intentionally grounded via only one connection to a ground reference; this plane, taken as a conductive unit with all of its metallic surfaces and grounding (earthing) wires bonded together, is insulated from contact with any other grounded metalwork in the building. 251
- 252. Isolated Ground Plane - A set of interconnected frames that is intentionally grounded via only one connection to a ground reference; this plane, taken as a conductive unit with all of its metallic surfaces and grounding (earthing) wires bonded together, is insulated from contact with any other grounded metalwork in the building. Synonym isolated bonding network. Isolated NRZ Pulse - A single bit period of logical value "1" with adjacent bit periods of logical value "0". Isolated Pulse - A pulse free from the effects of the other pulses in the same signal. (A suitable testing signal is a repetitive pattern of one "one" and seven "zeros".) Isolated RZ Pulse - Any bit period of logical value "1." Isolator - See optical isolator. A device that uses a short optical transmission path to accomplish electrical isolation between elements of a circuit. Note 1: The optical path may be air or a dielectric waveguide. Note 2: The transmitting and receiving elements of an optical isolator may be contained within a single compact module, for mounting, e.g., on a circuit board. Isotropic - 1. Pertaining to a material with properties, such as density, electrical conductivity, electric permittivity, magnetic permeability, or refractive index that do not vary with distance or direction. 2. Pertaining to a material with magnetic, electrical, or electromagnetic properties that do not vary with the direction of static or propagating magnetic, electrical, or electromagnetic fields within the material. Isotropic Antenna - A hypothetical antenna that radiates or receives equally in all directions. Note: Isotropic antennas do not exist physically but represent convenient reference antennas for expressing directional properties of physical antennas. Isotropic Gain - Synonym absolute gain. 1. Of an antenna, for a given direction and polarization, the ratio of (a) the power that would be required at the input of an ideal isotropic radiator to (b) the power actually supplied to the given antenna, to produce the same radiation intensity in the far-field region. Note 1: If no direction is given, the absolute gain of an antenna corresponds to the direction of maximum effective radiated power. Note 2: Absolute gain is usually expressed in dB. 2. Of a device, the ratio of (a) the signal level at the output of the device to (b) that of its input under a specified set of operating conditions. Note 1: Examples of absolute gain are no-load gain, full-load gain, and small-signal gain. Note 2: Absolute gain is usually expressed in dB. ISP - Abbreviation for Internet Service Provider. A company that provides connection to the Internet to companies or individuals via dial-up, ISDN, T1, or other connection. I2 - Abbreviation for Internet second generation. A proposed high-speed Internet for use exclusively by government researchers and academic institutions. IT - Abbreviation for information technology. The branch of technology devoted to (a) the study and application of data and the processing thereof; i.e., the automatic acquisition, storage, manipulation (including transformation), management, movement, control, display, switching, interchange, transmission or reception of data, and (b) the development and use of the hardware, software, firmware, and procedures associated with this processing. Iterative Impedance - In electrical circuits, for a four-terminal network, the impedance that, if connected across one pair of terminals, will match the impedance across the other pair of terminals. Note: The iterative impedance of a uniform line is the same as its characteristic impedance. 252
- 253. ITU - Abbreviation for International Telecommunication Union. A civil international organization established to promote standardized telecommunications on a worldwide basis. Note: The ITU-R and ITU-T are committees under the ITU. The ITU headquarters is located in Geneva, Switzerland. While older than the United Nations, it is recognized by the U.N. as the specialized agency for telecommunications. ITU-R - The Radiocommunications Sector of the ITU; responsible for studying technical issues related to radiocommunications, and having some regulatory powers. Note: A predecessor organization was the CCIR. ITU-T - Abbreviation for International Telecommunication Union--Telecommunication Standardization Sector. The Telecommunication Standardization Sector of the International Telecommunication Union (ITU). Note 1: ITU-T is responsible for studying technical, operating, and tariff Questions and issuing Recommendations on them, with the goal of standardizing telecommunications worldwide. Note 2: In principle, the ITU-T combines the standards-setting activities of the predecessor organizations formerly called the International Telegraph and Telephone Consultative Committee (CCITT) and the International Radio Consultative Committee (CCIR). IVDT - Abbreviation for integrated voice data terminal. See integrated station. IXC - Abbreviation for interexchange carrier. 1. A communications common carrier authorized to provide interexchange telecommunications services within world zone 1 using the North American numbering plan. 2. A telecommunications common carrier authorized to provide telecommunications services between LATAs. Note: The term "interexchange carrier" is also used to refer to any other entity that connects to the exchange access network at a point of termination (POT). 3. A carrier that provides connections between LATAs, where the calling or called customer is located in the United States. Note: This definition has no Canadian equivalent. However, the term "interexchange carrier" is used in the context of a carrier that provides connections extending across borders to carriers in the United States. J Jabber - In local area networks, transmission by a data station beyond the time interval allowed by the protocol. Jack - 1. A female fitting or connector that accepts a male mating component ("plug") to facilitate an electrical connection. Note: The term jack is frequently applied in applications involving communications signals, while the term receptacle is almost universally reserved for applications involving the distribution of electric power. 2. An analogous fitting or connector used to facilitate an optical fiber connection. See RJ-11 , RJ-14. and modular connector. Jacket - Synonym sheath. Of a communications or power cable, the outer covering or coverings of tough material, often plastic, that is resistant to environmental hazards such as abrasion, liquid intrusion, solar radiation, etc., and is used to protect cable component (s) such as optical fibers or metallic conductors that transport the signal or power. Note: There may be more than one sheath surrounding a given cable. For example, some cable designs use an inner sheath surrounded by metallic armor, over which is an outer sheath. Jamming - The deliberate radiation, reradiation, or reflection of electromagnetic energy for the purpose of disrupting enemy use of electronic devices, equipment, or systems. Jamming Margin - The level of interference (jamming) that a system is able to accept and still maintain a specified level of performance, such as maintain a specified bit-error ratio even though the signal-to-noise ratio is decreasing. 253
- 254. Jamming to Signal Ratio (J/S) - The ratio, usually expressed in dB, of the power of a jamming signal to that of a desired signal at a given point such as the antenna terminals of a receiver. Jam Signal - A signal that carries a bit pattern sent by a data station to inform the other stations that they must not transmit. Note 1: In carrier-sense multiple access with collision detection (CSMA/CD) networks, the jam signal indicates that a collision has occurred. Note 2: In carrier-sense multiple access with collision avoidance (CSMA/CA) networks, the jam signal indicates that the sending station intends to transmit. Note 3: "Jam signal" should not be confused with " electronic jamming." TM Java - A trademarked set of programming language technologies for creating and safely running software programs in both stand-alone and networked environments. Most graphics-based Web browsers can recognize and run Java codes. Java Applet - A small application-program component that typically executes in a client's Web browser, but can execute in a variety of other simple applications or devices; Java applets support the applet programming model and may be downloaded through the Internet via a Web site and run directly on a remote computer; Java applets are often used to create Web page effects. JavaBean - A portable, platform-independent, reusable component model that conforms to specification defining how Java objects interact. TM Java Database Connectivity (JDBC ) - An industry standard for database-independent connectivity between a computer platform or device operating in the JavaTM environment and a wide range of databases; the JDBC TM provides a call-level API (application program interface) for SQL-based (structured-query-language based) database access. JDBC - Abbreviation for Java database connectivity. Jerkiness - In a video display, the perception, by human vision faculties, of originally continuous motion as a sequence of distinct "snapshots." Note 1: The perception of continuous motion by human vision faculties is a manifestation of complex functions, i.e., characteristics, of the eyes and brain. When presented with a sequence of fixed, i.e., still, images of sufficient continuity and at a sufficiently frequent update rate, the brain interpolates intermediate images, and the observer subjectively appears to see continuous motion that in reality does not exist. Note 2: For example, the update rate of NTSC television displays is 30 frames (60 fields) per second. jfif or .jfif - A file-name extension that identifies an image file compressed with the Joint Photographic Experts Group (JPEG) format. TM Jini - A set of Java application program interfaces (APIs) to enable transparent networking of devices and services, thus eliminating the need for system or network administration intervention by a user. Jitter - 1. Abrupt and unwanted variations of one or more signal characteristics, such as the interval between successive pulses, the amplitude of successive cycles, or the frequency or phase of successive cycles. Note 1: Jitter must be specified in qualitative terms (e.g., amplitude, phase, pulse width or pulse position) and in quantitative terms (e.g., average, RMS, or peak-to-peak). Note 2: The low-frequency cutoff for jitter is usually specified at 1 Hz. 2. Random variability of data pass-through time. See timing jitter. Job - In computing, a unit of work that is defined by a user and that is to be accomplished by a computer. Note: A job is identified by a label and usually includes a set of computer programs, files, and control statements to the computer operating system. 254
- 255. Job-Recovery Control File - Synonym backup file. A copy of a file made for purposes of later reconstruction of the file, if necessary. Note: A backup file may be used for preserving the integrity of the original file and may be recorded on any suitable medium. Johnson Noise - Synonym thermal noise. The noise generated by thermal agitation of electrons in a conductor. The noise power, P, in watts, is given by P = kT f, where k is Boltzmann's constant in joules per kelvin, T is the conductor temperature in kelvins, and f is the bandwidth in hertz. Note 1: Thermal noise power, per hertz, is equal throughout the frequency spectrum, depending only on k and T. Note 2: For the general case, the above definition may be held to apply to charge carriers in any type of conducting medium. Joint - For optical fibers, a splice or connector. Joint Multichannel Trunking and Switching System - That composite multichannel trunking and switching system formed from assets of the Services, the Defense Communications System, other available systems, and/or assets controlled by the Joint Chiefs of Staff to provide an operationally responsive, survivable communication system, preferably in a mobile/transportable/recoverable configuration, for the joint force commander in an area of operations. Joint Random Buried Plant - Telecommunications outside plant that is directly buried in the same trench with power conductors, with no restriction regarding minimum separation between the two systems. Joint Telecommunications Resources Board (JTRB) - The body required to be established by Section 2(b) (3) of Executive Order No. 12472 to assist the Director of the Office of Science and Technology Policy in the exercise of assigned nonwartime emergency telecommunications functions. Joint Use Aerial Plant - Aerial telecommunications and power plant utilizing the same structure, such as poles. Journal - 1. A chronological record of data processing operations that may be used to reconstruct a previous or an updated version of a file. Synonym log. 2. In database management systems, the record of all stored data items that have values changed as a result of processing and manipulation of the data. Joy Stick - In computer graphics, a lever (with at least two degrees of freedom) that is used as an input unit, normally as a locator. J-PEG [ or JPEG] - Abbreviation for Joint Photographic Experts Group. 1. A standardized, if relatively lossy, file format for transporting, storing, and/or displaying data representing still images and graphical data. Note: Along with .gif, it is one of the most common ways that photos are moved over the Web. 2. Images compressed with the JPEG format and identified with the .jpg or .jpeg file-name extension. 3. An international standards group functioning under ISO and IEC developing an international consensus on an image compression algorithm for continuous-tone still color pictures. Judder - A temporal artifact associated with moving images, which artifact occurs when the image is sampled at one frame rate and converted to a different frame rate for display; as a result, motion vectors in the display may appear to represent continuously varying velocities. Note: The subjective effect of the artifact becomes more obvious when the frame-rate conversion is made by simple deletions or repetitions of selected frames (or fields). It may become less obvious when interpolated frames (or fields) are generated by using predictive algorithms. Julian Date - 1. The sequential day count reckoned consecutively beginning January 1, 4713 B.C. Note: The Julian date on January 1, 1990, was 2,446,892. 2. The sequential day count of the days of a year, reckoned 255
- 256. consecutively from the first day of January. Note: In modern times, the definition of Julian date has been corrupted to use the first day of the year as the point of reference. To avoid ambiguity with the traditional meaning, "day of year" rather than "Julian date" should be used for this purpose. Jumper - Synonym cross-connection. Connections between terminal blocks on the two sides of a distribution frame, or between terminals on a terminal block. Note: Connections between terminals on the same block are also called straps. Junction Point - Synonym node. 1. In network topology, a terminal of any branch of a network or an interconnection common to two or more branches of a network. Synonyms junction point, nodal point. 2. In a switched network, one of the switches forming the network backbone. Note: A node may also include patching and control facilities. 3. A technical control facility (TCF). 4. A point in a standing or stationary wave at which the amplitude is a minimum. In this sense, synonym null. Jurisdiction - 1. In telecommunications, the functional separation of telecommunications networks. A jurisdiction is one of the following four types: (a) local exchange carrier network; (b) interexchange carrier network; (c) end user network; (d) some combination of the above. 2. Loosely, and in a more general sense, the regulatory authority of the Federal Communications Commission as specified in the Communications Act of 1934, supplements thereto, and numerous court decisions; and the regulatory authority of state regulatory commissions as specified in the laws established by each state. Justification - The process of changing the digit rate of a digital signal in a controlled manner so that it is in accord with a digit rate different from its own inherent rate, usually without loss of information. Synonyms [loosely] bit stuffing, de-stuffing, justify. Justify - 1. To shift the contents of a register or a field so that the significant character at the specified end of the data is at a particular position. 2. To align text horizontally or vertically so that the first and last characters of every line, or the first and last line of the text, are aligned with their corresponding margins. Note 1: In English, text may be justified left, right, or both. Left justification is the most common. Note 2: The last line of a paragraph is usually only left justified. 3. To align data on a designated character position. K 3 k - Abbreviation for kilo (SI prefix for 10 ). See International System of Units. K - 1. Abbreviation for kelvin (s). See thermodynamic temperature. 2. When referring to data storage 10 capacity, 2 , or 1024 in decimal notation; however this usage of an upper case K is deprecated. Kalman Filter - A computational algorithm that processes measurements to deduce an optimum estimate of the past, present, or future state of a linear system by using a time sequence of measurements of the system behavior, plus a statistical model that characterizes the system and measurement errors, plus initial condition information. KA9Q - A popular implementation of TCP/IP and associated protocols for amateur packet radio systems. Kbps - Kilobytes per second. A kilobyte equals a thousand bytes. KDC - Abbreviation for key distribution center. [A] COMSEC facility generating and distributing key in electrical form. Kelvin (K) - A unit of thermodynamic temperature, taken as one of the base units of the International System 256
- 257. of Units (SI). The kelvin is defined by setting the thermodynamic temperature of the triple point of water at 273.16 K. Note 1: The kelvin was formerly called "degree Kelvin." The term "degree Kelvin" is now obsolete. No degree symbol is written with K, the symbol for kelvin(s). Note 2: In measuring temperature intervals, the degree Celsius is equal to the kelvin. The Celsius temperature scale is defined by setting 0 °C equal to 273.16 K Kelvin Temperature Scale - See thermodynamic temperature. See Kelvin (K). Kendall Effect - A spurious pattern or other distortion in a facsimile record copy caused by unwanted modulation products arising from the transmission of a carrier signal, and appearing in the form of a rectified baseband that interferes with the lower sideband of the carrier. Note: The Kendall effect occurs principally when the single-sideband width is greater than half of the facsimile carrier frequency. Kermit - An early generation protocol [a file-transfer and terminal-emulation program] developed for transfer of asynchronous data files, designed to help minimize the effects of interference and noise on analog telephone circuits. Kernel - A module of a program that forms a logical entity or performs a unit function. Note: The most vulnerable portion of code in a secure operating system is a special case of a kernel. Kerr Electro-Optic Effect - The creation of birefringence in a liquid that is not otherwise birefringent, by subjecting the liquid to an electric field. Note 1: The degree of birefringence, which is manifested as a difference in refractive indices for light of orthogonal linear polarizations, one of which is parallel to the induced optical axis, is directly proportional to the square of the applied electric field strength. Note 2: In the general case, the birefringence produced by the applied electric field can be used in conjunction with polarizers to modulate light. Devices that use this principle are called Kerr cells. Key - 1. Information (usually a sequence of random or pseudorandom binary digits) used initially to set up and periodically change the operations performed in crypto-equipment for the purpose of encrypting or decrypting electronic signals, for determining electronic counter-countermeasures patterns (e.g., frequency hopping or spread spectrum), or for producing other key. Note: "Key" has replaced the terms "variable," "key(ing) variable," and "cryptovariable." 2. Usually a sequence of random or pseudorandom bits used initially to set up and periodically change the operations performed in crypto-equipment for the purpose of encrypting or decrypting electronic signals, or for determining electronic counter-countermeasures patterns(e.g., frequency hopping or spread spectrum), or for producing other key. Key Agreement - 1. A key establishment protocol whose secret key is a function of information contributed by two or more participants, so that no party can predetermine the value of the key. 2. A method for negotiating a key value on-line without transferring the key, even in an encrypted form, e.g., the Diffie- Hellman technique. Key Authentication - The assurance of the legitimate participants in a key agreement that no other entity possesses the shared-secret key. Key-Auto-Key - Cryptographic logic using previous key to produce key. Keyboard - An input device used to enter data by manual depression of keys, which causes the generation of the selected code element. Keyboard Punch - Synonym keypunch. Historically, a keyboard-actuated punch that punches holes in a data medium. 257
- 258. Keyboard Recorder - A hidden program in a computer that stores user-typed input or other input and sends this data to the originator. Keyboard recorders are used for stealing user identifications, passwords, and other sensitive information. Key Bundle - An assemblage of two keys that are considered logically to be one key, in that one key alone cannot be manipulated. Key Component - One of two or more parameters that have the format of a cryptographic key that is added modulo-1 with one or more like parameters to form a cryptographic key. Key Confirmation - The assurance of the rightful participants in a key-establishment protocol that the intended recipient (s) of the shared key actually possess the shared key. Key Distribution Center (KDC) - [A] COMSEC facility generating and distributing key in electrical form. Key Encrypting Key - 1. A key that is used exclusively for encrypting and decrypting keys. 2. Key that encrypts or decrypts other key for transmission or storage. Key Encrypting Key Pair - In public-key cryptography, two key encrypting keys used together to encrypt other keys. Key Establishment - 1. A protocol that reveals a secret key to its legitimate participants for cryptographic use. 2. The procedure to share a common secret key among different parties by either key agreement or key transport. Key Generation Center - A facility within a group, which facility performs the function of generating keys for any specific key exchange transaction. Key Generator - A device, including associated alarms and self-tests, for generating cryptographic keys (and where needed, initialization vectors). Key Granularity - The number of individuals represented by a key, e.g., the finest granularity is one individual represented by one key; a coarser granularity is a node key. Keying - 1. The generating of signals by the interruption or modulation of a steady signal or carrier. 2. See chroma keying. Keying Material - 1. In encryption, the data (e.g., keys, certificates, and initialization vectors) necessary to establish and maintain cryptographic keying relationships. 2. [A] key, code, or authentication information in physical or magnetic form. Keying Relationship - The state existing between two parties such that they share at least one cryptographic key. Keying Variable - Deprecated synonym for key. Key Integrity - The assurance that a key (a) is always used in the proper order and key space, and (b) has not been altered. Key List - Printed sets of key settings for a specific cryptonet. Keylists may be produced in list, pad, or printed tape format. 258
- 259. Key Loader - An electronic, self-contained unit which is capable of storing at least one key and transferring that key, upon request, into cryptographic modules. Key Management - Supervision and control of the process whereby key is generated, stored, protected, transferred, loaded, used, and destroyed. Key Management Facility - The physically protected enclosure (e.g., room or device) and its contents where cryptographic elements (i.e., cryptographic hardware, software, firmware, keys, or initialization vectors) reside. Key Offset - 1. The process of applying a count value to a cryptographic key using the Boolean exclusive-OR function. 2. The count so added. Key Pair - 1. In public-key cryptography, a public key and its corresponding private key. 2. Two key- encrypting keys that are used in concert to encrypt other keys. Key Pair Updating - The recertification or replacement of a certificate authority's public/ private key pair. Key Production Key - Key used to initialize a keystream generator for the production of other electronically generated key. Key-Pulse Signal - The first signal in an MF (multifrequency) outpulsing format; a control signal used to prepare the customer installation (CI) to receive digits. Key Pulsing - A system of sending telephone calling signals in which the digits are transmitted by operation of a pushbutton key set. Note: The type of key pulsing commonly used by users and PBX operators is dual- tone multifrequency signaling. Each pushbutton causes generation of a unique pair of tones. In military systems, pushbuttons are also provided for additional signals, such as precedence. Synonym pulsing. Keypunch - Historically, a keyboard-actuated punch that punches holes in a data medium. Synonym keyboard punch. Key Security - In cryptology, the protection of keys against compromise. Key Service Message - A message used for transferring keys between subscribers. Key Set - A multiline or multifunction user terminal device. Key Set Identifier - A non-secret value that uniquely identifies a key set. Key Storage - In cryptology, storage of cryptographic keys in such a manner as (a) to protect them against unauthorized use, disclosure, or tampering, and (b) to erase them and re-initialize equipment upon tampering. Key Stream - [A] sequence of symbols (or their electrical or mechanical equivalents) produced in a machine or auto-manual cryptosystem to combine with plain text to produce cipher text, control transmission security processes, or produce key. Keystroke Verification - With respect to data entry via a keyboard, determination of the accuracy of data entry by the re-entry of the same data through the same (or another) keyboard. 259
- 260. Key System Unit – The controller that manages a multi-line Key telephone system. All incoming telephone lines and all telephone sets connect to the KSU. The KSU is usually mounted in a back room or telephone closet of the office it serves. Key Tag - Identification information associated with certain types of electronic key. Key Tape - Punched or magnetic tape containing key. Printed key in tape form is referred to as a key list. Key Telephone System (KTS) A multi-line telephone system with extension telephone sets. A Key system always has a Key System Unit (KSU) controller that all telephone sets attach to. Also, the Key system telephone sets have a series of buttons that are used to select the outside line you wish to use. In a local environment, terminals and equipment that provide immediate access from all terminals to a variety of telephone services without attendant assistance. Note: A KTS may interface with the public switched telephone network. Key Transport - The means by which a cryptographic key is passed from its origination point to its point(s) of actual use, whether by bonded courier, registered mail, over-the-air-rekeying (OTAR), or a number of other protected methods. Note: As a result of key transport, all rightful participants share a common secret key in such a way that the secret key is determined entirely by one party. Key Type - A characteristic of a key that distinguishes it as either a key-encrypting key or a data key. Key Updating - Irreversible cryptographic process for modifying key. Key Usage Vector - An identifier that specifies cryptographic services, modes, and key values in which the associated key may be used. Key Validation - In public key infrastructure (PKI) systems, the procedure allowing the receiver of a public key to verify that it conforms with the requirements for such a key; this procedure is used to counter certain types of attacks against the security of the PKI system. Synonym public key validation. Key Variable - Deprecated synonym for key. K-Factor - 1. In tropospheric radio propagation, the ratio of the effective Earth radius to the actual Earth radius. Note: The k-factor is approximately 4/3. 2. In ionospheric radio propagation, a correction factor that (a) is applied in calculations related to curved layers, and (b) is a function of distance and the real height of ionospheric reflection. 3 kHz - Abbreviation for kilohertz. A unit of frequency denoting one thousand (10 ) Hz. Killer App - Slang contraction of killer application. A successful and popular software application (often written by a third party), that is generally perceived to be superior in function or that employs the latest and most impressive techniques. 3 kilohertz (kHz) - A unit of frequency denoting one thousand (10 ) Hz. Kilometer - A unit of distance corresponding to 1000m. km - Abbreviation for kilometer. 260
- 261. Knee - In video, by convention, the circuitry introducing white compression into the opto-electronic transfer function and thereby modifying the curve for a more gradual approach to white clip. Knife-Edge Effect - In electromagnetic wave propagation, a redirection by diffraction of a portion of the incident radiation that strikes a well-defined obstacle such as a mountain range or the edge of a building. Note: The knife-edge effect is explained by Huygens' principle, which states that a well-defined obstruction to an electromagnetic wave acts as a secondary source, and creates a new wavefront. This new wavefront propagates into the geometric shadow area of the obstacle. Knowbot - Contraction of knowledge robot. A search tool that automatically seeks relevant online information based on the user's previously identified specifications. Synonyms droid, intelligent agent, personal agent, hotbot. Knowledge Robot - A component of a search engine that collects information from Internet resources. Synonyms droid, infobot, robotic librarian, search robot. Known-Plain-Text Attack - An analytical attack in which a cryptanalyst possesses a substantial quantity of corresponding plain text and cipher text. KSU (Key System Unit) – The controller that manages a multi-line Key telephone system. All incoming telephone lines and all telephone sets connect to the KSU. The KSU is usually mounted in a back room or telephone closet of the office it serves. kT - See noise power density. noise power density: The noise power in a bandwidth of 1 Hz, i.e., the noise power per hertz at a point in a noise spectrum. Note: The noise-power density of the internal noise that is contributed by a receiving system to an incoming signal is expressed as the product of Boltzmann's constant, k, and the equivalent noise temperature, T n. Thus, the noise-power density is often expressed simply as kT. KTS - Abbreviation for key telephone system. K-Type Patch Bay - A patching facility designed for patching and monitoring of balanced digital data circuits that support data rates up to 1 Mb/s. L Label - 1. An identifier within or attached to a set of data elements. 2. One or more characters that (a) are within or attached to a set of data elements and (b) represent information about the set, including its identification. 3. In communications, information within a message that is used to identify specific system parameters, such as the particular circuit with which the message is associated. Note: Messages that do not relate to call control should not contain a label. 4. In programming languages, an identifier that names a statement. 5. An identifier that indicates the sensitivity of the attached information. 6. For classified information, an identifier that indicates (a) the security level of the attached information or (b) the specific category in which the attached information belongs. 7. A field within a signaling message that contains information used to identify the circuit, call, or management transaction to which the message is related. Label Bureau - A computer or server that supplies content labels or Web-site ratings. Synonym rating server. Labeled Channel - In integrated services digital networks, (ISDN), a time-ordered set of all block payloads that have labels containing the same information, i.e., containing the same identifiers. 261
- 262. Labeled Interface Structure - In integrated services digital networks (ISDN), an interface structure that provides telecommunications services and signaling by means of labeled channels. Labeled Multiplexing - In integrated services digital networks (ISDN), multiplexing by concatenation of the blocks of the channels that have different identifiers in their labels. Labeled Statistical Channel - In integrated services digital networks (ISDN), a labeled channel in which the block payloads or the duration of each successive block is random. Laboratory Attack - Use of sophisticated signal recovery equipment in a laboratory environment to recover information from data storage media. Lambertian Radiator - See Lambertian source. Lambertian Reflector - See Lambertian source. Lambertian Source - An optical source that obeys Lambert's cosine law, i.e., that has an intensity directly proportional to the cosine of the angle from which it is viewed. Note: Conventional (surface-emitting) LEDs are approximately Lambertian. They have a large beam divergence. This results in a radiation pattern that resembles a sphere. Thus, most of their total optical output is not coupled into communication fibers. Lambert's Cosine Law - See Lambertian source. Lambert's Emission Law - Synonym Lambertian source. LAN - Local Area Network. A data communications network that lies within a limited space (such as a building) to connect telephone lines, computers, modems, printers, etc. LAN Application (software) - An application software package specifically designed to operate in a local- area-network environment. Land Line - An informal name for conventional telephone facilities. Note: Land lines include conventional twisted-pair lines, carrier facilities, and microwave radio facilities for supporting a conventional telephone channel, but do not include satellite links or mobile telephone links using radio transmissions. Land Mobile-Satellite Service - A mobile-satellite service in which mobile Earth stations are located on land. Land Mobile Service - A mobile service between base stations and land mobile stations, or between land mobile stations. Land Mobile Station - A mobile station in the land mobile service capable of surface movement within the geographical limits of a country or continent. Landscape Mode - 1. In facsimile, the mode for scanning lines across the longer dimension of a rectangular object, i.e., rectangular original. 2. In computer graphics, the orientation of an image in which the longer dimension is horizontal. 3. An orientation of printed text on a page such that the lines of text are parallel to the long dimension of the page. Note: If the page contains an image, such as a picture, and the page is viewed in the normal manner, the long dimension of the page would be parallel to the line that joins the eyes of the viewer. Land Station - A station in the mobile service not intended to be used while in motion. 262
- 263. Language - A set of characters, conventions, and rules that is used for conveying information. Language Processor - A program that performs tasks, such as translating and interpreting, required for processing a specified programming language. Note: Examples of language processors include a Fortran processor and a COBOL processor. LAN Operating System - See network operating system. - Software that (a) controls a Local Area network and its message (e.g., packet) traffic, and queues, (b) controls access by multiple users to network resources such as files, and (c) provides for certain administrative functions, including security. LAP-B - The Data Link Layer protocol as specified by ITU-T Recommendation X.25 (1989). LAP-D - Abbreviation for link access procedure D. A link protocol used in ISDN. Large Prime Factors - Specially constructed large prime numbers, viz., p1, p2, q1, and q2, each > 2100, where p1 |p-1, p2 |p+1, q1|q-1, and q2 |q+1, where p and q are the private prime factors. Laser - Acronym for light amplification by stimulated emission of radiation. A device that produces a coherent beam of optical radiation by stimulating electronic, ionic, or molecular transitions to higher energy levels so that when they return to lower energy levels they emit energy. Note 1: Laser radiation may be either temporally coherent, spatially coherent, or both. Note 2: The degree of coherence of laser radiation exceeds 0.88. Laser Chirp - An abrupt change of the center wavelength of a laser, caused by laser instability. Laser Diode - Synonym injection laser diode. - A laser that uses a forward-biased semiconductor junction as the active medium. Note: Stimulated emission of coherent light occurs at a p-n junction where electrons and holes are driven into the junction. Laser Disk - See optical disk. - A storage medium from which data is read and to which it is written by lasers. Optical disks can store much more data -- up to 6 gigabytes (6 billion bytes) -- than most portable magnetic media, such as floppies. Laser Intelligence (LASINT) - Technical and geolocation intelligence derived from laser systems; a subcategory of electro-optical intelligence. Laser Medium - Synonym active laser medium. - Within a laser, the material that emits coherent radiation or exhibits gain as the result of electronic or molecular transitions to a lower energy state or states, from a higher energy state or states to which it had been previously stimulated. Note: Examples of active laser media include certain crystals, gases, glasses, liquids, and semiconductors. Lasing - See laser. Lasing Threshold - The lowest excitation level at which laser output is dominated by stimulated emission rather than by spontaneous emission. LASINT - Acronym for laser intelligence. Last-In First-Out (LIFO) - A queuing discipline in which entities in a queue leave in the reverse order of the sequence in which they arrive. Note: Service, when available, is offered to the entity that has been in the LIFO queue the shortest time. 263
- 264. Last Number Redial - Synonym automatic redial. - A service feature that allows the user to dial, by depressing a single key or a few keys, the most recent telephone number dialed at that instrument. Note: Automatic redial is often associated with the telephone instrument, but may be provided by a PBX, or by the central office. LATA - Acronym for local access and transport area. - Geographical boundaries within which local telephone companies may provide local telephone services (and some limited toll services). There are 184 LATAs in the United States. Latency - The time it takes for a packet to travel from its point of origin to its point of destination. In telephony, the lower the latency, the better the communication. Latency has always been an issue with telephone communication taking place over exceptionally long distances (the United States to Europe, for example). With VoIP, however, latency takes on a new form because of the splitting of the message into packets (see packet-switched) and network delay in general. Lateral Offset Loss - 1. In fiber optics, a loss of optical power at a splice or connector, caused by a lateral, i.e., transverse, offset of the mating fiber cores, which offset causes an imperfect transfer of the optical signal from the "transmitting" fiber to the "receiving" fiber. Note: The effect of a given amount of lateral offset will depend on other parameters such as the relative diameters of the respective cores. For example: if, because of manufacturing tolerances, the "transmitting" core is smaller than the "receiving" core, the effect will be less than if both cores were the same size. 2. An analogous loss of optical power caused by lateral misalignment of the fiber and optical source. Synonym transverse offset loss. Launch Angle - 1. The angle, with respect to the normal, at which a light ray emerges from a surface. 2. The beam divergence at an emitting surface, such as that of a light-emitting diode (LED), laser, lens, prism, or optical fiber end face. 3. At an end face of an optical fiber, the angle between an input ray and the fiber axis. Note: If the end face of the fiber is perpendicular to the fiber axis, the launch angle is equal to the incidence angle when the ray is external to the fiber and the refraction angle when initially inside the fiber. Launching Fiber - An optical fiber used in conjunction with a source to excite the modes of another fiber in a particular fashion. Note: Launching fibers are most often used in test systems to improve the precision of measurements. Synonym injection fiber. Launch Numerical Aperture (LNA) - The numerical aperture of an optical system used to couple (launch) power into an optical fiber. Note 1: LNA may differ from the stated NA of a final focusing element if, for example, that element is underfilled or the focus is other than that for which the element is specified. Note 2: LNA is one of the parameters that determine the initial distribution of power among the modes of an optical fiber. Layer - 1. In radio wave propagation, see F region. 2. In telecommunications networks and open systems architecture, a group of related functions that are performed in a given level in a hierarchy of groups of related functions. Note: In specifying the functions for a given layer, the assumption is made that the specified functions for the layers below are performed, except for the lowest layer. Layered Protocol - The protocol reference model defined by layered structures based on and using the terminology of ITU-T Recommendations X.200 and X.210. The protocols referred to in this American National Standard conform to the OSI Reference Model for ISDN specified in ITU-T Recommendation I.320. Layered System - A system in which components are grouped, i.e., layered, in a hierarchical arrangement, such that lower layers provide functions and services that support the functions and services of higher layers. Note: Systems of ever-increasing complexity and capability can be built by adding or changing the layers to improve overall system capability while using the components that are still in place. 264
- 265. Layer Entity - An active element within a layer. Layer Function - A part of the activity of the layer entities. Layer Interface - The boundary between two adjacent layers in the model. Layer Service - A capability of the (N) layer and the layers beneath it, which is provided to (N + 1) layer entities, at the boundary between the (N) layer and the (N + 1) layer. Layer Service Elements - An indivisible component of the layer service made visible to the service user via layer service primitives. Layer Service Primitives - A means for specifying in detail the adjacent layer interactions Layer User Data - Data transferred between corresponding entities on behalf of the upper layer or layer management entities for which they are providing services. Lay Length - In communications cables--including fiber-optic cables--having the transmission media wrapped helically around a central member, the longitudinal distance along the cable required for one complete helical wrap; i.e., the total cable length divided by the total number of wraps. Note 1: In many fiber-optic cable designs, the lay length is shorter than in metallic cables of similar diameter, to avoid overstressing the fibers during the pulling associated with the installation operation. Note 2: The wraps, i.e., turns, that are referred to should not be confused with the twists given twisted metallic pairs, i.e., wires, to reduce electromagnetic coupling. Pairs of optical fibers are not given such twists. Synonym pitch. LBO - Abbreviation for line buildout. Synonym building out. - The process of adding a combination of inductance, capacitance, and resistance to a cable pair so that its electrical length may be increased by a desired amount to control impedance and loss characteristics. LCD - Abbreviation for liquid crystal display. - A display device that creates characters by means of the action of electrical signals on a matrix of liquid cells that become opaque when energized. Note: A liquid crystal display may be designed to be viewed by reflected or transmitted light. LCD TV - Abbreviation for Liquid Crystal Display Television. LCD televisions are sets that use LCD technology to produce images. Benefits of LCD technology include lower weight and reduced power requirements when compared to other display types. Often, LCD television screens can also be used as computer monitors. LCN- Abbreviation for Local Communication Network - A communication network within a TMN (telecommunications management network) that supports data communication functions (DCFs) normally at [specified] reference points q1 and q2. LCNs range from the simple to the complex. LCN examples include point-to-point connections and networks based on star and bus topologies. LDAP - Abbreviation for lightweight directory access protocol. A simplified version of the X.500 standard, which version consists of a set of protocols developed for accessing information directories. LDM - Abbreviation for limited distance modem. Leaky Bucket Counter - A counter that is incremented by one each time an event occurs and is decremented by a fixed value periodically. 265
- 266. Leaky Mode - In an optical fiber, a mode having a field that decays monotonically for a finite distance in the transverse direction but becomes oscillatory everywhere beyond that finite distance. Note: Leaky modes correspond to leaky rays in the terminology of geometric optics. Leaky modes experience attenuation, even if the waveguide is perfect in every respect. Synonym tunneling mode. Leaky Ray - In an optical fiber, a ray for which geometric optics would predict total internal reflection at the boundary between the core and the cladding, but which suffers loss by virtue of the curved core boundary. Note: Leaky rays correspond to leaky (i.e., tunneling) modes in the terminology of mode descriptors. Synonym tunneling ray. Leap Second - An occasional adjustment of one second, added to, or subtracted from, Coordinated Universal Time (UTC) to bring it into approximate synchronism with UT1, which is the time scale based on the rotation of the Earth. Note 1: Adjustments, when required, are made with respect to the last second of the last minute of the day (Universal Time) on one of two annual days of opportunity (June 30 or December 31). Note 2: The last minute of the day on which an adjustment is made will therefore have 61 or 59 seconds. The former is the usual case, and the latter, a theoretical possibility if ever needed. Note 3: An adjustment is required on any day of opportunity when it is anticipated that if unadjusted, UTC will deviate from UT1 by more than 0.9 second before the next day of opportunity. Leased Circuit - Dedicated common-carrier facilities and channel equipment used by a network to furnish exclusive private line service to a specific user or group of users. Leased Line - A phone line dedicated for exclusive use from one location to another. High speed connections require a leased line. Least Privilege - The principle requiring that each subject be granted the most restrictive set of privileges needed for the performance of authorized tasks. Application of this principle limits the damage that can result from accident, error, or unauthorized use of an information system (IS). Least Significant Bit - In a binary code, the bit or bit position that is assigned to, or represents, the smallest quantity or increment that can be represented by the code. Least-Time Principle - Synonym Fermat's principle. A principle stating that a ray of light follows the path that requires the least time to travel from one point to another, including reflections and refractions that may occur. LEC - Abbreviation for local exchange carrier. - A local telephone company, i.e., a communications common carrier that provides ordinary local voice-grade telecommunications service under regulation within a specified service area. LED - Abbreviation for light-emitting diode. - A semiconductor device that emits incoherent optical radiation when biased in the forward direction. Left-Hand (anti-clockwise) Polarized Wave - An elliptically or circularly polarized wave, in which the electric field vector, observed in the fixed plane, normal to the direction of propagation, whilst looking in the direction of propagation, rotates with time in a left-hand or anticlockwise direction. Leg - 1. A segment of an end-to-end route or path, such as a path from user to user via several networks and nodes within networks. Note: Examples of legs are several sequential microwave links between two switching centers and a transoceanic cable between two shore communications facilities, each connected to a node in a national network. 2. A connection from a specific node to an addressable entity, such as 266
- 267. communication link from a computer workstation to a hub. 3. A loop termination of a multipoint circuit that links a bridge to the end user location. Length Indicator (LI) - A six-bit field that defines message length and that is used to differentiate between message signal units, link status signal units, and fill-in signal units. LEO - Abbreviation for low Earth orbit. A term used to describe the orbital altitude range (500 to 2000 km above the surface of the Earth) of certain communications satellites. Note 1: Generally, LEO satellites are part of constellations of satellites that achieve wide coverage of the Earth's surface with lower power requirements and shorter propagation delays than can be achieved with, e.g. Geostationary orbit satellites, or MEO satellites. Note 2: LEO satellites may have equatorial or polar paths. Note 3: Two LEO groups have emerged: Little LEO for data-communications satellites and Big LEO for data-and-voice communications, each using preassigned frequency ranges. Letterbox - Letterbox is the term used when 16:9 content is viewed on a 4:3 screen. In order to display the widescreen content without distortion or missing parts of the picture, the television will place black bars at the top and bottom of the image. Level - 1. The absolute or relative voltage, current, or power at a particular point in a circuit or system. 2. A tier or layer of a hierarchical system, e.g., the Link-Level protocol, high-level computer language. Level Alignment - The adjustment of transmission levels of single links and of links in tandem to prevent problems such as overloading of transmission subsystems. Level of Protection - The extent to which protective measures, techniques, and procedures must be applied to information systems (IS) and networks based on risk, threat, vulnerability, system interconnectivity considerations, and information assurance needs. Levels of protection are: 1. Basic: The IS and networks requiring implementation of standard minimum security countermeasures. 2. Medium: The IS and networks requiring layering of additional safeguards above the standard minimum security countermeasures. 3. High: The IS and networks requiring the most stringent protection and rigorous security countermeasures. LF - Abbreviation for low frequency. - Any frequency in the band from 30 kHz to 300 kHz. See electromagnetic spectrum. library - 1. An assembly of objects, routines, programs, etc., that may be drawn upon for use in the performance of functions. 2. Synonym forum. Lifeline/Link-Up Program - A Federal program designed to provide telephone service to the poor and elderly at a reduced cost to assure they can be reached in case of an emergency. LIFO: Acronym for last-in first-out. A queuing discipline in which entities in a queue leave in the reverse order of the sequence in which they arrive. Note: Service, when available, is offered to the entity that has been in the LIFO queue the shortest time. Light - In a strict sense, the region of the electromagnetic spectrum that can be perceived by human vision, i.e., the visible spectrum, which is approximately the wavelength range of 0.4 m to 0.7 m. Note 1: In the laser and optical communications fields, custom and practice have extended usage of the term light to include the much broader portion of the electromagnetic spectrum that can be handled by the basic optical techniques used for the visible spectrum. Note 2: The region embraced by the term light has not been clearly defined, but by convention and usage, is considered to extend from the near-ultraviolet region of 267
- 268. approximately 0.3 m, through the visible region, and into the mid-infrared region to approximately 30 m. Light-Emitting Diode (LED) - A semiconductor device that emits incoherent optical radiation when biased in the forward direction. Lightguide - See optical fiber. Lightness - The brightness of an area subjectively judged relative to the brightness of a similarly illuminated area that appears to be white or highly transmitting. Lightning Down-Conductor - In a lightning protection subsystem, the conductor connecting the air terminal or overhead ground wire to the earth electrode subsystem. Lightning Protection Subsystem - All of the components used to protect a facility from the effects of lightning. Note: The lightning protection subsystem includes air terminals, lightning down- conductors, the earth electrode subsystem, air gaps, arresters, and their interconnections. Light Pen - A stylus, usually hand-held, that contains a photodetector or light source, and that allows interaction with a computer through a specially designed monitor screen. Light Valve - Synonym optical switch. - A switch that enables signals in optical fibers or integrated optical circuits (IOCs) to be selectively switched from one circuit to another. Note 1: An optical switch may operate by (a) mechanical means such as physically shifting an optical fiber to drive one or more alternative fibers, or (b) electro-optic effects, magneto-optic effects, or other methods. Note 2: Slow optical switches, such as those using moving fibers, may be used for alternate routing of an optical transmission path, e.g., routing around a fault. Fast optical switches, such as those using electro-optic or magneto-optic effects, may be used to perform logic operations. Limited Protection - A form of short-term communications security applied to the electromagnetic or acoustic transmission of unclassified information that warrants a degree of protection against simple analysis and easy exploitation but that does not warrant protection to the extent needed for security of classified information. Limited-Protection Voice Equipment - Equipment that provides limited security for unclassified voice communications. Limiter - A device in which the voltage or some other characteristic of the output signal is automatically prevented from exceeding a specified value. Limiter Circuit - A circuit of nonlinear elements that restricts the electrical excursion of a variable in accordance with specified criteria. Limiting - Any process by which a specified characteristic (usually amplitude) of the output of a device is prevented from exceeding a predetermined value. Note 1: Hard limiting (" clipping ") is a limiting action in which there is (a) over the permitted dynamic range, negligible variation in the expected characteristic of the output signal, and (b) a steady-state signal, at the maximum permitted level, for the duration of each period when the output would otherwise be required to exceed the permitted dynamic range in order to correspond to the transfer function of the device. Note 2: Soft limiting is limiting in which the transfer function of a device is a function of its instantaneous or integrated output level. The output waveform is therefore distorted, but not clipped. 268
- 269. Limits of Interference - In radio transmission, the maximum permissible interference as specified in recommendations of the International Special Committee on Radio Interference or other recognized authority. Line - 1. A physical medium for transferring electrical or electromagnetic energy from one point to another for purposes of communications. 2. A land line. 3. A metallic medium used for the transmission of electrical power. 4. A transmission medium, together with the associated equipment, required to provide the means of transporting information between two consecutive network elements, one of which originates the line signal and the other terminates the line signal. 5. Synonym scanning line. Line Adapter Circuit - See four-wire terminating set. - A balanced transformer used to perform a conversion between 4-wire and 2-wire operation. Note 1: For example, a 4-wire circuit may, by means of a 4-wire terminating set, be connected to a 2-wire telephone set. Also, a pair of 4-wire terminating sets may be used to introduce an intermediate 4-wire loop into a 2-wire circuit, in which loop repeaters may be situated to amplify signals in each direction without positive feedback and oscillation. Note 2: Four-wire terminating sets have been largely supplanted by resistance hybrids. Line Alarm Indication Signal (AIS) Code - The code generated by a regenerator upon loss of input signal or loss of frame. The line AIS signal will maintain operation of the downstream regenerators and therefore prevent generation of unnecessary alarms. At the same time, data and orderwire communication is retained between the regenerators and the downstream line terminating equipment Linear Analog Control - Synonym linear analog synchronization. Synchronization in which the functional relationships used to obtain synchronization are of simple proportionality. Linear Analog Synchronization - Synchronization in which the functional relationships used to obtain synchronization are of simple proportionality. Synonym linear analog control. Linear Combiner - A diversity combiner in which the combining consists of simple addition of two or more signals. Linear Device - A device for which the output is, within a given dynamic range, linearly proportional to the input. Linearity - The property of a system in which, if input signals X and Y result in system output S (X) and S (Y) respectively, the input signal aX + bY will result in the output aS (X) + bS (Y), where S is the system transfer function and a and b are scalars. Linear Key - In video technology and image processing, a process for the selective overlay of one video image upon another, as through chroma key. Note: Control of the ratio of foreground to background determined by the specifications derived from luminance information, and provided in the linear key data. Ratios to be applied are carried for each picture element in the alpha channel. The process permits realistic rendering of semi-transparent objects. Linearly Polarized (LP) Mode - A mode for which the field components in the direction of propagation are small compared to components perpendicular to that direction. Note: The LP description is an approximation that is valid for a weakly guiding optical fiber, including typical telecommunications grade fibers. Linear Network - See network topology. A network topology in which all nodes, i.e., stations, are connected together by a single bus. 269
- 270. Linear Optimization - In operations research, a procedure for locating the maximum or minimum of a linear function of variables that are subject to linear constraints. Synonym linear programming. Linear Polarization - Of an electromagnetic wave, confinement of the E-field vector or H-field vector to a given plane. Note: Historically, the orientation of a polarized electromagnetic wave has been defined in the optical regime by the orientation of the electric vector, and in the radio regime, by the orientation of the magnetic vector. Synonym plane polarization. Linear Predictive Coding (LPC) - A method of digitally encoding analog signals, which method uses a single- level or multilevel sampling system in which the value of the signal at each sample time is predicted to be a linear function of the past values of the quantized signal. Note: LPC is related to adaptive predictive coding (APC) in that both use adaptive predictors. However, LPC uses more prediction coefficients to permit use of a lower information bit rate than APC, and thus requires a more complex processor. Linear Programming (LP) - In operations research, a procedure for locating the maximum or minimum of a linear function of variables that are subject to linear constraints. Synonym linear optimization. Linear Topology -- See network topology. A network topology in which all nodes, i.e., stations, are connected together by a single bus. Line Balance - The degree of electrical similarity of the two conductors of a transmission line. Note: A high degree of line balance reduces pickup of extraneous disturbances of all kinds, including crosstalk. Line Buildout (LBO): Synonym building out. - The process of adding a combination of inductance, capacitance, and resistance to a cable pair so that its electrical length may be increased by a desired amount to control impedance and loss characteristics. Line Code - A code chosen for use within a communications system for transmission purposes. Note 1: A line code may differ from the code generated at a user terminal, and thus may require translation. Note 2: A line code may, for example, reflect a requirement of the transmission medium, e.g., optical fiber versus shielded twisted pair. Line Conditioning - The elimination of unintentional signals or noise induced or conducted on a telecommunications or information system signal, power, control, indicator, or other external interface line. Line Conduction - Unintentional signals or noise induced or conducted on a telecommunications or information system signal, power, control, indicator, or other external interface line. Line Driver - An amplifier used to enhance the transmission reliability of a usually digital intrafacility metallic transmission line, over extended distances, by driving the input to the transmission line with a higher than normal signal level. Note: An example of a line driver is an amplifier used to extend the range of an RS-232C digital signal beyond 50 feet (~15 m) while maintaining a specified bit-error ratio. Line Filter Balance - A network designed to maintain phantom group balance when one side of the group is equipped with a carrier system. Note: Since it must balance the phantom group for only voice frequencies, the line filter balance configuration is usually simple compared with the filter that it balances. Line Hit - See hit. - 1. A transient disturbance to, or momentary interruption of, a communication channel, power supply (especially that provided via a commercial electric power distribution network or grid, but not limited to same), etc. 270
- 271. Line Load Control - A network-provided service feature that allows selective denial of call origination to certain lines when excessive demands for service are required of a switching center. Line Loop - See loop. - A pair of wires, or its equivalent, between a customer's station and the central office from which the station is served. Synonym user line. Line Loopback - A signal used to command the far-end receiver to loopback the received line signal. ] Synonym [loosely] line loopback signal. Line Loopback Signal - See line loopback. Line Noise - In a telecommunications link or line facility, interference, from any source, that degrades performance. Note 1: Line noise is usually measured as a signal-to-noise ratio and as a set parameter used by engineers to determine the operating range of the system. Note 2: In analog lines, noise is usually measured in dbrnc (dB relative to -90 dBm, with C-message weighting). Note 3: In digital lines, noise is usually measured as a function of the number of errored bits per second or errors in the digital data stream. In digital systems with signal buffers, these errors may be linked to alarms, and to circuitry that enables the signal to be recovered to acceptable degree. Line-Of-Sight (LOS) Propagation - Of an electromagnetic wave, propagation in which the direct ray from the transmitter to the receiver is unobstructed, i.e., the transmission path is not established by or dependent upon reflection or diffraction. Note: The need for LOS propagation is most critical at VHF and higher frequencies. Line-Rate Conversion - A translation of standardized, existing video systems (using 525, 625, and 1125 total lines per frame) to proposed systems. Note: Current systems operate in a 2:1 interlace mode, i.e., with 262.5, 312.5, 562.5 lines per field and with concurrent temporal differences at field rates of 50.00, 59.94, or 60.00 fields per second. While simple transcoding by deletion or repetition can be applied, it is more commonly done by applying an algorithm to stored information in order to generate predictive line structures in the target system. Line-Route Map - A map or overlay for signal communications operations that shows the actual routes and types of construction of wire circuits in the field. It also gives the locations of switchboards and telegraph stations. Line Sharing - A technology that allows a single phone line to share incoming and outgoing access for multiple phone line connected devices. Typically Line Sharing Technology allows voice (phones and answering machine) and a fax machine or fax modem to operate on a shared phone line. Other applications include any variation of voice, a fax machine, fax/modem and/or modem(s). Incoming calls are automatically routed to the proper device(s). If the call comes in and it is a fax call, the call is automatically routed to the fax machine or fax modem. If the call is a modem call, it is routed to the correct modem. Voice calls are routes to phone(s) and/or answering machine. May require a security access code (SAC) in the dialing string to automatically switch to the modem. Since the need for to subscribe to a separate "fax line" from the local telephone company is eliminated, the return on investment (ROI) is very high. The initial cost of the device is returned in savings in a few months. After that you will save the monthly bills associated with fax, data or voice lines. For almost every business, line sharing technology is a smart investment. 271
- 272. Line Side - The portion of a device that is connected to external, i.e., outside plant, facilities such as trunks, local loops, and channels. Line Source - 1. In spectroscopy, an optical source that emits one or more spectrally narrow lines as opposed to a continuous spectrum. 2. In the geometric sense, an optical source having an emitting area in the form of a spatially narrow line, e.g., a slit. Synonym slit source. Line Spectrum - In optics, an emission or absorption spectrum consisting of one or more narrow spectral lines, as opposed to a continuous spectrum. Line Speed - See modulation rate. - The rate at which a carrier is varied to represent the information in a digital signal. Note: Modulation rate and information transfer rate are not necessarily the same. Line Terminating Equipment (LTE): Network elements that originate and/or terminate line signals. LTEs can originate, access, modify, or terminate the transport overhead, or can perform any combination of these actions. Line-to-Line Vorrelation - In facsimile, the correlation of object information from scanning line to scanning line. Note: Line-to-line correlation is used in two-dimensional encoding. Line Traffic Coordinator (LTC): In a DDN switching center, the processor that controls traffic on a line. Line Unit Network Termination (LUNT): The customer side of any digital subscriber line (DSL) that does not terminate on the customer installation. Line Verification - See busy verification. - In a public switched telephone network, a network-provided service feature that permits an attendant to verify the busy or idle state of station lines and to break into the conversation. Note: A 440-Hz tone is applied to the line for 2 seconds, followed by a 0.5-second burst every 10 seconds, to alert both parties that the attendant is connected to the circuit. Linewidth - See spectral width. - The wavelength interval over which the magnitude of all spectral components is equal to or greater than a specified fraction of the magnitude of the component having the maximum value. Note 1: In optical communications applications, the usual method of specifying spectral width is the full width at half maximum. This method may be difficult to apply when the spectrum has a complex shape. Another method of specifying spectral width is a special case of root-mean-square deviation where the independent variable is wavelength, , and f ( ) is a suitable radiometric quantity. Note 2: The relative spectral width , / , is frequently used where is obtained according to note 1, and is the center wavelength. Link - See Hypertext Link. 1. The communications facilities between adjacent nodes of a network. Synonym [loosely] telecommunications link. 2. A portion of a circuit connected in tandem with, i.e., in series with, other portions. 3. A radio path between two points, called a radio link. 4. In communications, a general term used to indicate the existence of communications facilities between two points. 5. A conceptual circuit, i.e., logical circuit, between two users of a network, that enables the users to communicate, even when different physical paths are used. Note 1: In all cases, the type of link, such as data link, downlink, duplex link, fiber optic link, line-of-sight link, point-to-point link, radio link and satellite link, should be identified. Note 2: A link may be simplex, half-duplex, or duplex. 6. In a computer program, a part, such as a single instruction or address, that passes control and parameters between separate portions of the program. 7. In hypertext, a logical connection between discrete units of data, or a hypertext connection between Web pages. Synonyms (in this sense) hotlink, hyperlink. 272
- 273. Linkage - In computer security, the purposeful combining of data or information from one data processing system with data or information from another system to derive protected information. Synonym fusion. Linked Registration - A type of AllCall registration feature, the use of which combines the registrations for incoming and outgoing calls for the current terminal address in a single procedure. However, unlike AllCall registration, a linked registration cannot be overridden in all or in part by: (a) InCall, remote InCall, AllCall, or remote AllCall registrations by the same UPT (Universal Personal Telecommunications service) user; (b) OutCall, remote OutCall, AllCall, remote AllCall, linked, or remote linked registrations by other UPT users. The UPT user must explicitly deregister a linked registration or override it by another linked or remote linked registration. Link Encryption - 1. The application of on-line crypto-operation to a link of a communications system so that all information passing over the link is encrypted in its entirety. 2. Encryption of information between nodes of a communications system. Linking Protection (LP) - In adaptive high-frequency (HF) radio, protection intended to prevent the establishment of unauthorized links or the unauthorized manipulation of legitimate links, and which are administered through an authorization process. Link Layer - Deprecated term for Data Link Layer. Layer 2 of the Open Systems Interconnection--Reference Model. This layer responds to service requests from the Network Layer and issues service requests to the Physical Layer. The Data Link Layer provides the functional and procedural means to transfer data between network entities and to detect and possibly correct errors that may occur in the Physical Layer. Note: Examples of data link protocols are HDLC and ADCCP for point-to-point or packet-switched networks and LLC for local area networks. See Open Systems Interconnection--Reference Model. Link Level - In the hierarchical structure of a primary or secondary station, the conceptual level of control or data processing logic that controls the data link. Note: Link-level functions provide an interface between the station high-level logic and the data link. Link-level functions include (a) transmit bit injection and receive bit extraction, (b) address and control field interpretation, (c) command response generation, transmission and interpretation, and (d) frame check sequence computation and interpretation. Link Orderwire - A voice or data communications circuit that (a) serves as a transmission link between adjacent communications facilities that are interconnected by a transmission link and (b) is used only for coordination and control of link activities, such as traffic monitoring and traffic control. Link Protocol - A set of rules relating to data communications over a data link. Note: Link protocols define data link parameters, such as transmission code, transmission mode, control procedures, and recovery procedures. Link Quality Analysis (LQA) - In adaptive high-frequency (HF) radio, the overall process by which measurements of signal quality are made, assessed, and analyzed. Note 1: In LQA, signal quality is determined by measuring, assessing, and analyzing link parameters, such as bit error ratio (BER), and the levels of the ratio of signal-plus-noise-plus-distortion to noise-plus-distortion (SINAD). Measurements are stored at--and exchanged between--stations, for use in making decisions about link establishment. Note 2: For adaptive HF radio, LQA is automatically performed and is usually based on analyses of pseudo-BERs and SINAD readings. Link Set - A set of signaling links directly connecting two signaling points. 273
- 274. Link State Control - The control that coordinates functions of the signaling link, including signal unit delimitation, signal unit alignment, error detection, error correction, initial alignment, signaling link error monitoring, and flow control. Link Status Signal Unit - A signal unit that contains status information about the signaling link in which it is transmitted. TM Linux - A freeware version of the Unix operating system. Lip Synchronization - The synchronization of audio and corresponding video signals so that there is no noticeable lack of simultaneity between them. Note: An example of a lip synchronization problem is the case in which television video and audio signals are transported via different facilities (e.g., a geosynchronous satellite link and a landline) that have significantly differently delay times, respectively. In such cases it is necessary to delay the audio electronically to allow for the difference in propagation times. Liquid Crystal Display (LCD) - A display device that creates characters by means of the action of electrical signals on a matrix of liquid cells that become opaque when energized. Note: A liquid crystal display may be designed to be viewed by reflected or transmitted light. List Address - In e-mail, an address used by mailing list subscribers to send e-mail to be distributed to each member of a discussion list, forum, interest group, mailing list, or newsgroup. List Processor - Software used to manage and administer a discussion-group list, an interest group list, or a mailing list. LISTSERV - Mailing lists that act as newsgroups. List Server - A functional unit (hardware and software) for operating a computer conferencing system by acting as a repository for electronic messages and redistributing those messages automatically or on- demand. Synonyms distribution list server, mailing list server. Live Link - A link, on a World Wide Web file, that connects to another layer of information. Livescript - See scripting language. LLC - Abbreviation for logical link control. See logical link control sublayer. - In a local-area- network/metropolitan-area-network (LAN /MAN) system, the part of the link level that (a) supports medium- independent data link functions and (b) uses the services of the medium access control sublayer to provide services to the network layer. LNA - Abbreviation for launch numerical aperture. - The numerical aperture of an optical system used to couple (launch) power into an optical fiber. Note 1: LNA may differ from the stated NA of a final focusing element if, for example, that element is underfilled or the focus is other than that for which the element is specified. Note 2: LNA is one of the parameters that determine the initial distribution of power among the modes of an optical fiber. Load - 1. The power consumed by a device or circuit in performing its function. 2. A power-consuming device connected to a circuit. 3. To enter data or programs into storage or working registers. 4. To insert data values into a database that previously contained no occurrences of data. 5. To place a magnetic tape reel on a tape drive, or to place cards into the card hopper of a card punch or reader. 274
- 275. Load Capacity - In pulse-code modulation (PCM), the level of a sinusoidal signal that has positive and negative peaks that coincide with the positive and negative virtual decision values of the encoder. Note: Load capacity is usually expressed in dBm0. Synonym overload point. Loader - A routine that reads data into main storage. Load Factor - The ratio of the average load over a designated period of time to the peak load occurring during that period. Loading - 1. The insertion of impedance into a circuit to change the characteristics of the circuit. 2. In multichannel communications systems, the insertion of white noise or equivalent dummy traffic at a specified level to simulate system traffic and thus enable analysis of system performance. 3. In telephone systems, the load, i.e., power level, imposed by the busy hour traffic. Note 1: The loading may be expressed as (a) the equivalent mean power and the peak power as a function of the number of voice channels or (b) the equivalent power of a multichannel complex or signal composite referred to zero transmission level point (0TLP). Note 2: Loading is a function of the number of channels and the specified voice channel mean power. Loading Characteristic - In multichannel telephone systems, a plot, for the busy hour, of the equivalent mean power and the peak power as a function of the number of voice channels. Note: The equivalent power of a multichannel signal referred to the zero transmission level point is a function of the number of channels and has for its basis a specified voice channel mean power. Loading Coil - A coil that does not provide coupling to any other circuit, but is inserted in a circuit to increase its inductance. Note 1: Loading coils inserted periodically in a pair of wires reduce the attenuation at the higher voice frequencies up to the cutoff frequency of the low-pass filter formed by (a) the inductance of the coils and distributed inductance of the wires, and (b) the distributed capacitance between the wires. Above the cutoff frequency, attenuation increases rapidly. Note 2: A common application of loading coils is to improve the voice-frequency amplitude response characteristics of twisted cable pairs. When connected across a twisted pair at regular intervals, loading coils, in concert with the distributed resistance and capacitance of the pair, form an audio-frequency filter that improves the high-frequency audio response of the pair. Note 3: When loading coils are in place, signal attenuation increases rapidly for frequencies above the audio cutoff frequency. Thus, when a pair is used to support applications that require higher frequencies, such as carrier systems, loading coils must be absent. Load Sharing - A process used to route signaling traffic over two or more signaling routes for purposes of traffic equalization or security. Lobe - 1. An identifiable segment of an antenna radiation pattern. Note: A lobe is characterized by a localized maximum bounded by identifiable nulls. 2. A pair of channels between a data station and a lobe attaching unit, one channel for sending and one for receiving, as seen from the point of view of the attached data station. Lobe Attaching Unit - In a ring network, a functional unit used to connect and disconnect data stations to and from the ring without disrupting network operations. Local Access and Transport Area (LATA) - Geographical boundaries within which local telephone companies may provide local telephone services (and some limited toll services). There are 184 LATAs in the United States. Under the terms of the Modification of Final Judgment (MFJ), a geographical area within which a divested Bell Operating Company (BOC) is permitted to offer exchange telecommunications and exchange access services. Note: Under the terms of the MFJ, the BOCs are generally prohibited from providing services that originate in one LATA and terminate in another. 275
- 276. Local Area Network (LAN) - A data communications system that (a) lies within a limited spatial area, (b) has a specific user group, (c) has a specific topology, and (d) is not a public switched telecommunications network, but may be connected to one. Note 1: LANs are usually restricted to relatively small areas, such as rooms, buildings, ships, and aircraft. Note 2: An interconnection of LANs within a limited geographical area, such as a military base, is commonly referred to as a campus area network. An interconnection of LANs over a city- wide geographical area is commonly called a metropolitan area network (MAN). An interconnection of LANs over large geographical areas, such as nationwide, is commonly called a wide area network (WAN). Local Battery - 1. In telegraphy, the source of power that actuates the telegraphic station recording instruments, as distinguished from the source of power that furnishes current to the line. 2. In telephony, a system in which each telephone instrument has its own source of power, as opposed to being powered from the central office. 3. A source of local power for a telephone instrument. Local call - 1. Any call using a single switching facility. 2. Any call for which an additional charge, i.e., toll charge, is not made to the calling or called party. Note: Calls such as those via "800" numbers do not qualify as local calls, because the called party is charged. Local Central Office - Synonym central office. 1. A common carrier switching center in which trunks and/or loops are terminated and switched. Note: In the DOD, "common carrier" is called "commercial carrier." Synonym switch. Other synonyms [loosely] end office, exchange, local exchange, local office, switching center (except in DOD DSN [formerly AUTOVON] usage), switching exchange, telephone exchange. 2. A switching unit, in a telephone system which provides service to the general public, having the necessary equipment and operations arrangements for terminating and interconnecting subscriber lines and trunks or trunks only. There may be more than one central office in a building. Local Channel - The portion of a private line circuit which is included in the exchange transmission plant. However, common usage of this term usually excludes information origination/termination equipment. Local Clock - A source of timing located in close proximity to an associated facility, such as a communications station, central office, or node. Note: The same clock might be a remote clock relative to some other facility. Local Communication Network (LCN) - A communication network within a TMN (telecommunications management network) that supports data communication functions (DCFs) normally at [specified] reference points q1 and q2. LCNs range from the simple to the complex. LCN examples include point-to-point connections and networks based on star and bus topologies. Local Exchange - Synonym central office. In telephone communication in the United States, a local exchange office is an office in a locality to which subscriber home and business lines are connected on what is called a local loop. The local exchange has switching equipment that can switch calls locally or to long-distance carrier phone offices. Local Exchange Carrier (LEC) - A local telephone company, i.e., a communications common carrier that provides ordinary local voice-grade telecommunications service under regulation within a specified service area. Local Exchange Loop - An interconnection between customer premises equipment and telephone central office. Local Line - See loop. A communications channel from a switching center or an individual message distribution point to the user terminal. Synonym subscriber line. 276
- 277. Local Loop - A pair of wires, or its equivalent, between a customer's station and the central office from which the station is served. Synonyms loop, user line. Local Measured Service - See measured-rate service. - Telephone service for which charges are made in accordance with the total connection time of the line. Local Node - A node which interfaces directly with customer equipment. Local Number Portability Charge (LNP) - Allows a customer to keep the same phone number and "port" it over to another service provider. This is new to wireless. The terms number portability (NP) and local number portability (LNP) are often used interchangeably. This charge may appear on the local portion of a phone bill if you live in an area where local number portability is provided. This fixed monthly charge allows local telephone companies to recover certain costs for providing “portability” to its customers. Local telephone companies may continue to assess this charge on their customers’ telephone bills for five years from the date the local telephone company first began itemizing the charge on the bill. This is not a tax. Local Office - 1. Synonym central office. 2. A central office serving primarily as a place of termination for subscriber lines and for providing telephone service to the subscribers on these lines. Local Orderwire - A communications circuit between a technical control facility and selected terminal or repeater locations within the communications complex. Note: In multichannel radio systems, the local orderwire is usually a handset connection at the radio location. Local Reference - A local number, unambiguously identifying an SCCP (signaling connection control part) connection within one SCCP entity. Local Side - The portion of a device that is connected to internal facilities, such as switches, patch panels, test bays and supervisory equipment. Lock and Key Protection System - A protection system that involves matching a key or password with a specific access requirement. Locked Mode - Synonym clock normal mode. - An operating condition of a clock in which the output signals are controlled by an external input reference. It is the expected mode. In normal mode, each clock in a chain has the same long-term average frequency, and the time error between the input and output of each clock is bounded. Only stratum 1 sources of timing require no input and therefore have a unique status of "normal" operation being equivalent to "freerun". Lock-in Frequency - A frequency at which a closed-loop system can acquire and track a signal. See lock-in range. Lock-in Range - 1. The range of frequencies within which a closed-loop system can acquire and track a signal. 2. The dynamic range within which a closed-loop system can acquire and track a signal. Lockout - 1. In telephone systems, treatment of a user's line or trunk that is in trouble, or in a permanent off- hook condition, by automatically disconnecting the line from the switching equipment. 2. In public telephone systems, a process that denies an attendant or other users the ability to reenter an established connection. 3. In a telephone circuit controlled by two voice-operated devices, the inability of one or both users to get through, either because of excessive local circuit noise or because of continuous speech from either or both 277
- 278. users. 4. In mobile communications, an arrangement of control circuits whereby only one receiver can feed the system at a time. Synonym receiver lockout system. 5. An arrangement for restricting access to use of all, or part of, a computer system. Synonym protection. Log - Synonym journal. A chronological record of data processing operations that may be used to reconstruct a previous or an updated version of a file. Logical Circuit - Synonym virtual circuit. A communications arrangement in which data from a source user may be passed to a destination user over various real circuit configurations during a single period of communication. Note: Virtual circuits are generally set up on a per-call basis and are disconnected when the call is terminated; however, a permanent virtual circuit can be established as an option to provide a dedicated link between two facilities. Logical Link Control (LLC) Sublayer - In a local-area-network/metropolitan-area-network (LAN /MAN) system, the part of the link level that (a) supports medium-independent data link functions and (b) uses the services of the medium access control sublayer to provide services to the network layer. Logical Route - Synonym virtual circuit. A communications arrangement in which data from a source user may be passed to a destination user over various real circuit configurations during a single period of communication. Note: Virtual circuits are generally set up on a per-call basis and are disconnected when the call is terminated; however, a permanent virtual circuit can be established as an option to provide a dedicated link between two facilities. Logical Signaling Channel - A logical channel that provides a signaling path within an information channel or within a physical signaling channel. Logical Topology - Of a network, the schematic configuration that reflects the network's function, use, or implementation without regard to the physical interconnection of network elements. Logic Bomb - 1. Malicious logic that causes damage to a data processing system when triggered by some specific system condition. [2382-pt.8] 2. [A] resident computer program triggering an unauthorized act when particular states of an information system (IS) are realized. Log In - To perform a login procedure. Synonym log on. Login - The procedure that is followed by a user in beginning a session, e.g., a period of terminal operation. Synonym logon. Login Name - The unique account name used to access a computer system. Also called user ID or user name, it is a way people identify themselves to their online service or Internet access provider. Log Off - To perform a log-off procedure. Synonym log out. Log-Off - The procedure that is followed by a user in closing a session, e.g., a period of terminal operation. Synonym log out. Logon - Synonym login. The procedure that is followed by a user in beginning a session, e.g., a period of terminal operation. Log On - Synonym log in. To perform a login procedure. 278
- 279. Log Out - Synonym log off. To perform a log-off procedure. Log-Periodic (LP) Antenna - A broadband, multi-element, unidirectional, narrow-beam antenna that has impedance and radiation characteristics that are regularly repetitive as a logarithmic function of the excitation frequency. Note: The length and spacing of the elements of a log-periodic antenna increase logarithmically from one end to the other. Synonym log-periodic array. Log-Periodic (LP) Array - Synonym log-periodic antenna. - A broadband, multi-element, unidirectional, narrow-beam antenna that has impedance and radiation characteristics that are regularly repetitive as a logarithmic function of the excitation frequency. Note: The length and spacing of the elements of a log- periodic antenna increase logarithmically from one end to the other. Long-Distance Call - Any telephone call to a destination outside the local service area of the calling station, whether inter-LATA or intra-LATA, and for which there is a charge beyond that for basic service. Synonym toll call. Long-Haul Communications - 1. In public switched networks, pertaining to circuits that span large distances, such as the circuits in inter-LATA, interstate, and international communications. 2. In the military community, communications among users on a national or worldwide basis. Note 1: Compared to tactical communications, long-haul communications are characterized by (a) higher levels of users, such as the National Command Authority, (b) more stringent performance requirements, such as higher quality circuits, (c) longer distances between users, including world wide distances, (d) higher traffic volumes and densities, (e) larger switches and trunk cross sections, and (f) fixed and recoverable assets. Note 2: "Long-haul communications" usually pertains to the U.S. Defense Communications System. Longitudinal Balance - 1. The electrical symmetry, with respect to ground, of the two wires of a pair 2. An expression of the difference in impedance of the two sides of a circuit. Longitudinal Offset Loss - Synonym gap loss. - 1. The power loss that occurs when an optical signal is transferred from one fiber to another that is axially aligned with it, but longitudinally separated from it. Note: The gap allows light from the "transmitting" fiber to spread out as it leaves the fiber endface. When it strikes the "receiving" fiber, some of the light will enter the cladding, where it is quickly lost. 2. An analogous form of coupling loss that occurs between an optical source, e.g., an LED, and an optical fiber. Note: Longitudinal Offset Loss is not usually significant at the optical detector, because the sensitive area of the detector is normally somewhat larger than the cross section of the fiber core. Unless the separation is substantial, all light emerging from the fiber, even though it diverges, will still strike the detector. Longitudinal Redundancy Check (LRC) - A system of error control based on the formation of a block check following preset rules. Note 1: The block check formation rules are applied in the same manner to each character. Note 2: A combination of longitudinal and vertical redundancy check allows the detection and correction of single bit errors. Synonym horizontal redundancy check. Longitudinal Voltage - A voltage induced or appearing along the length of a transmission medium. Note 1: Longitudinal voltage may be effectively eliminated by using differential amplifiers or receivers that respond only to voltage differences, e.g., those between the wires that constitute a pair. Note 2: Induced longitudinal voltages at low (power-line) frequencies can be greatly reduced by twisting parallel wires to create what are referred to as "twisted wire pairs." Long Line - A transmission line in a long-distance communications network. Note: Examples of long lines are TDM and FDM carrier systems, microwave radio links, geosynchronous satellite links, underground cables, aerial cables and open wire, and submarine cables. 279
- 280. Long-Range Aid to Navigation (loran) System - See loran. A long-range radio navigation position-fixing system consisting of an array of fixed stations that transmit precisely synchronized signals to mobile receivers. Note: A loran receiver measures differences in the times of arrival of the signals from the various stations. A fixed difference in the time of arrival of the signals from any two stations will define a hyperbolic arc on which the receiver must lie. Three or more stations are needed to remove ambiguities in the position of the receiver. Long-Range Radio Aid to Navigation System: See loran. A long-range radio navigation position-fixing system consisting of an array of fixed stations that transmit precisely synchronized signals to mobile receivers. Note: A loran receiver measures differences in the times of arrival of the signals from the various stations. A fixed difference in the time of arrival of the signals from any two stations will define a hyperbolic arc on which the receiver must lie. Three or more stations are needed to remove ambiguities in the position of the receiver. Long-Term Bit Error Rate - Bit error rate measured over a sufficiently long period, for example, one month. Long Silent Interval - A silent interval during a ringing cycle or pattern that lasts at least 1200 ms. Long-Term Stability - Of an oscillator, the degree of uniformity of frequency over time, when the frequency is measured under identical environmental conditions, such as supply voltage, load, and temperature. Note: Long-term frequency changes are caused by changes in the oscillator elements that determine frequency, such as crystal drift, inductance changes, and capacitance changes. Long Wavelength - In fiber optic communications, pertaining to optical wavelengths greater than 1 m. Look-Ahead-For-Busy (LFB) Information - Information concerning network resources available to support higher precedence calls. Note 1: Available resources include idle circuits and circuits used for lower precedence calls. Note 2: LFB information may be used to make call-path reservations. Loop - 1. A communications channel from a switching center or an individual message distribution point to the user terminal. Synonym subscriber line. 2. A pair of wires, or its equivalent, between a customer's station and the central office from which the station is served. Synonyms local loop, user line. 3. Go-and-return conductors of an electric circuit; a closed circuit. 4. A closed path under measurement in a resistance test. 5. A type of antenna, in the form of a circle or rectangle, usually used in direction-finding equipment and in UHF reception. 6. A sequence of instructions that may be executed iteratively while a certain condition prevails until the loop has been executed once. Loop-Back - 1. A method of performing transmission tests of access lines from the serving switching center, which method usually does not require the assistance of personnel at the served terminal. 2. A method of testing between stations (not necessarily adjacent) wherein two lines are used, with the testing being done at one station and the two lines interconnected at the distant station. 3. A patch, applied manually or automatically, remotely or locally, that facilitates a loop-back test. Loop Check - Synonym echo check. - A check to determine the integrity of transmission of data, whereby the received data are returned to the source for comparison with the originally transmitted data. Loop Closure - A condition in which the network presents a low-resistance tip-to-ring dc path at the network interface (NI). Loop Compensation Loss - The loss that could be provided by a digital loop carrier system or a fiber-in-the- loop system when a short customer analog access cable results in below-average attenuation. 280
- 281. Looped Dual Bus - A distributed-queue dual-bus (DQDB) scheme in which the head-of-bus functions for both buses are at the same location. Loop Filter - In a phase-locked loop, a filter located between the phase detector (or time discriminator) and the voltage controlled oscillator (or phase shifter). Loop Gain - 1. The total usable power gain of a carrier terminal or two-wire repeater. Note: The maximum usable gain is determined by, and may not exceed, the losses in the closed path. 2. The sum of the gains, expressed in dB, acting on a signal passing around a closed path, i.e., a loop. Loophole - synonym flaw. In computer security, an error of commission, an omission, or an oversight that allows protection mechanisms to be bypassed or disabled. Loop Noise - The noise contributed by one or both loops of a telephone circuit to the total circuit noise. Note: In a given case, it should be stated whether the loop noise is for one or both loops. Loop Open - A signal in which the network applies a high resistance between the tip and ring conductors at the network interface (NI). Loop Start - A supervisory signal given by a telephone or PBX in response to completing the loop path. A line or equipment that will establish a dial tone by completing a circuit between the two wires of the line. Automatic call processors, fax switches, all FAX machines and single-line phones, and most MODEMS are loop start equipment Loop Test - A test that uses a closed circuit, i.e., loop, to detect and locate faults. Loop Transmission - Multipoint transmission in which (a) all the stations in a network are serially connected in one closed loop, (b) there are no cross-connections, (c) the stations serve as regenerative repeaters, forwarding messages around the loop until they arrive at their destination stations, and (d) any station can introduce a message into the loop by interleaving it with other messages. Loose Buffer - See buffer. - In a fiber optic communication cable, one type of component used to encapsulate one or more optical fibers for the purpose of providing such functions as mechanical isolation, protection from physical damage and fiber identification. Note: The buffer may take the form of a miniature conduit, contained within the cable and called a loose buffer, or loose buffer tube, in which one or more fibers may be enclosed, often with a lubricating gel. A tight buffer consists of a polymer coating in intimate contact with the primary coating applied to the fiber during manufacture. Loran - Acronym for long-range radio navigation. A long-range radio navigation position-fixing system consisting of an array of fixed stations that transmit precisely synchronized signals to mobile receivers. Note: A loran receiver measures differences in the times of arrival of the signals from the various stations. A fixed difference in the time of arrival of the signals from any two stations will define a hyperbolic arc on which the receiver must lie. Three or more stations are needed to remove ambiguities in the position of the receiver. Synonyms long-range aid to navigation system, long-range radio aid to navigation system. LOS - Abbreviation for line of sight. See line-of-sight propagation. - Of an electromagnetic wave, propagation in which the direct ray from the transmitter to the receiver is unobstructed, i.e., the transmission path is not established by or dependent upon reflection or diffraction. Note: The need for LOS propagation is most critical at VHF and higher frequencies. 281
- 282. Loss - 1. The diminution, usually expressed in dB, of signal level in a communications medium. 2. The power, usually expressed in watts, consumed or dissipated by a circuit or component without accomplishing useful work or purpose; e.g., heating (hysteresis loss) that occurs in the core of a transformer. 3. In computer security, a quantitative measure of harm or deprivation resulting from a compromise. Lossless Compression - 1. In the storage of digital data, reduction, by the use of one or more appropriate algorithms, of the amount of data to be stored, in such a manner that the original data may be recovered precisely; i.e., in the exact original form. Note: The actual algorithm(s) applied to a given set of data may depend on the application (and hence, the statistical properties) of the data, e.g., for image storage. 2. An analogous real-time process applied to the transmission of digital data, with the objective of reducing the amount of data that need be transmitted per unit time; i.e., data rate, without compromising the ability to completely restore the data. 3. A digital image compression technique that allows for the removal of redundant bits without a resulting loss of image quality. Lossy Compression - 1. In video and multimedia, bit-rate reduction of an image signal by powerful algorithms that compress beyond what is achievable in lossless compression or in quasi-lossless compression. Note: Lossy compression accepts loss of information and introduction of artifacts that can be ignored as unimportant when viewed in direct comparison with the original. Lossy compression takes advantage of the subtended viewing angle for the intended display, the perceptual characteristics of human vision, the statistics of image populations, and the objectives of the display. 2. In video technology, a digital image compression technique that removes redundant bits from an image in return for a minor loss of image quality. Lossy Medium - A medium in which a significant amount of the energy of a propagating electromagnetic wave is absorbed per unit distance traveled by the wave. Lost Block - A block not delivered to the user within a specified maximum end-to-end block transfer time. Lost Call - A call that has not been completed for any reason other than cases where the call receiver (termination) is busy. Lost Frame - A frame that is not delivered to the destination user within an agreed-upon measurement period, and the network is responsible. The procedure used to reach agreement on the measurement period should allow for the possibility that more than one network may be involved in the connection. Low Earth Orbit - See LEO. A term used to describe the orbital altitude range (500 to 2000 km above the surface of the Earth) of certain communications satellites. Note 1: Generally, LEO satellites are part of constellations of satellites that achieve wide coverage of the Earth's surface with lower power requirements and shorter propagation delays than can be achieved with, e.g. Geostationary orbit satellites, or MEO satellites. Note 2: LEO satellites may have equatorial or polar paths. Note 3: Two LEO groups have emerged: Little LEO for data-communications satellites and Big LEO for data-and-voice communications, each using preassigned frequency ranges. Lower Frequency Ground - Deprecated term. See facility grounding system. - The electrically interconnected system of conductors and conductive elements that (a) provides multiple current paths to the earth electrode subsystem, and (b) consists of the earth electrode subsystem, the lightning protection subsystem, and the fault protection subsystem. Lowest Usable High Frequency (LUF) - The lowest frequency in the HF band at which the received field intensity is sufficient to provide the required signal-to-noise ratio for a specified time period, e.g., 0100 to 0200 UTC, on 90% of the undisturbed days of the month. 282
- 283. Low Frequency (LF) - Any frequency in the band from 30 kHz to 300 kHz. See electromagnetic spectrum. Low-Level Keying - Synonym low-level signaling. - The use on signal lines of voltage levels that are between the limits of positive and negative 6 volts. Low-Level Language - Synonym computer-oriented language. - A programming language in which words and syntax are designed for use on a specific computer or class of computers. Low-Level Modulation - Modulation of a signal, e.g., a carrier, at a point in a system or device, such as a radio transmitter, where the power level is low compared to the final output power. Low-Level Signaling - The use on signal lines of voltage levels that are between the limits of positive and negative 6 volts. Synonym low-level keying. Low-Pass Filter - A filter network that passes all frequencies below a specified frequency with little or no loss, but strongly attenuates higher frequencies. Low-Performance Equipment - 1. Equipment that has imprecise characteristics that do not meet system reliability requirements. 2. In military communications, equipment that has insufficiently exacting characteristics to permit its use in trunks or links. Note: Low-performance equipment may be used in loops if it meets loop performance requirements. 3. Tactical ground and airborne equipment that (a) has size, weight, and complexity characteristics that must be kept to a minimum and (b) is used in systems that have components with similar minimum performance characteristics. Low-Power Communication Device - A restricted radiation device, exclusive of those employing conducted or guided radio frequency techniques, used for the transmission of signs, signals (including control signals), writing, images and sounds or intelligence of any nature by radiation of electromagnetic energy. Examples: Wireless microphone, phonograph oscillator, radio-controlled garage door opener, and radio-controlled models. Low-Power FM Radio (LPFM) - A broadcast service that permits the licensing of 50- to 100-watt FM radio stations within a service radius of up to 3.5 miles and 1- to 10-watt FM radio stations within a service radius of 1 to 2 miles. Low-Power Television (LPTV) - A broadcast service that permits program broadcasting via television translators operating with low power. LPTV service includes the existing translator service and operates on a secondary basis to regular television stations. Transmitter output is limited to 1,000 watts for normal VHF stations and 100 watts when a VHF operation is on an allocated channel. LP - Abbreviation for linear programming, linking protection. L-pad - A pad composed of two discrete components, one series component and one shunt component. Note: In schematic representation, the components resemble the upper-case letter "L," hence the name. LPC - Abbreviation for linear predictive coding. - A method of digitally encoding analog signals, which method uses a single-level or multilevel sampling system in which the value of the signal at each sample time is predicted to be a linear function of the past values of the quantized signal. Note: LPC is related to adaptive predictive coding (APC) in that both use adaptive predictors. However, LPC uses more prediction coefficients to permit use of a lower information bit rate than APC, and thus requires a more complex processor. 283
- 284. LP Mode - Abbreviation for linearly polarized mode. - A mode for which the field components in the direction of propagation are small compared to components perpendicular to that direction. Note: The LP description is an approximation that is valid for a weakly guiding optical fiber, including typical telecommunications grade fibers. LP01 mode - Designation of the fundamental LP mode. See fundamental mode. LPTV - Abbreviation for Low-Power TV. These are TV stations who are locally-oriented broadcasters -- operated by high schools/colleges, churches/religious groups, local governments, small/large businesses and individual citizens. There is currently no deadline for these categories of stations to convert to digital broadcasting LQA - Abbreviation for link quality analysis. - In adaptive high-frequency (HF) radio, the overall process by which measurements of signal quality are made, assessed, and analyzed. Note 1: In LQA, signal quality is determined by measuring, assessing, and analyzing link parameters, such as bit error ratio (BER), and the levels of the ratio of signal-plus-noise-plus-distortion to noise-plus-distortion (SINAD). Measurements are stored at--and exchanged between--stations, for use in making decisions about link establishment. Note 2: For adaptive HF radio, LQA is automatically performed and is usually based on analyses of pseudo-BERs and SINAD readings. LRC Abbreviation for longitudinal redundancy check. - A system of error control based on the formation of a block check following preset rules. Note 1: The block check formation rules are applied in the same manner to each character. Note 2: A combination of longitudinal and vertical redundancy check allows the detection and correction of single bit errors. LSB - Abbreviation for least significant bit, lower sideband. LTC - Abbreviation for Line Traffic Coordinator - In a DDN switching center, the processor that controls traffic on a line. .l3 - A file-name extension that identifies a Motion Picture Experts Group (MPEG) audio file. [Bahorsky] LTE - Abbreviation for Line Terminating Equipment - Network elements that originate and/or terminate line signals. LTEs can originate, access, modify, or terminate the transport overhead, or can perform any combination of these actions. LUF - Acronym for lowest usable high frequency. - The lowest frequency in the HF band at which the received field intensity is sufficient to provide the required signal-to-noise ratio for a specified time period, e.g., 0100 to 0200 UTC, on 90% of the undisturbed days of the month. Luminance Range - 1. In CRT displays, the difference in brightness between the lightest and the darkest element of a scene or its display. 2. Of a CRT or other display device, the ratio of (a) the maximum brightness that is (or can be) displayed to (b) the minimum brightness that is (or can be) displayed. Luminance Signal - 1. In television technology, the signal that describes (a) the distribution of brightness levels within the image and (b) the equation for deriving that information from the camera output. 2. In composite color television, a signal that has major control of the brightness. Note: Luminance signal is a linear combination of gamma-corrected primary color signals. Luminescent Diode - See superluminescent LED. - A light-emitting diode in which there is stimulated emission with amplification but insufficient feedback for oscillations to build up to achieve lasing action. 284
- 285. Luminous Flux - The rate of flow of radiant energy. Note: Luminous flux is expressed in lumens Luminous Intensity - See candela. - The luminous intensity in a specified direction, of a monochromatic 12 source which has a frequency of 540 x 10 Hz and which has a radiant intensity, in the specified direction, of (1/683) watt per steradian. LUNT - Abbreviation for Line Unit Network Termination - The customer side of any digital subscriber line (DSL) that does not terminate on the customer installation. Lurker - In the Internet, a participant in a chat room or a subscriber to a mailing list or newsgroup who passively observes but does not actively participate in the exchange. Lurking - Passive participation in (i.e., monitoring) the activities of a mailing list, a newsgroup, an IRC channel, a video connection, or any other Internet communication device. Note: Lurking is generally carried out for the purpose of nondirected information gathering or to allow a new user to first understand the focus and the manners of a discussion group. Lynx - A World Wide Web browser that provides a character-based user interface to hypertext-based information. Note: Lynx can display only character-based portions of the hypertext-based information. M MAC - Abbreviation for medium access control. MAC Abbreviation for Message Authentication Code - 1. A bit string that is a function of both data (either plaintext or ciphertext) and a secret key, and that is attached to the data in order to allow data authentication. Note: The function used to generate the message authentication code must be a one-way function. 2. Data associated with an authenticated message allowing a receiver to verify the integrity of the message. Machine-Independent - In telecommunications, computer, and data processing systems, pertaining to operations, procedures, computer programs, and processing that do not depend upon specific hardware for their successful execution. Machine Instruction - An instruction that is written in a machine language and can be executed directly by the processor for which it was designed without translation or interpretation. Machine Learning - The ability of a device to improve its performance based on its past performance. Machine Language - A language that need not be modified, translated, or interpreted before it can be used by the processor for which it was designed. Note 1: The operation codes and addresses used in instructions written in machine language can be directly sensed by the arithmetic and control unit circuits of the processor for which the language is designed. Note 2: Instructions written in an assembly language or a high- level language must be translated into machine language before they can be executed by a processor. Note 3: Machine languages are usually used by computer designers rather than computer users. Machine-Oriented Language - Synonym computer-oriented language. - A programming language in which words and syntax are designed for use on a specific computer or class of computers. Machine-Readable Medium - A medium capable of storing data in a form that can be accessed by an automated sensing device. Note: Examples of machine-readable media include (a) magnetic disks, cards, 285
- 286. tapes, and drums, (b) punched cards and paper tapes, (c) optical disks, and (d) magnetic ink characters. Synonym automated data medium. Machine Word - Synonym computer word. - In computing, a group of bits or characters that occupies one or more storage locations and is treated by computers as a unit. Macrobend - A relatively large-radius bend in an optical fiber, such as might be found in a splice organizer tray or a fiber-optic cable that has been bent. Note: A macrobend will result in no significant radiation loss if it is of sufficiently large radius. The definition of "sufficiently large" depends on the type of fiber. Single- mode fibers have a low numerical aperture, typically less than 0.15, and are therefore are more susceptible to bend losses than other types. Normally, they will not tolerate a minimum bend radius of less than 6.5 to 7.5 cm (2.5 to 3 inches). Certain specialized types of single-mode fibers, however, can tolerate a far shorter minimum bend radius without appreciable loss. A graded-index multimode fiber having a core diameter of 50 m and a numerical aperture of 0.20 will typically tolerate a minimum bend radius of not less than 3.8 cm (1.5 inches). The fibers commonly used in customer-premises applications (62.5- m core) typically have a relatively high numerical aperture, (approximately 0.27), and can tolerate a bend radius of less than an inch (2.5 cm). Macrobend Loss - In an optical fiber, that loss attributable to macrobending. Synonym curvature loss. Magic Cookie - Synonym cookie. -1. A small piece of information that is automatically stored on a client computer by a Web browser and referenced to identify repeat visitors to a Web site and to tailor information in anticipation of the visitor's interests. Note: Some privacy advocates have objected to the use of cookies without a user's consent. 2. A general mechanism that server side connections (such as CGI scripts) can use both to store and to retrieve information on the client side of the connection. Note 1: A server, when returning an HTTP object to a client, may also send a piece of state information that the client will store. Included in that state object is a description of the range of URLs for which that state is valid. Any future HTTP requests made by the client that fall in that range will include a transmittal of the current value of the state object from the client back to the server. The state object is called a cookie. This simple mechanism provides a tool that enables new types of applications to be written for Web-based environments. Shopping applications can now store information about the currently selected items, for-fee services can send back registration information and free the client from retyping a user ID on subsequent connections, sites can store per-user preferences on the client, and have the client supply those preferences every time that site is accessed. Note 2: Session cookies are volatile in that they disappear at the end of a session, whereas persistent cookies are retained from one session to the next. Magnetic Card - A card with a magnetizable surface on which data can be stored and retrieved. Magnetic Circuit - 1. The complete closed path taken by magnetic flux. 2. A region of ferromagnetic material, such as the core of a transformer or solenoid, that contains essentially all of the magnetic flux. Magnetic Core Storage - In computer technology, a storage device that uses ferromagnetic materials such as iron, iron oxide, or ferrite and in such shapes as wires, toroids, and rods. Magnetic Disk - See diskette, hard disk. Magnetic Drum - A right circular cylinder with a magnetizable surface on which digital data can be stored and retrieved. Magnetic Remanence - A magnetic representation of residual information remaining on a magnetic medium after the medium has been cleared. 286
- 287. Magnetic Storm - A perturbation of the Earth's magnetic field, caused by solar disturbances, usually lasting for a brief period (several days) and characterized by large deviations from the usual value of at least one component of the field. Note: Magnetic storms can affect radio propagation because they disturb the ionosphere. Magnetic Tape - 1. A tape with a magnetizable surface on which data can be stored and retrieved. 2. A tape or ribbon of any material impregnated or coated with magnetic or other material on which information may be placed in the form of magnetically polarized spots. Magneto-Ionic Double Refraction - The combined effect of the Earth's magnetic field and atmospheric ionization, whereby a linearly polarized wave entering the ionosphere is split into two components called the ordinary wave and the extraordinary wave. Note: The component waves follow different paths, experience different attenuations, have different phase velocities, and, in general, are elliptically polarized in opposite senses. Magneto-Optic - See magneto-optic effect. Magneto-Optic Effect - Any one of a number of phenomena in which an electromagnetic wave interacts with a magnetic field, or with matter under the influence of a magnetic field. Note: The most important magneto- optic effect having application to optical communication is the Faraday effect, in which the plane of polarization is rotated under the influence of a magnetic field parallel to the direction of propagation. This effect may be used to modulate a lightwave. Mail Bombing - Synonym spamming. See flooding, spam. - Slang 1. Unwanted or unsolicited e-mail messages or mailing-list or newsgroup postings. 2. To send an advertisement or solicitation to large numbers of unsolicited recipients, usually via mailing lists or newsgroups. Mailbox-Type Facility - A facility in which a message from an originating user is stored until the destination user requests delivery of that message. Mail Exchange Record (MX record) - An entry in a domain name system database that directs the routing of mail by mail transfer agents. Mail Exploder - Part of an e-mail delivery system that allows a message to be automatically and efficiently delivered to a list of addresses, thus implementing mailing lists. Synonym exploder. Mail Gateway - A computer that connects two or more electronic mail systems (especially dissimilar mail systems on two different networks) and transfers messages between them. Note: The mapping and translation can be quite complex, and can require a store-and-forward scheme whereby the message is received from one system completely before it is transmitted to the next system after suitable translations. Mailing List - Any one of a number of automated e-mail distribution programs that provide a forum for information exchange for professional, educational, and special interest groups. Note: Subscribers post messages to the list address and messages are then distributed to all subscribers. Mailing List Server - Synonym list server. - A functional unit (hardware and software) for operating a computer conferencing system by acting as a repository for electronic messages and redistributing those messages automatically or on-demand. Mail Path - A series of machine names used to direct electronic mail from one user to another. 287
- 288. Mail Reflector - 1. Synonyms e-mail exploder, mail exploder. 2. A program that forwards e-mail to individuals at a (usually) unchanging e-mail address, even when the individuals change Internet service providers. Mailserver - A computer that provides e-mail management and storage space for messages pertaining to a group of subscribers. Mail User Agent - The software used to access and manage a user's electronic mail. Main Beam - Synonym main lobe. - Of an antenna radiation pattern, the lobe containing the maximum power (exhibiting the greatest field strength). Note: The horizontal radiation pattern, i.e., that which is plotted as a function of azimuth about the antenna, is usually specified. The width of the main lobe is usually specified as the angle encompassed between the points where the power has fallen 3 dB below the maximum value. The vertical radiation pattern, i.e., that which is plotted as a function of elevation from a specified azimuth, is also of interest and may be similarly specified. Main Distribution Frame (MDF) - A distribution frame on one part of which the external trunk cables entering a facility terminate, and on another part of which the internal user subscriber lines and trunk cabling to any intermediate distribution frames terminate. Note 1: The MDF is used to cross-connect any outside line with any desired terminal of the multiple cabling or any other outside line. Note 2: The MDF usually holds central office protective devices and functions as a test point between a line and the office. Note 3: The MDF in a private exchange performs functions similar to those performed by the MDF in a central office. Synonym (in telephony) main frame. Main Frame - A distribution frame on one part of which the external trunk cables entering a facility terminate, and on another part of which the internal user subscriber lines and trunk cabling to any intermediate distribution frames terminate. Note 1: The MDF is used to cross-connect any outside line with any desired terminal of the multiple cabling or any other outside line. Note 2: The MDF usually holds central office protective devices and functions as a test point between a line and the office. Note 3: The MDF in a private exchange performs functions similar to those performed by the MDF in a central office. Synonym (in telephony) main distribution frame. Mainframe - A large computer, usually one to which other computers and/or terminals are connected to share its resources and computing power. Main Lobe - Of an antenna radiation pattern, the lobe containing the maximum power (exhibiting the greatest field strength). Note: The horizontal radiation pattern, i.e., that which is plotted as a function of azimuth about the antenna, is usually specified. The width of the main lobe is usually specified as the angle encompassed between the points where the power has fallen 3 dB below the maximum value. The vertical radiation pattern, i.e., that which is plotted as a function of elevation from a specified azimuth, is also of interest and may be similarly specified. Synonym main beam. Main Station - A user instrument, e.g., telephone set or terminal, with a distinct call number designation, connected to a local loop, used for originating calls, and on which incoming calls from the exchange are answered. Main Storage - In a computer, program-addressable storage from which instructions and other data may be loaded directly into registers for subsequent execution or processing. Note 1: Main storage includes the total program-addressable execution space that may include one or more storage devices. Note 2: "Main storage" usually refers to large and intermediate computers, whereas " memory " usually refers to microcomputers, minicomputers, and calculators. 288
- 289. Maintainability - 1. A characteristic of design and installation, expressed as the probability that an item will be retained in or restored to a specified condition within a given period of time, when the maintenance is performed in accordance with prescribed procedures and resources. 2. The ease with which maintenance of a functional unit can be performed in accordance with prescribed requirements. Maintenance - 1. Any activity, such as tests, measurements, replacements, adjustments and repairs, intended to restore or retain a functional unit in a specified state in which the unit can perform its required functions. 2. [For materiel], All action taken to retain materiel in a serviceable condition or to restore it to serviceability. It includes inspection, testing, servicing, classification as to serviceability, repair, rebuilding, and reclamation. 3. [For materiel], All supply and repair action taken to keep a force in condition to carry out its mission. 4. [For materiel], The routine recurring work required to keep a facility (plant, building, structure, ground facility, utility system, or other real property) in such condition that it may be continuously used, at its original or designed capacity and efficiency for its intended purpose. Maintenance Control Circuit (MCC) - In a communications link, a circuit used by maintenance personnel for coordination. Note: An MCC is not available to operations or technical control personnel. Maintenance Hook - 1. A trapdoor in software that allows easy maintenance and development of additional features and that may allow entry into the program at unusual points or without the usual checks. 2. Special instructions (trapdoors) in software allowing easy maintenance and additional feature development. Since maintenance hooks frequently allow entry into the code without the usual checks, they are a serious security risk if they are not removed prior to live implementation. Maintenance Key - Key intended only for in-shop use. Major Lobe - See main lobe. - Of an antenna radiation pattern, the lobe containing the maximum power (exhibiting the greatest field strength). Note: The horizontal radiation pattern, i.e., that which is plotted as a function of azimuth about the antenna, is usually specified. The width of the main lobe is usually specified as the angle encompassed between the points where the power has fallen 3 dB below the maximum value. The vertical radiation pattern, i.e., that which is plotted as a function of elevation from a specified azimuth, is also of interest and may be similarly specified. Major Trading Area (MTA) – An area defined by the U.S. government and used by the Federal Communications Commission (FCC) to designate personal communications services market areas. Make Interval - 1. In dial-pulse signaling, that portion of the dial pulse in which the network applies a low resistance between the tip and ring conductors at the network interface (NI). 2. In dial-pulse signaling, that portion of the dial pulse in which the pulsing circuit is in its low-impedance condition. Malicious Applets - Small application programs automatically downloaded and executed that perform an unauthorized function on an information system. Malicious Code - Software or firmware capable of performing an unauthorized function on an information system (IS). Malicious Logic - 1. A program implemented in hardware, firmware, or software, and whose purpose is to perform some unauthorized or harmful action. Note: Examples of malicious logic are a logic bomb, a Trojan horse, a virus, a worm. [2382-pt.8] 2. Hardware, software, or firmware capable of performing an unauthorized function on an information system. 289
- 290. MAN - Acronym for metropolitan area network. - A data communications network that (a) covers an area larger than a campus area network and smaller than a wide area network (WAN), (b) interconnects two or more LANs, and (c) usually covers an entire metropolitan area, such as a large city and its suburbs. Managed Object - 1. In a network, an abstract representation of network resources that are managed. Note: A managed object may represent a physical entity, a network service, or an abstraction of a resource that exists independently of its use in management. 2. In telecommunications management, a resource within the telecommunications environment that may be managed through the use of operation, administration, maintenance, and provisioning application protocols. Management Domain - A collection of one or more management systems, and zero or more managed systems and management subdomains, that is administered by a single organization. Management Information System (MIS) - An organized assembly of resources and procedures required to collect, process, and distribute data for use in decision making. Management Inhibit - A procedure used in signaling traffic management to keep a signaling link unavailable to user-part-generated signaling traffic except for test and maintenance traffic. Management System - An application process within a management domain that affects monitoring and control functions on managed objects, management subdomains, or both. A management system may also communicate with its peers (that may be resident in other management domains). Synonym managing system. Managing System - Synonym management system. - An application process within a management domain that affects monitoring and control functions on managed objects, management subdomains, or both. A management system may also communicate with its peers (that may be resident in other management domains). Manchester Code - A code in which (a) data and clock signals are combined to form a single self- synchronizing data stream, (b) each encoded bit contains a transition at the midpoint of a bit period, (c) the direction of transition determines whether the bit is a "0" or a "1," and (d) the first half is the true bit value and the second half is the complement of the true bit value. Mandatory Fixed Part - Part of a message that contains those parameters that are mandatory and of fixed length for a particular message type. Mandatory Variable Part - Part of a message that contains mandatory parameters of variable length. Mandrel Wrapping - In multimode fiber optics, a technique used to modify the modal distribution of a propagating optical signal. Note: A cylindrical rod wrap consists of a specified number turns of fiber on a mandrel of specified size, depending on the fiber characteristics and the desired modal distribution. It has application in optical transmission performance tests, to simulate, i.e., establish, equilibrium mode distribution in a launch fiber (a fiber used to inject a test signal in another fiber that is under test). If the launch fiber is fully filled ahead of the mandrel wrap, the higher-order modes will be stripped off, leaving only lower-order modes. If the launch fiber is underfilled, e.g., as a consequence of being energized by a laser diode or edge-emitting LED, there will be a redistribution to higher-order modes until modal equilibrium is reached. Manipulation Detection - A procedure that is used to detect whether data have been modified either accidentally or intentionally. Synonym modification detection. 290
- 291. Manipulation Detection Code (MDC) - In cryptosystems, a bit string that is a function of data to which it is attached for the purpose of manipulation detection. Note 1: The resulting message (data plus MDC) may then be encrypted to achieve secrecy or data authentication. Note 2: The function used to generate the MDC must be public. Man-Machine System - A system in which the functions of a human operator and a machine are integrated. Manual Remote Rekeying - A procedure by which a distant crypto-equipment is rekeyed electrically, with specific actions required by the receiving terminal operator. MAP Pricing - Minimum Advertised Price (MAP Reicing) is the practice whereby a manufacturer and its distributors agree that the latter’s resellers will advertise the former's product at certain prices, at or above a price floor (minimum advertised price). These rules prevent resellers from competing too fiercely on price, thus driving down profits and lowering the manufacturer’s reputation as a creator of quality made products. A manufacturer may do this because it wishes to keep resellers profitable, and thus keeping the manufacturer profitable. Others contend that minimum advertised price maintenance, for instance, overcomes a failure in the market for distributional services by ensuring that distributors who invest in promoting the manufacturer's product are able to recoup the additional costs of such promotion in the price they charge consumers. Manufacturers also defend retail minimum advertised price by saying it ensures fair returns, both for manufacturer. According to such agreements, retailers can usually sell M.A.P. restricted items for any price they choose, but may not display in any print or online advertising, a price below the Minimum Advertisable Price. Definition: A suppliers pricing policy that does not permit its resellers to advertise prices below some specified amount. It can include the resellers' retail price as well (Source: retail.about.com) MAP Pricing enhances customer loyalty, product image and profits. Minimum Advertised Price or (MAP) requirements are common in the marketing world. Manufacturers often assign a minimum price point below which a retailer cannot advertise certain products. MAP pricing ensures that their product maintains a certain level of exclusivity and doesn’t become known as a cheap product. A Minimum Advertised Price (MAP) Policy alleviates brand degradation and reinforces the advantages of our products in the areas of quality, design, warranty, and service delivered by Multi-Link, Inc. It will protect stocking dealers from “unfair” online competition and makes sure that everyone makes money. Margin - 1. In communications systems, the maximum degree of signal distortion that can be tolerated without affecting the restitution, i.e., without its being interpreted incorrectly by the decision circuit. 2. The allowable error rate, deviation from normal, or degradation of the performance of, a system or device. Marine Broadcast Station - A coast station which makes scheduled broadcasts of time, meteorological, and hydrographic information. Marine Utility Station - A station in the maritime mobile service consisting of one or more hand-held radiotelephone units licensed under a single authorization. Each unit is capable of operation while being hand-carried by an individual. Maritime Air Communications - Communications systems, procedures, operations, and equipment that are used for message traffic between aircraft stations and ship stations in the maritime service. Note: Commercial, private, naval, and other ships are included in maritime air communications. Maritime Broadcast Communications Net - A communications net that is used for international distress calling, including international lifeboat, lifecraft, and survival-craft high-frequency (HF); aeronautical 291
- 292. emergency very high-frequency (VHF); survival ultra high-frequency (UHF); international calling and safety very high-frequency (VHF); combined scene-of-search-and-rescue; and other similar and related purposes. Note: Basic international distress calling is performed at either medium frequency (MF) or at high frequency (HF). Maritime Mobile-Satellite Service - A mobile-satellite service in which mobile Earth stations are located on board ships; survival craft stations and emergency position-indicating radiobeacon stations may also participate in this service. Maritime Mobile Service - A mobile service between coast stations and ship stations, or between ship stations, or between associated on-board communication stations; survival craft stations and emergency position-indicating radiobeacon stations may also participate in this service. Maritime Radionavigation-Satellite Service - A radionavigation-satellite service in which Earth stations are located on board ships. Maritime Radionavigation Service - A radionavigation service intended for the benefit and for the safe operation of ships. Mark - 1. In telegraphy, one of the two significant conditions of encoding. Note 1: The complementary significant condition is called a "space." Note 2: In modern digital communications, the two corresponding significant conditions of encoding are called "1" and "0." Synonyms marking pulse, marking signal. 2. A symbol or symbols that indicate the beginning or the end of a field, of a word, or of a data item in a file, record, or block. Marker Beacon - A transmitter in the aeronautical radionavigation service which radiates vertically a distinctive pattern for providing position information to aircraft. Marking Bias - The uniform lengthening of all marking signal pulse widths at the expense of the pulse widths of all spacing pulses. Marking End Distortion - See end distortion. - The continuation of marking pulses past the proper time. Marking Pulse - Synonym mark. - 1. In telegraphy, one of the two significant conditions of encoding. Note 1: The complementary significant condition is called a "space." Note 2: In modern digital communications, the two corresponding significant conditions of encoding are called "1" and "0." Synonyms marking signal. 2. A symbol or symbols that indicate the beginning or the end of a field, of a word, or of a data item in a file, record, or block. Marking Signal - Synonym mark. - 1. In telegraphy, one of the two significant conditions of encoding. Note 1: The complementary significant condition is called a "space." Note 2: In modern digital communications, the two corresponding significant conditions of encoding are called "1" and "0." Synonyms marking pulse. 2. A symbol or symbols that indicate the beginning or the end of a field, of a word, or of a data item in a file, record, or block. Mark Sequence - A string of mark bits (sent immediately before message transmission starts) to alert the customer installation (CI) to initiate certain actions. Marquee - 1. In computer display, a line of alphanumeric characters that scrolls through, and within, a defined area (window). 2. An HTML tag that enables the display of a marquee. 292
- 293. Martian - 1. [Slang] Pertaining to packets that are delivered to the wrong network as the result of bogus routing entries. 2. [Slang] A packet that has a completely bogus (nonregistered or ill-formed) Internet address. m-ary code - See n-ary code. m-ary signaling - See n-ary code. MASER - Acronym for microwave amplification by stimulated emission of radiation. A member of the general class of microwave oscillators based on molecular interaction with electromagnetic radiation. Mask - 1. In communications systems, to obscure, hide, or otherwise prevent information from being derived from a signal. Note 1: Masking is usually the result of interaction with another signal, such as noise, static, jamming, or other forms of interference. Note 2: Masking is not synonymous with erasing or deleting. 2. In computing and data processing systems, a pattern of bits that can be used to retain or suppress segments of another pattern of bits. Masked Threshold - The level at which an indistinguishable signal of interest becomes distinguishable from other signals or noise. Note: In acoustics, the masked threshold is usually expressed in dB. Masking - 1. In television and video technology, a process in which color signals are used to modify each other for the purpose of altering their color rendition. Note: The process is often accomplished by suitable cross coupling between primary color-signal channels. 2. One way of partial compensation for photo- receptor cot sensitivity, nonoptimum color filters, nonideal display phosphors, unwanted dye absorption, etc. Masquerade - The pretense by an entity to be a different entity in order to gain unauthorized access. Masquerading - A form of spoofing. Unauthorized use of legitimate Identification and Authentication (I&A) data, however it was obtained, to mimic a subject different from the attacker. Master Clock - A device that generates periodic, accurately spaced signals that are used for such purposes as timing, regulation of the operations of a processor, or generation of interrupts. Master File (MF) - The unique mandatory file containing access conditions and optionally DFs (dedicated files) and/or EFs (extended frames). Master Frequency Generator - In frequency-division multiplexing (FDM), equipment used to provide system end-to-end carrier frequency synchronization and frequency accuracy of tones. Note: The following types of oscillators are used in the Defense Communications System FDM systems: • Type 1 - A master carrier oscillator as an integral part of the multiplexer set. • Type 2 - A submaster oscillator equipment or slave oscillator equipment as an integral part of the multiplexer set. • Type 3 - An external master oscillator equipment that has extremely accurate and stable characteristics. Synonym master oscillator. Mastergroup - See group. 293
- 294. Master Key - Within a hierarchy of encrypting keys and transaction keys, the highest level of key-encrypting key. Master Oscillator - In frequency-division multiplexing (FDM), equipment used to provide system end-to-end carrier frequency synchronization and frequency accuracy of tones. Note: The following types of oscillators are used in the Defense Communications System FDM systems: • Type 1 - A master carrier oscillator as an integral part of the multiplexer set. • Type 2 - A submaster oscillator equipment or slave oscillator equipment as an integral part of the multiplexer set. • Type 3 - An external master oscillator equipment that has extremely accurate and stable characteristics. Synonym master frequency generator. Master-Slave Timing - Timing in which one station or node supplies the timing reference for all other interconnected stations or nodes. Master Station - 1. In a data network, the station that is designated by the control station to ensure data transfer to one or more slave stations. Note: A master station controls one or more data links of the data communications network at any given instant. The assignment of master status to a given station is temporary and is controlled by the control station according to the procedures set forth in the operational protocol. Master status is normally conferred upon a station so that it may transmit a message, but a station need not have a message to send to be designated the master station. 2. In navigation systems using precise time dissemination, a station that has the clock used to synchronize the clocks of subordinate stations. 3. In basic mode link control, the data station that has accepted an invitation to ensure a data transfer to one or more slave stations. Note: At a given instant, there can be only one master station on a data link. Matched Junction - A waveguide component having four or more ports, and so arranged that if all ports except one are terminated in the correct impedance, there will be no reflection of energy from the junction when the fourth port is driven by a transmission line having a matching impedance. Matching Gel - See gel. Index-matching material in the form of a gel. Material Absorption - See absorption. - In the transmission of electrical, electromagnetic, or acoustic signals, the conversion of the transmitted energy into another form, usually thermal. Note 1: Absorption is one cause of signal attenuation . Note 2: The conversion takes place as a result of interaction between the incident energy and the material medium, at the molecular or atomic level. Material Dispersion - See dispersion. In optical fiber communication, the wavelength dependence of the velocity of propagation (of the optical signal) on the bulk material of which the fiber is made. Note 1: Because every optical signal has a finite spectral width, material dispersion results in spreading of the signal. Note 2: Use of the redundant term " chromatic dispersion " is discouraged. Note 3: In pure silica, the basic material from which the most common telecommunication-grade fibers are made, material dispersion is minimum at wavelengths in the vicinity of 1.27 m (slightly longer in practical fibers). Material Dispersion Coefficient [M ( )]: In an optical fiber, pulse broadening per unit length of fiber and unit spectral width, usually expressed in picoseconds per (nanometer• kilometer). Note 1: For many silica- based fibers, M ( ) approaches zero at a specific wavelength 0 between 1.3 m and 1.5 m. At wavelengths shorter than 0, M ( ) is negative and increases with wavelength; at wavelengths longer than 0,, M ( ) is positive and decreases with wavelength. 294
- 295. Material Scattering - Of an electromagnetic wave, scattering that is attributable to the intrinsic properties of the material through which the wave is propagating. Note 1: Ionospheric scattering and Rayleigh scattering are examples of material scattering. Note 2: In an optical fiber, material scattering is caused by micro- inhomogeneities in the refractive indices of the materials used to fabricate the fiber, including the dopants used to modify the refractive index profile. Matrixing - The accomplishment of a color coordinate transformation by computational, electrical, optical, or by other means. Matte - An image or signal that represents or carries only transparent information that is intended to overlay or control another image or signal. MATV - Master Antenna. Common or master antenna system in apartment buildings, condominiums, high- rises, co-ops or other Multiple Dwelling Units (MDU) through which residents receive local TV stations. MAU - Abbreviation for medium access unit. - In a communications system, the equipment that adapts or formats the signal for transmittal over the communication medium. Note 1: An example of a MAU is an optical transmitter, which accepts an electrical signal at its input port and converts it to an optical signal accessible at its output port. Note 2: Some prefer to limit the term medium access unit to FDDI usage, with the term media converter being preferred for general usage. Synonym media converter. Maximal-Ratio Combiner - A diversity combiner in which (a) the signals from each channel are added together, (b) the gain of each channel is made proportional to the rms signal level and inversely proportional to the mean square noise level in that channel, and (c) the same proportionality constant is used for all channels. Synonyms ratio-squared combiner, post-detection combiner, predetection combining, selective combiner. Maximum Block Transfer Time - The maximum allowable waiting time between initiation of a block transfer attempt and completion of a successful block transfer. Maximum Calling Area - Geographic calling limits permitted to a particular access line based on requirements for the particular line. Note: Maximum calling area restrictions are imposed for network control purposes. Maximum Disengagement Time - The maximum allowable waiting time between initiation of a disengagement attempt and successful disengagement. Maximum Justification Rate - In a bit-stream, the maximum rate at which stuffing bits can be inserted into the stream. Synonym maximum stuffing rate. Maximum Keying Frequency - In facsimile systems, the frequency in hertz numerically equal to the spot speed divided by twice the X-dimension of the scanning spot. Maximum Modulating Frequency - In a facsimile transmission system, the highest picture frequency that is required. Note: The maximum modulating frequency and the maximum keying frequency are not necessarily equal. Maximum Stuffing Rate - In a bit-stream, the maximum rate at which stuffing bits can be inserted into the stream. Synonym maximum justification rate. 295
- 296. Maximum Time Interval Error (MTIE): The maximum error for all possible measurement intervals within the measurement period. Maximum Usable Frequency (MUF) - In radio transmission using reflection from the regular ionized layers of the ionosphere, the upper frequency limit that can be used for transmission between two points at a specified time. Note: MUF is a median frequency applicable to 50% of the days of a month, as opposed to 90% cited for the lowest usable high frequency (LUF) and the optimum traffic frequency (OFT). Maximum User Signaling Rate: The maximum rate, in bits per second, at which binary information can be transferred in a given direction between users over the telecommunications system facilities dedicated to a particular information transfer transaction, under conditions of continuous transmission and no overhead information. Maxwell's Equations - A set of partial differential equations that describe and predict the behavior of electromagnetic waves in free space, in dielectrics, and at conductor-dielectric boundaries. Note: Maxwell's equations expand upon and unify the laws of Ampere, Faraday, and Gauss, and form the foundation of modern electromagnetic theory. Mbone - Abbreviation for multicast backbone on the Internet. A part of the Internet designed to support IP multicasting by coordinating the transmission of messages to a single destination instead of allowing packets to travel by different routes. Mbps - Megabytes per second (MB is also used as an abbreviation for Megabyte). MCC - Abbreviation for maintenance control circuit. - In a communications link, a circuit used by maintenance personnel for coordination. Note: An MCC is not available to operations or technical control personnel. MCM - Abbreviation for multicarrier modulation. - A technique of transmitting data by dividing the data into several interleaved bit streams and using these to modulate several carriers. Note: MCM is a form of frequency-division multiplexing. MDF - Abbreviation for main distribution frame. - A distribution frame on one part of which the external trunk cables entering a facility terminate, and on another part of which the internal user subscriber lines and trunk cabling to any intermediate distribution frames terminate. Note 1: The MDF is used to cross-connect any outside line with any desired terminal of the multiple cabling or any other outside line. Note 2: The MDF usually holds central office protective devices and functions as a test point between a line and the office. Note 3: The MDF in a private exchange performs functions similar to those performed by the MDF in a central office. Synonym (in telephony) main frame. Meaconing - A system of receiving radio beacon signals and rebroadcasting them on the same frequency to confuse navigation. The meaconing stations cause inaccurate bearings to be obtained by aircraft or ground stations. Mean Power (of a radio transmitter) - The average power supplied to the antenna transmission line by a transmitter during an interval of time sufficiently long compared with the lowest frequency encountered in the modulation taken under normal operating conditions. Note: Normally, a time of 0.1 second, during which the mean power is greatest, will be selected. Mean Time Between Failures (MTBF) - 1. An indicator of expected system reliability calculated on a statistical basis from the known failure rates of various components of the system. Note: MTBF is usually 296
- 297. expressed in hours. 2. Of a system, over a long performance measurement period, the measurement period divided by the number of failures that have occurred during the measurement period. 3. For population of items, during a measurement period, the total functioning life of the population of items divided by the total number of failures within the population during the measurement period. Note 1: The total functioning life of the population may be calculated as the summation of the operating life of every item in the population over the measurement period. When computing the MTBF, any measure of operating life may be used, such as time, cycles, kilometers, or events. Note 2: For example, if a total of 1,000 events, such as data transfers, radio transmissions, or system boots, occurs in a population of items during a measurement period of 100 hours and there are a total of 10 failures among the entire population, the MTBF for each item is 4 (1000)(100)/10 = 10 hours. Mean Time Between Outages (MTBO): In a system, the mean time between equipment failures that result in loss of system continuity or unacceptable degradation. Mean Time To Repair (MTTR) - The total corrective maintenance time divided by the total number of corrective maintenance actions during a given period of time. Mean Time to Service Restoral (MTSR) - The mean time to restore service following system failures that result in a service outage. Note: The time to restore includes all time from the occurrence of the failure until the restoral of service. Measured blocking threshold - A value for measured blocking above which there is a statistically significant probability that the design blocking objective is not being met. Measured-Rate Service - Telephone service for which charges are made in accordance with the total connection time of the line. Measurement Period - See performance measurement period. - The period during which performance parameters are measured. Note: A performance measurement period is determined by required confidence limits and may vary as a function of the observed parameter values. User time is divided into consecutive performance measurement periods to enable measurement of user information transfer reliability. Mechanically Induced Modulation - Optical signal modulation induced by mechanical means. Note: An example of deleterious mechanically induced modulation is speckle noise created in a multimode fiber by an imperfect splice or imperfectly mated connectors. Mechanical disturbance of the fiber ahead of the joint will introduce changes in the modal structure, resulting in variations of joint loss. Mechanically Intermateable Connectors - Connectors that are mechanically mateable, without creating mechanical damage, and without regard to attenuation properties. Mechanical Splice - Of optical fibers, a splice, i.e., permanent joint, accomplished by aligning the mating fibers in some kind of mechanical fixture. Note 1: The fibers may be secured by mechanical means or with an optical adhesive. Note 2: When the fibers are secured by mechanical means, the gap between them is usually filled with an index-matching gel to reduce Fresnel reflection. Likewise, the optical adhesives that are used in conjunction with mechanical splices are formulated to have a refractive index that approximates that of the glass, and also serve to reduce Fresnel reflection. Media Converter - Synonym medium access unit (MAU). - In a communications system, the equipment that adapts or formats the signal for transmittal over the communication medium. Note 1: An example of a MAU is an optical transmitter, which accepts an electrical signal at its input port and converts it to an optical signal accessible at its output port. Note 2: Some prefer to limit the term medium access unit to FDDI usage, with the term media converter being preferred for general usage. 297
- 298. Media Gateway Control Protocol (MGCP) - Another protocol competing with H.323 (see also SIP), MGCP handles the traffic between media gateways and their controllers. Especially useful in multimedia applications: the media gateway converts from various formats for the switched-circuit network, and the controller handles conversion for the packet-switched network. Designed to take the workload away from IP telephones themselves and thereby make IP phones less complex and expensive. Media Stream - A sequence of presentation units intended to convey some specific content. Mediation - A process within the communications management network that acts on information passing between network elements (NEs) and operating systems (OSs) via a data communication network. Mediation uses standard interfaces and can be shared among several NEs, or several OSs, or between NEs and OSs. Mediation Function - In telecommunications network management, a function that routes or acts on information passing between network elements and network operations. Note 1: Examples of mediation functions are communications control, protocol conversion, data handling, communications of primitives, processing that includes decision-making, and data storage. Note 2: Mediation functions can be shared among network elements, mediation devices, and network operation centers. Medium - 1. In telecommunications, the transmission path along which a signal propagates, such as a wire pair, coaxial cable, waveguide, optical fiber, or radio path. 2. The material on which data are or may be recorded, such as plain paper, paper tapes, punched cards, magnetic tapes, magnetic disks, or optical disks. Medium Access Unit (MAU) - In a communications system, the equipment that adapts or formats the signal for transmittal over the communication medium. Note 1: An example of a MAU is an optical transmitter, which accepts an electrical signal at its input port and converts it to an optical signal accessible at its output port. Note 2: Some prefer to limit the term medium access unit to FDDI usage, with the term media converter being preferred for general usage. Synonym media converter. Medium Earth Orbit (MEO) - An orbital path configuration, between altitudes of 8,000 and 20,000 km, used by communication satellites that provide communications capabilities for such services as cellular telephone communications and GPS (global positioning system) signals. Classification Orbital Altitude (km above the earth) LEO 500-2,000 MEO 8,000-20,000 Geostationary Orbit 35,786 Medium Frequency (MF) - Frequencies from 300 kHz to 3000 kHz. See electromagnetic spectrum. Medium Interface Connector (MIC) - In communications systems, the connector at the interface point between the bus interface unit and the terminal, i.e., the medium interface point. Medium Interface Point (MIP) - In communication systems, the location at which the standards for the interface parameters between a terminal and the line facility are implemented. Medium-Power Talker - A hypothetical talker, within a log-normal distribution of talkers, whose volume lies at the medium power of all talkers determining the volume distribution at the point of interest. Note: When the distribution follows a log-normal curve (values expressed in decibels), the mean and standard deviation can be used to compute the medium-power talker. The talker volume distribution follows a log-normal curve and the medium-power talker is uniquely determined by the average talker volume. The medium-power 298
- 299. 2 talker volume, V, is given by V = V o+ 0.115 , where V o is the average of the talker volume distribution in 2 volume units (vu), and is the variance of the distribution. Medium-Term Bit Error Rate - Bit error rate that can be encountered for relatively short time periods (e.g., minutes), due to temporary malfunctions of, for example, transmission equipment. Megabyte (MB)- A million bytes or a thousand kilobytes. 6 Megahertz (MHz) - A unit of frequency denoting one million (10 ) Hz. Memory - 1. All of the addressable storage space in a processing unit and other internal memory that is used to execute instructions. 2. Loosely, the volatile, main storage in computers. See random access memory. Memory Scavenging - The collection of residual information from data storage. Menu - A displayed list of options from which a user selects actions to be performed. MEO - Abbreviation for medium Earth orbit. An orbital path configuration, between altitudes of 8,000 and 20,000 km, used by communication satellites that provide communications capabilities for such services as cellular telephone communications and GPS (global positioning system) signals. Classification Orbital Altitude (km above the earth) LEO 500-2,000 MEO 8,000-20,000 Geostationary Orbit 35,786 MERCAST - Acronym for merchant-ship broadcast system. Merchant-Ship Broadcast System (MERCAST) - A maritime shore-to-ship broadcast system in which the ocean areas are divided into primary broadcast areas each covered by a high-powered shore radio station that broadcasts simultaneously on one medium frequency (MF) and one or more high frequencies (HF) for routing messages to ocean-going ships. Note: In some instances, coast stations may repeat the messages. Meridional Ray - In fiber optics, a ray that passes through the optical axis of an optical fiber (in contrast with a skew ray, which does not). Mesh Network - See network topology. A network topology in which there are at least two nodes with two or more paths between them. Mesh Topology - See network topology. A network topology in which there are at least two nodes with two or more paths between them. Mesochronous - The relationship between two signals such that their corresponding significant instants occur at the same average rate. Message - 1. Any thought or idea expressed briefly in a plain or secret language, prepared in a form suitable for transmission by any means of communication. Note: A message may be a one-unit message or a multiunit message. 2. [In telecommunications,] Record information expressed in plain or encrypted language 299
- 300. and prepared in a format specified for intended transmission by a telecommunications system. 3. An arbitrary amount of information whose beginning and end are defined or implied. 4. A completed call, i.e., a communication in which a conversation or exchange of information took place between the calling and called parties. Message Alignment Indicator - In a signal message, data transmitted between the user part and the message transfer part to identify the boundaries of the signal message. Message Authentication - Determining that a message has not been changed since leaving its point of transmission, where: (a) the identity of the originator is verified, and (b) the source, uniqueness, and integrity of the message are verified. Message Authentication Code (MAC) - 1. A bit string that is a function of both data (either plaintext or ciphertext) and a secret key, and that is attached to the data in order to allow data authentication. Note: The function used to generate the message authentication code must be a one-way function. 2. Data associated with an authenticated message allowing a receiver to verify the integrity of the message. Message Body - 1. For the single message format, the message words. 2. For the multiple message format, the parameter messages. Message Broadcast - An electronic-mail conference capability using data terminals. Note: Control can be maintained by the user or by the network. Message Center - 1. An agency charged with the responsibility for handling and controlling communications traffic. The center normally includes message center, transmitting, and receiving facilities. 2. A facility that (a) serves as a node for a communications network, (b) is equipped for technical control and maintenance of the circuits originating, transiting, or terminating at the node, (c) may contain message-center facilities, and (d) may serve as a gateway. Synonyms comm center, communications center. Message Digest - See digest. Message Format - A predetermined or prescribed spatial or time-sequential arrangement of the parts of a message that is recorded in or on a data storage medium. Note: Messages prepared for electrical transmission are usually composed on a printed blank form with spaces for each part of the message and for administrative entries. Message Handling System (MHS) - In the ITU-T X.400 Recommendations, the family of services and protocols that provides the functions for global electronic-mail (e-mail) transfer among local mail systems. Message Switching - A method of handling message traffic through a switching center, either from local users or from other switching centers, whereby the message traffic is stored and forwarded through the system. Message Transfer Agent (MTA) - An OSI application process used to store and forward messages as described in the X.400 message handling system. Synonym Internet mail agent. Message Transfer Part - The part of a common-channel signaling system that transfers signal messages and performs associated functions, such as error control and signaling link security. Message Type - An assigned value used to identify the feature generating the message. 300
- 301. Metropolitan Area Network (MAN) - A data communications network that (a) covers an area larger than a campus area network and smaller than a wide area network (WAN), (b) interconnects two or more LANs, and (c) usually covers an entire metropolitan area, such as a large city and its suburbs. MGCP (Media Gateway Control Protocol) - Another protocol competing with H.323 (see also SIP), MGCP handles the traffic between media gateways and their controllers. Especially useful in multimedia applications: the media gateway converts from various formats for the switched-circuit network, and the controller handles conversion for the packet-switched network. Designed to take the workload away from IP telephones themselves and thereby make IP phones less complex and expensive. MHS (Message Handling System) - In the ITU-T X.400 Recommendations, the family of services and protocols that provides the functions for global electronic-mail (e-mail) transfer among local mail systems. MHz - Abbreviation for megahertz. MIC - Abbreviation for Medium Interface Connector - In communications systems, the connector at the interface point between the bus interface unit and the terminal, i.e., the medium interface point. Microbend - In an optical waveguide, sharp curvatures involving local axial displacements of a few micrometers and spatial wavelengths of a few millimeters. Note: Microbends can result from waveguide coating, cabling, packaging, and installation. Microbending can cause significant radiative loss and mode coupling. Microbending - See microbend. Microbend Loss - In an optical fiber, the optical power loss caused by a microbend. Microwave (mw) - Loosely, an electromagnetic wave having a wavelength from 300 mm to 10 mm (1 GHz to 30 GHz). Note: Microwaves exhibit many of the properties usually associated with waves in the optical regime, e.g., they are easily concentrated into a beam. Mimicking - [A] form of spoofing. Minimum Bend Radius - The radius below which an optical fiber or fiber-optic cable should not be bent. Note 1: The minimum bend radius is of particular importance in the handling of fiber-optic cables. It will vary with different cable designs. The manufacturer should specify the minimum radius to which the cable may safely be bent during installation, and for the long term. The former is somewhat shorter than the latter. Note 2: The minimum bend radius is in general also a function of tensile stresses, e.g., during installation, while being bent around a sheave while the fiber or cable is under tension. Note 3: If no minimum bend radius is specified, one is usually safe in assuming a minimum long-term low-stress radius not less than 15 times the cable diameter. MIP - Abbreviation for Medium Interface Point - In communication systems, the location at which the standards for the interface parameters between a terminal and the line facility are implemented. MIS - Abbreviation for Management Information System - An organized assembly of resources and procedures required to collect, process, and distribute data for use in decision making. Miscellaneous Taxes - Like many other consumer goods and services, certain telephone services are taxed by federal, state, and local governments. These charges may appear as a “gross receipts” tax. 301
- 302. Misdelivered Block - A block received by a user other than the one intended by the message source. Mobile Phone - A mobile radiotelephone, often in an automobile, that uses a network of short-range transmitters located in overlapping cells throughout a region, with a central station making connections to regular telephone lines. A hand-held mobile radiotelephone for use in an area divided into small sections (cells), each with its own short-range transmitter/receiver. Also called mobile telephone. A mobile phone is a device which behaves as a normal telephone whilst being able to move over a wide area (compare cordless phone which acts as a telephone only within a limited range). Mobile phones allow connections to be made to the telephone network, normally by directly dialling the other party's number on an inbuilt keypad. Most current mobile phones use a combination of radio wave transmission and conventional telephone circuit switching, though packet switching is already in use for some parts of the mobile phone network, especially for services such as Internet access and WAP. Some of the world's largest mobile phone manufacturers include Alcatel, Audiovox, Kyocera (formerly the handset division of Qualcomm), LG, Motorola, Nokia, Panasonic (Matsushita Electric), Philips, Samsung, Sagem, Sanyo, Siemens, SK Teletech, and Sony Ericsson. Mobile-Satellite Service - A radiocommunication service: • between mobile earth stations and one or more space stations, or between space stations used by this service; or • between mobile earth stations by means of one or more space stations. This service may also include feeder links necessary for its operation Mobile Service - A radiocommunication service between mobile and land stations, or between mobile stations. Mobile Station - 1. A station in the mobile service intended to be used while in motion or during halts at unspecified points. 2. One or more transmitters that are capable of operation while in motion. Modal Distribution - In an optical waveguide operating at a given wavelength, the number of modes supported, and their propagation time differences. Modal Noise - Noise generated in an optical fiber system by the combination of mode-dependent optical losses and fluctuation in the distribution of optical energy among the guided modes or in the relative phases of the guided modes. Synonym speckle noise. Mode - 1. In a waveguide or cavity, one of the various possible patterns of propagating or standing electromagnetic fields. Note 1: Each mode is characterized by frequency, polarization, electric field strength, and magnetic field strength. Note 2: The electromagnetic field pattern of a mode depends on the frequency, refractive indices or dielectric constants, and waveguide or cavity geometry. 2. Any electromagnetic field distribution that satisfies Maxwell's equations and the applicable boundary conditions. 3. In data communications, a protocol used to transfer data from switch to switch or from switch to terminal. 4. In statistics, the value associated with the highest peak in a probability density function. Mode Coupling - In an electromagnetic waveguide, the exchange of power among modes. Note: In a multimode optical fiber, mode coupling reaches statistical equilibrium, i.e., equilibrium mode distribution, after the equilibrium length has been traversed. 302
- 303. Modem - A device that allows computers and other electronic equipment to communicate through ordinary telephone lines. A modem converts digital signals from your computer into analog signals for transmission over a phone line (modulation) and also converts the analog signals from the phone into digital signals that your computer can read (demodulation). Moderator - In computer conferencing, a person who receives the prospective messages from conference attendees and may accept, modify, or reject them. Synonym conference controller. Modification Detection - Synonym manipulation detection. A procedure that is used to detect whether data have been modified either accidentally or intentionally. Modular Connector - A catch all term that describes a number of plugs and jacks used with telephone and other equipment Handset connectors have four contact positions. Line connectors are wider and have six positions (often, only two or four positions are loaded with contacts).See telephone jacks, RJ-11 and RJ-14. Modulation - The process, or result of the process, of varying a characteristic of a carrier, in accordance with an information-bearing signal. Modulation Factor - In amplitude modulation, the ratio of the peak variation actually used, to the maximum design variation in a given type of modulation. Note: In conventional amplitude modulation, the maximum design variation is considered that for which the instantaneous amplitude of the modulated signal reaches zero. When zero is reached, the modulation is considered 100%. Modulation Rate - 1. The rate at which a carrier is varied to represent the information in a digital signal. Note: Modulation rate and information transfer rate are not necessarily the same. 2. For modulated digital signals, the reciprocal of the unit interval of the modulated signal, measured in seconds. Modulator - A device that imposes a signal on a carrier. Monitor - 1. Software or hardware that is used to scrutinize and to display, record, supervise, control, or verify the operations of a system. Note: Possible uses of monitors are to indicate significant departures from the norm, or to determine levels of utilization of particular functional units. 2. A device used for the real-time temporary display of computer output data. Note: Monitors usually use cathode-ray-tube or liquid-crystal technology. Synonyms CRT, video display terminal, video display unit, visual display unit. Monitoring - 1. The act of listening, carrying out surveillance on, and/or recording the emissions of one's own or allied forces for the purposes of maintaining and improving procedural standards and security, or for reference, as applicable. 2. The act of listening, carrying out surveillance on, and/or recording of enemy 303
- 304. emissions for intelligence purposes. 3. The act of detecting the presence of radiation and the measurement thereof with radiation measuring instruments. Synonym radiological monitoring. Monomode Optical Fiber - Synonym single-mode optical fiber. An optical fiber in which only the lowest order bound mode can propagate at the wavelength of interest. Note 1: The lowest order bound mode is ascertained for the wavelength of interest by solving Maxwell's equations for the boundary conditions imposed by the fiber, e.g., core (spot) size and the refractive indices of the core and cladding. Note 2: The solution of Maxwell's equations for the lowest order bound mode will permit a pair of orthogonally polarized fields in the fiber, and this is the usual case in a communication fiber. Note 3: In step-index guides, single- mode operation occurs when the normalized frequency, V, is less than 2.405. For power-law profiles, single- mode operation occurs for a normalized frequency, V, less than approximately Note 4: In practice, the orthogonal polarizations may not be associated with degenerate modes. MTBF - Abbreviation for Mean Time Between Failures () - 1. An indicator of expected system reliability calculated on a statistical basis from the known failure rates of various components of the system. Note: MTBF is usually expressed in hours. 2. Of a system, over a long performance measurement period, the measurement period divided by the number of failures that have occurred during the measurement period. 3. For population of items, during a measurement period, the total functioning life of the population of items divided by the total number of failures within the population during the measurement period. Note 1: The total functioning life of the population may be calculated as the summation of the operating life of every item in the population over the measurement period. When computing the MTBF, any measure of operating life may be used, such as time, cycles, kilometers, or events. Note 2: For example, if a total of 1,000 events, such as data transfers, radio transmissions, or system boots, occurs in a population of items during a measurement period of 100 hours and there are a total of 10 failures among the entire population, the MTBF 4 for each item is (1000)(100)/10 = 10 hours. MTBO - Abbreviation for Mean Time Between Outages - In a system, the mean time between equipment failures that result in loss of system continuity or unacceptable degradation. MTIE - Abbreviation for Maximum Time Interval Error - The maximum error for all possible measurement intervals within the measurement period. MTSR - Abbreviation for Mean Time to Service Restoral - The mean time to restore service following system failures that result in a service outage. Note: The time to restore includes all time from the occurrence of the failure until the restoral of service. MTTR - Abbreviation for Mean Time To Repair - The total corrective maintenance time divided by the total number of corrective maintenance actions during a given period of time. MUF - Abbreviation for Maximum Usable Frequency - In radio transmission using reflection from the regular ionized layers of the ionosphere, the upper frequency limit that can be used for transmission between two points at a specified time. Note: MUF is a median frequency applicable to 50% of the days of a month, as opposed to 90% cited for the lowest usable high frequency (LUF) and the optimum traffic frequency (FOT). Multicarrier Modulation (MCM) - A technique of transmitting data by dividing the data into several interleaved bit streams and using these to modulate several carriers. Note: MCM is a form of frequency- division multiplexing. Multicast Backbone (Mbone) - See Mbone. A part of the Internet designed to support IP multicasting by coordinating the transmission of messages to a single destination instead of allowing packets to travel by different routes. 304
- 305. Multicasting - DTV technology that allows each digital broadcast station to split its digital bandwidth into two or more individual channels of programming and/or data services (For example, on Channel 7, you could watch sub-channel 7-1, 7-2, 7-3 or 7-4). Multichannel - Pertaining to communications, usually full-duplex communications, on more than one channel. Note: Multichannel transmission may be accomplished by time-division multiplexing, frequency- division multiplexing, phase-division multiplexing, or space diversity. Multi-Channel Sound - Feature of DTV that permits numerous streams of sound to be transmitted for a given program, providing stereo, surround sound, and even other languages. Multimedia Communication System - A system that handles more than one media stream in a synchronized way from the user's point of view. The system may allow interconnection of multiple parties, multiple connections, and the addition or deletion of resources and users within a single communication session. Multimode Distortion - A distortion mechanism, occurring in multimode fibers, in which the signal is spread in time because the velocity of propagation of the optical signal is not the same for all modes. Note 1: In the ray-optics analogy, multimode distortion in a step-index optical fiber may be compared to multipath propagation of a radio signal. The direct signal is distorted by the arrival of the reflected signal a short time later. In a step-index optical fiber, rays taking more direct paths through the fiber core, i.e., those which undergo the fewest reflections at the core-cladding boundary, will traverse the length of the fiber sooner than those rays which undergo more reflections. This results in distortion of the signal. Note 2: Multimode distortion limits the bandwidth of multimode fibers. For example, a typical step-index fiber with a 50- m core would be limited to approximately 20 MHz for a one-kilometer length, i.e., a bandwidth of 20 MHz•km. Note 3: Multimode distortion may be considerably reduced, but never completely eliminated, by the use of a core having a graded refractive index. The bandwidth of a typical off-the-shelf graded-index multimode fiber, having a 50- m core, may approach 1 GHz•km or more. Multimode graded-index fibers having bandwidths approaching 3 GHz•km have been produced. Note 4: Because of its similarity to dispersion in its effect on the optical signal, multimode distortion is sometimes incorrectly referred to as " intermodal dispersion," " modal dispersion," or " multimode dispersion." Such usage is incorrect because multimode distortion is not a truly dispersive effect. Dispersion is a wavelength-dependant phenomenon, whereas multimode distortion may occur at a single wavelength. Synonyms intermodal delay distortion, intermodal distortion. Multimode Optical Fiber - An optical fiber that supports the propagation of more than one bound mode. Note: A multimode optical fiber may be either a graded-index (GI) fiber or a step-index (SI) fiber. Multiparty Line - Synonym party line. In telephone systems, an arrangement in which two or more user end instruments, usually telephones, are connected to the same loop. Note: If selective ringing is not used, individual users may be alerted by different ringing signals, such as a different number of rings or a different combination of long and short rings. Party lines remain primarily in rural areas where loops are long. Privacy is limited and congestion often occurs. Multipath - The propagation phenomenon that results in radio signals' reaching the receiving antenna by two or more paths. Note 1: Causes of multipath include atmospheric ducting, ionospheric reflection and refraction, and reflection from terrestrial objects, such as mountains and buildings. Note 2: The effects of multipath include constructive and destructive interference, and phase shifting of the signal. Note 3: In facsimile and television transmission, multipath causes jitter and ghosting. Multiplex (MUX) - See multiplexing. The combining of two or more information channels onto a common transmission medium. Note: In electrical communications, the two basic forms of multiplexing are time- division multiplexing (TDM) and frequency-division multiplexing (FDM). In optical communications, the analog of FDM is referred to as wavelength-division multiplexing (WDM). 305
- 306. Multiplexer (MUX) - A device that combines multiple inputs into an aggregate signal to be transported via a single transmission channel. Synonym multiplexing equipment. Multiplexing (MUXing) - The combining of two or more information channels onto a common transmission medium. Note: In electrical communications, the two basic forms of multiplexing are time-division multiplexing (TDM) and frequency-division multiplexing (FDM). In optical communications, the analog of FDM is referred to as wavelength-division multiplexing (WDM). Multiplexing Equipment - Synonym multiplexer. - A device that combines multiple inputs into an aggregate signal to be transported via a single transmission channel. Multiplex Hierarchy - In frequency-division multiplexing, the rank of frequency bands occupied: 12 channels group 5 groups (60 channels) super group 5 super groups (300 channels) master group (CCITT--now, ITU-T) 10 super groups (600 channels) master group (U.S. standard) 6 U.S. master groups (3600 channels) jumbo group Multipoint - Synonym multiple. Multipoint Circuit - A circuit that interconnects three or more separate points. Must-Carry - The legal obligation of cable companies to carry the analog or digital signals of over-the-air local broadcasters. MW - Abbreviation for microwave. - Loosely, an electromagnetic wave having a wavelength from 300 mm to 10 mm (1 GHz to 30 GHz). Note: Microwaves exhibit many of the properties usually associated with waves in the optical regime, e.g., they are easily concentrated into a beam. MX Record - Abbreviation for mail exchange record. - An entry in a domain name system database that directs the routing of mail by mail transfer agents. N NA - Abbreviation for numerical aperture. 1. The sine of the vertex angle of the largest cone of meridional rays that can enter or leave an optical system or element, multiplied by the refractive index of the medium in which the vertex of the cone is located. Note: The NA is generally measured with respect to an object or image point and will vary as that point is moved. 2. For an optical fiber in which the refractive index decreases monotonically from n 1 on the axis to n 2 in the cladding, an expression of the extent of the fiber's ability to accept, in its bound modes, non-normal incident rays, given by NA = ( n 1 2 - n 2 2 ) ½ . Note: In multimode fibers, the term equilibrium numerical aperture is sometimes used. This refers to the numerical aperture with respect to the extreme exit angle of a ray emerging from a fiber in which equilibrium mode distribution has been established. 3. Loosely, the sine of the radiation or acceptance angle of an optical fiber, multiplied by the refractive index of the material in contact with the exit or entrance face. Note: This usage is approximate and imprecise, but is often encountered. Nailed-Up Circuit - Deprecated term. See dedicated circuit, permanent virtual circuit. A circuit designated for exclusive use by specified users. Note: DOD normally considers a dedicated circuit to be between two 306
- 307. users only. A virtual circuit used to establish a long-term connection between data terminal equipments (DTE). Note 1: In a PVC, the long-term association is identical to the data transfer phase of a virtual call. Note 2: Permanent virtual circuits eliminate the need for repeated call set-up and clearing. NAK - Acronym for negative-acknowledge character . A transmission control character sent by a station as a negative response to the station with which the connection has been set up. Note 1: In binary synchronous communication protocol , the NAK is used to indicate that an error was detected in the previously received block and that the receiver is ready to accept retransmission of that block. Note 2: In multipoint systems, the NAK is used as the not-ready reply to a poll. NAK Attack - In communications security systems, a security penetration technique that makes use of the negative-acknowledge transmission - control character and capitalizes on a potential weakness in a system that handles asynchronous transmission interruption in such a manner that the system is in an unprotected state against unauthorized access during certain periods. Naming Authority - With respect to Internet addressing, an entity responsible for the allocation of names. Note: Such naming is typically hierarchical, so that the authority to allocate domain names is restricted to a particular level within a domain, such as ".com", ".net", or ".gov". NAP - See Network Access Point. A centralized point where Internet traffic is exchanged or shared. Narrative Traffic - Traffic consisting of plain or encrypted messages written in a natural language and transmitted in accordance with standard formats and procedures. Note: Examples of narrative traffic include (a) messages that are placed on paper tape and transmitted via a teletypewriter ( TTY ), and on reception, are converted back to a printed page on another teletypewriter or teleprinter and (b) messages printed on a sheet of paper, transmitted via optical character recognition ( OCR ) equipment, and on reception, converted back to a printed page on a printer. Narrowband Modem - A modem whose modulated output signal has an essential frequency spectrum that is limited to that which can be wholly contained within, and faithfully transmitted through, a voice channel with a nominal 4- kHz bandwidth . Note: High frequency (HF) modems are limited to operation over a voice channel with a nominal 3-kHz bandwidth. Narrowband Radio Voice Frequency (NBRVF) - In narrowband radio, the nominal 3- kHz bandwidth allocated for single channel radio that provides a transmission path for analog and quasi-analog signals. Narrowband Signal - Any analog signal or analog representation of a digital signal whose essential spectral content is limited to that which can be contained within a voice channel of nominal 4- kHz bandwidth. Note: Narrowband radio uses a voice channel with a nominal 3-kHz bandwidth. n-ary code - A code that has n significant conditions, where n is a positive integer greater than 1. Note 1: The integer substituted for n indicates the specific number of significant conditions, i.e., quantization states, in the code. For example, an 8-ary code has eight significant conditions and can convey three bits per code symbol. Note 2: A prefix that indicates an integer, e.g., "bi," "tern," or "quater," may be used in lieu of a numeral, to produce "binary," "ternary," or "quaternary" (2, 3, and 4 states respectively). n-ary signaling - See n-ary code. NATA - Abbreviation for North American Telecommunications Association. 307
- 308. National Communications System (NCS) -1. The organization established by Section 1(a) of Executive Order No. 12472 to assist the President, the National Security Council, the Director of the Office of Science and Technology Policy, and the Director of the Office of Management and Budget, in the discharge of their national security emergency preparedness telecommunications functions. The NCS consists of both the telecommunications assets of the entities represented on the NCS Committee of Principals and an administrative structure consisting of the Executive Agent, the NCS Committee of Principals, and the Manager. 2. The telecommunications system that results from the technical and operational integration of the separate telecommunications systems of the several executive branch departments and agencies having a significant telecommunications capability. National Coordinating Center (NCC) for Telecommunications - The joint telecommunications industry/Federal Government operation established by the National Communications System to assist in the initiation, coordination, restoration, and reconstitution of National Security or Emergency Preparedness (NS/EP) telecommunications services or facilities. National Electric Code® (NEC) - A standard that governs the use of electrical wire, cable, and fixtures, and electrical and optical communications cable installed in buildings. Note: The NEC was developed by the NEC Committee of the American National Standards Institute ( ANSI ), was sponsored by the National Fire Protection Association (NFPA), and is identified by the description ANSI/NFPA 70-XXXX, the last four digits representing the year of the NEC revision. National Information Infrastructure (NII) - A proposed, advanced, seamless web of public and private communications networks, interactive services, interoperable hardware and software, computers, databases, and consumer electronics to put vast amounts of information at users' fingertips. Note: NII includes more than just the physical facilities (more than the cameras, scanners, keyboards, telephones, fax machines, computers, switches, compact disks, video and audio tape, cable, wire, satellites, optical fiber transmission lines, microwave nets , switches, televisions, monitors, and printers) used to transmit, store, process, and display voice, data, and images; it encompasses a wide range of interactive functions, user - tailored services, and multimedia databases that are interconnected in a technology-neutral manner that will favor no one industry over any other. Synonym information superhighway. National Number - The number identifying a calling user line within an area designated by a country code. National Prefix - A digit or combination of digits to be dialed by a calling subscriber, making a call to a subscriber in his own country but outside his own numbering area. It provides access to the automatic outgoing trunk equipment. National Security Information (NSI) - Information that has been determined, pursuant to Executive Order 12958 or any predecessor order, to require protection against unauthorized disclosure. National Security System - Any telecommunications or information system operated by the United States Government, the function, operation, or use of which: (a) involves intelligence activities; (b) involves cryptologic activities related to national security; (c) involves command and control of military forces; (d) involves equipment that is an integral part of a weapon or weapon system; or (e) is critical to the direct fulfillment of military or intelligence missions and does not include a system that is to be used for routine administrative and business applications (including payroll, finance, logistics, and personnel management applications). 40 U.S.C. Section 1452, Information Technology Management Reform Act of 1996. National Security or Emergency Preparedness telecommunications - See NS/EP telecommunications. National Television Standards Committee Standard - See NTSC standard. The North American standard (525-line interlaced raster -scanned video ) for the generation, transmission, and reception of television 308
- 309. signals. Note 1: In the NTSC standard, picture information is transmitted in vestigial- sideband AM and sound information is transmitted in FM. Note 2: In addition to North America, the NTSC standard is used in Central America, a number of South American countries, and some Asian countries, including Japan. Natural Frequency - The natural frequency of an antenna is the lowest frequency at which the antenna resonates without the addition of any inductance or capacitance. Nautical Mile (nmi) - A unit of distance used in navigation and based on the length of one minute of arc taken along a great circle. Note 1: Because the Earth is not a perfect sphere, various values have been assigned to the nautical mile. The value 1852 meters (6076.1 ft.) has been adopted internationally. Note 2: The nautical mile is frequently confused with the geographical mile, which is equal to 1 min of arc on the Earth's equator (6087.15 ft.). Navigate - To move around (a) within a series of Web pages, or (b) among different Web pages, by following hyperlinked paths within each document. Synonyms browsing, surfing. Navigation Assistant - Synonym droid. 1. In the Internet, an intelligent search tool that automatically seeks out relevant online information based on the user 's specifications. Synonyms agent, bot, crawler, hotbot, infobot, information agent, intelligent agent, Internet search engine, knowbot, knowledge robot, personal agent, robotic librarian, search robot, spider, Web crawler, Web spider, wizard. 2. In artificial intelligence, an entity with the ability to sense its environment and to act in such a way or to affect that environment; typically knowledge-based entities that can communicate with each other through some message -passing scheme. Navigator - Synonym droid. 1. In the Internet, a navigator is an intelligent search tool that automatically seeks out relevant online information based on the user 's specifications. Synonyms agent, bot, crawler, hotbot, infobot, information agent, intelligent agent, Internet search engine, knowbot, knowledge robot, personal agent, robotic librarian, search robot, spider, Web crawler, Web spider, wizard. 2. In artificial intelligence, a navigator is an entity with the ability to sense its environment and to act in such a way or to affect that environment; typically knowledge-based entities that can communicate with each other through some message -passing scheme. NBH - Abbreviation for network busy hour. See busy hour. In a communications system, NBH is the sliding 60-minute period during which occurs the maximum total traffic load in a given 24-hour period. Note 1: The busy hour is determined by fitting a horizontal line segment equivalent to one hour under the traffic load curve about the peak load point. Note 2: If the service time interval is less than 60 minutes, the busy hour is the 60-minute interval that contains the service timer interval. Note 3: In cases where more than one busy hour occurs in a 24-hour period, i.e., when saturation occurs, the busy hour or hours most applicable to the particular situation are used. NBRVF - Abbreviation for narrowband radio voice frequency. In narrowband radio, the nominal 3- kHz bandwidth allocated for single channel radio that provides a transmission path for analog and quasi-analog signals. NCC - Abbreviation for National Coordinating Center for Telecommunications. The NCC is the joint telecommunications industry/Federal Government operation established by the National Communications System to assist in the initiation, coordination, restoration, and reconstitution of National Security or Emergency Preparedness (NS/EP) telecommunications services or facilities. NC Code - Abbreviation for network channel (NC) code . NC Code is a code used to identify both switched and nonswitched channel services. Included in this code set are customer options associated with individual channel services, or feature groups and other switched services. 309
- 310. NCI Code - Abbreviation for network channel interface code . An encoded representation used to identify 5 interface elements located at a point of termination ( POT ) at central office or customer location. The interface elements are: total conductors, protocol, impedance, protocol options, and transmission level points. NC (no circuit) - A call disposition category for a call attempt that does not find an available outgoing trunk. NCS - Abbreviation for National Communications System, net control station. 1. The organization established by Section 1(a) of Executive Order No. 12472 to assist the President, the National Security Council, the Director of the Office of Science and Technology Policy, and the Director of the Office of Management and Budget, in the discharge of their national security emergency preparedness telecommunications functions. The NCS consists of both the telecommunications assets of the entities represented on the NCS Committee of Principals and an administrative structure consisting of the Executive Agent, the NCS Committee of Principals, and the Manager. 2. The telecommunications system that results from the technical and operational integration of the separate telecommunications systems of the several executive branch departments and agencies having a significant telecommunications capability. NDUB (network-determined user busy) - A condition of an interface, as determined by the network, based on the network's capability to terminate another call to that interface. The interface is said to be NDUB if any of the following conditions exist: (a) if the maximum number of information channels available has been reached and the network does not support the offering of additional calls beyond this number; (b) if the limit of additional offering had been reached; (c) if the maximum number of total calls supported for User B has been reached. Near Absolute Immunity - Near Absolute Immunity is a central office or similar facility 's ability to maintain continuity of operations without any operationally significant interruption of service from either hardware or software failures in the presence of one or more HEMP ( high-altitude electromagnetic pulse ) events. Near-End Crosstalk - Near-End Crosstalk is Crosstalk that is propagated in a disturbed channel in the direction opposite to the direction of propagation of a signal in the disturbing channel. Note: The terminals of the disturbed channel, at which the near-end crosstalk is present, and the energized terminal of the disturbing channel, are usually near each other. Near Field - Synonym near-field region. Near Field is defined as 1. The close-in region of an antenna wherein the angular field distribution is dependent upon distance from the antenna. Synonym near zone. 2. In optical fiber communications, the region close to a source or aperture. Note: The diffraction pattern in this region typically differs significantly from that observed at infinity and varies with distance from the source. Near-Field Diffraction Pattern - A Near-Field Diffraction Pattern is the diffraction pattern of an electromagnetic wave, which pattern is observed close to a source or aperture, as distinguished from a far- field diffraction pattern. Note: The pattern in the output plane is called the near-field radiation pattern. Synonym Fresnel diffraction pattern. Near-Field Region - A Near-Field Region is defined as 1. The close-in region of an antenna wherein the angular field distribution is dependent upon distance from the antenna. Synonyms near field , near zone . 2. In optical fiber communications , the region close to a source or aperture . Note: The diffraction pattern in this region typically differs significantly from that observed at infinity and varies with distance from the source. Near-Field Scanning - Near-Field Scanning is a technique for measuring the refractive- index profile of an optical fiber by using an extended source to illuminate an endface and measuring the point-by-point radiance at the exit face. 310
- 311. Near Real Time - Near Real Time is defined as 1. Pertaining to the delay introduced, by automated data processing, between the occurrence of an event and the use of the processed data, e.g., for display or feedback and control purposes. Note 1: For example, a near-real- time display depicts an event or situation as it existed at the current time less the processing time. Note 2: The distinction between near real time and real time is somewhat nebulous and must be defined for the situation at hand. 2. Pertaining to the timeliness of data or information which has been delayed by the time required for electronic communication and automatic data processing. This implies that there are no significant delays. Near-Vertical-Incidence Skywave - In radio propagation , Near-Vertical-Incidence Skywave is a wave that is reflected from the ionosphere at a nearly vertical angle and that is used in short-range communications to reduce the area of the skip zone and thereby improve reception beyond the limits of the ground wave. Near Zone - Synonym near-field region. Near Zone is defined as 1. The close-in region of an antenna wherein the angular field distribution is dependent upon distance from the antenna. Synonym near field. 2. In optical fiber communications, the region close to a source or aperture . Note: The diffraction pattern in this region typically differs significantly from that observed at infinity and varies with distance from the source. NEC - Abbreviation for National Electric Code ® - NEC is a standard that governs the use of electrical wire, cable, and fixtures, and electrical and optical communications cable installed in buildings. Note: The NEC was developed by the NEC Committee of the American National Standards Institute ( ANSI ), was sponsored by the National Fire Protection Association (NFPA), and is identified by the description ANSI/NFPA 70-XXXX, the last four digits representing the year of the NEC revision. Necessary Bandwidth -1. For a given class of emission, the width of the frequency band which is just sufficient to ensure the transmission of information at the rate and with the quality required under specified conditions. Note: Emissions useful for the adequate functioning of the receiving equipment, e.g., the emission corresponding to the carrier of reduced carrier systems, must be included in the necessary bandwidth. ( See Annex J of NTIA Manual of Regulations and Procedures for Federal Radio Frequency Management for formulas used to calculate necessary bandwidth.) 2. The calculated spectral width of an emission. Calculations are made using procedures set forth in part 2 of this chapter [of 47CFR ]. The bandwidth so calculated is considered to be the minimum necessary to convey information at the desired rate with the desired accuracy. Need To Know -Need to Know is 1. The legitimate requirement of a person or organization to know, access, or possess sensitive or classified information that is critical to the performance of an authorized, assigned mission. 2. The necessity for access to, or knowledge or possession of, specific information required to carry out official duties. Negation Circuit - Deprecated synonym for inverter. 1. In electrical engineering, a negation circuit is a device for converting direct current into alternating current. 2. In computers, a negation circuit is a device or circuit that inverts the polarity of a signal or pulse. Negative-Acknowledge Character (NAK) - A Negative-Acknowledge Character is a transmission control character sent by a station as a negative response to the station with which the connection has been set up. Note 1: In binary synchronous communication protocol , the NAK is used to indicate that an error was detected in the previously received block and that the receiver is ready to accept retransmission of that block. Note 2: In multipoint systems, the NAK is used as the not-ready reply to a poll. Negative Feedback - See feedback. If the feedback is degenerative (subtractive), it is called " negative feedback ," which reduces the gain and distortion, and increases linearity and stability. Note 1: Feedback may occur inadvertently, and be detrimental. 2. Information returned as a response to an originating source. 311
- 312. Negative Justification - Synonym de-stuffing. Negative justification is the controlled deletion of stuffing bits from a stuffed digital signal, to recover the original signal. Negative Pulse Stuffing - Synonym de-stuffing. Negative Pulse Stuffing is the controlled deletion of stuffing bits from a stuffed digital signal, to recover the original signal. N-Entity - An active element in the n -th layer of the Open Systems Interconnection--Reference Model ( OSI - RM) that (a) interacts directly with elements, i.e. , entities, of the layer immediately above or below the n -th layer, (b) is defined by a unique set of rules, i.e. , syntax, and information formats, including data and control formats, and (c) performs a defined set of functions. Note 1: The n refers to any one of the 7 layers of the OSI-RM. Note 2: In an existing layered open system, the n may refer to any given layer in the system. Note 3: Layers are conventionally numbered from the lowest, i.e., the physical layer, to the highest, so that the n + 1 layer is above the n -th layer and the n - 1 layer is below. NEP - Abbreviation for noise equivalent power. At a given data - signaling rate or modulation frequency , operating wavelength, and effective noise bandwidth, the radiant power that produces a signal-to-noise ratio of unity at the output of a given optical detector. Note 1: Some manufacturers and authors define NEP as the minimum detectable power per square root bandwidth. When defined this way, NEP has the units of watts per ( hertz ) 1/2 . Therefore, the term is a misnomer, because the units of power are watts. Note 2: Some manufacturers define NEP as the radiant power that produces a signal-to-dark-current noise ratio of unity. The NEP measurement is valid only if the dark-current noise dominates the noise level. Neper (Np) - A neper is a unit used to express ratios, such as gain, loss, and relative values. Note 1: The neper is analogous to the decibel, except that the Naperian base 2.718281828. . . is used in computing the ratio in nepers. Note 2: The value in nepers, Np , is given by Np = ln( x 1 / x 2 ), where x 1 and x 2 are the values of interest, and ln is the natural logarithm, i.e., logarithm to the base e. Note 3: One neper (Np) = 8.686 dB, where 8.686 = 20/(ln 10). Note 4: The neper is often used to express voltage and current ratios, whereas the decibel is usually used to express power ratios. Note 5: Like the dB, the Np is a dimensionless unit. Note 6: The ITU recognizes both units. Nested Command Menu - A command menu within another command menu. See command menu. Net - Synonym communications net. - An organization of stations capable of direct communication on a common channel or frequency. Net Browser - Abbreviation for network browser. A computer program for browsing hyperlinked documents (especially on the Web ). Note 1: A network browser formats and displays information so obtained in a form useful to the viewer. Note 2: A network browser may function in a graphical mode or in a text-only mode. Net Control Station (NCS) -1. A radio station that performs net control functions, such as controlling traffic and enforcing operational discipline. 2. A terminal in a secure telecommunications net responsible for distributing key in electronic form to the members of the net. Net Gain - Net Gain is the overall gain of a transmission circuit. Note 1: Net gain is measured by applying a test signal at an appropriate power level (see Note 5) at the input port of a circuit and measuring the power delivered at the output port. The net gain in dB is calculated by taking 10 times the logarithm of the ratio of the output power to the input power. Note 2: The net gain expressed in dB may be positive or negative. Note 3: If the net gain expressed in dB is negative, it is also called the " net loss." Note 4: If the net gain is expressed as a ratio, and the ratio is less than unity, a net loss is indicated. Note 5: The test signal must be chosen so that its power level is within the usual operating range of the circuit being tested. 312
- 313. Netiquette - [Slang] A contraction of network etiquette. The written or unwritten rules of etiquette that govern online interaction between users on the Internet. Note: Some typical rules are a ban on profane or offensive language, a requirement to respect other users, and a ban on floods of unsolicited advertisements. Netiquette rules may be enforced by a moderator or may be self-policed by other users. Net Loss - The overall loss of a transmission circuit. Net Loss Variation - The maximum change in net loss occurring in a specified portion of a communication system during a specified period. Net Operation - The operation of an organization of stations capable of direct communication on a common channel or frequency. Note: Net operations (a) allow participants to conduct ordered conferences among participants who usually have common information needs or related functions to perform, (b) are characterized by adherence to standard formats and procedures, and (c) are responsive to a common supervisory station, called the " net control station," which permits access to the net and maintains net operational discipline. Net Radio Interface (NRI) - An interface between a single- channel radio station (usually in a radio net ) and switched communications systems. NETS - Abbreviation for Nationwide Emergency Telecommunications Service. See Government Emergency Telecommunications Service. Network - A network is the total infrastructure for transmitting phone and/or Internet messages. 1. An interconnection of three or more communicating entities. 2. An interconnection of usually passive electronic components that performs a specific function (which is usually limited in scope), e.g., to simulate a transmission line or to perform a mathematical function such as integration or differentiation. Note: A network may be part of a larger circuit. 3. In television, a communication system consisting of a group of broadcasting stations that all transmit the same programs. (ABC, CBS, NBC) Network Access Point (NAP) - A centralized point where Internet traffic is exchanged or shared. Network Address - The signaling point code, containing for U.S. national networks, the network identification, network cluster, and network cluster member fields (24 bits). Network Administration - A group of network management functions that (a) provide support services, (b) ensure that the network is used efficiently, and (c) ensure prescribed service -quality objectives are met. Note: Network administration may include activities such as network address assignment, assignment of routing protocols and routing table configuration, and directory service configuration. Network Architecture - 1. The design principles, physical configuration, functional organization, operational procedures, and data formats used as the bases for the design, construction, modification, and operation of a communications network. 2. The structure of an existing communications network, including the physical configuration, facilities, operational structure, operational procedures, and the data formats in use. Network Availability - The probability a network can perform its required functions. Network Browser - A computer program for browsing hyperlinked documents (especially on the Web ). Note 1: A network browser formats and displays information so obtained in a form useful to the viewer. Note 2: A network browser may function in a graphical mode or in a text-only mode. 313
- 314. Network Busy Hour (NBH) - See busy hour. In a communications system, the sliding 60-minute period during which occurs the maximum total traffic load in a given 24-hour period. Note 1: The busy hour is determined by fitting a horizontal line segment equivalent to one hour under the traffic load curve about the peak load point. Note 2: If the service time interval is less than 60 minutes, the busy hour is the 60-minute interval that contains the service timer interval. Note 3: In cases where more than one busy hour occurs in a 24-hour period, i.e., when saturation occurs, the busy hour or hours most applicable to the particular situation are used. Network Cluster - The field in the U.S. signaling point code structure that identifies groups of signaling points and individual STPs (signaling transfer points) of a signaling network. Network Computer -1. Synonym thin client. 2. Any computer connected to a network. Network Connectivity - The topological description of a network that specifies, in terms of circuit termination locations and quantities, the interconnection of the transmission nodes. Network Control Program (NCP) - In a switch or network node , software designed to store and forward frames between nodes. Note: An NCP may be used in local area networks or larger networks. Network Data - Data that are specific to the functionality of the network. Network Element Function Block - A functional block that communicates with a telecommunications management network (TMN) for the purpose of being monitored, or controlled, or both. Network Element Location (NE location) - A building (such as a central office ) or nonbuilding location housing NEs. Communication within an NE location may be accomplished with minimal attention to such factors as noise, lightning protection, or the cost of bandwidth; communication outside an NE location uses suitable modems and uses conventional communications services or an EOC ( embedded operations channel ). Network Element (NE) - In integrated services digital networks, a piece of telecommunications equipment that provides support or services to the user. Network Engineering -1. In telephony, the discipline concerned with (a) determining internetworking service requirements for switched networks, and (b) developing and implementing hardware and software to meet them. 2. In computer science, the discipline of hardware and software engineering to accomplish the design goals of a computer network. 3. In radio communications, the discipline concerned with developing network topologies. Network Etiquette (netiquette): See netiquette. The written or unwritten rules of etiquette that govern online interaction between users on the Internet. Note: Some typical rules are a ban on profane or offensive language, a requirement to respect other users, and a ban on floods of unsolicited advertisements. Netiquette rules may be enforced by a moderator or may be self-policed by other users. Network Facility - The connection between the radio port controller and the PCS (personal communications services) switching center. Network Failure - A complete or partial failure of a component or components of a network because of malfunction or natural or human-caused disasters. Partial failures include degradation (and graceful degradation). 314
- 315. Network Failure Triple - A combination of the network 's unservability (U), duration (D), and extent (E) parameters that exceeds a threshold. Network File System (NFS) - See NFS. 1. A file system that is distributed over a computer network. 2. A file system, on a single computer, that contains the low- level networking files for an entire network. Network Identification - The field in the U.S. signaling point code structure that identifies signaling networks. Network Indicator (NI) - Information within the service information octet of the message signal unit that permits discrimination between national and international messages. Network Information Center (NIC) - See NIC. An entity that provides information management, technical support, and administrative services to users of a given network. Note: NICs can form a hierarchy. A specific NIC, designated at the " Internetwork information center" or " InterNIC," has been the authority that assigns the network numbers to the subnetworks that it connects to the Internet. Network Integrity - See network survivability. The (a) ability of a network to maintain or restore an acceptable level of performance during network failures by applying various restoration techniques, and (b) mitigation or prevention of service outages from network failures by applying preventive techniques. Network Interface - 1. The point of interconnection between a user terminal and a private or public network. 2. The point of interconnection between the public switched network and a privately owned terminal. Note: Code of Federal Regulations, Title 47, part 68, stipulates the interface parameters. 3. The point of interconnection between one network and another network. 4. The point of demarcation between the carrier's facilities and the customer installation, which establishes the technical interface and division of operational responsibility. In this definition, the term "customer" refers to the end-user. Network Interface Card (NIC) - See NIC. A network interface device ( NID ) in the form of a circuit card that is installed in an expansion slot of a computer to provide network access. Note: Examples of NICs are cards that interface a computer with an Ethernet LAN and cards that interface a computer with an FDDI ring network. Network Interface Device (NID) - 1. A device that performs interface functions, such as code conversion, protocol conversion, and buffering, required for communications to and from a network. 2. A device used primarily within a local area network (LAN) to allow a number of independent devices, with varying protocols, to communicate with each other. Note 1: An NID converts each device protocol into a common transmission protocol. Note 2: The transmission protocol may be chosen to accommodate directly a number of the devices used within the network without the need for protocol conversion for those devices by the NID. Synonym network interface unit. Network Interface Unit (NIU) - Synonym network interface device. Network Interworking - Cooperation among networks in the processing, management, and creation of services that span multiple networks. Network Inward Dialing (NID) - Synonym direct inward dialing. A service feature that allows inward-directed calls to a PBX to reach a specific PBX extension without human intervention. Network-Launched Application - In a computer networking environment, an application ( program ) that is centrally stored, e.g. , on a server, and copies of which may be accessed on demand by a client and used temporarily ( i.e. , for a single session) by the client ( e.g. , a desktop computer). Note: Multiple clients may make simultaneous use of a given network -launched application. 315
- 316. Network Layer - Layer 3. This layer responds to service requests from the Transport Layer and issues service requests to the Data Link Layer. The Network Layer provides the functional and procedural means of transferring variable length data sequences from a source to a destination via one or more networks while maintaining the quality of service requested by the Transport Layer. The Network Layer performs network routing, flow control, segmentation/desegmentation, and error control functions. See Open Systems Interconnection--Reference Model. Network Layer Relay - A function within the network layer by means of which one correspondent network entity forwards data to another correspondent network entity. Network Loss - Loss added to the network to control echo. Network Management - The execution of the set of functions required for controlling, planning, allocating, deploying, coordinating, and monitoring the resources of a telecommunications network, including performing functions such as initial network planning, frequency allocation, predetermined traffic routing to support load balancing, cryptographic key distribution authorization , configuration management, fault management, security management, performance management, and accounting management. Note: Network management does not include user terminal equipment. Network Manager - In network management, the entity that initiates requests for management information from managed systems or receives spontaneous management-related notifications from managed systems. Network Node (NN) - A grouping of one or more network elements (at one or more sites) which provides network related functions, and is administered as a single entity. A single site may contain more than one network node. For the purpose of this glossary, a network node is considered synonymous with a network element, and is usually at a single site. This restriction simplifies the definition of the network node interface (NNI) and INI, which would not apply between network elements. Network Number - An identification number, within a computer network or set of interconnected networks, that uniquely identifies a computer. Note: Under the Internet protocol system, the network number forms a part of the IP address of each computer in the network. Network Operating System (NOS) - Software that (a) controls a network and its message (e.g., packet) traffic, and queues, (b) controls access by multiple users to network resources such as files, and (c) provides for certain administrative functions, including security. Note 1: A network operating system is most frequently used with local area networks and wide area networks, but could also have application to larger network systems. Note 2: The upper 5 layers of the OSI--Reference Model provide the foundation upon which many network operating systems are based. Network Operation Center (NOC) - A round-the-clock operation where Network engineers monitor and troubleshoot technical equipment and connections. Network Operator - The operator responsible for the development, provision and maintenance of real- time networking services and for operating the corresponding networks. Network Outpulsing State - A call state in which the network transmits the caller's emergency service ID (CESID) to the public service answering point (PSAP) customer installation (CI). Network Outward Dialing (NOD) - Synonym direct outward dialing. An automated PBX service feature that provides for outgoing calls to be dialed directly from the user terminal. 316
- 317. Network Performance - The qualitative level at which a network fulfills its function. Network Provided Number (NPN) - An ISDN number, supplied by the calling user 's or the redirecting user's network , which is associated with the calling user or the redirecting user. It is possible that the NPN may have the same value as the user provided number (UPN) especially in cases where delivery of two calling party numbers is supported. The NPN may also be accompanied by a subaddress. Network Provider - The organization that maintains and operates the network components required for intelligent network (IN) functionality. A network provider may also take more than one role, e.g., also acting as service provider. Network Reliability - See network survivability. The (a) ability of a network to maintain or restore an acceptable level of performance during network failures by applying various restoration techniques, and (b) mitigation or prevention of service outages from network failures by applying preventive techniques. Network Restoration - Automatic or manual methods to return a network to its normal function in response to a network failure. Network Section - The network components that provide a virtual connection between two circuit sections. A network section may be either an access network section or a transit network section. Network Security: Protection of networks and their services from unauthorized modification, destruction, or disclosure. It provides assurance the network performs its critical functions correctly and there are no harmful side-effects. Network Security Architecture - A subset of network architecture specifically addressing security -relevant issues. Network Service Part - The combination of the MTP ( message transfer part ) and the SCCP ( signaling connection control part ). Network Site -1. A collection of functional units that provide network services and that belong to one management domain and are considered as a whole. [2382-pt.35] 2. A specific location that houses telecommunications equipment entities and/or facility terminations at that location, or a specific location that houses administrative operations . A location is usually designated as a network site when it houses one or more network applications. Network Surveillance - A process concerned with surveillance of the network as a whole. It includes activities for coordination and assigning priorities to maintenance actions. The information necessary to support this process comes from alarms, measurements, and indicators of operational (including congestion ) status. Network Side - The side of the network interface or the network functions as seen from the interface. Network Survivability - The (a) ability of a network to maintain or restore an acceptable level of performance during network failures by applying various restoration techniques, and (b) mitigation or prevention of service outages from network failures by applying preventive techniques. Network Survivability Model - The analytical processes for estimating how well network services will be affected and restored with transparencies to the users as a result of a failure. 317
- 318. Network Terminal Number (NTN) - In the ITU-T International X.121 format, the sets of digits that comprise the complete address of the data terminal end point. Note: For an NTN that is not part of a national integrated numbering format, the NTN is the 10 digits of the ITU-T X.25 14- digit address that follow the Data Network Identification Code (DNIC). When part of a national integrated numbering format, the NTN is the 11 digits of the ITU-T X.25 14-digit address that follow the DNIC. Network Terminating Interface (NTI) - Synonym for demarcation point. That point at which operational control or ownership of communications facilities changes from one organizational entity to another. Note: The demarcation point is usually the interface point between customer-premises equipment and external network service provider equipment. Network Termination - Network equipment that provides functions necessary for network operation of ISDN access protocols. Note: Network termination provides functions essential for transmission services. Network Termination 1 (NT1) - In Integrated Services Digital Networks ( ISDN ), a functional grouping of customer-premises equipment that includes functions that may be regarded as belonging to OSI Layer 1, i.e., functions associated with ISDN electrical and physical terminations on the user premises. Note: The NT1 forms a boundary to the network and may be controlled by the provider of the ISDN services. Network Termination 2 (NT2) - In Integrated Services Digital Networks ( ISDN ), an intelligent device that may include functionality for OSI Layers 1 through 3 (dependent on individual systems requirements). Network Topology - The specific physical, i.e., real, or logical, i.e., virtual, arrangement of the elements of a network. Note 1: Two networks have the same topology if the connection configuration is the same, although the networks may differ in physical interconnections, distances between nodes, transmission rates, and/or signal types. Note 2: The common types of network topology are illustrated [refer to the figure on this page] and defined in alphabetical order below: • bus topology: A network topology in which all nodes, i.e., stations, are connected together by a single bus. • fully connected topology: A network topology in which there is a direct path (branch) between any two nodes. Note: In a fully connected network with n nodes, there are n(n-1)/2 direct paths, i.e., branches. Synonym fully connected mesh network. • hybrid topology: A combination of any two or more network topologies. Note 1: Instances can occur where two basic network topologies, when connected together, can still retain the basic network character, and therefore not be a hybrid network. For example, a tree network connected to a tree network is still a tree network. Therefore, a hybrid network accrues only when two basic networks are connected and the resulting network topology fails to meet one of the basic topology definitions. For example, two star networks connected together exhibit hybrid network topologies. Note 2: A hybrid topology always accrues when two different basic network topologies are connected. • linear topology: See bus topology. A network topology in which all nodes, i.e., stations, are connected together by a single bus. • mesh topology: A network topology in which there are at least two nodes with two or more paths between them. • ring topology: A network topology in which every node has exactly two branches connected to it. • star topology: A network topology in which peripheral nodes are connected to a central node, which rebroadcasts all transmissions received from any peripheral node to all peripheral nodes on the network, including the originating node. Note 1: All peripheral nodes may thus communicate with all others by transmitting to, and receiving from, the central node only. Note 2: The failure of a transmission line, i.e., channel, linking any peripheral node to the central node will result in the isolation of that peripheral node from all others. Note 3: If the star central node is passive, the 318
- 319. originating node must be able to tolerate the reception of an echo of its own transmission, delayed by the two-way transmission time, i.e., to and from the central node, plus any delay generated in the central node. An active star network has an active central node that usually has the means to prevent echo-related problems. • tree topology: A network topology that, from a purely topologic viewpoint, resembles an interconnection of star networks in that individual peripheral nodes are required to transmit to and receive from one other node only, toward a central node, and are not required to act as repeaters or regenerators. Note 1: The function of the central node may be distributed. Note 2: As in the conventional star network, individual nodes may thus still be isolated from the network by a single- point failure of a transmission path to the node. Note 3: A single-point failure of a transmission path within a distributed node will result in partitioning two or more stations from the rest of the network. Network Trusted Computing Base (NTCB) - The totality of protection mechanisms within a network, including hardware, firmware, and software, the combination of which is responsible for enforcing a security policy. Network Utility - An internetwork administrative signaling mechanism in the call control procedure between packet switching public data networks. Network Weaving -1. In computer security, a penetration technique in which different communication networks are used to gain access to a data processing system to avoid detection and trace-back. 2. A penetration technique in which different communication networks are linked to access an information system (IS) to avoid detection and trace-back. Neutral -1. In ac power distribution, the conductor that (a) is intentionally grounded on the supply side of the service disconnect and (b) provides a current return path for ac power currents. 2. In three- phase ac "Y," i.e., wye, power distribution, the low-potential fourth wire that conducts only that current required to achieve electrical balance, i.e., to provide a return path for any current imbalance among the three phases. Neutral Direct-Current Telegraph System - A telegraph system in which (a) current flows during marking intervals and no current flows during spacing intervals for the transmission of signals over a line, and (b) the direction of current flow is immaterial. Synonyms single-current system, single-current transmission system, single-Morse system. Neutral Ground - An intentional ground applied to the neutral conductor or neutral point of a circuit, transformer, machine, apparatus, or system. Neutral Operation - A method of teletypewriter operation in which marking signals are formed by current pulses of one polarity, either positive or negative, and spacing signals are formed by reducing the current to zero or nearly zero. Neutral Relay - A relay in which the direction of movement of the armature does not depend upon the direction of the current in the circuit controlling the armature. New Customer Premises Equipment - All customer premises equipment not in service or in the inventory of a regulated telephone utility as of December 31, 1982. News Client - Synonym newsreader. A local software application ( client program ) that provides access by means of which a user may view one or more forums or newsgroups from one or more news servers. Note: Most newsreaders format and display information from the server in a form suitable to the user. 319
- 320. Newsfeed - Information distributed by a computer , e.g., one operated by an Internet service provider that maintains current articles within selected groups. Newsgroup - A discussion group in which you can leave messages for others to read on UseNet. Newsreader - A local software application ( client program ) that provides access by means of which a user may view one or more forums or newsgroups from one or more news servers. Note: Most newsreaders format and display information from the server in a form suitable to the user.Synonym news client. News Server - A server on a network that stores, organizes, and distributes messages for selected newsgroups. NF - Abbreviation for noise figure. Of an active device, over the bandwidth of interest, the contribution by the device itself to thermal noise at its output. The noise figure is usually expressed in decibels ( dB ), and is with respect to thermal noise power at the system impedance, at a standard noise temperature (usually 20 o C, 293 K) over the bandwidth of interest. It is determined by (a) measuring (determining) the ratio, usually expressed in dB, of the thermal noise power at the output, to that at the input, and (b) subtracting from that result, the gain, in dB, of the system. Typical noise figures range from 0.5 dB for very low noise devices, to 4 to 8 dB. In some systems, e.g., heterodyne systems, total output noise power includes noise from other than thermal sources, such as spurious contributions from image - frequency transformation, but noise from these sources is not considered in determining the noise figure. In this example, the noise figure is determined only with respect to that noise that appears in the output via the principal frequency transformation of the system, and excludes noise that appears via the image frequency transformation. NFS - Abbreviation for network file system. 1. A file system that is distributed over a computer network . 2. A file system, on a single computer, that contains the low- level networking files for an entire network. n -function - A defined action performed by an n -entity. Note: An n -function may be (a) a single action, i.e., a primitive function, or (b) a set of actions. 950 + WXXX - A carrier access code for obtaining switched access to interchange carriers where (a) the calling customer accesses the IC and passes the address information, if any, in two distinct operations; (b) the calling customer usually uses in-band signals to pass the address, if any, to the IC; and (c) the EC does not repeat the address information. Note: The X digits in WXXX are the carrier identification code for the IC, and W is 0 or 1. Nibble - Part of a byte, usually half of a byte. NIC -1. Abbreviation for network interface card. A network interface device ( NID ) in the form of a circuit card that is installed in an expansion slot of a computer to provide network access. Note: Examples of NICs are cards that interface a computer with an Ethernet LAN and cards that interface a computer with an FDDI ring network. 2. Abbreviation for network information center. An entity that provides information management, technical support, and administrative services to users of a given network. Note: NICs can form a hierarchy. A specific NIC, designated at the " Internetwork information center" or " InterNIC," has been the authority that assigns the network numbers to the subnetworks that it connects to the Internet. NID - Network Interface Device - A device used within a local area network, which allows a number of independent devices (computers, modems, etc.) to communicate with one another. Also, a device usually mounted on the outside of the customer's home that connects the customer's inside wiring to the telephone company's wiring and protects the customer's phone equipment from lightning and any large rise or fall in electricity. 320
- 321. NII (National Information Infrastructure) - A proposed, advanced, seamless web of public and private communications networks, interactive services, interoperable hardware and software, computers, databases, and consumer electronics to put vast amounts of information at users' fingertips. Note: NII includes more than just the physical facilities (more than the cameras, scanners, keyboards, telephones, fax machines, computers, switches, compact disks, video and audio tape, cable, wire, satellites, optical fiber transmission lines, microwave nets, switches, televisions, monitors, and printers) used to transmit, store, process, and display voice, data, and images; it encompasses a wide range of interactive functions, user- tailored services, and multimedia databases that are interconnected in a technology-neutral manner that will favor no one industry over any other. Synonym information superhighway. Nine-Hundred (900) Service - A telephone service via which the caller may access information on a charge- per- call or charge-per- time basis. NIU - Abbreviation for network interface unit. See network interface device. 1. A device that performs interface functions, such as code conversion, protocol conversion, and buffering, required for communications to and from a network. 2. A device used primarily within a local area network ( LAN ) to allow a number of independent devices, with varying protocols, to communicate with each other. Note 1: An NID converts each device protocol into a common transmission protocol. Note 2: The transmission protocol may be chosen to accommodate directly a number of the devices used within the network without the need for protocol conversion for those devices by the NID. Nmap - A security -violating, network - scanning tool that can scan a network using a variety of protocols, can operate in stealth mode, and can automatically identify remote operating systems. NMI - Abbreviation for nautical mile. A unit of distance used in navigation and based on the length of one minute of arc taken along a great circle. Note 1: Because the Earth is not a perfect sphere, various values have been assigned to the nautical mile. The value 1852 meters (6076.1 ft.) has been adopted internationally. Note 2: The nautical mile is frequently confused with the geographical mile, which is equal to 1 min of arc on the Earth's equator (6087.15 ft.). NNTP - Abbreviation for network news transfer protocol. An application protocol that provides the means to transfer files for computer conferences. NOC - See Network Operation Center A centralized organization responsible for the operation and maintenance of its network. No Circuit Double Prime (NC") - An SIT ( special information tone ) classification for call attempts that fail to find an available long distance service provider outgoing trunk. No Circuit (NC) - A call -disposition category for a call attempt that does not find an available outgoing trunk. No Circuit Prime (NC') - An SIT ( special information tone ) classification for call attempts that fail to find an available Local Service Provider outgoing trunk. NOD - Acronym for network outward dialing. An automated PBX service feature that provides for outgoing calls to be dialed directly from the user terminal. Nodal Clock - The principal clock or alternate clock located at a particular node that provides the timing reference for all major functions at that node. Nodal Point - Synonym node. 321
- 322. Node - 1. In network topology, a terminal of any branch of a network or an interconnection common to two or more branches of a network. Synonyms junction point, nodal point. 2. In a switched network, one of the switches forming the network backbone. Note: A node may also include patching and control facilities. 3. A technical control facility (TCF). 4. A point in a standing or stationary wave at which the amplitude is a minimum. In this sense, synonym null. Noise - 1. An undesired disturbance within the frequency band of interest; the summation of unwanted or disturbing energy introduced into a communications system from man-made and natural sources. 2. A disturbance that affects a signal and that may distort the information carried by the signal. 3. Random variations of one or more characteristics of any entity such as voltage, current, or data. 4. A random signal of known statistical properties of amplitude, distribution, and spectral density. 5. Loosely, any disturbance tending to interfere with the normal operation of a device or system. Noise Current -1. Interfering and unwanted electrical currents in a device or system. 2. In optical communications, the rms component of the optical detector output electrical current with no incoming signal present. Noise Equivalent Power (NEP) - At a given data - signaling rate or modulation frequency, operating wavelength, and effective noise bandwidth, the radiant power that produces a signal-to-noise ratio of unity at the output of a given optical detector. Note 1: Some manufacturers and authors define NEP as the minimum detectable power per square root bandwidth. When defined this way, NEP has the units of watts per ( hertz ) 1/2 . Therefore, the term is a misnomer, because the units of power are watts. Note 2: Some manufacturers define NEP as the radiant power that produces a signal-to-dark-current noise ratio of unity. The NEP measurement is valid only if the dark-current noise dominates the noise level. Noise Factor - Synonym noise figure. Of an active device, over the bandwidth of interest, the contribution by the device itself to thermal noise at its output. The noise figure is usually expressed in decibels ( dB ), and is with respect to thermal noise power at the system impedance, at a standard noise temperature (usually 20 o C, 293 K) over the bandwidth of interest. It is determined by (a) measuring (determining) the ratio, usually expressed in dB, of the thermal noise power at the output, to that at the input, and (b) subtracting from that result, the gain, in dB, of the system. Typical noise figures range from 0.5 dB for very low noise devices, to 4 to 8 dB. In some systems, e.g., heterodyne systems, total output noise power includes noise from other than thermal sources, such as spurious contributions from image - frequency transformation, but noise from these sources is not considered in determining the noise figure. In this example, the noise figure is determined only with respect to that noise that appears in the output via the principal frequency transformation of the system, and excludes noise that appears via the image frequency transformation. Noise Field - An indication of the level of background noise that the terminating end-point may play out in the absence of packets. Noise Figure (NF) - Of an active device, over the bandwidth of interest, the contribution by the device itself to thermal noise at its output. The noise figure is usually expressed in decibels ( dB ), and is with respect to thermal noise power at the system impedance, at a standard noise temperature (usually 20 o C, 293 K) over the bandwidth of interest. It is determined by (a) measuring (determining) the ratio, usually expressed in dB, of the thermal noise power at the output, to that at the input, and (b) subtracting from that result, the gain, in dB, of the system. Typical noise figures range from 0.5 dB for very low noise devices, to 4 to 8 dB. In some systems, e.g., heterodyne systems, total output noise power includes noise from other than thermal sources, such as spurious contributions from image - frequency transformation, but noise from these sources is not considered in determining the noise figure. In this example, the noise figure is determined only with respect to that noise that appears in the output via the principal frequency transformation of the system, and excludes noise that appears via the image frequency transformation. Synonym noise factor. 322
- 323. Noise Level - The noise power, usually relative to a reference. Note: Noise level is usually measured in dB for relative power or picowatts for absolute power. A suffix is added to denote a particular reference base or specific qualities of the measurement. Examples of noise-level measurement units are dBa, dBa(F1A), dBa(HA1), dBa0, dB, dBm(psoph), dBm0, dBm0P, dBrn, dBrnC, dBrn( f 1 -f 2 ), dBrn(144-line), pW, pWp , and pWp0. Noise Power - 1. The power generated by a random electromagnetic process. 2. Interfering and unwanted power in an electrical device or system. 3. In the acceptance testing of radio transmitters, the mean power supplied to the antenna transmission line by a radio transmitter when loaded with noise having a Gaussian amplitude-vs.- frequency distribution. Noise Power Density - The noise power in a bandwidth of 1 Hz, i.e. , the noise power per hertz at a point in a noise spectrum. Note: The noise-power density of the internal noise that is contributed by a receiving system to an incoming signal is expressed as the product of Boltzmann's constant, k, and the equivalent noise temperature, T n . Thus, the noise- power density is often expressed simply as k T . Synonym k T . Noise Suppression -1. Reduction of the noise power level in electrical circuits. 2. The process of automatically reducing the noise output of a receiver during periods when no carrier is being received. Noise Temperature - At a pair of terminals, the temperature of a passive system having an available noise power per unit bandwidth at a specified frequency equal to that of the actual terminals of a network. Note: The noise temperature of a simple resistor is the actual temperature of that resistor. The noise temperature of a diode may be many times the actual temperature of the diode. Noise Voltage -1. Interfering and unwanted voltage in an electronic device or system. 2. In optical communications, the rms component of the optical detector output electrical voltage with no incoming signal present. Noise Weighting - A specific amplitude-vs.-frequency characteristic that permits a measuring set to give numerical readings that approximate the interfering effects to any listener using a particular class of telephone instrument. Note 1: Noise weighting measurements are made in lines terminated either by the measuring set or the class of instrument. Note 2: The most widely used noise weightings were established by agencies concerned with public telephone service, and are based on characteristics of specific commercial telephone instruments, representing successive stages of technological development. The coding of commercial apparatus appears in the nomenclature of certain weightings. The same weighting nomenclature and units are used in military versions of commercial noise measuring sets. Noise Window - A notch, i.e., a dip, in the noise frequency spectrum characteristic of a device, such as a transmitter, receiver, channel, or amplifier, from external sources or internal sources. Note: The noise window is usually represented as a band of lower amplitude noise in a wider band of higher amplitude noise. Noisy Black -1. In facsimile or display systems, such as television, a nonuniformity in the black area of the image, i.e., document or picture, caused by the presence of noise in the received signal. 2. A signal or signal level that is supposed to represent a black area on the object, but has a noise content sufficient to cause the creation of noticeable white spots on the display surface or record medium. Noisy White -1. In facsimile or display systems, such as television , a nonuniformity in the white area of the image , i.e., , document or picture , caused by the presence of noise in the received signal . 2. A signal or signal level that is supposed to represent a white area on the object, but has a noise content sufficient to cause the creation of noticeable black spots on the display surface or record medium . 323
- 324. No-lone Zone - An Area, room, or space that, when staffed, must be occupied by two or more appropriately cleared individuals who remain within sight of each other. Nominal Bandwidth - The widest band of frequencies, inclusive of guard bands, assigned to a channel. Note: Nominal bandwidth should not be confused with the terms " necessary bandwidth," " occupied bandwidth," or " rf bandwidth." Nominal Bit Stuffing Rate - The rate at which stuffing bits are inserted when both the input and output bit rates are at their nominal values. Nominal Linewidth - In facsimile systems, the average separation between centers of adjacent scanning or recording lines. Nonassociated Common-Channel Signaling - A form of common-channel signaling where the signaling channel serves one or more trunk groups, at least one of which terminates at a point other than the signal transfer point at which the signaling channel terminates. Nonassociated Mode Of Signaling - The signaling mode in which messages involving two (nonadjacent) signaling points are communicated between them over two or more signaling links in tandem passing through one or more signaling transfer points other than those which are the origin and destination of the messages. Nonblocking Switch - A switch that has enough paths across it that an originated call can always reach an available line without encountering a busy condition. Non-Call Associated Signaling (NCAS) - Signaling that is independent of an end-to-end bearer connection, including support for the functions of registration, authentication, and validation. Nonce - In cryptography, a time - variant parameter, such as a counter or a time stamp, that is used in key management protocols to prevent message replay and other types of attacks. Noncentralized Operation - Operation that uses a control discipline for multipoint data communication links in which transmission may be between tributary stations or between the control station and tributary stations. Noncircularity - Synonym ovality. 1. The attribute of an optical fiber, the cross section of the core or cladding of which deviates from a perfect circle. 2. In an optical fiber, the degree of deviation, from perfect circularity, of the cross section of the core or cladding. Note 1: The cross sections of the core and cladding are assumed to first approximation to be elliptical. Quantitatively, the ovality of either the core or cladding is expressed as 2( a - b )/( a + b ), where a is the length of the major axis and b is the length of the minor axis. The dimensionless quantity so obtained may be multiplied by 100 to express ovality as a percentage. Note 2: Alternatively, ovality of the core or cladding may be expressed or specified by a tolerance field consisting of two concentric circles, within which the cross section boundaries must lie. Noncooperative Remote Rekeying - Synonym automatic remote rekeying. A procedure to rekey a distant crypto-equipment electronically without specific actions by the receiving terminal operator. Noncritical Technical Load - Of the total technical load at a facility during normal operation, the part that is not required for synchronous operation. 324
- 325. Nonerasable Storage - Synonym read-only memory. A memory in which data, under normal conditions, can only be read. Non-Fixed Access - In personal communications service ( PCS ), terminal access to a network in which there is no set relationship between a terminal and the access interface. Note: The access interface and the terminal each has its own separate "identifiers." The terminal may be moved from one access interface to another while maintaining the terminal's unique identity. Nonlinear Distortion - Distortion caused by a deviation from a linear relationship between specified input and output parameters of a system or component. Nonlinear Scattering - Direct conversion of a photon from one wavelength to one or more other wavelengths. Note 1: In an optical fiber, nonlinear scattering is usually not important below the threshold irradiance for stimulated nonlinear scattering. Note 2: Examples of nonlinear scattering are Raman and Brillouin scattering. Non-Listed Numbers - Specialized Directory Listings not listed in the phone book but are available through Directory Assistance. Nonloaded Twisted Pair - A twisted pair that has no intentionally added inductance. Nonoperational Load - Administrative, support, and housing power requirements. Non-Published Numbers - Specialized Directory Listings not available in the phone book or through Directory Assistance. Non-Repeated Video Frame (active frame) - See active video frame identification. The process of comparing each output video frame with its preceding frame(s) in sequence and quantifying the extent of correspondence between each pair; when there is limited correspondence between a pair of frames (such that the differences measured are distinguishable from the measurement noise ), and the corresponding input sequence of frames possesses distinguishable differences, then the current frame is categorized as an active frame. Nonrepudiation -1. The capability, in security systems, that guarantees that a message or data can be proven to have originated from a specific person. 2. Assurance the sender of data is provided with proof of delivery and the recipient is provided with proof of the sender's identity, so neither can later deny having processed the data. Nonresonant Antenna - Synonym aperiodic antenna. An antenna designed to have an approximately constant input impedance over a wide range of frequencies. Note: Examples of aperiodic antennas include terminated rhombic antennas and wave antennas. Non-Return-To-Zero (NRZ) - A code in which "1s" are represented by one significant condition and "0s" are represented by another, with no neutral or rest condition, such as a zero amplitude in amplitude modulation (AM), zero phase shift in phase-shift keying ( PSK ), or mid- frequency in frequency-shift keying ( FSK ). Note: For a given data signaling rate, i.e., bit rate, the NRZ code requires only one-half the bandwidth required by the Manchester code. Non-Return-To-Zero Change-On-Ones (NRZ1) - A code in which "1s" are represented by a change in a significant condition and "0s" are represented by no change. 325
- 326. Non-Return-To-Zero Mark (NRZ-M) - A binary encoding scheme in which a signal parameter, such as electric current or voltage, undergoes a change in a significant condition or level every time that a "one" occurs, but when a "zero" occurs, it remains the same, i.e. , no transition occurs. Note 1: The transitions could also occur only when "zeros" occur and not when "ones" occur. If the significant condition transition occurs on each "zero," the encoding scheme is called " non-return-to-zero space " ( NRZ -S). Note 2: NRZ-M and NRZ-S signals are technically interchangeable; i.e., one is the logical "NOT" (inverse) of the other. It is necessary for the receiver to have prior knowledge of which scheme is being used. Without such knowledge, it is impossible for the receiver to interpret the data stream correctly; i.e., its output may be the correct data stream or the logical inverse of the correct data stream. Synonyms conditioned baseband representation, differentially encoded baseband, non-return-to-zero one. Non-Return-To-Zero One (NRZ-1) - Synonym non-return-to-zero mark. Non-Return-To-Zero Space (NRZ-S) - A binary encoding scheme in which a signal parameter, such as electric current or voltage, undergoes a change in a significant condition or level every time that a "zero" occurs, but when a "one" occurs, it remains the same, i.e. , no transition occurs. Note 1: The transitions could also occur only when "ones" occur and not when "zeros" occur. If the significant condition transition occurs on each "one," the encoding scheme is called "non-return to zero mark " ( NRZ-M ). Note 2: NRZ-S and NRZ-M signals are technically interchangeable; i.e., one is the logical "NOT" (inverse) of the other. It is necessary for the receiver to have prior knowledge of which scheme is being used. Without such knowledge, it is impossible for the receiver to interpret the data stream correctly; i.e., its output may be the correct data stream or the logical inverse of the correct data stream. Synonym non-return-to-zero. Nonsecret Encryption - Synonym public key cryptography. The type of cryptography in which the encryption process is publicly available and unprotected, but in which a part of the decryption key is protected so that only a party with knowledge of both parts of the decryption process can decrypt the cipher text. Note: Commonly called non-secret encryption in professional cryptologic circles. FIREFLY is an application of public key cryptography. 2. An Encryption system using a linked pair of keys. What one pair of keys encrypts, the other pair decrypts. Nonshifted Fiber - Synonym dispersion-unshifted fiber. A single-mode optical fiber that has a nominal zero- dispersion wavelength in the 1.3- m transmission window. Nonsynchronous Data Transmission Channel - A data transmission channel in which separate timing information is not transferred between the data terminal equipment ( DTE ) and the data circuit terminating equipment ( DCE ). Nonsynchronous Network - Synonym asynchronous network. A network in which the clocks do not need to be synchronous or mesochronous. Nonsynchronous System - See asynchronous transmission. Data transmission in which the instant that each character , or block of characters, starts is arbitrary; once started, the time of occurrence of each signal representing a bit within the character, or block, has the same relationship to significant instants of a fixed time frame. Nonsynchronous Transmission - See asynchronous transmission. Data transmission in which the instant that each character , or block of characters, starts is arbitrary; once started, the time of occurrence of each signal representing a bit within the character, or block, has the same relationship to significant instants of a fixed time frame. Nontechnical Load - Of the total operational load at a facility during normal operation, the part used for support purposes, such as general lighting, heating, air-conditioning, and ventilating equipment. 326
- 327. Non-Transparent Loopback - A loopback in which the signal transmitted beyond the loopback point (the forward signal ) when the loopback is activated, is not the same as the received signal at the loopback point. The forward signal may be a defined signal or unspecified. Nontransparent Mode - A mode of operating a data transmission system in which control characters are treated and interpreted as such, rather than simply as data or text bits in a bit. Normal/Alarm (N/A) State Bit - A bit used in signaling packets to transfer information on alarm status across a permanent virtual circuit in the direction of transmission from the channelized side to the packetized side. The N/A bit set to 0 indicates normal operation. The N/A bit set to 1 indicates the existence of an alarm on the channelized access facility or error condition on the permanent virtual circuit. Normalized Frequency (V) -1. In an optical fiber, a dimensionless quantity 2. The ratio between an actual frequency and a reference value. 3. The ratio between an actual frequency and its nominal value. Normal Mode (Application Layer) - The mode of ACSE (association control service element) operation that results in the transfer of ACSE semantics, using the presentation service. Normal Mode (Presentation Layer) - The mode of operation of the Presentation Layer, which provides the full facilities of the presentation service. Normal Resolution Still Image - A still image transmitted in the ANSI Tl.314 video stream encoded to the same resolution as the previous motion video ( i.e., QCIF— quarter common intermediate format ). Note: This mode uses a bit 2 "document camera indicator." Normal Routing - The routing of a given signaling traffic stream under normal conditions (in the absence of failures). NORM state - A state that exists on a permanent virtual circuit connection when there are no alarm conditions on either the originating or terminating endpoints. The absence of alarms must be satisfied on both the channelized side and the packetized side. During the NORM state, signaling packets have their normal alarm (N/A) bit set to 0. North American Number Plan (NANP) - A plan for the allocation of unique 10- digit address numbers. The numbers consists of a 3-digit area ( numbering plan area ) code, a 3-digit office code, and a 4-digit line number. The plan also extends to format variations ( e.g., 3-digit and 7-digit address), prefixes ( e.g. , 1, 0, 01, and 011), and special code applications ( e.g., service access codes). Notarization - A method of changing a key -enciphering key so as to confirm the identities of the originator and the ultimate recipient. Notch - In a relatively wide band of frequencies, not necessarily of uniform amplitude, a narrow band of frequencies having relatively low amplitudes Notched Filter - Synonym band-stop filter. - A filter that attenuates, usually to very low levels, all frequencies between two non-zero, finite limits and passes all frequencies not within the limits. Note: A band-stop filter may be designed to stop the specified band of frequencies but usually only attenuates them below some specified level. Notched Noise - Noise from which a narrow band of frequencies has been removed. Note: Notched noise is usually used for testing devices or circuits. 327
- 328. Not-Ready Condition - At the data terminal equipment / data circuit-terminating equipment ( DTE / DCE ) interface , a steady-state condition that indicates that the DCE is not ready to accept a call -request signal or that the DTE is not ready to accept an incoming call. Np - Abbreviation for neper. A unit used to express ratios, such as gain, loss, and relative values. Note 1: The neper is analogous to the decibel, except that the Naperian base 2.718281828. . . is used in computing the ratio in nepers. Note 2: The value in nepers, Np , is given by Np = ln( x 1 / x 2 ), where x 1 and x 2 are the values of interest, and ln is the natural logarithm, i.e., logarithm to the base e. Note 3: One neper (Np) = 8.686 dB, where 8.686 = 20/(ln 10). Note 4: The neper is often used to express voltage and current ratios, whereas the decibel is usually used to express power ratios. Note 5: Like the dB, the Np is a dimensionless unit. Note 6: The ITU recognizes both units. NPA - Abbreviation for numbering plan area. A defined geographic area identified by a unique three- digit code used in the North American Number Plan Area. NRI - Abbreviation for net radio interface. An interface between a single- channel radio station (usually in a radio net ) and switched communications systems. NRZ - Abbreviation for non-return-to-zero. A code in which "1s" are represented by one significant condition and "0s" are represented by another, with no neutral or rest condition, such as a zero amplitude in amplitude modulation (AM), zero phase shift in phase-shift keying ( PSK ), or mid- frequency in frequency- shift keying ( FSK ). NRZ-M - Synonym non-return-to-zero mark. A binary encoding scheme in which a signal parameter, such as electric current or voltage, undergoes a change in a significant condition or level every time that a "one" occurs, but when a "zero" occurs, it remains the same, i.e. , no transition occurs. Note 1: The transitions could also occur only when "zeros" occur and not when "ones" occur. If the significant condition transition occurs on each "zero," the encoding scheme is called " non-return-to-zero space " ( NRZ -S). Note 2: NRZ-M and NRZ-S signals are technically interchangeable; i.e., one is the logical "NOT" (inverse) of the other. It is necessary for the receiver to have prior knowledge of which scheme is being used. Without such knowledge, it is impossible for the receiver to interpret the data stream correctly; i.e., its output may be the correct data stream or the logical inverse of the correct data stream. NS/EP telecommunications - Abbreviation for National Security or Emergency Preparedness telecommunications. Telecommunications services that are used to maintain a state of readiness or to respond to and manage any event or crisis (local, national, or international) that causes or could cause injury or harm to the population, damage to or loss of property, or degrade or threaten the national security or emergency preparedness posture of the United States. n-Sequence - A pseudorandom binary sequence of n bits that (a) is the output of a linear shift register and (b) has the property that, if the shift register is set to any nonzero state and then cycled, a pseudorandom binary sequence of a maximum of n = 2 m -1 bits will be generated, where m is the number of stages, i.e. , the number of bit positions in the register, before the shift register returns to its original state and the n -bit output sequence repeats. Note: The register may be used to control the sequence of frequencies for a frequency-hopping spread spectrum transmission system. NSFnet - The high-speed national network that superseded ARPA Net as the framework of the Internet. Note: NSFnet was created under the auspices of the National Science Foundation. NTI - Abbreviation for network terminating interface. That point at which operational control or ownership of communications facilities changes from one organizational entity to another. Note: The demarcation point 328
- 329. is usually the interface point between customer-premises equipment and external network service provider equipment. NTIA - Abbreviation for National Telecommunications and Information Administration. The President's principal adviser on telecommunications and information policy issues. NTN - Abbreviation for network terminal number. In the ITU-T International X.121 format, the sets of digits that comprise the complete address of the data terminal end point. Note: For an NTN that is not part of a national integrated numbering format, the NTN is the 10 digits of the ITU-T X.25 14- digit address that follow the Data Network Identification Code (DNIC). When part of a national integrated numbering format, the NTN is the 11 digits of the ITU-T X.25 14-digit address that follow the DNIC. NTSC - Abbreviation for National Television Systems Committee. This is the name of the current analog transmission standard used in the U.S., which the committee created in 1953. NTSC standard - Abbreviation for National Television Standards Committee standard. The North American standard (525-line interlaced raster -scanned video ) for the generation, transmission, and reception of television signals. Note 1: In the NTSC standard, picture information is transmitted in vestigial- sideband AM and sound information is transmitted in FM. Note 2: In addition to North America, the NTSC standard is used in Central America, a number of South American countries, and some Asian countries, including Japan. NTSC Tuner - A device built in to a TV set that allows reception of analog broadcasting. Nuclear Hardness -1. An expression of the extent to which the performance of a system, facility, or device is expected to degrade in a given nuclear environment. 2. The physical attributes of a system or component that will allow survival in an environment that includes nuclear radiation and electromagnetic impulses ( EMI ). Note 1: Nuclear hardness may be expressed in terms of either susceptibility or vulnerability. Note 2: The extent of expected performance degradation ( e.g., outage time, data lost, and equipment damage) must be defined or specified. The environment ( e.g., radiation levels, overpressure, peak velocities, energy absorbed, and electrical stress) must be defined or specified. 3. The physical attributes of a system or component that will allow a defined degree of survivability in a given environment created by a nuclear weapon. Note: Nuclear hardness is determined for specified or actual quantified environmental conditions and physical parameters, such as peak radiation levels, overpressure, velocities, energy absorbed, and electrical stress. It is achieved through design specifications and is verified by test and analysis techniques. Null -1. In an antenna radiation pattern, a zone in which the effective radiated power is at a minimum relative to the maximum effective radiated power of the main beam. Note 1: A null often has a narrow directivity angle compared to that of the main beam. Thus, the null is useful for several purposes, such as radio navigation and suppression of interfering signals in a given direction. Note 2: Because there is reciprocity between the transmitting and receiving characteristics of an antenna, there will be corresponding nulls for both the transmitting and receiving functions. 2. A dummy letter, letter symbol, or code group inserted in an encrypted message to delay or prevent its solution, or to complete encrypted groups for transmission or transmission security purposes. 3. In database management systems, a special value assigned to a row or a column indicating either unknown values or inapplicable usage. 4. Synonym node. Null Character (NUL) - In transmission systems, a control character (a) that is used to accomplish media-fill stuffing or a time-fill stuffing in storage device or in a data transmission line and (b) that may be inserted and removed from a series of characters without affecting the meaning of the series. Note: The null character may affect the control of equipment or the format of messages. Numbering Plan Area (NPA) - A defined geographic area identified by a unique three- digit code used in the North American Number Plan Area. Note 1: Defined geographic area could mean the entire area 329
- 330. encompassed by the North American Numbering Plan Area (for 800, 888, 877 codes, etc.). Note 2: By virtue of the overlay concept deployed in some states, there may be two (or more) NPAs assigned to the same defined geographic area. Numerical Aperture (NA) - 1. The sine of the vertex angle of the largest cone of meridional rays that can enter or leave an optical system or element, multiplied by the refractive index of the medium in which the vertex of the cone is located. Note: The NA is generally measured with respect to an object or image point and will vary as that point is moved. 2. For an optical fiber in which the refractive index decreases monotonically from n 1 on the axis to n 2 in the cladding, an expression of the extent of the fiber's ability to 2 2 ½ accept, in its bound modes, non-normal incident rays, given by NA = (n 1 -n 2 ) . Note: In multimode fibers, the term equilibrium numerical aperture is sometimes used. This refers to the numerical aperture with respect to the extreme exit angle of a ray emerging from a fiber in which equilibrium mode distribution has been established. 3. Loosely, the sine of the radiation or acceptance angle of an optical fiber, multiplied by the refractive index of the material in contact with the exit or entrance face. Note: This usage is approximate and imprecise, but is often encountered. Numerical Aperture Loss - A loss of optical power that occurs at a splice or a pair of mated connectors when the numerical aperture of the "transmitting" fiber exceeds that of the "receiving" fiber, even if the cores are precisely the same diameter and are perfectly aligned. Note 1: The higher numerical aperture of the transmitting fiber means that it emits a larger cone of light than the receiving fiber is capable of accepting, resulting in a coupling loss. Note 2: In the opposite case of numerical aperture mismatch, where the transmitting fiber has the lower numerical aperture, no numerical aperture loss occurs, because the receiving fiber is capable of accepting light from any bound mode of the transmitting fiber. n -Unit Code - A code in which the signals or groups of digits that represent coded items, such as characters, have the same number of signal elements or digits, namely n elements or digits, where n may be any positive integer. Note: An example of an n -unit code is the 7-unit code (8-unit with parity ) ASCII code. Each character is represented by a pattern of 7 binary digits. The units may also be characters or other special signs. n -User - In the ISO Open Systems Interconnection--Reference Model ( OSI--RM ), an n +1 entity that uses the services of the n - layer, and below, to communicate with another n +1 entity. Note: If n identifies a specific or a reference level, the n +1 layer is the layer above the n layer and the n -1 layer is the layer below the n layer. Thus, the n +2 layer is two layers above the n layer. NVIS - Abbreviation for near-vertical-incidence skywave. In radio propagation , a wave that is reflected from the ionosphere at a nearly vertical angle and that is used in short-range communications to reduce the area of the skip zone and thereby improve reception beyond the limits of the ground wave. NXX Code - In the North American direct distance dialing numbering plan, a central office code of three digits that designates a particular central office or a given 10,000-line unit of subscriber lines; "N" is any number from 2 to 9, and "X" is any number from 0 to 9. Nyquist Interval - The maximum time interval between equally spaced samples of a signal that will enable the signal waveform to be completely determined. Note 1: The Nyquist interval is equal to the reciprocal of twice the highest frequency component of the sampled signal. Note 2: In practice, when analog signals are sampled for the purpose of digital transmission or other processing, the sampling rate must be more frequent than that defined by Nyquist's theorem, because of quantization erro introduced by the digitizing process. The required sampling rate is determined by the accuracy of the digitizing process. Nyquist Rate - The reciprocal of the Nyquist interval, i.e., the minimum theoretical sampling rate that fully describes a given signal, i.e., enables its faithful reconstruction from the samples. Note: The actual sampling 330
- 331. rate required to reconstruct the original signal will be somewhat higher than the Nyquist rate, because of quantization errors introduced by the sampling process. Nyquist's Theorem - Synonym Sampling Theorem. A theorem, developed by H. Nyquist, which states that an analog signal waveform may be uniquely reconstructed, without error, from samples taken at equal time intervals. The sampling rate must be equal to, or greater than, twice the highest frequency component in the analog signal. O Object -1. In image processing, a sub-region of an image that is perceived as a single entity. Note: An image can contain more than one object. 2. In facsimile systems, the image, the likeness of which is to be transmitted. 3. A Passive entity containing or receiving information. Access to an object implies access to the information it contains. Object Oriented -1. Pertaining to, or characteristic of, a computer program consisting of (a) many relatively small, simple programs (subroutines), and (b) one monitor program, the function of which is to coordinate the exchange of data among the subroutines. Note: Subroutines designed under this concept may be stored in object libraries, and used by other computer programmers with similar functional requirements. 2. Pertaining to, or characteristic of, data to be processed by object-oriented programs. Note 1: Each data object in an object-oriented program may have multiple attributes associated with it. For example, if a data object were defined as a person, several appropriate attributes might be the person's birth date , social security number, and eye color. Note 2: The data and its attributes are considered as one object as they pass between subroutines. Note 3: Objects with similar attributes are considered as a particular class of objects. For example, "people" would be one class of objects and "automobiles" could be another, because the objects in the "automobiles" class are likely to have a completely different set of attributes associated with them. Object Persistence - In a video display, distortion wherein the entirety of some object (or objects) that appeared in a previous frame (and that should no longer appear) remain in the current frame and in subsequent frames as a faded image or as an outline. Object Retention - In a video display, distortion in which a fragment of an object that appeared in a previous frame (and should no longer appear) remains in the current and subsequent video frames. Object Reuse - Reassignment and re-use of a storage medium containing one or more objects after ensuring no residual data remains on the storage medium. Obsolete - In cryptography, pertaining to the state of a key that must no longer be used either to transmit information from the originator or to process received secure information. Obsolete Date - In encryption, the date and time when a key becomes obsolete. OC - Abbreviation for optical carrier. The nomenclature for the line rate of the optical transmission signal. OCCAbbreviation for other common carrier. Occupancy - For equipment, such as a circuit or a switch, the ratio of the actual time in use to the available time during a 1-hour period. Note 1: Occupancy is usually expressed in percent. Note 2: Occupancy may be plotted versus time of day. 331
- 332. Occupied Bandwidth -1. The width of a frequency band such that, below the lower and above the upper frequency limits, the mean powers emitted are each equal to a specified percentage B /2 of the total mean power of a given emission. Unless otherwise specified by the CCIR for the appropriate class of emission, the value of B /2 should be taken as 0.5%. Note 1: The percentage of the total power outside the occupied bandwidth is represented by B . Note 2: In some cases, e.g. , multichannel frequency-division multiplexing systems, use of the 0.5% limits may lead to certain difficulties in the practical application of the definition of occupied and necessary bandwidth; in such cases, a different percentage may prove useful. 2. The frequency bandwidth such that, below its lower and above its upper frequency limits, the mean powers radiated are each equal to 0.5% of the total mean power radiated by a given emission. Oceanographic Data Interrogating Station - A station in the maritime mobile service the emissions of which are used to initiate, modify or terminate functions of equipment directly associated with an oceanographic data station, including the station itself. Oceanographic Data Station - A station in the maritime mobile service located on a ship, buoy, or other sensor platform the emissions of which are used for transmission of oceanographic data. OCR - Abbreviation for optical character reader, optical character recognition. Octet - A byte of eight binary digits usually operated upon as an entity. Octet Alignment - The configuration of a field composed of an integral number of octets. Note: If the field is not divisible by eight, bits (usually zeros) are added to either the first octet (left justification ) or the last octet (right justification). OD - Abbreviation for optical density. Odd-Even Check - Synonym parity check. - A test that determines whether the number of ones or zeros in an array of binary digits is odd or even. Note: Odd parity is standard for synchronous transmission and even parity for asynchronous transmission. Odd Parity - See parity, parity check. OFC - Abbreviation for optical fiber, conductive. Note: OFC is the designation given by the National Fire Protection Association (NFPA) to interior fiber-optic cables which contain at least one electrically conductive, non-current-carrying component, such as a metallic strength member or vapor barrier, and which are not certified for use in plenum or riser applications. OFCP - Abbreviation for optical fiber, conductive, plenum. Note: OFCP is the designation given by the National Fire Protection Association (NFPA) to interior fiber-optic cables which contain at least one electrically conductive, non-current-carrying component such as a metallic strength member or vapor barrier, and which are certified for use in plenum applications. OFCR - Abbreviation for optical fiber, conductive, riser. Note: OFCR is the designation given by the National Fire Protection Association (NFPA) to interior fiber-optic cables which contain at least one electrically conductive, non-current-carrying component such as a metallic strength member or vapor barrier, and which are certified for use in riser applications. off-axis optical system - An optical system in which the optical axis of the aperture is not coincident with the mechanical center of the aperture. Note: The principal applications of off-axis optical systems are to avoid obstruction of the primary aperture by secondary optical elements, instrument packages, or sensors, and to 332
- 333. provide ready access to instrument packages or sensors at the focus. The engineering tradeoff of an off-axis optical system is an increase in image aberrations. Offered Load - The total load submitted to a trunk group. This value may be corrected for retrials during the engineering process. Off-Hook - If equipment is "off-hook", it is not idle but actively connected to the telephone line. - 1. In telephony, the condition that exists when an operational telephone instrument or other user instrument is in use, i.e., during dialing or communicating. Note: Off-hook originally referred to the condition that prevailed when the separate earpiece, i.e., receiver, was removed from its switchhook, which extended from a vertical post that also supported the microphone, and which connected the instrument to the line when not depressed by the weight of the receiver. 2. One of two possible signaling states, such as tone or no tone and ground connection versus battery connection. Note: If off-hook pertains to one state, on-hook pertains to the other. 3. The active state, i.e., closed loop, of a subscriber or PBX user loop. 4. An operating state of a communications link in which data transmission is enabled either for (a) voice or data communications or (b) network signaling. Off-Hook Service - Synonym hotline. Off-Hook Signal - In telephony, of a circuit, a signal indicating seizure, request for service, or a busy condition. Office Classification - Prior to divestiture, numbers that were assigned to offices according to their hierarchical function in the U.S. public switched telephone network. Note 1: The following class numbers are used: • Class 1: Regional Center (RC) • Class 2: Sectional Center (SC) • Class 3: Primary Center (PC) • Class 4: Toll Center (TC) [Only if operators are present; otherwise Toll Point (TP)] • Class 5: End Office (EO) [ Local central office] Note 2: Any one center handles traffic from one center to two or more centers lower in the hierarchy. Since divestiture, these designations have become less firm. Off Line - 1. In computer technology, the state or condition of a device or equipment that is not under the direct control of another device. 2. In computer technology, the status of a device that is disconnected from service. Off-Line -1. Pertaining to the operation of a functional unit when not under the direct control of the system with which it is associated. Note 1: Off-line units are not available for immediate use on demand by the system. Note 2: Off-line units may be independently operated. 2. Pertaining to equipment that is disconnected from a system, is not in operation, and usually has its main power source disconnected or turned off. Off-Line Cryptosystem - A cryptosystem in which encryption and decryption are performed independently of the transmission and reception functions. Off-Line Recovery - The process of recovering nonprotected message traffic by use of an off-line processor or central processing unit. 333
- 334. Off-Line Storage - Storage that is not under the control of a processing unit. Off-Net Calling - The process by which telephone calls that originate or pass through private switching systems in transmission networks are extended to stations in a public switched telephone system. Off-Premises Extension (OPX) - An extension telephone, PBX station, or key system station located on property that is not contiguous with that on which the main telephone, PBX, or key system is located. - Like a party line, an OPX is a line that serves more than one subscriber location. Examples of OPXs are offpremise answering services, and lines that serve more than one building. Your Automatic Call Processor will not operate fully if attached on a line with an OPX. Offset - In encryption, the process of applying Exclusive-OR logic to a target value and a known count. Offset Encryption - The process of encryption by using a key that has been offset. Offset Track - In information assurance, a track written at a nonstandard position on a diskette, as part of a method of copy protection . OffThe-Air -1. In radio communications systems, pertaining to a station that is completely shut down, i.e., that is not transmitting any signal, not even an unmodulated carrier. 2. In a radio station, pertaining to a particular source of modulation, such as a specific microphone, that is disconnected, i.e., is no longer capable of modulating the carrier. Note: The carrier may continue unmodulated or it may be modulated by another signal source. Off-The-Air Monitoring -1. In radio net operations, the listening, by the net- control station, to the transmissions of stations in the net, particularly to check the quality of their transmissions. Note: Off-the-air monitoring is usually performed during periods when the net-control station is not transmitting. 2. The listening, by a radio station, to its own transmissions by receiving the signal that has been transmitted by the transmitting antenna, to discover the quality of the signal being transmitted to other stations or being broadcast. Note: In off-the-air monitoring, the received signal must have traveled through the air a reasonable distance from the transmitting antenna and not be a signal that is tapped on its way to the transmitting antenna internal to the station or in the antenna transmission line, i.e., the feeder. The monitoring distance should be such that direct inductive or capacitive coupling between the transmitting antenna and monitor antenna does not occur. Off-the-Shelf - Pertaining to equipment already manufactured and available for delivery from stock. OFN - Abbreviation for optical fiber, nonconductive. Note: OFN is the designation given by the National Fire Protection Association (NFPA) to interior fiber-optic cables which contain no electrically conductive component, and which are not certified for use in plenum or riser applications. OFNP - Abbreviation for optical fiber, nonconductive, plenum. Note: OFNP is the designation given by the National Fire Protection Association (NFPA) to interior fiber-optic cables which contain no electrically conductive component, and which are certified for use in plenum applications. OFNR - Abbreviation for optical fiber, nonconductive, riser. Note: OFNR is the designation given by the National Fire Protection Association (NFPA) to interior fiber-optic cables which contain no electrically conductive component, and which are certified for use in riser applications. Oligarchically Synchronized Network - A synchronized network in which the timing of all clocks is controlled by a selected few clocks. 334
- 335. Omega - A global radionavigation system that enables user with special receivers to obtain position information by measuring phase difference between precisely timed signals radiated by a network of eight transmitting stations deployed worldwide. Note: The transmitted signals time -share transmission on frequencies of 10.2, 11.05, 11.33, and 13.6 kHz. Since the transmissions are coordinated with UTC (USNO), they also provide time reference. Omnidirectional Antenna - An antenna that has a radiation pattern that is nondirectional in azimuth. Note: The vertical radiation pattern may be of any shape. Omnidirectional Range Station - A radionavigation land station in the aeronautical radionavigation service providing direct indication of the bearing (omnibearing) of that station from an aircraft. ONA - Abbreviation for open network architecture. On-Board Communication Station - A low-powered mobile station in the maritime mobile service intended for use for internal communications on board a ship, or between a ship and its lifeboats and liferafts during lifeboat drills or operations, or for communication within a group of vessels being towed or pushed, as well as for line handling and mooring instructions. 144Line Weighting - In telephony, a noise weighting used in a noise measuring set to measure line noise as it would be perceived if the line were terminated with a No. 144- receiver, or a similar instrument. Note: The meter scale readings are in dBrn 144-Receiver Weighting - In telephony, a noise weighting used in a noise measuring set to measure noise across the receiver of an instrument equipped with a No. 144-receiver. Note: The meter scale readings are in dBrn One-Part Code - Code in which plain text elements and their accompanying code groups are arranged in alphabetical, numerical, or other systematic order, so one listing serves for both encoding and decoding. One-part codes are normally small codes used to pass small volumes of low- sensitivity information. One-Time Cryptosystem - Cryptosystem employing key used only once. One-Time Pad - A manual one-time cryptosystem produced in pad form. One-Way Communication - Communication in which information is always transferred in only one preassigned direction. Note 1: One-way communication is not necessarily constrained to one transmission path. Note 2: Examples of one-way communications systems include broadcast stations, one-way intercom systems, and wireline news services. One-Way Encryption - Synonym irreversible encryption. Encryption that produces ciphertext from which the original data cannot be reproduced. Note: Irreversible encryption is useful in authentication. For example, a password might be irreversibly encrypted and the resulting ciphertext stored. A password presented later would be irreversibly encrypted identically and the two strings of ciphertext compared. If they are identical, the presented password is correct. One-Way Function - A transfer function f which is relatively easy to compute, but for which, for a general value, y , within the selected range, it is computationally difficult to find a value x within the expected domain such that f(x) = y. There may be several values for y , for which finding x is not computationally difficult. 335
- 336. One-Way-Only Channel - A channel capable of transmission in only one direction, which cannot be reversed. Synonym unidirectional channel. One-Way Operation - Synonym simplex operation. Operation in which transmission occurs in one and only one preassigned direction. Note: Duplex operation may be achieved by simplex operation of two or more simplex circuits or channels. 2. Operating method in which transmission is made possible alternately in each direction of a telecommunication channel, for example by means of manual control. Note: In general, duplex operation and semiduplex operation require two frequencies in radiocommunication; simplex operation may use either one or two. Note 2: These two definitions are contradictory, however, both are in common use. The first one is used in telephony and the second one is used in radio. The user is cautioned to verify the nature of the service specified by this term. One-Way Reversible Operation - Synonym half-duplex operation. Operation in which communication between two terminals occurs in either direction, but in only one direction at a time. Note: Half-duplex operation may occur on a half-duplex circuit or on a duplex circuit, but it may not occur on a simplex circuit. One-Way Trunk - A trunk between two switching centers, over which traffic may be originated from one preassigned location only. Note 1: The traffic may consist of two-way communications; the expression "one way" refers only to the origin of the demand for a connection. Note 2: At the originating end, the one-way trunk is known as an "outgoing trunk" ; at the other end, it is known as an "incoming trunk". On-Hook - Another old term that gets its meaning from your telephone handset resting on the hook switch. If equipment is "On-hook", it is idle and not using the telephone line. - 1. In telephony, the condition that exists when an operational telephone, or other user instrument, is not in use. Note: On-hook originally referred to the storage of an idle telephone receiver, i.e., separate earpiece, on a hook that extended from a vertical post that supported the microphone also. The hook was mechanically connected to a switch that automatically disconnected the idle telephone from the network. 2. One of two possible signaling states, such as tone or no tone, or ground connection versus battery connection. Note: If on-hook pertains to one state, off-hook pertains to the other. 3. The idle state, i.e., open loop, of a subscriber or PBX user loop. 4. An operating state of a communications link in which data transmission is disabled and a high-impedance, i.e., open, circuit is presented to the link by the end instrument (s). Note: During the on-hook condition, the link is responsive to ringing signals. See on-hook state. On-Hook Signal - In telephony, of a circuit, a signal indicating a disconnect, unanswered call, or an idle condition. On-Hook State - A state in which the customer installation (CI) presents a high-resistance path at the network interface. On-Line - 1. Pertaining to the operation of a functional unit when under the direct control of the system with which it is associated. Note 1: On-line units are available for immediate use on demand by the system without human intervention. Note 2: On-line units may not be independently operated. 2. Pertaining to equipment that is connected to a system, and is in operation. 3. In computer technology, the state or condition of a device or equipment that is under the direct control of another device. 4. In computer technology, the status of a device that is functional and ready for service. Also spelled "on line" and "online." Online Computer System - A computer system that is a part of, or is embedded in, a larger entity, such as a communications system, and that interacts in real or near- real time with the entity and its users. 0n-Line Cryptosystem - A cryptosystem in which encryption and decryption are performed in association with the transmitting and receiving functions. 336
- 337. Online Shopping - A process in which images or listings of goods and services are viewed remotely via electronic means, e.g. , a vendor's Web site, items are selected for purchase, and the transaction is completed electronically with a credit card or an established credit account. Note: Various encryption schemes may be, and usually are, used to reduce the risks of sending sensitive information, such as credit- card numbers, over the Internet or other telecommunications facility. Online Software Upgrade - In computer networking, a software modification or installation performed remotely from an originating site ( e.g. , by authority of a network administrator) on a subject user's computer, by means of a special utility program that enables access to the subject computer whenever it is powered up and on line. Note: An online software upgrade may be performed (a) automatically, without the consent and, perhaps, without the knowledge of the user, (b) semi-automatically, in which case an application resident on the networked computer will, upon every bootup, automatically check the originating site and notify the user if an upgrade is available (if so, some kind of assenting action on the part of the user is necessary to retrieve it), or (c) manually, in which case the user must check the originating site periodically to determine whether an upgrade is available, and take some kind of assenting action to retrieve it. On-Premises Extension - An extension telephone, PBX station, or key system station located on property that is contiguous with that on which the main telephone, PBX, or key system is located. On-Premises Wiring - Customer-owned metallic or optical- fiber communications transmission lines, installed within or between buildings. Note: On- premises wiring may consist of horizontal wiring, vertical wiring, and backbone wiring, and may extend from the external network interface to the user work station areas. It includes the total communications wiring to transport current or future data, voice, LAN, and image information. On-Screen Button - A pictorial representation of a pushbutton on a display screen, which functions as a binary control, for example, on/off. On-The-Air -1. In radio communications systems, pertaining to a station that is transmitting a carrier, whether or not the carrier is modulated. 2. In a radio station, pertaining to a particular source of modulation, such as a specific microphone, that is connected, i.e., is capable of modulating the carrier. Open Circuit -1. In communications, a circuit available for use. 2. In electrical engineering, a circuit that contains an essentially infinite impedance. Note: An open circuit may be intentional, as in a switch, or may constitute a fault, as in a severed cable. Open Dual Bus - A dual bus in which the head-of-bus functions for both buses are at different locations. Open Network Architecture (ONA) - In the context of the FCC's Computer Inquiry III, the overall design of a communication carrier's basic network facilities and services to permit all users of the basic network to interconnect to specific basic network functions and interfaces on an unbundled, equal- access basis. Note: The ONA concept consists of three integral components: (a) basic serving arrangements (BSAs), (b) basic service elements (BSEs), and (c) complementary network services. Open-Security Environment -1. An environment in which protection of data and resources from accidental or malicious acts is achieved through normal operational procedures.2. An environment that does not provide sufficient assurance that applications and equipment are protected against the loss of confidentiality, integrity, or availability. Open Storage - Storage of classified information within an accredited facility, but not in General Services Administration approved secure containers, while the facility is unoccupied by authorized personnel. 337
- 338. Open Switching Interval (OSI) - An interval when the dc voltage applied between the tip and ring conductors of a line is removed, hence temporarily suspending line supervision and transmission. Open System - A system with characteristics that comply with specified, publicly maintained, readily available standards and that therefore can be connected to other systems that comply with these same standards. Open Systems Architecture -1. The layered hierarchical structure, configuration, or model of a communications or distributed data processing system that (a) enables system description, design, development, installation, operation, improvement, and maintenance to be performed at a given layer or layers in the hierarchical structure, (b) allows each layer to provide a set of accessible functions that can be controlled and used by the functions in the layer above it, (c) enables each layer to be implemented without affecting the implementation of other layers, and (d) allows the alteration of system performance by the modification of one or more layers without altering the existing equipment, procedures, and protocols at the remaining layers. Note 1: Examples of independent alterations include (a) converting from wire to optical fibers at a physical layer without affecting the data-link layer or the network layer except to provide more traffic capacity, and (b) altering the operational protocols at the network level without altering the physical layer. Note 2: Open systems architecture may be implemented using the Open Systems Interconnection-- Reference Model ( OSI--RM ) as a guide while designing the system to meet performance requirements. 2. Nonproprietary systems architecture. Open Systems Interconnection (OSI) - Pertaining to the logical structure for communications networks standardized by the International Organization for Standardization ( ISO ). Note: Adherence to the standard enables any OSI -compliant system to communicate with any other OSI-compliant system for a meaningful exchange of information. Open Systems Interconnection (OSI)--Architecture - Communications system architecture that adheres to the set of ISO standards relating to open systems architecture. Open Systems Interconnection (OSI)--Protocol Specification - The lowest level of abstraction within the OSI standards scheme. Note: Each OSI-- Protocol Specification operates at a single layer. Each defines the primitive operations and permissible responses required to exchange information between peer processes in communicating systems to carry out all or a subset of the services defined within the OSI-- Service Definitions for that layer. Open Systems Interconnection--Reference Model (OSI--RM) - An abstract description of the digital communications between application processes running in distinct systems. The model employs a hierarchical structure of seven layers. Each layer performs value-added service at the request of the adjacent higher layer and, in turn, requests more basic services from the adjacent lower layer: • Physical Layer: Layer 1. The lowest of seven hierarchical layers. The Physical layer performs services requested by the Data Link Layer. The major functions and services performed by the physical layer are: (a) establishment and termination of a connection to a communications medium; (b) participation in the process whereby the communication resources are effectively shared among multiple users, e.g., contention resolution and flow control; and, (c) conversion between the representation of digital data in user equipment and the corresponding signals transmitted over a communications channel. • Data Link Layer: Layer 2. This layer responds to service requests from the Network Layer and issues service requests to the Physical Layer. The Data Link Layer provides the functional and procedural means to transfer data between network entities and to detect and possibly correct errors that may occur in the Physical Layer. Note: Examples of data link protocols are HDLC and ADCCP for point-to- point or packet-switched networks and LLC for local area networks. 338
- 339. • Network Layer: Layer 3. This layer responds to service requests from the Transport Layer and issues service requests to the Data Link Layer. The Network Layer provides the functional and procedural means of transferring variable length data sequences from a source to a destination via one or more networks while maintaining the quality of service requested by the Transport Layer. The Network Layer performs network routing, flow control, segmentation/desegmentation, and error control functions. • Transport Layer: Layer 4. This layer responds to service requests from the Session Layer and issues service requests to the Network Layer. The purpose of the Transport Layer is to provide transparent transfer of data between end users, thus relieving the upper layers from any concern with providing reliable and cost-effective data transfer. • Session Layer: Layer 5. This layer responds to service requests from the Presentation Layer and issues service requests to the Transport Layer. The Session Layer provides the mechanism for managing the dialogue between end-user application processes. It provides for either duplex or half-duplex operation and establishes checkpointing, adjournment, termination, and restart procedures. • Presentation Layer: Layer 6. This layer responds to service requests from the Application Layer and issues service requests to the Session Layer. The Presentation Layer relieves the Application Layer of concern regarding syntactical differences in data representation within the end-user systems. Note: An example of a presentation service would be the conversion of an EBCDIC-coded text file to an ASCII-coded file. • Application Layer: Layer 7, the highest layer. This layer interfaces directly to and performs common application services for the application processes; it also issues requests to the Presentation Layer. The common application services provide semantic conversion between associated application processes. Note: Examples of common application services of general interest include the virtual file, virtual terminal, and job transfer and manipulation protocols. Open Systems Interconnection (OSI)--Service Definitions - The next lower level of abstraction below that of the OSI --Reference Model. The OSI-- Service Definitions for each layer define the layer's abstract interface and the facilities provided to the user of the service independent of the mechanism used to accomplish the service. Open Systems Interconnection (OSI)--Systems Management - In the Application Layer of the OSI -- Reference Model ( OSI--RM ), the set of functions related to the management and status of various resources identified in all layers of the OSI--RM. Open Waveguide - An all- dielectric waveguide in which electromagnetic waves are guided by a refractive index gradient so that the waves are confined to the guide by refraction or reflection from the outer surface of the guide or from surfaces within the guide. Note 1: In an open waveguide, the electromagnetic waves propagate, without radiation, within the waveguide, although evanescent waves coupled to internal waves may travel in the space immediately outside the waveguide. Note 2: Examples of open waveguides are (a) optical fibers and (b) planar waveguides in integrated optical circuits. Open Wire - Conductors that are separately supported with insulators on poles or towers above the surface of the Earth. Note 1: Open wire conductors may be insulated or uninsulated. Note 2: Open wire may be used in both communication applications and power applications. Operand - An entity on which an operation is performed. Operating System - An integrated collection of routines that service the sequencing and processing of programs by a computer. Note: An operating system may provide many services, such as resource allocation, scheduling, input / output control, and data management. Although operating systems are predominantly software, partial or complete hardware implementations may be made in the form of firmware. 339
- 340. Operating System Platform - Synonym platform. Operating Time -1. The time interval between the instant of occurrence of a specified input condition to a system and the instant of completion of a specified operation. 2. In communications, computer, and information processing systems, the time interval between the instant a request for service is received from a user and the instant of final release of all facilities by the user or either of two users. 3. In communications systems conference calls, the time interval between the instant a request for service is received from one of a group of concurrent users and the instant all but one of the users have released all facilities. Operation -1. The method, act, process, or effect of using a device or system. 2. A well-defined action that, when applied to any permissible combination of known entities, produces a new entity, e.g. , the process of addition in arithmetic--in adding 5 and 3 to obtain 8, the numbers 5 and 3 are the operands, the number 8 is the result, and the plus sign is the operator indicating that the operation performed is addition. 3. A program step, usually specified by a part of an instruction word, that is undertaken or executed by a computer. Note: Examples of operations include addition, multiplication, extraction, comparison, shift, transfer. Operational Data Security - Protection of data from either accidental or unauthorized intentional modification, destruction, or disclosure during input, processing, storage, transmission, or output operations. Operational Key - Key intended for use over-the-air for protection of operational information or for the production or secure electrical transmission of key streams. Operational Load - The total power requirements for communications facilities. Operational Service Period -1. A period during which a telecommunications service remains in an operational state. Note: The operational state must be defined in accordance with specified criteria. 2. A performance measurement period, or succession of performance measurement periods, during which a telecommunications service remains in an operational service state. Note: An operational service period begins at the beginning of the performance measurement period in which the telecommunications service enters the operational service state, and ends at the beginning of the performance measurement period in which the telecommunications service leaves the operational service state. Operational Service State - During any performance measurement period, a telecommunications service condition that existed when the calculated values of specified performance parameters were equal to or better than their associated outage thresholds. Operations - The term denoting the general classifications of services rendered to the public for which separate tariffs are filed, namely exchange, state toll and interstate toll. Operations Code - Code composed largely of words and phrases suitable for general communications use. Operations Security - The process denying to potential adversaries information about capabilities and/or intentions by identifying, controlling and protecting generally unclassified evidence of the planning and execution of sensitive activities. Operations System - A system that performs operations system functions (OSFs), that is, supports the processing of information related to operations, administration, maintenance, and provisioning for the telecommunications networks. Note: An operations system performs surveillance and testing functions to support customer access maintenance. 340
- 341. Operator Service Access Point (OSAP) - The functional entity that provides access to an operator service from an exchange in the network. The operator service may be co-located with the exchange or located elsewhere. Operator Service Provider - The company accepting the billing information, initiating the validation process, and recording the details of the call. Operator Services - A set of services including toll and assistance, listing services and intercept, associated with the originating connection network capability. Operator System - A stored program electronic system associated with one or more toll switching systems which provides centralized traffic service position functions for several local offices at one location. Operator Trunks - A general term, ordinarily applied to trunks between manually operated switchboard positions and local dial central offices in the same wire center. OPSEC - Acronym for operations security. The process denying to potential adversaries information about capabilities and/or intentions by identifying, controlling and protecting generally unclassified evidence of the planning and execution of sensitive activities. Optical Amplifier - See fiber amplifier. A device that amplifies an optical signal directly, without the need to convert it to an electrical signal, amplify it electrically, and reconvert it to an optical signal. Note 1: One type of fiber amplifier uses a doped fiber ( e.g. , a fiber doped with erbium), which bears the communication signal, and which is optically pumped with a laser having a high-powered continuous output at an optical frequency slightly higher than that of the communication signal. The signal is intensified by Raman amplification. Note 2: Because neither optical-electrical conversion nor electrical amplification takes place, this type of amplifier is well suited for a wide variety of applications, both digital and analog. Note 3: Because this type of amplifier does not require extraordinary frequency ( wavelength ) control of the pumping laser, it is relatively simple. optical repeater. Optical Attenuator - In optical communications, a device used to reduce the power level of an optical signal. Note 1: Optical attenuators used in fiber optic communications systems may use a variety of principles for their functioning. Those using the gap - loss principle are sensitive to the modal distribution ahead of the attenuator, and should be used at or near the transmitting end, or they may introduce less loss than intended. Optical attenuators using absorptive or reflective techniques avoid this problem. Note 2: The basic types of optical attenuators are fixed, step-wise variable, and continuously variable. Optical Axis -1. Of a refractive or reflective optical element, the straight line that is coincident with the axis of symmetry of the surfaces. Note: The optical axis of a system is often coincident with its mechanical axis, but it need not be, e.g., in the case of an off-axis parabolic reflector used to transmit signals to, or receive signals from, a geosynchronous satellite. 2. In a lens element, the straight line which passes through the centers of curvature of the lens surfaces. 3. In an optical system, the line formed by the coinciding principal axes of the series of optical elements. 4. In an optical fiber, synonym fiber axis [which is the preferred term]. Optical Beamsplitter - See beamsplitter. A device for dividing an optical beam into two or more separate beams. Note: An example of a beamsplitter is a partially reflecting mirror. Optical Cable - See fiber optic cable. A telecommunications cable in which one or more optical fibers are used as the propagation medium. Note 1: The optical fibers are surrounded by buffers, strength members, and jackets for protection, stiffness, and strength. Note 2: A fiber-optic cable may be an all-fiber cable, or contain both optical fibers and metallic conductors. One possible use for the metallic conductors is the transmission of electric power for repeaters. 341
- 342. Optical Cable Assembly - See cable assembly. A cable that is ready for installation in specific applications and usually terminated with connectors. Optical Carrier Level 1 (OC-1) - The optical signal that results from an optical conversion of an synchronous transport signal 1 (STS-1 signal). It is this signal that will form the basis of the interface. Optical Cavity - A region bounded by two or more mirrors that are aligned to provide multiple reflections of lightwaves. Note: The resonator in a laser is an optical cavity. In this sense, synonym resonant cavity. Optical Character Reader (OCR) - A device used for optical character recognition. Optical Character Recognition (OCR) - The machine identification of printed characters through use of light- sensitive devices. Optical Conductor - Deprecated synonym for optical fiber. A filament of transparent dielectric material, usually glass or plastic, and usually circular in cross section, that guides light. Note 1: An optical fiber usually has a cylindrical core surrounded by, and in intimate contact with, a cladding of similar geometry. Note 2: The refractive index of the core must be slightly higher than that of the cladding for the light to be guided by the fiber. Optical Connector - A demountable device for attaching a cabled or uncabled optical fiber to another, or to an active device such as a transmitter. Note 1: A connector is distinguished by the fact that it may be disconnected and reconnected, as opposed to a splice, which permanently joins two fibers. Note 2: Optical connectors are sometimes erroneously referred to as "couplers." Such usage is incorrect and is to be avoided. Optical Coupler - See directional coupler, star coupler, T-coupler. Optical Density (OD) - For a given wavelength, an expression of the transmittance of an optical element. Note 1: Optical density is expressed by log 10 (1/ T ) where T is transmittance. Note 2: The higher the optical density, the lower the transmittance. Note 3: Optical density times 10 is equal to transmission loss expressed in decibels, e.g. , an optical density of 0.3 corresponds to a transmission loss of 3 dB. Optical Detector - A transducer that generates an output signal when irradiated with optical energy. Optical Disk - A storage medium from which data is read and to which it is written by lasers. Optical disks can store much more data -- up to 6 gigabytes (6 billion bytes) -- than most portable magnetic media, such as floppies. Optical Dispersion - See dispersion. Optical Fiber - A filament of transparent dielectric material, usually glass or plastic, and usually circular in cross section, that guides light. Note 1: An optical fiber usually has a cylindrical core surrounded by, and in intimate contact with, a cladding of similar geometry. Note 2: The refractive index of the core must be slightly higher than that of the cladding for the light to be guided by the fiber. Synonym lightguide. Optical Fiber Cable - See fiber optic cable. A telecommunications cable in which one or more optical fibers are used as the propagation medium. Note 1: The optical fibers are surrounded by buffers, strength members, and jackets for protection, stiffness, and strength. Note 2: A fiber-optic cable may be an all-fiber cable, or contain both optical fibers and metallic conductors. One possible use for the metallic conductors is the transmission of electric power for repeaters. 342
- 343. Optical Fiber Coating - See primary coating. The plastic overcoat in intimate contact with the cladding of an optical fiber, applied during the manufacturing process. Note 1: The primary coating typically has an outside diameter of approximately 250 to 750 m, and serves to protect the fiber from mechanical damage and chemical attack. It also enhances optical fiber properties by stripping off cladding modes, and in the case where multiple fibers are used inside a single buffer tube, it suppresses cross- coupling of optical signals from one fiber to another. Note 2: The primary coating should not be confused with a tight buffer, or the plastic cladding of a plastic-clad- silica (PCS) fiber. Note 3: The primary coating, which typically consists of many layers, may be color-coded to distinguish fibers from one another, e.g., in a buffer tube containing multiple fibers. Optical Fiber, Conductive - See OFC. OFC is the designation given by the National Fire Protection Association (NFPA) to interior fiber-optic cables which contain at least one electrically conductive, non-current-carrying component, such as a metallic strength member or vapor barrier, and which are not certified for use in plenum or riser applications. Optical Fiber, Conductive, Plenum - See OFCP. OFCP is the designation given by the National Fire Protection Association (NFPA) to interior fiber-optic cables which contain at least one electrically conductive, non- current-carrying component such as a metallic strength member or vapor barrier, and which are certified for use in plenum applications. Optical Fiber, Conductive, Riser - See OFCR. OFCR is the designation given by the National Fire Protection Association (NFPA) to interior fiber-optic cables which contain at least one electrically conductive, non- current-carrying component such as a metallic strength member or vapor barrier, and which are certified for use in riser applications. Optical Fiber Jacket - See sheath. Of a communications or power cable, the outer covering or coverings of tough material, often plastic, that is resistant to environmental hazards such as abrasion, liquid intrusion, solar radiation, etc., and is used to protect cable component (s) such as optical fibers or metallic conductors that transport the signal or power. Note: There may be more than one sheath surrounding a given cable. For example, some cable designs use an inner sheath surrounded by metallic armor, over which is an outer sheath. Optical Fiber Link - See fiber optic link. A communications link that transmits signals by means of modulated light propagated in an optical fiber. Optical Fiber, Nonconductive - See OFN. OFN is the designation given by the National Fire Protection Association (NFPA) to interior fiber-optic cables which contain no electrically conductive component, and which are not certified for use in plenum or riser applications. Optical Fiber, Nonconductive, Plenum - See OFNP. OFNP is the designation given by the National Fire Protection Association (NFPA) to interior fiber-optic cables which contain no electrically conductive component, and which are certified for use in plenum applications. Optical Fiber, Nonconductive, Riser - See OFNR. Optical Fiber Nuclear Hardening - Design allowances made to prevent or ameliorate the effects of gamma or high-energy neutron radiation or bombardment, that causes some optical fibers to darken, increase attenuation, or depart from normal operating parameters. Note: Light sources, such as LEDs and lasers, and photodetectors, also need to be hardened to prevent similar malfunctions. 343
- 344. Optical Fiber Transfer Function - See transfer function. OFNR is the designation given by the National Fire Protection Association (NFPA) to interior fiber-optic cables which contain no electrically conductive component, and which are certified for use in riser applications. Optical Fiber Waveguide - See optical fiber. A filament of transparent dielectric material, usually glass or plastic, and usually circular in cross section, that guides light. Note 1: An optical fiber usually has a cylindrical core surrounded by, and in intimate contact with, a cladding of similar geometry. Note 2: The refractive index of the core must be slightly higher than that of the cladding for the light to be guided by the fiber. Optical Filter - In the optical regime, an element that selectively transmits or blocks a range of wavelengths, polarizations, etc., or selectively displaces a beam, e.g. , by virtue of birefringence. Optical Heterodyning - See optical mixing. Optical beating, i.e., the mixing, i.e. , heterodyning, of two lightwaves (incoming signal and local oscillator ) in a nonlinear device to produce a beat frequency low enough to be further processed by conventional electronic circuitry. Note: Optical mixing is the optical analog of heterodyne reception of radio signals. Optical Interconnection - In an integrated circuit or electronic module, the use of opto-electronic devices to make or facilitate connections, in lieu of a direct connection involving conducting or semiconducting materials. Optical Interface - In a fiber optic communications link, a point at which an optical signal is passed from one equipment or medium to another without conversion to an electrical signal. Optical Isolator - A device that uses a short optical transmission path to accomplish electrical isolation between elements of a circuit. Note 1: The optical path may be air or a dielectric waveguide. Note 2: The transmitting and receiving elements of an optical isolator may be contained within a single compact module, for mounting, e.g., on a circuit board. Synonym optoisolator. Optical Junction - Any physical interface in a fiber optic system. Note: Source to fiber, fiber to fiber, fiber to detector, beam to prism (or lens), fiber to lens, lens to fiber, are examples of optical junctions. Optical Line Code - Sequences of optical pulses suitably structured to permit information transfer over an optical link. Optical Line Pair -1. In optical measurements or specifications, a pair of usually straight contiguous stripes of equal width and having a defined degree of contrast, and which are used as one means of defining or determining resolution. Note 1: Resolution may be expressed in terms of line pairs per unit distance, or line pairs per unit angle. Note 2: Optical "targets," consisting of many contiguous line pairs, are sometimes used to measure optical resolution. Such targets may have line pairs of high contrast, in which one stripe is "white," or highly reflective, at the wavelength (s) of interest, and the adjacent one, "black," or highly absorbent at the wavelength(s) of interest. Other such targets may have line pairs of lower contrast ("shades of gray"). Resolution may be specified or measured with respect to either or both kinds of target. 2. In raster -scanned television technology, two adjacent scanning lines (traces). Optical Link - An optical transmission channel, including any repeaters or regenerative repeaters, designed to connect two electronic or opto-electronic communications terminals. Note: An optical link is sometimes held to include the terminal optical transmitters and receivers, especially in the case of a communications link utilizing separate electronic terminals originally designed for metallic transmission, and retrofitted for optical transmission. 344
- 345. Optically Active Material - A material that rotates the plane of polarization of light that passes through it. Optical Mixing - Optical beating, i.e., the mixing , i.e. , heterodyning, of two lightwaves (incoming signal and local oscillator ) in a nonlinear device to produce a beat frequency low enough to be further processed by conventional electronic circuitry. Note: Optical mixing is the optical analog of heterodyne reception of radio signals. [After FAA] Synonym optical heterodyning. Optical Modulator - Any device used to modify any characteristic of an optical signal (lightwave) for the purpose of conveying information. Optical Multiplexing - See wavelength-division multiplexing. Optical Network Unit (ONU) - A network element that is part of a fiber -in-the- loop system interfacing the customer analog access cables and the fiber facilities. Optical Path Length -1. In a medium of constant refractive index , n , the product of the geometric distance and the refractive index. 2. In a medium of varying refractive index, the integral of n s , where s is an element of length along the path, and n is the local refractive index. Note: Optical path length is proportional to the phase shift that a lightwave undergoes along a path. Optical Path Power Penalty - The extra optical power required to account for degradations due to reflections, intersymbol interference, and mode partition noise. Optical Power - See radiant power. The rate of flow of electromagnetic energy, i.e., radiant energy. Note 1: optical power is usually expressed in watts, i.e., joules per second. Note 2: The modifier is often dropped and "power" is used to mean "optical power". Optical Power Budget - In a fiber -optic communication link, the allocation of available optical power (launched into a given fiber by a given source) among various loss -producing mechanisms such as launch coupling loss, fiber attenuation, splice losses, and connector losses, in order to ensure that adequate signal strength (optical power) is available at the receiver. Note 1: The optical power budget is usually specified or expressed in dB. Note 2: The amount of optical power launched into a given fiber by a given transmitter depends on the nature of its active optical source ( LED or laser diode ) and the type of fiber, including such parameters as core diameter and numerical aperture. Manufacturers sometimes specify an optical power budget only for a fiber that is optimum for their equipment--or specify only that their equipment will operate over a given distance, without mentioning the fiber characteristics. The user must first ascertain, from the manufacturer or by testing, (a) the transmission losses for the type of fiber to be used, (b) the required signal strength for a given level of performance. Note 3: In addition to transmission loss, including those of any splices and connectors, allowance should be made for at least several dB of optical power margin losses, to compensate for component aging and to allow for future splices in the event of a severed cable. Optical Power Margin - In an optical communications link, the difference between (a) the optical power that is launched by a given transmitter into the fiber, less transmission losses from all causes, and (b) the minimum optical power that is required by the receive for a specified level of performance. Note 1: The optical power margin is usually expressed in dB. At least several dB of optical power margin should be included in the optical power budget. Note 2: The amount of optical power launched into a given fiber by a given transmitter depends on the nature of its active optical source ( LED or laser diode ) and the type of fiber, including such parameters as core diameter and numerical aperture. Optical Receiver - A device that detects an optical signal, converts it to an electrical signal, and processes the electrical signal as required for further use. 345
- 346. Optical Regenerator - See optical repeater. Optical Repeater - In an optical communication system, an optoelectronic device or module that receives an optical signal, amplifies it (or, in the case of a digital signal, reshapes, retimes, or otherwise reconstructs it), and retransmits it as an optical signal. Optical Return Loss (ORL) - The ratio (in dB ) of optical power arriving at the interface (P1) to the optical power reflected back from the same interface (P2). Optical Section - The part of the physical plant consisting of the fiber -optic cabling and connectors interconnected to provide the transport function between two adjacent repeater locations, between a repeater location and an adjacent terminal location, or between two adjacent terminal locations. The optical section extends between the point on the optical fiber just after the transmitter optical connector and the point on the optical fiber just before the receiver optical connector. Optical Source -1. In optical communications , a device that converts an electrical signal into an optical signal. Note: The two most commonly used optical sources are light-emitting diodes (LEDs) and laser diodes. 2. Test equipment that generates a stable optical signal for the purpose of making optical transmission loss measurements. Optical Spectrum - By custom and practice, the electromagnetic spectrum between the wavelengths of the vacuum ultraviolet at 0.001 m and the far infrared at 100 m. Note: The term "optical spectrum" originally applied only to that region of the electromagnetic spectrum visible to the normal human eye, but is now considered to include all wavelengths between the shortest wavelengths of radio and the longest of x- rays. At this writing, no formal spectral limits are recognized nationally or internationally. Optical Splitter - See directional coupler. Optical Switch - A switch that enables signals in optical fibers or integrated optical circuits (IOCs) to be selectively switched from one circuit to another. Note 1: An optical switch may operate by (a) mechanical means such as physically shifting an optical fiber to drive one or more alternative fibers, or (b) electro-optic effects, magneto-optic effects, or other methods. Note 2: Slow optical switches, such as those using moving fibers, may be used for alternate routing of an optical transmission path, e.g., routing around a fault. Fast optical switches, such as those using electro-optic or magneto-optic effects, may be used to perform logic operations. Optical System Power Margin - See power margin. The difference between available signal power and the minimum signal power needed to overcome system losses and still satisfy the minimum input requirements of the receiver for a given performance level. Note: System power margin reflects the excess signal level, present at the input of the receiver, that is available to compensate for (a) the effects of component aging in the transmitter, receiver, or physical transmission medium, and (b) a deterioration in propagation conditions. Optical Thickness -1. The product of the physical thickness of an isotropic optical element and its refractive index. 2. Of an optical system, the total optical path length through all elements. Optical Time Domain Reflectometer (OTDR) - An opto-electronic instrument used to characterize an optical fiber. Note 1: An OTDR injects a series of optical pulses into the fiber under test. It also extracts, from the same end of the fiber, light that is scattered back and reflected back. The intensity of the return pulses is measured and integrated as a function of time, and is plotted as a function of fiber length. Note 2: An OTDR 346
- 347. may be used for estimating the fiber's length and overall attenuation, including splice and mated- connector losses. It may also be used to locate faults, such as breaks. Optical Transmittance - See transmittance. The ratio of the transmitted power to the incident power. Note 1: In optics, transmittance is usually expressed as optical density or in percent. Optical Transmitter - A device that accepts an electrical signal as its input, processes this signal, and uses it to modulate an opto-electronic device, such as an LED or an injection laser diode, to produce an optical signal capable of being transmitted via an optical transmission medium. Optical Waveguide - Any structure having the ability to guide optical energy. Note: Optical waveguides may be (a) thin-film deposits used in integrated optical circuits (IOCs) or (b) optical fibers. Optimum Traffic Frequency - Synonym FOT. In the transmission of radio waves via ionospheric reflection, the highest effective, i.e., working, frequency that is predicted to be usable for a specified path and time for 90% of the days of the month. Note 1: The FOT is normally just below the value of the maximum usable frequency (MUF). In the prediction of usable frequencies, the FOT is commonly taken as 15% below the monthly median value of the MUF for the specified time and path. Note 2: The FOT is usually the most effective frequency for ionospheric reflection of radio waves between two specified points on Earth. Synonyms frequency of optimum transmission, optimum transmission frequency, optimum working frequency. Optimum Transmission Frequency - Synonym FOT. In the transmission of radio waves via ionospheric reflection, the highest effective, i.e., working, frequency that is predicted to be usable for a specified path and time for 90% of the days of the month. Note 1: The FOT is normally just below the value of the maximum usable frequency (MUF). In the prediction of usable frequencies, the FOT is commonly taken as 15% below the monthly median value of the MUF for the specified time and path. Note 2: The FOT is usually the most effective frequency for ionospheric reflection of radio waves between two specified points on Earth. Synonyms frequency of optimum transmission, optimum traffic frequency, optimum working frequency. Optimum Working Frequency - Synonym FOT. In the transmission of radio waves via ionospheric reflection, the highest effective, i.e., working, frequency that is predicted to be usable for a specified path and time for 90% of the days of the month. Note 1: The FOT is normally just below the value of the maximum usable frequency (MUF). In the prediction of usable frequencies, the FOT is commonly taken as 15% below the monthly median value of the MUF for the specified time and path. Note 2: The FOT is usually the most effective frequency for ionospheric reflection of radio waves between two specified points on Earth. Synonyms frequency of optimum transmission, optimum transmission frequency, optimum traffic frequency. Opto-Electronic - Pertaining to any device that functions as an electrical-to-optical or optical-to-electrical transducer, or an instrument that uses such a device in its operation. Note 1: Photodiodes, LEDs, injection laser diodes, and integrated optical circuit ( IOC ) elements are examples of opto-electronic devices commonly used in optical fiber communications . Note 2: "Electro-optical" is often erroneously used as a synonym. Optoisolator - Synonym optical isolator. A device that uses a short optical transmission path to accomplish electrical isolation between elements of a circuit. Note 1: The optical path may be air or a dielectric waveguide. Note 2: The transmitting and receiving elements of an optical isolator may be contained within a single compact module, for mounting, e.g., on a circuit board. OPX (Off Premise Extension) - Like a party line, an OPX is a line that serves more than one subscriber location. Examples of OPXs are offpremise answering services, and lines that serve more than one building. 347
- 348. Your Automatic Call Processor will not operate fully if attached on a line with an OPX. Orbit - The path, relative to a specified frame of reference, described by the center of mass of a satellite or other object in space subjected primarily to natural forces, mainly the force of gravity. Orbit Determination - The process of describing the past, present, or predicted position of a satellite in terms of orbital parameters. Order Of Diversity - The number of independently fading propagation paths or frequencies, or both, used in diversity reception. Orderwire Circuit - A voice or data circuit used by technical control and maintenance personnel for coordination and control actions relative to activation, deactivation, change, rerouting , reporting, and maintenance of communication systems and services. Synonyms engineering channel, engineering orderwire, service channel. Orderwire Multiplex - A multiplex carrier set specifically designed for the purpose of carrying orderwire traffic, as opposed to one designed for carrying mission traffic. Ordinary Ray - See birefringence. In a transparent material, anisotropism of the refractive index, which varies as a function of polarization as well as orientation with respect to the incident ray. Note 1: The term "birefringence" means, literally, " double refraction." Note 2: All crystals except those of cubic lattice structure exhibit some degree of anisotropy with regard to their physical properties, including refractive index. Other materials, such as glasses or plastics, become birefringent when subjected to mechanical strain. Note 3: Birefringent materials, including crystals, have the ability to refract an unpolarized incident ray into two separate, orthogonally polarized rays, which in the general case take different paths, depending on orientation of the material with respect to the incident ray. The refracted rays are referred to as the "ordinary," or "O" ray, which obeys Snell's Law, and the "extraordinary," or "E" ray, which does not. Organizer - See splice organizer. In optical communication, a device that facilitates the splicing or breaking out of fiber optic cables. Note: The organizer provides means to separate and secure individual buffer tubes, fibers, and/or pigtails. It also provides means to secure mechanical splices or protective sleeves used in connection with fusion splices, and has means to contain the slack fiber that remains after the splicing process is completed. Originating Connection - The connection between the termination of a user-network interface and an operator service access point that is used for communication between the user and the operator service. Originating Endpoint - In a wideband packet node, the point that receives channelized traffic, packetizes it, and sends it into the wideband packet network. Originating Line Information (OLI) - Information indicating a toll class of service for the call. Originating Line-Side Access - The ability to dial the appropriate 7- or 10- digit test number from a subscriber line. Originating Point Code (OPC) - A part of the routing label in a signaling message that uniquely identifies the originating point of that signaling message in a signaling network. Originating Trunk-Side Access - The ability to dial the appropriate test line number with trunk access using the appropriate test equipment. 348
- 349. Originating User - The user that initiates a particular information transfer transaction. Note: The originating user may be either the source user or the destination user. Origination Network - The signaling network that initiates a non-circuit-related message containing intermediate signaling network indication (ISNI) information; this network may send subsequent messages based on the received ISNI information. Originator - See access originator, disengagement originator. Originator-To-Recipient Speed Of Service - Synonym speed of service. Orthogonal Multiplex - A method of combining two or more digital signals that have mutually independent pulses, thus avoiding intersymbol interference. Orthogonal Sampling - In digital video, a sampling where the luminance and the color-difference samples are generated from pixels arranged in common, continuous vertical and horizontal lines on a rectilinear grid that remains constant field / frame to field/frame. Orthomode Transducer - A device forming part of an antenna feed and serving to combine or separate orthogonally polarized signals. Oscillator - An electronic circuit designed to produce an ideally stable alternating voltage or current. OSI - Abbreviation for Open Systems Interconnection. OSI--RM - Abbreviation for Open Systems Interconnection--Reference Model . OTAR - Abbreviation for over-the-air rekeying. OTDR - Abbreviation for optical time domain reflectometer. Other Common Carrier (OCC): A communications common carrier --usually an interexchange carrier --that offers communications services in competition with AT&T and/or the established U.S. telephone local exchange carriers. Outage - A telecommunications system service condition in which a user is completely deprived of service by the system. Note: For a particular system or a given situation, an outage may be a service condition that is below a defined system operational threshold, i.e., below a threshold of acceptable performance. See outage threshold. Outage Duration - That period of time between the onset of an outage and the restoration of service. Outage Probability - The probability that an outage will occur within a specified time period. Outage Ratio - The sum of all the outage durations divided by the time period of measurement. Outage State - See outage. Outage Threshold - For a supported performance parameter of a system, the value that establishes the minimum performance level at which the system is considered to remain in an operational state. Note: A 349
- 350. measured parameter value better than the outage threshold indicates that the system is in a system operational state. Out Call - A universal personal telecommunications ( UPT ) call type that permits a UPT user to make calls from any terminal on any network, and have access to his/her subscribed services limited only by the serving and/or assisting network's capabilities. Out-Call Registration - A feature that enables the universal personal telecommunications ( UPT ) user to register for outgoing calls from the current terminal address to allow outgoing calls to be made from that terminal address. When registered, upon accessing the UPT facilities, all outgoing UPT calls can be made from that terminal address for the duration specified by the UPT user (duration may also be specified in terms of number of outgoing UPT calls), or until a specified de- registration time . Outgoing UPT calls will be charged to the UPT subscriber. Normally, the UPT user will not have to carry out any further authentication procedures in order to make outgoing calls. However, optionally, a simplified authentication procedure may be used. A UPT user may register for outgoing calls to several terminal addresses simultaneously, but at any time only one UPT user/number may be registered for outgoing calls at the same terminal address. The UPT user may also explicitly de-register outgoing calls. Outgoing Access - The ability of a user to originate data calls via an ISDN. Out-Of-Area: An area not included in the subscribed service. An area may be defined in terms of a state/province, NPA, LATA, etc. Out-Of-Band Emission - Emission on a frequency or frequencies immediately outside the necessary bandwidth which results from the modulation process, but excluding spurious emission. Out-Of-Band Notification - In encryption, notification using a communication means other than the primary communication means. Out-Of-Band Signaling -1. Signaling that uses a portion of the channel bandwidth provided by the transmission medium, e.g. , the carrier channel, which portion is above the highest frequency used by, and is denied to, the speech or intelligence path by filters. Note: Out-of- band signaling results in a lowered high- frequency cutoff of the effective available bandwidth. 2. Signaling via a different channel (either FDM or TDM ) from that used for the primary information transfer. Out-Of-Frame-Alignment Time - The time during which frame alignment is effectively lost. Note: The out-of- frame-alignment time includes the time to detect loss of frame alignment and the alignment recovery time. Outpulsing - The process of transmitting address information over a trunk from one switching center or switchboard to another. Output - 1. Information retrieved from a functional unit or from a network, usually after some processing. 2. An output state, or sequence of states. 3. Pertaining to a device, process, or channel involved in the production of data by a computer or by any of its components. Output Angle - Synonym radiation angle. Output Rating -1. The expression of the stated power available at the output terminals of a transmitter when connected to the normal load or its equivalent. 2. Under specified ambient conditions, the expression of the power that can be delivered by a device over a long period of time without overheating. 350
- 351. Outside Plant - 1. In telephony, all cables, conduits, ducts, poles, towers, repeaters, repeater huts, and other equipment located between a demarcation point in a switching facility and a demarcation point in another switching facility or customer premises. Note: The demarcation point may be at a distribution frame , cable head, or microwave transmitter. 2. In DOD communications, the portion of intrabase communications equipment between the main distribution frame ( MDF ) and a user end instrument or the terminal connection for a user instrument. Out-Slot Signaling - Signaling performed in digital time slots that are not within the channel time slot. Outward Dialing - See direct outward dialing. Ovality -1. The attribute of an optical fiber, the cross section of the core or cladding of which deviates from a perfect circle. 2. In an optical fiber, the degree of deviation, from perfect circularity, of the cross section of the core or cladding. Note 1: The cross sections of the core and cladding are assumed to first approximation to be elliptical. Quantitatively, the ovality of either the core or cladding is expressed as 2( a - b )/( a + b ), where a is the length of the major axis and b is the length of the minor axis. The dimensionless quantity so obtained may be multiplied by 100 to express ovality as a percentage. Note 2: Alternatively, ovality of the core or cladding may be expressed or specified by a tolerance field consisting of two concentric circles, within which the cross section boundaries must lie. Synonym noncircularity. Overfill - 1. The condition that prevails when the numerical aperture of an optical source, such as a laser, light-emitting diode, or optical fiber, exceeds that of the driven element, e.g., optical fiber core. 2. The condition that prevails when the beam diameter of an optical source, such as a laser, light-emitting diode, or optical fiber, exceeds that of the driven element, e.g., optical fiber core. Note: In optical communications testing, overfill in both numerical aperture and mean diameter ( core diameter or spot size ) is usually required. Overflow -1. In telephony, the generation of potential traffic that exceeds the capacity of a communications system or subsystem. 2. In telephony, a count of telephone call attempts made on groups of busy trunks or access lines. 3. In telephony, traffic handled by overflow equipment. 4. In telephony, traffic that exceeds the capacity of the switching equipment and is therefore lost. 5. In telephony, on a particular route, excess traffic that is offered to another route, i.e. , an alternate route . 6. In digital computing, synonym for arithmetic overflow. 7. In digital communications, the condition that exists when the incoming data rate exceeds that which can be accommodated by a buffer, resulting in the loss of information. Overhead Bit - Any bit other than a user information bit. Overhead Communications - See overhead bit. Overhead Information - Digital information transferred across the functional interface between a user and a telecommunications system, or between functional units within a telecommunications system, for the purpose of directing or controlling the transfer of user information or the detection and correction of errors. Note: Overhead information originated by the user is not considered to be system overhead information. Overhead information generated within the communications system and not delivered to the user is system overhead information. Thus, the user throughput is reduced by both overheads while system throughput is reduced only by system overhead. Overlap Pulsing - An arrangement for exchange - carrier -to- interexchange carrier (EC-to- IC ) outpulsing that allows seizure of the EC-to-IC trunk and initiation of outpulsing prior to completion of dialing by the calling customer. 351
- 352. Overlay -1. One of several segments of a computer program that, during execution, occupies the same area of main storage, one segment at a time. 2. To use repeatedly the same areas of internal storage during different stages of the execution of a program. Overlay Cell - A larger cell that physically overlays one or more smaller cells. For example, intra-building cells may be encompassed by a larger campus cell. Overload - A load, placed on a device or facility, that is greater than the device or facility is capable of handling, i.e., capable of performing the functions for which it was designed. Note: Examples of overloads are (a) traffic on a communications system greater than the traffic capacity of the system, (b) for analog inputs, voltage levels above which an analog-to-digital converter cannot distinguish a change, and (c) in electrical circuits, an electrical current that will result in damage from overheating. Overload Point - Synonym load capacity. - In pulse-code modulation (PCM), the level of a sinusoidal signal that has positive and negative peaks that coincide with the positive and negative virtual decision values of the encoder. Note: Load capacity is usually expressed in dBm0. Overmodulation -1. The condition that prevails when the instantaneous level of the modulating signal exceeds the value necessary to produce 100% modulation of the carrier. Note 1: Overmodulation results in spurious emissions by the modulated carrier, and distortion of the recovered modulating signal. Note 2: Overmodulation in the sense of this definition is almost always considered a fault condition. 2. The condition that prevails when the mean level of the modulating signal is such that peaks in the modulating signal exceed the value necessary to produce 100% modulation of the carrier. Note: Overmodulation in the sense of this definition, if not excessive, is sometimes considered permissible. Override -1. To preempt, manually or automatically, a prescribed procedure. Note: For example, one might manually override a prescribed course of action programmed to occur in the event of a fault. 2. In telephony, the entering of or seizure of, a busy circuit, i.e. , an occupied circuit, by a party other than those using the circuit. Note: For example, an attendant might override a circuit after a busy verification, or a user with a higher precedence level might override a circuit. Overshoot - 1. In the transition of any parameter from one value to another, the transitory value of the parameter that exceeds the final value. Note: Overshoot occurs when the transition is from a lower value to a higher value. When the transition is from a higher value to a lower value, and the parameter takes a transitory value that is lower than the final value, the phenomenon is called undershoot. 2. The increased amplitude of a portion of a nonsinusoidal waveform, i.e., signal, at the output of a nonlinear circuit, e.g., a realizable amplifier, caused by the characteristics of the circuit. Note 1: Overshoot causes distortion of the signal. Note 2: Overshoot may result from circuit design parameters that are intended to decrease the response time of the circuit. Note 3: The amount of overshoot in a given circuit is designed to minimize response time while maintaining distortion of the signal within acceptable limits. The absence or presence of overshoot, and if present, its magnitude, is a function of a circuit design parameter called damping. 3. The result of an unusual atmospheric, e.g. , ionospheric, condition that causes microwave signals to be received where they are not intended. Overt Channel - A Communications path within a computer system or network designed for the authorized transfer of data. Over-The-Air Key Distribution - Providing electronic key via over-the-air rekeying, over-the-air key transfer, or cooperative key generation. Over-The-Air Key Transfer - Electronically distributing key without changing traffic encryption key used on the secured communications path over which the transfer is accomplished. 352
- 353. Over-The-Air Rekeying (OTAR) - Changing traffic encryption key or transmission security key in remote crypto -equipment by sending new key directly to the remote crypto-equipment over the communication path it secures. Over-The-Horizon Radar - A radar system that makes use of the atmospheric reflection and refraction phenomena to extend its range of detection beyond line of sight. Over-the-horizon radars may be either forward scatter or backscatter systems. Overtone - Of a sinusoidal wave, an integral multiple of the frequency, i.e., the fundamental, of the wave, other than the fundamental itself. Note 1: The first overtone is twice the frequency of the fundamental, and thus corresponds to the second harmonic; the second overtone is three times the frequency of the fundamental, and thus corresponds to the third harmonic, etc. Note 2: Use of the term overtone is generally confined to acoustic waves, especially in applications related to music. Overwrite Procedure - The Process of writing patterns of data on top of the data stored on a magnetic medium. P Packet - In data communication, a sequence of binary digits, including data and control signals, that is transmitted and switched as a composite whole. Note: The data, control signals, and possibly error control information, are arranged in a specific format. Packet Assembler/Disassembler (PAD) - A functional unit that enables data terminal equipment ( DTE ) not equipped for packet switching to access a packet- switched network . Packet Entry Event - A packet layer reference event that corresponds to a packet entering a network section (from a circuit section) or a packet entering a DTE (from an access circuit section). Packet Exit Event - A packet layer reference event that corresponds to a packet exiting a network section (to a circuit section), or a packet exiting a DTE (to an access circuit section). Packet Filter - A type of firewall in which each packet is examined and either allowed to pass- through, or is rejected, based on local security policy. Packet Format - The structure of, data, address, and control information in a packet. Note: The size and content of the various fields in a packet are defined by a set of rules that are used to assemble the packet. Packet Header - A header consisting of octets 4 to 8 (inclusive) of the frame (flags excluded from the octet numbers). Packet Internet Groper - See ping. Packetization Interval - Defines the duration of the sampled speech of the access channel that has been collected, coded, and packetized. The packetization interval for voice is 16 ms. Packet Layer Reference Event - The event that occurs when a packet crossing a section boundary changes the state of the packet layer interface. Packet Mode - A mode of operating a communications network in which packet switching is used rather than message switching. 353
- 354. Packet-Mode Terminal - Data terminal equipment ( DTE ) that can control, format, transmit, and receive packets. Packet Sniffer - 1. A dedicated device designed for the purpose of monitoring network traffic in order to recognize and decode certain packets of interest. 2. A software package that enables a general-purpose computer to recognize and decode certain packets of interest. Note: The packet sniffer is normally used by system administrators for network management and diagnostics, but is occasionally used by hackers for illicit purposes such as stealing a user's password or credit-card number. 3. Synonym sniffer. Packet Stream - A collection of logical links multiplexed together onto one physical channel between two endpoints of the wideband packet network . Packet-Switched Data Transmission Service - A service that (a) provides for the transmission of data in the form of packets, (b) switches data at the packet level , and (c) may provide for the assembly and disassembly of data packets. Packet-switched - Communication system that chops messages into small packets before sending them. All packets are addressed and coded so they can be recompiled at their destination. Each packet can follow its own path and therefore can work around problematic transmission segments. Packet switching is best when reaching a destination is the primary concern and latency is permissible, such as sending e-mail and loading Web pages. Packet Switching - The process of routing and transferring date by means of addressed packets so that a channel is occupied during the transmission of the packet only, and upon completion of the transmission the channel is made available for the transfer of other traffic. Packet-Switching Network - A switched network that transmits data in the form of packets. Packet-Switching Node - In a packet-switching network, a node that contains data switches and equipment for controlling, formatting, transmitting, routing, and receiving data packets. Note: In the Defense Data Network ( DDN ), a packet-switching node is usually configured to support up to thirty-two X.25 56-kb/s host connections, as many as six 56-kb/s interswitch trunk (IST) lines to other packet-switching nodes, and at least one Terminal Access Controller (TAC). Packet Transfer Mode - A method of information transfer, by means of packet transmission and packet switching, that permits dynamic sharing of network resources among many connections. Pad - A network, of fixed resistors, that attenuates signals by a fixed amount with negligible distortion. Note: The resistive network is called an attenuator if the resistance is adjustable. PAD - Acronym for packet assembler/disassembler. Padding - 1. In cryptography, a bit or a string of bits appended to a message either for filtering purposes or to cause the message to contain an even multiple of the number of bits required by the cryptographic algorithm. 2. One or more bits appended to a message in order to cause the message to contain the required number of bits or bytes. Padlocking - The use of special techniques to protect data or software against unauthorized copying. Pager - A small radio receiver designed to be carried by a person and to give an aural, visual, or tactile indication when activated by the reception of a radio signal containing its specific code. It may also 354
- 355. reproduce sounds and/or display messages that were also transmitted. Some pagers also transmit a radio signal acknowledging that a message has been received. Synonym - beeper. Paging - A one-way communications service from a base station to mobile or fixed receivers that provide signaling or information transfer by such means as tone, tone-voice, tactile, optical readout, etc. Paging and Radiotelephone Service - See PARS. Paging Receiver - See pager. Paired Cable - A cable made up of one or more separately insulated twisted-wire pairs, none of which is arranged with another to form quads. Paired Disparity Code - A code in which some or all of the characters are represented by two sets of digits of opposite disparity that are used in sequence so as to minimize the total disparity of a longer sequence of digits. Note 1: An alternate mark inversion signal is an implementation of a paired disparity code. Note 2: The digits may be represented by disparate physical quantities, such as two different frequencies, phases, voltage levels, magnetic polarities, or electrical polarities, each one of the pair representing a 0 or a 1. Pair-Gain System - A transmission system that uses concentrators or multiplexers so that fewer wire pairs may be used than would otherwise be required to provide service to a given number of subscribers. PAL - Acronym for phase alternation by line. A television signal standard (625 lines, 50 Hz, 220 V primary power ) used in the United Kingdom, much of the rest of western Europe, several South American countries, some Middle East and Asian countries, several African countries, Australia, New Zealand, and other Pacific island countries. PAL-M - A modified version of the phase -alternation-by-line ( PAL ) television signal standard (525 lines, 50 Hz, 220 V primary power ), used in Brazil. Palm Computer - See palm-top. Palm-Top - A small (pocket-size), hand-held computer, often including network-access software, personal- schedule software, and a basic word processor. A hand-held personal computer, lightweight, small, battery- powered, general-purpose programmable computer . It typically has a miniaturized full-function, typewriterlike keyboard for input and a small, full color, liquid-crystal display for output. In addition to an operating system that is compatible with that of a desktop computer, a palmtop will typically contain a word processor, a spreadsheet program, and a calendar and phone book. A variety of other programs can be loaded and executed, and data can usually be transferred to and from a desktop computer. Although some palmtops are like personal digital assistants in that they accept handwritten or touch screen input, they generally differ in that the palmtop has more memory, a keyboard, and a greater variety of available programs. PAM - Abbreviation for pulse-amplitude modulation. PAMA - Abbreviation for pulse-address multiple access. Panning - 1. On the viewing screen of a display device, e.g., a computer monitor , horizontal shifting of the entire displayed image. Note: The panning direction is at a right angle with respect to the scrolling direction. 2. In video technology, the use of a camera to scan a subject horizontally. 3. In antenna systems, successively 355
- 356. changing the azimuth of a beam of radio-frequency energy over the elements of a given horizontal region, or the corresponding process in reception. p / a r -Abbreviation for peak-to-average ratio. Parabolic Antenna - An antenna consisting of a parabolic reflector and a radiating or receiving element at or near its focus. Note: If the reflector is in the shape of a paraboloid of revolution, it is called a paraboloidal reflector; cylindrical paraboloids and off-axis paraboloids of revolution are also used. Parabolic Profile - In an optical fiber , a power-law index profile with the profile parameter , g, equal to 2. Synonym quadratic profile. Parallel Computer - A computer that has multiple arithmetic units or logic units that are used to accomplish parallel operations or parallel processing. Parallel Port - A port through which two or more data bits are passed simultaneously, such as all the bits of an 8-bit byte, and that requires as many input channels as the number of bits that are to be handled simultaneously. Parallel Processing - Pertaining to the concurrent or simultaneous execution of two or more processes in a single unit. Parallel-to-Serial conversion - Conversion of a stream of multiple data elements, received simultaneously, into a stream of data elements transmitted in time sequence, i.e. , one at a time. Parallel Transmission - 1. The simultaneous transmission of the signal elements of a character or other data item. 2. In digital communications, the simultaneous transmission of related signal elements over two or more separate paths. Note: Protocols for parallel transmission, such as those used for computer ports, have been standardized by ANSI. Parametric Amplifier (Paramp) - An amplifier that (a) has a very low noise level, (b) has a main oscillator that is tuned to the received frequency, (c) has another pumping oscillator of a different frequency that periodically varies the parameters, i.e., the capacitance or inductance, of the main oscillator circuit, and (d) enables amplification of the applied signal by making use of the energy from the pumping action. Note: Paramps with a variable-capacitance main-oscillator semiconductor diode are used in radar tracking and communications Earth stations, Earth satellite stations, and deep-space stations. The noise temperature of paramps cooled to the temperature of liquid helium, about 5 K, is in the range of 20 to 30 K. Paramp gains are about 40 dB. Parasitic Element - Of an antenna, a directive element that is not connected to a radio transmitter or receiver either directly or via a feeder, but is coupled to the driven element only by the fields. Synonym passive element. Parasitic Emission - In a communications system in which one or more electromagnetic sources are used, electromagnetic radiation --such as lightwaves, radio waves, microwaves, X-rays, or gamma rays from one or more of the sources--that is not harmonically related, i.e., is not coherent, with the transmitted carrier. Note: Parasitic emissions are usually caused by undesired oscillations or energy- level transitions in the sources. Paraxial Ray - In optical systems, a ray that is close to and nearly parallel with the optical axis. 356
- 357. Parity - 1. In binary-coded data, a condition that is maintained such that, in any permissible coded expression, the total number of 1s, or 0s, is always odd or always even. Note 1: Parity is used in error- detecting and error-correcting codes. Note 2: For example, in the ASCII code or in the International Telegraph Alphabet 5 (ITA-5) code as usually implemented, 7 bits are used to represent each character and 1 bit is used as a parity check bit. 2. Bit(s) used to determine whether a block of data has been altered. Parity Bit - An extra bit that can be added to a group of "0" bits and "1" bits to make the parity of the group odd or even. Note: The parity bit is discarded when the message is received. Parity Check - A test that determines whether the number of ones or zeros in an array of binary digits is odd or even. Note: Odd parity is standard for synchronous transmission and even parity for asynchronous transmission. Synonym odd-even check. Parking Party - Representative of the served user who parks a call via "call park". Par Meter - Abbreviation for peak-to-average ratio meter. A meter used to measure, calculate, and display the ratio of the peak power level to the time -averaged power level in a circuit, i.e. , the peak-to-average ratio ( p / a r). Note 1: A par meter is used as a quick means to identify degraded telephone channels. Note 2: A par meter is very sensitive to envelope delay distortion. The par meter may also be used for idle channel noise, nonlinear distortion, and amplitude-distortion measurements. Note 3: The peak-to-average ratio can be determined for many signal parameters, such as voltage, current, power, frequency, and phase. PARS - Abbreviation for paging and radiotelephone service. A radio service in which common carriers are authorized to offer and provide paging and radiotelephone service to the general public. This service was formerly titled Public Land Mobile Service. Partial-Dial Condition - A condition in which outpulsing has commenced, insufficient information has been received by the customer installation (CI) to process the call and no further outpulsing has been received from the network within a timed interval. Partitioned Security Mode - [An] information - system (IS) security mode of operation wherein all personnel have the clearance, but not necessarily formal access approval and need-to-know, for all information handled by an IS. Party ID -1. The served user 's (or controller 's) reference to a particular party within the context of a call. Note 1: Multiple parties may be associated with a given call, e.g., a conference call. Moreover, there may be multiple connections associated with a single party, e.g., a simultaneous voice and video call. Note 2: This service description assumes that there exists only one connection to a given party. 2. In a teleconference, any participant. Party Line - A line that serves more than one subscriber or user. In telephone systems, an arrangement in which two or more user end instruments, usually telephones, are connected to the same loop. Note: If selective ringing is not used, individual users may be alerted by different ringing signals, such as a different number of rings or a different combination of long and short rings. Party lines remain primarily in rural areas where loops are long. Privacy is limited and congestion often occurs. Synonym multiparty line. Passband - The portion of spectrum , between limiting frequencies (or, in the optical regime, limiting wavelengths), that is transmitted with minimum relative loss or maximum relative gain. Note 1: The limiting frequencies are defined as those at which the relative intensity or power decreases to a specified fraction of the maximum intensity or power. This decrease in power is often specified to be the half-power points, i.e. , 3 dB below the maximum power. Note 2: The difference between the limiting frequencies is called the bandwidth, and is expressed in hertz (in the optical regime, in nanometers or micrometers). 357
- 358. Passive Device - A device that does not require a source of energy for its operation. Note: Examples of passive devices are electrical resistors, electrical capacitors, diodes, optical fibers, cables, wires, glass lenses, and filters. Passive Element - Synonym parasitic element. Passive Satellite -1. In a satellite communications system, a satellite that only reflects signals from one Earth station to another, or from several Earth stations to several others. Note: Although the satellite acts passively by reflecting signals, it may contain active devices for station keeping. 2. An Earth satellite intended to transmit radio communication signals by reflection. Passive Sensor - A measuring instrument in the Earth exploration-satellite service or in the space research service by means of which information is obtained by reception of radio waves of natural origin. Passive Star: See star coupler. Passive Station - On a multipoint connection or a point-to-point connection using basic mode link control, any tributary station waiting to be polled or selected. Passive Threat - Of a data or information processing system, a threat of disclosure of information without changing the state of the system. Note: An example of a passive threat is one that could result in the recovery of sensitive information through the unauthorized interception of a data transmission. Passphrase - A sequence of characters, longer than the acceptable length of a password, that is transformed by a password system into a virtual password of acceptable length. Password - A code or word used to gain access to restricted data on a computer network. While passwords provide security against unauthorized users, the security system can only confirm that the password is legitimate, not whether the user is authorized to use the password. That's why it is important to safeguard passwords by: • Never disclosing your password to anyone. • Creating a password that consists of letters, numbers, and symbols. • Changing your password frequently. Password History - With respect to a given information system (IS) asset, a log of expired passwords, used primarily for automatic comparison with proposed new passwords. A password history is used to ensure that proposed new passwords were not used in the recent past, if ever, in connection with the IS asset in question. A password history may be limited to only a prescribed number of expired passwords (the usual case) with any overflow ( i.e., the earliest) being discarded as new ones are added; or it may retain expired passwords only for a prescribed period of time; or both. A password history represents a tool that may be used to ensure that passwords are not repeated within a period of time that is deemed consistent with the sensitivity of the protected information system asset. Password Length Equation - An equation that determines an appropriate password length, M , which provides an acceptable probability, P , that a password will be guessed in its lifetime. Note: The password length is given by M = (log S )/(log N ) where S is the size of the password space and N is the number of characters available. The password space is given by S = LR / P , where L is the maximum lifetime of a password and R is the number of guesses per unit of time. 358
- 359. Password Length Parameter - A basic parameter affecting the password length needed to provide a given degree of security. Note 1: Password length parameters are related by the expression P = LR / S , where P is the probability that a password can be guessed in its lifetime, L is the maximum lifetime a password can be used to log in to a system, R is the number of guesses per unit of time , and S is the number of unique algorithm-generated passwords (the password space). Note 2: The degree of password security is determined by the probability that a password can be guessed in its lifetime. Patch - 1. To connect circuits together temporarily. Note: In communications, patches may be made by means of a cord, i.e., a cable, known as a "patch cord." In automated systems, patches may be made electronically. 2. In a computer program, one or more statements inserted to circumvent a problem or to alter temporarily or permanently a usually limited aspect or characteristic of the functioning of the program, e.g., to customize the program for a particular application or environment. Patch and Test Facility (PTF) - A facility in which supporting functions, such as (a) quality control checking and testing of equipment, links, and circuits, (b) troubleshooting, (c) activating, changing, and deactivating of circuits, and (d) technical coordinating and reporting, are performed. Patch Bay - An assembly of hardware so arranged that a number of circuits, usually of the same or similar type, appear on jacks for monitoring, interconnecting, and testing purposes. Note 1: Patch bays are used at many locations, such as technical control facilities, patch and test facilities, and at telephone exchanges. Note 2: Patch bays facilitate flexibility in the use, routing or restoration of a variety of circuit types, such as dc, VF, group, coaxial, equal-level, and digital data circuits. Patch Panel - One segment of a patch bay. Path -1. In communications systems and network topologies, a route between any two points. 2. In radio communications, the route that (a) lies between a transmitter and a receiver and (b) may consist of two or more concatenated links. Note: Examples of paths are line-of-sight paths and ionospheric paths. 3. In a computer program, the logical sequence of instructions executed by a computer. 4. In database management systems, a series of physical or logical connections between records or segments, usually requiring the use of pointers. Path Attenuation - Synonym path loss. Path Clearance - In microwave line-of-sight communications , the perpendicular distance from the radio - beam axis to obstructions such as trees, buildings, or terrain. Note: The required path clearance is usually expressed, for a particular k -factor, as some fraction of the first Fresnel zone radius. Path Iintermodulation Noise - See intermodulation noise. Path Loss - In a communication system , the attenuation undergone by an electromagnetic wave in transit between a transmitter and a receiver . Note 1: Path loss may be due to many effects such as free-space loss, refraction, reflection, aperture - medium coupling loss, and absorption. Note 2: Path loss is usually expressed in dB. Synonym path attenuation. Path Overhead (POH) - Overhead assigned to and transported with the payload until the payload is demultiplexed. It is used for functions that are necessary to transport the payload. Path Profile - A graphic representation of the physical features of a propagation path in the vertical plane containing both endpoints of the path, showing the surface of the Earth and including trees, buildings, and other features that may obstruct the radio signal. Note: Profiles are drawn either with an effective Earth 359
- 360. radius simulated by a parabolic arc--in which case the ray paths are drawn as straight lines--or with a "flat Earth"-- in which case the ray paths are drawn as parabolic arcs. Path Quality Analysis - In a communications path, an analysis that (a) includes the overall evaluation of the component quality measures, the individual link quality measures, and the aggregate path quality measures, and (b) is performed by evaluating communications parameters, such as bit error ratio, signal-plus-noise- plus-distortion to noise-plus-distortion ratio, and spectral distortion. Path Quality Matrix - A data bank that contains path-quality analyses used to support path selection and routing determination. Note: In adaptive radio automatic link establishment, path quality matrices contain path quality data for single-link and multilink paths. Path Survey - The assembling of pertinent geographical and environmental data required to design a radio communication system. Pattern Recognition - The identification of objects and images by their shapes, forms, outlines, color, surface texture, temperature, or other attribute, usually by automatic means. Pawsey stub - A device for connecting an unbalanced coaxial feeder to a balanced antenna. PAX - Abbreviation for private automatic exchange. See PBX. Payload -1. In a set of data, such as a data field, block, or stream, being processed or transported, the part that represents user information and user overhead information, and may include user-requested additional information, such as network management and accounting information. Note: The payload does not include system overhead information for the processing or transportation system. Synonym mission bit stream. 2. The interface rate minus frame overhead. This is the act capability for information transfer provided for the next lower level of the hierarchy. Payload Loopback - A signal used to command the far-end receiver to loop back the received payload. Payload Module: The portion of a payload that completely occupies one or more channels. Payload Overhead - Bits that are assigned at the source and remain with the information payload until the payload reaches the sink and are used for functions associated with transporting the payload. Payload Pointer - The pointer that indicates the location of the beginning of the synchronous payload envelope. Pay Per Use Feature Blocking - Allows you to restricts all calls originating from your AT&T residential telephone line(s) from using any or all of the following Pay Per Use Features: Call Return, Call Trace, Repeat Dialing, or Three Way Calling. Pay-Per-Use Features - The following features are available on a per-use or per-occurrence basis rather than on a monthly subscription basis. With the exception of Call Trace, most local phone companies will charge for up to ten pay-per-use features and the ten uses will appear on the bill. After ten paid feature uses, there is no charge for additional per-use features nor will the additional uses appear on the bill. There is a charge for all Call Trace uses and these charges will be identified on the bill. The following features can usually be ordered on a per-use basis: Call Return, Call Trace, Repeat Dialing, and Three-Way Calling. 360
- 361. PBER - Abbreviation for pseudo bit-error ratio. In adaptive high- frequency (HF) radio, a bit error ratio derived by a majority decoder that processes redundant transmissions. Note: In adaptive HF radio automatic link establishment, PBER is determined by the extent of error correction, such as by using the fraction of non-unanimous votes in the 2-of-3 majority decoder. PBX (Private Branch Exchange) - An electronic multi-line telephone system, used primarily in very large applications with many extensions. The identifying feature of most PBXs is that you must dial 9 to get an outside line. PBXs generally use standard single-line telephones at extension locations. A pbx is a privately owned system for voice switching and other telephone related services. It routes calls from the public telephone system within an organization and allows direct internal calls. PBX Tie Trunk - See tie trunk. PBX Trunk - See trunk. PC - Abbreviation for carrier power (of a radio transmitter ). PCB - Abbreviation for power circuit breaker. PC FAX Board - A circuit board that is installed in a personal computer. Like a FAX, it attaches to your telephone line and is capable of transmitting and receiving images with other FAX Boards and FAX machines. A FAX board, when used with a printer and document scanner, operates like a modern FAX machine. PCM - Abbreviation for pulse-code modulation. Modulation in which a signal is sampled, and the magnitude (with respect to a fixed reference) of each sample is quantized and digitized for transmission over a common transmission medium. Note 1: In conventional PCM, before being digitized, the analog data may be processed (e.g., compressed), but once digitized, the PCM signal is not subjected to further processing (e.g., digital compaction) before being multiplexed into the aggregate data stream. Note 2: PCM pulse trains may be interleaved with pulse trains from other channels. PCM multiplex equipment - See multiplexer. PCS (Personal Communications Services) – Originally meant to describe digital service offered at a higher frequency (1900 MHz) than wireless, it is now used as a generic term for all digital (versus analog) wireless. PCS application - From a user -identity- module (UIM) perspective, the files, commands and data used to support PCS services. PCS number - A number that uniquely identifies a PCS user and is used to place or forward a call to that user. Synonyms personal number, UPT number. PCS session - That part of the card session dedicated to the PCS operation. PCS switching center - In personal communications service, a facility that (a) supports access -independent call control/ service control, and connection control ( switching ) functions, and (b) is responsible for interconnection of access and network systems to support end-to-end services. Note 1: The PCS switching center represents a collection of one or more network elements. Note 2: The term "center" does not imply a physical location. PCS System -In personal communications service, a collection of facilities that provides some combination of personal mobility, terminal mobility, and service profile management. Note: As used here, "facilities" 361
- 362. includes hardware, software, and network components such as transmission facilities, switching facilities, signaling facilities, and databases. PC-to-PC Internet Phone Free Internet phone systems such as Skype and FreeWorld Dialup can bypass the telephone system completely, allowing you to make free calls to other users within their respective networks. Some free networks have added services, such as Skype's Skypeout service, that let you call mobile and standard telephones for a metered fee. PC-to-Phone Telephony - a type of VoIP communication that involves making phone calls directly from a computer. Calls are placed using a special piece of software, which may be downloaded over the internet. PC-to-Phone is an extremely cheap and efficient way to communicate, and can result in savings of up to 80% when compared to making calls from a traditional telephone. PDF - An acronym for Portable Document Format, PDF is a file type created by Adobe Systems, Inc. that allows fully formatted, high-resolution documents to be easily transmitted across the Internet and viewed on any computer that has Adobe Acrobat Reader software. PDH - Acronym for plesiochronous digital hierarchy. PDH refers to the DS1/DS2/DS3 family of signals which were developed as an asynchronously multiplexed hierarchy for transmission systems which are now more frequently encountered as payload in a SONET system. PDM - Abbreviation for pulse-duration modulation. PDN - Abbreviation for public data network. PDS - Abbreviation for protected distribution system. PDU -Abbreviation for protocol data unit. PE - Abbreviation for phase -encoded. See phase-encoded recording. Peak Busy Hour - Synonym busy hour. - In a communications system, the sliding 60-minute period during which occurs the maximum total traffic load in a given 24-hour period. Note 1: The busy hour is determined by fitting a horizontal line segment equivalent to one hour under the traffic load curve about the peak load point. Note 2: If the service time interval is less than 60 minutes, the busy hour is the 60-minute interval that contains the service timer interval. Note 3: In cases where more than one busy hour occurs in a 24-hour period, i.e., when saturation occurs, the busy hour or hours most applicable to the particular situation are used. Peak Emission Wavelength - Of an optical emitter, the spectral line having the greatest power. Synonym peak wavelength. 362
- 363. Peak Envelope Power (of a radio transmitter) [PEP, pX, PX]: The average power supplied to the antenna transmission line by a transmitter during one radio frequency cycle at the crest of the modulation envelope taken under normal operating conditions. Peak Limiting - A process by which the absolute instantaneous value of a signal parameter is prevented from exceeding a specified value. Peer Entity - In layered systems, entities in the same layer but in different systems (nodes) that must exchange information to achieve a common objective. Peer-Entity Authentication - The corroboration that a peer entity in an association is the one claimed. peer group - In Open Systems Interconnection (OSI)--Architecture, a group of functional units in a given layer of a network in which all the functions performed by the functional units extend throughout the system at the same layer. Peering - The arrangement of information sharing between Internet Service Providers at various NAPs. Peer Protocol - A formal language used by peer entities to exchange user data. Peg Count -1. In communication systems, a count that is made of the number of times that an event or condition occurs. [From Weik '89] 2. In telephone systems, the process that provides counts of the calls of different service classes that occur during intervals of such frequency as to reliably indicate the traffic load. 3. A count of the attempts to seize, or a count of the actual seizures that occur, of various types of telephone trunks, access lines, switches, or other equipment. Pel - In a facsimile system, the smallest discrete scanning line sample containing only monochrome information , i.e. , not containing gray-scale information. Pen-Based Computer - A computer that uses pattern-recognition software to enable it to accept handwriting as a form of input. A stylus, which may contain special electronic circuitry, is used to write on the computer display or on a separate tablet. The earliest devices were limited to recognizing geometric shapes for computer graphics applications and neatly printed alphabetic characters. Pattern recognition has improved to the level where cursive input is now acceptable, especially in personal digital assistants , although such input is not always accurately interpreted by the software. Some software requires the use of a specially modified alphabet to enter data. Penetration - 1. The intentional passage, through a building wall or partition, or an equipment enclosure or chassis, of a signal -bearing communications medium, e.g., a cable, metallic or optical. 2. Unintended access to the information within a communications or information-processing device via a metallic path intended for another purpose, e.g., via the primary power connection. 3. [The] unauthorized act of bypassing the security mechanisms of a system. 4. The passage of an rf signal through a physical barrier, such as a partition, a wall, a building, or earth. 5. Unauthorized access to a data processing system. Penetration Testing - Security testing in which evaluators attempt to circumvent the security features of a system based on their understanding of the system design and implementation. PEP - Deprecated abbreviation for peak envelope power. Either "PX" or "pX" is now preferred. See peak envelope power, power. 363
- 364. Per-Call Key - A unique traffic encryption key generated automatically by certain secure telecommunications systems to secure single voice or data transmissions. Percentage Modulation -1. In angle modulation, the fraction of a specified reference modulation, expressed in percent. 2. In amplitude modulation, the modulation factor expressed in percent. Note: Percentage modulation may also be expressed in dB below 100% modulation. Percent Break - In pulsed telephone signaling ( dialing ), the ratio, expressed in percent, of (a) the open- circuit (break) time to (b) the sum of the open- and closed-circuit times of a single dial pulse cycle. Note: For example, at a pulse rate of 10 per second, the pulse period is 100 milliseconds. If, during each pulse period, the equipment generating the dial pulses ( e.g., a telephone set ) presents an open circuit (high impedance ) for 48 milliseconds, and a closed circuit (low impedance) for 52 milliseconds, the percent break is [48 ms/(48ms + 52ms)] = 0.48, or 48%. Performance Measurement Period - The period during which performance parameters are measured. Note: A performance measurement period is determined by required confidence limits and may vary as a function of the observed parameter values. User time is divided into consecutive performance measurement periods to enable measurement of user information transfer reliability. Perfect Forward Secrecy - In cryptography, of a key -establishment protocol, the condition in which the compromise of a session key or long-term private key after a given session does not cause the compromise of any earlier session. Performance Anomalies - A discrepancy between actual and desired characteristics of an item. An anomaly may or may not affect the ability of an item to perform a required function. Performance Management - In network management, (a) a set of functions that evaluate and report the behavior of telecommunications equipment and the effectiveness of the network or network element and (b) a set of various subfunctions, such as gathering statistical information, maintaining and examining historical logs, determining system performance under natural and artificial conditions, and altering system modes of operation. Performance Measurement Period - The period during which performance parameters are measured. Note: A performance measurement period is determined by required confidence limits and may vary as a function of the observed parameter values. User time is divided into consecutive performance measurement periods to enable measurement of user information transfer reliability. Performance Parameter - A quality, usually quantified by a numerical value, which quality characterizes a particular aspect, capability, or attribute of a system. Note: Examples of performance parameters are peg count and mean time between failures. Performance Primitives - Basic error events or other performance-related occurrences that may be detected by monitoring a digital signal. Performance Reliability - The ability of an item to perform a required function under given conditions for a given time period. Note 1: It is generally assumed that the item is in a state to perform this required function at the beginning of the time interval. Note 2: The term reliability is used as a measure of reliability performance. Performance Standard - A statement of general criteria that define a desired result without specifying the techniques for achieving that result. Synonym performance-based standard. 364
- 365. Periapsis - In a satellite orbit, the point that is closest to the gravitational center of the system consisting of the primary body and the satellite. Note: In an orbit about the Earth, periapsis is called perigee. In an orbit about the Moon, periapsis is called perilune, and in an orbit about the Sun, it is called perihelion. Perigee - Of a satellite orbiting the Earth, the point in the orbit at which the gravitational centers of the satellite and Earth are closest to one another. Perigee Altitude - See altitude of the apogee or of the perigee: The altitude of the apogee or perigee above a specified reference surface serving to represent the surface of the Earth. Note: In technical usage, the definite article is not used with the term apogee or perigee alone. A body orbiting the Earth is said simply to be "at apogee" or "at perigee." It may, however, properly be said to be "at the point of apogee" or "at the point of perigee." Periodic Antenna - An antenna that has an approximately constant input impedance over a narrow range of frequencies. Note: An example of a periodic antenna is a dipole array antenna. Synonym resonant antenna. Period (of a satellite) - The time elapsing between two consecutive passages of a satellite through a characteristic point on its orbit. Periods Processing - Processing of various levels of classified and unclassified information at distinctly different times. Under the concept of periods processing, the system must be purged of all information from one processing period before transitioning to the next. Under periods processing, the system must be purged of all information from one processing period before transitioning to the next when there are different users with differing authorizations. Peripheral Device - See peripheral equipment. Peripheral Equipment - In a data processing system, any equipment, distinct from the central processing unit, that may provide the system with additional capabilities. Note: Such equipment is often offline until needed for a specific purpose and may, in some cases, be shared among several users. Peripheral Node - Synonym endpoint node: In network topology, a node connected to one and only one branch. Periscope Antenna - An antenna configuration in which the transmitting antenna is oriented to produce a vertical radiation pattern, and a flat or off-axis parabolic reflector, mounted above the transmitting antenna, is used to direct the beam in a horizontal path toward the receiving antenna. Note: A periscope antenna facilitates increased terrain clearance without long transmission lines, while permitting the active equipment to be located at or near ground level for ease of maintenance. Permanent Bond - A bond not expected to require disassembly for operational or maintenance purposes. Permanent Signal (PS) -1. An extended off-hook condition not followed by dialing. 2. A connect signal from the network that has not been followed by network outpulsing within a timed interval. Permanent Storage - A storage device in which stored data are nonerasable Permanent Virtual Circuit (PVC) - A virtual circuit used to establish a long-term connection between data terminal equipments ( DTE ). Note 1: In a PVC, the long-term association is identical to the data transfer phase of a virtual call. Note 2: Permanent virtual circuits eliminate the need for repeated call set-up and clearing. Deprecated synonym nailed-up circuit. 365
- 366. Permissible Interference - Observed or predicted interference which complies with quantitative interference and sharing criteria contained in these [Radio] Regulations or in CCIR Recommendations or in special agreements as provided for in these Regulations. Permuter - A device used in crypto-equipment to change the order in which the contents of a shift register are used in various nonlinear combining circuits. Persistent Data - Information that endures beyond a single instance of use, e.g., longer than one call attempt. Personal Agent - Synonym droid. See bot. Personal Authenticating Information (PAI) - Information such as a secret password, a badge, or biometric data —or any combination of these—used to authenticate a user's identity. Personal Communications Service - See PCS. A set of capabilities that allows some combination of terminal mobility, personal mobility, and service profile management. Note 1: The flexibility offered by PCS can supplement existing telecommunications services, such as cellular radio, used for NS/EP missions. Note 2: PCS and UPT are sometimes mistakenly assumed to be the same service concept. UPT allows complete personal mobility across multiple networks and service providers. PCS may use UPT concepts to improve subscriber mobility in allowing roaming to different service providers, but UPT and PCS are not the same service concept. Personal De-registration - The process by which end users cancel a previous registration to a terminal. Personal Digital Assistant - [personal digital assistant] (PDA), lightweight, hand-held computer designed for use as a personal organizer with communications capabilities. A typical PDA has no keyboard, relying instead on special hardware and pen-based computer software to enable the recognition of handwritten input, which is entered on the surface of a liquid crystal display screen. In addition to including such applications as a word processor, spreadsheet, calendar, and address book, PDAs are used as notepads, appointment schedulers, and wireless communicators for sending and receiving data, faxes, and electronic-mail messages. Introduced in 1993, PDAs achieved only modest acceptance during the remainder of the decade due to their relatively high price and limited applications. Personal Identification Number (PIN) - A code or password, unique to or associated with, a specific user, and entered into a data-processing device for purposes of verifying the identity of a person requesting, e.g., a transaction or access. Personal Mobility - In universal personal telecommunications (UPT), (a) the ability of a user to access telecommunication services at any UPT terminal on the basis of a personal identifier, and (b) the capability of the network to provide those services in accord with the user's service profile. Note 1: The personal mobility aspects of personal communications are based on the UPT number. Note 2: Personal mobility involves the network's capability to locate the terminal associated with the user for the purposes of addressing, routing, and charging the user for calls. Note 3: "Access" is intended to convey the concepts of both originating and terminating services. Note 4: Management of the service profile by the user is not part of personal mobility. Personal Mobility Controller - In UPT (universal personal telecommunications), a facility that provides the control logic for user authentication, service request validation, location management, alerting, user access to service profile, privacy, access registration, and call management. 366
- 367. Personal Mobility Management - In PCS(personal communication service ), the capability that (a) provides authentication of user identification and maintains user location information in the service profile, (b) controls the completion of calls based on user-specified incoming call management contained in the service profile, (c) provides translation between user identification and identification of the terminal currently associated with the user for the completion of calls to the use's current location, and (d) controls the services and features available to the user based on the user's subscription and in conjunction with user-specified terminal access configurations. Personal Number - A number that uniquely identifies a PCS or UPT user ( universal personal telecommunications service user) and is used to place, or forward, a call to that user. Note: Before the full implementation of UPT service, the use of the term UPT number may, in some contexts, be subject to misinterpretation. The personal number is a UPT number, and is the basis of the personal mobility aspects of PCS. The term is provided as an alternative term for use where appropriate to avoid such a misinterpretation. Synonym PCS number. Personal Registration - In universal personal telecommunications, the process of associating a UPT user with a specific terminal. Personal Station - A light-weight, pocket-sized FPLMTS terminal (Future Public Land Mobile Telecommunication Systems terminal). Personal Terminal - In personal communications service, a lightweight, small, portable terminal that provides the capability for the user to be either stationary or in motion while accessing and using telecommunication services. Informal synonym brick. Personalized Ringing - A phone company service that you could subscribe to where you are issued a different ring pattern for specific phone numbers that call you. For instance, you could assign a double ring to any calls that come from your mother's phone number and a triple ring for any calls that come from your daughter's phone number. When you mom calls you, your phone rings with a double ring pattern, When your daughter calls from here home phone number, it rings with a triple ring pattern and when anyone else calls, the phones ring like normal. The phone companies advertise personalized ringing service for when you want to know if your kids, spouse or the boss is calling. With this feature all the people you need to talk to will be identified by the personalized ring or tone and you will know to answer their call. Note: If you want to have two separate phone numbers each with its own distinctive ring pattern on one line, in this case "personalized ring" is NOT what you want. You will need to subscribe to "distinctive ring" instead. PGP - Abbreviation for pretty good privacy. A publicly available implementation of a public-key encryption system using no trusted third party. Note: PGP can be used to apply a digital signature to a message without actually encrypting the text of the message. This is normally used in public postings where the user wants all readers to be able to see the message text and also wants the reader to be able to confirm that the message is unaltered from its original form. Once a digital signature is created with PGP, it is impossible for anyone to modify either the message or the signature without the modification being detected by PGP. Phantom Circuit - A third circuit derived from two suitably arranged pairs of wires, called side circuits, with each pair of wires being a circuit in itself and at the same time acting as one conductor of the third circuit. Note: The side circuits are coupled to their respective drops by center-tapped transformers, usually called "repeat coils." The center taps are on the line side of the side circuits. Current from the phantom circuit is 367
- 368. split evenly by the center taps. This cancels crosstalk from the phantom circuit to the side circuits. Synonym [loosely] phantom facility. Phantom Facility - A transmission facility derived with repeating coils from two or more pairs of wires. Synonyms phantom circuit, phantom pair. Note: The name "phantom" is derived from the fact that balanced, center-tapped transformers, called "repeat(ing)" coils in telephone parlance, can be used, e.g., in conjunction with two twisted pairs, to create a third, electrically isolated transmission path ("phantom pair") by splitting the latter's electrical signal between the two twisted pairs (called "side circuits") in such a fashion as to cancel inductive interference from the phantom circuit to the side circuits, and vice versa. Phantom Group - Three circuits that are derived from simplexing two physical circuits to form a phantom circuit. Phase - 1. Of a periodic, varying phenomenon, e.g., an electrical signal or electromagnetic wave, any distinguishable instantaneous state of the phenomenon, referred to a fixed reference or another periodic varying phenomenon. Note 1: Phase, i.e., phase time (frequently abbreviated simply to "phase" in informal usage), can be specified or expressed by time of occurrence relative to a specified reference. Note 2: The phase of a periodic phenomenon can also be expressed or specified by angular measure, with one period usually encompassing 360&176; (2 radians). Note 3: Phase may be represented (a) in polar coordinates by M , where M is the magnitude and is the phase angle, and (b) in Cartesian coordinates, i.e., an Argand diagram, as (a + jb), where a is a real component and b is an imaginary component such that tan = (b /a), 2 2 ½ where is the phase angle, and the magnitude, M, is (a + b ) 2. A distinguishable state of a phenomenon. 3. That period of time during which a specified function occurs in a sequential list of functions. Phase Angle - Of a periodic wave, the number of suitable units of angular measure between a point on the wave and a reference point. Note 1: The reference point may be a point on another periodic wave. The waves may be plotted on a suitable coordinate system, such as a Cartesian plot, with degrees or other angular measure usually plotted on the abscissa and amplitude on the ordinate. Usually, at least one full cycle of each wave is plotted, with 360&176; (2 radians) encompassing one full cycle. The reference points may be any significant instants on the waves, such as where they cross the abscissa axis. Note 2: The use of angular measure to define the relationship between a periodic wave and a reference point is derived from the projection of a rotating vector onto the real axis of an Argand diagram. Note 3: The value of the phase angle of a point on the wave is the point on the abscissa that corresponds to the point on the wave. Note 4: The phase angle of a vector may be written as M , where M is the magnitude of the vector and is the phase angle relative to the specified reference. Phase Bandwidth - Of a network or device, the width of the continuous frequency range over which the phase -vs.-frequency characteristic does not depart from linearity by more than a stated amount. Phase Coherence - The state in which two signals maintain a fixed phase relationship with each other or with a third signal that can serve as a reference for each. Phase Coherent - See phase coherence. Phase Constant - The imaginary part of the axial propagation constant for a particular mode, usually expressed in radians per unit length. Phased Array - A group of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions. Note 1: The relative amplitudes of--and constructive and destructive interference effects among--the signals radiated by the individual antennas determine the 368
- 369. effective radiation pattern of the array. Note 2: A phased array may be used to point a fixed radiation pattern, or to scan rapidly in azimuth or elevation. Phase Delay - In the transmission of a single- frequency wave from one point to another, the delay of an arbitrary point in the wave that identifies its phase. Note: Phase delay may be expressed in any convenient unit, such as seconds, degrees, radians, or wavelengths. Phase Departure - 1. A phase deviation from a specified value. 2. An unintentional deviation from the nominal phase value. Phase Detector - A circuit or instrument that detects the difference in phase between corresponding points on two signals. Phase Deviation - In phase modulation, the maximum difference between the instantaneous phase angle of the modulated wave and the phase angle of the unmodulated carrier. Note: For a sinusoidal modulating wave, the phase deviation, expressed in radians, is equal to the modulation index. Phase Diagram - A graphic representation of the phase relationships between two or more waveforms. Note: A phase diagram may be represented as a vector diagram or as an amplitude-vs.- time diagram. Phase Difference - The time interval or phase angle by which one wave leads or lags another. Synonym phase offset. Phase-Locked Loop (PLL) - An electronic circuit that controls an oscillator so that it maintains a constant phase angle relative to a reference signal. Note: Phase-locked loops are widely used in space communications for coherent carrier tracking and threshold extension, bit synchronization, and symbol synchronization. Phase Offset - Synonym phase difference. Phase-Shift Keying (PSK) - 1. In digital transmission, angle modulation in which the phase of the carrier is discretely varied in relation either to a reference phase or to the phase of the immediately preceding signal element, in accordance with data being transmitted. 2. In a communications system, the representing of characters, such as bits or quaternary digits, by a shift in the phase of an electromagnetic carrier wave with respect to a reference, by an amount corresponding to the symbol being encoded. Note 1: For example, when encoding bits, the phase shift could be 0° for encoding a "0," and 180° for encoding a "1," or the phase shift could be -90 for "0" and +90° for a "1," thus making the representations for "0" and "1" a total of 180° apart. Note 2: In PSK systems designed so that the carrier can assume only two different phase angles, each change of phase carries one bit of information, i.e., the bit rate equals the modulation rate. If the number of recognizable phase angles is increased to 4, then 2 bits of information can be encoded into each signal element; likewise, 8 phase angles can encode 3 bits in each signal element. Synonyms biphase modulation, phase-shift signaling. Phase Term - In the propagation of an electromagnetic wave in a uniform waveguide, such as an optical fiber or metal waveguide, the parameter that indicates the phase change per unit distance of the wave at any point along the waveguide. Phone - 1. Abbreviation for telephone, telephony. 2. Loosely, the voice-operation mode in radio communications. 369
- 370. Phone Company Voice Mail - A phone company feature that answers calls and takes messages when you are on the phone, on the internet, sending a fax, or not at home. This feature also works when the electrical power is out. You can access your voicemail box through a local access number. You enter your PIN and follow the appropriate prompts to use the service. There is a maximum capacity for messages, minutes per message, and message retention length, as outlined in marketing information for your local phone company. Call Forwarding Busy/No Answer must be ordered but will not be billed when Voice Mail is ordered. Phone Jack - n : a jack for plugging in a telephone [syn: telephone jack]. Phone Fax Switch - A device that allows a single phone line to be shared for multiple devices. Typically a Phone Fax Switch would allow voice (phones and answering machine) and a fax machine or fax modem to operate on a shared phone line. Other applications include any variation of voice, a fax machine, fax/modem and/or modem(s). Incomming calls are automatically routed to the proper device(s). If the call comes in and it is a fax call, the call is automatically routed to the fax machine or fax .modem. If the call is a modem call, it is routed to the correct modem. Voice calls are routes to phone(s) and/or answering machine. May require a security access code (SAC) in the dialing string to automatically switch to the modem. Synonym Automatic Line Sharing Device . Fax Switch , Automatic Fax Switch . Phone Line Switch - - A device that allows one or more phone lines to be shared for multiple phone connected devices. A common application would allow voice (phones and answering machine) and a fax machine or fax modem to operate transparently on a single phone line thus eliminating the monthly costs associated with a dedicated phone line. Applications include any variation of voice, a fax machine, fax/modem and/or modem(s). Incoming calls are automatically routed to the proper device(s) with no human intervention. If the call comes in and it is a fax call, the call is automatically routed to the fax machine or fax modem. If the call is a modem call, it is routed to the correct modem. Voice calls are routes to phone(s) and/or answering machine. May require a security access code (SAC) in the dialing string to automatically switch to the modem. Synonym Automatic Line Sharing Device . Fax Switch , Automatic Fax Switch . Phone Line Sharing - A technology that allows a single phone line to share incoming and outgoing access for multiple devices. Typically Phone Line Sharing Technology allows voice (phones and answering machine) and a fax machine or fax modem to operate on a shared phone line. Other applications include any variation of voice, a fax machine, fax/modem and/or modem(s). Incoming calls are automatically routed to the proper device(s). If the call comes in and it is a fax call, the call is automatically routed to the fax machine or fax modem. If the call is a modem call, it is routed to the correct modem. Voice calls are routes to phone(s) and/or answering machine. May require a security access code (SAC) in the dialing string to automatically switch to the modem. All outgoing calls access the line from any device. Optional "barge-in protection" protects any voice or data call from being accessed by other telephone equipment on the same line. Since the need for to subscribe to a separate "fax line" or "modem line" from the local telephone company is eliminated, the return on investment (ROI) is very high. The initial cost of the device is returned in savings in a few months. After that you will save the monthly bills associated with fax, data or voice lines. For almost every business, phone line sharing technology is a smart investment. Photocurrent - The current that flows through a photosensitive device, such as a photodiode, as the result of exposure to radiant power. Note 1: The photocurrent may occur as a result of the photoelectric, photoemissive, or photovoltaic effect. Note 2: The photocurrent may be enhanced by internal gain caused by interaction among ions and photons under the influence of applied fields, such as occurs in an avalanche photodiode (APD). 370
- 371. Photodetector (PD) - A transducer capable of accepting an optical signal and producing an electrical signal containing the same information as in the optical signal. Note: The two main types of semiconductor photodetectors are the photodiode (PD) and the avalanche photodiode (APD). Photodiode - A semiconductor diode that produces, as a result of the absorption of photons, (a) a photovoltage or (b) free carriers that support the conduction of photocurrent. Note: Photodiodes are used for the detection of optical communication signals and for the conversion of optical power to electrical power. Photon - A discrete packet, i.e., quantum, of electromagnetic energy. Note: The energy of a photon is h , where h is Planck's constant and is the frequency of the electromagnetic wave. Photovoltaic Effect - The production, as a result of the absorption of photons, of a voltage difference across a pn junction. Note: The voltage difference is caused by the internal drift of holes and electrons. Physical Layer - Layer 1. The lowest of seven hierarchical layers. The Physical layer performs services requested by the Data Link Layer. The major functions and services performed by the physical layer are: (a) establishment and termination of a connection to a communications medium; (b) participation in the process whereby the communication resources are effectively shared among multiple users, e.g., contention resolution and flow control; and, (c) conversion between the representation of digital data in user equipment and the corresponding signals transmitted over a communications channel. See Open Systems Interconnection--Reference Model. Physical Security - See communications security. The component of communications security that results from all physical measures necessary to safeguard classified equipment, material, and documents from access thereto or observation thereof by unauthorized persons. PIC Freeze – Pre-subscribed Interexchange Carrier Freeze. An agreement between a customer and their local telephone company to prevent “slamming” on their long distance telephone bill. Picture - Synonym image. In the field of image processing, a two-dimensional representation of a scene. Pigtail - A short length of optical fiber that is permanently affixed to an active device, e.g., LED or laser diode, and is used to couple the device, using a splice or connector, to a longer fiber. 2. A short length of single-fiber cable, usually tight-buffered, that has an optical connector on one end and a length of exposed fiber at the other end. Note: The exposed fiber of the pigtail is then spliced to one fiber of a multifiber trunk, i.e., arterial, cable, to enable the multifiber cable to be "broken out" into individual single-fiber cables that may be connected to a patch panel or an input or output port of an optical receiver or transmitter. 3. A short length of electrical conductor permanently affixed to a component, used to connect the component to another conductor. Pilot - 1. A signal, usually a single frequency, transmitted over a communications system for supervisory, control, equalization, continuity, synchronization, or reference purposes. Note: Sometimes it is necessary to employ several independent pilot frequencies. Most radio relay systems use radio or continuity pilots of their own but transmit also the pilot frequencies belonging to the carrier frequency multiplex system. 2. See palm- top. PIN - Abbreviation for personal identification number. A code or password, unique to or associated with, a specific user, and entered into a data-processing device for purposes of verifying the identity of a person requesting, e.g., a transaction or access. 371
- 372. Ping - a geeky way of describing the action of one computer sending a signal to another computer, of course expecting some kind of response. Ping web services comprise only one out of several specific applications of XML-RPC web services. Pipeline - An extremely high-speed, large capacity bandwidth connection. Pitch - Synonym lay length. - In communications cables--including fiber-optic cables--having the transmission media wrapped helically around a central member, the longitudinal distance along the cable required for one complete helical wrap; i.e., the total cable length divided by the total number of wraps. Note 1: In many fiber-optic cable designs, the pitch is shorter than in metallic cables of similar diameter, to avoid overstressing the fibers during the pulling associated with the installation operation. Note 2: The wraps, i.e., turns, that are referred to should not be confused with the twists given twisted metallic pairs, i.e., wires, to reduce electromagnetic coupling. Pairs of optical fibers are not given such twists. Pixel - In a raster-scanned imaging system, the smallest discrete scanning line sample that can contain gray scale information. Plain Old Telephone Service (POTS) - Nothing more than a standard telephone line, the kind Ma Bell and then AT&T handled exclusively before the deregulation of the telephone industry. Upgrade your POTS to DSL, and you have broadband; add VoIP, and you have a system that uses POTS, the PSTN, and the Internet in one (ideally) seamless system. Plain Text - Unencrypted information. Note: Plain text includes voice. Synonym clear text. Planck's constant - The constant of proportionality, represented by the symbol h, that relates the energy E of -34 a photon with the frequency of the associated wave through the relation E = h , where h = 6.626 × 10 joule•second. Plane Polarization - Synonym linear polarization. - Of an electromagnetic wave, confinement of the E-field vector or H-field vector to a given plane. Note: Historically, the orientation of a polarized electromagnetic wave has been defined in the optical regime by the orientation of the electric vector, and in the radio regime, by the orientation of the magnetic vector. Plane Wave - 1. A wave whose surfaces of constant phase are infinite parallel planes normal to the direction of propagation. 2. An electromagnetic wave that predominates in the far-field region of an antenna, and has a wavefront that is essentially in a plane. Note: In free space, the characteristic impedance of a plane wave is 377 . Plant - All the facilities and equipment used to provide telecommunications services. Note: Plant is usually characterized as outside plant or inside plant . Outside plant, for example, includes all poles, repeaters and unoccupied buildings housing them, ducts, and cables--including the "inside" portion of interfacility cables outward from the main distributing frame (MDF) in a central office or switching center. Inside plant includes the MDF and all equipment and facilities within a central office or switching center. Point Code (PC) - A unique address code that identifies a service provider (SP) within a signaling network. Point of Interface (POI) - In a telecommunications system, the physical interface between the local access and transport area (LATA) access and inter-LATA functions. Note: The interface point is used to establish the technical interface, the test points, and the points of operational responsibility. Synonym interface point. Point of Presence (POP) - A location where a you can connect to a network through local telephone 372
- 373. lines. Point-to-Point Protocol - A program that allows a computer to use a telephone line and modem to make TCP/IP connections. Polarity - A term used to describe the order of two electrical points – one positive and the other negative. On an RJ-11 female jack, the green lead should be positive with respect to the red lead to ensure proper operation with all equipment. Polarization - Of an electromagnetic wave, the property that describes the orientation, i.e., time-varying direction and amplitude, of the electric field vector. Note 1: States of polarization are described in terms of the figures traced as a function of time by the projection of the extremity of a representation of the electric vector onto a fixed plane in space, which plane is perpendicular to the direction of propagation. In general, the figure, i.e., polarization, is elliptical and is traced in a clockwise or counterclockwise sense, as viewed in the direction of propagation. If the major and minor axes of the ellipse are equal, the polarization is said to be circular. If the minor axis of the ellipse is zero, the polarization is said to be linear. Rotation of the electric vector in a clockwise sense is designated right-hand polarization, and rotation in a counterclockwise sense is designated left-hand polarization. Note 2: Mathematically, an elliptically polarized wave may be described as the vector sum of two waves of equal wavelength but unequal amplitude, and in quadrature (having their respective electric vectors at right angles and /2 radians out of phase). PON (Passive Optical Network) - a fiber-based network built without active electronics. Because a PON network uses optical splitters rather than costly active electronics, it is less expensive to build and maintain than a network that uses active electronics. PONs are still more expensive than copper-based networks. A PON network is usually used in a local loop to connect customers to the central office. BPON (Broadband Passive Optical Network) is a broadband PON. POP - See Point of Presence and Post Office Protocol POPs (Population equivalents) – The population of a market multiplied by the percentage ownership of that market. Positive Feedback - Synonym regeneration. In a regenerative repeater, the process by which digital signals are amplified, reshaped, retimed, and retransmitted. Positive Justification - Synonym bit stuffing. - The insertion of noninformation bits into data. Note 1: Stuffed bits should not be confused with overhead bits. Note 2: In data transmission, bit stuffing is used for various purposes, such as for synchronizing bit streams that do not necessarily have the same or rationally related bit rates, or to fill buffers or frames. The location of the stuffing bits is communicated to the receiving end of the data link, where these extra bits are removed to return the bit streams to their original bit rates or form. Bit stuffing may be used to synchronize several channels before multiplexing or to rate-match two single channels to each other. Post-Detection Combiner - A diversity combiner in which (a) the signals from each channel are added together, (b) the gain of each channel is made proportional to the rms signal level and inversely proportional to the mean square noise level in that channel, and (c) the same proportionality constant is used for all channels. Synonym maximal-ratio combiner. Post Office Protocol (POP) - A system that allows hosts to get e-mail from a server. POTS (Plain Old Telephone Service) - Nothing more than a standard telephone line, the kind Ma Bell and then AT&T handled exclusively before the deregulation of the telephone industry. Upgrade your POTS to 373
- 374. DSL, and you have broadband; add VoIP, and you have a system that uses POTS, the PSTN, and the Internet in one (ideally) seamless system. Power - 1. The rate of transfer or absorption of energy per unit time in a system. 2. Whenever the power of a radio transmitter etc. is referred to, it shall be expressed in one of the following forms, according to the class of emission, using the arbitrary symbols indicated: • peak envelope power (PX or pX); • mean power (PY or pY); • carrier power (PZ or pZ). For different classes of emission, the relationships between peak envelope power, mean power and carrier power, under the conditions of normal operation and of no modulation, are contained in CCIR Recommendations which may be used as a guide. For use in formulae, the symbol p denotes power expressed in watts and the symbol P denotes power expressed in decibels relative to a reference level. Power Density - Deprecated synonym for irradiance. Radiant power incident per unit area upon a surface. Note: Irradiance is usually expressed in watts per square meter, but may also be expressed in joules per square meter. Power-Law Index Profile - For optical fibers, a class of graded-index profiles Note 1: is often used in place of g. Hence, this is sometimes called an alpha profile. Note 2: For this class of profiles, multimode distortion is smallest when g takes a particular value depending on the material used. For most materials, this optimum value is approximately 2. When g increases without limit, the profile tends to a step-index profile. PPP - See Point to Point Protocol Precedence - In communications, a designation assigned to a message by the originator to indicate to communications personnel the relative order of handling and to the addressee the order in which the message is to be noted. [After JP1] Note: The descending order of precedence for military messages is FLASH, IMMEDIATE, PRIORITY, and ROUTINE. Precise Time - A time mark that is accurately known with respect to an accepted reference time standard. 14 Note: Current uncertainty among international standards is approximately 1 part in 10 as of 1995. Predetection Combining - A diversity combiner in which (a) the signals from each channel are added together, (b) the gain of each channel is made proportional to the rms signal level and inversely proportional to the mean square noise level in that channel, and (c) the same proportionality constant is used for all channels. Synonym maximal-ratio combiner. Preemption - The seizure, usually automatic, of military system facilities that are being used to serve a lower precedence call in order to serve immediately a higher precedence call. Prefix - In telephone communications, an indicator consisting of one or more digits, that allows the selection of different types of number formats (e.g., local, national or international), transit networks and/or the service. Note 1: Prefixes are not part of the number and are not signaled over internetwork and international boundaries. Note 2: When prefixes are used, they are always entered by the user or by automatic calling equipment. Presentation Layer - Layer 6 of the See Open Systems Interconnection--Reference Model. This layer responds to service requests from the Application Layer and issues service requests to the Session Layer. The 374
- 375. Presentation Layer relieves the Application Layer of concern regarding syntactical differences in data representation within the end-user systems. Note: An example of a presentation service would be the conversion of an EBCDIC-coded text file to an ASCII-coded file. See Open Systems Interconnection-- Reference Model. Primary Coating - The plastic overcoat in intimate contact with the cladding of an optical fiber, applied during the manufacturing process. Note 1: The primary coating typically has an outside diameter of approximately 250 to 750 m, and serves to protect the fiber from mechanical damage and chemical attack. It also enhances optical fiber properties by stripping off cladding modes, and in the case where multiple fibers are used inside a single buffer tube, it suppresses cross-coupling of optical signals from one fiber to another. Note 2: The primary coating should not be confused with a tight buffer, or the plastic cladding of a plastic- clad-silica (PCS) fiber. Note 3: The primary coating, which typically consists of many layers, may be color- coded to distinguish fibers from one another, e.g., in a buffer tube containing multiple fibers. Synonyms primary polymer coating, primary polymer overcoat. Primary Polymer Coating - Synonym primary coating. Primary Polymer Overcoat - Synonym primary coating. Primary Power - The source of electrical power that usually supplies the station main bus. Note 1: The primary power source may be a Government-owned generating plant or a public utility power system. Note 2: A Class A primary power source assures, to a high degree of reliability, a continuous supply of ac electrical power. Primary Radar: A radiodetermination system based on the comparison of reference signals with radio signals reflected from the position to be determined. Primary Rate Interface (PRI) - An integrated services digital network (ISDN) interface standard (a) that is designated in North America as having a 23B+D channels, (b) in which all circuit-switched B channels operate at 64 kb/s, and (c) in which the D channel also operates at 64 kb/s. Note: The PRI combination of channels results in a digital signal 1 (T1) interface at the network boundary. Priority - 1. Priority, unless specifically qualified, is the right to occupy a specific frequency for authorized uses, free of harmful interference from stations of other agencies. [NTIA] 2. Synonym priority level. 3. In DOD record communications systems, one of the four levels of precedence used to establish the time frame for handling a given message. 4. In DOD voice communications systems, one of the levels of precedence assigned to a subscriber telephone for the purpose of preemption of telephone services. Priority Level - In the Telecommunications Service Priority system, the level that may be assigned to an NS/EP telecommunications service, which level specifies the order in which provisioning or restoration of the service is to occur relative to other NS/EP or non-NS/EP telecommunication services. Note: Priority levels authorized are designated (highest to lowest) "E," "1," "2," "3," "4," and "5" for provisioning and "1," "2," "3," "4," and "5" for restoration. Synonym priority. Privacy - 1. In a communications system or network, the protection given to information to conceal it from unauthorized persons having access to the system or network at large. Synonym segregation. 2. In a communications system, protection given to unclassified information, such as radio transmissions of law enforcement personnel, that requires safeguarding from unauthorized persons. 3. In a communications system, the protection given to prevent unauthorized disclosure of the information in the system. Note 1: The required protection may be accomplished by various means, such as by communications security measures and by directives to operating personnel. Note 2: The limited protection given certain voice and 375
- 376. data transmissions by commercial crypto equipment is sufficient to deter a casual listener, but cannot withstand a competent cryptanalytic attack. Privacy Screener with Caller ID, Name and ACR - Privacy Screener is a phone company feature that works with Caller ID (required feature) to stop unwanted telemarketers. Privacy Screener automatically intercepts unavailable, unknown, blocked or private calling telephone numbers. Interception occurs before the phone rings. Privacy Screener requires the callers to identify themselves. The caller can hang up when prompted to identify themselves; but if they choose to identify themselves, the phone rings, the Privacy Screener displays on the Caller ID unit and the caller's name is heard when the phone is answered. You then choose whether or not to accept the call. Additionally, if it is a telemarketer, the touch of a button instructs the Privacy Screener service to tell the caller to remove your name from the calling list. Private Branch Exchange (PBX) - An electronic multi-line telephone system, used primarily in very large applications with many extensions. The identifying feature of most PBXs is that you must dial 9 to get an outside line. PBXs generally use standard single-line telephones at extension locations. Private Exchange (PX) - A private telecommunication switch that usually includes access to the public switched network. Private Line - 1. In telephone industry usage, a service that involves dedicated circuits, private switching arrangements, predefined transmission paths, or combination thereof, whether virtual or physical, and which provide communications between specific locations. 2. Among subscribers to the public switched telephone network (s), a one-party switched access line. Private Line Service - 1. A service for communications between specified locations for a continuous period or for regularly recurring periods at stated hours. 2. A service whereby facilities for communication between two or more designated points are set aside for the exclusive use or availability for use of a particular customer and authorized users during stated periods of time. Private Prime Factors - In cryptographic applications, the two prime numbers, namely p and q, whose product pq is the modulus n. Processor - In a computer, a functional unit that interprets and executes instructions. Note: A processor consists of at least an instruction control unit and an arithmetic unit. Profile Dispersion - In an optical fiber, that dispersion attributable to the variation of refractive index contrast with wavelength. Profile dispersion is a function of the profile dispersion parameter. Profile Parameter (g) - In the power-law index profile of an optical fiber, the parameter, g, that defines the shape of the refractive-index profile. Note: The optimum value of g for minimum dispersion is approximately 2. Program - 1. A plan or routine for solving a problem on a computer. Note: Processing may include the use of an assembler, a compiler, an interpreter, or a translator to prepare the program for execution, as well as the execution of the program. The sequence of instructions may include statements and necessary declarations. 2. A sequence of instructions used by a computer to do a particular job or solve a given problem. 3. To design, write, and test programs. Programmable Security Access Codes (SAC's) -Transfer of a call is executed by dialing the programmed SAC for each voice/data device connected to the fax switch. SAC's are programmable (using a touch tone phone only) up to 4 characters long-digits 0 through 9 and symbols * Touch Tone Pulse Dial (star) and # (pound). Fax 376
- 377. switches will not detect SAC's dialed from "calling" pulse phones-only from touch tone phones. Call transfers dialed by a pulse phone are limited to phones hooked to or on the same line as the fax switch and are limited to transfer to the "FAX" port only. The pulse dial SAC for this is fixed at "2" You must also have the "Pulse Select" feature on if you use a pulse dial phone to transfer a call. Programming Language - An artificial language that is used to generate or to express computer programs. Note: The language may be a high-level language, an assembly language, or a machine language. Propagation - The motion of waves through or along a medium. Note: For electromagnetic waves, propagation may occur in a vacuum as well as in material media. Proration - 1. The proportional distribution or allocation of parameters, such as noise power and transmission losses, among a number of tandem-connected items, such as equipment, cables, links, or trunks, in order to balance the performance of communications circuits. Synonym budgeting. 2. In a telephone switching center, the distribution or allocation of equipment or components proportionally among a number of functions, to provide a requisite grade of service. Protected Hook Flash -This feature allows the fax switch to be compatible with certain multi-line KSU phone systems. Some KSU systems do not allow touch tones (DTMF tones) to be generated from a telephone key pad after an inbound call has arrived. With Protected Hook flash "on" the phone system can be "fooled" into generating touch tones by striking the flash key Calls can then be manually transferred between devices by dialing the proper security access code. Factory preset is "off." Protection - Synonym lockout. 1. In telephone systems, treatment of a user's line or trunk that is in trouble, or in a permanent off-hook condition, by automatically disconnecting the line from the switching equipment. 2. In public telephone systems, a process that denies an attendant or other users the ability to reenter an established connection. 3. In a telephone circuit controlled by two voice-operated devices, the inability of one or both users to get through, either because of excessive local circuit noise or because of continuous speech from either or both users. 4. In mobile communications, an arrangement of control circuits whereby only one receiver can feed the system at a time. Synonym receiver lockout system. 5. An arrangement for restricting access to use of all, or part of, a computer system. Protocol - 1. A formal set of conventions governing the format and control of interaction among communicating functional units. Note: Protocols may govern portions of a network, types of service, or administrative procedures. For example, a data link protocol is the specification of methods whereby data communications over a data link are performed in terms of the particular transmission mode, control procedures, and recovery procedures. 2. In layered communications system architecture, a formal set of procedures that are adopted to facilitate functional interoperation within the layered hierarchy. 3. A set of rules and formats, semantic and syntactic, permitting information systems (IS's) to exchange information. Provisioning - 1. In telecommunications, the setting in place and configuring of the hardware and software required to activate a telecommunications service for a customer; in many cases the hardware and software may already be in place and provisioning entails only configuration tasks such as creating (or modifying) a customer record in a database and associating it with the service(s) and service level for which the customer has subscribed. 2. The act of acquiring telecommunications service from the submission of the requirement through the activation of service. Note 1: Provisioning includes all associated transmission, wiring, and equipment. Note 2: In NS/EP telecommunication services, "provisioning" and "initiation" are synonymous and include altering the state of an existing priority service or capability. 3. Processes that arrange and connect equipment and facilities, and create their associated software and data base translations, in response to service demands and forecasts. In this sense, provisioning does not include equipment installations, but rather the state of the equipment, i.e., in service, out of service, stand by, reserved, etc., the state of which may also be controlled by provisioning functions. 4. The act of supplying 377
- 378. telecommunication service to a user, including all associated transmission, wiring, and equipment. 5. The process of establishing and supplying telecommunications service to a user, including an associated transmission, wiring, and telecommunications company equipment. PSK - Abbreviation for phase-shift keying. - 1. In digital transmission, angle modulation in which the phase of the carrier is discretely varied in relation either to a reference phase or to the phase of the immediately preceding signal element, in accordance with data being transmitted. 2. In a communications system, the representing of characters, such as bits or quaternary digits, by a shift in the phase of an electromagnetic carrier wave with respect to a reference, by an amount corresponding to the symbol being encoded. Note 1: For example, when encoding bits, the phase shift could be 0° for encoding a "0," and 180° for encoding a "1," or the phase shift could be -90 for "0" and +90° for a "1," thus making the representations for "0" and "1" a total of 180° apart. Note 2: In PSK systems designed so that the carrier can assume only two different phase angles, each change of phase carries one bit of information, i.e., the bit rate equals the modulation rate. If the number of recognizable phase angles is increased to 4, then 2 bits of information can be encoded into each signal element; likewise, 8 phase angles can encode 3 bits in each signal element. Psophometer - An instrument that provides a visual indication of the audible effects of disturbing voltages of various frequencies. Note: A psophometer usually incorporates a weighting network. The characteristics of the weighting network depend on the type of circuit under investigation, such as whether the circuit is used for high-fidelity music or for normal speech. Psophometric Weighting - A noise weighting established by the International Consultative Committee for Telephony (CCIF, which became CCITT and, more recently, ITU-T), designated as CCIF-1951 weighting, for use in a noise measuring set or psophometer. Note: The shape of this characteristic is virtually identical to that of F1A weighting. The psophometer is, however, calibrated with a tone of 800 Hz, 0 dBm, so that the corresponding voltage across 600 ohms produces a reading of 0.775 V. This introduces a 1-dBm adjustment in the formulas for conversion with dBa. PSTN (Public Switched Telephone Network) - The network of wires, signals, and switches that lets one telephone connect to another anywhere in the world. Some VoIP services provide a gateway from the Internet to the PSTN and vice versa. Public Key Cryptography - 1. The type of cryptography in which the encryption process is publicly available and unprotected, but in which a part of the decryption key is protected so that only a party with knowledge of both parts of the decryption process can decrypt the cipher text. Note: Commonly called non-secret encryption in professional cryptologic circles. FIREFLY is an application of public key cryptography. 2. [An] Encryption system using a linked pair of keys. What one pair of keys encrypts, the other pair decrypts. Public Switched Network (PSN) - 1. Any common carrier network that provides circuit switching among public users. Note: The term is usually applied to public switched telephone networks, but it could be applied more generally to other switched networks, e.g., packet-switched public data networks. 2. A switched network accessible by the public for the purpose of originating and terminating telecommunications messages. 3. Any common carrier switched network, whether by wire or radio, including local exchange carriers, interexchange carriers, and mobile service providers, that use the North American Numbering Plan in connection with the provision of switched services. Public Switched Telephone Network (PSTN) - The network of wires, signals, and switches that lets one telephone connect to another anywhere in the world. Some VoIP services provide a gateway from the Internet to the PSTN and vice versa. 378
- 379. Public Utilities Commission (PUC): In the United States, a state regulatory body charged with regulating intrastate utilities, including telecommunications systems. Note: In some states this regulatory function is performed by public service commissions or state corporation commissions. Pulse - 1. A rapid, transient change in the amplitude of a signal from a baseline value to a higher or lower value, followed by a rapid return to the baseline value. 2. A rapid change in some characteristic of a signal, e.g., phase or frequency, from a baseline value to a higher or lower value, followed by a rapid return to the baseline value. Pulse Amplitude - The magnitude of a pulse parameter, such as the field intensity, voltage level, current level, or power level. Note 1: Pulse amplitude is measured with respect to a specified reference and therefore should be modified by qualifiers, such as "average," "instantaneous," "peak," or "root-mean- square." Note 2: Pulse amplitude also applies to the amplitude of frequency- and phase-modulated waveform envelopes. Pulse Broadening - An increase in pulse duration. Note: Pulse broadening may be specified by the impulse response, the root-mean-square pulse broadening, or the full-duration-at-half-maximum pulse broadening. Pulse-Code Modulation (PCM) - Modulation in which a signal is sampled, and the magnitude (with respect to a fixed reference) of each sample is quantized and digitized for transmission over a common transmission medium. Note 1: In conventional PCM, before being digitized, the analog data may be processed (e.g., compressed), but once digitized, the PCM signal is not subjected to further processing (e.g., digital compaction) before being multiplexed into the aggregate data stream. Note 2: PCM pulse trains may be interleaved with pulse trains from other channels. Pulse Duration - 1. In a pulse waveform, the interval between (a) the time, during the first transition, that the pulse amplitude reaches a specified fraction (level) of its final amplitude, and (b) the time the pulse amplitude drops, on the last transition, to the same level. Note: The interval between the 50% points of the final amplitude is usually used to determine or define pulse duration, and this is understood to be the case unless otherwise specified. Other fractions of the final amplitude, e.g., 90% or 1/e (where e = 2.71828. . .), may also be used, as may the root-mean-square (rms) value of the pulse amplitude. Deprecated synonyms pulse length, pulse width. 2. In radar, measurement of pulse transmission time in microseconds, that is, the time the radar's transmitter is energized during each cycle. Pulse Length - Deprecated synonym for pulse duration. Pulse Repetition Rate: The number of pulses per unit time. Pulse String - A series of pulses having similar characteristics. Synonym pulse train. Pulse Train - A series of pulses having similar characteristics. Synonym pulse string. Pulse Width - Deprecated synonym for pulse duration. Q QA - Abbreviation for quality assurance. 1. All actions taken to ensure that standards and procedures are adhered to and that delivered products or services meet performance requirements. 2. The planned systematic activities necessary to ensure that a component, module, or system conforms to established technical requirements. 3. The policy, procedures, and systematic actions established in an enterprise for the 379
- 380. purpose of providing and maintaining a specified degree of confidence in data integrity and accuracy throughout the life cycle of the data, which includes input, update, manipulation, and output. QOS (Quality of Service): Refers to the quality of the voice call over a VoIP network. A major issue in VoIP communications, because the high quality of telephone calls has always been taken for granted. Latency, packet loss, network jitter, and many other factors contribute to QOS measurements, and numerous solutions have been offered by vendors of routers and other network components. QRS - Abbreviation for quasi-random signal. A signal consisting of a bit sequence that approximates a random signal. [T1.201-1989] The unframed QRS (QRSS, QRTS, QRW) for DS1 consists of a PRBS with a 20- stage shift register with a constraint that forces the "put to a one" when the next 14 bits in the sequence would be zeros. The QRS generates every combination of 20-bit words, repeats every 1,048,575 bits, and contains high density sequences, low density sequences, and sequences that change from low density to high density and vice versa. When transmitted as the payload of a DS1 signal (framed), the QRS meets the pulse density definition "a" criteria, providing a maximum of 15-sequential zeros (14 + 1 when the frame bit is a zero), but does not meet the pulse density definition "b" criteria. (ANSI Tl.403 states: 'the quasi-random signal may be transmitted without meeting these pulse density constraints.') Contrast with pseudorandom number sequence. QRW - Abbreviation for quasi-random word. Quad - A group of four wires composed of two pairs twisted together. Note: The pairs have a fairly long length of twist and the quad a fairly short length of twist. Quadded Cable - A cable formed of multiples of quads, paired and separately insulated, and contained under a common jacket. QUADRANT - [A] short name referring to technology that provides tamper-resistant protection to crypto- equipment. Quadratic Profile - Synonym parabolic profile. In an optical fiber, a power-law index profile with the profile parameter, g, equal to 2. Quadrature - 1. The state of being separated in phase by 90° ( /2 radians). 2. Pertaining to the phase relationship between two periodic quantities varying with the same period, that is, with the same frequency or repetition rate, when the phase difference between them is one-quarter of their period. quadrature amplitude modulation (QAM): 1. Quadrature modulation in which the two carriers are amplitude modulated. 2. In analog communications, the representation (i.e., transmission) of digital information by encoding bit sequences of fixed, specified length (number of bits), and representing these bit sequences as a function of (a) the amplitude of an analog carrier; or (b) a phase shift of the analog carrier with respect to the phase that represented the preceding bit sequence, and where the permissible phase shift is an integral multiple of /2 radians (90°, or one-quarter unit interval); or (c) both. Note 1: The name quadrature originates from the stipulation that a phase shift, when required, must be an integral multiple of p/2 radians, i.e., one-quarter of a cycle (unit interval, or baud). Note 2: A representative QAM table is presented below. If the baud (carrier) rate is 1200 Hz (the usual case in modems used on conventional telephone lines), this QAM scheme permits transmission of a data rate of 9600 b/s, which is the product of the baud rate and the number of permissible phase-amplitude states. Any continuous bit stream may be represented as a combination of the eight permissible bit sequences in the above table, and transmitted as such. Note 3: According to mathematical theory, there is no limit to the 380
- 381. data rate that may be supported by, or associated with, a given baud rate in a perfectly stable, noiseless transmission environment. In practice, the governing factors are the amplitude (and consequently, phase) stability, and the amount of noise present, in both the terminal equipment and the transmission medium (carrier frequency, or communication channel) involved. Nor does the permitted relative (incremental) phase shift necessarily have to be a multiple of /2 radians, but of course the name "quadrature" would not apply if any other minimum phase shift were specified or permitted. Quadrature Modulation - Modulation using two carriers out of phase by 90° and modulated by separate signals. Quadrature Phase-Shift Keying (QPSK) - Phase-shift keying in which four different phase angles are used. Note: In QPSK, the four angles are usually out of phase by 90°. Synonyms quadriphase, quaternary phase- shift keying. Quadriphase - Synonym quadrature phase-shift keying. Quadruple Diversity - In radio communication, diversity transmission and reception in which four independently fading signals are used. Note: Quadruple diversity may be accomplished through the use of space, frequency, angle, time, or polarization multiplexing, or combinations of these. Quadruply Clad Fiber - A single-mode optical fiber that has four claddings. Note 1: Each cladding has a refractive index lower than that of the core. With respect to one another, their relative refractive indices are, in order of distance from the core, lowest, highest, lower, higher. Note 2: A quadruply clad fiber has the advantage of very low macrobending losses. It also has two zero-dispersion points, and moderately low dispersion over a wider wavelength range than a singly clad fiber or a doubly clad fiber. Quality Assurance (QA) - 1. All actions taken to ensure that standards and procedures are adhered to and that delivered products or services meet performance requirements. 2. The planned systematic activities necessary to ensure that a component, module, or system conforms to established technical requirements. 3. The policy, procedures, and systematic actions established in an enterprise for the purpose of providing and maintaining a specified degree of confidence in data integrity and accuracy throughout the life cycle of the data, which includes input, update, manipulation, and output. Quality Control (QC) - A management function whereby control of the quality of (a) raw materials, assemblies, produced materiel, and components, (b) services related to production, and (c) management, production, and inspection processes is exercised for the purpose of preventing undetected production of defective materiel or the rendering of faulty services. Quality Factor - In a reactive circuit, the ratio of the reactance in ohms divided by the resistance in ohms. Quality of Service (QOS) - 1. The performance specification of a communications channel or system. Note: QOS may be quantitatively indicated by channel or system performance parameters, such as signal-to-noise ratio (S/N), bit error ratio (BER), message throughput rate, and call blocking probability. 2. A subjective rating of telephone communications quality in which listeners judge transmissions by qualifiers, such as excellent, good, fair, poor, or unsatisfactory. 3. Refers to the quality of the voice call over a VoIP network. A major issue in VoIP communications, because the high quality of telephone calls has always been taken for granted. Latency, packet loss, network jitter, and many other factors contribute to QOS measurements, and numerous solutions have been offered by vendors of routers and other network components. Quantization - A process in which the continuous range of values of an analog signal is sampled and divided into nonoverlapping (but not necessarily equal) subranges, and a discrete, unique value is assigned to each 381
- 382. subrange. Note: An application of quantization is its use in pulse-code modulation. If the sampled signal value falls within a given subrange, the sample is assigned the corresponding discrete value for purposes of modulation and transmission. Quantization Error - Distortion that results from the quantization process. Synonym quantizing distortion. Quantization Level - In the quantization process, the discrete value assigned to a particular subrange of the analog signal being quantized. Quantization Noise - Synonym quantizing noise. Noise caused by the error of approximation in quantization. Note: Quantizing noise is dependent on the particular quantization process used and the statistical characteristics of the quantized signal. Quantized Feedback - In a digital feedback loop, the digital signal that is fed back. Note 1: Several forms of analog-to-digital converters contain a quantized feedback loop following the basic A-D converter. Note 2: The feedback signal is often processed before introducing it to the loop. Quantizing Distortion - Distortion that results from the quantization process. Synonym quantization error. Quantizing Levels - In digital transmission, the number of discrete signal levels transmitted as the result of signal digitization. Quantizing Noise - Noise caused by the error of approximation in quantization. Note: Quantizing noise is dependent on the particular quantization process used and the statistical characteristics of the quantized signal. Synonym quantization noise. Quantum Efficiency - In an optical source or detector, the ratio of the number of output quanta to the number of input quanta. Note: Input and output quanta need not both be photons. Quantum-Limited Operation - Synonym quantum-noise-limited operation. Quantum Noise - Noise attributable to the discrete and probabilistic nature of physical phenomena and their interactions. Note 1: Quantum noise represents the fundamental limit of the achievable signal-to-noise ratio of an optical communication system. This limit is never achieved in practice. Note 2: Examples of quantum noise are photon noise in an optical signal and shot noise in an electrical conductor or semiconductor. Quantum-Noise-Limited Operation - Operation wherein the minimum detectable signal is limited by quantum noise. Synonym quantum-limited operation. Quarter Common Intermediate Format (QCIF) - A video format defined in ITU-T Recommendation H.261 that is characterized by 176 luminance pixels on each of 144 lines, with half as many chrominance pixels in each direction. Note: QCIF has one-fourth as many pixels as the full common intermediate format. Quartz Clock - A clock containing a quartz oscillator that determines the accuracy and precision of the clock. Quartz Oscillator - An oscillator in which a quartz crystal is used to stabilize the frequency. Note: The piezoelectric property of the quartz crystal results in a nearly constant output frequency, which is dependent upon the crystal size, shape, and excitation. Quasi-Analog Signal - A digital signal that has been converted to a form suitable for transmission over a specified analog channel. Note: The specification of the analog channel should include frequency range, 382
- 383. bandwidth, signal-to-noise ratio, and envelope delay distortion. When quasi-analog form of signaling is used to convey message traffic over dial-up telephone systems, it is often referred to as voice-data. A modem may be used for the conversion process. Quasi-Analog Transmission - Transmission in which a special-purpose modulator is used to convert digital signals into an analog form suitable for transmission over an analog voice-grade circuit. Note: A complementary demodulator is used to recover the digital signal at the other end of the circuit. See modem. Quasi-Associated Mode of Signaling - A limited case of the nonassociated mode of signaling in which the path taken by a message through the signaling network is predetermined and fixed at a given point in time. Quasi-Lossless Compression - In video and multimedia applications, the bit-rate reduction of an image signal, by an algorithm that recognizes the high degree of correlation ascertainable in specific images. Note 1: The final image does not replicate the original when viewed in direct comparison, but the losses are designed to be unrecognizable under the intended display conditions. Note 2: The algorithm may often apply transform coding, predictive techniques, and other modeling to the image signal, along with some form of entropy encoding. Note 3: While the image appears unaltered to normal human vision, it may show losses and artifacts when analyzed by other systems (i.e., chroma key, computerized image analysis, etc.). Note 4: The lost information cannot be extracted from the compressed bit stream. Quasi-Random Signal (QRS) - See QRS. A signal consisting of a bit sequence that approximates a random signal. [T1.201-1989] The unframed QRS (QRSS, QRTS, QRW) for DS1 consists of a PRBS with a 20-stage shift register with a constraint that forces the "put to a one" when the next 14 bits in the sequence would be zeros. The QRS generates every combination of 20-bit words, repeats every 1,048,575 bits, and contains high density sequences, low density sequences, and sequences that change from low density to high density and vice versa. When transmitted as the payload of a DS1 signal (framed), the QRS meets the pulse density definition "a" criteria, providing a maximum of 15-sequential zeros (14 + 1 when the frame bit is a zero), but does not meet the pulse density definition "b" criteria. (ANSI Tl.403 states: 'the quasi-random signal may be transmitted without meeting these pulse density constraints.') Contrast with pseudorandom number sequence. Quaternary Phase-Shift Keying - Synonym quadrature phase-shift keying. Phase-shift keying in which four different phase angles are used. Note: In QPSK, the four angles are usually out of phase by 90°. Quaternary Signal - A digital signal having four significant conditions. Query Call - In adaptive high-frequency (HF) radio, an automatic-link-establishment (ALE) call that requests responses from stations having connectivity to the destination specified in the call. Queue - A set of items, such as telephone calls or packets, arranged in sequence. Note: Queues are used to store events occurring at random times and to service them according to a prescribed discipline that may be fixed or adaptive. Queue Traffic - 1. A series of outgoing or incoming calls waiting for service. 2. In a store-and-forward switching center, the outgoing messages awaiting transmission at the outgoing line position. Queuing - The process of entering elements into or removing elements from a queue. Queuing Delay - 1. In a switched network, the time between the completion of signaling by the call originator and the arrival of a ringing signal at the call receiver. Note: Queues may be caused by delays at the originating switch, intermediate switches, or the call receiver servicing switch. 2. In a data network, the sum 383
- 384. of the delays between the request for service and the establishment of a circuit to the called data terminal equipment (DTE). 3. In a packet-switched network, the sum of the delays encountered by a packet between the time of insertion into the network and the time of delivery to the addressee. Queuing Theory - The theoretical study of waiting lines, expressed in mathematical terms--including components such as number of waiting lines, number of servers, average wait time, number of queues or lines, and probabilities of queue times' either increasing or decreasing. Note: Queuing theory is directly applicable to network telecommunications, server queuing, mainframe computer queuing of telecommunications terminals, and advanced telecommunications systems. Quieting - In an FM receiver, the phenomenon that results in less noise when an unmodulated carrier is present than when there is no carrier present. Note: Quieting is expressed in dB. Quiet Zone - With respect to the rf spectrum, an area in which emissions are restricted for the purpose of minimizing possible impact on the operations of radio astronomy or other activities that are highly sensitive to rf interference. Quincunx Sampling - 1. In a digital video system, a sampling structure where the luminance and color- difference samples are generated from pixels arranged on one of two congruent rectilinear grids. Note: One grid is displaced horizontally from the other by half the horizontal pixel spacing. The alternate grid is usually chosen for alternate lines, but may also be chosen for alternate field /frames. 2. In a digital video system, a sampling structure with an array of samples where alternate rows of pixel samples are displaced horizontally in the grid by half of the pitch of the pixel samples along the remaining rows. Note: The name of this sampling was chosen directly from the classical Latin, quincunx, for the symbolic resemblance to the figure "5" (as seen in the "X" arrangement of pips on dice or playing cards). R Raceway - Within a building, an enclosure, i.e., channel, used to contain and protect wires, cables, or bus bars. Rack - A frame upon which one or more units of equipment are mounted. Note: DOD racks are always vertical. Racon - See radar beacon. rad - Acronym for radiation absorbed dose. The basic unit of measure for expressing absorbed radiant energy per unit mass of material. Note 1: A rad corresponds to an absorption of 0.01 J/kg, i.e., 100 ergs/g. Note 2: The absorbed radiant energy heats, ionizes, and/or destroys the material upon which it is incident. Radar - Acronym for radio detection and ranging. 1. A radio detection system that transmits short bursts (pulses) of rf energy and detects their echoes from objects (targets) such as aircraft or ships. Note: The round-trip propagation time for the echo return may be used to determine the target's range (distance from the radar's antenna). If the transmitting antenna has a narrow beam (the usual case), the azimuth or elevation of the target may also be determined. Synonym primary radar. 2. A radio detection device that provides information on range, azimuth, and/or elevation of objects. 3. A radiodetermination system based on the comparison of reference signals with radio signals reflected, or retransmitted, from the position to be determined. Radar Beacon (racon) - 1. A transmitter - receiver associated with a fixed navigational mark which, when triggered by a radar, automatically returns a distinctive signal which can appear on the display of the 384
- 385. triggering radar, providing range, bearing and identification information. 2. A receiver-transmitter combination which sends out a coded signal when triggered by the proper type of pulse, enabling determination of range and bearing information by the interrogating station or aircraft. Radar Blind Range - The range that corresponds to the situation in which a radar transmitter is on and hence the receiver must be off, so that the radar transmitted signal does not saturate, i.e., does not blind, its own receiver. Note: Radar blind ranges occur because there is a time interval between transmitted pulses that corresponds to the time required for a pulse to propagate to the object, i.e., to the target, and its reflection to travel back. This causes an attempt to measure the range just as the radar transmitter is transmitting the next pulse. However, the receiver is off, therefore this particular range cannot be measured. The width of the range value that cannot be measured depends on the duration of the time that the radar receiver is off, which depends on the duration of the transmitted pulse. The return-time interval could be coincident with the very next radar-transmitted pulse, i.e., the first pulse following a transmitted pulse, or the second, or the third, and so on, giving rise to a succession of blind ranges. The blind ranges are given by r m = ( m c)/(2 fn ), where r m is the blind range for a given value of m , m is a positive integer that indicates which of the blind ranges is being determined, c is the velocity of electromagnetic wave propagation in vacuum (approximately 3 × 10 8 m/s), f is the radar pulse repetition rate, and n is the refractive index of the transmission medium (nearly 1 for air). The radar blind range is independent of the radar radio frequency ( rf ) of the radar pulse. Radian (rad.) - A unit of plane angle measure equal to the angle subtended at the center of a circle by an arc equal in length to the radius of the circle. Note: One radian is equal to 360°/2 , which is approximately 57° 17' 44.6". Radiant Power - The rate of flow of electromagnetic energy, i.e., radiant energy. Note 1: Radiant power is usually expressed in watts, i.e., joules per second. Note 2: The modifier is often dropped and "power" is used to mean "radiant power". Deprecated synonyms flux, radiant flux. Radiant Energy - Energy in the form of electromagnetic waves. Note 1: Radiant energy may be calculated by integrating radiant power with respect to time. Note 2: Radiant energy is usually expressed in joules. Radiant Flux - Deprecated synonym for radiant power. Radiation - 1. In communication, the emission of energy in the form of electromagnetic waves. 2. The outward flow of energy from any source in the form of radio waves. Radiation Mode - For an optical fiber, an unbound mode. Note: In an optical fiber, a radiation mode is one having fields that are transversely oscillatory everywhere external to the waveguide, and which exists even at the limit of zero wavelength. Synonym unbound mode. Radiation Pattern - 1. The variation of the field intensity of an antenna as an angular function with respect to the axis. Note: A radiation pattern is usually represented graphically for the far-field conditions in either horizontal or vertical plane. 2. In fiber optics, the relative power distribution at the output of a fiber or active device as a function of position or angle. Note 1: The near-field radiation pattern describes the radiant emittance (W•m-2) as a function of position in the plane of the exit face of an optical fiber. Note 2: The far- field radiation pattern describes the irradiance as a function of angle in the far-field region of the exit face of an optical fiber. Note 3: The radiation pattern may be a function of the length of the fiber, the manner in which it is excited, and the wavelength. Synonym directivity pattern. Radio - 1. Telecommunication by modulation and radiation of electromagnetic waves. 2. A transmitter, receiver, or transceiver used for communication via electromagnetic waves. 3. A general term applied to the use of radio waves. 385
- 386. Radiobeacon Station - A station in the radionavigation service the emissions of which are intended to enable a mobile station to determine its bearing or direction in relation to the radiobeacon station. Radiocommunication - Telecommunication by means of radio waves. Radiocommunication Service - A service as defined in this Section [of the Radio Regulations] involving the transmission, emission and/or reception of radio waves for specific telecommunication purposes. In these regulations, unless otherwise stated, any radiocommunication service relates to terrestrial radiocommunication. Radio Detection and Ranging - See radar. Radiodetermination - The determination of the position, velocity and/or other characteristics of an object, or the obtaining of information relating to these parameters, by means of the propagation properties of radio waves. Radiodetermination-Satellite Service - A radiocommunication service for the purpose of radiodetermination involving the use of one or more space stations. This service may also include feeder links necessary for its own operation. Radio Field Intensity - Synonym field strength. 1. The magnitude of an electric, magnetic, or electromagnetic field at a given point. Note: The field strength of an electromagnetic wave is usually expressed as the rms value of the electric field, in volts per meter. The field strength of a magnetic field is usually expressed in amperes per meter 2. The electric field strength in the horizontal plane. Radio Frequency - See RF. Of, or pertaining to, any frequency within the electromagnetic spectrum normally associated with radio wave propagation. Note: For designation of subdivisions, see electromagnetic spectrum and its associated diagram. Radio Horizon - The locus of points at which direct rays from an antenna are tangential to the surface of the Earth. Note: If the Earth were a perfect sphere and there were no atmospheric anomalies, the radio horizon would be a circle. In practice, the distance to the radio horizon is affected by the height of the transmitting antenna, the height of the receiving antenna, atmospheric conditions, and the presence of obstructions, e.g., mountains. Radiolocation - Radiodetermination used for purposes other than those of radionavigation. Radiological Monitoring - Synonym monitoring. - 1. The act of listening, carrying out surveillance on, and/or recording the emissions of one's own or allied forces for the purposes of maintaining and improving procedural standards and security, or for reference, as applicable. 2. The act of listening, carrying out surveillance on, and/or recording of enemy emissions for intelligence purposes. 3. The act of detecting the presence of radiation and the measurement thereof with radiation measuring instruments. Radionavigation - 1. Radiolocation intended for the determination of position or direction or for obstruction warning in navigation. 2. Radiodetermination used for the purposes of navigation, including obstruction warning. Radionavigation-Satellite Service - A radiodetermination-satellite service used for the purpose of radionavigation. This service may also include feeder links necessary for its operation. 386
- 387. Radio Paging - The use of a pocket-size radio receiver capable of alerting its wearer that there is a phone call, either from a displayed phone number or to a predesignated number. Note: Radio paging may be considered a subset of paging. Synonym beeping. Radio Regulations Board: A permanent organization of the International Telecommunication Union (ITU) that implements frequency assignment policy and maintains the Master International Frequency Register (MIFR). Note: Formerly International Frequency Registration Board (IFRB). Radio Wave - An electromagnetic wave of a frequency arbitrarily lower than 3000 GHz. Synonym Hertzian wave. RAM - Acronym for random access memory. - A read /write, nonsequential-access memory used for the storage of instructions and data. Note 1: RAM access time is essentially the same for all storage locations. Note 2: RAM is characterized by a shorter access time than disk or tape storage. Note 3: RAM is usually volatile. Random Access Memory (RAM) - A read /write, nonsequential-access memory used for the storage of instructions and data. Note 1: RAM access time is essentially the same for all storage locations. Note 2: RAM is characterized by a shorter access time than disk or tape storage. Note 3: RAM is usually volatile. Random Noise - Noise consisting of a large number of transient disturbances with a statistically random time distribution. Note: Thermal noise is an example of random noise. Raster - A predetermined pattern of scanning lines within a display space. Note: An example of a raster is the pattern followed by an electron beam scanning the screen of a television camera or receiver. Raster Graphics - Synonym [loosely] bitmapped graphics. Ratio-Squared Combiner - A diversity combiner in which (a) the signals from each channel are added together, (b) the gain of each channel is made proportional to the rms signal level and inversely proportional to the mean square noise level in that channel, and (c) the same proportionality constant is used for all channels. Synonym maximal-ratio combiner. Ray - A geometric representation of a lightwave by a line normal to the electromagnetic wavefront; i.e., in the direction of propagation of the wave. Rayleigh Scattering - Of an electromagnetic wave propagating in a material medium, scattering caused by refractive-index inhomogeneities that are small compared to the wavelength. Note 1: Rayleigh scattering losses vary as the reciprocal of the fourth power of the wavelength. Note 2: Ionospheric scattering is caused partly by Rayleigh scattering. Ray Optics - Synonym geometric optics. The branch of optics that describes light propagation in terms of rays. Note 1: Rays are bent at the interface between two dissimilar media, and may be curved in a medium in which the refractive index is a function of position. Note 2: The ray in ray optics is perpendicular to the wavefront in physical optics. RBOC - Regional Bell Operating Company. In December 1983, a federal judge ordered AT&T to divide their 22 telephone companies into seven regional operating companies. The United States Department of Justice placed several restrictions on the RBOCs: they were not allowed to provide long distance, equipment manufacturing, or information services. 387
- 388. Read - [A] fundamental operation in an information system (IS) that results only in the flow of information from an object to a subject. Real Time Protocol (RTP) - Also known as Real Time Transport Protocol. Controls the transmission of packets of data that demands low latency (such as audio and video). Supports real-time transmission over IP networks and streaming as one means of delivery. Received Noise Power - 1. The calculated or measured noise power, within the bandwidth being used, at the receive end of a circuit, channel, link, or system. 2. The absolute power of the noise measured or calculated at a receive point. Note: The related bandwidth and the noise weighting must also be specified. 3. The value of noise power, from all sources, measured at the line terminals of telephone set's receiver. Note: Either flat weighting or some other specific amplitude-frequency characteristic or noise weighting characteristic must be associated with the measurement. Receiver - The sink or terminator of any signal on a transmission medium. Recipient - The switch or network to which a subscriber's directory number has been ported. Recording Density - Synonym bit density.The number of bits recorded per unit length, area, or volume. Note: Recording Density is the reciprocal of bit pitch. Record Traffic - 1. Traffic that is recorded, in permanent or quasipermanent form, by the originator, the addressee, or both. 2. Traffic that is permanently or semipermanently recorded in response to administrative procedures or public law. Recovery - In a database management system, the procedures and capabilities available for reconstruction of the contents of a database to a state that prevailed before the detection of processing errors and before the occurrence of a hardware or software failure that resulted in the destruction of some or all of the stored data. RED - Rural Economic Development. A program administered by TDS Telecom and other phone companies which includes advocating for rural development funding at the Federal and State levels. This program is designed to support local companies’ efforts with economic development projects in their communities. Redundancy - 1. In the transmission of data, the excess of transmitted message symbols over that required to convey the essential information in a noise-free circuit. Note: Redundancy may be introduced intentionally (as in the case of error detection or correction codes) or inadvertently (such as by oversampling a band-limited signal, inefficient formats, etc.). 2. In a communication system, surplus capability usually provided to improve the reliability and quality of service. Redundant Connectivity - A system of backup connections that ensures the network will continue functioning even if a problem is encountered on one of the connections. Reference Antenna - An antenna that may be real, virtual, or theoretical, and has a radiation pattern that can be used as a basis of comparison with other antenna radiation patterns. Note: Examples of reference antennas are unit dipoles, half-wave dipoles, and isotropic, i.e., omnidirectional antennas. Reference Point - In ISDN, a logical point between two, nonoverlapping functional groups. Note: When equipment is placed at a reference point, that reference point is designated an interface. 388
- 389. Reflected Code - Synonym Gray code. - A binary code in which consecutive decimal numbers are represented by binary expressions that differ in the state of one, and only one, one bit. Reflecting Layer - In the ionosphere, a layer that has a free-electron density sufficient to reflect radio waves. Note 1: The principal reflecting layers are the E, F1, and F2 layers in the daylight hemisphere. Note 2: A critical frequency is associated with the reflection by each layer. Reflection - The abrupt change in direction of a wave front at an interface between two dissimilar media so that the wave front returns into the medium from which it originated. Note 1: Reflection may be specular (i.e., mirror-like) or diffuse (i.e., not retaining the image, only the energy) according to the nature of the interface. Note 2: Depending on the nature of the interface, i.e., dielectric-conductor or dielectric-dielectric, the phase of the reflected wave may or may not be inverted. Reflection Loss - 1. At a discontinuity or impedance mismatch, e.g., in a transmission line, the ratio of the incident power to the reflected power. Note 1: Reflection loss is usually expressed in dB. Refractive index ( , n) - Of a medium, the ratio of the velocity of propagation of an electromagnetic wave in vacuum to its velocity in the medium. Synonym index of refraction. Note: When the Greek character eta is unavailable, the letter n is used to represent the refractive index. Refractive Index Contrast - In an optical fiber, a measure of the relative difference in refractive index of the 2 2 2 core and cladding. Note: Refractive index contrast, , is given by = (n 1 -n 2 )/(2n 1 ), where n 1 is the maximum refractive index in the core and n 2 is the refractive index of the homogeneous cladding. Refractive Index Profile - Of the cross section of an optical fiber, the description, i.e., plot, of the value of the refractive index as a function of distance from the fiber axis along a diameter. Synonyms index profile, refraction profile. Regeneration - 1. In a regenerative repeater, the process by which digital signals are amplified, reshaped, retimed, and retransmitted. Synonym positive feedback. 2. In a storage or display device, the restoration of stored or displayed data that have deteriorated. Note: For example, conventional cathode-ray tube displays must be continually regenerated for the data to remain displayed. 3. In computer graphics, the sequence of events needed to generate a display image from its representation in storage. Regenerative Repeater - A repeater, designed for digital transmission, in which digital signals are amplified, reshaped, retimed, and retransmitted. Synonym regenerator. Regenerator - 1. - A repeater, designed for digital transmission, in which digital signals are amplified, reshaped, retimed, and retransmitted. Synonym regenerative repeater. 2. A device that reconstructs and retransmits a received pulse train. Register - 1. A device, accessible to one or more input circuits, that accepts and stores data. Note: A register is usually used only as a device for temporary storage of data. 2. A temporary-memory device used to receive, hold, and transfer data (usually a computer word) to be operated upon by a processing unit. Note: Computers typically contain a variety of registers. General purpose registers may perform many functions, such as holding constants or accumulating arithmetic results. Special purpose registers perform special functions, such as holding the instruction being executed, the address of a storage location, or data being retrieved from or sent to storage. Registration - 1. The accurate positioning of, or the degree of accuracy in the positioning of, an entity relative to (a) another entity, or (b) an independent frame of reference. Note: For example, in color graphics 389
- 390. applications involving the superposition of several colored rasters, such as in a CRT display, good registration (usually termed " convergence " in this context) is of paramount importance if the resulting image is not to have false colors, especially around the edges of objects. 2. In telephony, see FCC registration program. 3. In computer networking, the official assignment of a name (Internet Protocol address) to an information object or device, in a way that makes the assignment unduplicated anywhere else in the network and makes the device available for other devices to communicate with. Relative Address - In computer and data processing programming, an address that is expressed as a difference in relation to a base address. Relative Spectral Width - See spectral width. The wavelength interval over which the magnitude of all spectral components is equal to or greater than a specified fraction of the magnitude of the component having the maximum value. Note 1: In optical communications applications, the usual method of specifying spectral width is the full width at half maximum. This method may be difficult to apply when the spectrum has a complex shape. Another method of specifying spectral width is a special case of root-mean-square deviation where the independent variable is wavelength, , and f ( ) is a suitable radiometric quantity. Note 2: The relative spectral width , / , is frequently used where is obtained according to note 1, and is the center wavelength. Relative Transmission Level - The ratio of the signal power, at a given point in a transmission system, to a reference signal power. Note: The ratio is usually determined by applying a standard test tone at zero transmission level point (or applying adjusted test tone power at any other point) and measuring the gain or loss to the location of interest. A distinction should be made between the standard test tone power and the expected median power of the actual signal required as the basis for the design of transmission systems. Relay - 1. To retransmit a received message from one station to another station. 2. An electromechanical or semiconductor switch (i.e., solid-state relay) in which a current or voltage applied across one port or terminal controls electrical currents or voltages that appear across another terminal or terminals. Reliability - 1. The ability of an item to perform a required function under stated conditions for a specified period of time. 2. The probability that a functional unit will perform its required function for a specified interval under stated conditions. 3. The continuous availability of communication services to the general public, and emergency response activities in particular, during normal operating conditions and under emergency circumstances with minimal disruption. Remote Access - 1. Pertaining to communication with a data processing facility from a remote location or facility through a data link. 2. A PABX service feature that allows a user at a remote location to access by telephone PABX features, such as access to wide area telephone service (WATS) lines. Note: For remote access, individual authorization codes are usually required. Remote Clock - 1. A clock that is remote from a particular facility, such as a communications station or node, with which it is associated. 2. A clock that is remote from another clock to which it is to be compared. Remote Linked Registration - A feature by which a linked registration for one specified terminal address can be carried out from another terminal address. Remote Terminal - The location at which there is a transition between a telecommunications carrier facility and the local lines serving the individual customers. Reorder Tone - See busy signal. In telephony, an audible or visual signal that indicates that the called number is occupied or otherwise unavailable. 390
- 391. Repeat Dialing - You can activate this feature by dialing a code and the last outgoing call placed by you will be automatically redialed. If the telephone number called is not busy, the call will complete. If the telephone number called is busy, you will hear a confirmation tone, you can then hang up. Once you hang up, the network will monitor the busy/idle status of both lines every 45 seconds for up to 30 minutes. During that time, the network will ring your home telephone number once the telephone number called is no longer busy. Dials a busy telephone number for 30 minutes and rings your phone when the dialed number is clear. After reaching a busy number, hang up, then pick up the phone again and dial *66 to activate. To cancel Repeat Dial press*86 . Repeat Dial does not work with long distance calls or 800 numbers. Repeater - 1. An analog device that amplifies an input signal regardless of its nature, i.e., analog or digital. 2. A digital device that amplifies, reshapes, retimes, or performs a combination of any of these functions on a digital input signal for retransmission. Note: The term "repeater" originated with telegraphy and referred to an electromechanical device used to regenerate telegraph signals. Use of the term has continued in telephony and data communications. 3. A fixed transmitter that retransmits the signals of other stations. Requests - See click-through. - The process of clicking on a Web advertisement and going directly to the advertiser's Web site. Synonyms ad clicks, clicks. Request-To-Send Signal - A signal that is generated by a receiver in order to condition a remote transmitter to commence transmission. Reradiation -1. Radiation, at the same or different wavelengths, i.e., frequencies, of energy received from an incident wave. 2. Undesirable radiation of signals locally generated in a radio receiver. Note: Radiation might cause interference or reveal the location of the device. Rerouting - Recommencement of route selection from the first point of routing control, when congestion is encountered at some intermediate switching point in the connection that is to be established. Resident - Pertaining to computer programs that remain on a particular storage device. Residual Error Rate - Synonym undetected error ratio. The ratio of the number of bits, unit elements, characters, or blocks incorrectly received and undetected, to the total number of bits, unit elements, characters, or blocks sent. Resolution - In computers, resolution is the number of pixels (individual points of color) contained on a display monitor, expressed in terms of the number of pixels on the horizontal axis and the number on the vertical axis. The sharpness of the image on a display depends on the resolution and the size of the monitor. The same pixel resolution will be sharper on a smaller monitor and gradually lose sharpness on larger monitors because the same number of pixels are being spread out over a larger number of inches. A given computer display system will have a maximum resolution that depends on its physical ability to focus light (in which case the physical dot size - the dot pitch - matches the pixel size) and usually several lesser resolutions. For example, a display system that supports a maximum resolution of 1280 by 1023 pixels may also support 1024 by 768, 800 by 600, and 640 by 480 resolutions. Note that on a given size monitor, the maximum resolution may offer a sharper image but be spread across a space too small to read well. Display resolution is not measured in dots per inch as it usually is with printers. However, the resolution and the physical monitor size together do let you determine the pixels per inch. Typically, PC monitors have somewhere between 50 and 100 pixels per inch. For example, a 15-inch VGA (see display modes) monitor 391
- 392. has a resolution of 640 pixels along a 12-inch horizontal line or about 53 pixels per inch. A smaller VGA display would have more pixels per inch. Resonance - In an electrical circuit, the condition that exists when the inductive reactance and the capacitive reactance are of equal magnitude, causing electrical energy to oscillate between the magnetic field of the inductor and the electric field of the capacitor. Note 1: Resonance occurs because the collapsing magnetic field of the inductor generates an electric current in its windings that charges the capacitor and the discharging capacitor provides an electric current that builds the magnetic field in the inductor, and the process is repeated. Note 2: At resonance, the series impedance of the two elements is at a minimum and the parallel impedance is a maximum. Resonance is used for tuning and filtering, because resonance occurs at a particular frequency for given values of inductance and capacitance. Resonance can be detrimental to the operation of communications circuits by causing unwanted sustained and transient oscillations that may cause noise, signal distortion, and damage to circuit elements. Note 3: At resonance the inductive reactance and the capacitive reactance are of equal magnitude. Therefore, L = 1/ C, where = 2 f, in which f is the resonant frequency in hertz, L is the inductance in henrys, and C is the capacity in farads when standard SI units are used. Restoration - Of an impaired (degraded) or unserviceable telecommunications service or facility, action taken to repair it and return it to service. Note: Permanent or temporary restoration may be accomplished by various means, such as patching, rerouting, substitution of component parts, etc. Return Loss - The ratio, at the junction of a transmission line and a terminating impedance or other discontinuity, of the amplitude of the reflected wave to the amplitude of the incident wave. Note 1: Return loss is usually expressed in dB. Note 2: Return loss is a measure of the dissimilarity between impedances in metallic transmission lines and loads, or between refractive indices in dielectric media, e.g., optical fibers. RF - Also rf. Abbreviation for radio frequency. Of, or pertaining to, any frequency within the electromagnetic spectrum normally associated with radio wave propagation. Note: For designation of subdivisions, see electromagnetic spectrum and its associated diagram. Ringback - A tone produced by telephone processing equipment that signals to the caller that the called party is being rung. Automatic Call Processors produce a ringback tone to the caller when ringing a device. Ringback Tone- A tone produced by telephone processing equipment that signals to the caller that the called party is being rung. Automatic Call Processors produce a ringback tone to the caller when ringing a device. Ringing - Oscillations that occur in the output of systems after a sudden change in the input. Ringing Cycle - In traditional telephony, a nominal period (usually approximately 6 seconds) composed of alternate (a) ringing signals (ringing current) and (b) a silent interval. Ringing Signal - 1. The alternating current (ac) component of the alerting signal. 2. An ac signal applied across the network interface (NI) of such magnitude, frequency, and duration to cause an electromechanical ringer to ring. Used to alert the customer installation (CI) of an incoming call. Ring Topology - See network topology. A network topology in which every node has exactly two branches connected to it. RJ-11 - The most common telephone jack is the RJ-11 jack, which can have six conductors but usually is implemented with four. The RJ-11 jack is likely to be the jack that your household or office phones are plugged into from the ordinary "untwisted" wire (sometimes called "gray satin" or "flat wire") people are 392
- 393. most familiar with. In turn, the jacks connect to the "outside" longer wires known as twisted pair that connect to the telephone company central office or to a private branch exchange (PBX). The four wires are usually characterized as a red and green pair and a black and white pair. The red and green pair typically carry voice or data. On an outside phone company connection, the black and white pair may be used for low-voltage signals such as phone lights. On a PBX system, they may be used for other kinds of signaling. See telephone jacks. A computer that uses a dial-up modem to connect to a network is usually plugged into an RJ-11 jack. RJ-11 Wiring Standard - A specific wiring arrangement for using a g-position modular connector to attach exactly one telephone line. The two wires of the telephone line are attached to the two center contacts of an RJ-11 modular jack (the wires are often color-coded red and green). All connections to your automatic call processor must be wired according to this RJ-11 standard. See telephone jacks. RJ-14 - The RJ-14 is similar to the RJ-11, but the four wires are used for two phone lines. Typically, one set of wires (for one line) contains a red wire and a green wire. The other set contains a yellow and black wire. Each set carries one analog "conversation" (voice or data). See telephone jacks. RJ-14 Wiring Standard - Utilizes a six position modular connector wired to two separate telephone lines. This application is used almost exclusively on dual line telephones. Line 1 is attached to the center two contacts (like RJ-ll), and Line 2 is attached to the next outer two contacts (often color-coded yellow and black). See RJ- 14. See telephone jacks. RJ-45 - The RJ-45 is a single-line jack for digital transmission over ordinary phone wire, either untwisted or twisted. The interface has eight pins or positions. For connecting a modem, printer, or a data PBX at a data rate up to 19.2 Kbps, you can use untwisted wire. For faster transmissions in which you're connecting to an Ethernet 10BASET network, you need to use twisted pair wire. (Untwisted is usually a flat wire like common household phone extension wire. Twisted is often round.) There are two varieties of RJ-45: keyed and unkeyed. Keyed has a small bump on its end and the female complements it. Both jack and plug must match. Roaming Service - Is the ability to get access to the Internet when away from home at the price of a local call or at a charge considerably less than the regular long-distance charges. For example, if you normally get access to the Internet from an access provider in Brooklyn, New York and are travelling to Hong Kong, you can call a designated access provider in Hong Kong. Instead of paying long distance charges to your local 393
- 394. provider in Brooklyn, you pay the local phone connection charge in Hong Kong and possibly a modest additional charge for the service. Robot - Computer software that runs continuously and responds automatically to a user's activity. Note: Some robots are created for the benefit of the user, such as those that send information when a user requests it, those that perform automated searches, and those that monitor messages in a forum and delete messages that are repetitive or violate the forum's rules of netiquette. Other robots are created to harm the user (e.g., a computer virus) or spam the user (e.g., a program that, whenever a user posts a message to a forum, automatically sends a response to the user containing unrelated advertisements). Robotic Librarian - Synonym droid. Roll Over - A service provided by most phone companies that allows several lines to be tied together. A single number is generally dialed by all callers. If that line is busy, the phone company will "roll-over" the call to another line in that group. Also called "hunt-group" or "rotary". ROM - Acronym for read-only memory. Roofing Filter - A low-pass filter used to reduce unwanted higher frequencies. Room Noise Level - Synonym ambient noise level. Room Preset - In multimedia and virtual reality, information that may be used to select a video source, and then control the video source to provide the desired view. The ability to provide presets is optional and may not be supported in all terminals. Root - In computer science, the highest level of a hierarchy. Root-Mean-Square (rms) Deviation - A single quantity, rms, characterizing a function Root-Mean-Square (rms) Pulse Broadening - The temporal rms deviation of the impulse response of a system. Root-Mean-Square (rms) Pulse Duration - A special case of root-mean-square deviation where the independent variable is time and f ( t ) describes the pulse waveform. Rope Lay Conductor - A conductor composed of a central core surrounded by one or more layers of helically wound groups of wires. Rotary - An ambiguous term. "Rotary Group" means a roll-over group, and "Rotary Dialing" means pulse dialing. Rotary Dial - A signaling mechanism--usually incorporated within a telephone set--that when rotated and released, generates dc pulses required for establishing a connection in a telephone system. Rotary Dialing - means pulse dialing. Rotary Group -A service provided by most phone companies that allows several lines to be tied together. A single number is generally dialed by all callers. If that line is busy, the phone company will "roll-over" the call to another line in that group. Also called "hunt-group", "rollover" and more recently "busy-line transfer". 394
- 395. Rotary Hunting - Hunting in which all the numbers in the hunt group are selected in a prescribed order. Note: In modern electronic switching systems, the numbers in the hunt group are not necessarily selected in consecutive order. Rotary Switching - In telephone systems, an electro-mechanical switching method whereby the selecting mechanism consists of a rotating element using several groups of wipers, brushes, and contacts. Rotational Position Sensing: [In magnetic media,] A technique used to locate a given sector, a desired track, and a specific record by continuous comparison of the read / write head position with appropriate synchronization signals. Rounding - Deleting the least-significant digits of a number and applying some rule of correction to the part retained. Round-Trip Delay Time -1. The elapsed time for transit of a signal over a closed circuit. Note: Round-trip delay time is significant in systems that require two-way interactive communication such as voice telephony or ACK / NAK data systems where the round-trip time directly affects the throughput rate. It may range from a very few microseconds for a short line-of-sight ( LOS ) radio system to many seconds for a multiple- link circuit with one or more satellite links involved. This includes the node delays as well as the media transit time. 2. In primary or secondary radar systems, the time required for a transmitted pulse to reach a target and for the echo or transponder reply to return to the receiver. Route - 1. In communications systems operations, the geographical path that is followed by a call or message over the circuits that are used in establishing a chain of connections. 2. To determine the path that a message or call is to take in a communications network. Note: In a Transmission Control Protocol / Internet Protocol (TCP/IP) internet, each IP datagram is routed separately. The route a datagram follows may include many gateways and many physical networks. 3. To construct the path that a call or message is to take in a communications network in going from one station to another or from a source user end instrument to a destination user end instrument. Route Diversity - The allocation of circuits between two points over more than one geographic or physical route with no geographic points in common. Route Index - A pointer to a specific trunk group. Route List - A specific list of trunk groups. Route Matrix - In communications network operations, a record that indicates the interconnections between pairs of nodes in the network, and is used to produce direct routes, alternate routes, and available route tables from point to point. Router - Highly sophisticated systems that connect local area networks (LANs). The router reads the network layer address of all packets transmitted by a network, and forwards only those addressed to another network. Route Verification - Procedures that permit a signaling point to determine the accuracy and consistency of its routing data by sending a test message and analyzing the response message to determine whether the sent message traversed the expected route. Routine - A computer program, called by another program, that may have some general or frequent use. 395
- 396. Routine Message - A category of precedence to be used for all types of messages that justify transmission by rapid means unless of sufficient urgency to require a higher precedence. Routing - The process of determining and prescribing the path or method to be used for establishing telephone connections or forwarding messages. Routing Address - Synonym routing number, routing table. Routing Diagram - In a communications system, a diagram that (a) shows all links between all switchboards, exchanges, switching centers, and stations in the system, such as the links between primary relay , major relay, minor relay, and tributary stations as well as supplementary links, (b) is used to identify the stations and links, and (c) is used to indicate tape-relay routes, transfer circuits, refile circuits, radio links, operational status, line conditions, and other network information required for network operations and management. Routing Directory - See routing table. Routing Indicator (RI) -1. A group of letters assigned to indicate: (a) the geographic location of a station; (b) a fixed headquarters of a command, activity, or unit at a geographic location; and (c) the general location of a tape relay or tributary station to facilitate the routing of traffic over the tape relay networks. 2. In a message header, an address, i.e., group of characters, that specify routing instructions for the transmission of the message to its final destination. Note: Routing indicators may also include addresses of intermediate points. Routing Label - The part of the message label that is used for message routing in the signaling network. It includes the destination point code, the originating point code, and the signaling link selection field. Routing Number - Synonym routing address, routing table. Routing Protocol - In an internet, a service protocol that is used (by routers, but not by hosts) to maintain routing tables; routing protocols are classified as either (a) interior gateway protocols, or (b) exterior gateway protocols. Routing Table - A matrix associated with a network control protocol, which gives the hierarchy of link routing at each node. RQ - Abbreviation for repeat-request. See ARQ. RSL - Abbreviation for received signal level. RTA - Abbreviation for remote trunk arrangement. RTP - (Real Time Protocol) - Also known as Real Time Transport Protocol. Controls the transmission of packets of data that demands low latency (such as audio and video). Supports real-time transmission over IP networks and streaming as one means of delivery. RTTY - Abbreviation for radio teletypewriter. Rubidium Clock - A clock containing a quartz oscillator stabilized by a rubidium standard. Rubidium Standard - A frequency standard in which a specified hyperfine transition of electrons in rubidium- 87 atoms is used to control the output frequency. Note: A rubidium standard consists of a gas cell, which has 396
- 397. an inherent long-term instability. This instability relegates the rubidium standard to its status as a secondary standard. Run - The execution of one or more computer jobs or programs. Run-Length Encoding - A redundancy -reduction technique for facsimile in which a run of consecutive picture elements having the same state ( gray scale or color) is encoded into a single code word. Rural Radio Service - A public radio service rendered by fixed stations on frequencies below 1000 MHz used to provide (1) Basic Exchange Telecommunications Radio Service, which is public message communication service between a central office and subscribers located in rural areas, (2) public message communication service between landline central offices and different exchange areas which it is impracticable to interconnect by any other means, or (3) private line telephone, telegraph, or facsimile service between two or more points to which it is impracticable to extend service via landline. Rural Subscriber Station -1. A fixed station in the rural radio service used by a subscriber for communication within a central office station. 2. One or more fixed transmitters in the rural radiotelephone service that receive service from central office transmitters. RUS - Rural Utilities Service. The RUS is an agency of the United States Department of Agriculture. It’s a source of financing and technical assistance for rural telecommunication systems. RWI - Abbreviation for radio and wire integration. RX - Abbreviation for receive, receiver. RZ - Abbreviation for return-to-zero. S Safeguarding Statement - [A] statement affixed to a computer output or printout that states the highest classification being processed at the time the product was produced and requires control of the product, at that level, until determination of the true classification by an authorized person. Synonym [in INFOSEC] banner. Safety Service - Any radiocommunication service used permanently or temporarily for the safeguarding of human life and property. Sampled Data - Data in which the information content exists only for instantaneous values measured or determined at or for discrete intervals. Note: Sampled data can be analog or digital. Sampling - See signal sampling. The process of obtaining a sequence of instantaneous values of a particular signal characteristic, usually at regular time intervals. Sampling Frequency - See sampling rate. The number of samples taken per unit time, i.e., the rate at which signals are sampled for subsequent use, such as for modulation, coding, and quantization. Sampling Interval - The reciprocal of the sampling rate, i.e. , the interval between corresponding points on two successive sampling pulses of the sampling signal. 397
- 398. Sampling Rate - The number of samples taken per unit time, i.e., the rate at which signals are sampled for subsequent use, such as for modulation, coding, and quantization. Deprecated synonym sampling frequency. Sampling Theorem - Synonym Nyquist's theorem. A theorem, developed by H. Nyquist, which states that an analog signal waveform may be uniquely reconstructed, without error, from samples taken at equal time intervals. The sampling rate must be equal to, or greater than, twice the highest frequency component in the analog signal. Sanitize - [In INFOSEC, the] process to remove information from media such that data recovery is not possible. It includes removing all classified labels, markings, and activity logs. Sanitizing - Of a recording medium, erasing or overwriting all data in such a manner that it cannot be recovered, even by extraordinary, e.g., laboratory, means. Note: Sanitizing is distinguished from simply "deleting" or "erasing" data. For example, a software-based deletion command may simply mark a file or block of data to the effect that it may be overwritten during a subsequent "save" of different data. Until such a save is performed, the deleted data may be recovered, sometimes by the simple expedient of executing a software command. Likewise, digital data, for example, may be "erased," from a magnetic recording medium, but still be recoverable if subjected to laboratory techniques that can identify residual magnetism left after the erasure. SAP - Abbreviation for service access point. - 1. A physical point at which a circuit may be accessed. 2. In an Open Systems Interconnection (OSI) layer, a point at which a designated service may be obtained. Satellite - A body which revolves around another body of preponderant mass and which has a motion primarily and permanently determined by the force of attraction of that other body. Note: A parent body and its satellite revolve about their common center of gravity. Satellite Access - In satellite communications systems, the establishment of contact with a communications satellite space station. Note: An example of satellite access is access at the moment at which an Earth station commences to use a satellite space station as a signal repeater, i.e. , to use its transponder. Each radio frequency (rf) carrier that is relayed by a satellite space station at any time occupies an access channel. Accesses, i.e., channels, are distinguishable by various system parameters, such as frequency, time, or code. Satellite Communications - A telecommunications service provided via one or more satellite relays and their associated uplinks and downlinks. Satellite Digital Audio Radio Service (SDARS) - 1. A satellite-based direct-broadcast radio service in which digitally encoded audio entertainment material is broadcast to Earth-based receivers, either directly from an orbiting satellite, or--in cases in which the receiver is in a shielded location--from the satellite to the receiver via a repeater station. 2. A radiocommunication service in which audio programming is digitally transmitted by one or more space stations directly to fixed, mobile, and/or portable stations, and which may involve complementary repeating terrestrial transmitters, telemetry, tracking and control facilities. 3. A radiocommunication service in which compact-disc quality programming is digitally transmitted by one or more space stations. Satellite Earth Terminal - Synonym Earth terminal. In a satellite link, one of the non-orbiting communications stations that receives, processes, and transmits signals between itself and a satellite. Note: Earth terminals may be at mobile, fixed, airborne, and waterborne Earth terminal complexes. Satellite Emergency Position-Indicating Radiobeacon - An Earth station in the mobile-satellite service the emissions of which are intended to facilitate search and rescue operations. 398
- 399. Satellite Link - A radio link between a transmitting Earth station and a receiving Earth station through one satellite. A satellite link comprises one uplink and one downlink. Satellite Network - A satellite system or a part of a satellite system, consisting of only one satellite and the cooperating Earth stations. Satellite Operation - See satellite PBX. A PBX system that is not equipped with attendant positions, and is associated with an attended main PBX system. Note: The main attendant provides attendant functions for the satellite system. Satellite PBX - See satellite operation. A PBX system that is not equipped with attendant positions, and is associated with an attended main PBX system. Note: The main attendant provides attendant functions for the satellite system. Satellite Period - See period (of a satellite). The time elapsing between two consecutive passages of a satellite through a characteristic point on its orbit. Satellite Relay - An active or passive satellite repeater that relays signals between two Earth terminals. Satellite System - A space system using one or more artificial Earth satellites. Saturation - 1. In a communications system, the condition in which a component of the system has reached its maximum traffic handling capacity. Note: Saturation is equivalent to one erlang per circuit. 2. The point at which the output of a linear device, such as a linear amplifier, deviates significantly from being a linear function of the input when the input signal is increased.Note: Modulation often requires that amplifiers operate below saturation. Scalability - The degree to which video and image formats can be sized in systematic proportions for distribution over communications channels of varying capacities. Scan - 1. To examine sequentially, part by part. 2. To examine every reference in every entry in a file routinely as part of a retrieval scheme. 3. In radar, one complete rotation of the interrogating antenna. 4. In SONAR, to search 360° or a specific search sector by the use of phased array of transducers. 5. To sweep, i.e., rotate, a beam about a point or about an axis. Scan Line - The line produced on a recording medium frame by a single sweep of a scanner. In an imaging system, the path traversed by a scanning spot during a single line sweep. Scanner - A device that examines a spatial pattern, one part after another, and generates analog or digital signals corresponding to the pattern. Note: Scanners are often used in mark sensing, pattern recognition, and character recognition. Scanning - 1. In telecommunications systems, examination of traffic activity to determine whether further processing is required. Note: Scanning is usually performed periodically. 2. In television, facsimile, and picture transmission, the process of successively analyzing the colors and densities of the object according to a predetermined pattern. 3. The process of tuning a device through a predetermined range of frequencies in prescribed increments and at prescribed times. Note: Scanning may be performed at regular or random increments and intervals. 4. In radar and radio direction-finding, the slewing of an antenna or radiation pattern for the purpose of probing in a different direction. Note 1: In radar, scanning may be mechanical, using a rotary microwave joint to feed the antenna, or electronic, using a phased array of radiators, the radiated pattern (beam) of which depends on the relative phases of the signals fed to the individual 399
- 400. radiators. Note 2: In civilian air traffic control radar, scanning usually implies continuous rotation of the antenna or beam about a vertical axis. In military radars, scanning may occur about other than a vertical axis, and may not encompass a full 360°. Scanning Direction - In facsimile transmitting equipment, the scanning of an object, such as a message surface or the developed plane in the case of a drum, along parallel lines in a specified pattern. Note 1: The scanning direction is equivalent to scanning over a right-hand helix on a drum. Note 2: The orientation of the message on the scanning plane will depend upon its dimensions. Note 3: In facsimile receiving equipment, scanning from right to left and top to bottom, is called "positive" reception and from left to right and top to bottom, is called "negative" reception. Note 4: Scanning direction conventions are included in CCITT Recommendations for phototelegraphic equipment. Scanning Field - In facsimile systems, the total of the areas that are actually explored by the scanning spot during the scanning of the object by the transmitter or during scanning of the record medium by the receiver. Scanning Line - In an imaging system, the path traversed by a scanning spot during a single line sweep. Scanning Line Frequency - In facsimile, the frequency at which a fixed line perpendicular to the direction of scanning is crossed by a scanning spot. Note: The scanning line frequency is equivalent to drum speed in some mechanical systems. Synonym scanning line rate. Scanning Line Length - In facsimile systems, the total length of a scanning line, equal to the spot speed divided by the scanning line frequency. Note: The scanning line length is usually greater than the length of the available line. Scanning Line Period - In facsimile systems, the time interval between (a) the instant at which the scanning spot probes or writes to a given spot on one scanning line, and (b) the instant at which the scanning spot probes or writes to the corresponding spot on the next scanning line. Scanning Line Rate - Synonym scanning line frequency. In facsimile, the frequency at which a fixed line perpendicular to the direction of scanning is crossed by a scanning spot. Note: The scanning line frequency is equivalent to drum speed in some mechanical systems. Scanning Pitch - The distance between the centers of consecutive scanning lines. Scanning Rate - In facsimile and television systems, the rate of displacement of the scanning spot along the scanning line. Scanning Spot - In facsimile systems, the area on the object, i.e., the original, covered instantaneously by the pickup system of the scanner. Scan-Stop Lockup - In automatic link establishment (ALE) radios, the undesired condition in which the normal process of (a) scanning radio channels, (b) stopping on the desired channel, or (c) returning to scan is terminated by the equipment. Scatter - See scattering. Scattering - Of a wave propagating in a material medium, a phenomenon in which the direction, frequency, or polarization of the wave is changed when the wave encounters discontinuities in the medium, or interacts 400
- 401. with the material at the atomic or molecular level. Note: Scattering results in a disordered or random change in the incident energy distribution. Scattering Center - In the microstructure of a transmission medium, a site at which electromagnetic waves are scattered. Note 1: Examples of scattering centers are vacancy defects; interstitial defects; inclusions, such as a gas molecules, hydroxide ions, iron ions, and trapped water molecules; and microcracks or fractures in dielectric waveguides. Note 2: Scattering centers are frozen in the medium when it solidifies and may not necessarily cause Rayleigh scattering, which varies inversely as the fourth power of the wavelength. For example, in glass optical fibers, there is a high attenuation band at 0.95 m, primarily caused by scattering and absorption by OH (hydroxyl) ions. Scattering Coefficient - The factor that expresses the attenuation caused by scattering, e.g. , of radiant or acoustic energy, during its passage through a medium. Note: The scattering coefficient is usually expressed in units of reciprocal distance. Scattering Cross Section - The area of an incident wavefront, at a reflecting surface or medium, such as an object in space, through which will pass radiant energy, that, if isotropically scattered from that point, would produce the same power at a given receiver as is actually provided by the entire reflecting surface. Scattering Loss - The part of the transmission (power) loss that results from scattering within a transmission medium or from roughness of a reflecting surface. SCC - Abbreviation for specialized common carrier. A common carrier offering a limited type of service or serving a limited market. Scene - In video, synonymous with clip. Scene Cut - Video imagery in which consecutive frames are highly uncorrelated. Scene Cut Response - In video systems, the perceived impairments associated with a scene cut. Schematic - 1. A diagram, drawing, or sketch that details the elements of a system, such as the elements of an electrical circuit or the elements of a logic diagram for a computer or communications system. 2. Pertaining to a diagram, drawing, or sketch that details the elements of a system, such as the elements of an electrical circuit or the elements of a logic diagram for a computer or communications system. Scintillation - In electromagnetic wave propagation, a small random fluctuation of the received field strength about its mean value. Note: Scintillation effects become more significant as the frequency of the propagating wave increases. Scrambler - A device that transposes or inverts signals or otherwise encodes a message at the transmitter to make the message unintelligible at a receiver not equipped with an appropriately set descrambling device. Note: Scramblers usually use a fixed algorithm or mechanism. However, a scrambler provides communications privacy that is inadequate for classified traffic. Scratch Pad Store (SPS) - Temporary key storage in crypto-equipment. Scream - Synonym bang. - The exclamation point character (!) used in early addressing schemes to separate the names of individual machines. Note: Scream-style addressing is no longer common. 401
- 402. Screen - 1. In a telecommunications, computing, or data processing system, to examine entities that are being processed to determine their suitability for further processing. 2. A nonferrous metallic mesh used to provide electromagnetic shielding. 3. To reduce undesired electromagnetic signals and noise by enclosing devices in electrostatic or electromagnetic shields. 4. A viewing surface, such as that of a cathode ray tube or liquid crystal display (LCD). Screen Capture - In computers, the process or act by which the data currently displayed on a monitor, usually representing a single frame of information, are stored or processed in a graphical format. Note: A screen capture thus represents an instantaneous "snapshot" of the state of the display. Screened-Host Gateway - Synonym bastion host. A host computer that, in a screened subnetwork, performs the functions of a firewall. Screened Subnetwork - A subnetwork that permits access from both untrusted external networks and from trusted internal networks, but does not permit traffic flow between the two. Screening Router - A network router capable of discriminating network-based traffic on the protocol type and the value of the protocol fields within the packet. Script - A relatively short computer program that performs one specific task. Note: A script is normally used to automate complex or advanced features or procedures within a system. Scripts are commonly used to process user information from Web pages (for example, a search engine is a script). Scripting Language - A programming language supported by and specific to a particular program. Note: A scripting program is normally used to automate complex or advanced features or procedures within the program. Scroll - In a display device, to move the display window of the screen vertically to view the contents of a stored document. Note: Scrolling may be performed continuously or incrementally. Scroll-Mode Terminal - A terminal in which the data are displayed (or pass by) a line at a time. SCSI - Acronym for small computer system interface. An intelligent interface device that expands a microprocessor (CPU) bus to facilitate connections to multiple peripherals (e.g., CD-ROM drives, hard drives, or scanners) and exchange data with those peripherals via a separate communications bus. Note 1: The original SCSI was capable of supporting up to 7 devices at a data rate of 5 Mb/s over an 8-bit parallel bus. Subsequent SCSI versions feature a parallel communications bus having greater width and speed. Note 2: Since SCSI exchanges data with the peripherals over a separate communications bus rather than the processor bus, the CPU can devote the saved processing time to other tasks. Note 3: Pronounced "scuzzy." SDARS ( Satellite Digital Audio Radio Service) - 1. A satellite-based direct-broadcast radio service in which digitally encoded audio entertainment material is broadcast to Earth-based receivers, either directly from an orbiting satellite, or--in cases in which the receiver is in a shielded location--from the satellite to the receiver via a repeater station. 2. A radiocommunication service in which audio programming is digitally transmitted by one or more space stations directly to fixed, mobile, and/or portable stations, and which may involve complementary repeating terrestrial transmitters, telemetry, tracking and control facilities. 3. A radiocommunication service in which compact-disc quality programming is digitally transmitted by one or more space stations. SDLC - Abbreviation for synchronous data link control. In a data network, a bit-oriented protocol for the control of synchronous transmission over data links. 402
- 403. SDTV - Abbreviation for Standard Definition TV. A TV with an internal digital tuner. SDTV has the basic digital television format closest to traditional analog TV. Search Engine - A specialized program that facilitates information retrieval from large segments of the Internet. Note 1: Search engines attempt to help a user locate desired information or resources by seeking matches to user-specified key words. The usual method for finding and isolating this information is to compile and maintain an index of Web resources that can be queried for the key words or concepts entered by the user. The indices are often built from specific resource lists, and may also be created from the output of Web crawlers, wanderers, robots, spiders, or worms. The indices are usually compiled during times of minimum network traffic. Note 2: Different engines are appropriate for different kinds of searches, and most can be optimized for specified results. Search robot - See bot, droid. Search Time - In data processing systems, the time interval required to locate a particular data element, record, or file in a storage device. Search Vehicles - Sources that offer a variety of methods to obtain information on the WWW (e.g. catalogs, directories, search engines, spiders). SECAM - Acronym for système electronique couleur avec memoire. A television signal standard (625 lines, 50 Hz, 220 V primary power) used in France, eastern European countries, the former USSR, and some African countries. Second (s) - In the International System of Units (SI), the time interval equal to 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom. Secondary Channel - In a system in which two channels share a common interface, a channel that has a lower data signaling rate (DSR) capacity than the primary channel. Secondary Emission - Particles or radiation, such as photons, Compton recoil electrons, delta rays, secondary cosmic rays, and secondary electrons, that are produced by the action of primary radiation on matter. Secondary Frequency Standard - A frequency standard that does not have inherent accuracy, and therefore must be calibrated against a primary frequency standard. Note: Secondary standards include crystal oscillators and rubidium standards. A crystal oscillator depends for its frequency on its physical dimensions, which vary with fabrication and environmental conditions. A rubidium standard is a secondary standard even though it uses atomic transitions, because it takes the form of a gas cell through which an optical signal is passed. The gas cell has inherent inaccuracies because of gas pressure variations, including those induced by temperature variations. There are also variations in the concentrations of the required buffer gases, which variations cause frequency deviations. Secondary Radar - A radiodetermination system based on the comparison of reference signals with radio signals retransmitted from the position to be determined. Note: An example of secondary radar is the transponder-based surveillance of aircraft. Synonym secondary surveillance radar. Secondary Radiation - See secondary emission. Particles or radiation, such as photons, Compton recoil electrons, delta rays, secondary cosmic rays, and secondary electrons, that are produced by the action of primary radiation on matter. 403
- 404. Secondary Service Area - The service area of a broadcast station served by the skywave and not subject to objectionable interference and in which the signal is subject to intermittent variations in strength. Secondary Station - In a communications network, a station that (a) is responsible for performing unbalanced link-level operations as instructed by the primary station and (b) interprets received commands and generates responses. Secondary Surveillance Radar - Synonym secondary radar. A radiodetermination system based on the comparison of reference signals with radio signals retransmitted from the position to be determined. Note: An example of secondary radar is the transponder-based surveillance of aircraft. Secondary Time Standard - A time standard that requires periodic calibration against a primary time standard. Second Dialtone - 1. Dialtone presented to the call originator after an access code has been dialed for access to a second, outside, telecommunications system or service. 2. Dialtone returned to the call originator after she/he has dialed an access number and has reached a switch providing access to modem, to a fax machine, to another telephone, etc. Second Window - Of silica-based optical fibers, the transmission window at approximately 1.3 m. Note: The second window is the minimum-dispersion window in silica-based glasses. SECOR - : Acronym for secure voice cord board . A desk-mounted patch panel that provides the capability for controlling (a) sixteen 50-kb/s wideband or sixteen 2400-b/s narrowband user lines and (b) 5 narrowband trunks to DSN or other narrowband facilities. SECTEL - Acronym for secure telephone. See STU. A U.S. Government-approved telecommunications terminal that protects the transmission of sensitive or classified information in voice, data, and facsimile systems. Section Boundary - The boundary that separates a network section from the adjacent circuit section, or separates an access circuit section from the adjacent DTE (data terminal equipment). Synonym boundary Sector - A predetermined, addressable angular part of a track or band on a magnetic drum or magnetic disk. Sectoring - In magnetic or optical disk storage media, the division of tracks into a specified number of segments, for the purpose of organizing the data stored thereon. Secure Communications - Telecommunications deriving security through use of type 1 products and/or protected distribution systems. Secure Internet Protocols - A set of security rules or standards that determines how computers talk to each other on a network. Secure Telephone Unit - See STU. A U.S. Government-approved telecommunications terminal that protects the transmission of sensitive or classified information in voice, data, and facsimile systems. Secure Transmission - 1. In transmission security, see secure communications . 2. In spread-spectrum systems, the transmission of binary coded sequences that represent information that can be recovered only by persons or systems that have the proper key for the spread-spectrum code-sequence generator, i.e., have a synchronized generator that is identical to that used for transmission. 404
- 405. Secure Voice Cord Board - See SECORD. A desk-mounted patch panel that provides the capability for controlling (a) sixteen 50-kb/s wideband or sixteen 2400-b/s narrowband user lines and (b) 5 narrowband trunks to DSN or other narrowband facilities. Security - 1. A condition that results from the establishment and maintenance of protective measures that ensure a state of inviolability from hostile acts or influences. 2. With respect to classified matter, the condition that prevents unauthorized persons from having access to official information that is safeguarded in the interests of national security. 3. Measures taken by a military unit, an activity or installation to protect itself against all acts designed to, or which may, impair its effectiveness. Security Filter - 1. In communications security, the hardware, firmware, or software used to prevent access to specified data by unauthorized persons or systems, such as by preventing transmission, preventing forwarding messages over unprotected lines or circuits, or requiring special codes for access to read-only files. 2. [An] AIS trusted subsystem that enforces security policy on the data that passes through it. Security Kernel - 1. In computer and communications security, the central part of a computer or communications system hardware, firmware, and software that implements the basic security procedures for controlling access to system resources. 2. A self-contained usually small collection of key security-related statements that (a) works as a part of an operating system to prevent unauthorized access to, or use of, the system and (b) contains criteria that must be met before specified programs can be accessed. 3. Hardware, firmware, and software elements of a trusted computing base that implement the reference monitor concept. Security Management - In network management, the set of functions (a) that protects telecommunications networks and systems from unauthorized access by persons, acts, or influences and (b) that includes many subfunctions, such as creating, deleting, and controlling security services and mechanisms; distributing security-relevant information; reporting security-relevant events; controlling the distribution of cryptographic keying material; and authorizing subscriber access, rights, and privileges. Seek - To position selectively the access mechanism of a direct access [storage] device. Seek Time - The time required for the access arm of a direct-access storage device to be positioned on the appropriate track. Synonym positioning time. Segment - In a distributed queue dual bus (DQDB) network, a protocol data unit (PDU) that (a) consists of 52 octets transferred between DQDB-layer peer entities as the information payload of a slot, (b) contains a header of 4 octets and a payload of 48 octets, and (c) is either a pre-arbitrated segment or a queued arbitrated segment. Segmented Encoding Law - An encoding law in which an approximation to a curve defined by a smooth encoding law is obtained by a number of linear segments. Synonym piecewise linear encoding law. Segregation - In a communications system or network, the protection given to information to conceal it from persons having access to the system or network. Seizing - The temporary dedication of various parts of a communications system to a specific use, usually in response to a user request for service. Note: The parts seized may be automatically connected, such as by direct distance dialing (DDD), or may require operator intervention. Seizure Signal - In telephone systems, a signal used by the calling end of a trunk or line to indicate a request for service. Note: A seizure signal also locks out the trunk or line to other demands for service. 405
- 406. Selcall - Acronym for selective calling. Calling from one station in which call identification is sent to signal automatically one or more remote stations and to establish links among them. Note 1: Selective calling may be used to un-mute the speakers at designated stations or to initiate a handshake for link establishment. Note 2: Selective calling is specified in CCIR Recommendations for HF and VHF/UHF radio, generally for ship- to-shore, ship-to-ship, aircraft-to-aircraft, and aircraft-to-ground communications. Selection Position - Synonym decision instant. In the reception of a digital signal, the instant at which a decision is made by a receiving device as to the probable value of a signal condition. Selective Calling - See selcall. Calling from one station in which call identification is sent to signal automatically one or more remote stations and to establish links among them. Note 1: Selective calling may be used to un-mute the speakers at designated stations or to initiate a handshake for link establishment. Note 2: Selective calling is specified in CCIR Recommendations for HF and VHF/UHF radio, generally for ship- to-shore, ship-to-ship, aircraft-to-aircraft, and aircraft-to-ground communications. Selective Combiner - A diversity combiner in which (a) the signals from each channel are added together, (b) the gain of each channel is made proportional to the rms signal level and inversely proportional to the mean square noise level in that channel, and (c) the same proportionality constant is used for all channels. Synonyms ratio-squared combiner, post-detection combiner, predetection combining, maximal-ratio combiner. Selective Fading - Fading in which the components of the received radio signal fluctuate independently. Selective Jamming - See electronic warfare. Any military action involving the use of electromagnetic and directed energy to control the electromagnetic spectrum or to attack the enemy. The three major subdivisions within electronic warfare are: electronic attack, electronic protection, and electronic warfare support. Selective Ringing - In a party line, ringing only the desired user instrument. Note: Without selective ringing, all the instruments on the party line will ring at the same time, selection being made by the number of rings. Selectivity - A measure of the ability of a receiver to discriminate between a wanted signal on one frequency and unwanted signals on other frequencies. Self-Authentication - 1. A procedure in which a transmitting station, i.e., a calling station, establishes its own validity without the participation of the receiving station, i.e., the called station. Note: The calling station establishes its own authenticity and the called station is not required to challenge the calling station. Self- authentication is usually used only when one-time authentication systems are used to derive the authentication. 2. Implicit authentication, to a predetermined level, of all transmissions on a secure communications system. Self-Delineating Block - A block in which a bit pattern or a flag identifies the beginning or end of a block. Self-Synchronizing Code - A code in which the symbol stream formed by a portion of one code word, or by the overlapped portion of any two adjacent code words, is not a valid code word. Note 1: A self- synchronizing code permits the proper framing of transmitted code words provided that no uncorrected errors occur in the symbol stream. Note 2: External synchronization is not required. Note 3: High-level data link control (HDLC) and Advanced Data Communication Control Procedures (ADCCP) frames represent self- synchronizing code words. 406
- 407. Semiautomated Tactical Command and Control System - A machine-aided command and control system in which human intervention is required in varying degrees to operate the system. Semiautomatic Switching System - 1. In telephone systems, a switching system in which telephone operators receive call instructions orally from users and complete them by automatic equipment. 2. At tape- relay intermediate stations, the manual routing or rerouting of taped messages without rekeying them. Semiconductor Laser - Synonym injection laser diode. A laser that uses a forward-biased semiconductor junction as the active medium. Note: Stimulated emission of coherent light occurs at a p-n junction where electrons and holes are driven into the junction. Synonyms diode laser, laser diode. Semiduplex Operation - 1. A method which is simplex operation at one end of the circuit and duplex operation at the other. Footnote: In general, duplex operation and semiduplex operation require two frequencies in radiocommunication; simplex operation may use either one or two. 2. Operation of a communications network in which a base station operates in a duplex mode with a group of remote stations operating in a half-duplex mode. Note: The terms "half-duplex" and "simplex" are used differently in wire and radio communications. Sender - A device that accepts address information from a register or routing information from a translator, and then transmits the proper routing information to a trunk or to local equipment. Note: Sender and register functions are often combined in a single unit. Sending-End Crossfire - In teletypewriter (TTY) systems, interference, in a given channel, caused by transmissions from one or more adjacent TTY channels transmitting from the end at which the crossfire, i.e., interference, is measured. Sensitive Information - Information, the loss, or misuse, or unauthorized access to or modification of which could adversely affect the national interest or the conduct of federal programs, or the privacy to which individuals are entitled to under 5 U.S.C. Section 552a (the Privacy Act), but that has not been specifically authorized under criteria established by an Executive Order or an Act of Congress to be kept secret in the interest of national defense or foreign policy. Sensitivity - In an electronic device, e.g., a communications system receiver, or detection device, e.g., PIN diode, the minimum input signal required to produce a specified output signal having a specified signal-to- noise ratio, or other specified criteria. Note 1: The signal input may be expressed as power in dBm or as field strength in microvolts per meter, with input network impedance stipulated. Note 2: "Sensitivity" is sometimes improperly used as a synonym for "responsivity." Sensor - A device that responds to a physical stimulus, such as thermal energy, electromagnetic energy, acoustic energy, pressure, magnetism, or motion, by producing a signal, usually electrical. Sentinel - See flag. In data transmission or processing, an indicator, such as a signal, symbol, character, or digit, used for identification. Note: A sentinel may be a byte, word, mark, group mark, or letter that signals the occurrence of some condition or event, such as the end of a word, block, or message. Separate Channel Signaling - Signaling in which the whole or a part of one or more channels in a multichannel system is used to provide for supervisory and control signals for the message traffic channels. Note: The same channels, such as frequency bands or time slots, that are used for signaling are not used for message traffic. Contrast with common-channel signaling. Septet - A byte composed of seven binary elements. Synonym seven-bit byte. 407
- 408. Sequence - An arrangement of items according to a specified set of rules, for example, items arranged alphabetically, numerically, or chronologically. Sequential Access - Synonym serial access. 1. Pertaining to the sequential or consecutive transmission of data into or out of a device, such as a computer, transmission line, or storage device. 2. A process by which data are obtained from a storage device or entered into a storage device in such a way that the process depends on the location of those data and on a reference to data previously accessed. Sequential Logic Element - A device that has at least one output channel and one or more input channels, all characterized by discrete states, such that the state of each output channel is determined by the previous states of the input channels. Sequential Transmission - Synonym serial transmission. The sequential transmission of the signal elements of a group representing a character or other entity of data. Note: The characters are transmitted in a sequence over a single line, rather than simultaneously over two or more lines, as in parallel transmission. The sequential elements may be transmitted with or without interruption. Serial - 1. Pertaining to a process in which all events occur one after the other; for example, the serial transmission of the bits of a character according to the CCITT V.25 protocol. 2. Pertaining to the sequential or consecutive occurrence of two or more related activities in a single device or channel. 3. Pertaining to the sequential processing of the individual parts of a whole, such as the bits of a character or the characters of a word, using the same facilities for successive parts. Serial Access -: 1. Pertaining to the sequential or consecutive transmission of data into or out of a device, such as a computer, transmission line, or storage device. 2. A process by which data are obtained from a storage device or entered into a storage device in such a way that the process depends on the location of those data and on a reference to data previously accessed. Synonym sequential access. Serial Computer - 1. A computer that has a single arithmetic and logic unit. 2. A computer, some specified characteristic of which is serial; for example, a computer than manipulates all bits of a word serially. Serializer - See parallel-to-serial conversion. Conversion of a stream of multiple data elements, received simultaneously, into a stream of data elements transmitted in time sequence, i.e. , one at a time. Serial Line Internet Protocol (SLIP) - See Dialup Service Serial Port - A port through which data are passed serially, i.e. , one bit at a time, and that requires only one input channel to handle a set of bits, e.g., all the bits of a byte. Contrast with parallel port. Serial-to-Parallel Conversion - Conversion of a stream of data elements received in time sequence, i.e., one at a time, into a data stream consisting of multiple data elements transmitted simultaneously. Contrast with parallel-to-serial conversion. Serial Transmission - The sequential transmission of the signal elements of a group representing a character or other entity of data. Note: The characters are transmitted in a sequence over a single line, rather than simultaneously over two or more lines, as in parallel transmission. The sequential elements may be transmitted with or without interruption. Synonym sequential transmission. Series T Junction - A three-port waveguide junction that has an equivalent circuit in which the impedance of the branch waveguide is predominantly in series with the impedance of the main waveguide at the junction. 408
- 409. Server - A network device that provides service to the network users by managing shared resources. Note 1: The term is often used in the context of a client-server architecture for a local area network (LAN). Note 2: Examples are a printer server and a file server. Service - In the Open Systems Interconnection--Reference Model (OSI--RM), a capability of a given layer, and the layers below it, that (a) is provided to the entities of the next higher layer and (b) for a given layer, is provided at the interface between the given layer and the next higher layer. Service Access - In personal communications service (PCS), the ability for the network to provide user access to features and to accept user service requests specifying the type of bearer services or supplementary service that the users want to receive from the PCS network. Service Access Point (SAP) - 1. A physical point at which a circuit may be accessed. 2. In an Open Systems Interconnection (OSI) layer, a point at which a designated service may be obtained. Service Bit - A system overhead bit used for providing a network service, such as a request for a repetition or for a numbering sequence. Note: A service bit is not a check bit. Service Channel - Synonym orderwire circuit. A voice or data circuit used by technical control and maintenance personnel for coordination and control actions relative to activation, deactivation, change, rerouting, reporting, and maintenance of communication systems and services. Synonyms engineering channel, engineering orderwire. Service Class - See class of service. 1. A designation assigned to describe the service treatment and privileges given to a particular terminal. 2. A subgrouping of telephone users for the purpose of rate distinction. Note: Examples of class of service subgrouping include distinguishing between (a) individual and party lines, (b) Government and non-Government lines, (c) those permitted to make unrestricted international dialed calls and those not so permitted, (d) business, residence, and coin-operated, (e) flat rate and message rate, and (f) restricted and extended area service. 3. A category of data transmission provided by a public data network in which the data signaling rate, the terminal operating mode, and the code structure, are standardized. Note: Class of service is defined in CCITT Recommendation X.1. Service Data Unit (SDU) - In layered systems, a set of data that is sent by a user of the services of a given layer, and is transmitted to a peer service user semantically unchanged. Service Feature - In telephony, any of a number of special functions that may be specified initially, or added to, the user's basic service. Note: Modern telephone switches are capable of providing a wide variety of service features, such as call forwarding and call waiting. Service Identification - The information that uniquely identifies an NS/EP telecommunications service to the service vendor and the service user. Service Integrity - The degree to which a service is provided without excessive impairment, once obtained. Service Outage - The state of a service when (a) a network failure impairs or prevents the initiation of new requests for the service, (b) continued use of the service is impaired or not possible, or (c) certain service parameters fall outside prescribed limits. Service Probability - The probability of obtaining a specified (or higher) grade of service during a given period of time. 409
- 410. Service Profile - Synonym UPT service profile. In universal personal telecommunications service, a record that contains all information related to a UPT user, which information is required to provide that user with UPT service such as subscriptions to basic and supplementing services and call-routing preferences. Note: Each UPT service profile is associated with a single UPT number. Service Profile Management - Synonym UPT service profile management. In universal personal telecommunications service, authorized access to and manipulation of the UPT service profile. Note: UPT service profile management can be performed by the UPT user, by the UPT customer (subscriber), or by the UPT service provider. Service Program - Synonym utility program. A computer program that is in general support of the operations and processes of a computer. Note: Examples of utility programs include diagnostic programs, trace programs, input routines, and programs used to perform routine tasks, i.e., perform everyday tasks, such as copying data from one storage location to another. Synonyms service routine, utility routine, utility program. Service Provider - 1. An organization that provides services for content providers and for users of a computer network. Note: The services may include access to the computer network, content hosting, server of a private message handling system, news server, etc. 2. A company, organization, administration, business, etc., that sells, administers, maintains, charges for, etc., the service. The service provider may or may not be the provider of the network. Service Routine - Synonym utility program. A computer program that is in general support of the operations and processes of a computer. Note: Examples of utility programs include diagnostic programs, trace programs, input routines, and programs used to perform routine tasks, i.e., perform everyday tasks, such as copying data from one storage location to another. Synonyms service program, utility routine, utility program. Service Signals - Signals that enable data systems equipment to function correctly, and possibly to provide ancillary facilities. Synonym housekeeping signals. Service Termination Point - The last point of service rendered by a commercial carrier under applicable tariffs. Note 1: The service termination point is usually on the customer premises. Note 2: The customer is responsible for equipment and operation from the service termination point to user end instruments. Note 3: The service termination point usually corresponds to the demarcation point. Service User - An individual or organization, including a service vendor, that is provided a telecommunications service for which a priority level has been requested or assigned. Session Initiation Protocol (SIP) - Communication protocol that operates similarly to H.323 but is less complex and more Internet- and Web-friendly. Fully modular and designed from the ground up for functioning over IP networks, it can be tailored more easily than H.323 for Internet applications. SIP and H.323 can and do coexist. See also MGCP. Session Layer - Layer 5 of the Open Systems Interconnection--Reference Model. . This layer responds to service requests from the Presentation Layer and issues service requests to the Transport Layer. The Session Layer provides the mechanism for managing the dialogue between end-user application processes. It provides for either duplex or half-duplex operation and establishes checkpointing, adjournment, termination, and restart procedures. See Open Systems Interconnection--Reference Model. Set - 1. A finite or infinite number of objects, entities, or concepts, that have a given property or properties in common. 2 . To configure all or part of a device into a specified state. 410
- 411. Set-Top Box - A stand-alone device that receives and decodes programming so that it may be displayed on a television. Set-top boxes may be used to receive broadcast, cable, and satellite programming. Seven-Bit Byte - Synonym septet. A byte composed of seven binary elements. Seven-Hundred (700) Service - A personal telephone service that allows individuals to receive, via a single number, telephone calls in various locations (e.g. , home, office, or car) from call originators using the same common carrier. Sexadecimal - Synonym hexadecimal. 1. Characterized by a selection, choice or condition that has sixteen possible different values or states. 2. Pertaining to a fixed-radix numeration system in which the radix is sixteen. Sextet - A byte composed of six binary elements. Synonym six-bit byte. S-F - Abbreviation for store-and-forward. Pertaining to communications systems in which messages are received at intermediate routing points and recorded i.e., stored, and then transmitted, i.e., forwarded, to the next routing point or to the ultimate recipient. SF - Abbreviation for single-frequency. See single-frequency signaling. In telephony, signaling in which dial pulses or supervisory signals are conveyed by a single voice-frequency tone in each direction. Note 1: An SF signaling unit converts E & M signaling to a format (characterized by the presence or absence of a single voice-frequency tone), which is suitable for transmission over an ac path, e.g. , a carrier system. The SF tone is present in the idle state and absent during the seized state. In the seized state, dial pulses are conveyed by bursts of SF tone, corresponding to the interruptions in dc continuity created by a rotary dial or other dc dialing mechanism. Note 2: The SF tone may occupy a small portion of the user data channel spectrum, e.g., 1600 Hz or 2600 Hz ("in-band" SF signaling), usually with a notch filter at the precise SF frequency, to prevent the user from inadvertently disconnecting a call if user data has a sufficiently strong spectral content at the SF frequency. The SF tone may also be just outside the user voice band, e.g., 3600 Hz. Note 3: The Defense Data Network (DDN) transmits dc signaling pulses or supervisory signals, or both, over carrier channels or cable pairs on a 4-wire basis using a 2600-Hz signal tone. The conversion into tones, or vice versa, is done by SF signal units. SFTS - Abbreviation for standard frequency and time signal. See standard time and frequency signal service. In the United States, standard time and frequency signals, broadcast on very precise carrier frequencies by the U.S. Naval Observatory and the National Institute of Standards and Technology (NIST), formerly the National Bureau of Standards (NBS). Note: The Radio Regulations (RR) define an identical international service as standard frequency and time signal service .SGML - Abbreviation for Standard Generalized Mark-up Language. A file format for storage of text and graphics files. Shadow Loss - 1. The attenuation caused to a radio signal by obstructions in the propagation path. 2. In a reflector antenna, the relative reduction in the effective aperture of the antenna caused by the masking effect of other antenna parts, such as a feed horn or a secondary reflector, which parts obstruct the radiation path. Shannon (Sh) - The unit of information derived from the occurrence of one of two equiprobable, mutually exclusive, and exhaustive events. Note: A bit may, with perfect formatting and source coding, contain 1 Sh of information. However, the information content of a bit is usually be less than 1 Sh. 411
- 412. Shannon's Law - A statement defining the theoretical maximum rate at which error-free digits can be transmitted over a bandwidth-limited channel in the presence of noise, usually expressed in the form C = W log2(1 + S /N ), where C is the channel capacity in bits per second, W is the bandwidth in hertz, and S /N is the signal-to-noise ratio. Note: Error-correction codes can improve the communications performance relative to uncoded transmission, but no practical error correction coding system exists that can closely approach the theoretical performance limit given by Shannon's law. Shaping Network - A network inserted in a circuit for the purpose of improving or modifying the waveform of signals. Sharpness - The informal, subjective evaluation of detail in the clarity or resolution seen in an image. Note: Often sharpness and resolution are assumed to be directly related, because images possessed of greater sharpness are assumed to have greater resolution. An increase in subjective sharpness is usually reported when objects are more clearly delineated from each other and from background having hard, sharply defined edges. A major contribution to subjective sharpness is this high contrast at edge transitions, as is emphasized by both edge enhancement and aperture correction, for example. In many practical systems, increasing the contrast at edge transitions is often accompanied by a reduction in fine detail, and under these conditions sharpness and resolution may describe opposite characteristics. Sheath - Of a communications or power cable, the outer covering or coverings of tough material, often plastic, that is resistant to environmental hazards such as abrasion, liquid intrusion, solar radiation, etc., and is used to protect cable component(s) such as optical fibers or metallic conductors that transport the signal or power. Note: There may be more than one sheath surrounding a given cable. For example, some cable designs use an inner sheath surrounded by metallic armor, over which is an outer sheath. Synonym jacket. Sheath Miles - The actual length of cable in route miles. Shell - In a computer environment, an operating system command interpreter, i.e., a software utility that reads an input specifying an operation, and that may perform, direct, or control the specified operation. Note 1: For example, a shell may permit a user to switch among application programs without terminating any of them. Note 2: A shell may take its input from either a user terminal or from a file. Shell Access - Basic Dialup Access to the Internet offering e-mail and mail forwarding, telnet, FTP and IRC. SHF - Abbreviation for super high frequency. See electromagnetic spectrum. Shield - 1. A housing, screen, sheath, or cover that substantially reduces the coupling of electric, magnetic, or electromagnetic fields into or out of circuits or transmission lines. 2. A protective cover that prevents the accidental contact of objects or persons with parts or components operating at hazardous voltage levels. Shielded Pair - A 2-wire transmission line surrounded by a sheath of conductive material that protects it from the effects of external fields and confines fields produced within the line. Shielded Twisted Pair - A transmission line composed of a twisted 2-wire metallic transmission line surrounded by a sheath of conductive material that protects it from the effects of external fields and confines fields produced within the line. Shielding - See shield. 1. A housing, screen, sheath, or cover that substantially reduces the coupling of electric, magnetic, or electromagnetic fields into or out of circuits or transmission lines. 2. A protective cover that prevents the accidental contact of objects or persons with parts or components operating at hazardous voltage levels. 412
- 413. Shielding Effectiveness - The factor that expresses the attenuation caused by scattering, e.g., of radiant or acoustic energy, during its passage through a medium. Note: The scattering coefficient is usually expressed in units of reciprocal distance. Shift - 1. The movement of some or all of the characters or bits of a word by the same number of character or bit positions in the direction of a specified end of a word. 2. In radar, the ability to move the origin of a radial display away from the center of the cathode ray tube. Shift Register - A storage device, usually in a central processing unit (CPU), in which device a serially ordered set of data may be moved, as a unit, into a discrete number of storage locations. Note 1: Shift registers may be configured so that the stored data may be moved in more than one direction. Note 2: Shift registers may be configured so that data may be entered and stored from multiple inputs. Note 3: Shift registers may be grouped into arrays of two or more dimensions in order to perform more complex data operations. Ship Earth Station - A mobile Earth station in the maritime mobile-satellite service located on board ship. Ship's Emergency Transmitter - A ship's transmitter to be used exclusively on a distress frequency for distress, urgency or safety purposes. Ship Station - A mobile station in the maritime mobile service located on board a vessel which is not permanently moored, other than a survival craft station. Shock Excitation - Synonym impulse excitation. The production of oscillation in a circuit or device by impressing a stimulus (signal) for a period that is extremely short compared to the duration of the oscillation that it produces. Short Haul Toll Traffic - A general term applied to message toll traffic between nearby points. In common usage, this term is ordinarily applied to message toll traffic between points less than 20 to 50 miles apart. Shortwave - In radio communications, pertaining to the band of frequencies approximately between 3 MHz and 30 MHz. Note: "Shortwave" is not a term officially recognized by the international community. Short Wavelength - In optical communication, optical radiation having a wavelength less than approximately 1 m. Shot Noise - The noise caused by random fluctuations in the motion of charge carriers in a conductor. Note: There is often a minor inconsistency in referring to shot noise in an optical system: many authors refer to 2 shot noise loosely when speaking of the mean square shot noise current (amperes ) rather than noise power (watts). SI - Abbreviation for International System of Units. International System of Units (SI) SI - International System of Units (SI): The modern form of the metric system, which has been adopted by the United States and most other nations. Note: The SI is constructed from seven base units for independent physical quantities. Tables showing these values are included below and are current as of Fall 1995. SI Prefixes. The common metric prefixes are; Multiplacation Factor Prefix Name Prefix Symbol 413
- 414. 12 1 000 000 000 000 = 10 tera T 9 1 000 000 000 = 10 giga G 6 1 000 000 = 10 mega M 3 1 000 = 10 kilo k 2 100 = 10 hecto h 1 10 = 10 deka da -1 0.1 = 10 deci d -2 0.01 = 10 centi c -3 0.001 = 10 milli m -6 0.000 001 = 10 micro -9 0.000 000 001 = 10 nano n -12 0.000 000 000 001 = 10 pico p SI Base Units Quantity Unit Name Unit Symbol length meter m mass kilogram kg time second s electric current ampere A thermodynamic temperature kelvin K amount of substance mole mol luminous intensity candela cd SI derived units. Derived units are formed by combining base units and other derived units according to the algebraic relations linking the corresponding quantities. The symbols for derived units are obtained by means of the mathematical signs for multiplication, division, and use of exponents. For example, the SI unit for -1 velocity is the meter per second (m/s or m•s ), and that for angular velocity is the radian per second (rad/s -1 or rad•s ). Some derived SI units have been given special names and symbols, as listed in this table. Expression in Terms of Quantity Unit Name Unit Symbol Other SI Units Absorbed dose, specific energy imparted, gray Gy J/kg kerma, absorbed dose index Activity (of a radionuclide) becquerel Bq 1/s Celsius temperature degree Celsius C K Dose equivalent sievert Sv J/kg Electric capacitance farad F C/V Electric charge, quantity of electricity coulomb C A•s Electric conductance siemens S A/V Electric inductance henry H Wb/A Electric potential, potential difference, volt V W/A 414
- 415. electromotive force Electric resistance ohm V/A Energy, work, quantity of heat joule J N•m 2 Force newton N kg•m/s Frequency (of a periodic phenomenon) hertz Hz 1/s 2 Illuminance lux lx lm/m Luminous flux lumen lm cd•sr Magnetic flux weber Wb V•s 2 Magnetic flux density tesla T Wb/m Plane angle radian rad m/m Power, radiant flux watt W J/s 2 Pressure, stress pascal Pa N/m 2 2 Solid angle steradian sr m /m This HTML version of FS-1037C was last generated on Fri Aug 23 00:22:38 MDT 1996 Sideband - In amplitude modulation (AM), a band of frequencies higher than or lower than the carrier frequency, containing energy as a result of the modulation process. Note: Amplitude modulation results in two sidebands. The frequencies above the carrier frequency constitute what is referred to as the "upper sideband"; those below the carrier frequency, constitute the "lower sideband." In conventional AM transmission, both sidebands are present. Transmission in which one sideband is removed is called " single- sideband transmission." Sideband Transmission - See single-sideband transmission. Signal - 1. Detectable transmitted energy that can be used to carry information. 2. A time-dependent variation of a characteristic of a physical phenomenon, used to convey information. 3. As applied to electronics, any transmitted electrical impulse. 4. Operationally, a type of message, the text of which consists of one or more letters, words, characters, signal flags, visual displays, or special sounds, with prearranged meaning and which is conveyed or transmitted by visual, acoustical, or electrical means. Signal Booster - A device that receives an incoming broadcast signal, amplifies it, and retransmits it on the same frequency. Such devices are used to improve communications in locations within the normal coverage area of a broadcast system where the signal is blocked or shielded due to natural terrain or man-made obstacles. Signal Compression - 1. In analog (usually audio) systems, reduction of the dynamic range of a signal by controlling it as a function of the inverse relationship of its instantaneous value relative to a specified reference level. Note 1: Signal compression is usually expressed in dB. Note 2: Instantaneous values of the input signal that are low, relative to the reference level, are increased, and those that are high are decreased. Note 3: Signal compression is usually accomplished by separate devices called "compressors." It is used for many purposes, such as (a) improving signal-to-noise ratios prior to digitizing an analog signal for transmission over a digital carrier system, (b) preventing overload of succeeding elements of a system, or (c) matching the dynamic ranges of two devices. Note 4: Signal compression (in dB) may be a linear or nonlinear function of the signal level across the frequency band of interest and may be essentially instantaneous or have fixed or variable delay times. Note 5: Signal compression always introduces distortion, which is usually 415
- 416. not objectionable, if the compression is limited to a few dB. Note 6: The original dynamic range of a compressed signal may be restored by a circuit called an " expander." 2. In facsimile systems, a process in which the number of pels scanned on the original is larger than the number of encoded bits of picture information transmitted. Signaling - 1. The use of signals for controlling communications. 2. In a telecommunications network, the information exchange concerning the establishment and control of a connection and the management of the network, in contrast to user information transfer. 3. The sending of a signal from the transmitting end of a circuit to inform a user at the receiving end that a message is to be sent. Signaling Message - 1. An assembly of signaling information pertaining to a call that includes, but is not limited to, management transactions, that is transferred (between signaling points) as an entity. 2. An assembly of signaling information that pertains to a call management transaction, and the like and that is transferred as an entity. Signals Intelligence (SIGINT) - 1. A category of intelligence comprising, either individually or in combination, all communications intelligence, electronics intelligence, and foreign instrumentation signals intelligence, however transmitted. [JP 1-02] 2. Intelligence derived from communications, electronics, and foreign instrumentation signals. SIGINT - Acronym for signals intelligence. 1. A category of intelligence comprising, either individually or in combination, all communications intelligence, electronics intelligence, and foreign instrumentation signals intelligence, however transmitted. 2. Intelligence derived from communications, electronics, and foreign instrumentation signals. Signal - 1. Detectable transmitted energy that can be used to carry information. 2. A time-dependent variation of a characteristic of a physical phenomenon, used to convey information. 3. As applied to electronics, any transmitted electrical impulse. 4. Operationally, a type of message, the text of which consists of one or more letters, words, characters, signal flags, visual displays, or special sounds, with prearranged meaning and which is conveyed or transmitted by visual, acoustical, or electrical means. Signal Center - A combination of signal communication facilities operated by the Army in the field and consisting of a communications center, telephone switching central and appropriate means of signal communications. Signal Compression - 1. In analog (usually audio) systems, reduction of the dynamic range of a signal by controlling it as a function of the inverse relationship of its instantaneous value relative to a specified reference level. Note 1: Signal compression is usually expressed in dB. Note 2: Instantaneous values of the input signal that are low, relative to the reference level, are increased, and those that are high are decreased. Note 3: Signal compression is usually accomplished by separate devices called "compressors." It is used for many purposes, such as (a) improving signal-to-noise ratios prior to digitizing an analog signal for transmission over a digital carrier system, (b) preventing overload of succeeding elements of a system, or (c) matching the dynamic ranges of two devices. Note 4: Signal compression (in dB) may be a linear or nonlinear function of the signal level across the frequency band of interest and may be essentially instantaneous or have fixed or variable delay times. Note 5: Signal compression always introduces distortion, which is usually not objectionable, if the compression is limited to a few dB. Note 6: The original dynamic range of a compressed signal may be restored by a circuit called an "expander." 2. In facsimile systems, a process in which the number of pels scanned on the original is larger than the number of encoded bits of picture information transmitted. Signal Contrast - In facsimile, the ratio of the level of the white signal to the level of the black signal. Note: Signal contrast is usually expressed in dB. 416
- 417. Signal Conversion Equipment - Synonym modem. 1. In general, a device that both modulates and demodulates signals. 2. In computer communications, a device used for converting digital, signals into, and recovering them from, quasi-analog signals suitable for transmission over analog communications channels. Note: Many additional functions may be added to a modem to provide for customer service and control features. Synonym signal conversion equipment. 3. In FDM carrier systems, a device that converts the voice band to, and recovers it from, the first level of frequency translation. Signal Distance - 1. A measure of the difference between a given signal and a reference signal. Note: For analog signals, the signal distance is the root mean square difference between the given signal and a reference signal over a symbol period. 2. Synonym Hamming distance. The number of digit positions in which the corresponding digits of two binary words of the same length are different. Note 1: The Hamming distance between 1011101 and 1001001 is two. Note 2: The concept can be extended to other notation systems. For example, the Hamming distance between 2143896 and 2233796 is three, and between "toned" and "roses" it is also three. Signal Distortion - See distortion. 1. In a system or device, any departure of the output signal waveform from that which should result from the input signal waveform's being operated on by the system's specified, i.e. , ideal, transfer function. Note: Distortion may result from many mechanisms. Examples include nonlinearities in the transfer function of an active device, such as a vacuum tube, transistor, or operational amplifier. Distortion may also be caused by a passive component such as a coaxial cable or optical fiber, or by inhomogeneities, reflections, etc., in the propagation path. 2. In start-stop teletypewriter signaling, the shifting of the significant instants of the signal pulses from their proper positions relative to the beginning of the start pulse. Note: The magnitude of the distortion is expressed in percent of an ideal unit pulse length. Signal Droop - In an otherwise essentially flat-topped rectangular pulse, distortion characterized by a decline of the pulse top. See illustration under waveform. Signal Element - A part of a signal, distinguished by its nature, magnitude, duration, transition, or relative position. Note: Examples of signal elements include signal transitions, significant conditions, significant instants, and binary digits (bits). Signal Expansion - Restoration of the dynamic range of a compressed signal. Contrast with signal compression. Signal Frequency Shift - 1. Any change in frequency. 2. Any change in the frequency of a radio transmitter or oscillator. Note: In the radio regime, frequency shift is also called rf shift. 3. See frequency-shift telegraphy. 4. In facsimile, a frequency modulation system where one frequency represents picture black and another frequency represents picture white. Frequencies between these two limits may represent shades of gray. 5. An intentional frequency change used for modulation purposes. Signaling - 1. The use of signals for controlling communications. 2. In a telecommunications network, the information exchange concerning the establishment and control of a connection and the management of the network, in contrast to user information transfer. 3. The sending of a signal from the transmitting end of a circuit to inform a user at the receiving end that a message is to be sent. Signaling Channel - A data channel in combination with its associated signaling terminal equipment. Signaling Connection Control Part (SCCP) - 1. A component part of SS7 protocol that provides additional functions to the message transfer part (MTP) to provide for Connectionless and Connection Oriented network services to transfer signaling information between exchanges and specialized centers in telecommunication networks. The combination of the MTP and the SCCP is called Network Service part. 2. 417
- 418. The part of SS7 that provides additional functions to the MTP to cater to both connectionless as well as connection-oriented network services and to achieve an OSI-compatible network service. Signaling Data Link - A combination of two data channels operating together in a single signaling system. Signaling Link - A transmission facility that consists of a signaling data link and its transfer control functions, used for reliable transfer of a signaling message. Signaling Message - 1. An assembly of signaling information pertaining to a call that includes, but is not limited to, management transactions, that is transferred (between signaling points) as an entity. [T1.226- 1992] 2. An assembly of signaling information that pertains to a call management transaction, and the like and that is transferred as an entity. Signaling Path - In a transmission system, a path used for system control, synchronization, checking, signaling, and service signals used in system management and operations rather than for the data, messages, or calls of the users. Signaling Rate - The aggregate rate at which data pass a point in the transmission path of a data transmission system. Note 1: The DSR is usually expressed in bits per second. Note 3: For serial transmission in a single channel, the DSR reduces to (1/T )log2n ; with a two-condition modulation, i.e. , n =2, the DSR is 1/T . Note 4: For parallel transmission with equal unit intervals and equal numbers of significant conditions on each channel, the DSR is (m /T )log2 n ; in the case of a two-condition modulation, this reduces to m /T . Note 5: The DSR may be expressed in bauds, in which case, the factor log2ni in the above summation formula should be deleted when calculating bauds. Note 6: In synchronous binary signaling, the DSR in bits per second may be numerically the same as the modulation rate expressed in bauds. Signal processors, such as four-phase modems, cannot change the DSR, but the modulation rate depends on the line modulation scheme, in accordance with Note 4. For example, in a 2400 b/s 4-phase sending modem, the signaling rate is 2400 b/s on the serial input side, but the modulation rate is only 1200 bauds on the 4-phase output side. Signaling System No. 7 (SS7) - A common-channel signaling system defined by the CCITT in the 1988 Blue Book, in Recommendations Q.771 through Q.774. Note: SS7 is a prerequisite for implementation of an Integrated Services Digital Network (ISDN). Signaling Time Slot - In TDM carrier systems, a time slot starting at a particular phase or instant in each frame and allocated to the transmission of signaling (supervisory and control) data. Signal Intelligence - 1. A category of intelligence comprising, either individually or in combination, all communications intelligence, electronics intelligence, and foreign instrumentation signals intelligence, however transmitted. 2. Intelligence derived from communications, electronics, and foreign instrumentation signals. Signal Level - In a communications system, the signal power or intensity at a specified point and with respect to a specified reference level, e.g., 1 mW. Signal Message - In communications systems, a message, i.e., an assembly of signaling information, that (a) includes associated message alignment and service indications, (b) pertains to a call, and (c) is transferred via the message transfer part. Signal-Plus-Noise-Plus-Distortion to Noise-Plus-Distortion Ratio - See SINAD. - 1. The ratio of (a) total received power, i.e., the received signal-plus-noise-plus-distortion power to (b) the received noise-plus- distortion power. 2. The ratio of (a) the recovered audio power, i.e., the original modulating audio signal plus 418
- 419. noise plus distortion powers from a modulated radio frequency carrier to (b) the residual audio power, i.e., noise-plus-distortion powers remaining after the original modulating audio signal is removed. Note: The SINAD is usually expressed in dB. Signal-Plus-Noise-to-Noise Ratio ((S +N )/N ) - At a given point in a communications system, the ratio of (a) the power of the desired signal plus the noise to (b) the power of the noise. Note: The (S +N )/N ratio is usually expressed in dB. Signal Processing - The processing--such as detection, shaping, converting, coding, and time positioning--of signals, that results in their transformation into other forms, such as other waveshapes, power levels, and coding arrangements. Signal Processing Gain - 1. The ratio of (a) the signal-to-noise ratio of a processed signal to (b) the signal-to- noise ratio of the unprocessed signal. Note: Signal processing gain is usually expressed in dB. 2. In a spread- spectrum communications system, the signal gain, signal-to-noise ratio, signal shape, or other signal improvement obtained by coherent band spreading, remapping, and reconstitution of the desired signal. Signal Reference Subsystem - The portion of a facility grounding system that (a) provides reference planes, such as ground-return circuits, for all of the signal paths in the facility and (b) is isolated from other circuits, especially isolated from circuits that carry fault, lightning discharge, and power distribution currents. Signal Regeneration - Signal processing that restores a signal so that it conforms to its original characteristics. Signal-Return Circuit - A current-carrying return path from a load back to the signal source, i.e., the low side of the closed loop energy transfer circuit between a source-load pair. Signal Sampling - The process of obtaining a sequence of instantaneous values of a particular signal characteristic, usually at regular time intervals. Signal Transition - 1. In the modulation of a carrier, a change from one significant condition to another. Note 1: Examples of signal transitions are a change from one electrical current, voltage, or power level to another; a change from one optical power level to another; a phase shift; or a change from one frequency or wavelength to another. Note 2: Signal transitions are used to create signals that represent information, such as "0" and "1" or "mark" and "space." 2. For channel-associated signaling, a change in state of the A bit for 2- state signaling, A and/or B bit in 4-state signaling, or the A, B, C, and/or D bit for 16-state signaling. Significant Condition - In the modulation of a carrier, one of the values of the signal parameter chosen to represent information. Note 1: Examples of significant conditions are an electrical current, voltage, or power level; an optical power level; a phase value; or a frequency or wavelength chosen to represent a "0" or a "1"; or a "mark" or a "space." Note 2: The duration of a significant condition is the time interval between successive significant instants. Note 3: A change from one significant condition to another is called a " signal transition." Note 4: Signal transitions are used to create signals that represent information, such as "0" and "1" or "mark" and "space." Note 5: Significant conditions are recognized by an appropriate device. Each significant instant is determined when the appropriate device assumes a condition or state usable for performing a specific function, such as recording, processing, or gating. Significant Instant - In a signal, any instant at which a significant condition of a signal begins or ends. Note: Examples of significant instants include the instant at which a signal crosses the baseline or reaches 10% or 90% of its maximum value. 419
- 420. Silent Interval - Any portion of a ringing cycle during which the ringing signal is not being applied. Silent Transfer Destination-After activating either Silent Transfer feature, you will want to tell The Stick where to route the call. The "Destination" program feature gives you the option of routing all after-hours calls to either the fax or modem. Factory preset is to the port labeled "FAX". Silica - Silicon dioxide (SiO2). Note 1: Silica may occur in crystalline or amorphous form, and occurs naturally in impure forms such as quartz and sand. Note 2: Silica is the basic material of which the most common communication-grade optical fibers are presently made. Silicon Dioxide (SiO2): See silica. Simulate - To represent certain features of the behavior of a physical or abstract system by the behavior of another system. Note 1: For example, delay lines may be used to simulate propagation delay and phase shift caused by an actual transmission line. Note 2: A simulator may imitate only a few of the operations and functions of the unit it simulates. SINAD - Abbreviation for signal-plus-noise-plus-distortion to noise-plus-distortion ratio. 1. The ratio of (a) total received power, i.e., the received signal-plus-noise-plus-distortion power to (b) the received noise-plus- distortion power. 2. The ratio of (a) the recovered audio power, i.e., the original modulating audio signal plus noise plus distortion powers from a modulated radio frequency carrier to (b) the residual audio power, i.e., noise-plus-distortion powers remaining after the original modulating audio signal is removed. Note: The SINAD is usually expressed in dB. Single Bill Fee - Many long distance companies are now adding a fee to the phone bills of customers who are billed for long distance service through their local phone companies. TDS Long Distance does not charge this fee. Single-Mode Fiber - Synonym single-mode optical fiber. Single-Mode Optical Fiber - An optical fiber in which only the lowest order bound mode can propagate at the wavelength of interest. Note 1: The lowest order bound mode is ascertained for the wavelength of interest by solving Maxwell's equations for the boundary conditions imposed by the fiber, e.g., core (spot) size and the refractive indices of the core and cladding. Note 2: The solution of Maxwell's equations for the lowest order bound mode will permit a pair of orthogonally polarized fields in the fiber, and this is the usual case in a communication fiber. Note 3: In step-index guides, single-mode operation occurs when the normalized frequency, V, is less than 2.405. Synonyms monomode optical fiber, single-mode fiber, single- mode optical waveguide, unimode fiber. Single-Mode Optical Waveguide - Synonym single-mode optical fiber. Single-Phase Voltage and Frequency - Europe and most other countries in the world use a voltage which is twice that of the US. It is between 220 and 240 volts, whereas in Japan and in most of the Americas the voltage is between 100 and 127 volts. The system of three-phase alternating current electrical generation and distribution was invented by a nineteenth century creative genius named Nicola Tesla. He made many careful calculations and measurements and found out that 60 Hz (Hertz, cycles per second) was the best frequency for alternating current (AC) power generating. He preferred 240 volts, which put him at odds with Thomas Edison, whose direct current (DC) systems were 110 volts. Perhaps Edison had a useful point in the safety factor of the lower voltage, but DC couldn't provide the power to a distance that AC could. 420
- 421. When the German company AEG built the first European generating facility, its engineers decided to fix the frequency at 50 Hz, because the number 60 didn't fit the metric standard unit sequence (1,2,5). At that time, AEG had a virtual monopoly and their standard spread to the rest of the continent. In Britain, differing frequencies proliferated, and only after World War II the 50-cycle standard was established. A big mistake, however. Not only is 50 Hz 20% less effective in generation, it is 10-15% less efficient in transmission, it requires up to 30% larger windings and magnetic core materials in transformer construction. Electric motors are much less efficient at the lower frequency, and must also be made more robust to handle the electrical losses and the extra heat generated. Today, only a handful of countries (Antigua, Guyana, Peru, the Philippines, South Korea and the Leeward Islands) follow Tesla’s advice and use the 60 Hz frequency together with a voltage of 220- 240 V. Originally Europe was 110 V too, just like Japan and the US today. It has been deemed necessary to increase voltage to get more power with less losses and voltage drop from the same copper wire diameter. At the time the US also wanted to change but because of the cost involved to replace all electric appliances, they decided not to. At the time (50s-60s) the average US household already had a fridge, a washing-machine, etc., but not in Europe. The end result is that now, the US seems not to have evolved from the 50s and 60s, and still copes with problems as light bulbs that burn out rather quickly when they are close to the transformer (too high a voltage), or just the other way round: not enough voltage at the end of the line (105 to 127 volt spread !). Note that currently all new American buildings get in fact 220 volts split in two 110 between neutral and hot wire. Major appliances, such as virtually all drying machines and ovens, are now connected to 220 volts. Americans who have European equipment, can connect it to these outlets. There are 214 countries listed below. 175 of the countries mentioned use 220-240 volts (50 or 60 Hz). The 39 other countries use 100-127 volts. 421
- 422. COUNTRY SINGLE-PHASE VOLTAGE FREQUENCY Afghanistan 220 V 50 Hz Albania 230 V 50 Hz Algeria 230 V 50 Hz American Samoa 120 V 60 Hz Andorra 230 V 50 Hz Angola 220 V 50 Hz Anguilla 110 V 60 Hz Antigua 230 V 60 Hz Argentina 220 V 50 Hz Armenia 230 V 50 Hz Aruba 127 V 60 Hz Australia 240 V 50 Hz Austria 230 V 50 Hz Azerbaijan 220 V 50 Hz Azores 230 V 50 Hz Bahamas 120 V 60 Hz Bahrain 230 V 50 Hz Balearic Islands 230 V 50 Hz Bangladesh 220 V 50 Hz Barbados 115 V 50 Hz Belarus 230 V 50 Hz Belgium 230 V 50 Hz Belize 110 V / 220 V 60 Hz Benin 220 V 50 Hz Bermuda 120 V 60 Hz Bhutan 230 V 50 Hz Bolivia 230 V 50 Hz Bosnia & Herzegovina 230 V 50 Hz Botswana 230 V 50 Hz Brazil 127 V / 220 V* 60 Hz Brunei 240 V 50 Hz Bulgaria 230 V 50 Hz Burkina Faso 220 V 50 Hz Burundi 220 V 50 Hz Cambodia 230 V 50 Hz Cameroon 220 V 50 Hz Canada 120 V 60 Hz Canary Islands 230 V 50 Hz Cape Verde 230 V 50 Hz Cayman Islands 120 V 60 Hz Central African Republic 220 V 50 Hz 422
- 423. Chad 220 V 50 Hz Channel Islands (Guernsey & Jersey) 230 V 50 Hz Chile 220 V 50 Hz China, People's Republic of 220 V 50 Hz Colombia 110 V 60 Hz Comoros 220 V 50 Hz Congo, People's Rep. of 230 V 50 Hz Congo, Dem. Rep. of (formerly Zaire) 220 V 50 Hz Cook Islands 240 V 50 Hz Costa Rica 120 V 60 Hz Côte d'Ivoire 220 V 50 Hz (Ivory Coast) Croatia 230 V 50 Hz Cuba 110 V / 220 V 60 Hz Cyprus 230 V 50 Hz Czech Republic 230 V 50 Hz Denmark 230 V 50 Hz Djibouti 220 V 50 Hz Dominica 230 V 50 Hz Dominican Republic 110 V 60 Hz East Timor 220 V 50 Hz Ecuador 110 V 60 Hz Egypt 220 V 50 Hz El Salvador 115 V 60 Hz Equatorial Guinea 220 V 50 Hz Eritrea 230 V 50 Hz Estonia 230 V 50 Hz Ethiopia 220 V 50 Hz Faeroe Islands 230 V 50 Hz Falkland Islands 240 V 50 Hz Fiji 240 V 50 Hz Finland 230 V 50 Hz France 230 V 50 Hz French Guyana 220 V 50 Hz Gabon 220 V 50 Hz Gambia 230 V 50 Hz Gaza 230 V 50 Hz Georgia 220 V 50 Hz Germany 230 V 50 Hz Ghana 230 V 50 Hz Gibraltar 230 V 50 Hz Greece 230 V 50 Hz Greenland 230 V 50 Hz 423
- 424. Grenada (Windward Islands) 230 V 50 Hz Guadeloupe 230 V 50 Hz Guam 110 V 60 Hz Guatemala 120 V 60 Hz Guinea 220 V 50 Hz Guinea-Bissau 220 V 50 Hz Guyana 240 V 60 Hz Haiti 110 V 60 Hz Honduras 110 V 60 Hz Hong Kong 220 V 50 Hz Hungary 230 V 50 Hz Iceland 230 V 50 Hz India 240 V 50 Hz Indonesia 230 V 50 Hz Iran 230 V 50 Hz Iraq 230 V 50 Hz Ireland (Eire) 230 V 50 Hz Isle of Man 230 V 50 Hz Israel 230 V 50 Hz Italy 230 V 50 Hz Jamaica 110 V 50 Hz Japan 100 V 50 Hz / 60 Hz** Jordan 230 V 50 Hz Kenya 240 V 50 Hz Kazakhstan 220 V 50 Hz Kiribati 240 V 50 Hz Korea, South 220 V 60 Hz Kuwait 240 V 50 Hz Kyrgyzstan 220 V 50 Hz Laos 230 V 50 Hz Latvia 230 V 50 Hz Lebanon 230 V 50 Hz Lesotho 220 V 50 Hz Liberia 120 V 60 Hz Libya 127 V / 230 V 50 Hz Liechtenstein 230 V 50 Hz Lithuania 230 V 50 Hz Luxembourg 230 V 50 Hz Macau 220 V 50 Hz Macedonia 230 V 50 Hz Madagascar 127 V / 220 V 50 Hz Madeira 230 V 50 Hz 424
- 425. Malawi 230 V 50 Hz Malaysia 240 V 50 Hz Maldives 230 V 50 Hz Mali 220 V 50 Hz Malta 230 V 50 Hz Martinique 220 V 50 Hz Mauritania 220 V 50 Hz Mauritius 230 V 50 Hz Mexico 127 V 60 Hz Micronesia, Federal States of 120 V 60 Hz Moldova 230 V 50 Hz Monaco 230 V 50 Hz Mongolia 230 V 50 Hz Montserrat (Leeward Islands) 230 V 60 Hz Morocco 220 V 50 Hz Mozambique 220 V 50 Hz Myanmar (formerly Burma) 230 V 50 Hz Namibia 220 V 50 Hz Nauru 240 V 50 Hz Nepal 230 V 50 Hz Netherlands 230 V 50 Hz Netherlands Antilles 127 V / 220 V 50 Hz New Caledonia 220 V 50 Hz New Zealand 230 V 50 Hz Nicaragua 120 V 60 Hz Niger 220 V 50 Hz Nigeria 230 V 50 Hz Norway 230 V 50 Hz Oman 240 V 50 Hz Pakistan 230 V 50 Hz Palau 120 V 60 Hz Panama 110 V 60 Hz Papua New Guinea 240 V 50 Hz Paraguay 220 V 50 Hz Peru 220 V 60 Hz Philippines 220 V 60 Hz Poland 230 V 50 Hz Portugal 230 V 50 Hz Puerto Rico 120 V 60 Hz Qatar 240 V 50 Hz Réunion Island 230 V 50 Hz Romania 230 V 50 Hz 425
- 426. Russian Federation 230 V 50 Hz Rwanda 230 V 50 Hz St. Kitts and Nevis (Leeward Islands) 230 V 60 Hz St. Lucia (Windward Islands) 230 V 50 Hz St. Vincent (Windward Islands) 230 V 50 Hz San Marino 230 V 50 Hz Saudi Arabia 110 V / 220 V*** 60 Hz*** Senegal 230 V 50 Hz Serbia & Montenegro 230 V 50 Hz Seychelles 240 V 50 Hz Sierra Leone 230 V 50 Hz Singapore 230 V 50 Hz Slovakia 230 V 50 Hz Slovenia 230 V 50 Hz Somalia 220 V 50 Hz South Africa 230 V 50 Hz Spain 230 V 50 Hz Sri Lanka 230 V 50 Hz Sudan 230 V 50 Hz Suriname 127 V 60 Hz Swaziland 230 V 50 Hz Sweden 230 V 50 Hz Switzerland 230 V 50 Hz Syria 220 V 50 Hz Tahiti 110 V / 220 V 60 Hz Tajikistan 220 V 50 Hz Taiwan 110 V 60 Hz Tanzania 230 V 50 Hz Thailand 220 V 50 Hz Togo 220 V 50 Hz Tonga 240 V 50 Hz Trinidad & Tobago 115 V 60 Hz Tunisia 230 V 50 Hz Turkey 230 V 50 Hz Turkmenistan 220 V 50 Hz Uganda 240 V 50 Hz Ukraine 230 V 50 Hz United Arab Emirates 220 V 50 Hz United Kingdom 230 V 50 Hz United States of America 110 V 60 Hz Uruguay 220 V 50 Hz Uzbekistan 220 V 50 Hz 426
- 427. Venezuela 120 V 60 Hz Vietnam 220 V 50 Hz Virgin Islands 110 V 60 Hz Western Samoa 230 V 50 Hz Yemen, Rep. of 230 V 50 Hz Zambia 230 V 50 Hz Zimbabwe 220 V 50 Hz * In Brazil there is no standard voltage. Most states use 127 V electricity (Acre, Amapá, Amazonas, Espírito Santo, Mato Grosso do Sul, Maranhão, Pará, Paraná, Rondônia, Roraima, Sergipe and Minas Gerais). Other – mainly northeastern – states are on 220 V (Alagoas, Brasília, Ceará, Mato Grosso, Goiás, Paraíba, Rio Grande do Norte, Santa Catarina and Tocantins). Although in most parts of the states of Bahia, São Paulo, Rio de Janeiro and Rio Grande do Sul 127 V is used, the cities of Jequié, Jundiaí, São Bernardo do Campo, Novo Friburgo, Bagé, Caxias do Sul and Pelotas run on 220 V. The states of Pernambuco and Piauí use 220 V, except for the cities of Paulista and Teresina (127 V). ** Although the mains voltage in Japan is the same everywhere, the frequency differs from region to region. Eastern Japan uses predominantly 50 Hz (Tokyo, Kawasaki, Sapporo, Yokohoma, Sendai), whereas Western Japan prefers 60 Hz (Osaka, Kyoto, Nagoya, Hiroshima). *** Saudi Arabia uses 110 V in many parts of the country, such as the Dammam and al-Khobar area (situated in the eastern province of Ash Sharqiyah). 220 V can be commonly found as well, especially in hotels. Single-Sideband (SSB) Transmission - Sideband transmission in which only one sideband is transmitted. Note: The carrier may be suppressed. Sink - 1. An absorber of energy. 2. In communications, a device that receives information, control, or other signals from a source. 3. A location at which a specified multiplex structure is terminated through connected equipment removing the frame alignment signal and disassembling the channel time slots. Simple Mail Transfer Protocol (SMTP) - A method of transferring e-mails between computers on a network. SIP (Session Initiation Protocol): Communication protocol that operates similarly to H.323 but is less complex and more Internet- and Web-friendly. Fully modular and designed from the ground up for functioning over IP networks, it can be tailored more easily than H.323 for Internet applications. SIP and H.323 can and do coexist. See also MGCP. Site - 1. The totality of all of the Internet facilities—http, ftp, etc. —offered by an individual or an organization. 2. A Web location where Web pages are found. Synonym (in this sense) Web site. Note: A Web site describes only those resources available through the World Wide Web. Skew Ray - In a multimode optical fiber, a bound ray that travels in a helical path along the fiber and thus (a) is not parallel to the fiber axis, (b) does not lie in a meridional plane, and (c) does not intersect the fiber axis. Slamming - When a telephone customer’s long distance service has been switched from one long distance company to another without the customer’s permission. This is illegal. SLC - Subscriber Line Charge. A monthly fee paid by telephone customers. The money is used to compensate the local telephone company for part of the cost of maintenance and installation of the telephone wire, poles, and other facilities that link a customer’s home to the telephone network. 427
- 428. Slewing - 1. Rotating a directional antenna or transducer rapidly about one or more axes. 2. Changing the frequency or pulse repetition rate of a signal source. 3. Changing the tuning of a receiver, usually by sweeping through many or all frequencies. 4. Redirecting the beam of a fixed antenna array by changing the relative phases of the signals feeding the antenna elements. SLIP - See Serial Line Internet Protocol or Dialup Access SLiPPP (Serial Line Internet Point to Point Protocol) - A popular Dialup Access service that comes with a Shell Account, a dedicated IP address, a unique Domain Address and high-speed 28.8 modems. Slit Source - 1. In spectroscopy, an optical source that emits one or more spectrally narrow lines as opposed to a continuous spectrum. 2. In the geometric sense, an optical source having an emitting area in the form of a spatially narrow line, e.g., a slit. Synonym line source. Smart Bot - Abbreviation for smart robot. See bot. Smart Robot - See bot. SMDS - See Switched Multimegabit Data Service SMTP - See Simple Mail Transfer Protocol Snell's Law - A law of geometric optics that defines the amount of bending that takes place when a light ray strikes a refractive boundary, e.g., an air-glass interface, at a non-normal angle. If a ray travels from a medium of lower refractive index into a medium of higher refractive index, it is bent toward the normal; if it travels from a medium of higher refractive index to a medium of lower index, it is bent away from the normal. If the incident ray travels in a medium of higher refractive index toward a medium of lower refractive index at such an angle that Snell's law would call for the sine of the refracted ray to be greater than unity (a mathematical impossibility); This reflection occurs even in the absence of a metallic reflective coating (e.g., aluminum or silver). This phenomenon is called " total internal reflection." The smallest angle of incidence, with respect to the normal at the refractive boundary, which angle will support total internal reflection, is called the " critical angle." Softphone - A software app that gives you the ability to make and receive calls over the Internet using your PC and a headset or a microphone and speakers. A softphone's interface can look like a traditional phone dial pad or more like an IM client. Software - 1. A set of computer programs, procedures, and associated documentation concerned with the operation of a data processing system; e.g., compilers, library routines, manuals, and circuit diagrams. 2. Information (generally copyrightable) that may provide instructions for computers; data for documentation; and voice, video, and music for entertainment or education. Solid State - 1. (electronics). Pertaining to circuits where signals pass through solid semiconductor material such as transistors and diodes as opposed to vacuum tubes where signals pass through a vacuum. The term was introduced to describe the transition from valve-based amplifiers to transistorised amplifiers. Solid-state components last much longer than their thermionic counterparts because of their greater resistance to shock, vibration and mechanical wear. An electronic component or circuit made of solid materials, such as transistors, chips and bubble memory. There is no mechanical action in a solid state device, although an unbelievable amount of electromagnetic action takes place within. 428
- 429. For data storage, solid state devices are much faster and more reliable than mechanical disks and tapes, but are more expensive. Although solid state costs continually drop, disks, tapes and optical disks also continue to improve their cost/performance ratio. The first solid state device was the "cat's whisker" of the 1930s. A whisker-like wire was moved around on a solid crystal in order to detect a radio signal. 2. (in physics) - the solid state is one of the three phases of matter (solid, liquid, and gas). Characteristic of or relating to the physical properties of solid materials especially electromagnetic or thermodynamic or structural properties of crystalline solids SONET - Acronym for synchronous optical network. An interface standard for synchronous optical-fiber transmission, applicable to the Physical Layer of the OSI Reference Model. Note: SONET uses a basic bit rate of 51.840 Mb/s, called OC-1 (optical carrier 1). The SONET hierarchy consists of preset integral multiples of OC-1, i.e., OC-3, OC-12, OC-48, etc. Sounding - In automated HF radio systems, the broadcasting of a very brief signal, containing the station address, station identifier, or call sign, to permit receiving stations to measure link quality. Sound Wave - The pattern of disturbance caused by the movement of energy traveling through a medium (such as air, water, or any other liquid or solid matter) as it propagates away from the source of the sound. The source is some object that causes a vibration, such as a ringing telephone, or a person's vocal chords. The vibration disturbs the particles in the surrounding medium; those particles disturb those next to them, and so on. The pattern of the disturbance creates outward movement in a wave pattern, like waves of seawater on the ocean. The wave carries the sound energy through the medium, usually in all directions and less intensely as it moves farther from the source. The idea that sound moves in waves goes back (at least) to about 240 B.C. The Greek philosopher Chrysippus (c. 240 B.C.), the Roman architect and engineer Vetruvius (c. 25 B.C.), and the Roman philosopher Boethius (A.D. 480-524) each theorized that sound movement might take a wave form. Source Language - In computing, data processing, and communications systems, a language from which statements are translated. Note: Translators, assemblers, and compilers prepare target language programs, usually machine-language programs, from source language programs, usually high-level language programs written by programmers. Source User - The user providing the information to be transferred to a destination user during a particular information transfer transaction. Synonym information source. Space - In telegraphy, one of the two significant conditions of encoding. Note 1: The complementary significant condition is called a " mark." Note 2: In modern digital communications, the two corresponding significant conditions of encoding are called "zero" and "one." Synonyms spacing pulse, spacing signal. Spam - Slang 1. Unwanted or unsolicited e-mail messages or mailing-list or newsgroup postings. 2. To send an advertisement or solicitation to large numbers of unsolicited recipients, usually via mailing lists or newsgroups. Spare - An individual part, subassembly, or assembly supplied for the maintenance or repair of systems or equipment. 429
- 430. Speckle Noise - Synonym modal noise. - Noise generated in an optical fiber system by the combination of mode-dependent optical losses and fluctuation in the distribution of optical energy among the guided modes or in the relative phases of the guided modes. Spectral Density - For a specified bandwidth of radiation consisting of a continuous frequency spectrum, the total power in the specified bandwidth divided by the specified bandwidth. Note: Spectral density is usually expressed in watts per hertz. Spectral Width - The wavelength interval over which the magnitude of all spectral components is equal to or greater than a specified fraction of the magnitude of the component having the maximum value. Note 1: In optical communications applications, the usual method of specifying spectral width is the full width at half maximum. This method may be difficult to apply when the spectrum has a complex shape. Another method of specifying spectral width is a special case of root-mean-square deviation where the independent variable is wavelength, , and f ( ) is a suitable radiometric quantity. Note 2: The relative spectral width , / , is frequently used where is obtained according to note 1, and is the center wavelength. Spectrum - 1. Federal government designation of a range of frequencies for a category of use or uses. For example, the Federal Communications Commission (FCC) allocated the 1900 MHz band for personal communications services. Allocation, typically accomplished in years-long FCC proceedings, tracks new technology development. However, the FCC can shift existing allocations to accommodate changes in spectrum demand. As an example, some UHF television channels were recently reallocated to public safety. 2. A range of electromagnetic radio frequencies used in the transmission of radio, data, and video. Speech Digit Signaling - Synonym bit robbing. - In digital carrier systems, the practice or technique of preempting, at regular intervals and for the purpose of transmitting signaling information, one digit time slot that (a) is associated with the given user channel for which signaling is required, and (b) is used primarily for transporting encoded speech via that channel. Note 1: Bit robbing is an option in networks compatible with T-carrier, e.g., an ISDN. Note 2: In conventional T-carrier systems, bit robbing uses, in every sixth frame, the time slot associated with the least significant bit. Speed Dialing - 1. Synonym abbreviated dialing. 2. Dialing at a speed greater than the normal ten pulses per second. Speed Dialing 8 - Allows you to use preprogrammed one digit dialing to complete calls (local, regional toll, or long distance). Up to eight numbers may be stored in memory. This feature is compatible with Speed Dial 30, which would then give you up to 38 storable numbers. Allows you to program up to eight frequently called phone numbers for dialing with a single-digit code. To activate dial 74# and wait for the dial tone. Enter the one-digit code you’ve selected followed by the corresponding phone number (up to 15 digits). Several short tones will confirm your entry. Repeat this procedure for up to seven more numbers. To call a speed-dial number wait for the dial tone and press the one-digit code of the number you wish to call followed by #. Speed Dialing 30 - Allows you to use preprogrammed one, or two, digit dialing to complete calls (local, regional toll or long distance). Up to 30 numbers may be stored in memory. This feature is compatible with Speed Dial 8, which would then give you up to 38 storable numbers. Allows you to program up to 30 frequently called phone numbers for dialing with a two-digit code. To activate dial 74# and wait for the dial tone. Enter the one-digit code you’ve selected followed by the corresponding phone number (up to 15 digits). Several short tones will confirm your entry. Repeat this 430
- 431. procedure for up to seven more numbers. To call a speed-dial number wait for the dial tone and press the one-digit code of the number you wish to call followed by #. Spider - See bot, droid. Splice - 1. To join, permanently, physical media that conduct or transmit power or a communication signal. 2. A device that so joins conducting or transmitting media. 3. The completed joint. Splice Organizer - In optical communication, a device that facilitates the splicing or breaking out of fiber optic cables. Note: The organizer provides means to separate and secure individual buffer tubes, fibers, and/or pigtails. It also provides means to secure mechanical splices or protective sleeves used in connection with fusion splices, and has means to contain the slack fiber that remains after the splicing process is completed. Splitter - See directional coupler, T-coupler, tee coupler. - A transmission coupling device for separately sampling (through a known coupling loss) either the forward (incident) or the backward (reflected) wave in a transmission line. Note: A directional coupler may be used to sample either a forward or backward wave in a transmission line. A unidirectional coupler has available terminals or connections for sampling only one direction of transmission; a bidirectional coupler has available terminals for sampling both directions. Spontaneous Emission - Radiation emitted when the internal energy of a quantum mechanical system drops from an excited level to a lower level without regard to the simultaneous presence of similar radiation. Note: Examples of spontaneous emission include radiation from an LED, and radiation from an injection laser below the lasing threshold. Spoofing - 1. [The] interception, alteration, and retransmission of a cipher signal or data in such a way as to mislead the recipient.2. [An] attempt to gain access to an AIS by posing as an authorized user. 3. Unauthorized use of legitimate Identification and Authentication (I&A) data, however it was obtained, to mimic a subject different from the attacker. Impersonating, masquerading, piggybacking, and mimicking are forms of spoofing. Spot Speed - In facsimile systems, the speed of the scanning or recording spot along the available line. Note: The spot speed is usually measured on the object or on the recorded copy. SS7 - Abbreviation for Signaling System No. 7. - A common-channel signaling system defined by the CCITT in the 1988 Blue Book, in Recommendations Q.771 through Q.774. Note: SS7 is a prerequisite for implementation of an Integrated Services Digital Network (ISDN). SSL - The Secure Sockets Layer (SSL) is a common protocol for managing the security of data transmission over the Internet. You can tell if a Web page is encrypted by looking for the "lock" graphic within your browser window. Sites that need to transfer sensitive information such as passwords and credit card information from the browser to the server must have SSL enabled. TDS uses SSL for your protection. Standard - 1. Guideline documentation that reflects agreements on products, practices, or operations by nationally or internationally recognized industrial, professional, trade associations or governmental bodies. Note: This concept applies to formal, approved standards, as contrasted to de facto standards and proprietary standards, which are exceptions to this concept. 2. An exact value, a physical entity, or an abstract concept, established and defined by authority, custom, or common consent to serve as a reference, model, or rule in measuring quantities or qualities, establishing practices or procedures, or evaluating results. A fixed quantity or quality. 431
- 432. Standby - 1. In computer and communications systems operations, pertaining to a power-saving condition or status of operation of equipment that is ready for use but not in use. Note: An example of a standby condition is a radio station operating condition in which the operator can receive but is not transmitting. 2. Pertaining to a dormant operating condition or state of a system or equipment that permits complete resumption of operation in a stable state within a short time. 3. Pertaining to spare equipment that is placed in operation only when other, in-use equipment becomes inoperative. Note: Standby equipment is usually classified as (a) hot standby equipment, which is warmed up, i.e., powered and ready for immediate service, and which may be switched into service automatically upon detection of a failure in the regular equipment, or (b) cold standby equipment, which is turned off or not connected to a primary power source, and which must be placed into service manually. Star Network - See network topology. An active star network has an active central node that usually has the means to prevent echo-related problems. Star Topology - See network topology. A network topology in which peripheral nodes are connected to a central node, which rebroadcasts all transmissions received from any peripheral node to all peripheral nodes on the network, including the originating node. Note 1: All peripheral nodes may thus communicate with all others by transmitting to, and receiving from, the central node only. Note 2: The failure of a transmission line, i.e., channel, linking any peripheral node to the central node will result in the isolation of that peripheral node from all others. Note 3: If the star central node is passive, the originating node must be able to tolerate the reception of an echo of its own transmission, delayed by the two-way transmission time, i.e., to and from the central node, plus any delay generated in the central node. An active star network has an active central node that usually has the means to prevent echo-related problems. Start Signal - 1. A signal that prepares a device to receive data or to perform a function. 2. In start-stop transmission, a signal at the beginning of a character that prepares the receiving device for the reception of the code elements. Note: A start signal is limited to one signal element usually having the duration of a unit interval. Start-Stop Transmission - 1. Asynchronous transmission in which a start pulse and a stop pulse are used for each symbol. 2. Signaling in which each group of code elements corresponding to an alphanumeric character is (a) preceded by a start signal that serves to prepare the receiving mechanism for the reception and registration of a character and (b) followed by a stop signal that serves to bring the receiving mechanism to rest in preparation for the reception of the next character. Statement - 1. In programming languages, a language construct that represents a set of declarations or a step in a sequence of actions. 2. In computer programming, a symbol string or other arrangement of symbols. 3. In computer programming, a meaningful expression or generalized instruction, represented in a source language. Stimulated Emission - In a quantum mechanical system, the radiation emitted when the internal energy of the system drops from an excited level (induced by the presence of radiant energy at the same frequency) to a lower level. Note: An example of stimulated emission is the radiation from an injection laser diode operated above the lasing threshold. Stop Signal - 1. In start-stop transmission, a signal at the end of a character that prepares the receiving device for the reception of a subsequent character. A stop signal is usually limited to one signal element having any duration equal to or greater than a specified minimum value. 2. A signal to a receiving mechanism to wait for the next signal. Storage - (1) The capacity of a device to hold and retain data. (2) Short for mass storage. 432
- 433. Store-and-Forward (S-F) - Pertaining to communications systems in which messages are received at intermediate routing points and recorded i.e., stored, and then transmitted, i.e., forwarded, to the next routing point or to the ultimate recipient. Start Message - Synonym go-ahead notice. - In a tape-relay communications system, a service message, usually sent to a relay station or to a tributary station, that contains a request to the operator to resume transmitting over a specified channel or channels. Synonyms go-ahead message, start notice. Start Notice - Synonym go-ahead notice. - In a tape-relay communications system, a service message, usually sent to a relay station or to a tributary station, that contains a request to the operator to resume transmitting over a specified channel or channels. Synonyms go-ahead message, start message . State Subscriber Line Charge - A charge mandated by some state public service or utility commissions to compensate the local phone company for part of the cost of providing local telephone lines associated with state services, i.e. intrastate long distance and local exchange services. Station - 1. A telephone set attached to a multi-line Key system or PBX. An automatic call processor will work on a PBX station extension, but WILL NOT work on a Key system station extension. 2. One or more transmitters or receivers or a combination of transmitters and receivers, including the accessory equipment, necessary at one location for carrying on a radiocommunication service, or the radio astronomy service. Each station shall be classified by the service in which it operates permanently or temporarily. Step-Index Profile - For an optical fiber, a refractive index profile characterized by a uniform refractive index within the core and a sharp decrease in refractive index at the core-cladding interface. Note 1: The step- index profile corresponds to a power-law index profile with the profile parameter approaching infinity. Note 2: The step-index profile is used in most single-mode fibers and some multimode fibers. Steradian (sr) - The metric unit of solid angle. See International System of Units. Stick - Business quality Single Line Automatic Call Processor. Line sharing device for small or home business as well large corporations and organizations. Automatically routes calls to the assigned device. The Stick allows up to three telecommunication devices plus an answering machine to share one single phone line. This is our most popular fax switch. Click here to find out more. Stimulated Emission - In a quantum mechanical system, the radiation emitted when the internal energy of the system drops from an excited level (induced by the presence of radiant energy at the same frequency) to a lower level. Note: An example of stimulated emission is the radiation from an injection laser diode operated above the lasing threshold. Storage - 1. The retention of data in any form, usually for the purpose of orderly retrieval and documentation. 2. A device consisting of electronic, electrostatic, electrical, hardware, or other elements into which data may be entered, and from which data may be obtained, as desired. Store - To copy data from a CPU to memory, or from memory to a mass storage device. Store-and-Forward (S-F) - Pertaining to communications systems in which messages are received at intermediate routing points and recorded i.e., stored, and then transmitted, i.e., forwarded, to the next routing point or to the ultimate recipient. 433
- 434. Strength Member - Any component of a communication cable, metallic or optical, the function of which is to protect the transport medium, i.e., conductor or fiber, from excessive tensile and bending stresses during installation and while in service. Stratum - The number of a clock (in a hierarchical synchronization distribution system) that defines the quality of the clock by specifying parameters such as frequency accuracy, pull-in range, and noise performance. Note: Only stratum 1 clocks may operate independently; other clocks are slaved directly or indirectly to a stratum 1 clock. String - A sequence of data elements, such as bits or characters, considered as a whole. Stuffing - See bit stuffing, de-stuffing. is the insertion of one or more bits into a transmission unit as a way to provide signaling information to a receiver. The receiver knows how to detect and remove or disregard the stuffed bits. Subassembly - A major subdivision of an assembly consisting of a package of parts, elements, and circuits that perform a specific function. Subcarrier - A carrier used to modulate another carrier. Note: The modulated carrier can be used to modulate another carrier, and so on, so that there can be several levels of subcarriers, i.e., several intermediate carriers. Subscriber - The party identified in the account records of a common carrier as responsible for payment of the telephone bill. (1.) Any adult person authorized by such party to change telecommunications services or to charge services to the accounts; or (2.) any person contractually or otherwise lawfully authorized to represent such party. Successful Block Transfer - The transfer of a correct, nonduplicate, user information block between the source user and intended destination user. Note: Successful block transfer occurs when the last bit of the transferred block crosses the functional interface between the telecommunications system and the intended destination user. Successful block transfer can only occur within a defined maximum block transfer time after initiation of a block transfer attempt. Successful Disengagement - The termination of user information transfer between a source user and a destination user in response to a disengagement request. Note: Successful disengagement occurs at the earliest moment at which either user is able to initiate a new information transfer transaction. Sunspot - In the photosphere, i.e., visible disk of the Sun, a dark marking that manifests a magnetic anomaly that is associated with interference with radio communications on Earth. Note: Sunspot activity, i.e., the number of sunspots occurring at a given time or on a given day, is cyclic. The period of a cycle, from maximum through minimum and back to maximum sunspot count, is approximately 11 years. Supergroup - See group, multiplex hierarchy. Superluminescent LED - A light-emitting diode in which there is stimulated emission with amplification but insufficient feedback for oscillations to build up to achieve lasing action. Surface Wave - A wave that is guided along the interface between two different media or by a refractive index gradient. Note 1: The field components of the wave diminish with distance from the interface. Note 2: Optical energy is not converted from the surface wave field to another form of energy and the wave does not have a component directed normal to the interface surface. Note 3: In optical fiber transmission, 434
- 435. evanescent waves are surface waves. Note 4: In radio transmission, ground waves are surface waves that propagate close to the surface of the Earth, the Earth having one refractive index and the atmosphere another, thus constituting an interface surface. Surge Protector - See Surge Suppressor Surge Suppressor - A surge suppressor (sometimes optimistically called a "surge protector") is a device inserted in the alternating current (AC) utility line and/or telephone line to prevent damage to electronic equipment from voltage "spikes" called transients. A more accurate term for this type of device is "transient suppressor." A typical surge suppressor is a small box with several utility outlets, a power switch, and a 3- wire cord for plugging into a wall outlet. In most countries where electronic equipment is used, the effective AC utility voltage is 110 to 120 volts; the peak voltage is on the order of plus-or-minus 160 to 170 volts at a frequency of 60 hertz. But transients, which arise from various causes, commonly reach peak levels of several hundred volts. These pulses are of short duration, measured in microseconds (units of 10-6 second), but in that time, they can cause hardware to malfunction. The worst type of transient occurs when lightning strikes in the vicinity (it is not necessary for a power line to be directly hit). Such a "spike" can peak at thousands of volts and cause permanent damage to equipment. A surge suppressor prevents the peak AC voltage from going above a certain threshold such as plus-or-minus 200 volts. semiconductor devices are used for this purpose. The power line is effectively short-circuited to electrical ground for transient pulses exceeding the threshold, while the flow of normal 60-Hz current is unaffected. For the suppressor to work, a 3-wire AC power connection must be used. "Cheater" adapters, which allow 3-wire appliances to be used with 2-wire outlets or extension cords, defeat the electrical ground connection and render most surge suppressors ineffective. Surge suppressors should be used as a matter of habit with all semiconductor-based electronic and computer hardware, including peripherals such as printers, monitors, external disk drives, and modems. But the suppressor should not be relied upon to provide protection against lightning-induced transients. The safest procedure, inconvenient though it be, is to ensure that all susceptible hardware is plugged into the suppressor box, and to unplug the suppressor's main power cord when the equipment is not in use if you live in a thunderstorm-prone area. Surveillance - 1. The use of (usually) electronic means, passive or active, to obtain information about the nature, position, or movement of, e.g., aircraft (cooperative or non-cooperative, friendly or unfriendly), sources of electromagnetic emissions, etc. 2. Nonintrusive monitoring of digital signals in real time to recognize performance degradations and failures and system intrusion attempts. SVGA - Abbreviation for Super Video Graphics Array. This is a display mode with a resolution of 800 x 600 pixels. Switch - A device that opens or closes circuits, completes or breaks an electrical path. Switched Circuit - In a communications network , a circuit that may be temporarily established at the request of one or more of the connected stations. Switched Multimegabit Data Service (SMDS) - A new standard for extremely high-speed data transfer (up to 34 Mbps). 435
- 436. Switching - The controlling or routing of signals in circuits to execute logical or arithmetic operations or to transmit data between specific points in a network. Note: Switching may be performed by electronic, optical, or electromechanical devices. Switching Center - In communications systems, a facility in which switches are used to interconnect communications circuits on a circuit-, message-, or packet-switching basis. Synonyms, in telephony, central office, switching exchange, switching facility. Deprecated synonym switch. Switching Exchange - Synonym switching center. Switching System - 1. A communications system consisting of switching centers and their interconnecting media. 2. Part of a communication system organized to temporarily associate functional units, transmission channels or telecommunication circuits for the purpose of providing a desired telecommunication facility. Note: Examples of NATO-owned switching systems are IVSN and TARE. Symmetry - The attribute describing the relationship of information flow between two (or more) access points or reference points involved in a communication. Symmetry characterizes the structure associated with a telecommunication service or a connection. Values associated with this attribute are unidirectional, bidirectional symmetric, and bidirectional asymmetric. Synchronism - 1. The state of being synchronous. 2. For repetitive events with the same, multiple, or submultiple repetition rates, a relationship among the events such that a significant instant of one event bears a fixed time relationship to a corresponding instant in another event. Note: Synchronism is maintained when there is a fixed, i.e. , constant, phase relationship among the group of repetitive events. 3. The simultaneous occurrence of two or more events at the same instant on the same coordinated time scale. Synchronization -1. The attaining of synchronism between the frequencies or between the frequencies and phases of two or more signals. 2. The obtaining of a desired fixed relationship among corresponding significant instants of two or more signals. 3. A state of simultaneous occurrences of significant instants among two or more signals. Synchronous - 1. Pertaining to the relationship of two or more repetitive signals that have simultaneous occurrences of significant instants. Note: " Isochronous " and " anisochronous " pertain to characteristics. " Synchronous " and " asynchronous " pertain to relationships. 2. Pertaining to synchronism. Synchronous Optical Network - See SONET. System - 1. Any organized assembly of resources and procedures united and regulated by interaction or interdependence to accomplish a set of specific functions. 2. A combination of two or more interrelated equipment (sets) arranged in a functional package to perform an operational function or to satisfy a requirement. 3. A collection of personnel, equipment, and methods organized to accomplish a set of specific functions. System Overhead Information - See overhead information. - Digital information transferred across the functional interface between a user and a telecommunications system, or between functional units within a telecommunications system, for the purpose of directing or controlling the transfer of user information or the detection and correction of errors. Note: Overhead information originated by the user is not considered to be system overhead information. Overhead information generated within the communications system and not delivered to the user is system overhead information. Thus, the user throughput is reduced by both overheads while system throughput is reduced only by system overhead. 436
- 437. T 12 T - Abbreviation for tera (10 ). See International System of Units. T-1 - - A leased line connection that can carry 1,544,000 bits per second. The T-1 carrier is the most commonly used digital transmission service in the United States, Canada, and Japan. It consists of 24 separate channels using pulse code modulation (PCM) signals with time-division multiplexing (TDM). T-1 lines were originally designed to transmit digitized voice signals. Current applications also include digital data transmission. T1 lines originally used copper wire but now also include optical and wireless media. A T-1 Outstate System has been developed for longer distances between cities. Internet access providers are commonly connected to the Internet as a point-of-presence (POP) on a T1 line owned by a major telephone network. Many businesses also use T1 lines to connect to an Internet access provider. See T-carrier. T-3 - A leased line connection that can carry 44,736,000 bits per second. The T-3 carrier is a digital transmission that consists of 672 individual channels, each of which supports 64 Kbps using pulse code modulation (PCM) signals with time-division multiplexing (TDM). T-3 lines were originally designed to transmit digitized voice signals. Current applications also include digital data transmission. T3 lines originally used copper wire but now also include optical and wireless media. A T-3 Outstate System has been developed for longer distances between cities. Internet access providers are sometimes connected to the Internet as a point-of-presence (POP) on a T3 line owned by a major telephone network. Some businesses also use T3 lines to connect to an Internet access provider. T1 (carrier) - The generic designator for any of several digitally multiplexed telecommunications carrier systems. Note 1: The designators for T-carrier in the North American digital hierarchy correspond to the designators for the digital signal (DS) level hierarchy. See the associated table below. Note 2: T-carrier systems were originally designed to transmit digitized voice signals. Current applications also include digital data transmission. Note 3: If an "F" precedes the "T", a fiber optic cable system is indicated at the same rates. Note 4: The table below lists the designators and rates for current T-Carrier systems. Note 5: The North American and Japanese hierarchies are based on multiplexing 24 voice-frequency channels and multiples thereof, whereas the European hierarchy is based on multiplexing 30 voice-frequency channels and multiples thereof. - See T-carrier. T1 Line - A full-duplex digital transmission facility that is composed of transmission media (optical or metallic) and regenerators that carry one DS1 signal. T3 (carrier) - A dedicated leased phone line connection supporting data rates of 44,736,000 bits per second. A T-3 line actually consists of 672 individual channels, each of which supports 64 Kbps. T-3 lines are used mainly by Internet Service Providers (ISPs) connecting to the Internet backbone and for the backbone itself. T-3 lines are sometimes referred to as DS3 lines. - See T-carrier. T3 Line - A full-duplex digital transmission facility that is composed of transmission media (optical or metallic) and regenerators that carry one DS3 signal. 437
- 438. Tactical Automatic Digital Switching System (TADSS) - A transportable store-and-forward message-switching system used for rapid deployment in support of tactical forces. Tactical Command and Control (C2) Systems - The equipment, communications, procedures, and personnel essential to a commander for planning, directing, coordinating, and controlling tactical operations of assigned forces pursuant to assigned missions. Tactical Communications - Communications in which information of any kind, especially orders and decisions, are conveyed from one command, person, or place to another within the tactical forces, usually by means of electronic equipment, including communications security equipment, organic to the tactical forces. Note: Tactical communications do not include communications provided to tactical forces by the Defense Communications System (DCS), to nontactical military commands, and to tactical forces by civil organizations. Tactical Communications System - A communications system that (a) is used within, or in direct support of, tactical forces, (b) is designed to meet the requirements of changing tactical situations and varying environmental conditions, (c) provides securable communications, such as voice, data, and video, among mobile users to facilitate command and control within, and in support of, tactical forces, and (d) usually requires extremely short installation times, usually on the order of hours, in order to meet the requirements of frequent relocation. Tactical Data Information Link (TADIL) - A standardized communications link, approved by the Joint Staff, that is suitable for transmission of digital information, and is characterized by standardized message formats and transmission characteristics. Tactical Data Information Link--A (TADIL--A) - A netted link in which one unit acts as a net control station and interrogates each unit by roll call. Note: Once interrogated, that unit transmits its data to the net. This means that each unit receives all the information transmitted. This is a direct transfer of data and no relaying is involved. Tactical Data Information Link--B (TADIL--B) - A point-to-point data link between two units which provides for simultaneous transmission and reception of data (duplex). Tactical Load - For the host service tactical forces, the total power requirements for communications, including the requirements for weapons, detection, command and control systems, and related support functions. Note: The tactical load is a part of the operational load. TADIL - Acronym for tactical data information link. TADSS - Acronym for Tactical Automatic Digital Switching System. Tagged Image File Format (TIFF) - A file format used to store an image using the particular data structure of the file. TAI - Abbreviation for International Atomic Time. Tail Circuit - 1. A circuit which connects the serial lines of two modems together. 2. A communications line from the end of a major transmission link, such as a microwave link, satellite link, or LAN, to the end-user location. Note: A tail circuit is a part of a user-to-user connection. Tailgate - To gain unauthorized physical access by following an authorized person through a controlled door. 438
- 439. Tailing - In facsimile systems, the excessive prolongation of the decay of the signal. Synonym hangover. Take - See clip. 1. In moving picture or television technology, a relatively short, continuous set of frames (often including the associated audio, if any), stored on a recording medium. Synonyms clip, scene. 2. In audio, a short, uninterrupted sound track. Note: Both audio and video clips may be part of a digitized information package, e.g., on a Web page. 3. To limit to a predetermined level (e.g., at the output of an otherwise linear amplifier) the amplitude of an otherwise linear signal. Note: In contrast with an analog compression circuit, which reduces the dynamic range of a signal but retains its basic waveform, a clipping circuit treats (processes, amplifies) a signal in a linear fashion unless the output level reaches a certain threshold, which it may not exceed, and at which it remains unless the input decreases to a level at which the processed output level is lower than the clipping level. Takeoff Angle - Synonym departure angle. - The angle between the axis of the main lobe of an antenna pattern and the horizontal plane at the transmitting antenna. Tampering - 1. Penetration or modification of internal operations, or the insertion of active or passive tapping mechanisms, to determine the nature of, or monitor or record , e.g., secret data. 2. Unauthorized modification altering the proper functioning of INFOSEC equipment. 3. Unauthorized modification of sensitive systems or sensitive information. Tandem - 1. Pertaining to an arrangement or sequencing of networks, circuits, or links, in which the output terminals of one network, circuit, or link are connected directly to the input terminals of another network, circuit, or link. Note: For example, concatenated microwave links constitute a tandem connection. 2. A switching system in the message network that establishes trunk-to-trunk connections. Tandems may be further identified as local tandems, LATA tandems, or access tandems. Tandem Area - The general areas served by the local offices having direct trunks to or from the tandem office. This area may consist of one or more communities or may include only a portion of a relatively large city. Tandem Center - In a switched public telecommunications network, a facility that connects trunks to trunks and does not connect any local loops. Tandem Circuit - A general classification of circuits or trunks between a tandem central office unit and any other central office or switchboard. Synonym tandem trunk. Tandem Connection - A call switched at a tandem office. Tandem Office - A central office unit used primarily as an intermediate switching point for traffic between local central offices within the tandem area. Where qualified by a modifying expression, or other explanation, this term may be applied to an office employed for both the interconnection of local central offices within the tandem area and for the interconnection of these local offices with other central offices, e.g., long haul tandem office. Tandem Signaling - One of the most difficult conditions for speech coders to perfom well in is the case where a digital speech-coded signal is transmitted from the mobile to the base station, and then demodolated into an analog signal which is then speech coded for retransmission as a digital signal over a landline or wireless link. This situation, called tandem signaling, tends to exaggerate the bit errors originally received at the base station. Tandem signaling is difficult to protect against, but is an important evaluation criterion in the evaluation of speech coders. As wireless systems proliferate, there will be a greater demand for mobile-to- mobile communications, and such links will, by definition, involve at least two independent, noisy tandems. 439
- 440. Tandem Tie Trunk Network (TTTN) - An arrangement that permits sequential connection of tie trunks between PBX and Centrex® locations by using tandem operation. Note: Tandem operation permits two or more dial tie trunks to be connected at a tandem center to form a through connection. Tandem Trunk - Synonym tandem circuit. - A general classification of circuits or trunks between a tandem central office unit and any other central office or switchboard. Tap - 1. To draw energy from a circuit. 2. To monitor, with or without authorization, the information that is being transmitted via a communications circuit. 3. To extract a portion of the signal from an optical fiber or communications link. Note: One method of tapping an optical fiber is to bend it to a relatively short radius, thus promoting radiation of a portion of the optical signal. Tapered Fiber - An optical fiber in which the cross section, i.e., cross-sectional diameter or area, varies, i.e., increases or decreases, monotonically with length. Tape Relay - A method of retransmitting TTY traffic from one channel to another, in which messages arriving on an incoming channel are recorded in the form of perforated tape, this tape then being either fed directly and automatically into an outgoing channel, or manually transferred to an automatic transmitter for transmission on an outgoing channel. Target Language - In computing, data processing, and communications systems, a language into which statements are translated. Note: Translators, assemblers, and compilers prepare target language programs, usually machine-language programs, from source language programs, usually high-level language programs written by programmers. Tariff - Documents filed by a telephone company with a state public utility commission and the FCC describing its services and the payments to be charged for the services. The published schedule of rates or charges for a specific unit of equipment, facility, or type of service such as might be provided by a telecommunications common carrier. TASI - Acronym for time-assignment speech interpolation. TAT - Abbreviation for transatlantic telecommunications (cable). Note: TAT formerly stood for transatlantic telephone (cable). T-carrier - In telecommunications, T-carrier is the generic designator for any of several digitally multiplexed telecommunications carrier systems originally developed by Bell Labs and used in North America and Japan. The basic unit of the T-carrier system is the DS0, which has a transmission rate of 64 kbit/s, and is commonly used for one voice circuit. Note 1: The designators for T-carrier in the North American digital hierarchy correspond to the designators for the digital signal (DS) level hierarchy. See the associated table below. Note 2: T-carrier systems were originally designed to transmit digitized voice signals. Current applications also include digital data transmission. Note 3: If an "F" precedes the "T", a fiber optic cable system is indicated at the same rates. Note 4: The table below lists the designators and rates for current T-Carrier systems. Note 5: The North American and Japanese hierarchies are based on multiplexing 24 voice-frequency channels and multiples thereof, whereas the European hierarchy is based on multiplexing 30 voice-frequency channels and multiples thereof. The E-carrier system, where 'E' stands for European, is incompatible with the T-carrier and is used just about everywhere else in the world besides North America and Japan. It typically uses the E1 line rate and the E3 line rate. The E2 line rate is less commonly used. 440
- 441. TCB - Abbreviation for trusted computing base. - [The] totality of protection mechanisms within a computer system, including hardware, firmware, and software, the combination of which is responsible for enforcing a security policy. Note: The ability of a trusted computing base to enforce correctly a unified security policy depends on the correctness of the mechanisms within the trusted computing base, the protection of those mechanisms to ensure their correctness, and the correct input of parameters related to the security policy. TCF - Abbreviation for technical control facility. - A physical plant, or a designated and specially configured part thereof, that (a) contains the equipment necessary for ensuring fast, reliable, and secure exchange of information, (b) typically includes distribution frames and associated panels, jacks, and switches and monitoring, test, conditioning, and orderwire equipment, and (c) allows telecommunications systems control personnel to exercise operational control of communications paths and facilities, make quality analyses of communications and communications channels, monitor operations and maintenance functions, recognize and correct deteriorating conditions, restore disrupted communications, provide requested on-call circuits, and take or direct such actions as may be required and practical to provide effective telecommunications services. T-Coupler - A passive optical coupler having three ports (three fibers). Note 1: Two isolated inputs may be combined into one output; or one input, into two isolated outputs. Note 2: The amount of coupling loss, usually expressed in dB, between ports is determined by the design and construction of the coupler. [After FAA] Synonyms directional coupler, splitter, tee coupler. TCP - Abbreviation for Transmission Control Protocol. In the Internet Protocol suite, a standard, connection- oriented, full-duplex, host-to-host protocol used over packet-switched computer communications networks. Note 1: TCP corresponds closely to the ISO Open Systems Interconnection--Reference Model (OSI--RM) Layer 4 (Transport Layer). Note 2: The OSI--RM uses TP-0 or TP-4 protocols for transmission control. See Transmission Control Protocol/Internet Protocol TCP/IP - Abbreviation for Transmission Control Protocol / Internet Protocol. Two interrelated protocols that are part of the Internet protocol suite. Note 1: TCP operates on the OSI Transport Layer and breaks data into packets. IP operates on the OSI Network Layer and routes packets. Note 2: TCP/IP was originally developed by the U.S. Department of Defense. TCP/IP Suite - The suite of interrelated protocols associated with Transmission Control Protocol / Internet Protocol. Note 1: The TCP/IP Suite includes, but is not limited to, protocols such as TCP, IP, UDP, ICMP, FTP, and SMTP. Note 2: Additional application and management protocols are sometimes considered part of the TCP/IP Suite. This includes protocols such as SNMP. TCS - Abbreviation for trusted computer system. 1. [An] information system (IS) employing sufficient hardware and software assurance measures to allow simultaneous processing of a range of classified or sensitive information. 2. A data processing system that provides sufficient computer security to allow for concurrent access to data by users with different access rights and to data with different security classification and security categories. TCU - Abbreviation for teletypewriter control unit. - A device that controls and coordinates operations between teletypewriters and message switching centers. TDD - Abbreviation for Telecommunications Device for the Deaf. - A machine that uses typed input and output, usually with a visual text display, to enable individuals with hearing or speech impairments to communicate over a telecommunications network. TDEA Decryption Operation - the transformation of a 64-bit block I into a 64-bit block O that is defined as follows: O = DK1(EK2(DK3(I))). The standard specifies the following keying options for bundle (K1, K2, K3) 441
- 442. • Keying Option 1 - K1, K2, and K3 are independent keys; • Keying Option 2 - K1 and K2 are independent keys and K3 = K1; • Keying Option 3 - K1 = K2 = K3. TDM - Abbreviation for time-division multiplexing. - 1. Digital multiplexing in which two or more apparently simultaneous channels are derived from a given frequency spectrum, i.e., bit stream, by interleaving pulses representing bits from different channels. Note: Successive pulses represent bits from successive channels, e.g., voice channels in a T1 system. 2. A multiplexing technique whereby two or more channels are derived from a transmission mediuim by dividing access to the medium into sequential intervals. Each channel has access to the entire bandwidth of the medium during its interval. This implies that one transmitter uses one channel to send several bit streams of information. TDMA - Abbreviation for time-division multiple access. - 1. A communications technique that uses a common channel (multipoint or broadcast) for communications among multiple users by allocating unique time slots to different users. Note: TDMA is used extensively in satellite systems, local area networks, physical security systems, and combat-net radio systems. 2. A multiple access technique whereby users share a transmission medium by being assigned and using (one at a time) for a limited number of time division multiplexed channels; implies that several transmitters use one channel for sending several bit streams. TE - Abbreviation for transverse electric. See transverse electric mode. A mode whose electric field vector is normal to the direction of propagation. Note: TE modes may be useful modes in waveguides. In an optical fiber, TE and TM modes correspond to meridional rays. Technical Area - In the military community, an area in which temperature, humidity, or access is controlled because it contains equipment, such as communications, computing, control, or support equipment, that requires such controls. Technical Control Facility (TCF) - A physical plant, or a designated and specially configured part thereof, that (a) contains the equipment necessary for ensuring fast, reliable, and secure exchange of information, (b) typically includes distribution frames and associated panels, jacks, and switches and monitoring, test, conditioning, and orderwire equipment, and (c) allows telecommunications systems control personnel to exercise operational control of communications paths and facilities, make quality analyses of communications and communications channels, monitor operations and maintenance functions, recognize and correct deteriorating conditions, restore disrupted communications, provide requested on-call circuits, and take or direct such actions as may be required and practical to provide effective telecommunications services. Technical Control Hubbing Repeater - Synonym data conferencing repeater. - A device that enables any one user of a group of users to transmit a message to all other users in that group. Technical Load - The portion of the operational load required for communications, tactical operations, and ancillary equipment including necessary lighting, air-conditioning, or ventilation required for full continuity of communications. Technical Vulnerability - In information handling, a hardware, software, or firmware weakness, or design deficiency, that leaves a system open to assault, harm, or unauthorized exploitation, either externally or internally, thereby resulting in unacceptable risk of information compromise, information alteration, or service denial. TED - Abbreviation for trunk encryption device. - A bulk encryption device used to provide secure communications over a wideband digital transmission link. Note: A TED is usually located between the output of a trunk group multiplexer and a wideband radio or cable facility. 442
- 443. Tee Coupler - A passive coupler that has three ports. Synonyms directional coupler, splitter, T-coupler. TEK - Abbreviation for traffic encryption key. - [A] key used to encrypt plain text or to superencrypt previously encrypted text and/or to decrypt cipher text. Teleaction Service - In Integrated Services Digital Network (ISDN) applications, a telecommunications service that uses very short messages with very low data transmission rates between the user and the network. Telecommand - The use of telecommunication for the transmission of signals to initiate, modify or terminate functions of equipment at a distance. Telecommunication - 1. Any transmission, emission, or reception of signs, signals, writing, images and sounds or intelligence of any nature by wire, radio, optical or other electromagnetic systems. 2. Any transmission, emission, or reception of signs, signals, writings, images, sounds, or information of any nature by wire, radio, visual, or other electromagnetic systems. Telecommunication Administration - An administration, or the part of a combined postal and telecommunication administration, concerned with the provision of telecommunication service. Telecommunication Architecture - See network architecture. - 1. The design principles, physical configuration, functional organization, operational procedures, and data formats used as the bases for the design, construction, modification, and operation of a communications network. 2. The structure of an existing communications network, including the physical configuration, facilities, operational structure, operational procedures, and the data formats in use. Telecommunications - Telecommunications is any process that enables one or more users to pass to one or more other users information of any nature delivered in any usable form, by wire, radio, visual, or other electrical, electromagnetic, optical means. The word is derived from the Greek tele, "far off," and the Latin communicare "to share." Telecommunications Center - See communications center. - 1. An agency charged with the responsibility for handling and controlling communications traffic. The center normally includes message center, transmitting, and receiving facilities. 2. A facility that (a) serves as a node for a communications network, (b) is equipped for technical control and maintenance of the circuits originating, transiting, or terminating at the node, (c) may contain message-center facilities, and (d) may serve as a gateway. Telecommunications Closet - In a premises distribution system, a telecommunications closet is an area for connecting the horizontal and backbone wiring and for containing active or passive PDS equipment. Telecommunications Device for the Deaf (TDD) - A machine that uses typed input and output, usually with a visual text display, to enable individuals with hearing or speech impairments to communicate over a telecommunications network. Telecommunication Sector - The sector that includes the telecommunications service providers, network operators, regulators, manufacturers, subscribers, and users. Telecommunications Facilities - The aggregate of equipment, such as radios, telephones, teletypewriters, facsimile equipment, data equipment, cables, and switches, used for providing telecommunications services. Telecommunications Infrastructure - The organizations, personnel, procedures, facilities, and networks employed to transmit and receive information by electrical or electronic means. Note 1: Telecommunications 443
- 444. facilities include, but are not necessarily limited to, terrestrial radio, metallic and optical fiber cables, artificial Earth satellite communications, radio and television stations (traditional broadcast as well as cable and satellite broadcast), public switched telephone network (s), etc. Note 2: Examples of advanced telecommunications infrastructure facilities are direct broadcast satellite (DBS), digital audio broadcasting (DAB), Advanced Digital Television, and the Global Positioning System (GPS), which is used extensively for precise navigation and timing. Telecommunications Link - A communications facility or channel, including feeder and local distribution plant, having a termination in a center in the telecommunications network. Examples of such a link include (but are not necessarily restricted to): optical-fiber cable, coaxial cable, metallic cables, transmitting and receiving antenna. Telecommunications Load Equipment - Equipment powered from a primary or secondary distribution of a centralized dc power system owned or operated by exchange and interexchange carriers. Telecommunications Management Network (TMN) - A network that interfaces with a telecommunications network at several points in order to receive information from, and to control the operation of, the telecommunications network. Note: A TMN may use parts of the managed telecommunications network to provide for the TMN communications. Telecommunications Network - A telecommunications network is a system of interconnected facilities designed to carry traffic from a variety of telecommunications services. The network has two different but related aspects. In terms of its physical components, it is a facilities network. In terms of the variety of telecommunications services that it provides, it can support a set of many traffic networks, each representing a particular interconnection of facilities. Telecommunications Relay Center Fee/Charge/Surcharge - This state fee helps pay for the relay center that transmits and translates calls for people who are deaf, hard-of-hearing or speech disabled. Mandated nationally by Congress with the passage of the Americans with Disabilities Act, it may also be called “Telecommunication Devices for the Deaf Tax.” Telecommunications Security - See communications security. Measures and controls taken to deny unauthorized persons information derived from telecommunications and to ensure the authenticity of such telecommunications. Note: Communications security includes cryptosecurity, transmission security, emission security, and physical security of COMSEC material. [INFOSEC] • (a) cryptosecurity: [The] component of communications security that results from the provision of technically sound cryptosystems and their proper use. [NIS] • (b) emission security: Protection resulting from all measures taken to deny unauthorized persons information of value which might be derived from intercept and analysis of compromising emanations from crypto-equipment, AIS, and telecommunications systems. [NIS] • (c) physical security: The component of communications security that results from all physical measures necessary to safeguard classified equipment, material, and documents from access thereto or observation thereof by unauthorized persons. [JP 1-02] • (d) transmission security: [The] component of communications security that results from the application of measures designed to protect transmissions from interception and exploitation by means other than cryptanalysis. Telecommunications Service - 1. Any service provided by a telecommunication provider. 2. A specified set of user-information transfer capabilities provided to a group of users by a telecommunications system. Note: The telecommunications service user is responsible for the information content of the message. The 444
- 445. telecommunications service provider has the responsibility for the acceptance, transmission, and delivery of the message. Telecommunications Service Priority (TSP) Service - A regulated service provided by a telecommunications provider, such as an operating telephone company or a carrier, for NS/EP telecommunications. Note: The TSP service replaced Restoration Priority (RP) service effective September 1990. Telecommunications Service Priority (TSP) System - A system that provides a means for telecommunications users to obtain priority treatment from service providers for the NS/EP telecommunications requirements. Note: The TSP system replaced the Restoration Priority (RP) system effective September 1990. Telecommunications Service Priority (TSP) System User - Any individual, organization, or activity that interacts with the NS/EP TSP System. Telecommunications System - See communications system. A collection of individual communications networks, transmission systems, relay stations, tributary stations, and data terminal equipment (DTE) usually capable of interconnection and interoperation to form an integrated whole. Note: The components of a communications system serve a common purpose, are technically compatible, use common procedures, respond to controls, and operate in unison. Telecommunications System Operator - The organization responsible for providing telecommunications services to users. Teleconference - The live exchange of information among persons and machines remote from one another but linked by a telecommunications system. Note: The telecommunications system may support the teleconference by providing audio, video, and data services by one or more means, such as telephone, telegraph, teletype, radio, and television. Telegram - Written matter intended to be transmitted by telegraphy for delivery to the addressee. This term also includes radiotelegrams unless otherwise specified. In this definition the term telegraphy has the same general meaning as defined in the [1979 General Worldwide Administrative Radio Conference] Convention. Telegraph - See telegraphy. A form of telecommunication which is concerned in any process providing transmission and reproduction at a distance of documentary matter, such as written or printed matter or fixed images, or the reproduction at a distance of any kind of information in such a form. For the purposes of the Radio Regulations, unless otherwise specified therein, telegraphy shall mean a form of telecommunication for the transmission of written matter by the use of a signal code. Telegraphy - A form of telecommunication which is concerned in any process providing transmission and reproduction at a distance of documentary matter, such as written or printed matter or fixed images, or the reproduction at a distance of any kind of information in such a form. For the purposes of the Radio Regulations, unless otherwise specified therein, telegraphy shall mean a form of telecommunication for the transmission of written matter by the use of a signal code. Telemeter - A measuring, transmitting, and receiving device used in telemetry. Any scientific instrument for observing events at a distance and transmitting the information back to the observer. Telemetered, Telemetering, Telemeters - To measure, transmit, and receive (data) automatically from a distant source, as from a spacecraft or an electric power grid. 445
- 446. Telemetry - 1. The use of telecommunication for automatically indicating or recording measurements at a distance from the measuring instrument. 2. The transmission of nonvoice signals for the purpose of automatically indicating or recording measurements at a distance from the measuring instrument. Telephone - A user end instrument that is used to transmit and receive voice-frequency signals. Telephone Book - A directory of the names of telephone subscribers with their telephone numbers and often their addresses. A directory containing an alphabetical list of telephone subscribers and their telephone numbers. Telephone Booth - A small enclosure containing a public telephone. Also a slang term referring to one of the many phone terminals on the floor of the New York Stock Exchange that is used by floor traders to receive orders. Telephone Exchange - Synonym for central office. A central system of switches and other equipment that establishes connections between individual telephones. Also called switchboard. A workplace that serves as a telecommunications facility where lines from telephones can be connected together to permit communication. In the field of telecommunications, a telephone exchange (US: telephone switch) is a piece of equipment that connects phone calls. It is what makes your phone calls "work" in the sense of making connections and relaying the speech information. The term exchange can also be used to refer to an area served by a particular switch. And more narrowly, it can refer to the first three digits of the local number. In the past, the first two or three digits would map to a mnemonic exchange name, e.g. 869–1234 was formerly TOwnsend 9–1234, and before that (in some localities) might have been TOWnsend 1234 (only the capital letters and numbers being dialed). In December of 1930, New York City became the first locality in the United States to adopt the two-letter, five-number format; it remained alone in this respect until after World War II, when other municipalities across the country began to follow suit (in some areas, most notably much of California, telephone numbers in the 1930s and early 1940s consisted of only six digits, two letters which began the exchange name followed by four numbers, as in DUnkirk 0799). Prior to the mid-1950s, the number immediately following the name could never be a "0" or "1;" indeed, "0" was never pressed into service at all, except in the immediate Los Angeles area (the "BEnsonhurst 0" exchange mentioned in an episode of the popular TV sitcom The Honeymooners was fictitious). In 1955, the Bell System attempted to standardize the process of naming exchanges by issuing a "recommended list" of names to be used for the various number combinations. In 1961, New York Telephone introduced "selected- letter" exchanges, in which the two letters did not mark the start of any particular name (example: FL 6- 9970), and by 1965 all newly-connected phone numbers nationwide consisted of numerals only (Wichita Falls, Texas had been the first locality in the United States to implement the latter, having done so in 1958; meanwhile, pre-existing numbers continued to be displayed the old way in many places well into the 1970s). The United Kingdom never adopted the two-letter, five-number format, remaining with the three-letter, four-number format until converting to all-numeric phone numbers in 1968. In the United States, the word exchange can also have the technical meaning of a local access and transport area under the Modification of Final Judgment (MFJ). Telephone Jack - In the U. S., telephone jacks are also known as registered jacks, sometimes described as RJ- XX, and are a series of telephone connection interfaces (receptacle and plug) that are registered with the U.S. Federal Communications Commission (FCC). They derive from interfaces that were part of AT&T's Universal Service Order Codes (USOC) and were adopted as part of FCC regulations (specifically Part 68, 446
- 447. Subpart F. Section 68.502). The term jack sometimes means both receptacle and plug and sometimes just the receptacle. RJ-11 The most common telephone jack is the RJ-11 jack, which can have six conductors but usually is implemented with four. The RJ-11 jack is likely to be the jack that your household or office phones are plugged into from the ordinary "untwisted" wire (sometimes called "gray satin" or "flat wire") people are most familiar with. In turn, the jacks connect to the "outside" longer wires known as twisted pair that connect to the telephone company central office or to a private branch exchange (PBX). The four wires are usually characterized as a red and green pair and a black and white pair. The red and green pair typically carry voice or data. On an outside phone company connection, the black and white pair may be used for low-voltage signals such as phone lights. On a PBX system, they may be used for other kinds of signaling. A computer that uses a dial-up modem to connect to a network is usually plugged into an RJ-11 jack. RJ-14 The RJ-14 is similar to the RJ-11, but the four wires are used for two phone lines. Typically, one set of wires (for one line) contains a red wire and a green wire. The other set contains a yellow and black wire. Each set carries one analog "conversation" (voice or data). RJ-45 The RJ-45 is a single-line jack for digital transmission over ordinary phone wire, either untwisted or twisted. The interface has eight pins or positions. For connecting a modem, printer, or a data PBX at a data rate up to 19.2 Kbps, you can use untwisted wire. For faster transmissions in which you're connecting to an Ethernet 10BASET network, you need to use twisted pair wire. (Untwisted is usually a flat wire like common household phone extension wire. Twisted is often round.) There are two varieties of RJ-45: keyed and unkeyed. Keyed has a small bump on its end and the female complements it. Both jack and plug must match. Telephone Line Sharing - A technology that allows a single phone line to share incoming and outgoing access for multiple devices. Typically Telephone Line Sharing Technology allows voice (phones and answering 447
- 448. machine) and a fax machine or fax modem to operate on a shared phone line. Other applications include any variation of voice, a fax machine, fax/modem and/or modem(s). Incoming calls are automatically routed to the proper device(s). If the call comes in and it is a fax call, the call is automatically routed to the fax machine or fax modem. If the call is a modem call, it is routed to the correct modem. Voice calls are routes to phone(s) and/or answering machine. May require a security access code (SAC) in the dialing string to automatically switch to the modem. Since the need for to subscribe to a separate "fax line" from the local telephone company is eliminated, the return on investment (ROI) is very high. The initial cost of the device is returned in savings in a few months. After that you will save the monthly bills associated with fax, data or voice lines. For almost every business, a telephone line sharing technology is a smart investment. Telephone Network - The system of wires, fiber-optic cables, satellites and transmission towers that transmit telephone messages from caller to receiver. Telephone Number - The unique network address that is assigned to a telephone user, i.e., subscriber, for routing telephone calls. Telephone Plug - A telephone plug is a type of male connector used to connect a telephone to the telephone wiring in a home or business, and in turn to a local telephone network. It is inserted into its female counterpart, a telephone "jack", commonly fixed to a wall or baseboard. The standard for telephone plugs varies from country to country, though the RJ11 "modular connector" has become by far the most common. A connection standard, such as "RJ11", specifies not only the physical connector, but how it is wired (the "pinout"). Modular connectors are specified for the Registered Jack series of connectors, as well as for Ethernet and other connectors, such as 4P4C (4 position, 4 contacts) modular connectors, the de facto standard on handset cables, often improperly referred to as "RJ" connectors Telephone Switch - A large-scale computer used to route telephone calls in a central office. Such devices are made by Lucent, Nortel and others. Telephone Tag - A series of unsuccessful calls exchanged by two people who are attempting to contact each other by telephone. Telephonic - 1. Of or relating to telephones. 2. Transmitted or conveyed by telephone. Telephony - 1. The branch of science devoted to the transmission, reception, and reproduction of sounds, such as speech and tones that represent digits for signaling. Note 1: Transmission may be via various media, such as wire, optical fibers, or radio. Note 2: Analog representations of sounds may be digitized, transmitted, and, on reception, converted back to analog form. Note 3: "Telephony" originally entailed only the transmission of voice and voice-frequency data. Currently, it includes new services, such as the transmission of graphics information. 2. A form of telecommunication set up for the transmission of speech or, in some cases, other sounds. 3. The technology and manufacture of telephone equipment. 4. The transmission of sound between distant stations, especially by radio or telephone. Meaning "sound over distance," it refers to electronically transmitting the human voice. In the beginning, telephony dealt only with analog signals in the circuit-switched networks of the telephone companies. It later referred to a mix of analog and digital circuits, but still with the telephone industry. Starting in the 1990s, telephony began to embrace sending voice over IP (VoIP) networks, which is now deployed by common carriers, private enterprises and independent VoIP providers. 448
- 449. Telephoto - 1. Of or relating to a photographic lens or lens system used to produce a large image of a distant object. 2. Of or relating to an instrument that electrically transmits photographs. 3. Pertaining to pictures transmitted via a telecommunications system. Telephotograph - 1. A telephoto. 2. A photograph transmitted and reproduced over a distance. Telephotography - 1. The process or technique of photographing distant objects, using a telephoto lens on a camera. 2. The technique or process of transmitting charts, pictures, and photographs over a distance. Teleprinter - A typewriter-like terminal with a keyboard and built-in printer. It can be a desktop or portable unit. Teleprinters were quite common years ago as input terminals for computers, but have given way to the video screen. Teleprinter-like devices are still used in retail applications where receipts are necessary. Teleprinters were widely used starting with the very first computers. They lived well into the 1970s as a computer input device. Any keyboard and printing unit can be called a teleprinter. Paper tape was widely used on teleprinters to record incoming data. The reel of tape in this picture is on the lower left side of the unit. (Image courtesy of General Electric Company.) A teletypewriter that can only receive data and does not have a keyboard for transmission. Teleprocessing - The combining of telecommunications and computer operations interacting in the automatic processing, reception, and transmission of data and/or information. [JP 1-02] Note: Teleprocessing includes human-machine interface equipment. Teleran - An air-traffic control system in which the image of a ground-based radar unit is televised to aircraft in the vicinity so that pilots may see their positions in relation to other aircraft. Teletext - An electronic communications system in which printed information is broadcast by television signal to sets equipped with decoders. An international store-and-forward essentially error-free communications service that is defined by the CCITT (now the ITU-T), has a data signaling rate (DSR) of 2400 b/s over switched telephone networks, and has a communications protocol that supports the CCITT Group 4 facsimile service. Teletraining - Training that (a) in which usually live instruction is conveyed in real time via telecommunications facilities, (b) that may be accomplished on a point-to-point basis or on a point-to- multipoint basis, and (c) may assume many forms, such as a teleseminar, a teleconference, or an electronic classroom, usually including both audio and video. Synonyms distance learning, distance training, electronic classroom, virtual instruction. Teletype - A trademark used for a teletypewriter. Teletypewriter (TTY) - A printing telegraph instrument that has a signal-actuated mechanism for automatically printing received messages. An electromechanical typewriter that either transmits or receives messages coded in electrical signals carried by telegraph or telephone wires. Note 1: A TTY may have a keyboard similar to that of a typewriter for sending messages. Note 2: Radio circuits carrying TTY traffic are called "RTTY circuits" or "RATT circuits." Teletypewriter Control Unit (TCU) - A device that controls and coordinates operations between teletypewriters and message switching centers. 449
- 450. Teletypewriter Exchange Service (TWX) - A switched teletypewriter service in which suitably arranged teletypewriter stations are provided with lines to a central office for access to other such stations. Teletypewriter Signal Distortion - The shifting of signal pulse transitions from their proper positions relative to the beginning of the start pulse. Note: The magnitude of the distortion is expressed in percent of a perfect unit pulse length. Synonym start-stop TTY distortion. Television (TV) - A form of telecommunication for the transmission of transient images of fixed or moving objects.Note 1: The picture signal is usually accompanied by the sound signal. Note 2: In North America, TV signals are generated, transmitted, received, and displayed in accordance with the NTSC standard. Telex - 1. A communications system consisting of teletypewriters connected to a telephonic network (automatic exchanges) to send and receive signals. 2. A message sent or received by such a system. (TELetypewriter EXchange) An international, dial-up data communications service administered in the U.S. by AT&T, MCI and other providers. Developed in the U.S. and other European countries in the 1930s, it was the first data communications service that used typewriter-like terminals (teletypewriters). Prior to Telex, telegrams and cablegrams were the primary method for delivering a text message. By the 1960s, Telex became a worldwide, realtime, data communications service. Although diminishing each year, Telex is still used for commerce in more than 200 countries. Telex started out transmitting Baudot code at 50 bps. Although upgraded, it is still a low-speed data service. It was originally administered worldwide by various carriers and the local PTTs. Western Union handled the U.S., and in 1971, purchased and integrated the Bell System's TWX service. AT&T acquired Western Union's Telex service in 1991. Telex Machine - A character printer connected to a telegraph that operates like a typewriter Telnet - A program that allows Internet users to login to computers other than their host. Telnet also refers to the act of doing so. The TCP/IP standard network virtual terminal protocol that is used for remote terminal connection service and that allows a user at one site to interact with systems at other sites as if that user terminal were directly connected to computers at those sites. TEM - Abbreviation for transverse electric and magnetic mode. - A mode whose electric and magnetic field vectors are both normal to the direction of propagation. Note: The TEM mode is the most useful mode in a coaxial cable. TEMPEST - 1. [A] Short name referring to investigation, study, and control of compromising emanations from information systems (IS) equipment. 2. To shield against compromising emanations. Temporal Application - A video application requiring high temporal resolution, i.e., reduced jerkiness, possibly at the expense of reduced spatial resolution. Note: An example of temporal applications is the ability to accurately discern moving image features such as facial expressions and lip movements. Temporal Edge Noise - In a video display, that form of edge busyness that is characterized by time-varying sharpness at the edges of objects. Terminal - A device capable of sending, receiving, or sending and receiving information over a communications channel. 450
- 451. Terminal Access Controller (TAC) - A host computer that accepts terminal connections, usually from dial-up lines, and that allows the user to invoke Internet remote log-on procedures, such as Telnet. Terminal Adapter - An interfacing device employed at the "R" reference point in an ISDN environment that allows connection of a non-ISDN terminal at the physical layer to communicate with an ISDN network. Note: Typically, a terminal adapter will support standard RJ-11 telephone connection plugs for voice and RS-232C, V.35 and RS-449 interfaces for data. Terminal Data - Data maintained for each terminal including the current terminal location (and capabilities). Terminal Deregistration - The process by which a wireless terminal's previous location registration is canceled. Terminal Endpoint (TE) Functional Group - A functional group that includes functions broadly belonging to Layer 1 and higher layers of the ITU-T Recommendation X.200 Reference Model. Note 1: The functions of a TE functional group are performed on various types of equipment, or combinations of equipment, such as digital telephones, data terminal equipment, and/or integrated work stations. Note 2: Examples of TE functions are protocol-handling, maintenance, interface, and connection functions. Terminal Equipment - 1. Communications equipment at either end of a communications link, used to permit the stations involved to accomplish the mission for which the link was established. 2. In radio-relay systems, equipment used at points where data are inserted or derived, as distinct from equipment used only to relay a reconstituted signal. 3. Telephone and telegraph switchboards and other centrally located equipment at which communications circuits are terminated. 4. Equipment that originates or terminates signals at the specified rate. Terminal Identifier - A code identifying a specific terminal. Terminal Impedance - 1. The impedance as measured at the unloaded output terminals of transmission equipment or a line that is otherwise in normal operating condition. 2. The ratio of voltage to current at the output terminals of a device, including the connected load. Terminal Mobility - In commercial wireless networks, the ability of a terminal, while in motion, to access telecommunication services from different locations, and the capability of the network to identify and locate that terminal. Terminal Mobility Controller - A device that provides the control logic for terminal authentication, location management, alerting, and routing to radio personal terminal / radio terminations (RPT/RTs). Terminal Mobility Management - In personal communications service (PCS), (a) providing authentication of terminal information, (b) maintaining terminal location and capability information for each terminal, and (c) providing translation between terminal identification and location (routing address) for the completion of calls to terminals. Terminal Registration - The process of associating a terminal with a terminal registration area. Terminal Registration Area - A territory in which a wireless terminal is registered for terminal mobility. Terminal Service Profile (TSP) - Information that the service provider maintains for a given user to characterize the services offered by the network to that user. A TSP may be allocated to an interface or to a particular user equipment or a group of user equipment. 451
- 452. Terminal Type - The variety of terminal or the originator (e.g., dual-tone multifrequency (DTMF) phone, ISDN terminal). Terminating Endpoint - In a wideband packet node, the part of the node that receives packetized traffic, depacketizes it, and then plays it back as channelized traffic. Terminating Network Function - Of a UPT call, any network function associated with the termination of the call to the destination terminal. Termination - 1. The load connected to a transmission line, circuit, or device. Note: For a uniform transmission line, if the termination impedance is equal to the characteristic impedance of the line, wave reflections from the end of the line will be avoided. 2. In hollow metallic waveguides, the point at which energy propagating in the waveguide continues in a nonwaveguide propagation mode into a load. 3. An impedance, often resistive, that is connected to a transmission line or piece of equipment as a dummy load, for test purposes. Terminus - A device used to terminate, position, and hold an optical fiber within a connector. Ternary Signal - A signal that can assume, at any given instant, one of three significant conditions, such as power level, phase position, pulse duration, or frequency. Note: Examples of ternary signals are (a) a pulse that can have a positive, zero, or negative voltage value at any given instant, (b) a sine wave that can assume phases of 0°, 120°, or 240° relative to a clock pulse, and (c) a carrier wave that can assume any one of three different frequencies depending on three different modulation signal significant conditions. Terrestrial Broadcasting - A broadcast signal transmitted over-the-air to an antenna. Terrestrial Microwave Radio - Terrestrial microwave radio is a transmission systems consisting of at least two radio transmitter/receivers (transceivers) connected to high gain antennas (directional antennas which concentrate electromagnetic or radiowave energy in narrow beams) focused in pairs on each other. The operation is point-to-point, that is, communications are established between two and only two antennas (installations) with line-of-sight visibility. This can be contrasted to point-to- multipoint systems like broadcast radio or television. Terrestrial Radiocommunication - Any radiocommunication other than space radiocommunication or radio astronomy. Terrestrial Station - A station effecting terrestrial radiocommunication. In these [Radio] Regulations, unless otherwise stated, any station is a terrestrial station. Test and Validation - Physical measurements taken (a) to verify conclusions obtained from mathematical modeling and analysis or (b) for the purpose of developing mathematical models. Test Antenna - An antenna of known performance characteristics used in determining transmission characteristics of equipment and associated propagation paths. Test Key - Key intended for testing of COMSEC equipment or systems. Test Point - A point within a piece of equipment or an equipment string that provides access to signals for the purpose of fault isolation. 452
- 453. Test Tone - A tone sent at a predetermined level and frequency through a transmission system for test purposes, such as for facilitating measurements and for aligning gains and losses in the system. Text Format vs. HTML Format - Some Web applications, such as e-mail or Web pages, can either be viewed in Text or HTML formats. Text formats generally display only the words (text) in an e-mail or on a Web page and not graphics, such as artwork or photos. HTML format allows display of both text and graphics. TGM - Abbreviation for trunk group multiplexer. THD - Abbreviation for total harmonic distortion. - Of a signal, the ratio of (a) the sum of the powers of all harmonic frequencies above the fundamental frequency to (b) the power of the fundamental frequency. Note 1: The THD is usually expressed in dB. Note 2: Measurements for calculating the THD are made at the output of a device under specified conditions. Thermal Noise: The noise generated by thermal agitation of electrons in a conductor. The noise power, P, in watts, is given by P = kT f, where k is Boltzmann's constant in joules per kelvin, T is the conductor temperature in kelvins, and f is the bandwidth in hertz. Note 1: Thermal noise power, per hertz, is equal throughout the frequency spectrum, depending only on k and T. Note 2: For the general case, the above definition may be held to apply to charge carriers in any type of conducting medium. Synonym Johnson noise. Thermal Radiation - 1. Electromagnetic radiations emitted from a heat or light source as a consequence of its temperature; it consists essentially of ultraviolet, visible, and infrared radiations. [JP1] 2. The heat and light produced by a nuclear explosion. Thermodynamic Temperature - A measure, in kelvins (K), proportional to the thermal energy of a given body at equilibrium. Note 1: A temperature of 0 K is called "absolute zero," and coincides with the minimum molecular activity (i.e., thermal energy) of matter. Note 2: Thermodynamic temperature was formerly called "absolute temperature." Note 3: In practice, the International Temperature Scale of 1990 (ITS-90) serves as the basis for high-accuracy temperature measurements in science and technology. The Stick - Business quality Single Line Automatic Call Processor. Line sharing device for small or home business as well large corporations and organizations. Automatically routes calls to the assigned device. The Stick allows up to three telecommunication devices plus an answering machine to share one single phone line. This is our most popular fax switch. For more information: The Stick brochure , The Stick online manual. THF - Abbreviation for tremendously high frequency. See electromagnetic spectrum. Thin Client (computing) - A server-centric computing model in which the application software, data, and CPU power resides on a network server rather than on the client computer (s). Note 1: This computing philosophy allows administrators to purchase one relatively powerful and expensive server and be confident that any external terminal, regardless of its power or sophistication, can run applications on the server. Most "shopping" Web pages, for example, are thin-client applications (i.e., the client needs nothing more than a browser and a connection to the network to be able to search the "shopping" page and to order products). Local area networks can use thin-client modeling to install only one copy of necessary programs onto the main server for many clients on the network to use. Note 2: Server software is required to interface clients with the software on the server. Synonyms Internet appliance (computing), Internet box (computing), network computer. 453
- 454. Thin-Client Software - Computer programs that reside on a server and react to external requests from a client. Note: This is in contrast to software that is installed on each client computer in a network. Software that resides only on a single server can be maintained and updated with minimal effort. Thin-Film Laser - A laser that is constructed by thin-film deposition techniques on a substrate for use as a light source, is usually used to drive thin-film optical waveguides, and may be used in integrated optical circuits. Thin-Film Optical Modulator - A modulator that consists of multilayered films of material of different optical characteristics, is capable of modulating transmitted light by using electro-optic, electro-acoustic, or magneto-optic effects to obtain signal modulation, and may be used as a component in integrated optical circuits. Thin-Film Optical Multiplexer - A multiplexer that consists of multilayered films of material of different optical characteristics, is capable of multiplexing transmitted light by using electro-optic, electro-acoustic, or magneto-optic effects to obtain signal multiplexing, and may be used as a component in integrated optical circuits. Thin-Film Optical Switch - A switch that consists of multilayered films of material of different optical characteristics, that is capable of switching transmitted light by using electro-optic, electro-acoustic, or magneto-optic effects to obtain signal switching, and is usually used as a component in integrated optical circuits. Note: Thin-film optical switches may support only one propagation mode. Thin-Film Optical Waveguide - A slab-dielectric waveguide that consists of multilayered films of material of different optical characteristics, is capable of guiding an optical signal, and may be used as a component in integrated optical circuits. Third-Order Intercept Point - A point (a) that is an extrapolated convergence--not directly measurable--of intermodulation distortion products in the desired output and (b) that indicates how well a receiver performs in the presence of strong nearby signals. Note: Determination of a third-order intercept point is accomplished by using two test frequencies that fall within the first intermediate frequency mixer passband. Usually, the test frequencies are about 20 to 30 kHz apart. Third Window - Of silica-based optical fibers, the transmission window at approximately 1.55 m. Note: The third window is the minimum-loss window in silica-based fibers. Thread - In computer conferencing, a set of sequential messages containing closely related information. Threat - 1. Capabilities, intentions, and attack methods of adversaries to exploit, or any circumstance or event with the potential to cause harm to, information or an information system. [NIS] 2. Any circumstance or event with the potential to harm an information system (IS) through unauthorized access, destruction, disclosure, modification of data, and/or denial of service. Threat Analysis - Examination of information to identify the elements comprising a threat. Threat Assessment - [A] formal description and evaluation of threat to an information system (IS). Three-Way Calling - A switching system service feature that permits users to add a third party to an established connection at a different number during a call, without the assistance of an attendant or operator. 454
- 455. Allows you to speak to two separate people at the same time. To use, start by placing a call to the first person. Once that person is on the line, press the switch hook or “flash” button briefly. This places the first party on hold and gives you a dial tone to reach the second person. Then dial the second number. Once the second person answers press the switch hook to connect everyone. Threshold - 1. The minimum value of a signal that can be detected by the system or sensor under consideration. 2. A value used to denote predetermined levels, such as those pertaining to volume of message storage, i.e., in-transit storage or queue storage, used in a message switching center. 3. The minimum value of the parameter used to activate a device. 4. The minimum value a stimulus may have to create a desired effect. Threshold Current - In a laser, the driving current corresponding to lasing threshold. Threshold Extension - See FM threshold extension. - A change in the value of the FM threshold of a receiver. Note: FM threshold extension may be obtained by decreasing the operational bandwidth, thus decreasing the received noise power and allowing the threshold of the desired signal to occur at a lower signal input level. Threshold Frequency - In opto-electronics, the frequency of incident radiant energy below which there is no photo-emissive effect. Through Group - A group of 12 voice-frequency channels transmitted as a unit through a carrier system. Through-Group Equipment - In carrier telephone transmission, equipment that accepts the signal from a group receiver output and attenuates it to the proper signal level for insertion, without frequency translation, at the input of a group transmitter. Throughput - 1. The number of bits, characters, or blocks passing through a data communication system, or portion of that system. Note 1: Throughput may vary greatly from its theoretical maximum. Note 2: Throughput is expressed in data units per period of time; e.g., in the DDN, as blocks per second. 2. The maximum capacity of a communications channel or system. 3. A measure of the amount of work performed by a system over a period of time, e.g., the number of jobs per day. Through Supergroup - An aggregate of 60 voice-frequency channels, i.e., five groups, transmitted as a unit through a carrier system. Through-Supergroup Equipment - In carrier telephone transmission, equipment that accepts the multiplexed signal from a supergroup receiver output, amplifies it without frequency translation, and provides the proper signal level to the input of a supergroup transmitter equipment. THz - Abbreviation for terahertz. See electromagnetic spectrum. TIA - Abbreviation for Telecommunications Industry Association. Ticket - In computer security, a representation of one or more access rights that a possessor has to an object. Note: The ticket represents an access permission. Ticketed Call - A call for which a record is made of certain facts concerning the call, such as the time it was placed, the duration, the call originator, call destination numbers, and, where applicable, the attendant's name or initials. 455
- 456. Ticket-Oriented - [In security, a] computer protection system in which each subject maintains a list of unforgeable bit patterns called tickets, one for each object a subject is authorized to access. TIE - Acronym for time interval error. - 1. The time difference between a real clock and an ideal uniform time scale, after a time interval following perfect synchronization between the clock and the scale. 2. The variation in time delay of a given timing signal with respect to an ideal timing signal over a particular time period. Tie Trunk - A telephone line that directly connects two private branch exchanges (PBXs). TIFF (Tag Image File Format) - A common format for exchanging raster graphics (bitmap) images between application programs, including those used for scanner images. A TIFF file can be identified as a file with a ".tiff" or ".tif" file name suffix. The TIFF format was developed in 1986 by an industry committee chaired by the Aldus Corporation (now part of Adobe Software). Microsoft and Hewlett-Packard were among the contributors to the format. One of the most common graphic image formats, TIFF files are commonly used in desktop publishing, faxing, 3-D applications, and medical imaging applications. TIFF files can be in any of several classes, including gray scale, color palette, or RGB full color, and can include files with JPEG, LZW, or CCITT Group 4 standard run-length image compression. Time - 1. An epoch, i.e., the designation of an instant on a selected time scale, astronomical or atomic. It is used in the sense of time of day [JP1] 2. On a time scale, the interval between two events, or the duration of an event. 3. An apparently irreversible continuum of ordered events. 4. That which characterizes, or is characterized by, the observed and apparently irreversible continuum of ordered events. Time Ambiguity - A situation in which more than one different time or time measurement can be obtained under the stated conditions. Time-Assignment Speech Interpolation (TASI) - An analog technique used on certain long transmission links to increase voice-transmission capacity. Note: TASI works by switching additional users onto any channel temporarily idled because an original user has stopped speaking. When the original user resumes speaking, that user will, in turn, be switched to any channel that happens to be idle. Time Block - An arbitrary grouping of several consecutive hours of a day, usually for a particular season, during which it is assumed that propagation data are statistically homogeneous. Time Bomb - 1. In COMSEC, a logic bomb to be activated at a predetermined time. 2. [A] resident computer program that triggers an unauthorized act at a predefined time. Time Code - A code used for the transmission and identification of time signals. Note: In telecommunications systems, the format of the time code must be specified. Time Code Ambiguity - The shortest interval between successive repetitions of the same time code value. Note: For example, in a time code in which year-of-century is the most slowly changing field, the time code ambiguity would be 100 years; for a digital clock in which hours and minutes up to a maximum of 11:59 are displayed, the time code ambiguity would be 12 hours. Time Code Resolution - The interval between two successive time code states. Note: Time code resolution is determined by the most rapidly changing symbol position within the time code. For example, for a digital clock that displays hours and minutes, the time code resolution would be 1 minute. 456
- 457. Time-Consistent Busy Hour (TCBH) - The identical hour each day during which, over a number of days, the highest average traffic is measured. Time Diversity - Transmission in which signals representing the same information are sent over the same channel at different times. Note: Time diversity is often used over systems subject to burst error conditions, and at intervals adjusted to be longer than an error burst. Time-Division Multiple Access (TDMA) - 1. A communications technique that uses a common channel (multipoint or broadcast) for communications among multiple users by allocating unique time slots to different users. Note: TDMA is used extensively in satellite systems, local area networks, physical security systems, and combat-net radio systems. 2. A multiple access technique whereby users share a transmission medium by being assigned and using (one at a time) for a limited number of time division multiplexed channels; implies that several transmitters use one channel for sending several bit streams. Time-Division Multiplexing (TDM) - 1. Digital multiplexing in which two or more apparently simultaneous channels are derived from a given frequency spectrum, i.e., bit stream, by interleaving pulses representing bits from different channels. Note: Successive pulses represent bits from successive channels, e.g., voice channels in a T1 system. 2. A multiplexing technique whereby two or more channels are derived from a transmission mediuim by dividing access to the medium into sequential intervals. Each channel has access to the entire bandwidth of the medium during its interval. This implies that one transmitter uses one channel to send several bit streams of information. Time Division Switch - A time division switch is a switch that implements the switch matrix using the TDM process, in a time-slot interchange (TSI) arrangement (usually denoted by T in combined time and space division switches). Time-Division Switching - Switching of time-division multiplexed (TDM) channels by shifting bits between time slots in a TDM frame. Time-Domain Reflectometer (TDR) - An electronic instrument used to characterize and locate faults in metallic cables (e.g., twisted pair, coax). Note 1: A TDR transmits a fast rise time pulse along the conductor. The resulting reflected pulse is measured at the input as a function of time and displayed on the instrument or plotted, as a function of cable length. Note 2: A TDR may be used to verify cable impedance characteristics, splice and connector location and associated losses, and estimate cable lengths. Time-Gated Direct-Sequence Spread Spectrum - Direct-sequence spread spectrum where the transmitter is on only for a short fraction of a time interval. The on-time can be periodic or random within a time interval. Time Guard Band - A time interval left vacant on a channel to provide a margin of safety against intersymbol interference in the time domain between sequential operations, such as detection, integration, differentiation, transmission, encoding, decoding, or switching. Time Instability - The fluctuation of the time interval error caused by the instability of a real clock. Time Interval Error (TIE) - 1. The time difference between a real clock and an ideal uniform time scale, after a time interval following perfect synchronization between the clock and the scale. 2. The variation in time delay of a given timing signal with respect to an ideal timing signal over a particular time period. Time Jitter - Short-term variation or instability in the duration of a specified time interval. 457
- 458. Time Marker - A reference signal, often repeated periodically, enabling the correlation of specific events with a time scale, such as for establishing synchronization. Time of Occurrence - The date of an event, i.e., the instant an event occurs, with reference to a specified time scale. Time-Out - 1. A network parameter related to an enforced event designed to occur at the conclusion of a predetermined elapsed time. 2. A specified period of time that will be allowed to elapse in a system before a specified event is to take place, unless another specified event occurs first; in either case, the period is terminated when either event takes place. Note: A time-out condition can be canceled by the receipt of an appropriate time-out cancellation signal. 3. An event that occurs at the end of a predetermined period of time that began at the occurrence of another specified event. The time-out can be prevented by an appropriate signal. Time Scale - 1. A time measuring system defined to relate the passage of temporal events since a selected epoch. Note: The internationally recognized time interval is the second. Time scales are graduated in intervals such as seconds, minutes, hours, days, and years, and in fractions of a second, such as milliseconds, nanoseconds, and picoseconds. 2. Time coordinates placed on the abscissa (x-axis) of Cartesian-coordinate graphs used for depicting waveforms and similar phenomena. Time Scale Factor - A multiplier used to transform the real time of occurrence of an event or a problem into system time, such as that of a telecommunications system or a computer. Time Server - The server maintaining and distributing the correct date and time over a computer network. Note: There is usually a special time-distribution protocol. Time-Sharing - 1. The interleaving of two or more independent processes on one functional unit. 2. Pertaining to the interleaved use of computer time that enables two or more users to execute programs concurrently. Time Slot - 1. Period of time during which certain activities are governed by specific regulations. [JP1] 2. A time interval that can be recognized and uniquely defined. Time Stamp (TS) - 1. A data field in which is recorded (typically with a resolution of 1 millisecond) the cumulative variable queuing delay experienced by a packet in traversing the network. [After T1.509-1995] 2. With respect to a recorded network event, a data field in which is recorded the time (time of day or other instant of elapsed time) at which the event took place. Time Standard - A stable device that emits signals at equal intervals such that their count may be used as a clock. Time Tick - A time mark output of a clock system. Time-Variant Value - In cryptography, a value that changes with each transaction or with each message value. Timing Jitter - The short-term variations of the significant instants of a digital signal from their ideal positions in time. Here short term implies phase oscillations of frequency greater than or equal to 10 Hz. Timing jitter may lead to crosstalk and/or distortion of the original analog signal and is a potential source of slips at the input ports of digital switches. It may also cause slips and resultant errors in asynchronous digital multiplexes. 458
- 459. Timing Recovery - The derivation of a timing signal from a received signal. Timing Signal - 1. The output of a clock. 2. A signal used to synchronize interconnected equipment. Timing Tracking Accuracy - A measure of the ability of a timing synchronization system to minimize the clock difference between a master clock and any slaved clock. T-Interface - For basic rate access in an Integrated Services Digital Network (ISDN) environment, a user-to- network interface reference point that (a) is characterized by a four-wire, 144-kb/s (2B+D) user rate, (b) accommodates the link access and transport layer function in the ISDN architecture, (c) is located at the user premises, (d) is distance sensitive to the servicing network terminating equipment, and (e) functions in a manner analogous to that of the Channel Service Units (CSUs) and the Data Service Units (DSUs). Tip and Ring - An archaic term that gets its meaning from the old switchboard plugs. Each plug had a tip connector and a ring connector. Now, tip and ring refer to the two conductors that make up a single telephone line. TLM - Abbreviation for telemetry. TM - Abbreviation for transverse magnetic. See transverse magnetic mode. TOD - Abbreviation for time of day. See time of occurrence. Token - In certain local-area-network protocols, a group of bits that serves as a symbol of authority, is passed among data stations, and is used to indicate the station that is temporarily in control of the transmission medium. Token-Bus Network - A bus network in which a token passing procedure is used. Token Passing - A network access procedure in which a token passes from station to station and the only station allowed to transmit information is the station with the token. Token Passing Bus LAN (IEEE 802.4) - A token passing bus LAN is a LAN using a deterministic access mechanism and topology in which all stations actively attached to the bus "listen" for a broadcast token or supervisory frame. Stations wishing to transmit must receive the token before doing so; however the next logical station to transmit may not be the next physical station on the bus. Access is controlled by pre- assigned priority algorithms. Token Passing Ring LAN (IEEE 802.5) - A token passing ring LAN is a LAN using a deterministic access mechanism and topology, in which a supervisory frame (or token) is passed from station to adjacent station sequentially. Stations wishing to transmit must wait for the "free" token to arrive before transmitting data. In a token ring LAN the start and end points of the medium are physically connected, leading to a ring topology. Token Ring Adapter - A network interface card (NIC) designed to attach a client workstation to a token ring computer network and operate as a token-passing interface. Token-Ring Network - See network topology. Toll Call - A call to any location outside the local service area. Otherwise known as a long distance call. 459
- 460. Tolerance - The permissible range of variation of some characteristic from its nominal value. Tolerance Field - 1. The region between two curves, such as circles or rectangles, used to specify the tolerance on component size and geometry. 2. Pertaining to the cross section of an optical fiber, when used to specify the respective diameters and ovalities of, and concentricity error between, the core and cladding; two concentric annular regions which define the core-cladding boundary and the cladding outer boundary. Note: Dimensions are usually expressed in micrometers ( m). The larger annular region is defined by concentric circles of diameter [D C+ D C] and [D C- D C], where D C is the nominal diameter of the cladding and D C is the cladding diameter tolerance. The smaller annular region is defined by concentric circles of diameter [D c+ D c] and [D c- D c], where D c is the nominal diameter of the core and D c is the core diameter tolerance. When the core and cladding boundaries of the cross section of the fiber in question fall entirely within their respective defined areas, the fiber meets the specification. 3. Of the cross section of a given optical fiber, when used to characterize the respective diameters and ovalities of the core and cladding, and the concentricity error between the core and cladding; two such pairs of concentric circles, the concentric pairs not necessarily being concentric with one another. Note 1: One pair of concentric circles characterizes the core, and the other pair, the cladding. The cladding ovality is characterized by the smallest circle that circumscribes its cross section, and the largest circle that fits within its cross section. (The cross section is assumed, to a first approximation, to be elliptical in shape, so these defining circles will be concentric.) The core cross section is characterized by an analogous pair of circles, also concentric with one another, but not necessarily with those defining the cladding cross section. Note 2: The distance between the centers of the two concentric pairs (core pair and cladding pair) defines the offset between the core and cladding (the " core-cladding offset," also called the "concentricity error"). The width of the annulus defined by the cladding circles determines the ovality of the cladding, and the width of the annulus defined by the core determines the ovality of the core. Toll Call - See long-distance call. Toll Center - An office (or group of offices) within a city which generally handles the originating and incoming toll traffic for that city to or from other toll center areas and which handles through switched traffic. The toll center normally handles the inward toll traffic for its tributary exchanges and, in general, either handles the outward traffic originating at its tributaries or serves as the outlet to interexchange circuits for outward traffic ticketed and timed at its tributaries. Toll centers are listed as such in the Toll Rate and Route Guide. Toll Center Area - The areas served by a toll center, including the toll center city and the communities served by tributaries of the toll center. Toll Center Toll Office - A toll office (as contrasted to a local office) in a toll center city. toll circuit - A general term applied to interexchange trunks used primarily for toll traffic. Toll Connecting Trunk - A general classification of trunks carrying toll traffic and ordinarily extending between a local office and a toll office, except trunks classified as tributary circuits. Examples of toll connecting trunks include toll switching trunks, recording trunks, and recording-completing trunks. toll diversion - A system service feature by which users are denied the ability to place toll calls without the assistance of an attendant. Toll Office - A central office used primarily for supervising and switching toll traffic. Toll Quality - The voice quality resulting from the use of a nominal 4-kHz telephone channel. Note: Toll quality may be quantized in terms of a specified bit error ratio. 460
- 461. Toll Switching Trunk - A trunk connecting one or more end offices to a toll center as the first stage of concentration for intertoll traffic. Note: Operator assistance or participation may be an optional function. In U.S. common carrier telephony service, a toll center designated "Class 4C" is an office where assistance in completing incoming calls is provided in addition to other traffic; a toll center designated "Class 4P" is an office where operators handle only outbound calls, or where switching is performed without operator assistance. Tone - An electrically generated single-frequency sinusoidal oscillation. Tone Detection Device - Tone detection devices "listen" for one of three things: 1.)CNG tones that automatically route the call to the fax if they are present, DTMF tones (DUAL TONE MULTIFREQUENCY) are commonly called "touch-tones" Modem calls are routed by DTMF placed in the dialing string from the connecting modem software. These extra digits are known as the security access codes (SAC)s. 3.) No tones - when there are no tones present, the device sends the call to the default device which is usually voice (phones, phone system, or answering machine). Tone detection devices require no additional services from the phone company to operate. Tones - • AUTO FAX TONE (CNG ) - This tone is produced by virtually all FAX machines when it dials the receiving FAX machine’s number from memory. Older FAX machines and some current models that do not have speed-dial memory will not produce CNG. CNG is a medium-pitch tone (1100 Hz) that last 1/2 second and repeats every 3-1/2 seconds. A FAX machine will produce CNG for about 45 seconds after it dials the receiving FAX number. • CARRIER AND DATA - very loud screech that is produced when the FAX machines or MODEMs are actually transferring data. Unlike CNG or DTMF, carrier and data will be constantly changing. • DTMF (DUAL TONE MULTIFREQUENCY) - This tone is commonly called "touch-tone". Not all push- button phones are capable of producing the DTMF tones. • RINGBACK - A tone produced by telephone processing equipment that signals to the caller that the called party is being rung. Your ATX-300 produces a ringback tone to the caller when ringing a device. Tone Diversity - In a voice frequency telegraph (VFTG) transmission system, the use of two channels to carry the same information. Note: Tone diversity is usually achieved by twinning the channels of a 16-channel VFTG to obtain 8 channels with dual diversity. Tone Signaling - See dual-tone multifrequency signaling. Tool - Synonym utility program. Top-Level Domain Name - In Internet addressing, a domain name identifying the highest hierarchical level in the geographical or organizational structure of the addressing system in Internet. Note: In Internet, the top- level domain name is either an ISO country name, or an English abbreviation such as "com," "edu," "gov," "mil," "net," or "org." Topography - The specification and arrangement in physical locations of actual communication and information system components which implement the topology. Topology - See network topology. 461
- 462. Torn-Tape Relay - An antiquated tape relay system in which the perforated tape is manually transferred by an operator to the appropriate outgoing transmitter. Total Channel Noise - The sum of random noise, intermodulation noise, and crosstalk. Note: Total channel noise does not include impulse noise because different techniques are required for its measurement. Total Harmonic Distortion (THD) - Of a signal, the ratio of (a) the sum of the powers of all harmonic frequencies above the fundamental frequency to (b) the power of the fundamental frequency. Note 1: The THD is usually expressed in dB. Note 2: Measurements for calculating the THD are made at the output of a device under specified conditions. Total Internal Reflection - The reflection that occurs when light, in a higher refractive-index medium, strikes an interface, with a medium with a lower refractive index, at an angle of incidence (with respect to the normal) greater than the critical angle. See Snell's law Total Line Length - In facsimile, the spot speed divided by the scanning line frequency. Note: The total line length may be greater than the length of the available line. Touchpad - A pad that is electrically sensitive to touch, often used as the pointing device in laptops. You can also tap on it for clicks, but some people find that annoying if they bump the pad while typing. Touch Panel - See touch-sensitive. Touch Screen - See touch-sensitive. Touch-Sensitive - Pertaining to a device that allows a user to interact with a computer system by touching an area on the surface of the device with a finger, pencil, or other object; for example, a touch-sensitive keypad or screen. Touch Tone Dialing - See dual-tone multifrequency (DTMF) signaling. TP - transaction processing. Trace Packet - In a packet-switching network, a unique packet that causes a report of each stage of its progress to be sent to the network control center from each visited system element. Trace Program - A computer program that performs a check on another computer program by exhibiting the sequence in which the instructions are executed and usually the results of executing the instructions. Track - On a data medium, a path associated with a single read / write head position as data move past the head. Trackball - A ball that can be rotated about its center and that is used as an input device, e.g., to position a cursor. Synonym control ball. Track Density - The number of tracks per unit length, measured in a direction perpendicular to the direction in which the tracks are read. Tracking Error - The deviation of a dependent variable with respect to a reference function. 462
- 463. Tracking Mode - An operational mode during which a system is operating within specified movement limits relative to a reference. Tracking Phase - See tracking mode. Traffic - 1. The information moved over a communication channel. 2. A quantitative measurement of the total messages and their length, expressed in CCS or other units, during a specified period of time. Traffic Analysis - 1. In a communications system, the analysis of traffic rates, volumes, densities, capacities, and patterns specifically for system performance improvement. 2. [The] study of communications characteristics external to the text. 3. The analysis of the communications-electronic environment for use in the design, development, and operation of new communications systems. 4. In cryptology, the inference of information from observation and analysis of the presence, absence, amount, direction, and frequency of the traffic flow. 5. [The] Study of communications patterns. Traffic Capacity - The maximum traffic per unit of time that a given telecommunications system, subsystem, or device can carry under specified conditions. Traffic Encryption Key (TEK) - [A] key used to encrypt plain text or to superencrypt previously encrypted text and/or to decrypt cipher text. Traffic Engineering - The determination of the numbers and kinds of circuits and quantities of related terminating and switching equipment required to meet anticipated traffic loads throughout a communications system. Traffic-Flow Security - 1. The protection resulting from features, inherent in some crypto-equipment, that conceal the presence of valid messages on a communications circuit; normally achieved by causing the circuit to appear busy at all times. 2. Measures used to conceal the presence of valid messages in an on-line cryptosystem or secure communications system. Note: Encryption of sending and receiving addresses and causing the circuit to appear busy at all times by sending dummy traffic are two methods of traffic-flow security. A more common method is to send a continuous encrypted signal, whether or not traffic is being transmitted. Traffic Intensity - A measure of the average occupancy of a facility during a specified period of time, normally a busy hour, measured in traffic units (erlangs) and defined as the ratio of the time during which a facility is occupied (continuously or cumulatively) to the time this facility is available for occupancy. Note: A traffic intensity of one traffic unit (one erlang) means continuous occupancy of a facility during the time period under consideration, regardless of whether or not information is transmitted. Synonym call intensity. Traffic Load - The total traffic carried by a trunk or trunk group during a specified time interval. Traffic Monitor - In a communications network, a service feature that provides basic data on the amount and type of traffic handled by the network. Traffic Over First Routes - A term applied to the routing of traffic and denoting routing via principal route for traffic between any two points as distinguished from alternate routes for such traffic. Traffic Overflow - 1. That condition wherein the traffic offered to a portion of a communication system exceeds its capacity and the excess may be blocked or may be provided with alternate routing. 2. The excess traffic itself. 463
- 464. Traffic Padding - 1. In COMSEC, a countermeasure that generates spurious data in transmission media to make traffic analysis or decryption more difficult. 2. In reliability techniques, see pilot-make-busy circuit. 3. Generation of spurious communications or data units to disguise the amount of real data units being sent. Traffic Register - See register. Traffic Service Position System (TSPS) - A stored program electronic system associated with one or more toll switching systems which provides centralized traffic service position functions for several local offices at one location. Traffic Unit - Synonym erlang. Traffic Usage Recorder - A device for measuring and recording the amount of telephone traffic carried by a group, or several groups, of switches or trunks. Trailer - Protocol control information located at the end of a protocol data unit (PDU). Tranquility - [The] property whereby the security level of an object cannot change while the object is being processed by an information system (IS). Transaction Capabilities (TC) - 1. A means based upon the OSI –Reference Model to support applications in telecommunications networks. 2. Protocol functions and procedures that control non-circuit related information exchange among signaling points in SS7 networks. It provides a general purpose approach to the introduction of new services within a network as well as a framework for service architecture for providing internetwork services. Transaction capabilities includes the application layer protocol called transaction capabilities application part (TCAP) as well as the supporting Presentation, Session, and Transport layers called the application service part (ASP). Transaction Integrity - The degree to which a transaction flowing through a network reaches its intended destination without impairment of its function, content or meaning. Transaction-Oriented Application - Applications that exchange messages that are time-critical, bursty, and often limited in length, to perform an indivisible or elemental unit of work for OAM&P (operations, administration, maintenance, and provisioning) applications. Transceiver - 1. A device that performs, within one chassis, both transmitting and receiving functions. 2. In military communications, the combination of transmitting and receiving equipment that (a) is in a common housing, (b) usually is designed for portable or mobile use, (c) uses common circuit components for both transmitting and receiving, and (d) provides half-duplex operation. Transcoding - The direct digital-to-digital conversion from one encoding scheme, such as voice LPC-10, to a different encoding scheme without returning the signals to analog form. Note: The transcoded signals, i.e., the digital representations of analog signals may be any digital representation of any analog signal, such as voice, facsimile, or quasi-analog signals. Transcoding Gain - The factor by which the bit rate of a 64-kb/s channel is reduced when transcoding is used, e.g., when a transcoder conforming to ANSI T1.303 (i.e., ADPCM 32-kb/s) is used, the transcoding gain will equal 2. Transcoding gain equals 1 when no transcoding is used. Transducer - A device for converting energy from one form to another for the purpose of measurement of a physical quantity or for information transfer. 464
- 465. TRANSEC - Abbreviation for transmission security. See communications security. Transfer - To send information from one location and to receive it at another. Transfer Allowed (TFA) - A procedure included in the signaling route management (functionality) that is used to inform a signaling point that a signaling route to a specific destination has become available. Transfer Capacity - The maximum sustainable rate of information transfer. Transfer Characteristics - Those intrinsic parameters of a system, subsystem, or equipment which, when applied to the input of the system, subsystem, or equipment, will fully describe its output. Transfer Controlled (TFC) - A procedure included in the signaling route management (functionality) that is used to inform a signaling point of congestion status of a signaling route. Transfer Function - 1. A mathematical statement that describes the transfer characteristics of a system, subsystem, or equipment. 2. The relationship between the input and the output of a system, subsystem, or equipment in terms of the transfer characteristics. Note 1: When the transfer function operates on the input, the output is obtained. Given any two of these three entities, the third can be obtained. Note 2: Examples of simple transfer functions are voltage gains, reflection coefficients, transmission coefficients, and efficiency ratios. An example of a complex transfer function is envelope delay distortion. Note 3: For a negative feedback circuit, the transfer function, T, is given by where e o is the output, e i is the input, G is the forward gain, and H is the backward gain, i.e., the fraction of the output that is fed back and combined with the input in a subtracter. 3. Of an optical fiber, the complex mathematical function that expresses the ratio of the variation, as a function of modulation frequency, of the instantaneous power of the optical signal at the output of the fiber, to the instantaneous power of the optical signal that is launched into the fiber. Note: The optical detectors used in communication applications are square-law devices. Their output current is proportional to the input optical power. Because electrical power is proportional to current, when the optical power input drops by one-half (3 dB), the electrical power at the output of the detector drops by three- quarters (6 dB). Transfer Mode - In an integrated services digital network, (ISDN), a method of transmitting, multiplexing, and switching. Transfer Prohibited (TFP) - A procedure included in the signaling route management (functionality) that is used to inform a signaling point of the unavailability of a signaling route. Transfer Rate - See data transfer rate. - The rate at which data is transferred in some amount of bits per second. Transfer Restricted (TFR) - A procedure included in the signaling route management (functionality) that is used to inform a signaling point of the restriction of a signaling route. Transfer Syntax -That concrete syntax used in the transfer of data between open systems. Transient - See dynamic variation. Transistor -An electronic device that acts like an electrically activated switch but has no moving parts, so it can switch millions of times per second. 465
- 466. Transit Delay - Between two given points in an integrated services digital network (ISDN), the time between the moment that the first bit of a data unit, such as a frame or block, passes the first given point and the moment that bit passes the second given point, plus the transmission time of the data unit. Note: Transit delay is defined only between pairs of boundaries. Transit delay of a FPDU states at the time t1 at which the first bit of the FPDU crosses the first boundary, and ends at the time t2 at which the last bit of the FPDU crosses the second boundary. Transit delay = t2-t1. Transit Network Identification - A network service feature that specifies the sequence of networks used to establish or partially establish a virtual circuit. Transit Network Section - A network section between two internet circuit sections. Transit Node - A node that interfaces with other nodes, and does not directly interface with customer equipment. Transit Time - Synonym phase delay. Transition - In a signal, the changing from one significant condition to another. Note: Examples of transitions are the changing from one voltage level to another in a data stream, the shifting from one phase position to another in phase-shift keying, and the translation from one frequency to another in frequency-shift keying. Transition Frequency - The frequency associated with the difference between two discrete energy levels in an atomic system, Note: If a transition from E 2 to E 1 occurs, a photon with frequency f 2,1 is likely to be emitted. If the atomic system is at energy level E 1, and a photon of frequency f 2,1 is absorbed, the energy level will be raised to E 2. Transition Zone - Synonym intermediate-field region. Translate - In cryptography, the process of offset decrypting a key or set of keys using a transportation key shared with one center and then offset encrypting the same key or keys under a transportation key shared with a different center. Translating Program - Synonym translator. Translation Signaling Point (TSP) - A signaling point that performs SCCP (signal connection control part) global title translation. It is also known as SCCP Relay Node. The translation performed may be intermediate, in which case the TSP is referred to as "intermediate translation signaling point" (ITSP), or final, in which case the TSP is referred to as "final translation signaling point" Translator - 1. A device that converts information from one system of representation into equivalent information in another system of representation. Note: An example of a translator in telephony is the device that converts dialed digits into call-routing information. 2. A computer program that translates from one language into another language and in particular from one programming language into another programming language. Synonym translating program. 3. In FM and TV broadcasting, a repeater station that receives a primary station's signal, amplifies it, shifts it in frequency, and rebroadcasts it. 4. A device that converts one frequency to another. Transliterate - To convert the characters of one alphabet to the corresponding characters of another alphabet. 466
- 467. Transmission - 1. The dispatching, for reception elsewhere, of a signal, message, or other form of information. 2. The propagation of a signal, message, or other form of information by any means, such as by telegraph, telephone, radio, television, or facsimile via any medium, such as wire, coaxial cable, microwave, optical fiber, or radio frequency. 3. In communications systems, a series of data units, such as blocks, messages, or frames. 4. The transfer of electrical power from one location to another via conductors. Transmission Control Protocol / Internet Protocol - Two interrelated protocols that are part of the Internet protocol suite. Note 1: TCP operates on the OSI Transport Layer and breaks data into packets. IP operates on the OSI Network Layer and routes packets. Note 2: TCP/IP was originally developed by the U.S. Department of Defense. Transmission Line - The material medium or structure that forms all or part of a path from one place to another for directing the transmission of energy, such as electric currents, magnetic fields, acoustic waves, or electromagnetic waves. Note: Examples of transmission lines include wires, optical fibers, coaxial cables, rectangular closed waveguides, and dielectric slabs. Transmission Security (TRANSEC) - 1. See communications security. 2. [A] Component of COMSEC resulting from the application of measures designed to protect transmissions from interception and exploitation by means other than cryptanalysis. Transmission Block - 1. A group of bits or characters transmitted as a unit and usually containing an encoding procedure for error control purposes. 2. In data transmission, a group of records sent, processed, or recorded as a unit. Note: A transmission block is usually terminated by an end-of-block character (EOB), end- of-transmission-block character (ETB), or end-of-text character (EOT or ETX). Transmission Buffer - Storage (viz., buffer storage) in the signaling link control for signal units not yet transmitted. Transmission Channel - See channel. Transmission Coefficient - 1. The ratio of the transmitted field strength to the incident field strength of an electromagnetic wave when it is incident upon an interface surface between media with two different refractive indices. 2. In a transmission line, the ratio of the amplitude of the complex transmitted wave to that of the incident wave at a discontinuity in the line. 3. The probability that a portion of a communications system, such as a line, circuit, channel or trunk, will meet specified performance criteria. Note: The value of the transmission coefficient is inversely related to the quality of the line, circuit, channel or trunk. Transmission Control Character - See control character. Transmission Control Protocol (TCP) - One of the core protocols of the Internet protocol suite. Using TCP, applications on networked hosts can create connections to one another, over which they can exchange data. The protocol guarantees reliable and in-order delivery of sender to receiver data. TCP also distinguishes data for multiple, concurrent applications (e.g. Web server and email server) running on the same host. TCP supports many of the Internet's most popular application protocols and resulting applications, including the World Wide Web, email and Secure Shell. Transmission Control Protocol/Internet Protocol (TCP/IP) - A set of communications protocols or software necessary to access the Internet. A network protocol that controls host-to-host transmissions over packet- switched communication networks. 467
- 468. Transmission Frame - A data structure, beginning and ending with delimiters, that consists of fields predetermined by a protocol for the transmission of user data and control data. Transmission Level - At a specified point in a telecommunications system, the power that is measured when a standard test signal, e.g., 0 dBm or -16 dBm at 1000 Hz, is transmitted from a corresponding reference point. Note: The transmission level is usually expressed in dBm. Transmission Level Point (TLP) - In a telecommunications system, a test point, i.e., a point where a signal may be inserted or measured, and for which the nominal power of a test signal is specified. Note 1: In practice, the abbreviation, TLP, is usually used, and it is modified by the nominal level for the point in question. For example, where the nominal level is 0 dBm, the expression 0 dBm TLP, or simply, 0TLP, is used. Where the nominal level is -16 dBm, the expression -16 dBm TLP, or -16TLP, is used. Note 2: The nominal transmission level at a specified TLP is a function of system design and is an expression of the design gain or loss. Note 3: Voice-channel transmission levels, i.e., TLPs, are usually specified for a frequency of approximately 1000 Hz. Note 4: The TLP at a point at which an end instrument, e.g., a telephone set, is connected is usually specified as 0 dBm. Transmission Line - The material medium or structure that forms all or part of a path from one place to another for directing the transmission of energy, such as electric currents, magnetic fields, acoustic waves, or electromagnetic waves. Note: Examples of transmission lines include wires, optical fibers, coaxial cables, rectangular closed waveguides, and dielectric slabs. Transmission Loss - The decrease in power that occurs during transmission from one point to another. Note: Transmission loss is usually expressed in dB. Transmission Medium - Any material substance, such as fiber-optic cable, twisted-wire pair, coaxial cable, dielectric-slab waveguide, water, and air, that can be used for the propagation of signals, usually in the form of modulated radio, light, or acoustic waves, from one point to another. Note: By extension, free space can also be considered a transmission medium for electromagnetic waves, although it is not a material medium. Transmission Security (TRANSEC) - 1. See communications security. 2. [A] Component of COMSEC resulting from the application of measures designed to protect transmissions from interception and exploitation by means other than cryptanalysis. Transmission Security Key (TSK) - [A] key that is used in the control of TRANSEC (transmission security) processes, such as frequency hopping and spread spectrum. Transmission Service Channel - In video systems, the one-way transmission path between two designated points. Transmission System - Part of a communication system organized to accomplish the transfer of information from one point to one or more other points by means of signals. Note: Examples of NATO-owned transmission systems are SATCOM, ACE HIGH and CIP-67. Transmission Time - In facsimile, the interval between the start of picture signals and the detection of the end-of-message signal by the receiver for a single document. Transmission Window - Synonym spectral window. See window. Transmissivity - Obsolete. See transmittance. 468
- 469. Transmit-After-Receive Time Delay - The time interval from removal of rf energy at the local receiver input until the local transmitter is automatically keyed on and the transmitted rf signal amplitude has increased to 90% of its steady-state value. An Exception: High-frequency (HF) transceiver equipment is normally not designed with an interlock between receiver squelch and transmitter on-off key. The transmitter can be keyed on at any time, independent of whether or not a signal is being received at the receiver input. Transmit Flow Control - In data communications systems, control of the rate at which data are transmitted from a terminal so that the data can be received by another terminal. Note 1: Transmit flow control may occur between data terminal equipment (DTE) and a switching center, via data circuit-terminating equipment (DCE), or between two DTEs. The transmission rate may be controlled because of network or DTE requirements. Note 2: Transmit flow control can occur independently in the two directions of data transfer, thus permitting the transfer rates in one direction to be different from the transfer rates in the other direction. Transmit Objective Loudness Rating (TOLR) - The ratio in dB of the sound pressure produced by a speaker to the voltage produced by a telephone and loop as defined by ANSI /IEEE 661-1997. Transmit Signal -The signal sent across an interface la or lb from the associated equipment. Transmittance - The ratio of the transmitted power to the incident power. Note 1: In optics, transmittance is usually expressed as optical density or in percent. Note 2: Transmittance was formerly called " transmission." Transmitter - The source or generator of any signal on a transmission medium. Transmitter Attack-Time Delay - The interval from the instant a transmitter is keyed-on to the instant the transmitted radio frequency (rf) signal amplitude has increased to a specified level, usually 90% of its key-on steady-state value. Note: The transmitter attack-time delay excludes the time required for automatic antenna tuning. Transmitter Central Wavelength Range ( tmax- tmin): In optical communication, the total allowed range of transmitter central wavelengths caused by the combined worst-case variations due to manufacturing, temperature, aging, and any other significant factors. Transmitter Power Output Rating - The power output of a radio transmitter under stated conditions of operation and measurement. Note: Power output ratings may be made against a number of criteria, e.g., peak envelope power, peak power, mean power, carrier power, noise power, or stated intermodulation level. Transmitter-Receiver Pair - A one-way 15-kHz program system comprised of a transmitting terminal connected via a DS1 digital link to a receiving terminal. Transmitter Release-Time Delay - The interval from the instant a transmitter is keyed-off to the instant the transmitted radio frequency (rf) signal amplitude has decreased to a specified level, usually 10% of its key-on steady-state value. Transmultiplexer - Equipment that transforms signals derived from frequency-division multiplex equipment, such as group or supergroups, to time-division-multiplexed signals having the same structure as those derived from PCM multiplex equipment, such as primary or secondary PCM multiplex signals, and vice versa. Transparency - 1. The property of an entity that allows another entity to pass thorough it without altering either of the entities. 2. In telecommunications, the property that allows a transmission system or channel to 469
- 470. accept, at its input, unmodified user information, and deliver corresponding user information at its output, unchanged in form or information content. Note: The user information may be changed internally within the transmission system, but it is restored to its original form prior to the output without the involvement of the user. 3. The quality of a data communications system or device that uses a bit-oriented link protocol that does not depend on the bit sequence structure used by the data source. 4. An image fixed on a clear base by means of a photographic printing, chemical, or other process, especially adaptable for viewing by transmitted light. Transparent Interface - An interface that allows the connection and operation of a system, subsystem, or equipment with another without modification of system characteristics or operational procedures on either side of the interface. Transparent Loopback - A loopback in which the signal is transmitted beyond the loopback point (the forward signal). Transparent Network - See transparency. Transponder - 1. An automatic device that receives, amplifies, and retransmits a signal on a different frequency. 2. An automatic device that transmits a predetermined message in response to a predefined received signal. Note: An example of transponders is in identification-friend-or-foe systems and air-traffic- control secondary radar (beacon radar) systems. 3. A receiver-transmitter that will generate a reply signal upon proper interrogation. Transport - 1. In telecommunications, to convey information from one location to another. 2. Facilities associated with the carriage of OC-1 or higher level signals. Transportability - 1. In communications, the quality of equipment, devices, systems, and associated hardware that permits their being moved from one location to another to interconnect with locally available complementary equipment, devices, systems, associated hardware, or other complementary facilities. Note: Transportability implies the use of standardized components, such as standardized plugs and transmission media. 2. The capability of materiel to be moved by towing, self-propulsion, or carrier through any means, such as railways, highways, waterways, pipelines, oceans, and airways. Transportable Station - A station which is transferred to various fixed locations but is not intended to be used while in motion. Transport Layer - Layer 4. This layer responds to service requests from the Session Layer and issues service requests to the Network Layer. The purpose of the Transport Layer is to provide transparent transfer of data between end users, thus relieving the upper layers from any concern with providing reliable and cost- effective data transfer. See Open Systems Interconnection--Reference Model. Transport Overhead - The overhead added to the STS SPE (synchronous transport signal-- synchronous payload envelope) for transport purposes. Transport overhead consists of line and section overhead. Transposition - In INFOSEC, encryption that rearranges bits or characters according to some scheme. Note: The resulting ciphertext is called transposition cipher. Transverse Electric and Magnetic (TEM) Mode - A mode whose electric and magnetic field vectors are both normal to the direction of propagation. Note: The TEM mode is the most useful mode in a coaxial cable. 470
- 471. Transverse Electric (TE) Mode - A mode whose electric field vector is normal to the direction of propagation. Note: TE modes may be useful modes in waveguides. In an optical fiber, TE and TM modes correspond to meridional rays. Transverse Magnetic (TM) Mode - A mode whose magnetic field vector is normal to the direction of propagation. Note: TM modes may be useful in waveguides. In an optical fiber, TE and TM modes correspond to meridional rays. Transverse Offset Loss - Synonym lateral offset loss. - 1. In fiber optics, a loss of optical power at a splice or connector, caused by a lateral, i.e., transverse, offset of the mating fiber cores, which offset causes an imperfect transfer of the optical signal from the "transmitting" fiber to the "receiving" fiber. Note: The effect of a given amount of lateral offset will depend on other parameters such as the relative diameters of the respective cores. For example: if, because of manufacturing tolerances, the "transmitting" core is smaller than the "receiving" core, the effect will be less than if both cores were the same size. 2. An analogous loss of optical power caused by lateral misalignment of the fiber and optical source. Transverse Parity Check - A parity check performed on a group of binary digits recorded on parallel tracks of a data medium, such as a magnetic disk, tape, drum, or card. Transverse Redundancy Check (TRC) - In synchronized parallel bit streams, a redundancy check (a) that is based on the formation of a block check following preset rules, (b) in which the check-formation rule applied to blocks is also applied to characters, and (c) in which the check is made on parallel bit patterns. Note 1: When the TRC is based on a parity bit applied to each character and block, the TRC can only detect, with limited certainty, whether or not there is an error. It cannot correct the error. Detection cannot be guaranteed because an even number of errors in the same character or block will escape detection, regardless of whether odd or even parity is used. Note 2: Two-dimensional arrays of bits may be used to represent characters or blocks in synchronized parallel data streams. When TRC is combined with longitudinal redundancy checking (LRC), individual erroneous bits can be corrected. Synonym vertical redundancy check. Transverse Resolution - In a facsimile receiver, the dimension that (a) is perpendicular to a scanning line and (b) is the smallest recognizable detail of the image produced by the shortest signal capable of actuating the facsimile receiver under specified conditions. Trapdoor - A hidden software or hardware mechanism, usually created for testing and troubleshooting, that may be used to circumvent computer security. Trapped Electromagnetic Wave - An electromagnetic wave that enters a layer of material that is surrounded on both sides by a layer of material of a lesser refractive index such that, if the wave is traveling parallel or nearly parallel to the surfaces of the layers and hence the incident angles with the surfaces are greater than the critical angle, i.e., the angles are grazing with the surface, total internal reflection will occur on both sides and hence trap the wave. Note: Dielectric slabs, optical fibers, and layers of air can serve as an electromagnetic wave trap, thus confining the wave to a given direction of propagation and to a given point. Trapped Mode - Synonym bound mode. In an optical fiber, a mode that (a) has a field intensity that decays monotonically in the transverse direction everywhere external to the core and (b) does not lose power to radiation. Note: Except for single-mode fibers, the power in trapped modes is predominantly contained in the core of the fiber. Trapped Ray - In an optical fiber, a ray that is confined primarily to the core. Synonyms bound ray, guided ray. 471
- 472. Traveling Wave - A wave that (a) propagates in a transmission medium, (b) has a velocity determined by the launching conditions and the physical properties of the medium, and (c) may be a longitudinal or transverse wave. Note 1: For the purposes of this definition, free space may be considered a medium, although it is not a physical medium. Note 2: A traveling wave is not a wave that is reduced to a standing wave by reflections from a distant boundary. Note 3: Examples of traveling waves are radio waves propagating in free space, lightwaves propagating in optical fibers, water waves on the surface of the ocean, and seismic waves. Tree Network - See network topology. Tree Search - In a tree structure, a search in which it is possible to decide, at each step, which part of the tree may be rejected without a further search. Tree Structure - A hierarchical organization in which a given node is considered to be an ancestor of all the lower level nodes to which the given node is connected. Note 1: The root node, i.e., the base node, is an ancestor of all the other nodes. Note 2: In a tree structure there is one and only one path from any point to any other point. Tree Topology - A network topology that, from a purely topologic viewpoint, resembles an interconnection of star networks in that individual peripheral nodes are required to transmit to and receive from one other node only, toward a central node, and are not required to act as repeaters or regenerators. Note 1: The function of the central node may be distributed. Note 2: As in the conventional star network, individual nodes may thus still be isolated from the network by a single-point failure of a transmission path to the node. Note 3: A single-point failure of a transmission path within a distributed node will result in partitioning two or more stations from the rest of the network. See network topology. T Reference Point - In Integrated Services Digital Networks (ISDN), the conceptual point dividing NT2 and NT1 functional groupings in a particular ISDN arrangement. Tremendously High Erequency (THF) - Frequencies from 300 GHz to 3000 GHz. See electromagnetic spectrum. Triaxial Cable - A specialized form of coaxial cable, circular in cross-section and consisting of (a) a center conductor, often a solid wire but sometimes braided; separated by an insulating material from (b) a concentric solid or braided conductor which is in turn separated by an insulating material from (c) a third solid or braided conductor, concentric with the first two; and (d) a protective sheath. Tributary Circuit - A circuit between a tributary office and a toll switchboard or intertoll dialing equipment in a toll center city. Tributary Office - A local office which is located outside the exchange in which a toll center is located, which has a different rate center from its toll center and which usually tickets and times only a part of its originating toll traffic, but which may ticket or time all or none, of such traffic. The toll center handles all outward traffic not ticketed and timed at the tributary and normally switches all inward toll traffic from outside the tributary's toll center to the tributary. Tributary offices are indicated as such in the Toll Rate and Route Guide. Tributary Station - 1. In a data network, a station other than the control station. 2. On a multipoint connection or a point-to-point connection using basic mode link control, any data station other than the control station. 472
- 473. Trim Effect - In a crystal oscillator, the degradation of frequency-vs.-temperature stability, and marked frequency offset, resulting from frequency adjustment which produces a rotation or distortion, or both, of the inherent frequency-vs.-temperature characteristic. Triple Data Encryption Algorithm (TDEA) - An encryption algorithm whose key consists of three DES (Data Encryption Standard) keys, which is also referred to as a key bundle. Note 1: A DES key consists of 64 binary digits ("0"s or "1"s) of which 56 bits are randomly generated and used directly by the algorithm. (The other 8 bits, which are not used by the algorithm, may be used for error detection.) Note 2: Each TDEA encryption/decryption operation (as specified in ANSI X9.52) is a compound operation of DES encryption and decryption operations. Let EK(I) and DK(I) represent the DES encryption and decryption of I using DES key K respectively. The following operations are TDEA encryption operation: the transformation of a 64-bit block I into a 64-bit block O that is defined as follows: O = EK3(DK2(EK1(I))). TDEA Decryption Operation - the transformation of a 64-bit block I into a 64-bit block O that is defined as follows: O = DK1(EK2(DK3(I))). The standard specifies the following keying options for bundle (K1, K2, K3) • Keying Option 1 - K1, K2, and K3 are independent keys; • Keying Option 2 - K1 and K2 are independent keys and K3 = K1; • Keying Option 3 - K1 = K2 = K3. Triple Precision - Characterized by the use of three computer words to represent a number in accordance with required precision. Triplet - A byte composed of three bits. Synonym three-bit byte. Tristimulus Values - In a given trichromatic system, the amounts of the three reference color stimuli required to match the light considered in a given chromatic system. TRI-TAC - Acronym for tri-services tactical. See tactical communications. TRI-TAC Equipment - Equipment that (a) accommodates the transition from current manual and analog systems to fully automated digital systems and (b) provides for message switching, voice communications circuit switching, and the use of secure voice terminals, digital facsimile systems, and user digital voice terminals. Trojan Horse - 1. An apparently harmless program containing malicious logic that allows the unauthorized collection, falsification, or destruction of data. 2. [A] program containing hidden code allowing the unauthorized collection, falsification, or destruction of information. Troposcatter - Synonym tropospheric scatter. Troposphere - 1. The lower layers of atmosphere, in which the change of temperature with height is relatively large. It is the region where clouds form, convection is active, and mixing is continuous and more or less complete. 2. The layer of the Earth's atmosphere, between the surface and the stratosphere, in which temperature decreases with altitude and which contains approximately 80% of the total air mass. Note: The thickness of the troposphere varies with season and latitude. It is usually 16 km to 18 km thick over tropical regions, and less than 10 km thick over the poles. Tropospheric Duct - See atmospheric duct. 473
- 474. Tropospheric Scatter - 1. The propagation of radio waves by scattering as a result of irregularities or discontinuities in the physical properties of the troposphere. [NTIA] [RR] [JP1] 2. A method of transhorizon communications using frequencies from approximately 350 MHz to approximately 8400 MHz. Note: The propagation mechanism is still not fully understood, though it includes several distinguishable but changeable mechanisms such as propagation by means of random reflections and scattering from irregularities in the dielectric gradient density of the troposphere, smooth-Earth diffraction, and diffraction over isolated obstacles (knife-edge diffraction). Synonym troposcatter. Tropospheric Wave - A radio wave that is propagated by reflection from a place of abrupt change in the dielectric constant, or its gradient, in the troposphere. Note: In some cases, a ground wave may be so altered that new components appear to arise from reflection in regions of rapidly changing dielectric constant. When these components are distinguishable from the other components, they are called "tropospheric waves." TRS Cable (Tip, Ring, Sleeve Cable) - An analog cable used to connect audio devices. It typically comes in 1/4" and 1/8" diameters. It is balanced, as opposed to the unbalanced signals of RCA cables. True Color - The name given to 32-bit, 16.7 million color representation. True Parity - This term has come about with the advent of logical parity memory. It simply means that the parity memory actually does something useful instead of just issuing positives over and over. True Power - Synonym effective power. TrueType - This is a font standard developed by Apple and used in Mac OS version 7. Later, Apple licensed the technology to Microsoft, which used it in Windows 3.1 and continues to use it today. However, Apple and Microsoft TrueType fonts are not compatible. Truncated Binary Exponential Backoff - In carrier sense multiple access with collision avoidance (CSMA/CA) networks and in carrier sense multiple access with collision detection (CSMA/CD) networks, the algorithm used to schedule retransmission after a collision such that the retransmission is delayed by an amount of time derived from the slot time and the number of attempts to retransmit. Truncation - The deletion or omission of a leading or a trailing portion of a string in accordance with specified criteria. Truncation Error - In the representation of a number, the error introduced when one or more digits are dropped. Trunk - A communication line between two switching systems. In other words, a telephone line. A line that connects to the telephone company CO (central office). Trunk Circuit Identification Code (TCIC) - A unique identity assigned to each SS7 message trunk interconnecting two switches. Trunk Encryption Device (TED) - A bulk encryption device used to provide secure communications over a wideband digital transmission link. Note: A TED is usually located between the output of a trunk group multiplexer and a wideband radio or cable facility. Trunk Group - Two or more trunks of the same type between two given points. 474
- 475. Trunk Group Multiplexer (TGM) - A time-division multiplexer that combines individual digital trunk groups into a higher rate bit stream for transmission over wideband digital communications links. Trunk Group Serial Number (TGSN) - A unique alphanumeric code used to identify a trunk group. Trunk Hunting - See hunting. Trust - In cryptology and cryptosystems, that characteristic allowing one entity to assume that a second entity will behave exactly as the first entity expects. Note: Trust may apply only for some specific function. The critical role of trust in the authentication framework is to describe the relationship between an authenticating entity and a certification authority; an authenticating entity must be certain that it can trust the certification authority to create only valid and reliable certificates. Trusted Computer System (TCS) - 1. [An] information system (IS) employing sufficient hardware and software assurance measures to allow simultaneous processing of a range of classified or sensitive information. 2. A data processing system that provides sufficient computer security to allow for concurrent access to data by users with different access rights and to data with different security classification and security categories. Trusted Computing Base (TCB) - [The] totality of protection mechanisms within a computer system, including hardware, firmware, and software, the combination of which is responsible for enforcing a security policy. Note: The ability of a trusted computing base to enforce correctly a unified security policy depends on the correctness of the mechanisms within the trusted computing base, the protection of those mechanisms to ensure their correctness, and the correct input of parameters related to the security policy. Trusted Distribution - [A] method for distributing trusted computing base (TCB) hardware, software, and firmware components that protects the TCB from modification during distribution. Trusted Identification Forwarding - [The] identification method used in information system (IS) networks whereby the sending host can verify an authorized user on its system is attempting a connection to another host. The sending host transmits the required user authentication information to the receiving host. Trusted Path - [The] Mechanism by which a person using a terminal can communicate directly with the trusted computing base (TCB). Trusted path can only be activated by the person or the TCB and cannot be imitated by untrusted Trusted Process - [A] process that has privileges to circumvent the system security policy and has been tested and verified to operate only as intended. Trusted Recovery - [The] ability to ensure recovery without compromise after a system failure. Trusted Software - [The] software portion of a trusted computing base (TCB). Trusted Third-Party - A security authority trusted by communicating entities with respect to specific security- related activities (e.g., for the purpose of authentication). Truth Table - 1. An operation table for a logic operation. 2. A table that describes a logic function by listing all possible combinations of input values and indicating, for each combination, the output value. TSEC Nomenclature - [In security, the] system for identifying the type and purpose of certain items of COMSEC material. 475
- 476. TSK - Abbreviation for transmission security key. TSP - Abbreviation for Telecommunications Service Priority. TSPS - Abbreviation for traffic service position system. TSPS Complex - All groups of operator positions, wherever located, associated with the same TSPS stored program control units. TSP System - See Telecommunications Service Priority system. TTTN - Abbreviation for tandem tie trunk network. TTY - Abbreviation for teletypewriter. TTY/TDD - Telephone Typewriter and Telephone Device for the Deaf. A telecommunication device for the hearing impaired using teletypewriter principals. The users call a special operator number and third-party translation. Tuning - Adjusting the parameters and components of a circuit so that it resonates at a particular frequency or so that the current or voltage is either maximized or minimized at a specific point in the circuit. Note: Tuning is usually accomplished by adjusting the capacitance or the inductance, or both, of elements that are connected to or in the circuit. Tunneling - 1. In computer networking, a technique for connecting two networks via a third, while totally isolating the connected traffic from other traffic in the third network. [After 2382-pt.35] 2. Technology enabling one network to send its data via another network's connections. Tunneling works by encapsulating a network protocol within packets carried by the second network. Tunneling Mode - Synonym leaky mode. In an optical fiber, a mode having a field that decays monotonically for a finite distance in the transverse direction but becomes oscillatory everywhere beyond that finite distance. Note: Leaky modes correspond to leaky rays in the terminology of geometric optics. Leaky modes experience attenuation, even if the waveguide is perfect in every respect. Tunneling Ray - Synonym leaky ray. In an optical fiber, a ray for which geometric optics would predict total internal reflection at the boundary between the core and the cladding, but which suffers loss by virtue of the curved core boundary. Note: Leaky rays correspond to leaky (i.e., tunneling) modes in the terminology of mode descriptors. Turing Machine - A mathematical model of a device that changes its internal state and reads from, writes on, and moves a potentially infinite tape, all in accordance with its present state, thereby constituting a model for computer-like behavior. Turnaround Time - In a half-duplex circuit, the time required to reverse the direction of transmission from transmit to receive or vice versa. Turnkey - Pertaining to a procurement process that (a) includes contractual actions at least through the system, subsystem, or equipment installation phase and (b) may include follow-on contractual actions, such as testing, training, logistical, and operational support. Note: Precise definition of the types of allowable contractual features are contained in the Federal Acquisition Regulations (FAR). 476
- 477. TWAIN (Toolkit Without An Interesting Name) - A set of operations that allow scanners to have a standard interface to software. This allows the use of your favorite graphics package with your favorite scanner without worrying if one will support the other. As long as both are TWAIN-complaint they will work together. Twin Cable - A cable composed of two parallel conductors separated from each other by a ribbon-like insulator or encased by a foam insulator. Synonym twin-lead. Twin-Lead - Synonym twin cable. A term that refers to a two-conductor ribbon cable commonly used as a transmission line for TV signals. Twin-Lead Adapter - A device for connecting a Twin Lead cable to a coaxial cable. Twinplex - A frequency-shift-keyed (FSK) carrier telegraphy system in which four unique tones, i.e., two pairs of tones, are transmitted over a single transmission channel, such as one twisted pair. Note: One tone of each pair represents a " mark " and the other a "space." Twin Sideband Transmission - See independent-sideband transmission. Twist - In telephony, a change, as a function of temperature, in the shape of the frequency-vs.-attenuation response curve, i.e., characteristic, of a transmission line. Twisted Pair - A pair of individually insulated conductors (wires) twisted together and treated as an entity in the transmission of electrical signals or power (e.g., from an electronic power supply to a circuit). Note 1: In communications cables, the twisted pair is usually if not always composed of two individually insulated solid conductors (wires). In other applications, e.g., in a power-supply application, each of the insulated conductors may consist of stranded wire. Note 2: Because the wires are twisted together, interfering signals tend to create opposing electromagnetic forces at frequent intervals, reducing the effect of the interference on the signal or power supply voltage being conducted. Note 3: Twisted pairs may be used for bit rates up to 1 Mb/s over short distances (<100 m) and lower bit rates over longer distances. More sophisticated driver and receiver circuits facilitate similar or higher data rates over longer distances. Note 4: Unshielded twisted pairs (UTPs) are used extensively in telephone networks and in many data communications applications. Twisted Pair Cable - See paired cable. Two-Out-Of-Five Code - A binary-coded decimal notation in which (a) each decimal digit is represented by a binary numeral consisting of five binary digits of which two are of one kind, called "ones," and three are of the other kind, called "zeros" and (b) the usual weights assigned to the digit positions are 0-1-2-3-6, except that "zero" is represented as 01100. Two-Part Code - Code consisting of an encoding section, in which the vocabulary items (with their associated code groups) are arranged in alphabetical or other systematic order; and a decoding section, in which the code groups (with their associated meanings) are arranged in a separate alphabetical or numeric order. Two-Person Control - Continuous surveillance and control of positive control material at all times by a minimum of two authorized individuals, each capable of detecting incorrect and unauthorized procedures with respect to the task being performed, and each familiar with established security and safety requirements. Two-Person Integrity (TPI) - [A] system of storage and handling designed to prohibit individual access to certain COMSEC keying material by requiring the presence of at least two authorized persons, each capable of detecting incorrect or unauthorized security procedures with respect to the task being performed. 477
- 478. Two-Pilot Regulation - In frequency-division multiplexed (FDM) systems, the use of two pilot frequencies within a band so that the differential change in attenuation with respect to temperature, i.e., twist, can be detected and compensated by a regulator. Two-Sample Deviation - The square root of the Allan variance Two-Sample Variance - Synonym Allan variance. Two-Source Frequency Keying - Synonym frequency-exchange signaling. Two-Tone Keying: - In telegraphy systems, keying in which the modulating wave causes the carrier to be modulated with a single tone for the " mark " and modulated with a different single tone for the "space." Two-Tone Telegraph - See two-tone keying. Two-way Alternate Operation - Synonym half-duplex operation. Two-Way Simultaneous Operation - Synonym duplex operation. Two-Wire Circuit - Also 2-wire circuit. A full-duplex communications circuit that utilizes only two metallic conductors, e.g., a single twisted pair. TWX® - Acronym for teletypewriter exchange service. TX - Abbreviation for transmitter, transmit. Type 1 Product - Classified or controlled cryptographic item for securing classified and sensitive U.S. Government information, when appropriately keyed. The term refers only to products, and not to information, key, services, or controls. Type 1 products contain classified algorithms. They are available to U.S. Government users, their contractors, and federally sponsored non-U.S. Government activities subject to export restrictions in accordance with International Traffic in Arms Regulation. Type 2 Product - Unclassified cryptographic equipment, assembly, or component, endorsed by the National Security Agency, for use in national security systems as defined in Title 40 U.S.C. Section 1452. [INFOSEC-99] Note: The term refers only to products, and not to information, key, services, or controls. Type 2 products may not be used for classified information, but contain classified National Security Agency algorithms that distinguish them from products containing the unclassified data algorithm. Type 2 products are subject to export restrictions in accordance with the International Traffic in Arms Regulation. Type 3 Algorithm - [A] cryptographic algorithm that has been registered by the National Institute of Standards and Technology (NIST) and published as a Federal Information Processing Standard (FIPS) for use in protecting unclassified sensitive, information or commercial information. Type 4 Algorithm - [An] unclassified cryptographic algorithm that has been registered by the National Institute of Standards and Technology (NIST), but not published as a Federal Information Processing Standard (FIPS). Types of Calls - • Local — A call within your local calling area covered by your local calling plan. 478
- 479. • Local Toll (Regional Toll) — A call beyond your local calling area, but not far enough to be long distance. These calls are subject to per-minute charges, which vary by state. • In-State Long Distance — A call to a number outside your local calling area, but still within the borders of your state. • State-to-State Long Distance — A call to a number in a different state. U UDP - Abbreviation for user datagram protocol. An Internet protocol for datagram service. UHF - Abbreviation for ultra high frequency. See electromagnetic spectrum. Frequencies from 300 MHz to 3000 MHz. This is the part of the radio spectrum from 300 to 3000 megahertz, which includes TV channels 14-69. After the DTV transition, UHF TV will be changed to 470 to 698 MHz, which includes channels 14-51. U Interface - For basic-rate access in an Integrated Services Digital Network (ISDN) environment, a user-to- network interface reference point that is characterized by the use of a 2-wire-loop transmission system that (a) conveys information between the 4-wire user-to-network interface, i.e., the S/ T reference point, and the local exchange, (b) is located in the servicing central office, and (c) is not as distance sensitive as a service using a T interface. ULF - Abbreviation for ultra low frequency. See electromagnetic spectrum. Frequencies from 300 Hz to 3000 Hz. Ultra High Frequency (UHF) - Frequencies from 300 MHz to 3000 MHz. See electromagnetic spectrum. Ultra Low Frequency (ULF) - Frequencies from 300 Hz to 3000 Hz. See electromagnetic spectrum. Ultraviolet (uv) - The portion of the electromagnetic spectrum in which the longest wavelength is just below the visible spectrum, extending from approximately 4 nm to approximately 400 nm. Note: Some authorities place the lower limit of uv at values between 1 and 40 nm, 1 nm being the upper wavelength limit of x-rays. The 400-nm limit is the lowest visible wavelength, i.e., the highest visible frequency, violet. See electromagnetic spectrum. Ultrawideband - See UWB. 1. Referring to any radio or wireless device where the occupied bandwidth is greater than 25% of the center frequency or greater than 1.5 GHz. 2. A radio or wireless system that uses narrow pulses (on the order of 1 to 10 nanoseconds), also called carrierless or impulse systems, for communications and sensing (short-range radar). 3. A radio or wireless system that uses time-domain modulation methods (e.g., pulse-position modulation) for communications applications, or time-domain processing for sensing applications. Unallowable Character - Synonym illegal character. A character, or a combination of bits, that is not valid in a given system according to specified criteria, such as with respect to a specified alphabet, a particular pattern of bits, a rule of formation, or a check code. Synonyms false character, forbidden character, improper character, illegal character, unused character. Unassigned Cell - A cell identified by a standardized virtual path identifier (VPI) and virtual channel identifier (VCI) value, which has been generated and does not carry information from an application using the ATM Layer Connection. Unauthorized Disclosure - Exposure of information to individuals not authorized to receive it. 479
- 480. Unavailability - A expression of the degree to which a system, subsystem, or equipment is not operable and not in a committable state at the start of a mission, when the mission is called for at an unknown, i.e., random, time. Note 1: The conditions determining operability and committability must be specified. Note 2: Expressed mathematically, unavailability is 1 minus the availability. Note 3: Unavailability may also be expressed mathematically as the ratio of the total time a functional unit is not capable of being used during a given interval to the length of the interval, e.g., if the unit is not capable of being used for 68 hours a week, the unavailability is 68/168. Unbalanced Line - A transmission line, such as a coaxial cable, in which the magnitudes of the voltages on the two conductors are not equal with respect to ground. Unbalanced Modulator - A modulator in which the modulation factor is different for the alternate half-cycles of the carrier. Synonym asymmetrical modulator. Unbalanced Wire Circuit - A circuit in which the two sides are inherently electrically dissimilar. Unbound Mode - Synonym radiation mode. For an optical fiber, an unbound mode. Note: In an optical fiber, a radiation mode is one having fields that are transversely oscillatory everywhere external to the waveguide, and which exists even at the limit of zero wavelength. Unbundling - In the context of the FCC's Computer III Inquiry, the process of separating individual tariffed offerings and services that are associated with a specific element in the CEI or ONA tariff from other tariffed basic service offerings. Unclassified - Information that has not been determined pursuant to Executive Order (E.O.) 12958 or any predecessor order to require protection against unauthorized disclosure and that is not designated as classified. Underflow - In computing, a condition occurring when a machine calculation produces a non-zero result that is smaller than the smallest non-zero quantity that the machine's storage unit is capable of storing or representing. Underground Cable - A communication cable designed to be placed under the surface of the Earth in a duct system that isolates it from direct contact with the soil. Underground Plant - Cable and wire plant, together with closures appropriate for the application, that is placed below ground in structures such as conduit or ducts. Underlap - In facsimile, a defect that occurs when the width of the scanning line is less than the scanning pitch. Undershoot - See overshoot. When the transition is from a higher value to a lower value, and the parameter takes a transitory value that is lower than the final value, the phenomenon is called undershoot. Undesired Signal - Any signal that tends to produce degradation in the operation of equipment or systems. Undetected Error Rate - Deprecated synonym for undetected error ratio. The ratio of the number of bits, unit elements, characters, or blocks incorrectly received and undetected, to the total number of bits, unit elements, characters, or blocks sent. 480
- 481. Undetected Error Ratio - The ratio of the number of bits, unit elements, characters, or blocks incorrectly received and undetected, to the total number of bits, unit elements, characters, or blocks sent. Synonyms residual error rate, undetected error rate [deprecated] . Undisturbed Day - A day during which neither sunspot activity nor ionospheric disturbance causes detectable interfere with radio communications. Unequipped Indication - A code placed in unequipped channels by originating equipment to indicate to path terminating equipment that the channel is intentionally unoccupied so that alarms can be inhibited. Unexpected Frame - A valid frame that cannot be processed. The frame itself is perfectly legitimate. Its unexpected character is defined by two conditions: the specific type of frame and the state of the receiver. The layer-2 protocol states define the proper sequence in which frames are expected to occur. The receiver will compare received frames with its own protocol state to determine whether or not a valid frame is unexpected. UNICOM station - Synonym aeronautical advisory station. An aeronautical station used for advisory and civil defense communications primarily with private aircraft stations. Unidirectional - The condition where information flow is provided only in one direction. Unidirectional Channel - Synonym one-way-only channel. A channel capable of transmission in only one direction, which cannot be reversed. Unidirectional Operation - Operation in which data are transmitted from a transmitter to a receiver in only one direction. Unidirectional Path - A path that logically connects a single path source with the associated path sink. Uniform Encoding - An analog-to-digital conversion process in which, except for the highest and lowest quantization steps, all of the quantization subrange values are equal. Synonym uniform quantizing. Uniform Linear Array - An antenna composed of a relatively large number of usually identical elements arranged in a single line or in a plane with uniform spacing and usually with a uniform feed system. Uniform Quantizing - Synonym uniform encoding. An analog-to-digital conversion process in which, except for the highest and lowest quantization steps, all of the quantization subrange values are equal. Uniform Resource Locator (URL) - The standard for giving an WWW Internet address (e.g. http://www.faxswitch.com) Uniform-Spectrum Random Noise - See white noise. Noise having a frequency spectrum that is continuous and uniform over a specified frequency band. Note: Uniform-Spectrum Random Noise has equal power per hertz over the specified frequency band. Synonym additive white gaussian noise. Uniform Time Scale - A time scale made up of equal intervals. Uniform Transmission Line - A transmission line that has distributed electrical properties, i.e., resistance, inductance, and capacitance per unit length, that are constant along the line, and in which the voltage-to- current ratio does not vary with distance along the line, if the line is terminated in its characteristic impedance. Note 1: Examples of uniform transmission lines are coaxial cables, twisted pairs, and single wires 481
- 482. at constant height above ground, all of which have no changes in geometry, materials, or construction along their length. Note 2: In a uniform transmission line, signal attenuation is a function of the length of the line and the frequency of the signal. Unilateral Control System - Synonym unilateral synchronization system. A system of synchronization in which signals from a single location are used to synchronize clocks at one or more other locations. Unilateral Synchronization System - A system of synchronization in which signals from a single location are used to synchronize clocks at one or more other locations. Synonym unilateral control system. Unimode Fiber - Synonym single-mode optical fiber. An optical fiber in which only the lowest order bound mode can propagate at the wavelength of interest. Note 1: The lowest order bound mode is ascertained for the wavelength of interest by solving Maxwell's equations for the boundary conditions imposed by the fiber, e.g., core (spot) size and the refractive indices of the core and cladding. Note 2: The solution of Maxwell's equations for the lowest order bound mode will permit a pair of orthogonally polarized fields in the fiber, and this is the usual case in a communication fiber. Note 3: In step-index guides, single-mode operation occurs when the normalized frequency, V, is less than 2.405. Unit Impulse - A mathematical artifice consisting of an impulse of infinite amplitude and zero width, and having an area of unity. Note: The unit impulse is useful for the mathematical expression of the impulse response, i.e., the transfer function, of a device. Synonym Dirac delta function. Unit Interval - In isochronous transmission, the longest interval of which the theoretical durations of the significant intervals of a signal are all whole multiples. Universal Personal Telecommunications Number - Synonym UPT number. In universal personal telecommunications service, the number that uniquely identifies a UPT user and that is used to place a call to, or to forward a call to, that user. Note: A user may have multiple UPT numbers, e.g., a business UPT number for business calls and a private UPT number for private calls. In the case of multiple numbers, each UPT number is considered, from a network vantage point, to identify a distinct UPT user, even if all such numbers identify the same person or entity. Universal Personal Telecommunications (UPT) Service - A telecommunications service that provides personal mobility and service profile management. Note 1: UPT service involves the network capability of identifying uniquely a UPT user by means of a UPT number. Note 2: The general principles of UPT are given in ITU-T Recommendation F.850. Note 3: UPT and PCS are sometimes mistakenly assumed to be the same service concept. UPT allows complete personal mobility across multiple networks and service providers. PCS may use UPT concepts to improve subscriber mobility in allowing roaming to different service providers, but UPT and PCS are not the same service concept. Universal Service Fund Surcharge - Telephone customers also may see charges on their local and long distance bills for universal service. Companies are required by the FCC to contribute to a federal universal service fund (USF). The USF helps to make phone service affordable and available to all Americans, including those with low incomes, those living in areas where the costs of providing telephone service is high, schools, libraries, and rural health care providers. These fees vary by amount and by company. USF surcharges may also be assessed at the state level. UNIX - The most common multi-user operating system for servers on the Internet. Unwanted Current - With respect to telecommunications plant, any current that is not intentionally supplied from the central office or from telephone equipment. 482
- 483. Upconvert - A process by which a digital, high-definition television takes a lower-definition picture and converts it into a higher-definition picture. This may be done by doubling each line as it is drawn on the screen, or by using advanced algorithms to interpolate the data between each lower-resolution line, filling in the missing image. Update - The regeneration of a display to show current status, based on changes to the previously displayed data. Note: An update can be accomplished upon user request or by automatic means. Upload - To transfer a file or information from your computer to another. UPT - See Universal Personal Telecommunications Service. UPT Number - In universal personal telecommunications service, the number that uniquely identifies a UPT user and that is used to place a call to, or to forward a call to, that user. Note: A user may have multiple UPT numbers, e.g., a business UPT number for business calls and a private UPT number for private calls. In the case of multiple numbers, each UPT number is considered, from a network vantage point, to identify a distinct UPT user, even if all such numbers identify the same person or entity. Synonym universal personal telecommunications number. UPT User - In universal personal telecommunications service, a person who (or entity that) has access to universal personal telecommunications (UPT) services and who has been assigned a UPT number. URL - See Uniform Resource Locator Usage - Synonym occupancy. For equipment, such as a circuit or a switch, the ratio of the actual time in use to the available time during a 1-hour period. Note 1: Usage is usually expressed in percent. Note 2: Usage may be plotted versus time of day. User - 1. A person, organization, or other entity (including a computer or computer system), that employs the services provided by a telecommunication system, or by an information processing system, for transfer of information. Note: A user functions as a source or final destination of user information, or both. Synonym subscriber. 2. [In security, a] person or process authorized access to an IS (information system); [an] individual defined, registered, and bound to a public key structure by certification authority. User Datagram Protocol (UDP) - In the Internet Protocol suite, a standard, low-overhead, connectionless, host-to-host protocol that is used over packet-switched computer communications networks, and that allows an application program on one computer to send a datagram to an application program on another computer. Note: The main difference between UDP and TCP is that UDP provides connectionless service, whereas TCP does not. User Name - Your user name, also called user ID or account name, is the same as your login name. This is the name by which you and your electronic mailbox are identified online. User Information - Information transferred across the functional interface between a source user and a telecommunications system for delivery to a destination user. Note: In telecommunications systems, user information includes user overhead information. User Information Bit - A bit transferred from a source user to a telecommunications system for delivery to a destination user. Note 1: User information bits do not include the overhead bits originated by, or having their primary functional effect within, the telecommunications system. Note 2: User information bits are encoded to form channel bits. 483
- 484. User Information Block - A block that contains at least one user information bit. User Overhead Information - See overhead information. - Digital information transferred across the functional interface between a user and a telecommunications system, or between functional units within a telecommunications system, for the purpose of directing or controlling the transfer of user information or the detection and correction of errors. Note: Overhead information originated by the user is not considered to be system overhead information. Overhead information generated within the communications system and not delivered to the user is system overhead information. Thus, the user throughput is reduced by both overheads while system throughput is reduced only by system overhead. User Part - A functional part of the common channel signaling system that transfers signaling messages via the message transfer part. Different types of user parts exist (e.g., for telephone and data services), each of which is specified to a particular use of the signaling system. USF - Universal Service Fund. The National Exchange Carrier Association administers the USF. This is a mechanism designed to keep local exchange rates at reasonable levels, especially in high-cost, rural areas. The fund gets money from a surcharge on phone lines and uses those funds to offset telecommunication expenses in the high-cost areas. UseNet Newsfeed - A huge, world wide "Users Network" of discussion groups, or newsgroups, connecting and sharing information from hundreds of thousands of machines. Utility Program - A computer program that is in general support of the operations and processes of a computer. Note: Examples of utility programs include diagnostic programs, trace programs, input routines, and programs used to perform routine tasks, i.e., perform everyday tasks, such as copying data from one storage location to another. Synonyms service program, service routine, tool, utility routine. UUCP Service (UNIX to UNIX Copy Program) - A method of transferring files between UNIX computers that includes Electronic mail. UWB - Abbreviation for ultrawideband. 1. Referring to any radio or wireless device where the occupied bandwidth is greater than 25% of the center frequency or greater than 1.5 GHz. 2. A radio or wireless system that uses narrow pulses (on the order of 1 to 10 nanoseconds), also called carrierless or impulse systems, for communications and sensing (short-range radar). 3. A radio or wireless system that uses time-domain modulation methods (e.g., pulse-position modulation) for communications applications, or time-domain processing for sensing applications. V Validation - 1. Tests to determine whether an implemented system fulfills its requirements. 2. The checking of data for correctness or for compliance with applicable standards, rules, and conventions. 3. [The] process of applying specialized security test and evaluation procedures, tools, and equipment needed to establish acceptance for joint usage of an AIS by one or more departments or agencies and their contractors. Note: This action will include, as necessary, final development, evaluation, and testing, preparatory to acceptance by senior security test and evaluation staff specialists. 4. In universal personal telecommunications, the process of verifying that a user or terminal is authorized to access UPT services. Value-Added Carrier: - A company that sells the services of a value-added network. Value-Added Network (VAN) - A network using the communication services of other commercial carriers, using hardware and software that permit enhanced telecommunication services to be offered. 484
- 485. VAN - Acronym for value-added network. Variable Length Buffer - A buffer into which data may be entered at one rate and removed at another rate without changing the data sequence. Note: Most first-in first-out (FIFO) storage devices are variable-length buffers in that the input rate may be variable while the output rate is constant or the output rate may be variable while the input rate is constant. Various clocking and control systems are used to allow control of underflow or overflow conditions. Variable Slope Delta Modulation - A type of delta modulation in which the size of the steps of the approximated signal is progressively increased or decreased as required to make the approximated signal closely match the input analog wave.Same as continuously variable slope delta modulation. Variance - In statistics, in a population of samples, the mean of the squares of the differences between the respective samples and their mean Variant - 1. One of two or more code symbols which have the same plain text equivalent. 2. One of several plain text meanings that are represented by a single code group. Variation Monitor - In ac power distribution, a device for sensing deviations of any measured variable, such as voltage, current, or frequency, and capable of initiating a programmed action, such as transfer to other power sources, when programmed limits of voltage, current, frequency, or time are exceeded, or providing an alarm, or both. vars - Abbreviation for volt-amperes reactive. In alternating-current power transmission and distribution, the product of the rms voltage and amperage, i.e., the apparent power, multiplied by the sine of the phase angle between the voltage and the current. Note 1: Vars represents the power not consumed by a reactive load, i.e., when there is a phase difference between the applied voltage and the current. Note 2: Only effective power, i.e., the actual power delivered to or consumed by the load, is expressed in watts. Volt- amperes reactive is properly expressed only in volt-amperes, never watts. Note 3: To maximize transmission efficiency, vars must be minimized by balancing capacitive and inductive loads, or by the addition of an appropriate capacitive or inductive reactance to the load. VC - Abbreviation for virtual circuit. A communications arrangement in which data from a source user may be passed to a destination user over various real circuit configurations during a single period of communication. (188) Note: Virtual circuits are generally set up on a per-call basis and are disconnected when the call is terminated; however, a permanent virtual circuit can be established as an option to provide a dedicated link between two facilities. Synonyms logical circuit, logical route. V-Chip - The V-chip is a technology that enables parents to block television programming based on a program's rating. The ratings are encoded within the television signal. The V-chip reads the encoded rating information of each program and blocks shows according to the parents' blocking selections. VCR: Abbreviation for Video Cassette Recorder. VDU: Abbreviation for visual display unit. 1. Software or hardware that is used to scrutinize and to display, record, supervise, control, or verify the operations of a system. Note: Possible uses of monitors are to indicate significant departures from the norm, or to determine levels of utilization of particular functional units. 2. A device used for the real-time temporary display of computer output data. Note: Monitors usually use cathode-ray-tube or liquid-crystal technology. Synonyms video display terminal, video display unit, visual display unit. 485
- 486. Vector Processor - Synonym array processor. A processor capable of executing instructions in which the operands may be arrays rather than data elements. Velocity of Propagation - Of an electrical or electromagnetic signal, its speed in a physical medium such as a coaxial cable or optical fiber. Verified Off-Hook - In telephone systems, a service provided by a unit that is inserted on each end of a transmission circuit for the purpose of verifying supervisory signals on the circuit. See automatic ringdown circuit. Vertex Angle - In an optical fiber, the angle formed by the extreme bound meridional rays accepted by the fiber, or emerging from it, equal to twice the acceptance angle; the angle formed by the largest cone of light accepted by the fiber or emitted from it. Vertical Redundancy Check (VRC) - Synonym transverse redundancy check (TRC) . In synchronized parallel bit streams, a redundancy check (a) that is based on the formation of a block check following preset rules, (b) in which the check-formation rule applied to blocks is also applied to characters, and (c) in which the check is made on parallel bit patterns. Note 1: When the TRC is based on a parity bit applied to each character and block, the TRC can only detect, with limited certainty, whether or not there is an error. It cannot correct the error. Detection cannot be guaranteed because an even number of errors in the same character or block will escape detection, regardless of whether odd or even parity is used. Note 2: Two-dimensional arrays of bits may be used to represent characters or blocks in synchronized parallel data streams. When VRC is combined with longitudinal redundancy checking (LRC), individual erroneous bits can be corrected. Very High Frequency (VHF) - Frequencies from 30 MHz to 300 MHz. This is the part of the radio spectrum from 30 to 300 megahertz, which includes TV Channels 2-13, and the FM broadcast band. Very Low Frequency (VLF) - Frequencies from 3 kHz to 30 kHz. Vestigial Sideband (VSB) Transmission - Modified AM transmission in which one sideband, the carrier, and only a portion of the other sideband are transmitted. VF - Abbreviation for voice frequency. Pertaining to those frequencies within that part of the audio range that is used for the transmission of speech. (188) Note 1: In telephony, the usable voice-frequency band ranges from approximately 300 Hz to 3400 Hz. Note 2: In telephony, the bandwidth allocated for a single voice-frequency transmission channel is usually 4 kHz, including guard bands. Synonym voice band. VFCT - Abbreviation for voice frequency carrier telegraph. A method of multiplexing one or more dc telegraph channels onto a nominal 4-kHz voice frequency channel. Synonym voice frequency carrier telegraph. VFCTG - Abbreviation for voice-frequency carrier telegraph. A method of multiplexing one or more dc telegraph channels onto a nominal 4-kHz voice frequency channel. Synonym voice frequency carrier telegraph. VF patch bay - See voice frequency primary patch bay. A patching facility that provides the first appearance of local-user VF circuits in the technical control facility (TCF). Note: The VF primary patch bay provides patching, monitoring, and testing for all VF circuits. Signals will have various levels and signaling schemes depending on the user terminal equipment. 486
- 487. VFTG - Abbreviation for voice-frequency telegraph. A method of multiplexing one or more dc telegraph channels onto a nominal 4-kHz voice frequency channel. Synonym voice frequency carrier telegraph. VGA - Abbreviation for Video Graphics Array. This is a display mode with a resolution of 640 x 480 pixels. VHF - Abbreviation for very high frequency. Frequencies from 30 MHz to 300 MHz which includes TV Channels 2-13, and the FM broadcast band. Via Net Loss (VNL) - Pertaining to circuit performance prediction and description that allows circuit parameters to be predetermined and the circuit to be designed to meet established criteria by analyzing actual, theoretical, and calculated losses. Video - 1. An electrical signal containing timing (synchronization), luminance (intensity), and often chrominance (color) information that, when displayed on an appropriate device, gives a visual image or representation of the original image sequences. 2. Pertaining to the sections of a television system that carry television signals, either in unmodulated or modulated form. 3. Pertaining to the demodulated radar signal that is applied to a radar display device.4. Pertaining to the bandwidth or data rate necessary for the transmission of real-time television pictures. Note: In practice, the baseband bandwidth required for the transmission of NTSC television pictures (not including the audio carriers) is approximately 5 MHz. Video Codec - See codec. 1. An assembly consisting of an encoder and a decoder in one piece of equipment. (188) 2. A circuit that converts analog signals to digital code and vice versa. 3. An electronic device that converts analog signals, such as video and voice signals, into digital form and compresses them to conserve bandwidth on a transmission path. (188) Note: Codecs in this sense are used in this sense for video conferencing systems. Acronym for coder-decoder . Videoconference: See video teleconference. 1. A teleconference that includes video communications. 2. Pertaining to a two-way electronic communications system that permits two or more persons in different locations to engage in the equivalent of face-to-face audio and video communications. Note: Video teleconferences may be conducted as if all of the participants were in the same room. Video Display Terminal - Synonym visual display unit. See monitor. 1. Software or hardware that is used to scrutinize and to display, record, supervise, control, or verify the operations of a system. Note: Possible uses of monitors are to indicate significant departures from the norm, or to determine levels of utilization of particular functional units. 2. A device used for the real-time temporary display of computer output data. Note: Monitors usually use cathode-ray-tube or liquid-crystal technology. Synonym video display unit. Video Display Unit - Synonym visual display terminal. See monitor. 1. Software or hardware that is used to scrutinize and to display, record, supervise, control, or verify the operations of a system. Note: Possible uses of monitors are to indicate significant departures from the norm, or to determine levels of utilization of particular functional units. 2. A device used for the real-time temporary display of computer output data. Note: Monitors usually use cathode-ray-tube or liquid-crystal technology. Synonym video display terminal, Video Frame - In video display, one complete scanned image from a series of video images. Note: A video frame is usually composed of two interlaced fields. Videophone - 1. A telephone that is coupled to an imaging device that enables the call receiver or the call originator, or both, to view one another as on television, if they so desire. 2. A military communications terminal that (a) has video teleconference capability, (b) is usually configured as a small desktop unit, designed for one operator, and (c) is a single, integrated unit. 487
- 488. Video Teleconference - 1. A teleconference that includes video communications. 2. Pertaining to a two-way electronic communications system that permits two or more persons in different locations to engage in the equivalent of face-to-face audio and video communications. Note: Video teleconferences may be conducted as if all of the participants were in the same room. Video Teleconferencing Unit (VTU) - Equipment that performs video teleconference functions, such as coding and decoding of audio and video signals and multiplexing of video, audio, data, and control signals, and that usually does not include I/O devices, cryptographic devices, network interface equipment, network connections, or the communications network to which the unit is connected. View - In satellite communications, the quality or degree of visibility of a satellite to a ground station; i.e., the degree to which the satellite is sufficiently above the horizon and clear of obstructions so that it is within a clear line of sight by an Earth terminal. Note: A pair of satellite Earth terminals has a satellite in mutual view when both have unobstructed line-of-sight contact with the satellite simultaneously. Viewdata - A type of information-retrieval service in which a subscriber can (a) access a remote database via a common carrier channel, (b) request data, and (c) receive requested data on a video display over a separate channel. Note: The access, request, and reception are usually via common carrier broadcast channels. Contrast with teletext. Violation - See AMI violation. A "mark" that has the same polarity as the previous "mark" in the transmission of alternate mark inversion (AMI) signals. Note: In some transmission protocols, AMI violations are deliberately introduced to facilitate synchronization or to signal a special event. Virtual Call - A call, established over a network, that uses the capabilities of either a real or virtual circuit by sharing all or any part of the resources of the circuit for the duration of the call. Virtual Call Capability - A service feature in which (a) a call set-up procedure and a call disengagement procedure determine the period of communication between two data terminal equipments (DTEs) in which user data are transferred by the network in the packet mode of operation, (b) end-to-end transfer control of packets within the network is required, (c) data may be delivered to the network by the call originator before the call access phase is completed, but the data are not delivered to the call receiver if the call attempt is unsuccessful, (d) the network delivers all the user data to the call receiver in the same sequence in which the data are received by the network, and (e) multi-access DTEs may have several virtual calls in progress at the same time. Synonym virtual call facility. Virtual Call Facility - Synonym virtual call capability. A service feature in which (a) a call set-up procedure and a call disengagement procedure determine the period of communication between two data terminal equipments (DTEs) in which user data are transferred by the network in the packet mode of operation, (b) end-to-end transfer control of packets within the network is required, (c) data may be delivered to the network by the call originator before the call access phase is completed, but the data are not delivered to the call receiver if the call attempt is unsuccessful, (d) the network delivers all the user data to the call receiver in the same sequence in which the data are received by the network, and (e) multi-access DTEs may have several virtual calls in progress at the same time. Synonym virtual call capability. Virtual Carrier Frequency - In radio or carrier systems in which no carrier is transmitted, e.g., single sideband or double sideband with suppressed carrier, the location in the frequency spectrum that the carrier would occupy if it were present. Virtual Channel - In telecommunications, a channel designation which differs from the actual channel or frequency on which the signal travels. The term is most often applied to television, where Digital Television (DTV) channels are in-band adjacent to analog ones. 488
- 489. A station branded as Channel 8, for example, might actually use channel 32 for its ATSC or DVB transmission, but a Virtual Channel Map allows viewers to tune in the station on channel 8 on a digital set. The virtual channel thus enables viewers to tune in the station by choosing the same channel number as they would have previously. Virtual Circuit (VC) - A communications arrangement in which data from a source user may be passed to a destination user over various real circuit configurations during a single period of communication. Note: Virtual circuits are generally set up on a per-call basis and are disconnected when the call is terminated; however, a permanent virtual circuit can be established as an option to provide a dedicated link between two facilities. Synonyms logical circuit, logical route. Virtual Circuit Capability - A network-provided service feature in which a user is provided with a virtual circuit. Note: Virtual circuit capability is not necessarily limited to packet mode transmission. For example, an analog signal may be converted to a digital signal and then be routed over the network via any available route. Virtual Connection - A logical connection that is made to a virtual circuit. Virtual Height - The apparent height of an ionized layer, as determined from the time interval between the transmitted signal and the ionospheric echo at vertical incidence. Virtual Host - A Web site that includes a customized Domain Name and unique IP address to your home page, giving the appearance that you have your own server directly connected to the Internet. Virtual Instruction - Synonym teletraining. Training that (a) in which usually live instruction is conveyed in real time via telecommunications facilities, (b) that may be accomplished on a point-to-point basis or on a point-to-multipoint basis, and (c) may assume many forms, such as a teleseminar, a teleconference, or an electronic classroom, usually including both audio and video. Synonyms distance learning, distance training, electronic classroom, virtual instruction. Virtual Memory - In computer systems, the memory as it appears to, i.e., as it is available to, the operating programs running in the central processing unit (CPU). Note: The virtual memory may be smaller, equal to, or larger than the real memory present in the system. Virtual Network - A network that provides virtual circuits and that is established by using the facilities of a real network Virtual Office - A work environment in which employees work cooperatively from different locations using a computer network. Virtual Path - See virtual circuit. A communications arrangement in which data from a source user may be passed to a destination user over various real circuit configurations during a single period of communication. Note: Virtual circuits are generally set up on a per-call basis and are disconnected when the call is terminated; however, a permanent virtual circuit can be established as an option to provide a dedicated link between two facilities. Synonyms logical circuit, logical route. Virtual phone number - A feature of VoIP that allows you to attach additional phone numbers with different area codes to your basic VoIP service. This feature allows people to phone you without incurring long- distance charges from the same or adjacent nontoll area codes. All outgoing calls, however, are billed as if coming from your main phone number. Virtual phone numbers typically each cost a few extra dollars per month. 489
- 490. Virtual Reality - An interactive, computer-generated simulated environment with which users can interact using specialized peripherals such as data gloves and head-mounted computer-graphic displays. Virtual Storage - The storage space that may be regarded as addressable main storage by the user of a computer system in which virtual addresses are mapped into real addresses. Note: The size of virtual storage is limited by the addressing scheme of the computer system and by the amount of auxiliary storage available, and not by the actual number of main storage locations. Virus - 1. An unwanted program which places itself into other programs, which are shared among computer systems, and replicates itself. Note: A virus is usually manifested by a destructive or disruptive effect on the executable program that it affects. 2. Self-replicating, malicious program segment that attaches itself to an application program or other executable system component and leaves no obvious signs of its presence. Visual Display Unit (VDU) - See monitor. 1. Software or hardware that is used to scrutinize and to display, record, supervise, control, or verify the operations of a system. Note: Possible uses of monitors are to indicate significant departures from the norm, or to determine levels of utilization of particular functional units. 2. A device used for the real-time temporary display of computer output data. Note: Monitors usually use cathode-ray-tube or liquid-crystal technology. Visual Telephone Services - A group of audiovisual services including videophone as defined in ITU-T Recommendation F.721 and videoconferencing (defined in ITU-T H-Series Recommendations). Virtual Terminal (VT) - In open systems, an application service that (a) allows host terminals on a multi-user network to interact with other hosts regardless of terminal type and characteristics, (b) allows remote log-on by local-area-network managers for the purpose of management, (c) allows users to access information from another host processor for transaction processing, and (d) serves as a backup facility. Virus - An unwanted program which places itself into other programs which are shared among computer systems, and replicates itself. Note: A virus is usually manifested by a destructive or disruptive effect on the executable program that it affects. Visible Spectrum - The region of the electromagnetic spectrum that can be perceived by human vision, approximately the wavelength range of 0.4 m to 0.7 m. Visual Display Unit (VDU) - See monitor. 1. Software or hardware that is used to scrutinize and to display, record, supervise, control, or verify the operations of a system. Note: Possible uses of monitors are to indicate significant departures from the norm, or to determine levels of utilization of particular functional units. 2. A device used for the real-time temporary display of computer output data. Note: Monitors usually use cathode-ray-tube or liquid-crystal technology. Synonyms video display terminal, video display unit, monitor. Vitreous Silica - Glass consisting of almost pure silicon dioxide (SiO2). Synonym fused silica . Silicon dioxide (SiO2). Note 1: Silica may occur in crystalline or amorphous form, and occurs naturally in impure forms such as quartz and sand. Note 2: Silica is the basic material of which the most common communication-grade optical fibers are presently made. VLF - Abbreviation for very low frequency. Frequencies from 3 kHz to 30 kHz. VNL - Abbreviation for via net loss. Pertaining to circuit performance prediction and description that allows circuit parameters to be predetermined and the circuit to be designed to meet established criteria by analyzing actual, theoretical, and calculated losses. 490
- 491. Voice Frequency (VF) - Pertaining to those frequencies within that part of the audio range that is used for the transmission of speech. Note 1: In telephony, the usable voice-frequency band ranges from approximately 300 Hz to 3400 Hz. Note 2: In telephony, the bandwidth allocated for a single voice-frequency transmission channel is usually 4 kHz, including guard bands. Synonym voice band. V Number - In an optical fiber, a dimensionless Synonym normalized frequency (V ). Vocoder - Abbreviation for voice-coder. A device that usually consists of a speech analyzer, which converts analog speech waveforms into narrowband digital signals, and a speech synthesizer, which converts the digital signals into artificial speech sounds. Note 1: For COMSEC purposes, a vocoder may be used in conjunction with a key generator and a modulator-demodulator to transmit digitally encrypted speech signals over narrowband voice communications channels. These devices are used to reduce the bandwidth requirements for transmitting digitized speech signals. Note 2: Some analog vocoders move incoming signals from one portion of the spectrum to another portion. Vodas - Acronym for voice-operated device anti-sing. A device used to prevent overall voice-frequency singing in a two-way telephone circuit by ensuring that transmission can occur in only one direction at any given instant. Vogad - Acronym for voice-operated gain-adjusting device. A device that has a substantially constant output amplitude over a wide range of input amplitudes. Voice Band - Synonym voice frequency. Pertaining to those frequencies within that part of the audio range that is used for the transmission of speech. (188) Note 1: In telephony, the usable voice-frequency band ranges from approximately 300 Hz to 3400 Hz. Note 2: In telephony, the bandwidth allocated for a single voice-frequency transmission channel is usually 4 kHz, including guard bands. Synonym voice frequency.. Voice Coder - See vocoder. A device that usually consists of a speech analyzer, which converts analog speech waveforms into narrowband digital signals, and a speech synthesizer, which converts the digital signals into artificial speech sounds. Note 1: For COMSEC purposes, a vocoder may be used in conjunction with a key generator and a modulator-demodulator to transmit digitally encrypted speech signals over narrowband voice communications channels. These devices are used to reduce the bandwidth requirements for transmitting digitized speech signals. Note 2: Some analog vocoders move incoming signals from one portion of the spectrum to another portion. Voice-Data Signal - See quasi-analog signal. A digital signal that has been converted to a form suitable for transmission over a specified analog channel. Note: The specification of the analog channel should include frequency range, bandwidth, signal-to-noise ratio, and envelope delay distortion. When quasi-analog form of signaling is used to convey message traffic over dial-up telephone systems, it is often referred to as voice- data. A modem may be used for the conversion process. Voice Fax Switch - A device that allows one or more phone lines to be shared for multiple phone connected devices. A common application would allow voice (phones and answering machine) and a fax machine and/or fax modem to operate transparently on a single phone line thus eliminating the monthly costs associated with a dedicated phone line. Applications include any variation of voice, a fax machine, fax/modem and/or modem(s). Incomming calls are automatically routed to the proper device(s) with no human intervention. If the call comes in and it is a fax call, the call is automatically routed to the fax machine or fax.modem. If the call is a modem call, it is routed to the correct modem. Voice calls are routes to phone(s) and/or answering machine. May require a security access code (SAC) in the dialing string to automatically switch to the modem. 491
- 492. Voice Frequency (VF) - Pertaining to those frequencies within that part of the audio range that is used for the transmission of speech. (188) Note 1: In telephony, the usable voice-frequency band ranges from approximately 300 Hz to 3400 Hz. Note 2: In telephony, the bandwidth allocated for a single voice-frequency transmission channel is usually 4 kHz, including guard bands. Synonym voice band. Voice Frequency Carrier Telegraph (VFCT) - Synonym voice-frequency telegraph. A method of multiplexing one or more dc telegraph channels onto a nominal 4-kHz voice frequency channel. Voice-Frequency (VF) Channel - A channel capable of carrying analog and quasi-analog signals. Voice Frequency (VF) Primary Patch Bay - A patching facility that provides the first appearance of local-user VF circuits in the technical control facility (TCF). Note: The VF primary patch bay provides patching, monitoring, and testing for all VF circuits. Signals will have various levels and signaling schemes depending on the user terminal equipment. Voice-Frequency Telegraph (VFTG): A method of multiplexing one or more dc telegraph channels onto a nominal 4-kHz voice frequency channel. Synonym voice frequency carrier telegraph. Voice Grade - In the public regulated telecommunications services, a service grade that is described in part 68, Title 47 of the Code of Federal Regulations [CFR] . Note: Voice-grade service does not imply any specific signaling or supervisory scheme. Voice Mail - a specific application of an interactive voice response system. In its simplest form it mimics the functions of an answering machine, but uses a centralised system rather than equipment at the individual telephone. However it can be far more sophisticated, with the ability to forward messages to another voice mailbox and send simultaneous messages to multiple voice mailboxes, add voice notes to a message, store messages for future delivery, make calls to a telephone or paging service when a message is received, transfer callers to another phone for personal assistance and play different message greetings to different callers. Voicemail messages are stored in media used by computers to store other forms of data (hard drives, optical drives, and tape). Many voicemail systems also offer an automated attendant facility, allowing callers answered by the system to dial a selected person's mail box or telephone. Voicemail systems are found associated with many office telephone systems or (PBX). They may also be associated with public telephone lines as network services. Mobile phones generally have voicemail as a standard network feature. The Phone Company Voice Mail feature answers calls and takes messages when you are on the phone, on the internet, sending a fax, or not at home. This feature also works when the electrical power is out. You can access your voicemail box through a local access number. You enter your PIN and follow the appropriate prompts to use the service. There is a maximum capacity for messages, minutes per message, and message retention length, as outlined in marketing information. Call Forwarding Busy/No Answer must be ordered but will not be billed when Voice Mail is ordered. Voice Mail Plus - A phone company feature that includes the same functionality as Voice Mail except it provides additional mailboxes and recording time. Call Forwarding Busy/No Answer must be ordered but not billed when Voice Mail is ordered. Voice-Operated Device Anti-Sing - See vodas. A device used to prevent overall voice-frequency singing in a two-way telephone circuit by ensuring that transmission can occur in only one direction at any given instant. 492
- 493. Voice-Operated Gain-Adjusting Device - See vogad. A device that has a substantially constant output amplitude over a wide range of input amplitudes. Voice Operated Relay Circuit - Synonym vox. An acoustoelectric transducer and a keying relay connected so that the keying relay is actuated when sound, or voice, energy above a certain threshold is sensed by the transducer. Note: A vox is used to eliminate the need for push-to-talk operation of a transmitter by using voice energy to turn on the transmitter. Voice Operated Transmit - Synonym vox. An acoustoelectric transducer and a keying relay connected so that the keying relay is actuated when sound, or voice, energy above a certain threshold is sensed by the transducer. Note: A vox is used to eliminate the need for push-to-talk operation of a transmitter by using voice energy to turn on the transmitter. Voice-Plus Circuit - Synonym composited circuit. A circuit that can be used simultaneously either for telephony and dc telegraphy or for telephony and signaling. Note: Separation of the two may be accomplished by frequency discrimination. VoIP – (Voice over Internet Protocol) – A technology used to transmit voice over a data network using Internet Protocol, such as the Internet or intranet networks. VoIP is the technology behind Internet phones. VoIP works by digitizing voice signals and sending them as packets through the same networking channels as your data. VoIP Telephony - VoIP is a technology that is used to send voice information in the form of digital data packets, over Internet Protocol, as opposed to using traditional telephone lines. VoIP calls can be placed either from an ordinary telephone (broadband phone), or from a computer, using PC-to-Phone software. VoIP Telephony has proven to be a considerably cheaper and more efficient way to make phone calls, and has become one of the fastest growing trends in telecommunications. Volatile Storage - A storage device in which the contents are lost when power is removed. Volatility - See data volatility. Pertaining to the rate of change in the values of stored data over a period of time. Voltage Standing Wave Ratio (VSWR) - In a transmission line, the ratio of maximum to minimum voltage in a standing wave pattern. Note: The VSWR is a measure of impedance mismatch between the transmission line and its load. The higher the VSWR, the greater the mismatch. The minimum VSWR, i.e., that which corresponds to a perfect impedance match, is unity. Volt-Amperes Reactive (vars) - In alternating-current power transmission and distribution, the product of the rms voltage and amperage, i.e., the apparent power, multiplied by the sine of the phase angle between the voltage and the current. Note 1: Vars represents the power not consumed by a reactive load, i.e., when there is a phase difference between the applied voltage and the current. Note 2: Only effective power, i.e., the actual power delivered to or consumed by the load, is expressed in watts. Volt-amperes reactive is properly expressed only in volt-amperes, never watts. Note 3: To maximize transmission efficiency, vars must be minimized by balancing capacitive and inductive loads, or by the addition of an appropriate capacitive or inductive reactance to the load. Volume - A portion of data, with its physical storage medium, that can be handled conveniently as a unit. Note: An example of a volume is a "floppy" diskette. 493
- 494. Volume Unit (VU) - A unit of measurement of the power of an audio-frequency signal, as measured by a vu meter. Note 1: The vu meter is built and used in accordance with American National Standard C16.5-1942. Note 2: When using the vu meter to measure sine wave test tone power, 0 vu equals 0 dBm. VOX - An acoustoelectric transducer and a keying relay connected so that the keying relay is actuated when sound, or voice, energy above a certain threshold is sensed by the transducer. Note: A vox is used to eliminate the need for push-to-talk operation of a transmitter by using voice energy to turn on the transmitter. Synonyms voice operated relay circuit , voice operated transmit. V Reference Point - The interface point in an ISDN environment between the line termination and the exchange termination. VSB - Abbreviation for vestigial sideband. See vestigial sideband transmission. Modified AM transmission in which one sideband, the carrier, and only a portion of the other sideband are transmitted. V-series Recommendations - Sets of telecommunications protocols and interfaces defined by CCITT (now ITU-T) Recommendations. Note: Some of the more common V.-series Recommendations are: • V.21: A CCITT Recommendation for modem communications over standard commercially available lines at 300 b/s. This protocol is generally not used in the United States. • V.22bis: A CCITT Recommendation for modem communications over standard commercially available voice-grade channels at 2,400 b/s and below. • V.32: A CCITT Recommendation for modem communications over standard commercially available voice-grade channels at 9.6 kb/s and below. • V.32bis: A CCITT Recommendation for modem communication over standard commercially available voice-grade channels at 14.4 kb/s and below. • V.34: An ITU-T Recommendation for modem communication over standard commercially available voice-grade channels at 28.8 kb/s and below. • V.42: A CCITT Recommendation for error correction on modem communications. • V.42bis: A CCITT Recommendation for data compression on a modem circuit. • V.FAST: A new CCITT Recommendation for high-speed modems currently under development. VSWR - Abbreviation for voltage standing wave ratio. In a transmission line, the ratio of maximum to minimum voltage in a standing wave pattern. Note: The VSWR is a measure of impedance mismatch between the transmission line and its load. The higher the VSWR, the greater the mismatch. The minimum VSWR, i.e., that which corresponds to a perfect impedance match, is unity. VU - Abbreviation for volume unit. A unit of measurement of the power of an audio-frequency signal, as measured by a vu meter. (188) Note 1: The vu meter is built and used in accordance with American National Standard C16.5-1942. Note 2: When using the vu meter to measure sine wave test tone power, 0 vu equals 0 dBm. Vulnerability - 1. In communications security, see susceptibility. 2. The extent to which a system will degrade when subjected to a specified set of environmental conditions. 3. In communications interference, see susceptibility threshold. 4. In cryptology, the point of weakness within the encrypted system where threats can occur, such as equipment, facilities, hardware, software, operating systems and personnel. 5. [A] weakness in an information system (IS), [in] system security procedures, [in] internal controls, or [in] implementation that could be exploited. W 494
- 495. Wafer - A thin slice of semiconducting material, such as a silicon crystal, upon which microcircuits are constructed by diffusion and deposition of various materials. Note: Millions of individual circuit elements, constituting hundreds of microcircuits, may be constructed on a single wafer. The individual microcircuits are separated by scoring and breaking the wafer into individual chips ("dice"). Wallpaper - A graphic image that serves as a background for a Web page or for a computer operating system's screen. WAIS - Acronym for Wide Area Information Servers. A distributed text searching system that uses the protocol standard ANS Z39.50 to search index databases on remote computers. Note 1: WAIS libraries are most often found on the Internet. Note 2: WAIS allows users to discover and access information resources on the network without regard to their physical location. Note 3: WAIS software uses the client-server model. WAN - Wide Area Network. A data communications network which expands a LAN to link up with other LANs in remote buildings. A physical or logical network that provides data communications to a larger number of independent users than are usually served by a local area network (LAN) and is usually spread over a larger geographic area than that of a LAN. Note 1: WANs may include physical networks, such as Integrated Services Digital Networks (ISDNs), X.25 networks, and T1 networks. Note 2: A metropolitan area network (MAN) is a WAN that serves all the users in a metropolitan area. WANs may be nationwide or worldwide. Wander - Relative to jitter and swim, long-term random variations of the significant instants of a digital signal from their ideal positions. Note 1: Wander variations are those that occur over a period greater than 1 s (second). Note 2: Jitter, swim, wander, and drift have increasing periods of variation in that order. Warm Boot - Synonym warm restart. Warm Restart - 1. A sequence of operations that is performed to reset a previously running system, after an unintentional shutdown. Synonym warm start. 2. In computer operations, the restarting of equipment, after a sudden shutdown, that allows reuse of previously retained initialized input data, retained programs, and retained output queues. Note 1: A warm restart may be needed after a program failure. Note 2: A warm start or restart cannot occur if initial data, programs, and files are not retained after closedown. Synonyms hot boot, warm boot. Warm Start - Synonym warm restart. Warner Exemption - A statutory exemption pertaining to the acquisition of telecommunications systems that meet the exclusionary criteria of the Warner Amendment, Public Law 97-86, 1 December 1981, which is also known as the Brooks Bill. Note: Use of FTS2000 by U.S. Government agencies is mandatory when telecommunications are required. However, the Warner Amendment excludes the mandatory use of FTS2000 in instances related to maximum security. Watermark - 1. A copyright-protection method of embedding a code into a digital audio or video file to attempt to thwart piracy or unlicenced use. 2. In desktop publishing, an inserted (and usually faint) overlay of an image or text onto pages of a document. Note: The watermark is usually visible on the computer screen in WYSIWIG fashion and on the printed pages of the final document. The watermark often verifies authenticity of authorship or release authority. WATS - Acronym for Wide Area Telephone Service. .wav - A file extension name for one format [i.e., a wave format] of a sound file. 495
- 496. Wave Equation - See Maxwell's equations. Waveform - The representation of a signal as a plot of amplitude versus time. Wavefront - The surface defined by the locus of points that have the same phase, i.e., have the same path length from the source. Note 1: The wavefront is perpendicular to the ray that represents an electromagnetic wave. Note 2: The plane in which the electric and magnetic field vectors lie is tangential to the wavefront at every point. Note 3: The vector that represents the wavefront indicates the direction of propagation. Note 4: For parallel, i.e., collimated, rays, the wavefront is plane. For rays diverging from a point, or converging toward a point, the wavefront is spherical. For rays with varying divergence or convergence, the wavefront has other shapes, such as ellipsoidal and paraboloidal, depending on the nature of the source. Waveguide - A material medium that confines and guides a propagating electromagnetic wave. Note 1: In the microwave regime, a waveguide normally consists of a hollow metallic conductor, usually rectangular, elliptical, or circular in cross section. This type of waveguide may, under certain conditions, contain a solid or gaseous dielectric material. Note 2: In the optical regime, a waveguide used as a long transmission line consists of a solid dielectric filament (optical fiber), usually circular in cross section. In integrated optical circuits an optical waveguide may consist of a thin dielectric film. Note 3: In the rf regime, ionized layers of the stratosphere and refractive surfaces of the troposphere may also act as a waveguide. Waveguide Dispersion - See dispersion. Dispersion, of importance only in single-mode fibers, caused by the dependence of the phase and group velocities on core radius, numerical aperture, and wavelength. Note 1: For circular waveguides, the dependence is on the ratio, a / , where a is the core radius and is the wavelength. Note 2: Practical single-mode fibers are designed so that material dispersion and waveguide dispersion cancel one another at the wavelength of interest. Waveguide Scattering - Scattering (other than material scattering) that is attributable to variations of geometry and refractive index profile of an optical fiber. Wave Impedance - At a point in an electromagnetic wave, the ratio of the electric field strength to the magnetic field strength. Note 1: If the electric field strength is expressed in volts per meter and the magnetic field strength is expressed in ampere-turns per meter, the wave impedance will have the units of ohms. For -7 free space, these values are 4 × 10 H/m (henries per meter) and (1/36 ) F/m (farads per meter), from which 120 , i.e., 377, ohms is obtained. In dielectric materials, the wave impedance is 377/n, where n is the refractive index. Note 2: Although the ratio is called the wave impedance, it is also the impedance of the free space or the material medium. Wavelength - The distance between points of corresponding phase of two consecutive cycles of a wave. Note: The wavelength, , is related to the propagation velocity, v, and the frequency, f, by = v /f. Wavelength-Division Multiplexing (WDM) - In optical fiber communications, any technique by which two or more optical signals having different wavelengths may be simultaneously transmitted in the same direction over one fiber, and then be separated by wavelength at the distant end. Wavelength Stability - Of an optical source during a specified period, the maximum deviation of the peak wavelength from its mean value. Wave Trap - A device used to exclude unwanted frequency components, such as noise or other interference, of a wave. Note: Traps are usually tunable to permit selection of unwanted or interfering signals. 496
- 497. WDM - Abbreviation for wavelength-division multiplexing. Weak Bit - A bit intentionally written on a diskette with a weak magnetic field strength that may be interpreted as zero or one and that is written as part of a method of copy protection. Weakly Guiding Fiber - An optical fiber in which the refractive index contrast is small (substantially less than 1%). Web - See World Wide Web. Web Browser - A user interface (usually graphical) to hypertext information on the World Wide Web. Web Crawler - Synonym spider. Web Document - An HTML (hypertext markup language) document available on the World Wide Web. Webmaster - The person responsible for the production and maintenance of a Web site. A person or group of people responsible for the design, implementation, management, and maintenance of a Web site. Note: Webmastery often includes the fields of network configuration, interface, and graphics design, software development, business strategy, writing, marketing, and project management. Web node - Synonyms Web site, Web server. Web Page - An HTML document accessible on the World Wide Web. Note: The number and types of features that can be offered on a web page is growing almost exponentially. Web Page Search Engine - Loosely synonymous with portal. See droid. Web Phone - See Internet phone. Web Ring - A confederation of (usually linked) Web sites that serve a particular special interest group or that have similar or related content. Web Server - A software program or server computer equipped to offer World Wide Web access. Note: A web server accommodates requests from users, retrieves requested files or applications, and issues error messages. Web Site - A collection of Web documents that Internet users can access to learn information about a particular subject or company. One or more web pages available on the World Wide Web, usually consisting of a home page and often additional pages accessed via the home page via hyperlinks. Note: Web sites have been expanded and now provide many online services such as free e-mail, news, chat, and personalized functions like stock quotes, local weather, and sports. Web sites get much of their revenue from advertising. Webspace - The virtual space created by the World Wide Web or a subset of that space occupied by a particular Web site. Web Spider - Synonym droid. See also spider. Web Surfer: Synonym cybernaut. See also droid. 497
- 498. Web Television - The concept of providing Internet access (usually Web access and e-mail) in a format that can be viewed on a standard television set rather than on the customer's computer. The service usually consists of a set top box that is connected to the user's television, a keyboard, and a telephone line. Webzine - Synonym for e-zine, which is an abbreviation for electronic magazine. A periodical publication that is stored on a file server and that may be distributed or accessed via a computer network.Note: An e-zine that is distributed primarily over the Web is also referred to as a webzine. Weighted Standard Work Second: A measurement of traffic operating work which is used to express the relative time required to handle the various kinds of calls or work functions, and which is weighted to reflect appropriate degrees of waiting to serve time. Weighting Network - A network having a loss that varies with frequency in a predetermined manner, and which network is used for improving or correcting transmission characteristics, or for characterizing noise measurements. Whip Antenna - A flexible rod antenna, usually between 1/10 and 5/8 wavelength long, supported on a base insulator White Area - The area or population which does not receive interference-free primary service from an authorized AM station or does not receive a signal strength of at least 1 mV/m from an authorized FM station. White Facsimile Transmission - 1. In an amplitude-modulated facsimile system, transmission in which the maximum transmitted power corresponds to the minimum density, i.e., the white area, of the object. 2. In a frequency-modulated facsimile system, transmission in which the lowest transmitted frequency corresponds to the minimum density i.e., the white area, of the object. White Noise - Noise having a frequency spectrum that is continuous and uniform over a specified frequency band. Note: White noise has equal power per hertz over the specified frequency band. Synonym: additive white gaussian noise. White Pages - 1. A hard copy telephone directory listing of subscriber names, addresses, and telephone numbers. Note: White pages is associated with the residential subscriber listings in the standard direSctories distributed by the Bell System before divestiture. 2. An electronic information database that contains user names and their associated network addresses, in the manner of a telephone directory. Note : Electronic white pages usually contain additional information, such as office location, phone number, and mailstop. White Signal - In facsimile systems, the signal resulting from scanning a minimum-density area, i.e., the white area, of the object. Who-Are-You (WRU) Character - A transmission-control character used for (a) switching on an answer-back unit in the station with which the connection has been established, (b) triggering the receiving unit to transmit an answer-back code to the terminal that transmitted the WRU signal, and (c) initiating a response that might include station identification, an indication of the type of equipment that is in service, and the status of the station. Note 1: The WRU signal corresponds to the 7-bit code assigned to the WRU. Note 2: The receiving unit may be a telegraph unit, data terminal equipment (DTE), or other unit. Synonym WRU signal. Wi-Fi – A technology that provides short-range, high-speed data connections between mobile data devices (such as laptops) and nearby Wi-Fi access points (hardware connected to a wired network). 498
- 499. Wide Area Information Servers (WAIS) - A distributed text searching system that uses the protocol standard ANS Z39.50 to search index databases on remote computers. Note 1: WAIS libraries are most often found on the Internet. Note 2: WAIS allows users to discover and access information resources on the network without regard to their physical location. Note 3: WAIS software uses the client-server model. Wide Area Network (WAN) - A physical or logical network that provides data communications to a larger number of independent users than are usually served by a local area network (LAN) and is usually spread over a larger geographic area than that of a LAN. Note 1: WANs may include physical networks, such as Integrated Services Digital Networks (ISDNs), X.25 networks, and T1 networks. Note 2: A metropolitan area network (MAN) is a WAN that serves all the users in a metropolitan area. WANs may be nationwide or worldwide. Wide Area Telephone Service (WATS) - A toll service offering for customer dial type telecommunications between a given customer station and stations within specified geographic rate areas employing a single access line between the customer location and the serving central office. Each access line may be arranged for either outward (OUT-WATS) or inward (IN-WATS) service or both. [47 CFR Pt.36-A] Note: The offering is for fixed-rate inter- and intra-LATA services measured by zones and hours. Wideband - 1. The property of any communications facility, equipment, channel, or system in which the range of frequencies used for transmission is greater than 0.1 % of the midband frequency. Note: "Wideband" has many meanings depending upon application. "Wideband" is often used to distinguish it from "narrowband," where both terms are subjectively defined relative to the implied context. 2. In communications security systems, a bandwidth exceeding that of a nominal 4-kHz telephone channel. 3. The property of a circuit that has a bandwidth wider than normal for the type of circuit, frequency of operation, or type of modulation. 4. In telephony, the property of a circuit that has a bandwidth greater than 4 kHz. 5. Pertaining to a signal that occupies a broad frequency spectrum. Synonym broadband. Wideband Channel - A communication channel of a bandwidth equivalent to twelve or more voice-grade channels. Wideband Modem - 1. A modem whose modulated output signal can have an essential frequency spectrum that is broader than that which can be wholly contained within, and faithfully transmitted through, a voice channel with a nominal 4-kHz bandwidth. (188) 2. A modem whose bandwidth capability is greater than that of a narrowband modem. Widescreen - 1. A term used generally to describe an aspect ratio wider than 4:3. For television, this refers to the 16 x 9 aspect ratio. Wildcard Character - 1. A character that may be substituted for any of a defined subset of all possible characters. Note 1: In high-frequency (HF) radio automatic link establishment, the wildcard character "?" may be substituted for any one of the 36 characters, "A" through "Z" and "0" through "9." Note 2: Whether the wildcard character represents a single character or a string of characters must be specified. (188) 2. In computer (software) technology, a character that can be used to substitute for any other character or characters in a string. Note: The asterisk (*) usually substitutes as a wildcard character for any one or more of the ASCII characters, and the question mark (?) usually substitutes as a wildcard character for any one ASCII character. Wild-Point Detection - A test to determine whether a value conforms to specified criteria. Note: A wild-point detection can be used to eliminate questionable data points from subsequent processing. Synonym reasonableness check. WIN - Abbreviation for WWMCCS Intercomputer Network. 499
- 500. Window - 1. In fiber optics, a band of wavelengths at which an optical fiber is sufficiently transparent for practical use in communications applications. Synonyms spectral window, transmission window. See first window, second window, third window. 2. In imagery, a portion of a display surface in which display images pertaining to a particular application can be presented. Note: Different applications can be displayed simultaneously in different windows. 3. A period during which an event can occur, can be expected to occur, or is allowed to occur. Windowing - Sectioning of a video display area into two or more separate regions for the purpose of displaying images from different sources. Note: In windowing, one window could display data, another motion video from a remote site, and another, graphics. Wink - In telephone switching systems, a single supervisory pulse, i.e., the momentary presence of, or interruption of, a supervisory signal. Note: An example of a wink is the momentary flash of a supervisory light on an attendant's switchboard. Wink Pulsing - In telephone switching systems, recurring pulsing in which the off-condition is relatively short compared to the on-condition. Note: On key-operated telephone instruments, the hold position, i.e., the hold condition, of a line is often indicated by wink pulsing the associated lamp at 120 pulses per minute. During 6% of the pulse period the lamp is off and 94% of the period the lamp is on, i.e., 30 ms (milliseconds) off and 470 ms on. Wired Radio Frequency Systems - Systems employing restricted radiation devices in which the radio frequency energy is conducted or guided along wires or in cables, including electric power and telephone lines. Wireless – Voice and data telecommunications technology that uses the radio-frequency spectrum rather than wires for transmitting and receiving voice, data and video signals. Wireless is a term used to describe telecommunications in which electromagnetic waves (rather than some form of wire) carry the signal over part or all of the communication path. Some monitoring devices, such as intrusion alarms, employ acoustic waves at frequencies above the range of human hearing; these are also sometimes classified as wireless. The first wireless transmitters went on the air in the early 20th century using radiotelegraphy (Morse code). Later, as modulation made it possible to transmit voices and music via wireless, the medium came to be called "radio." With the advent of television, fax, data communication, and the effective use of a larger portion of the spectrum, the term "wireless" has been resurrected. Descriptive of a network or terminal that uses electromagnetic waves (including rf, infrared, laser, visible light–and acoustic energy) rather than wire conductors for telecommunications. Wireless Access - Terminal access to the network which uses wireless technology. Wireless Access Mode - In personal communications service, interfacing with a network access point by means of a standardized air interface protocol without the use of a hardwired connection to the network Wireless Mobility Management - In Personal Communications Service (PCS), the assigning and controlling of wireless links for terminal network connections. Note: Wireless mobility management provides an "alerting" function for call completion to a wireless terminal, monitors wireless link performance to determine when an automatic link transfer is required, and coordinates link transfers between wireless access interfaces.. Wireless Services Provider - A company that provides wireless telecommunication service to customers, e.g., cellular service providers, radio common carriers, paging companies. 500
- 501. Wireless Terminal - Any mobile terminal, mobile station, personal station, or personal terminal using non- fixed access to the network. Wireline – A conventional (wired) telephone network versus a wireless network. Wireline Common Carrier - Common carriers [that] are in the business of providing landline local exchange telephone service. Wizard - An intelligent, trainable Web spider. Synonyms droid, smart bot, spider. Word - A character string or a bit string considered to be an entity for some purpose. Note: In telegraph communications, six character intervals are defined as a word when computing traffic capacity in words per minute, which is computed by multiplying the data signaling rate in baud by 10 and dividing the resulting product by the number of unit intervals per character. Word Length - The number of characters or bits in a word. Word Processing: The use of a computer system to manipulate text. Note: Examples of word processing functions include entering, editing, rearranging, sorting, storing, retrieving, displaying, and printing text. Synonym text processing. Work Space - In computers and data processing systems, the portion of main storage that is used by a computer program for the temporary storage of data. Work Station - 1. In automated systems, such as computer, communications, and control systems, the input, output, display, and processing equipment that provides the operator-system interface. 2. A configuration of input, output, display, and processing equipment that constitutes a stand-alone system not requiring external access. Working Loop - A revenue producing pair of wires, or its equivalent, between a customer's station and the central office from which the station is served. World Numbering Plan - A plan created by the International Telegraph and Telephone Consultative Committee (CCITT--now, the ITU-T) that provides each telephone subscriber with a unique number. Each world telephone number consists of a country code followed by the national number. By international agreement, the number of digits in the country code plus national number is limited to a total of 15 digits. World Time - Time scale, based on the second (SI), as defined and recommended by the CCIR, and maintained by the Bureau International des Poids et Mesures (BIPM). For most practical purposes associated with the Radio Regulations, UTC is equivalent to mean solar time at the prime meridian (0° longitude), formerly expressed in GMT. [NTIA] [RR] Note 1: The maintenance by BIPM includes cooperation among various national laboratories around the world. Note 2: The full definition of UTC is contained in CCIR Recommendation 460-4. (188) Note 3 : The second was formerly defined in terms of astronomical phenomena. When this practice was abandoned in order to take advantage of atomic resonance phenomena ("atomic time") to define the second more precisely, it became necessary to make occasional adjustments in the "atomic" time scale to coordinate it with the workaday mean solar time scale, UT-1, which is based on the somewhat irregular rotation of the Earth. Rotational irregularities usually result in a net decrease in the Earth's average rotational velocity, and ensuing lags of UT-1 with respect to UTC. Note 4: Adjustments to the atomic, i.e., UTC, time scale consist of an occasional addition or deletion of one full second, which is called a leap second. Twice yearly, during the last minute of the day of June 30 and December 31, Universal Time, adjustments may be made to ensure that the accumulated difference between UTC and UT-1 will not exceed 501
- 502. 0.9 s before the next scheduled adjustment. Historically, adjustments, when necessary, have usually consisted of adding an extra second to the UTC time scale in order to allow the rotation of the Earth to "catch up." Therefore, the last minute of the UTC time scale, on the day when an adjustment is made, will have 59 or 61 seconds. Synonyms Coordinated Universal Time , Z Time, Zulu Time. World Wide Web (WWW) - A HyperText system that allows users to navigate, or look through, linked documents and resources. Also Web, WWW, W3. A global, virtual-network based hypertext information system that uses the Internet as its transport mechanism to display computer screens (or Web pages) of graphical, video, textual, and even audio information. Note: In a hypertext system, one navigates by clicking hyperlinks, which display another document which also contains hyperlinks. In Web navigation, the next document seen could be housed on a computer next door or half-way around the world. Created in 1989 at a research institute in Switzerland, the Web relies upon browsers and the hypertext transport protocol (http), an Internet standard that specifies how an application can locate and acquire resources stored on another computer on the Internet. Most Web documents are created using hypertext markup language (html), a coding system for WWW documents. Incorporating hypermedia (graphics, sounds, animations, video), the Web has become a popular medium for publishing information on the Internet. With the development of secured server protocol (https), the Web is now a commercial medium whereby consumers can browse on- line catalogs and purchase merchandise using secure, encrypted credit card information that is protected from interception. Synonym Web. The World Wide Web is an international, virtual-network-based information service composed of Internet host computers that provide on-line information in a specific hypertext format. Note 1: WWW servers provide hypertext metalanguage (HTML) formatted documents using the hypertext transfer protocol (HTTP). Note 2: Information on the WWW is accessed with a hypertext browser such as Mosaic, Viola, or Lynx. Note 3: No hierarchy exists in the WWW, and the same information may be found by many different approaches. Worm - 1. A computer virus capable of disrupting a computer program. 2. A self-contained program that can propagate itself through systems or networks. Note: Worms are often designed to use up available resources such as storage or processing time. 3. [An] independent program that replicates from machine to machine across network connections, often clogging networks and computer systems as it spreads. 4. Acronym for write once, read many (times). Note: A worm drive is used in recording data on a disk such that the data can then be read but not erased. Worst Hour of the Year - That hour of the year during which the median noise over any radio path is at a maximum. Note: This hour is considered to coincide with the hour during which the greatest transmission loss occurs. W-Profile Fiber - A single-mode fiber that has two claddings. Note 1: Each cladding has a refractive index that is lower than that of the core. Of the two claddings, inner and outer, the inner cladding has the lower refractive index. Note 2 : A doubly clad fiber has the advantage of very low macrobending losses. It also has two zero-dispersion points, and low dispersion over a much wider wavelength range than a singly clad fiber. (from the fact that a symmetrical plot of its refractive index profile superficially resembles the letter W). Synonyms depressed-cladding fiber, depressed-inner-cladding fiber, doubly clad fiber. Wrapping - 1. In a network using dual counter-rotating ring architecture, reconfiguration to circumvent a failed link or node. 2. In open systems architecture, the use of a network to connect two other networks, thus providing an increased interaction capability between the two connected networks. Note: Recurring application of wrapping usually results in a hierarchical structure. Write - To make a permanent or transient recording of data in a storage device or on a data medium. 502
- 503. Write Cycle Time - The minimum time interval between the starts of successive write cycles of a storage device that has separate reading and writing cycles. Write Head - A magnetic head capable of writing only. Write Protection Label - See write-protect tab. Write-Protect Tab - A movable or removable tab, label, or other device, the presence or absence of which on the casing of a recording medium prevents writing on the medium. Note: An example of a write-protect tab is the sliding tab on a 3½-inch (8.85-cm) magnetic diskette of the type used in conjunction with desktop computers. WRU signal - Synonym who-are-you (WRU) character. A transmission-control character used for (a) switching on an answer-back unit in the station with which the connection has been established, (b) triggering the receiving unit to transmit an answer-back code to the terminal that transmitted the WRU signal, and (c) initiating a response that might include station identification, an indication of the type of equipment that is in service, and the status of the station. Note 1: The WRU signal corresponds to the 7-bit code assigned to the WRU. Note 2: The receiving unit may be a telegraph unit, data terminal equipment (DTE), or other unit. WWMCCS - Abbreviation for Worldwide Military Command and Control System. WWW - See World Wide Web X X-bits: Unassigned overhead bits. Transmitters should code these bits as zeros while receivers are required to be capable of ignoring the value contained in these bits. X-dimension of recorded spot - In facsimile systems, the effective recorded spot dimension measured in the direction of the recorded line. Note 1: By "effective recorded spot dimension" is meant the largest center-to- center spacing between recorded spots, which gives minimum peak-to-peak variation of density of the recorded line. Note 2: "X-dimension of recorded spot" implies that the facsimile equipment response to a constant density in the object (original) is a succession of discrete recorded spots. X-dimension of scanning spot - In facsimile systems, the distance between the centers of adjacent scanning spots measured in the direction of the scanning line on the object. Note: The numerical value of the X- dimension of scanning spot depends upon the type of system. Xerographic recording - Recording enabled by the scanning action of an optical beam on a photoconducting surface on which an electrostatically charged latent image is developed with a resinous powder (toner). XML- Abbreviation for eXtensible Markup Language. A trimmed specification or version of the Standard Generalized Markup Language (SGML) that allows Web developers to create customized tags for additional functionality. XO- Abbreviation for crystal oscillator. XOFF - An abbreviation for the ASCII transmission-control character meaning "Transmitter off." XON - An abbreviation for the ASCII transmission-control character meaning "Transmitter on." 503
- 504. X.-series Recommendations - Sets of data telecommunications protocols and interfaces defined by CCITT (now, ITU-T) Recommendations. Note: Some of the more common X.-series Recommendations are: • X.25: A Recommendation for public packet switched communications between a network user and the network itself. • X.75: A Recommendation for public packet switched communications between network hubs. • X.400: An addressing scheme for use with e-mail. • X.500: An addressing scheme for directory services. XT- Abbreviation for crosstalk. X-Y Mount - Synonym altazimuth mount. Y Yagi Antenna -1. A linear end-fire antenna, consisting of three or more half-wave elements (one driven, one reflector, and one or more directors). Note 1: A Yagi antenna offers very high directivity and gain. Note 2: The formal name for a "Yagi antenna" is "Yagi-Uda array." 2. A type of directional antenna system, generally designed for UHF frequencies, which is ideal for receiving most DTV stations. Ranging in size from several inches to many feet, a Yagi Antenna is the most common design for rooftop antennas. Y-Dimension of Recorded Spot - In facsimile systems, the distance between the centers of adjacent recorded spots on adjacent lines measured perpendicular to the recorded line. Y-Simension of Scanning Spot - In facsimile systems, the distance between the centers of adjacent scanning spots on adjacent lines measured perpendicular to the scanning line on the object. Note: The numerical value of the Y-dimension of scanning spot depends upon the type of system. Yellow Alarm - An indication provided to a source device indicating a signal failure condition at a sink device. Synonyms remote alarm indication, yellow alarm signal. Yellow Alarm Signal - Synonym yellow alarm. Yellow Pages - 1. A hard copy telephone directory listing of business subscriber names, addresses, and telephone numbers. Note: Yellow pages is associated with the residential subscriber listings in the standard directories distributed by the Bell System before divestiture. 2. An electronic information database that contains business names and their associated network addresses, in the manner of a telephone directory. Note : Electronic yellow pages usually contain additional information, such as office location, phone number, and mailstop. Z Z - Z is an abbreviation for Zulu time. See Coordinated Universal Time. - Time scale based on the second (SI), as defined and recommended by the CCIR, and maintained by the Bureau International des Poids et Mesures (BIPM). For most practical purposes associated with the Radio Regulations, UTC is equivalent to mean solar time at the prime meridian (0° longitude), formerly expressed in GMT. Note 1: The maintenance by BIPM includes coordinating inputs from time standards belonging to various national laboratories around the world, which inputs are averaged to create the international time standard (second). Note 2: The full definition of UTC is contained in CCIR Recommendation 460-4. Note 3: The second was formerly defined in terms of astronomical phenomena. When this practice was abandoned in order to take advantage of atomic resonance phenomena (" atomic time ") to define the second more precisely, it became necessary to make 504
- 505. occasional adjustments in the "atomic" time scale to coordinate it with the workaday mean solar time scale, UT-1, which is based on the somewhat irregular rotation of the Earth. Rotational irregularities usually result in a net decrease in the Earth's average rotational velocity, and ensuing lags of UT-1 with respect to UTC. Note 4: Adjustments to the atomic, i.e., UTC, time scale consist of an occasional addition or deletion of one full second, which is called a leap second. Twice yearly, during the last minute of the day of June 30 and December 31, Universal Time, adjustments may be made to ensure that the accumulated difference between UTC and UT-1 will not exceed 0.9 s before the next scheduled adjustment. Historically, adjustments, when necessary, have usually consisted of adding an extra second to the UTC time scale in order to allow the rotation of the Earth to "catch up." Therefore, the last minute of the UTC time scale, on the day when an adjustment is made, will have 61 seconds. Synonyms World Time, Z Time, Zulu Time. ZBTSI (zero-byte time slot interchange) - A technique applied to a DS1 frame to ensure pulse density requirements are met, where bits 2 through 193 of each frame are scrambled to minimize the occurrence of all-zero octets. When an all-zero octet is contiguous to another octet with zeros and they would combine to violate the ones density requirement, an algorithm is invoked where some all-zero octets are replaced by an address chain. The reverse algorithms are performed by the receiving terminal. Zero-bit Insertion - A bit-stuffing technique used with bit-oriented protocols to ensure that six consecutive "1" bits never appear between the two flags that define the beginning and the ending of a transmission frame. Note: When five consecutive "1" bits occur in any part of the frame other than the beginning and ending flag, the sending station inserts an extra "0" bit. When the receiving station detects five "1" bits followed by a "0" bit, it removes the extra "0" bit, thereby restoring the bit stream to its original value. Synonyms zero insertion, zero stuffing. Zero dBm Transmission Level Point (0 dBm TLP) - In a communication system, a point at which the reference level is 1 mW, i.e., 0 dBm. Note: The actual power level of the communications traffic is not necessarily 0 dBm. It is usually below the reference level. The reference is for system design and test purposes. Synonym zero transmission level point. Zero-Dispersion Slope - In a single-mode optical fiber, the rate of change of dispersion, with respect to wavelength, at the fiber's zero-dispersion wavelength. Note 1: In silica-based optical fibers, the zero- dispersion wavelength occurs at approximately 1.3 m, but this wavelength may be shifted toward the minimum-loss window by the addition of dopants to the fiber material during manufacture. Note 2: Doubly and quadruply clad single-mode fibers have two zero-dispersion points, and thus two zero-dispersion slopes. Zero-Dispersion Wavelength = 1. In a single-mode optical fiber, the wavelength or wavelengths at which material dispersion and waveguide dispersion cancel one another. Note: In all silica-based optical fibers, minimum material dispersion occurs naturally at a wavelength of approximately 1.3 m. Single-mode fibers may be made of silica-based glasses containing dopants that shift the material-dispersion wavelength, and thus, the zero-dispersion wavelength, toward the minimum-loss window at approximately 1.55 m. The engineering tradeoff is a slight increase in the minimum attenuation coefficient. 2. Loosely, in a multimode optical fiber, the wavelength at which material dispersion is minimum, i.e., essentially zero. Synonym minimum-dispersion wavelength. Aero Dispersion Window - Synonym minimum-dispersion window. Zerofill - To fill unused storage locations in an information system (IS) with the representation of the character denoting "0". Zero Insertion - See zero-bit insertion. A bit-stuffing technique used with bit-oriented protocols to ensure that six consecutive "1" bits never appear between the two flags that define the beginning and the ending of a transmission frame. Note: When five consecutive "1" bits occur in any part of the frame other than the 505
- 506. beginning and ending flag, the sending station inserts an extra "0" bit. When the receiving station detects five "1" bits followed by a "0" bit, it removes the extra "0" bit, thereby restoring the bit stream to its original value. Zeroize - To remove or eliminate the key from a crypto-equipment or fill device. Zeroized - Electronically stored data that have been degaussed, erased, or overwritten. Zero-Level Decoder - A decoder that yields an analog level of 0 dBm at its output when the input is the digital milliwatt signal. Note: The signal is a 1-kHz sine wave. 0 + (7 or 10 digits) = A feature of the North American Numbering Plan that identifies customer dialed calls that are operator assisted, either by electronic or manual (human) means. Zero Stuffing - See zero-bit insertion. A bit-stuffing technique used with bit-oriented protocols to ensure that six consecutive "1" bits never appear between the two flags that define the beginning and the ending of a transmission frame. Note: When five consecutive "1" bits occur in any part of the frame other than the beginning and ending flag, the sending station inserts an extra "0" bit. When the receiving station detects five "1" bits followed by a "0" bit, it removes the extra "0" bit, thereby restoring the bit stream to its original value. Zero Suppression - The elimination of nonsignificant zeros from a numeral. ZTLP - Abbreviation for zero transmission level point. Zero Transmission Level P oint (0TLP) - Synonym zero dBm transmission level point. - In a communication system, a point at which the reference level is 1 mW, i.e., 0 dBm. Note: The actual power level of the communications traffic is not necessarily 0 dBm. It is usually below the reference level. The reference is for system design and test purposes. Synonym zero transmission level point. Zip-cord - In optical communications, a two-fiber cable consisting essentially of two single-fiber cables having their jackets conjoined by a strip of jacket material. Note 1: This name is borrowed from electrical terminology referring to lamp cord. As with lamp cord, optical zip-cord may be easily furcated by slitting or tearing the two jackets apart, permitting the installation of optical connectors. Note 2: Zip-cord cables include both loose-buffer and tight-buffer designs. Zone - See communications zone, Fresnel zone, skip zone. Zone of Influence - The area surrounding a power station that is raised in potential above a remote or true grounding (earthing) point. Zone of Protection - The space, adjacent to a lightning protection system, that is substantially immune to direct lightning strokes. Zone of Silence - Synonym skip zone. Zooming- The act of changing the scale of a display, generally without changing the amount of screen space it occupies. Z Time - Abbreviation for Zulu Time. See Coordinated Universal Time. 506
- 507. Zulu Time (Z) - Synonym Coordinated Universal Time. Formerly a synonym for Greenwich Mean Time. 507