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First Things
First
CHAPTER
1
1
Source: Telecom Crash Course
Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2004 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.

Telecommunications, like all highly visible and interesting fields, is full
of apocryphal stories, technical myths, and fascinating legends. Everyone
in the field seems to know someone who knows the outside plant repair
person who found the poisonous snake in the equipment box in the man-
hole1
, the person who was on the cable-laying ship when they pulled up
the cable that had been bitten through by some species of deep water
shark, some collection of seriously evil hackers, or the backhoe driver
who cut the cable that put Los Angeles off the air for 12 hours.
There is also a collection of techno-jargon that pervades the tele-
commnications industry and often gets in the way of the relatively
straightforward task of learning how all this stuff actually works.
To ensure that such things don’t get in the way of absorbing what’s in
this book, I’d like to begin with a discussion of some of them.
This is a book about telecommunications, which is the science of com-
municating over distance (tēle-, from the Greek tēle, “far off”). It is, how-
ever, fundamentally dependent upon data communications, the science
of moving traffic between computing devices so that the traffic can be
manipulated in some way to make it useful. Data, in and of itself, is not
particularly useful, consisting as it does of a stream of ones and zeroes
that is only meaningful to the computing device that will receive and
manipulate those ones and zeroes. The data does not really become use-
ful until it is converted by some application into information, because a
human can generally understand information. The human then acts
upon the information using a series of intuitive processes that further
convert the information into knowledge, at which point it becomes truly
useful. Here’s an example:A computer generates a steady stream of ones
and zeroes in response to a series of business activities involving the
computer that generates the ones and zeroes. Those ones and zeroes are
fed into another computer, where an application converts them into a
spreadsheet of sales figures (information) for the store from which they
originated. A financial analyst studies the spreadsheet, calculates a few
ratios, examines some historical data (including not only sales numbers
but demographics, weather patterns, and political trends), and makes an
informed prediction about future stocking requirements and advertising
focal points for the store based on the knowledge that the analyst was
able to create from the distilled information.
Data communications rely on a carefully designed set of rules that
governs the manner in which computers exchange data. These rules are
called protocols, and they are centrally important to the study of data
Chapter 1
2
1I realize that this term has fallen out of favor today, but I use it here for historical accuracy.
First Things First

communications. Dictionaries define protocol as “a code of correct con-
duct.” From the perspective of data communications, they define it as “a
standard procedure for regulating the transmission of data between com-
puters,” which is itself “a code of correct conduct.” These protocols, which
will be discussed in detail later in this book, provide a widely accepted
methodology for everything from the pin assignments on physical con-
nectors to the sublime encoding techniques used in secure transmission
systems. Simply put, they represent the many rule sets that govern the
game. Many countries play football, for example, but the rules are all
slightly different. In the United States, players are required to weigh
more than a car, yet be able to run faster than one. In Australian Rules
football, the game is declared forfeit if it fails to produce at least one body
part amputation on the field or if at least one player doesn’t eat another.
They are both football, however. In data communications, the problem is
similar; there are many protocols out there that accomplish the same
thing. Data, for example, can be transmitted from one side of the world
to the other in a variety of ways including T1, E1, microwave, optical
fiber, satellite, coaxial cable, and even through the water. The end result
is identical: the data arrives at its intended destination. Different proto-
cols, however, govern the process in each case.
A discussion of protocols would be incomplete without a simultaneous
discussion of standards. If protocols are the various sets of rules by which
the game is played, standards govern which set of rules will be applied
for a particular game. For example, let’s assume that we need to move
traffic between a PC and a printer. We agree that in order for the PC to
be able to transmit a printable file to the printer, both sides must agree
on a common representation for the zeroes and ones that make up the
transmitted data. They agree, for example (and this is only an example)
that they will both rely on a protocol that represents a zero as the
absence of voltage and a one as the presence of a three-volt pulse on the
line, as shown in Figure 1-1. Because they agree on the representation,
the printer knows when the PC is sending a one and when the PC is
sending a zero. Imagine what would happen if they failed to agree on
such a simple thing beforehand. If the transmitting PC decides to repre-
sent a one as a 300-volt pulse and the printer is expecting a three-volt
3
First Things First
1 1 1 1
0 0 0 0
1
Figure 1-1
Voltage
representations
of data.
First Things First

pulse, the two devices will have a brief (but inspired) conversation, the
ultimate result of which will be the release of a small puff of silicon
smoke from the printer.
Now they have to decide on a standard that they will use for actually
originating and terminating the data that they will exchange. They are
connected by a cable (see Figure 1-2) that has nine pins on one end and
nine jacks on the other. Logically, the internal wiring of the cable would
look like Figure 1-3. However, when we stop to think about it, this one-
to-one correspondence of pin-to-socket will not work. If the PC transmits
on pin 2, which in our example is identified as the send data lead, it will
arrive at the printer on pin 2—the send data lead. This would be analo-
gous to holding two telephone handsets together so that two communi-
cating parties can talk. It won’t work without a great deal of hollering.
Instead, some agreement has to be forged to ensure that the traffic
placed on the send-data lead somehow arrives on the receive data lead
and vice versa. Similarly, the other leads must be able to convey infor-
mation to the other end so that normal transmission can be started and
stopped. For example, if the printer is ready to receive the print file, it
might put voltage on the data terminal ready (DTR) lead, which signals
to the PC that it is ready to receive traffic. The PC might respond by set-
ting its own DTR lead high as a form of acknowledgment, followed by
Chapter 1
4
Send Data
(pin 2) Ground
Carrier
Data Set Ready
Data Terminal Ready
Receive Data
Request to Send
Clear to Send
Figure 1-2
Pin
assignments
on a cable
connector.
Figure 1-3
Logical wiring
scheme.
First Things First

transmission of the file that is to be printed. The printer will keep its
DTR lead high until it wants the PC to stop sending. For example, if the
printer senses that it is running out of buffer space because the PC is
transmitting faster than the slower printer can print, it will drop the
DTR lead, causing the PC to temporarily halt its transmission of the
print file.As soon as the printer is ready to receive again, it sets the DTR
lead high once again, and printing resumes. As long as both the trans-
mitter and the receiver abide by this standard set of rules, data commu-
nications will work properly. This process of swapping the data on the
various leads of a cable, incidentally, is done by the modem—or by a null
modem cable that makes the communicating devices think they are talk-
ing to a modem. The null modem cable is wired so that the send-data
lead on one end is connected to the receive data lead on the other end and
vice-versa; similarly, a number of control leads such as the carrier detect
lead, the DTR lead, and the data set ready (DSR) leads are wired
together so that they give false indications to each other to indicate that
they are ready to proceed with the transmission, when in fact no
response from the far end modem has been received.
Standards: Where Do They
Come From?
Physicists, electrical engineers, and computer scientists generally design
data communications protocols. For example, the Transmission Control
Protocol (TCP) and the Internet Protocol (IP) were written during the
heady days of the Internet back in the 1960s by such early pioneers as
Vinton Cerf and the late John Postel. (I want to say “back in the last cen-
tury” to make them seem like real pioneers.) Standards, on the other
hand, are created as the result of a consensus-building process that can
take years to complete. By design, standards must meet the require-
ments of the entire data and telecommunications industry, which is of
course global. It makes sense, therefore, that some international body is
responsible for overseeing the creation of international standards. One
such body is the United Nations. Its 150 plus member nations work
together in an attempt to harmonize whatever differences they have at
various levels of interaction, one of which is international telecommuni-
cations. The International Telecommunications Union (ITU), a sub-
organization of the UN, is responsible for not only coordinating the
5
First Things First
First Things First

creation of worldwide standards but also publishing them under the aus-
pices of its own sub-organizations.These include the Telecommunications
Standardization Sector (TSS, sometimes called the ITU-T, and formerly
the Consultative Committee on International Telegraphy and Telephony,
the CCITT), the Telecommunications Development Sector (TDS), and the
Radio Communication Sector (RCS, formerly the Consultative Commit-
tee on International Radio, the CCIR). The organizational structure is
shown in Figure 1-4.
Of course, the UN and its sub-organizations cannot perform this
task alone, nor should they. Instead, they rely upon the input of hun-
dreds of industry-specific organizations as well as local, regional,
national, and international standards bodies that feed information,
perspectives, observations, and technical direction to the ITU, which
serves as the coordination entity for the overall international
standards creation process. These include the American National
Standards Institute (ANSI), the European Telecommunications Stan-
dards Institute (ETSI, formerly the Conference on European Post and
Telegraph, CEPT), Telcordia (formerly Bellcore, now part of SAIC), the
International Electrotechnical Commission (IEC), the European
Computer Manufacturers Association (ECMA), and a host of others.
It is worthwhile to mention a bit about the ITU as a representative
standards body. Founded in 1947 as part of the United Nations, it
descended from a much older body called the Union Telegraphique,
founded in 1865 and chartered to develop standards for the emerging
telegraph industry. Over the years since its creation, the ITU and its
three principal member bodies have developed three principal goals:
■ To maintain and extend international cooperation for the
improvement and interconnectivity of equipment and systems
through the establishment of technical standards.
Chapter 1
6
UN
ITU
TDS
TSS RCS
Figure 1-4
The ITU
organizational
structure.
First Things First

■ To promote the development of the technical and natural facilities
(read spectrum) for most efficient applications.
■ To harmonize the actions of national standards bodies to attain
these common aims, and most especially to encourage the
development of communications facilities in developing countries.
The Telecommunications
Standardization Sector
The goals of the TSS, according to the ITU, are as follows:
■ To fulfill the purposes of the union relating to telecommunication
standardization by studying technical, operating, and tariff
questions and adopting formal recommendations on them with a
view to standardizing telecommunications on a worldwide basis.
■ To maintain and strengthen its pre-eminence in international
standardization by developing recommendations rapidly.
■ To develop recommendations that acknowledge market and trade-
related considerations.
■ To play a leading role in the promotion of cooperation among
international and regional standardization organizations and
forums and consortia concerned with telecommunications.
■ To address critical issues that relate to changes due to competition,
tariff principles, and accounting practices.
■ To develop recommendations for new technologies and applications
such as appropriate aspects of the GII and Global multimedia and
mobility.
The Telecommunications
Standardization Bureau
The Telecommunication Standardization Bureau provides secretarial
support for the work of the ITU-T Sector and services for the participants
in ITU-T work, diffuses information on international telecommunications
7
First Things First
First Things First

worldwide, and establishes agreements with many international stan-
dards development organizations. These functions include:
■ Study group management The management team of the study
groups is composed of the chairman, vice-chairmen of the study
group, chairmen of the working parties, and the TSB
counselor/engineer.
■ Secretarial support and meeting organization TSB provides
secretariat services for ITU-T assemblies and study group meetings.
TSB counselors and engineers coordinate the work of their study
group meetings, and their assistants ensure the flow of meeting
document production.
■ Logistics services The TSB provides services, such as meeting
room allocation, registration of participants, document distribution,
and facilities for meeting participants.
■ Approval of recommendations and other texts The TSB
organizes and coordinates the approval process of recommendations.
■ Access to ITU-T documents for ITU-T members The TSB
organizes and controls the dispatch of documents in paper form to
participants in ITU-T work and provides Electronic Document
Handling services (EDH) that enable easy and rapid exchange of
documents, information, and ideas among ITU-T participants in
order to facilitate the work of standards development. The ITU-T
participants can have electronic access, via TIES, to study group
documents such as reports, contributions, delayed contributions,
temporary and liaison documents, and so on.
The TSB also provides the following services:
■ Maintenance of the ITU-T Website and distribution of information
about the activities of the sector including the schedule of meetings,
TSB circulars, collective letters, and all working documents.
■ Update services for the list of ITU-T recommendations, the ITU-T
work programmer database, the ITU-T patent statements database,
and the ITU-T terms and definitions database Sector Abbreviations
and Definitions for a Telecommunications Thesaurus-Oriented
Database (SANCHO), as well as update services for other databases
as required.
■ Country code number assignment for telephone, data, and other
services.
■ Registrar services for Universal International Freephone Numbers
(UIFN).
Chapter 1
8
First Things First

■ Technical information on international telecommunications and
collaborates closely with the ITU radio communication sector and
with the ITU telecommunication development sector for matters of
interest to developing countries.
■ Provides administrative and operational information through the
ITU Operational Bulletin.
■ Coordinates the editing, publication, and posting of the
recommendations.
The Radio Bureau
The functions of the radio bureau include:
■ Administrative and technical support to radio communication
conferences, radio communication assemblies and study groups,
including working parties and task groups.
■ Application of the provisions of the Radio Regulations and various
regional agreements.
■ Recording and registration of frequency assignments and also
orbital characteristics of space services and maintenance of the
master international frequency register.
■ Consulting services to member states on the equitable, effective, and
economical use of the radio-frequency spectrum and satellite orbits,
and investigates and assists in resolving cases of harmful
interference.
■ Preparation, editing, and dispatch of circulars, documents, and
publications developed within the sector.
■ Delivers technical information and seminars on national frequency
management and radio communications, and works closely with the
telecommunication development bureau to assist developing
countries.
The Standards
A word about the publications of the ITU. First of all, they are referred to
as recommendations because the ITU has no enforcement authority over
the member nations that use them. Its strongest influence is exactly that
—the ability to influence its member telecommunications authorities to
use the standards because it makes sense to do so on a global basis.
9
First Things First
First Things First

The standards are published every four years, following enormous
effort on the part of the representatives that sit on the organization’s
task forces. These representatives hail from all corners of the industry;
most countries designate their national telecommunications company
(where they still exist) as the representative to the ITU-T, while others
designate an alternate, known as a Recognized Private Operating Agency
(RPOA).The United States, for example, has designated the Department
of State as its duly elected representative body. Other representatives
may include manufacturers (Lucent, Cisco, Nortel, and Fujitsu), research
and development organizations (Bell Northern Research, Bell Laborato-
ries, and Xerox PARC), and other international standards bodies.
At any rate, the efforts of these organizations, companies, govern-
ments, and individuals result in the creation of a collection of new
and revised standards recommendations published on a four-year cycle.
Historically, the standards are color-coded, published in a series of large
format soft-cover books, differently colored on a rotating basis. For exam-
ple, the 1984 books were red; the 1988 books, blue; the 1992 books, white.
It is common to hear network people talking about “going to the blue
book.” They are referring (typically) to the generic standards published
by the ITU for that particular year. It is also common to hear people talk
about the CCITT. Old habits die hard:The organization ceased to exist in
the early 1990s, replaced by the ITU-T.The name is still commonly used,
however.
The activities of the ITU-T are parceled out according to a cleverly
constructed division of labor. Three efforts result: study groups, which
create the actual recommendations for telecom equipment, systems, net-
works, and services (there are currently 15 study groups), plan commit-
tees, which develop plans for the intelligent deployment and evolution of
networks and network services, and specialized autonomous groups
(three currently) that produce resources that support the efforts of devel-
oping nations. The study groups are listed in the following:
■ SG 2 Operational aspects of service provision, networks, and
performance
■ SG 3 Tariff and accounting principles, including related
telecommunications economic and policy issues
■ SG 4 Telecommunication management, including TMN
■ SG 5 Protection against electromagnetic environment effects
■ SG 6 Outside plant
■ SG 7 Data networks and open system communications
Chapter 1
10
First Things First

■ SG 9 Integrated broadband cable networks and television and
sound transmission
■ SG 10 Languages and general software aspects for
telecommunication systems
■ SG 11 Signaling requirements and protocols
■ SG 12 End-to-end transmission performance of networks and
terminals
■ SG 13 Multi-protocol and IP-based networks and their
internetworking
■ SG 15 Optical and other transport networks
■ SG 16 Multimedia services, systems, and terminals
■ SSG Special Study Group “IMT-2000 and beyond”
Structure of Standards Documents
The standards are published in a series of alphabetically arranged
documents, available as books, online resources, and CDs. They are
functionally arranged according to the alphabetical designator of the
standard as follows:
A Organization of the work of ITU-T
B Means of expression: definitions, symbols, and classification
C General telecommunication statistics
D General tariff principles
E Overall network operation, telephone service, service operation,
and human factors
F Non-telephone telecommunication services
G Transmission systems and media, digital systems, and networks
H Audiovisual and multimedia systems
I Integrated services digital network
J Transmission of television, sound programs, and other
multimedia signals
K Protection against interference
L Construction, installation, and protection of cables and other
elements of outside plant
11
First Things First
First Things First

M TMN and network maintenance: international transmission
systems, telephone circuits, telegraphy, facsimile, and leased
circuits
N Maintenance: international sound program and television
transmission circuits
O Specifications of measuring equipment
P Telephone transmission quality, telephone installations, local
line networks
Q Switching and signaling
R Telegraph transmission
S Telegraph services terminal equipment
T Terminals for telematic services
U Telegraph switching
V Data communication over the telephone network
X Data networks and open-system communication
Y Global information infrastructure and Internet protocol aspects
Z Languages and general software aspects for telecommunication
systems
Within each letter designator can be found specific, numbered recom-
mendations. For example, recommendation number 25 in the “X” book
contains the specifications for transporting packet-based data across a
public network operating in packet mode. This, of course, is the now-
famous X.25 packet switching standard. Similarly, Q.931 provides the
standard for signaling in ISDN networks, and so on. The documents are
remarkably easy to read and contain vast amounts of information. I am
always surprised to discover how many people who work in telecommu-
nications have never read the ITU standards. Take this, then, as my rec-
ommendation: Find some of them and flip through them. They can be
very useful.
I spent some time writing about the ITU and its standards activities
simply to explain the vagaries of the process (one of my favorite telecom
jokes goes like this:“There are two things you never want to watch being
made. One of them is sausage; the other is standards.”) and the role of
these bodies. The ITU is representative of the manner in which all stan-
dards are developed, although the frequency of update, the cycle time,
the relative levels of involvement of the various players, and the breadth
of coverage of the documents vary dramatically.
Chapter 1
12
First Things First

The Network
For years now, communications networks have been functionally
depicted as shown in Figure 1-5: a big, fluffy, opaque cloud, into which
disappear lines representing circuits that magically reappear on the
other side of the cloud. I’m not sure why we use clouds to represent net-
works; knowing what I know about their complex innards and how they
work, a hairball would be a far more accurate representation.
In truth, clouds are pretty good representations of networks from the
point of view of the customers that use them. Internally, networks are
remarkably complex assemblages of hardware and software as you will
see in the chapter on telephony. Functionally, however, they are straight-
forward: customer traffic goes into the network on the Gozinta; the traf-
fic then emerges, unchanged, on the Gozouta. How it happens is
unimportant to the customer; all they care about is that the network
receives, interprets, transports, and delivers their voice/video/images/
data/music to the destination in a correct, timely, and cost-effective fash-
ion. Later in the book we will discuss the various technologies that live
within the network, but for now suffice it to say that its responsibilities
fall into two categories: access and transport, as illustrated in Figure 1-6.
Network Access
As the illustration shows, network access is exactly that: the collection of
technologies that support connectivity between the customer and the
13
First Things First
Gozinta
Gozouta
Figure 1-5
The network
cloud.
First Things First

transport resources of the network. At its most common level, access is
the local loop, the two-wire circuit that connects a customer’s telephone to
the local switch that provides telephony service to that customer. As the
network has become more data-aware, other solutions have emerged that
provide greater bandwidth as well as multiservice capability. ISDN,
which uses the two-wire local loop, provides greater bandwidth than the
traditional analog local loop through digitization and time-division mul-
tiplexing (both explained shortly). Digital Subscriber Line, or DSL, is also
a local loop-based service, but offers even more diverse service than ISDN
in the areas where it is available. Cable modem service, which does not
use the telephony local loop, offers high downstream (toward the cus-
tomer) bandwidth and smaller upstream (from the customer) capacity.
Wireless services, including LMDS, MMDS, satellite, cellular, and others,
represent another option for access connectivity. All of these will be dis-
cussed in greater detail later in the book.
Miscellaneous Additional Terms A number of other terms need to
be introduced here as well, the first of which are Data Terminal Equip-
ment (DTE) and Data Circuit Terminating Equipment (DCE). DTE is
exactly that—it is the device that a user employs to gain access to the
network. A DCE is the device that actually terminates the circuit at the
customer’s premises, typically a modem. One important point: because
the bulk of the usage is over the Public Switched Telephone Network
(PSTN), which is optimized for the transport of voice, the primary role
of the DCE is to make the customer’s DTE look and smell and taste and
feel like a telephone to the network. For example, if the DTE is a PC, then
Chapter 1
14
Access
Transport
Access
Figure 1-6
Access vs.
transport
regions of the
network.
First Things First

the modem’s job is to collect the high-frequency digital signals being pro-
duced by the PC and modulate them into a range of frequencies that are
acceptable to the bandwidth-limited voiceband of the telephone network.
That’s where the name comes from, incidentally—modulate/demodulate
(mo-dem).
Another pair of terms that must be introduced here is parallel and ser-
ial. You have undoubtedly seen the ribbon cables that are used to trans-
port data inside a PC, or the parallel wires etched into the motherboard
inside the PC. These parallel conductors are called a bus, and are used
for the high-speed transport of multiple simultaneous bits in parallel
fashion from one device inside the computer to another. Serial transmis-
sion, on the other hand, is used for the single-file transport of multiple
bits, one after the other, usually deployed outside a computer.
Finally, we offer simplex, half-duplex, and full-duplex transmission.
Simplex transmission means one-way only, like a radio broadcast. Half-
duplex transmission means two-way, but only one way at a time, like CB
radio. Finally, full-duplex means two-way simultaneous transmission,
like telephony or two-way data transmission.
Network Transport
The fabric of the network cloud is a rich and unbelievably complex col-
lection of hardware and software that moves customer traffic from an
ingress point to an egress point, essentially anywhere in the world. It’s a
function that we take entirely for granted because it is so ingrained in
day-to-day life, but stop for a moment to think about what the network
actually does. Not only does it deliver voice and data traffic between end
points, but it does so easily and seamlessly, with various levels of service
quality as required to any point on the globe (and in fact beyond) in a
matter of seconds—and with zero human involvement. It is the largest
fully automated machine on the planet and represents one of the great-
est technological accomplishments of all time. Think about that: I can
pick up a handset here in Vermont, dial a handful of numbers, and sec-
onds later a telephone rings in Ouagadougou, Burkina Faso, in North
Central Africa. How that happens borders on the miraculous. We will
explore it in considerably greater detail later in the book.
Transport technologies within the network cloud fall into two cate-
gories: fixed transport and switched transport. Fixed transport, some-
times called private line or dedicated facilities, includes such
technologies as T-1, E-1, DS-3, SONET, SDH, dedicated optical channels,
15
First Things First
First Things First

and microwave. Switched technologies include modem-based telephone
transport, X.25 packet switching, frame relay, and Asynchronous Trans-
fer Mode (ATM). Together with the access technologies described previ-
ously and customer premises technologies such as Ethernet, transport
technologies offer the infrastructure components required to craft an
end-to-end solution for the transport of customer information.
The Many Flavors of Transport
Over the last few years the network has been functionally segmented
into a collection of loosely defined regions that define unique service
types. These include the local area, the metropolitan area, and the wide
area, sometimes known as the core. Local area networking has histori-
cally defined a network that provides services to an office, a building, or
even a campus. Metro networks generally provide connectivity within a
city, particularly to multiple physical locations of the same company.
They are usually deployed across a ring architecture. Wide area net-
works, often called core, provide long distance transport and are typically
deployed using a mesh networking model.
Transport Channels
The physical circuit over which the customer is transported in a network
is often referred to as a facility. Facilities are characterized by a number
of qualities such as distance, quality (signal level, noise, and distortion
coefficients), and bandwidth. Distance is an important criterion because
it places certain design limitations on the network, making it more
expensive as the circuit length increases. Over distance, signals tend to
weaken and become noisy, and specialized devices (amplifiers, repeaters,
and regenerators) are required to periodically clean up the signal qual-
ity and maintain the proper level of loudness to ensure intelligibility and
recognizability at the receiving end.
Quality is related to distance in the sense that they share many of the
same affecting factors. Signal level is clearly important, as is noise, both
of which were just discussed. Distortion is a slightly different beast and
must be taken care of equally carefully. Noise is a random event in net-
works caused by lightning, fluorescent lights, electric motors, sunspot
activity, and squirrels chewing on wires and is unpredictable and largely
random. Noise, therefore, cannot be anticipated with any degree of accu-
racy; its effects can only be recovered from.
Chapter 1
16
First Things First

Distortion, on the other hand, is a measurable, unchanging character-
istic of a transmission channel and is usually frequency-dependent. For
example, certain frequencies transmitted over a particular channel will
be weakened, or attenuated, more than other frequencies. If we can mea-
sure this, then we can condition the channel to equalize the treatment
that all frequencies receive as they are transmitted down that channel.
This process is indeed known as conditioning and is part of the higher
cost involved in buying a dedicated circuit for data transmission.
Bandwidth is the last characteristic that we will discuss here, and the
quest for more of it is one of the Holy Grails of telecommunications. Band-
width is a measure of the number of bits that can be transmitted down a
facility in any one-second period. In most cases it is a fixed characteristic
of the facility and is the characteristic that most customers pay for. The
measure of bandwidth is bits-per-second, although today the measure is
more typically thousands (kilobits), millions (megabits) or billions (giga-
bits) per second.
Facilities are often called channels, because physical facilities are
often used to carry multiple streams of user data through a process
called multiplexing. Multiplexing is the process of enabling multiple
users to share access to a transport facility either by taking turns or
using separate frequencies within the channel. If the users take turns, as
shown in Figure 1-7, the multiplexing process is known as time division
multiplexing because time is the variable that determines when each
user gets to transmit through the channel. If the users share the chan-
nel by occupying different frequencies, as shown in Figure 1-8, the
process is called frequency division multiplexing because frequency is the
variable that determines who can use the channel. It is often said that in
time division multiplexing, users of the facility are given all of the
17
First Things First
Inbound
Traffic
Multiplexer
Inbound Facility
Figure 1-7
Time division
multiplexing
(TDM).
First Things First

Chapter 1
18
Subscriber 1: 0-4,000 Hz
Subscriber 2: 4,000-8,000 Hz
Figure 1-8
Frequency
division
multiplexing
(FDM).
frequency some of the time, because they are the only ones using the
channel during their timeslot. In frequency division multiplexing, users
are given some of the frequency all of the time because they are the only
ones using their particular frequency band at any point.
Analog versus Digital Signaling:
Dispensing with Myths
Frequency division multiplexing is normally considered to be an analog
technology, while time division multiplexing is a digital technology.
The word analog means something that bears a similarity to something
else, while the word digital means discrete. Analog data, for example,
typically illustrated as some form of sine wave such as that shown in Fig-
ure 1-9, is an exact representation of the values of the data being trans-
mitted. The process of using manipulated characteristics of a signal to
represent data is called signaling.
We should also introduce a few terms here just to keep things margin-
ally confusing. When speaking of signaling, the proper term for digital is
baseband, while the term for analog signaling is broadband. When talk-
ing about data (not signaling), the term broadband means big channel.
The sine wave, undulating along in real time in response to changes in
one or more parameters that control its shape, represents the exact value
of each of those parameters at any point in time. The parameters are
First Things First

amplitude, frequency, and phase. We will discuss each in turn. Before
we do, though, let’s relate analog waves to the geometry of a circle. Trust
me—this helps.
Consider the diagram shown in Figure 1-10. As the circle rolls along
the flat surface, the dot will trace the shape shown by the line.This shape
is called a sine wave. If we examine this waveform carefully, we notice
some interesting things about it. First of all, every time the circle com-
pletes a full revolution (360 degrees), it draws the shape shown in Fig-
ure 1-11. Thus halfway through its path, indicated by the zero point on
the graph, the circle has passed through 180 degrees of travel. This
makes sense, because a circle circumscribes 360 degrees.
The reason this is important is because we can manipulate the char-
acteristics of the wave created in this fashion to cause it to carry varying
amounts of information.Those characteristics, amplitude, frequency, and
phase, can be manipulated as follows.
Amplitude Modulation
Amplitude is a measure of the loudness of a signal. A loud signal, such
as that currently thumping through the ceiling of my office from my 16
year-old son’s upstairs bedroom, has high-amplitude components, while
lower volume signals are lower in amplitude. Examples are shown in
Figure 1-12. The dashed line represents a high-amplitude signal, while
the solid line represents a lower-amplitude signal. How could this be
used in the data communications realm? Simple: Let’s let high ampli-
tude represent a digital zero, and low amplitude represent a digital
one. If I then send four high amplitude waves followed by four low-
amplitude waves, I have actually transmitted the series 00001111.This
technique is called amplitude modulation (AM); modulation simply
means “vary.”
19
First Things First
Figure 1-9
Sine wave.
First Things First

Frequency Modulation
Frequency modulation (FM) is similar to amplitude modulation, except
that instead of changing the loudness of the signal, we change the
number of signals that pass a point in a given second, illustrated in Fig-
Chapter 1
20
Figure 1-10
Creating a sine
wave.
0° 90° 180° 270° 360°
Figure 1-11
Sine wave.
Figure 1-12
Amplitude
modulation.
First Things First

ure 1-13. The left side of the graph contains a lower frequency signal
component, while a higher frequency component appears to its right. We
can use this technique in the same way we used AM: If we let a high-fre-
quency component represent a zero, and a low-frequency component rep-
resent a one, then I can transmit our 00001111 series by transmitting
four high-frequency signals followed by four low-frequency signals.
An interesting historical point about FM:The technique was invented
by radio pioneer Edwin Armstrong in 1933. Armstrong, shown in Fig-
ure 1-14, created FM as a way to overcome the problem of noisy radio
transmission. Prior to FM’s arrival,AM was the only technique available
and it relied on modulation of the loudness of the signal and the inher-
ent noise to make it stronger. FM did not rely on amplitude, but rather
on frequency modulation, and was therefore much cleaner and offered
significantly higher fidelity than AM radio.
Many technical historians of World War II believe that Armstrong’s
invention of FM transmission played a pivotal role in the winning of
the war. When WW II was in full swing, FM technology was only
available to Allied forces. AM radio, the basis for most military
21
First Things First
Figure 1-13
Frequency
modulation.
Figure 1-14
Edwin
Armstrong
(photo
courtesy
Lucent Bell
Laboratories).
First Things First

communications at the time, could be jammed by simply transmitting
a powerful signal that overloaded the transmissions of military radios.
FM, however, was not available to the Axis powers and, therefore,
could not be jammed as easily.
Phase Modulation
Phase modulation (PM) is a little more difficult to understand than the
other two modulation techniques. Phase is defined mathematically as
“the fraction of a complete cycle elapsed as measured from a particular
reference point.” Consider the drawing shown in Figure 1-15. The two
waves shown in the diagram are exactly 90 degrees “out of phase” of each
other because they do not share a common start point—wave B begins 90
degrees later than wave A. In the same way that we used amplitude and
frequency to represent zeroes and ones, we can manipulate the phase of
the wave to represent digital data.
Digital Signaling
Data can be transmitted in a digital fashion as well. Instead of a
smoothly undulating wave crashing on the computer beach, we can use
Chapter 1
22
0°
90°
270°
360°
A B
Figure 1-15
Phase
modulation.
First Things First

an approximation of the wave to represent the data. This technique is
called digital signaling. In digital signaling, an interesting mathematical
phenomenon, called the Fourier Series, is called into play to create what
most people call a square wave, shown in Figure 1-16. In the case of dig-
ital signaling, the Fourier Series is used to approximate the square
nature of the waveform. The details of how the series actually works are
beyond the scope of this book, but suffice it to say that by mathematically
combining the infinite series of odd harmonics of a fundamental wave,
the ultimate result is a squared off shape that approximates the square
wave that commonly depicts data transmission. This technique is called
digital signaling, as opposed to the amplitude, frequency, and phase-
dependent signaling techniques used in analog systems.
In digital signaling, zeroes and ones are represented as either the
absence or presence of voltage on the line, and in some cases by either
positive or negative voltage—or both. Figure 1-17, for example, shows a
technique in which a zero is represented by the presence of positive volt-
age, while a one is represented as zero voltage. This is called a unipolar
signaling scheme. Figure 1-18 shows a different technique, in which a
zero is represented as positive voltage, while a one is represented as neg-
ative voltage.This is called a non-return to zero signaling scheme, because
zero voltage has no value in this technique. Finally, Figure 1-19 demon-
strates a bipolar system. In this technique, the presence of voltage repre-
sents a one, but notice that every other one is opposite in polarity from the
one that preceded it and the one that follows it. Zeroes, meanwhile, are
represented as zero voltage. This technique, called Alternate Mark Inver-
sion, or AMI, is commonly used in T- and E-Carrier systems for reasons
that will be discussed later.
23
First Things First
Figure 1-16
Square wave.
0
1 1 1 1
0
Figure 1-17
Unipolar
signaling
scheme.
First Things First

There are other techniques in use, but these are among the most
common.
Clearly, both analog and digital signaling schemes can be used to rep-
resent digital data depending upon the nature of the underlying trans-
mission system. It is important to keep the difference between data and
signaling techniques clearly separate. Data is the information that is
being transported, and it can be either analog or digital in nature. For
example, music is a purely analog signal because its values constantly
vary over time. It can be represented, however, using either analog or
digital signaling techniques. The zeroes and ones that spew forth from a
computer are clearly digital information, but they too can be represented
either analogically or digitally. For example, the broadband access tech-
nology known as Digital Subscriber Line (DSL) is not digital at all: there
are analog modems at each end of the line, which means that analog sig-
naling techniques are used to represent the digital data that is being
transmitted over the local loop.
Combining Signaling Techniques
for Higher Bit Rates
Let’s assume that we are operating in an analog network. Under the
standard rules of the analog road, one signaling event represents one bit.
For example, a high-amplitude signal represents a one, and a low ampli-
Chapter 1
24
0 0
1 1
Figure 1-18
Non-Return to
Zero (NRZI)
signaling
scheme.
1
0 0 0 0
1
1 1
Figure 1-19
Bipolar
signaling
scheme.
First Things First

tude signal represents a zero. But what happens if we want to increase
our bit rate? One way is to simply signal faster. Unfortunately, the rules
of physics limit the degree to which we can do that. In the 1920s, a senior
researcher at Bell Laboratories who has now become something of a
legend in the field of communications came to the realization that the
bandwidth of the channel over which the information is being transmit-
ted has a direct bearing on the speed at which signaling can be done
across that channel. According to Harry Nyquist, the broader the chan-
nel, the faster the signaling rate can be. In fact, put another way, the
signaling rate can never be faster than two times the highest frequency
that a given channel can accommodate. Unfortunately, the telephone
local loop was historically engineered to support the limited bandwidth
requirements of voice transmission. The traditional voice network was
engineered to deliver 4 kHz of bandwidth to each local loop2
, which
means that the fastest signaling rate achievable over a telephony local
loop is 8,000 baud. Yet during the late 1980s and the early 1990s, it was
common to see advertisements for 9,600 baud modems.This is where the
confusion of terms becomes obvious: as it turns out, these were 9,600 bit-
per-second modems —a big difference. This, however, introduces a whole
new problem: How do we create higher bit rates over signal rate-limited
(and therefore bandwidth limited) channels?
To achieve higher signaling rates, one of two things must be done:
either broaden the channel, which is not always feasible, or figure out a
way to have a single signaling event convey more than a single bit.
Consider the following example. We know from our earlier discussion
that we can represent two bits by sending a high-amplitude signal fol-
lowed by a low-amplitude signal (high-amplitude signal represents a zero,
low- amplitude signal represents a one). What would happen, though, if
we were to combine amplitude modulation with frequency modulation?
Consider the four waveforms shown in Figure 1-20. By combining the two
possible values of each characteristic (high and low frequency or ampli-
tude), we create four possible states, each of which can actually represent
two bits as shown in Figure 1-21. Consider what we have just done. We
have created a system in which each signaling event represents two bits,
which means that our bit rate is twice our signaling rate.
It’s time to introduce a new word: Baud.
25
First Things First
2 One way in which this was done was through the use of load coils. Load coils are electrical
traps that tune the local loop to a particular frequency range, only allowing certain frequen-
cies to be carried. This created a problem later for digital technologies, as we will discuss.
First Things First

Baud is the signaling rate. It may or may not be the same as the bit
rate, depending on the scheme being used.
Figure X shows a system in which we are encoding four bits for each
signal, a technique known as quad-bit encoding.This scheme, sometimes
called Quadrature Amplitude Modulation, or QAM (pronounced Kwăm),
permits a single signal to represent four bits, which means that there is
a 4:1 ratio between the bit rate and the signaling rate. Thus, it is possi-
ble to achieve higher bit rates in the bandwidth-limited telephony local
loop by using multi-bit encoding techniques such as QAM.The first “high
bit rate modems (9,600 bits-per-second) used this technique of a varia-
tion of it to overcome the design limitations of the network. In fact, these
multi-bit schemes are also used by the cable industry to achieve the high
bit rates they need to operate their multimedia broadband networks.
There is one other limitation that must be mentioned: noise. Look at
Figure 1-22. Here we have a typical QAM graph, but now we have added
noise, in the form of additional points on the graph that have no implied
value. When a receiver sees them, however, how does it know which
points are noise and which are data? Similarly, the oscilloscope trace
shown in Figure 1-23 of a high-speed transmission would be difficult to
interpret if there were noise spikes intermingled with the data. There is,
therefore, a well-known relationship between the noise level in a circuit
Chapter 1
26
HA, LF HA, HF LA, LF LA, HF
Figure 1-20
Di-bit encoding
scheme.
Frequency
Amplitude
High
Low
Low High
11
10
01
00
Figure 1-21
Di-bit values.
First Things First

and the maximum bit rate that is achievable over that circuit, a
relationship that was first described by Bell Labs researcher Claude
Shannon, shown in Figure 1-24 and widely known as the father of infor-
mation theory. In 1948 Shannon published A Mathematical Theory of
27
First Things First
1001 1000
0000 0001
1100
1101
1011
1010
1110
1111
0111
0101
0011
0100
0010
Figure 1-22
Quadrature
amplitude
modulation
(QAM)
Figure 1-23
Oscilloscope
trace.
First Things First

Communication, which is now universally accepted as the framework for
modern communications. We won’t delve into the complex (but fascinat-
ing) mathematics that underlie Shannon’s Theorem, but suffice it to say
that his conclusions are seminal: the higher the noise level in a circuit,
the lower the achievable bandwidth. The bottom line? Noise matters. It
matters so much, in fact, that network designers and engineers make its
elimination the first order of business in their overall strategies for cre-
ating high-bandwidth networks. This is one of the reasons that optical
fiber-based networks have become so critically important in modern
transport systems—they are far less subject to noise and absolutely
immune to the electromagnetic interference that plagues copper-based
networks. Cable companies that now offer data services have the same
issues and concerns. Every time a customer decides to play installer by
adding a cable spur for a new television set in their home and crimping
the connector on the end of the cable with a pair of pliers instead of a tool
specifically designed for the purpose, they create a point where noise can
leak into the system, causing problems for everyone.
It gets even more melodramatic than that: According to John Judson,
a cable systems maintenance manager in the Midwest, unauthorized
connection to the cable network can cause problems that go way beyond
unauthorized access to service. “Cable networks are high-frequency sys-
tems,” he observes. “Some of the harmonics created in cable networks
just happen to fall within the range of frequencies used in avionics, and
therefore have the potential to affect aviation communications and nav-
Chapter 1
28
Figure 1-24
Claude
Shannon
(Photo
courtesy
Lucent Bell
Laboratories).
First Things First

29
First Things First
igation. So, when you see the cable truck that looks like a commercial
fishing boat cruising the neighborhood with all the antennas on top,
they’re looking for signal leakage from unauthorized taps. They will find
them and they will come in and fix them, and you will get a bill for it. So,
if you want to add a connection in the house, call us.”
That completes our introduction of common terms, with one exception:
The Internet.
The Internet: What Is It?
The Internet is a vast network of networks, recognized as the fastest
growing phenomenon in human history. In the words of Douglas Adams,
author of A Hitchhiker’s Guide to the Galaxy, the Internet is “Big. Really
big. Vastly, hugely, mind-bogglingly big.” It is getting bigger: the Internet
doubles in size roughly every 10 months, and that growth rate is
expected to continue.
Not only is the Internet global in physical scope, it is universally rec-
ognized. Everybody knows about the Internet. In 1993, it came booming
into the public consciousness, put down roots, spread like a biological
virus, and flourished. Like other famous public figures, it has been on the
cover of every major magazine in the world, has been the star of books,
articles, TV shows, and movies, has been praised as the most significant
social force in centuries, and debased as the source of a plethora of world-
wide ills. Yet, for all this fame and notoriety, little is actually known
about the Internet itself—at least, its private side. It is known to be a
vast network of interconnected networks, with new appendages connect-
ing approximately every 10 minutes. According to the Network Wizards’
Internet Domain Survey http://www.nw.com, it connects approxi-
mately 110 million host computers, provides services to approximately
350 million users, and comprises roughly 500,000 interconnected net-
works worldwide.
The World Wide Web (WWW)
The World Wide Web was first conceived by Tim Berners-Lee, considered
to be the “Father of the World Wide Web.” A physicist by training,
Berners-Lee began his career in the computer and telecommunications
First Things First

Chapter 1
30
industries following graduation from Oxford, before accepting a consult-
ing position as a software engineer with the European Organization for
Nuclear Research (CERN) during the late 1970s.
During his stint in Geneva, Berners-Lee observed that CERN suffers
from the problems that plague most major organizations: information
location, management, and retrieval. CERN is a research organization
with large numbers of simultaneous ongoing projects, a plethora of inter-
nally published documentation, and significant turnover of people. Much
of the work conducted at CERN revolves around large-scale, high-energy
physics collaborations that demand instantaneous information sharing
between physicists all over the world. Berners-Lee found that his ability
to quickly locate and retrieve specific information was seriously impaired
by the lack of a single common search capability and the necessarily dis-
persed nature of the organization. To satisfy this need, he collaborated
with Robert Cailliau to write the first WWW client, a search and archive
program that they called Enquire. Enquire was never published as a
product, although Berners-Lee, Cailliau, and the CERN staff used it
extensively. It did, however, prove to be the foundation for the WWW.
In May of 1990, Berners-Lee published Information Management: A
Proposal, in which he described his experiences with hypertext systems
and the rationale for Enquire. He described the system’s layout, feel, and
function as being similar to Apple’s Hypercard, or the old Adventure
game in which players moved from page to page as they navigated
through the game. Remember this? Some of you will:
⬎YOU FIND YOURSELF IN A SMALL ROOM. THERE IS A DOOR TO
THE LEFT.
⬎⬎OPEN DOOR
Enquire had no graphics, and was therefore rudimentary compared to
modern Web browsers. To its credit, the system ran on a multiuser plat-
form and could therefore be accessed simultaneously by multiple users.
To satisfy the rigorous demands of the CERN staff, Berners-Lee and
Cailliau designed the system around the following parameters:
■ It had to offer remote access from across a diversity of networks.
■ It had to be system and protocol independent, because CERN was
home to a wide variety of system types—VM/CMS, Mac, VAX/VMS,
and Unix.
■ It had to run in a distributed processing environment.
■ It had to offer access to all existing data types as well as to new
types that would follow.
First Things First

■ It had to support the creation of personal, private links to new data
sources as each user saw fit to create them.
■ It had to support, in the future, diverse graphics types.
■ It (ideally) had to support a certain amount of content and data
analysis.
In November 1990, Berners-Lee wrote and published, with Robert
Cailliau, WorldWide Web: A Proposal for a HyperText Project. In it,
the authors described an information retrieval system in which large
and diverse compendia of information could be searched, accessed, and
reviewed freely, using a standard user interface based on an open,
platform-independent design.This paper relied heavily on Berners-Lee’s
earlier paper.
In WorldWide Web: A Proposal for a HyperText Project, Berners-Lee
and Cailliau proposed the creation of a “World Wide Web” of information
that would enable the various CERN entities to access the information
they needed based on a common and universal set of protocols, file
exchange formats, and keyword indices. The system would also serve as
a central (although architecturally distributed) repository of information
and would be totally platform-independent. Furthermore, the software
would be available to all and distributed free of charge.
Once the paper had been circulated for a time, the development of
what we know today as the WWW occurred with remarkable speed. The
first system was developed on a NeXT platform. The first general release
of the WWW inside CERN occurred in May of 1991, and in December, the
world was notified of the existence of the WWW (known then as W3)
thanks to an article in the CERN computer newsletter.
Over the course of the next few months, browsers began to emerge.
Erwise, a GUI client, was announced in Finland, and Viola was released
in 1992 by Pei Wei of O’Reilly & Associates. NCSA joined the W3 consor-
tium, but didn’t announce their Mosaic browser until February of 1993.
Throughout all of this development activity, W3 servers, based on the
newly released Hypertext Transfer Protocol (HTTP) that enabled diverse
sites to exchange information, continued to proliferate. By January of
1993, there were 50 known HTTP servers; by October there were over
200, and WWW traffic comprised 1 percent of aggregate NSF backbone
traffic. Very quietly, the juggernaut had begun.
In May 1994, the first international WWW conference was held at
CERN in Geneva, and from that point on they were organized routinely,
always to packed houses and always with a disappointed cadre of over-
subscribed would-be attendees left out in the cold.
31
First Things First
First Things First

From that point on, the lines that clearly define “what happened
when” begin to blur. NCSA’s Mosaic product, developed largely by Marc
Andreessen at the University of Illinois in Chicago, hit the mainstream
and brought the WWW to the masses. Andreessen, together with Jim
Clark, would go on to found Netscape Corporation shortly thereafter.
The following timeline shows the highlights of the Internet’s colorful
history (as well as a few other great unrelated moments).Thanks to PBS
for helping to put this together.
Internet Timeline (1960—1997)
1960 There is no Internet . . .
1961 Still no Internet . . .
1962 The RAND Corporation begins research into robust,
distributed communication networks for military
command and control.
1962—1969 The Internet is first conceived in the early 60s. Under
the leadership of the Department of Defense’s
Advanced Research Project Agency (ARPA), it grows
from a paper architecture into a small network
(ARPANET) intended to promote the sharing of super-
computers among researchers in the United States.
1963 Beatles play for the Queen of England.
1964 Dr. Strangelove portrays nuclear holocaust, which new
networks must survive.
1965 The DOD’s Advanced Research Project Association
begins work on ARPANET. ARPA sponsors research
into a cooperative network of time-sharing computers.
1966 U.S. Surveyor probe lands safely on moon.
1967 First ARPANET papers presented at Association
for Computing Machinery Symposium. Delegates
at a symposium for the Association for Computing
Machinery in Gatlinburg, TN discuss the first plans
for the ARPANET.
1968 First generation of networking hardware and software
designed.
1969 ARPANET connects first four universities in the
United States. Researchers at four U.S. campuses
create the first hosts of the ARPANET, connecting
Chapter 1
32
First Things First

Stanford Research Institute, UCLA, UC Santa
Barbara, and the University of Utah.
1970 ALOHANET developed at the University of Hawaii.
1970—1973 The ARPANET is a success from the very beginning.
Although originally designed to enable scientists to
share data and access remote computers, e-mail quickly
becomes the most popular application. The ARPANET
becomes a high-speed digital post office as people use it
to collaborate on research projects and discuss topics of
various interests.
1971 The ARPANET grows to 23 hosts connecting
universities and government research centers around
the country.
1972 The InterNetworking Working Group becomes the first
of several standards-setting entities to govern the
growing network. Vinton Cerf is elected the first
chairman of the INWG, and later becomes known as a
“Father of the Internet.”
1973 The ARPANET goes international with connections to
University College in London, England and the Royal
Radar Establishment in Norway.
1974—1981 Bolt, Beranek & Newman opens Telenet, the first
commercial version of the ARPANET. The general
public gets its first vague hint of how networked
computers can be used in daily life as the commercial
version of the ARPANET goes online. The ARPANET
starts to move away from its military/research roots.
1975 Internet operations transferred to the Defense
Communications Agency.
1976 Queen Elizabeth goes online with the first royal e-mail
message.
1977 UUCP provides e-mail on THEORYNET.
1978 TCP checksum design finalized.
1979 Tom Truscott and Jim Ellis, two grad students at Duke
University, and Steve Bellovin at the University of
North Carolina establish the first USENET
newsgroups. Users from all over the world join these
discussion groups to talk about the Net, politics,
religion, and thousands of other subjects.
33
First Things First
First Things First

1980 Mark Andreessen turns eight. In 14 more years he will
revolutionize the Web with the creation of Mosaic.
1981 ARPANET has 213 hosts. A new host is added
approximately once every 20 days.
1982—1987 The term Internet is used for the first time. Bob Kahn
and Vinton Cerf are key members of a team that
creates TCP/IP, the common language of all Internet
computers. For the first time the loose collection of
networks that made up the ARPANET is seen as an
internet, and the Internet as we know it today is born.
The mid-1980s mark a boom in the personal computer
and super-minicomputer industries. The combination of
inexpensive desktop machines and powerful, network-
ready servers enables many companies to join the
Internet for the first time. Corporations begin to use
the Internet to communicate with each other and with
their customers.
1983 TCP/IP becomes the universal language of the
Internet.
1984 William Gibson coins the term cyberspace in his novel
Neuromancer. The number of Internet hosts exceeds
1,000.
1985 Internet e-mail and newsgroups now part of life at
many universities.
1986 Case Western Reserve University in Cleveland, Ohio
creates the first Freenet for the Society for Public
Access Computing.
1987 The number of Internet hosts exceeds 10,000.
1988–1990 Internet worm unleashed. The Computer Emergency
Response Team (CERT) is formed to address security
concerns raised by the Worm. By 1988 the Internet is
an essential tool for communications, however it also
begins to create concerns about privacy and security in
the digital world. New words, such as hacker, cracker,
and electronic break-in, are created. These new worries
are dramatically demonstrated on Nov. 1, 1988 when
a malicious program called the “Internet Worm”
Chapter 1
34
First Things First

temporarily disables approximately 6,000 of the 60,000
Internet hosts. System administrator turned author,
Clifford Stoll, catches a group of cyberspies, and writes
the best-seller The Cuckoo’s Egg. The number of
Internet hosts exceeds 100,000. A happy victim of its
own unplanned, unexpected success, the ARPANET is
decommissioned, leaving only the vast network-of-
networks called the Internet. The number of hosts
exceeds 300,000.
1991 The World Wide Web is born!
1991—1993 Corporations wishing to use the Internet face a serious
problem: Commercial network traffic is banned from
the National Science Foundation’s NSFNET, the
backbone of the Internet. In 1991 the NSF lifts the
restriction on commercial use, clearing the way for
the age of electronic commerce. At the University of
Minnesota, a team led by computer programmer Mark
MaCahill releases gopher, the first point-and-click
way of navigating the files of the Internet in 1991.
Originally designed to ease campus communications,
gopher is freely distributed on the Internet. MaCahill
calls it “the first Internet application my mom can
use.” 1991 is also the year in which Tim Berners-Lee,
working at CERN in Switzerland, posts the first
computer code of the WWW in a relatively innocuous
newsgroup, “alt.hypertext.” The ability to combine
words, pictures, and sounds on Web pages excites many
computer programmers who see the potential for
publishing information on the Internet in a way
that can be as easy as using a word processor. Marc
Andreessen and a group of student programmers
at NCSA (the National Center for Supercomputing
Applications located on the campus of University of
Illinois at Urbana Champaign) will eventually develop
a graphical browser for the WWW called Mosaic.
Traffic on the NSF backbone network exceeds 1 trillion
bytes per month. One million hosts have multi-media
access to the Internet over the MBone. The first audio
35
First Things First
First Things First

and video broadcasts take place over a portion of the
Internet known as the “MBone.” More than 1,000,000
hosts are part of the Internet. Mosaic, the first
graphics-based Web browser, becomes available. Traffic
on the Internet expands at a 341,634 percent annual
growth rate.
1994 The Rolling Stones broadcast the Voodoo Lounge tour
over the M-Bone. Marc Andreessen and Jim Clark form
Netscape Communications Corp. Pizza Hut accepts
orders for a mushroom, pepperoni with extra cheese
over the Net, and Japan’s Prime Minister goes online at
www.kantei.go.jp. Backbone traffic exceeds 10 trillion
bytes per month.
1995 NSFNET reverts back to a research project, leaving the
Internet in commercial hands. The Web now comprises
the bulk of Internet traffic. The Vatican launches
www.vatican.va. James Gosling and a team of
programmers at Sun Microsystems release an Internet
programming language called Java, which radically
alters the way applications and information can be
retrieved, displayed, and used over the Internet.
1996 Nearly 10 million hosts online. The Internet covers the
globe. As the Internet celebrates its 25th anniversary,
the military strategies that influenced its birth become
historical footnotes. Approximately 40 million people
are connected to the Internet. More than $1 billion per
year changes hands at Internet shopping malls, and
Internet related companies like Netscape are the
darlings of high-tech investors. Users in almost 150
countries around the world are now connected to the
Internet. The number of computer hosts approaches
10 million.
Within 30 years, the Internet has grown from a Cold War concept for
controlling the tattered remains of a post-nuclear society to the Infor-
mation Superhighway. Just as the railroads of the 19th century enabled
the Machine Age and revolutionized the society of the time, the Internet
takes us into the Information Age, and profoundly affects the world in
which we live.
Chapter 1
36
First Things First

The Age of the Internet Arrives
1997 Today some people telecommute over the Internet,
allowing them to choose where to live based on quality
of life, not proximity to work. Many cities view the
Internet as a solution to their clogged highways and
fouled air. Schools use the Internet as a vast electronic
library, with untold possibilities. Doctors use the
Internet to consult with colleagues half a world away.
Even as the Internet offers a single Global Village, it
threatens to create a second class citizenship among
those without access. As a new generation grows up as
accustomed to communicating through a keyboard as
in person, life on the Internet will become an
increasingly important part of life on Earth.
We will discuss the Internet in greater detail later in the book. How-
ever, just for the sake of fun, consider the following few pages that present
a comparison of two technographs—one of the state of telecommunica-
tions in 1994, the other in 1999. It is not intended to be inclusive, but
rather a comparison of moments in time. What a difference half-a-decade
makes—and how incredibly fast this industry moves. Furthermore,
consider the great buildup that occurred in 1999 in the telecom industry,
followed a year later by the great meltdown of 2000—2001. What will the
next five years look like? We begin in 1994—a mere seven years ago.
1994
Frame Relay has been introduced, standards are in place, and service
offerings are beginning to appear. At this point, Frame Relay is a data-
only service and there is no concept that it could be more than that.
Meanwhile, ATM is still in the conceptual mode, and in the marketplace
there is a lot of discussion about whether to go with Frame Relay as a
primary backbone technology or wait for ATM. SMDS is growing as a
high-bandwidth solution. LAN switching is a year away. Cisco Systems
has about 40 percent of the router marketplace, Synoptics and Wellfleet
are still separate companies, and discussion is underway about some-
thing called fast LAN technologies. Four, 10, and 16 Mbps are still the
norm, however. By some estimates, Novell owns 65—70 percent of the
37
First Things First
First Things First

server marketplace; IPX dominates the LAN and TCP/IP is about two
years overdue to be terminated (at least according to the Department of
Defense, which is still waiting for OSI). NT Server does not exist. There
is no Windows 95; DOS and Windows 3.11 are alive and well, and the
Macintosh is a powerful player in the desktop environment. Unix is still
for tech weenies.
Change is in the wind on the regulatory front, and it is dawning on the
telecommunications industry that the current regulatory model is not
appropriate given the rumble of enhanced competition that seems to be
underway. Actual changes, however, have not yet been proposed.
The Internet, thanks to the WWW, has now been in the public eye for
a year. Tim Berners-Lee has quietly rolled out his CERN-based browser,
and Mosaic has become the browser of choice for the bulk of the market.
Netscape is a corporate upstart on the verge of revolutionizing access to
the Web. The NSF has just started to fund NAPs in the Internet world,
as the government is beginning to question its own role in the process.As
the Internet’s popularity and incursion grow, AOL bumps heads with
Prodigy and Compuserve. Hundreds, if not thousands of online service
providers come out of the woodwork. However, even as it enters the third
year of annual doubling in size, the Internet still isn’t seen as having
lasting importance in corporate America; Microsoft’s Encarta doesn’t
even have an entry for the term. Nevertheless, the Internet Engineering
Task Force (IETF), a loose consortium of Internet techies responsible for
the technology of the Internet, starts working on the next generation
Internet Protocol (IPng). One notable feature of IPng is that it will have
128-bit addresses; predictions are that IP’s current 32-bit address space
will be exhausted by 1998.
Because of growing interest in the Web, access technologies are hot
and everybody wants more bandwidth over the local loop. Most modem
technologies in use operate at a whopping 14.4 Kbps, but 28.8 Kbps
modems are on the market and work is underway to achieve 33.6. ISDN
continues to wallow in uncertainty, plagued by spotty availability, con-
flicting implementation standards, and questions about its value.
The corporate world is undergoing its own evolution at this time.
Microsoft, Cisco, and other corporations are at the elbow of their corpo-
rate development curve. There are seven RBOCs. The only significant
competitive players, other than the independents, are Teleport and MFS.
SONET standards are still considered somewhat immature; OC-48 is
a laughable dream. Cell phones are considered to be an innovative,
“designer” technology, and most people complain about battery life. IRID-
IUM shows promise as the next great wireless network.
Chapter 1
38
First Things First

2000 and the beginning of the next millennium—or is that 2001?—is
just six years away. What a party that will be!!
1999
Five years later, Frame Relay is a mature technology, routinely carrying
data, voice, and video. It has become a premier private-line replacement
technology.ATM is also mature, and is not only widely deployed, it is also
being considered as the core technology for the next generation network.
But ATM to the desktop is dead because of Fast Ethernet and even faster
Ethernet (see the following), and ATM for even campus area networks is
anybody’s guess.
The current regulatory environment is—well, exciting. We now have
three RBOCs instead of seven, two major IXCs (assuming that the
Sprint/WorldCom merger takes place), and a plethora of CLECs, DLECs,
ITSPs, ISPs, and other berserkers disrupting the market model. Fur-
thermore, we are very close to seeing true competition at both the local
and long- distance levels between the IXCs and the ILECs.
Al Gore is resting comfortably after giving birth to the Internet, which
has become the central focal point in the telecommunications industry—
as well as in virtually every other industry. Significant spin-off technolo-
gies abound, including Voice over IP, VPNs, Web-enabled call centers,
voice-enhanced Web sites, electronic commerce, and the newly emerged
E-business. The term “dot-com” has entered the lexicon and become
part of everyday life. Whole portfolios are built around these Cinderella
companies.
Traditional modem technology now provides 56 Kbps access (well, sort
of . . . ), but other technologies have leapfrogged that, including cable
modems at 10 Mbps, wireless options like LMDS, and a variety of DSL
services that offer bandwidth levels between 9 and 52 Mbps. SMDS is, for
all intents and purposes, dead, and ISDN continues to wallow in uncer-
tainty, plagued by spotty availability, conflicting implementation stan-
dards, and questions about its value. But Internet access gave ISDN new
life, at least temporarily.
Fast and gigabit Ethernet are commonplace. LAN switching is fast
becoming widely embedded technology. Optical fiber is widely deployed
in local networks. WDM, DWDM, and UDWDM provide massive band-
width over optical fiber. SONET is mature, and in fact is being discussed
in some venues as if it is reaching the end of its useful life with the pro-
liferation of WDM technologies. Companies like Qwest and Level3 are
39
First Things First
First Things First

taking advantage of them to carve out niches for themselves in the band-
width marketplace. In fact, bandwidth has become a commodity, traded
on spot markets alongside soy beans and pork bellies.
A feeding frenzy is underway as the telecommunications market con-
verges. Companies are buying each other apace as they jockey for posi-
tion in the greatest game in town, and they are doing so by implementing
new applications with names like “Enterprise resource planning” and
“Customer relationship management.”
Cellular telephony is ubiquitous, and integrated handsets are hitting
the market. Iridium, once a shining star, is in receivership.AOL is a pow-
erhouse as the biggest ISP on the planet. They now own CompuServe,
and Prodigy has become invisible. Windows 2000 is on the market, and
Apple’s future as a real player is uncertain. Due to the popularity of
Linux, Unix has entered the mindset and vocabulary of ordinary people
on the street. Firewalls, still uncommon five years ago, are now finding a
market as home-based computer systems obtain 24⫻7 access to the
Internet using cable modems and DSL technologies.
IP is now ubiquitous. NetWare version 5 will run natively over IP. All
32-bit versions of Windows (Windows 95, and so on) have a built-in
TCP/IP kernel. IP version 6 (IPv6) is three years old but has yet to see
widespread implementation. The IETF is now an international stan-
dards organization, sanctioned by ISO. Cisco dominates the router mar-
ketplace at the high- and middle-range, and is even a force at the
low-end.
2000 came and went without incident. IT professionals who planned
to have a New Years Eve party in their offices waiting for the ringing
telephones, lost power, crashed computers, and other unnatural disasters
that would inevitably occur at 00:00:00.00 on 1/1/2000, were sorely
disappointed.
Chapter Summary
This chapter is designed to acquaint the reader with the fundamental
terms and concepts that characterize the data and telecommunications
worlds today. Now we can move deeper into the magic. In the next chap-
ter, we introduce the design, philosophy, structure, and use of data com-
munications protocols.
Chapter 1
40
First Things First

Protocols
CHAPTER
2
2
Source: Telecom Crash Course

Click.
One simple action kicks off a complex series of events that results in
the transmission of an e-mail message, the creation of a digital medical
image, or the establishment of a videoconference between a child and a
grandmother. The process through which this happens is a remarkable
symphony of technological complexity, and it is all governed by a collec-
tion of rules called protocols. This chapter is dedicated to them.
Data Communications
Systems and Functions
If I were to walk up to you on the street and extend my hand in greeting,
you would quite naturally reach your hand out, grab mine, and shake it
—in most parts of the world. We agree to abide by a commonly accepted
set of social rules, one of which is shaking hands as a form of greeting. It
doesn’t work everywhere. In Tibet, it is customary to extend one’s tongue
as far as it can be extended as a form of greeting (clearly a sign of a great
culture!). In China, unless you are already friends with the person you are
greeting, it is not customary to touch in any fashion. You, of course, have
a choice when I extend my hand. You could hit it, lick it, or spit in it. But
because of the accepted rules that govern western society, you would take
my hand in yours and shake it. These rules that govern communication,
any form of communication, are called protocols. And the process of using
protocols to convey information is called data communications. It’s no
accident, incidentally, that the obnoxious racket that analog modems
make when they are attempting to connect to each other is called a hand-
shake. The noise they make is their attempt to negotiate a common set of
rules that works for both of them for that particular session.
The Science of
Communications
Data communication is the procedure required to collect, package, and
transmit data from one computing device to another, typically (but not
always) over a wide area network (WAN). It is a complex process with
many layers of functionality. To understand data communications, we
Chapter 2
42
Protocols

must break it into its component parts and examine each part individu-
ally, relying on the old adage that “the only way to eat an elephant is one
bite at a time.” Like a Russian Matryoshka doll, such as the one shown
in Figure 2-1, data communications comprises layer upon layer of oper-
ational functionality that work together to accomplish the task at hand,
namely, the communication of data.These component parts are known as
protocols, and they have one responsibility: to ensure the integrity of the
data that they transport from the source device to the receiver.
This data integrity is measured in the following ways (see Figure 2-2):
■ Bit level integrity Ensures that the bits themselves are not
changed in value as they transit the network
■ Data integrity Guarantees that the bits are recognizable as
packaged entities called frames or cells
■ Network integrity Provides for the assured delivery of those
entities, now in the form of packets, from a source to a destination
■ Message integrity Not only guarantees the delivery of the
packets, but in fact their sequenced delivery to ensure the proper
arrival of the entire message
■ Application integrity Provides for the proper execution of the
responsibilities of each application
Protocols exist in a variety of forms and are not limited to data com-
munications applications. Military protocols define the rules of engage-
ment that modern armies agree to abide by, diplomatic protocols define
Protocols 43
Figure 2-1
Russian
Matryoshka
dolls.
Protocols

the manner in which nations interact and settle their political and geo-
graphic differences, and medical protocols document the manner in
which medications are used to treat illness. The word protocol is defined
as a set of rules that facilitates communication. Data communications,
then, is the science built around the protocols that govern the exchange
of digital data between computing systems.
Data Communications
Networks
Data communications networks are often described in terms of their
architectures, as are protocols. Protocol architectures are often said to be
layered because they are carefully divided into highly related but non-
overlapping functional entities. This “division of labor” not only makes it
easier to understand how data communications work, but also makes the
deployment of complex networks far easier.
The amount of code (lines of programming instructions) required to
successfully execute the complex task of data transmission is quite large.
Chapter 2
44
Application Integrity
Message Integrity
Network Integrity
Data Integrity
Bit—level Integrity
Figure 2-2
The various
integrity levels
of the OSI
Model.
Protocols

If the program that carries out all of the functions in that process were
written as a single, large, monolithic chunk of code, then it would be
difficult to make a change to the program when updates are required,
because of the monolithic nature of the program. Now imagine the
following: instead of a single set of code, we break the program into func-
tional pieces, each of which handles a particular, specific function
required to carry out the transmission task properly. With this model,
changes to a particular module of the overall program can be accom-
plished in a way that only affects that particular module, making the
process far more efficient.This modularity is one of the great advantages
of layered protocols.
Consider the following simple scenario, shown in Figure 2-3. A
PC-based e-mail user in Madrid with an account at ISP Terra Networks
wants to send a large, confidential message to another user in Marseilles.
The Marseilles user is attached to a mainframe-based corporate e-mail
system. In order for the two systems to communicate, a complex set of
challenges must first be overcome. Let’s examine them a bit more closely.
The first and most obvious challenge that must be overcome is the dif-
ference between the actual user interfaces on the two systems. The
PC-based system’s screen presents information to the user in a Graphi-
cal User Interface (GUI, pronounced ‘gooey’) format that is carefully
designed to make it intuitively easy to use. It eliminates the need to rely
on the old command-line syntax that was used in DOS environments.
The mainframe system was created with intuitive ease of use in mind,
but because a different company designed the interface for a mainframe
host, under a different design team, it bears minimal resemblance to the
PC system’s interface. Both are equally capable, but completely different.
As a result of these differences, if we were to transmit a screen of
information from the PC directly to the mainframe system, it would be
unreadable simply because the two interfaces do not share common field
names or locations.
The next problem that must be addressed is security, illustrated in
Figure 2-4.We mentioned earlier that the message that is to be sent from
Protocols 45
Madrid Marseilles
Figure 2-3
PC-to-
mainframe
communications.
Protocols

the user in Madrid is confidential, which means that it should probably
be encrypted to protect its integrity. And because the message is large,
the sender will probably compress it to reduce the time it takes to trans-
mit it. Compression, which will be discussed in more detail later, is sim-
ply the process of eliminating redundant information from a file before it
is transmitted or stored to make it easier to manage.
Another problem has to do with the manner in which the information
being transmitted is represented. The PC-based Eudora message
encodes its characters using a 7-bit character set, the American Stan-
dard Code for Information Interchange (ASCII). A sample of the ASCII
codeset is shown later in Table 2-1. Mainframes, however, often use a dif-
ferent codeset called the Extended Binary Coded Decimal Interchange
Code (EBCDIC). The ASCII traffic must be converted to EBCDIC if the
mainframe is to understand it, and vice versa, as shown in Figure 2-5.
Binary Arithmetic Review
It’s probably not a bad idea to review binary arithmetic for just a
moment, since it seems to be one of the least understood details of data
communications. I promise, this will not be painful. I just want to offer a
quick explanation of the numbering scheme and the various codesets
that result.
Chapter 2
46
Madrid Marseilles
5
0
3
5
3
0 25
2
0
1
5
0
Figure 2-4
Managing
security.
Madrid:
7-bit ASCII
Marseilles:
8-bit EBCDIC
Figure 2-5
Code
conversion.
Protocols

Modern computers are often referred to as digital computers because
the values they use to perform their function are limited (remember, the
word digital means discrete).Those values are nominally zero and one. In
other words, a value can either be one or zero, on or off, positive or nega-
tive, presence of voltage or absence of voltage, or presence of light or
absence of light.Two possible values exist for any given situation, and this
type of system is called binary. The word means a system that comprises
two distinct components or values. Computers operate using base 2 arith-
metic, whereas humans use base 10. Let me take you back to second grade.
When we count, we arrange our numbers in columns that have values
based on multiples of the number 10, as shown in Figure 2-6. Here we
see the number 6,783, written using the decimal numbering scheme. We
easily understand the number as it is written because we are taught to
count in base 10 from an early age.
Computers, however, don’t speak in base 10. Instead, they speak in
base 2. Instead of having columns that are multiples of 10, they use
columns that are multiples of two, as shown in Figure 2-7. In base 10, the
columns are (reading from the right):
■ Ones
■ Tens
■ Hundreds
■ Thousands
■ Ten thousands
■ Hundred thousands
■ Millions
■ And so on
In base 2, the columns are
■ Ones
■ Twos
Protocols 47
Thousands Tens
Hundreds Ones
6,783
Figure 2-6
Base 10
numbering
scheme.
Protocols

■ Fours
■ Eights
■ Sixteens
■ Thirty-twos
■ Sixty-fours
■ One hundred twenty-eights
■ Two hundred fifty-sixes
■ Five hundred twelves
■ One thousand twenty-fours
■ And so on
So our number, 6,783, would be written as follows in base two:
1101001111111
From right to left that’s one 1, one 2, one 4, one 8, one 16, one 32, one
64, no 128, no 256, one 512, no 1,024, one 2,048, and one 4,096. Add them
all up (1⫹2⫹4⫹8⫹16⫹32⫹64⫹512⫹2048⫹4096) and you should get
6,783.
That’s binary arithmetic. Most PCs today use the 7-bit ASCII charac-
ter set shown in Table 2-1. The mainframe, however (remember the
mainframe?), uses EBCDIC.What happens when a 7-bit ASCII PC sends
information to an EBCDIC mainframe system that only understands
8-bit characters? Clearly, problems would result. Something therefore
has to take on the responsibility of translating between the two systems
so that they can intelligibly transfer data.
Chapter 2
48
Two thousand
forty-eights
Five
hundred
twelves
Four
thousand
ninety-sixes
Sixteens
1101001111111
One
twenty-
eights
Thirty-
twos Eights Twos
One
thousand
twenty-fours
Two-
hundred
fifty
sixes
Sixty-
fours
Fours Ones
Figure 2-7
Base 2
numbering
scheme.
Protocols

49
Protocols
Character ASCII Value Decimal Value
0 0110000 48
1 0110001 49
2 0110010 50
3 0110011 51
4 0110100 52
5 0110101 53
6 0110110 54
7 0110111 55
8 0111000 56
9 0111001 57
A 1000001 65
B 1000010 66
C 1000011 67
D 1000100 68
E 1000101 69
F 1000110 70
G 1000111 71
H 1001000 72
I 1001001 73
J 1001010 74
K 1001011 75
L 1001100 76
M 1001101 77
N 1001110 78
O 1001111 79
P 1010000 80
Q 1010001 81
R 1010010 82
S 1010011 83
T 1010100 84
U 1010101 85
V 1010110 86
W 1010111 87
X 1011000 88
Y 1011001 89
Z 1011010 90
Table 2-1
ASCII
Codeset.
Protocols

Another problem that arises has to do with the logical relationship
between the applications running in the two systems. Although the PC
most likely supports the e-mail account of a single user, the mainframe
undoubtedly hosts hundreds, perhaps thousands of accounts, and must
therefore ensure that users receive their mail and only their mail. Some
kind of user-by-user and process-by-process differentiation is required to
maintain the integrity of the system and its applications. This is illus-
trated graphically in Figure 2-8.
The next major issue has to do with the network over which the
information is to be transmitted from Madrid to Marseilles. In the past,
information was either transmitted via a dedicated and very expensive
point-to-point circuit, over the relatively slow public switched telephone
network, or PSTN. Today, however, most modern networks are packet-
based, meaning that messages are broken into small, easily routable
pieces, called packets, prior to transmission. Of course, this adds an addi-
tional layer of complexity to the process.What happens if one of the pack-
ets fails to arrive at its destination? Or, what if the packets arrive at the
destination out of order? Some process must be in place to manage these
challenges and overcome the potentially disastrous results that could
occur.
Computer networks have a lot in common with modern freeway sys-
tems, including the tendency to become congested. Congestion results in
delay, which some applications do not tolerate well. What happens if
some or all of the packets are badly delayed, as shown in Figure 2-9?
What is the impact on the end-to-end quality of service (QoS)?
Another vexing problem that often occurs is errors in the bitstream.
Any number of factors, including sunspot activity, the presence of electric
Chapter 2
50
Figure 2-8
Logical session
management.
Protocols

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*** START OF THE PROJECT GUTENBERG EBOOK MARGARET
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MARGARET CAPEL.
VOL. II.
MARGARET CAPEL.
A NOVEL.

BY THE AUTHOR OF
"THE CLANDESTINE MARRIAGE."
IN THREE VOLUMES.
VOL. II.
LONDON:
RICHARD BENTLEY, NEW BURLINGTON STREET.
1846.
LONDON:
Printed by Schulze and Co. 13 Poland Street
MARGARET CAPEL.

CHAPTER I.
Where'er we gaze, above, around, below,
What rainbow tints, what magic charms are found!
Rock, river, forest, mountain, all abound;
And bluest skies that harmonise the whole.
Beneath, the distant torrent's rushing sound,
Tells where the volumed cataract doth roll,
Between those hanging rocks that shock yet please the
soul.
BYRON.
There is a portion of the coast in one of the southern counties of
England, which, without aspiring to the sublimity of foreign scenery,
possesses a certain grandeur from the abruptness and variety of its
outline. High cliffs stand boldly forward into the sea, while the
intermediate shore rises and falls in gentle and uncertain
undulations. For many miles inland, this irregular character of the
surface continues. The ground rises and falls so suddenly, that in
many places the trees which clothe the tops of the hills, almost shut
out the sky from the spectator in the valley; while many coloured
rocks, vary by their wild forms and rich tints, the even line of
verdure which extends over the precipitous sides of these ravines.
This part of the country is rich in scenes of peculiar beauty. Brooks
trickle from the shade of deep thickets, or sparkle in stony cells
overgrown with creepers at the foot of a confused heap of broken
rocks.
Hill and dale crowd upon each other in quick succession—every turn
in the way leads to fresh aspects of the prospect. Now the traveller's
view is bounded by high banks, overgrown with trees and tangled
brushwood; now the ground breaks away in such a gradual slope,

that the sea may be discerned in the distance, trembling in the
sunshine, or breaking in rough foam upon the long brown line of the
beach.
Half way between one of these bold headlands and the shore, there
stood a beautiful cottage, with a thickly wooded hill at the back, and
a highly cultivated plot of garden ground in the front: while the side
of the house stood so near the edge of a sudden descent in the cliff,
that nothing but a broad terrace-walk intervened between the
garden-windows, and the abrupt declivity which was washed by the
waves when the tide was higher than usual.
It was a brilliant evening. The sun had almost descended to the
horizon, and a long pathway of golden light fell upon the calm sea,
and the wet sand from which the waves had just receded.
A dim radiance seemed to fill the air, and to blend hills, trees, and
sky together in one soft and many tinted confusion of colours; while
the lengthened rays threaded their brilliant way among the slender
stems of the trees, and dropped like diamonds upon the dark
rivulets that lay in shadow among the brushwood during the early
part of the day.
It was an evening when the whole earth looked so bright, so costly,
steeped in sunlight, and surrendered to the stillness which belongs
to that quiet hour, that it seemed as if this lower world might be fitly
inhabited only by fairies or other such fragile creatures of the
imagination. Such, however, were not the denizens of the cottage by
the hill-side; but a comely old lady in an antique cap and black silk
gown, who had the appearance of a house-keeper, or confidential
servant, and who was leaning over the Gothic gate at the end of the
shrubbery, and looking along the winding road, as if on the watch
for some expected travellers.
Her patience was not put to any lengthened test. In a few minutes,
a carriage was seen rapidly advancing to the house. The old woman

retreated to the porch; the carriage drew up, and a lady of a
commanding aspect descended, followed by a slight graceful girl.
"Ah! nurse, dear nurse! how glad I am to see you!" exclaimed the
young lady, throwing herself into the old woman's arms.
"Welcome to England! Welcome back, my darling!" said the nurse,
endeavouring to execute a curtsey to the elder lady, while
imprisoned in the embrace of the younger one.
"I am rejoiced to see you again, nurse Grant," said Mrs. Fitzpatrick,
the elder of the two ladies, "Aveline, my love, we are just in the way
here—let us go in."
"Yes, mamma. I long to see the dear rooms again. How comfortable
every thing looks! Nurse, come in. Mamma, you said that nurse
should drink tea with us to-night."
"Yes, if nurse pleases," said the lady, as they went into the drawing-
room, where tea was awaiting them in all the English delicacy of that
meal. "Aveline has been depending on your company all the way
from Southampton, Mrs. Grant."
"Bless her, the darling!" said the old woman. "She is tired with her
journey, is she not? I hope she means to eat something. A fresh
egg, or some cold chicken, Miss Aveline?"
"Eat, nurse! you will see how I eat;" said the young lady drawing to
the table. "I should be ashamed that anybody but you should see
me eat after a long journey. I am so hungry!"
"Her appetite is very good," said Mrs. Fitzpatrick, in a decided tone.
"She is come back in every respect, nurse, better than she was. Her
stay in Italy has been of the utmost advantage to her."
"Thank God!" said Mrs. Grant, looking earnestly at the young lady.
"There is some good then in foreign parts."

"Oh, nurse!" cried Aveline. "Not a word against Italy. It is the only
country to enjoy and improve life. If it were not that this is our
home, I could have spent my life at Naples, or—Sorrento."
"You were very fond of Sorrento," said Mrs. Fitzpatrick, looking
inquiringly at her daughter.
"Yes. That is, I was tired of it at last. It was a great relief to go on to
Milan, there is something in the sea-side that—a monotony I mean—
after—"
"Yet, you could have spent your life there;" said Mrs. Fitzpatrick in a
subdued tone.
"In Italy, mamma? At any place in Italy. It is not the spot, but the
thin warm air that makes me feel so full of life. Oh, dear nurse, you
do look so handsome. You cannot think how ugly the old Italian
women are, with their thick brown skins and deep wrinkles, and
coarse grizzled hair. English people have certainly a more delicate
texture. Even I was thought pretty in Italy."
"Pretty in Italy!" said the old lady indignantly. "I fancy, Miss Aveline,
the gentlemen must be much changed since my time, if you are not
thought pretty anywhere."
"Oh, hush, nurse!" said Aveline lifting up her finger. "It is only safe
to tell little children they are pretty. Grown up ones are too ready to
believe it."
"It is little matter here, Miss Aveline," said the old woman. "You have
no neighbours."
"No neighbours, nurse? I was but waiting until we had finished tea
to ask you about them all. How is the good old widow by the church
—and Mrs. Wood, the baker—and young Mrs. Wood at the post-
office? And Harding, the carpenter—and the fisherman's family on
the other side of the cliff? Is little Jane as pretty as ever? Of course
not. Her father I know has cut all her curls off, as he always does,

and she is beginning to lose her teeth; so that she will not be fit to
look at for these ten years."
While she was talking on in this lively manner, the old woman kept
her eyes fixed on her face with a serious and anxious expression.
Aveline was fearfully thin; her hands, which she used in speaking,
more than an English woman, were almost transparent; and from
fatigue, the blue veins had risen over them in every direction. The
colour in her cheeks was fixed like a bright spot of rouge under each
eye, giving a brilliancy that was almost fierce in its expression to
eyes that were dark as night, and remarkable for their size.
Mrs. Fitzpatrick, who followed the nurse's looks with an eagerness
that she could scarcely repress, caught her eye and remained silent,
fixing her gaze upon the old woman's countenance with an intensity
that she could hardly sustain. It seemed as if she ardently desired to
read the nurse's opinion of her child, but was equally anxious that
she should not then express it.
"Well, nurse," said Aveline, "what news? I hope all these good
people are not dead, that you keep such a profound silence upon
their proceedings."
"All pretty much as you left them, Miss Aveline," said the nurse,
rousing herself from her contemplation. "I cannot speak positively
with respect to the beauty of the fisherman's children; though I
always see three or four curly heads round his door when I pass. He
lost one poor little one in the winter with the whooping cough. The
neighbours said it was a mercy, as he had such a large family, but I
don't know that the parents felt the less on that account."
"Poor people!" said Aveline. "I'll tell you what, mamma, I shall get
up early to-morrow, and go down to the cottage with Susan, and
buy some prawns for breakfast; and then I shall see what the
children would like as a present. I am always so glad when people
are in want of nice clean little straw bonnets. There is nothing

romantic in giving away flannel petticoats or thick worsted
stockings."
"Remember, Miss Aveline," said the nurse, "that you give away a
great deal of comfort with those warm clothes."
"And if you intend to take a long walk to-morrow," said Mrs.
Fitzpatrick, "you had better not sit up later to-night. You have had a
long journey, and should be prudent; though you bore it remarkably
well."
But Aveline was unwilling to retire. Although she was evidently
suffering from over fatigue, she persisted in wandering restlessly
round the room, looking at all the trifling ornaments with which it
was strewn. Mrs. Grant noticed with pain that her step was languid,
and that she stooped very much as she walked. Presently she was
seized with a distressing fit of coughing.
"A lozenge, if you please, Mamma," said Aveline, coming up to her
mother's chair.
"Now Aveline I know you are tired," said Mrs. Fitzpatrick, "take your
lozenges and go to bed at once. She always coughs," she said
turning to Mrs. Grant, "when she is over fatigued. She always did
from a child." "Come, Miss Aveline," said Mrs. Grant, "I am going
home in a minute—let me see you off. Dear heart! how I recollect
the time when you were a little girl; what a trouble there always was
to get you to bed."
"Why what particular secrets have you good people to talk over that
you wish me away?" said Aveline laughing, "what account have you
to give mamma of the turkey poults and the guinea fowls that I may
not hear? But, good night, nurse; you will have me plaguing you
early to-morrow, at your cottage, and pillaging your strawberry
beds, which you know are a great deal better than ours. As for you,
mamma, I shall not say good night, because you will be upstairs
long before I am asleep."

"Her spirits are excellent, nurse," said Mrs. Fitzpatrick, in a tone that
seemed as if she was desirous to be assured of the fact.
"They are—very high, Ma'am;" said Mrs. Grant. "How do you think
she is looking?" asked Mrs. Fitzpatrick.
"I shall tell better to-morrow, Ma'am," said the old woman with
rather an unsteady voice; "I should like, I confess to see her looking
a little less thin."
"She was always thin as a child if you remember, Mrs. Grant, and
when a girl grows very tall, she naturally grows thin at the same
time. I think nothing of that."
"No, no, Ma'am," said Mrs. Grant cheerfully, "young girls will look
thin sometimes."
"She was very ill at Nice you know; the north-east wind brought
back her cough and frightened us very much. And we had a
desponding kind of a man as our medical attendant. There is
nothing so unfavourable to an invalid as one of those over-anxious
people about them. But, you see, now the weather is warm she is
getting on nicely."
Mrs. Grant felt her hopes sinking fast away before the news that the
medical man's opinion was an unfavourable one. She thought it a
bad sign that he should despond, where no particular interest led
him to exaggerate the case.
"You can have no idea," said Mrs. Fitzpatrick, "of what we suffered
at Nice. You have heard of the prejudice the Italians entertain
against any illness that they consider to be of a consumptive
tendency. And Aveline having something of a cough—in short, Mrs.
Grant, they fancied that my poor child was in a decline; and when
she was at the worst, they took fright, and ordered us out of our
lodgings at a moment's notice. Aveline was too ill to travel—our
hostess was peremptory—and I knew well that no other house
would take us in. It was then that a country-woman of ours, a Mrs.

Maxwell Dorset, hearing of our distress, sought us out, and instantly
offered us apartments in her house. It was impossible to stand on
ceremony at such a time. I accepted her kindness, and had we been
her nearest relatives, we could not have been more warmly
welcomed nor more carefully attended."
"Thank God that you are safe again on English ground," said the old
nurse; "where, at least, we do not turn sick people into the streets,
the Pagans! And Heaven reward the good lady who took compassion
on you in your need."
And so saying, Mrs. Grant took her departure.
As soon as Mrs. Fitzpatrick was alone, she sat down before her
writing case, and leaning her head on her hand seemed lost in
thought. She had but few and distant relations, and since her
widowhood had lived in such retirement, that except two or three
neighbouring families she numbered as few friends. She had in early
life, lived much in the world; but having withdrawn into solitude, the
world had paid her the usual compliment, and forgotten her
existence. She had lost several children when very young, and all
her affections centred upon this only girl whose health was so
precarious. She wrote a few lines to a medical man of some
eminence who lived a few miles off, to announce her return, and to
beg that he would lose no time in paying them a visit.
"It is best to be upon the safe side;" she said to herself, "Aveline is
gaining strength; but Mr. Lindsay may point out some means that
would escape me. He is so clever, and has known her constitution
from a child. I am sure he will think she is improved by her
residence abroad."
So saying she rose to retire for the night; and casting her eyes round
the room, she saw lying about, Aveline's gloves, her handkerchief
and scarf, which she had thrown aside and forgotten, with the
carelessness of youth. These she gathered up and folded together
with that indescribable air of tenderness, which, in a mother,

sometimes extends itself to the trifles that her child has worn or
touched; and then went up stairs to take a last look at Aveline—and
to sleep, if she could.

CHAPTER II.
Mighty power, all powers above!
Great unconquerable Love!
Thou who liest in dimple sleek,
On the tender virgin's cheek:
Thee the rich and great obey;
Every creature owns thy sway.
O'er the wide earth, and o'er the main
Extends thy universal reign.
SOPHOCLES.
Perhaps few things are more curious to those who, as bystanders,
contemplate the game of life, than to see how in the stream of time,
persons the most divided, and the least likely to be brought into
contact, are whirled by those resistless waves nearer and nearer,
until at last they meet; or if no collision takes place, still the course
of the one, draws into its channel, or modifies in some strange way
the course of the other.
Margaret little thought as she sat dreaming over her lot at Ashdale,
that a sick girl in another county, whom she had never seen, and
whose name she had never heard, was to exercise a strange
influence over her future fate.
Mr. Haveloc was constantly at Ashdale. He went, it is true,
backwards and forwards from his own place to that of Mr. Grey, but
his visits to his home were wonderfully short, and those at Ashdale
longer and longer. His attention, his devotion to Margaret increased
daily; she never had occasion to form a wish. He seemed to divine
all her thoughts, to anticipate everything that she could by possibility
enjoy. And his was especially the kind of character to interest her;
his failings were not of a nature to come in her way, and the

earnestness of his disposition suited her ideas of the romance of
love. She was not likely to mistake a devotion that knew no pause,
that entertained no other idea than herself day after day.
Then his knowledge, which though rather desultory, was unusual in
a man who had not to earn his living—his command of languages,
his accomplishments—all things that he never cared to bring
forward, but that accident discovered to her by degrees, increased
his power over her mind.
Men cannot forgive acquirement in a woman, though they will
sometimes pardon a sort of natural cleverness; but it is a common
story that women are swayed by genius or learning in a man.
Margaret was hardly aware of the impatience of his temper, which
he never showed except to Mr. Casement, when she fully
sympathised with him; but she daily noticed his attention to her
uncle, his anxiety about his health, and the readiness with which he
would give up his evenings to amuse his old friend. All that she had
heard of him before their acquaintance was merged into the facts
which were to his advantage. She remembered the defence of the
lady and her daughter in Calabria. She forgot all about Mrs. Maxwell
Dorset.
At first, after her rejection of Hubert Gage, she was a good deal
annoyed and distressed by his perseverance. He called on Mr. Grey,
he wrote to her, he described himself as distracted, herself as
mistaken. He was determined to believe that they were made for
each other; and that Margaret was under some strong delusion
when she did not think as he did on that subject. Margaret began to
dread and dislike the very name of Hubert Gage; she feared to meet
him in her walks; every ring at the bell gave her the apprehension
that he was coming to see her. And whether it was his youth or his
disposition, that must be blamed for the fact, he acted very
unreasonably in the affair. He did not take his disappointment at all
like a philosopher; and to crown everything, when Captain Gage had
with infinite difficulty procured him a ship, he declined the

appointment, upon some trivial excuse, and persisted in remaining in
the neighbourhood; to the great vexation of his family, and the
annoyance of Margaret.
At last he was persuaded to accompany his brother who was
returning to Ireland; and then Margaret had an interval of peace.
She was able to see Elizabeth whenever she pleased; and Mr. Grey
left off pitying poor Hubert, when he no longer saw him passing the
house, or looking disconsolate at church.
As Margaret had no female companion, her natural delicacy of
feeling told her that she ought never to be alone with Mr. Haveloc:
but those quiet evenings were almost tête-á-tête when her uncle
slept in his easy chair, and she sat working by the fire, with Mr.
Haveloc always by her side, talking or reading to her in a low voice,
or making her speak Italian, and playfully correcting her mistakes.
And when the spring mellowed into summer, and Mr. Grey had his
chair moved to the large window that opened upon the broad
terrace, Mr. Haveloc would persuade Margaret to pace up and down
the walk, always in sight, though not in hearing, of her kind uncle,
whose great delight was to watch them as they passed and
repassed.
The moon had risen, and gleamed brightly behind one of the dark
cedars upon the lawn. Part of the smooth turf was almost whitened
by its peculiar light, while the trees cast their inky shadows forward
upon the grass. Every flower, half closed and hung with dew, gave
forth its sweetest fragrance.
"And you like sunlight really better than this, Mr. Haveloc?" said
Margaret, as they paused to look upon the landscape.
"Good honest sunlight—strong enough to steep everything in mist, I
really do," replied Mr. Haveloc.
"You are thinking of Italy?"
"No; of English sunshine. I never think of Italy."

These last words were spoken as if he meant to infer that there was
something a great deal more attractive than Italy in her near
neighbourhood.
Her hand was resting on his arm; he pressed it, and she did not
attempt to withdraw it. She felt, no doubt respecting his love; he
expressed it in his manner, and she was sure he would not act a
falsehood. It was all under her uncle's eye, and if he had
disapproved of it, he would have put a stop to it before now. It
made her perfectly happy, and a little frightened only when she
thought he was on the point of saying something decisive. She
would so gladly have gone on exactly as they were then.
"This is very pretty," said Mr. Haveloc, as they again paused opposite
to the dark mournful cedars.
"Oh, beautiful!" returned Margaret. "If there were but some old oaks
about the place: but those ash-trees in the meadow near the copse
—those are really splendid, are they not?"
"Very fine! When I was staying here as Mr. Grey's ward, I believe I
used to sketch those trees once a week."
"I wish I could sketch!"
"Do you? I have no respect for the arts; I had rather a person should
appreciate pictures than paint them."
"But do you not think painting them helps one to appreciate them?"
"I think it teaches one to know the difficulties, but not to feel the
sentiment."
"Uncle Grey, do you smell the Chinese honeysuckle?" asked
Margaret, pausing before the window.
"Yes my love; it is very strong to-night."
"Are you ready for your tea, uncle?"

"I shall be in about ten minutes, my dear."
"Can you guess ten minutes, Mr. Haveloc?"
Mr. Haveloc looked at his watch, and could not distinguish the
figures. Margaret thought she could see better. He held the watch to
her—she pored over it in vain.
"You must guess it now, Mr. Haveloc."
"Mr. Grey is not very particular," said Mr. Haveloc, "I think I may
venture."
They walked on to the end of the terrace.
"Do you recollect one day when I kept the dinner waiting," said Mr.
Haveloc.
"Oh, yes! I remember," said Margaret with a sigh—it was the day
that had begun her troubles with Hubert Gage. "Mr. Casement was
so cross because he could not fathom your business with Mr. Grey."
"What a long deliverance we have had from the old monster," said
Mr. Haveloc.
"Oh, yes! I was so glad when—" Margaret stopped short.
"When he was laid up with the rheumatism," added Mr. Haveloc,
laughing.
"Oh, no! not exactly. One ought not to be glad of that; but really, I
think I rejoiced that anything kept him out of the way."
"Gessina is growing quite fat," said Mr. Haveloc, as the beautiful
creature bounded towards them.
"Stop! I am going to carry her," said Margaret stooping down.
"Cannot you trust me to do that?" asked Mr. Haveloc.
"No; because I am going to wrap her in a corner of my shawl."

"Stay, do not give her too much," said Mr. Haveloc, assisting in the
distribution of the shawl, "you must take care of yourself, in the
evening air."
"She has had so much running about to-day," said Margaret.
"Yes, I saw you taking her out to exercise this morning, before
breakfast."
"Did you? When we were on the lawn?"
"Yes, with that Indian-rubber ball you made her a present of."
"You laugh, but it is a capital ball for Gessina to play with."
"I thought Gessina and her mistress both seemed to enjoy it very
much."
"I did not know you were up then, Mr. Haveloc."
"I had not left my room, I confess."
"How very idle!"
"Oh, it was! but then I had been sitting up half the night."
"What a strange fancy of yours."
"I was writing letters."
"What! with all the day before you?"
"I like to spend the day in your company."
Here a low growl that seemed hardly human, made both start
violently. Margaret dropped Gessina. Mr. Haveloc turned sharply
round.
"Ugh! little woman; are you going to give us tea to-night?" growled
Mr. Casement.

"Oh, dear yes, Sir. I declare I did not know what time it was," said
Margaret hastily.
"There is not the slightest hurry," said Mr. Haveloc detaining
Margaret by the hand, "there can be no possible occasion for you to
make tea before the usual time."
Margaret looked up in deprecation of his contemptuous tone. Mr.
Casement turned to hobble back to the house.
"Ugh, sweethearts!" he grumbled, as he left them.
Margaret blushed crimson. Mr. Haveloc still holding her hand,
walking slowly and silently in the same direction. At last, in that calm
voice which in people of impatient temper always marks strong
emotion, he said:—
"He is right Margaret—I love you!"
Margaret was excessively agitated—she trembled violently; but the
transparent candour of her nature did not now desert her. In a
faltering tone she replied: "I thought so."
"Come along, little woman," said Mr. Casement as Margaret stepped
in at the window. "It is well I am come among you again. Poor uncle
is laid on the shelf now; that's very plain."
"Did I keep you waiting, uncle?" said Margaret softly as she took her
place before the urn.
"No, my love, never mind what he says. You know his ways by this
time."
"Come, sit down, youngster, and don't make a fuss. Take it easy,"
said Mr. Casement addressing Mr. Haveloc, who was behind
Margaret's chair.
Margaret ventured to cast an imploring glance at Mr. Haveloc, who
regarded Mr. Casement as if he should like to reduce him to ashes;

but being unprovided with any apparatus for this ceremony, he sat
down beside Margaret, without making any reply.
It seemed as if Mr. Casement would never go that evening. He
wrangled through one game of piquet after another; at last he got
up. "Well, good night Master Grey," he said, "if you are blind-folded,
I am not. Those young ones have been muttering at the window
there, ever since we sat down to cards."
"What is it Claude?" asked Mr. Grey, as soon as Mr. Casement had
gone.
Mr. Haveloc told him what it was. Margaret laid her head on her
uncle's shoulder—he put his arm round her waist. "Well then,
Claude," he said, "your best plan is to set off to-morrow morning;
the sooner you go, the sooner you will come back."
Margaret looked up with a face suddenly blanched even to her lips.
"What—go away—leave me, uncle?" she said. Her voice failed her;
almost her breath; she had not believed it possible that they should
ever be parted.
Mr. Grey explained to Margaret as he had before explained to Mr.
Haveloc his reasons for insisting on this measure.
When he had finished, she burst into one of those paroxysms of
tears that she only gave way to under very strong emotion. Mr.
Haveloc hung over her chair in speechless distress. Mr. Grey
endeavoured in the tenderest manner to moderate her agitation.
"You see, my child," he said, "you are but seventeen, and very
young for your age; and this fellow here, somewhere about two-
and-twenty. It is very important you should both know your own
minds a little more clearly than you can do now. In such serious
affairs, it is right to be very cautious. You see, my dear little girl,
what day of the month is it? You see, a year soon passes; and next
14th of June, he will be here again."

Margaret checked her tears, and tried to reward his efforts with a
smile.
"Well, then, Claude, you and I must have a little conversation
together. Wish him good night, my child; you had better part now
and not see each other to-morrow morning. It is wisest, is it not
Claude? There give her a kiss and have done with it. That's good
children!"
Margaret was speechless with grief: the last words Mr. Haveloc
addressed to her as he led her to the door, were, "If I ever bestow a
thought upon another, forget me; I can invoke no heavier curse
upon my head."

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