Handout web technology.doc1

WEEK ONE
The Concept of the Internet

Historical background of the Internet

Discuss Intranet and Extranet

WEEK TWO
The Economics, Social, Political, Educational and Cultural
benefits of Internet

WEEK THREE
Various Internet services like:
Information search – (on last page)
E-commerce
E-mail
File Transfer Protocol (FTP)
Bulletin Board Service
Audio-Video Communication
Digital Library
World Wide Web
Telnet and other services

WEEK FOUR
Understand the basic hardware required for Internet
connectivity: Discuss MODEM and its functions

Explain the Data transfer rate of various MODEM

WEEK FIVE
Explain the concept of Wireless Transmission and
Bandwidth

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Discuss various wireless transmission media:
VSAT
Radio etc

WEEK SIX
Discuss obstacle to effective Transmission

Discuss the Steps required to connect a PC to the Internet

WEEK SEVEN
Discuss Problems of Telecommunication infrastructure in
Nigeria: Technical know-how

WEEK EIGHT
Economic factors in Nigeria – Poverty level of the people;
level of awareness

WEEK NINE
The government policies on Internet Access

Explain the concept of ISP and the need for it

WEEK TEN
Explain the economic effect of using local or foreign ISP

Describe Domain Name System (DNS) and its space

WEEK ELEVEN
Explain how to name servers in the DNS
Revision

WEEK TWELVE
EXAMINATION

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LECTURER: MR. M.A. ADEWUSI

THE CONCEPT OF THE INTERNET
Internet can be termed as the interconnection of the variety of networks and computers.
Internet makes use of the internet protocol and the transmission Control protocol. Internet
opened the doors of communication between the various stations. Internet facilitates
storing and transmission of large volumes of data. The internet is one of the most
powerful communication tools today.

In the 1990’s internet gained popularity in the masses. People started becoming aware of
the uses of internet. Internet helped the people to organize their information and files in a
systematic order. Various researches were conducted on internet. Gopher was the first
frequently used hypertext interface.

In 1991, a network based implementation with respect to the hypertext was made. The
technology was inspired by many people. With the advent of the World Wide Web search
engine the popularity of internet grew on an extensive scale. Today, the usage of internet
is seen in science, commerce and nearly all the fields

There are various ways and means to access the internet. With the advancement in
technology people can now access internet services through their cell phones, play
stations and various gadgets. There are large numbers of internet service providers as
well.

With the development and the wide spread application of internet electronic mail people
from all across the globe come together and communication has become much easier than
ever before. Messages, in the form of Emails could be send in at any corner of the world
within fractions of seconds. Emails also facilitated mass communication (one sender
many receivers).

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Emails, video conferencing, live telecast, music, news, e-commerce are some of the
services made available due to internet. Entertainment has taken new dimensions with
the increase of internet and all we see it's a continuous development and transformation.

THE WEB2.0 CONCEPT

"Web 2.0" refers to what is perceived as a second generation of web development and
web design. It is characterized as facilitating communication, information sharing,
interoperability, User-centered design[1] and collaboration on the World Wide Web. It has
led to the development and evolution of web-based communities, hosted services, and
web applications. Examples include social-networking sites, video-sharing sites, wikis,
blogs, mashups and folksonomies.

The term "Web 2.0" was coined by Darcy DiNucci in 1999. In her article "Fragmented
Future," she writes[2]

The Web we know now, which loads into a browser window in essentially static
screenfuls, is only an embryo of the Web to come. The first glimmerings of Web 2.0 are
beginning to appear, and we are just starting to see how that embryo might develop. ...
The Web will be understood not as screenfuls of text and graphics but as a transport
mechanism, the ether through which interactivity happens. It will [...] appear on your
computer screen, [...] on your TV set [...] your car dashboard [...] your cell phone [...]
hand-held game machines [...] and maybe even your microwave.

Her arguments about Web 2.0 are nascent yet hint at the meaning that is associated with
it today.

The term is now closely associated with Tim O'Reilly because of the O'Reilly Media
Web 2.0 conference in 2004.[3][4] Although the term suggests a new version of the World
Wide Web, it does not refer to an update to any technical specifications, but rather to
cumulative changes in the ways software developers and end-users utilize the Web.
According to Tim O'Reilly:

Web 2.0 is the business revolution in the computer industry caused by the move to the
Internet as a platform, and an attempt to understand the rules for success on that new
platform.[5]

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However, whether it is qualitatively different from prior web technologies has been
challenged. For example, World Wide Web inventor Tim Berners-Lee called the term a
"piece of jargon"[6].

HISTORICAL BACKGROUNG OF THE INTERNET

1950

As early as 1950 work began on the defense system know as the Semi-Automatic
Ground Environment, or SAGE. This defense system was thought to be required to
protect the US mainland from the new Soviet long range bombers and missile carriers
such as the Tupolev. IBM, MIT and Bell Labs all worked together to build the SAGE
continental air defense network that became operational in 1959.

SAGE became the most advanced network in the world at the time of its creation and
consisted of early warning radar systems on land, sea, and even air courtesy of AWACS
planes. The network technology lead to more advanced systems and protocols that would
one day become the Internet, as well as common hardware items such as the mouse,
magnetic memory (tape), computer graphics, and the modem.

1957

In 1957 the USSR launched the first earth-orbiting artificial satellite and kicked off the
space race in a big way. The United States, suddenly fearful of Russian space platforms
armed with nuclear weapons, needed an agency designed to combat this menace. ARPA,
or Advanced Research Projects Agency, was founded in 1958 and was given the mission
of making the US the leader in science and technology. In 1972 ARPA was renamed the
Defense Advanced Research Projects Agency (DARPA). As of 1996 the agency is once
again called ARPA.

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ARPA hired J.C.R. Licklider in 1962 to become the Director of their Information
Processing Techniques Office (IPTO). Licklider’s works eventually lead to the field of
interactive computing, and is the foundation for the field of Computer Science in general.
Lickliders work with computer timesharing helped usher in the practical use of the
computer network.

1962 – Rise of the Modem and the Conceptual Internet

AT&T released the first commercially available modem, the Bell 103. The modem was
the first with full-duplex transmission capability and had a speed of 300 bits per second.

The first real conceptual plan of the Internet was being seen in a series of memos released
by J.C.R Licklider where he referred to a “Galactic Network” that connected all users and
data in the world. These memos grew from his first paper on the subject Man-Computer
Symbiosis released in 1960, although this early work covered human interaction with
computers and less about human to human communication. In 1962 the aptly named On-
Line Man Computer Communications was released and dealt with the concept of social
interaction through computer networks.

Birth of the World Wide Web

1992 – ISOC

Founded in 1992, The Internet Society (ISOC) is a non-profit organization that assists in
the development of Internet education, policy and standards. The organization has offices
in the U.S and Switzerland and works toward an Internet evolution that will benefit the
entire world.

ISOC is the home of organizations responsible for Internet infrastructure standards, the
Internet Engineering Task Force, and the Internet Architecture Board (IAB). ISOC is also
a clearinghouse for Internet education and information and a facilitator for Internet
activities all over the world. ISOC has run network training programs for developing
countries and assisted in the connecting of almost every country to the Internet.

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1994 - The Web Browser is Born

Jim Clark and Mark Andreessen founded Mosaic Communications in 1994. Andreessen
had been the leader of a software project at the University of Illinois called Mosaic, the
fist publically available web browser. Jim and Mark changed the name of Mosaic
Communications to Netscape Communications and their web browser was soon released
to a frantically growing market.

Netscape was the largest browser firm in the world very quickly and dominated the
market. Software releases seemed to come out monthly if not faster and it was these
Netscape offerings that lead to the term “internet time”. Business was moving faster
everyday. By 1995 Netscape had an 80% market share.

1995 - Windows 95 and the Browser Wars

Windows 95 was released by Microsoft and took the world by storm. The software giant
solidified its OS presence and began to make its way into homes across the world. A little
know program included with the OS was Internet Explorer, a web browser. Microsoft
wanted to challenge Netscape’s dominance in the browser market, and had the OS
platform to do it with. Netscape pushed the boundaries of browser technology and made
technological leaps forward on an almost daily basis. Netscape was considered the most
advanced browser available, and Microsoft had years of catching up to do. One key
difference however was Internet Explorer was free and Netscape was not. This was
difficult to overcome but Netscape pushed forward in what was now being called The
Browser Wars.

Although the term Browser Wars generally refers to the competition in the marketplace
of the various web browsers in the early and mid 90’s it is most commonly used in
reference to Internet Explorer and Netscape Navigator. Microsoft eventually captured
Netscape’s market share, and Netscape Navigator ceased to be. Firefox is now the
primary browser competitor to Internet Explorer.

1998 – ICANN is Formed

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ICANN is the Internet Corporation for Assigned Names and Numbers and is a not-for-
profit public benefit corporation. ICANN helps coordinate the unique identifiers ever
computer needs to be able to communicate via the Internet. It is by these identifiers
computers can find each other, and without them no communication would be possible.

ICAAN is dedicated to keeping the Internet the Internet secure, stable, and interoperable.

1999 – Y2K Looms

Y2K was short for “the year 2000 software problem” and was also called The
Millennium Bug. The problem has been the subject of many books and news reports, and
was discussed by Usenet users as early as 1985.

The heart of the problem was that it was thought that computer programs would produce
erroneous information or simply stop working because they stored years using only two
digits. This would mean the year 200 would be represented with 00 and appear to be the
year 1900 to the computer.

Government committees were set up to drive contingency plans around the Y2K issue
that would help mitigate damages caused to crucial infrastructure such as utilities,
telecommunication, banking and more. Although the failing of military systems was
discussed in public forums, the danger there was minimal as the closed systems were all
Y2K compliant. Public fears of the Y2K “disaster” grew as the date approached.

Although there was no Y2K disaster either due to concerted efforts or simply because
there never was a great danger, there were benefits to the issue such as the proliferation
of data back up systems and power contingency systems that protect businesses today.

One of the few Y2K incidents was the US timekeeper (USNO) reported the new year as
19100 on 01/01/2002

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2001 – HDTV over an IP Network

Level 3 Communications Inc and the University of Southern California successfully
demonstrate the first transmission of uncompressed real-time gigabit high-definition
television over an Internet Protocol optic network. This demonstration proved the
technology they were using would support high speed data steaming without packet
differentiation. Without the need of data packets, HDTV anywhere begins to be
discussed.

INTRANET AND EXTRANET
Introduction

A key requirement in today's business environment is the ability to communicate more
effectively, both internally with your employees and externally with your trading partners
and customers.

An intranet is a private - internal - business network that enables your employees to share
information, collaborate, and improve communications.

An extranet enables your business to communicate and collaborate more effectively with
selected business partners, suppliers and customers. An extranet can play an important
role in enhancing business relationships and improving supply chain management.

An intranet is a business' own private website. It is a private business network that uses
the same underlying structure and network protocols as the internet and is protected from
unauthorised users by a firewall.

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Intranets enhance existing communication between employees, and provide a common
knowledge base and storage area for everyone in your business. They also provide users
with easy access to company data, systems and email from their desktops.

Because intranets are secure and easily accessible via the internet, they enable staff to do
work from any location simply by using a web browser. This can help small businesses to
be flexible and control office overheads by allowing employees to work from almost any
location, including their home and customer sites.

Other types of intranet are available that merge the regular features of intranets with those
often found in software such as Microsoft Office. These are known as online offices or
web offices. Creating a web office will allow you to organise and manage information
and share documents and calendars using a familiar web browser function, which is
accessible from anywhere in the world.

Types of content found on intranets:

• administrative - calendars, emergency procedures, meeting room bookings,
procedure manuals and membership of internal committees and groups
• corporate - business plans, client/customer lists, document templates, branding
guidelines, mission statements, press coverage and staff newsletters
• financial - annual reports and organisational performance
• IT - virus alerts, tips on dealing with problems with hardware, software and
networks, policies on corporate use of email and internet access and a list of
online training courses and support
• marketing - competitive intelligence, with links to competitor websites, corporate
brochures, latest marketing initiatives, press releases, presentations
• human resources - appraisal procedures and schedules, employee policies,
expenses forms and annual leave requests, staff discount schemes, new vacancies
• individual projects - current project details, team contact information, project
management information, project documents, time and expense reporting

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• external information resources - route planning and mapping sites, industry
organisations, research sites and search engines.

Benefits of intranets and extranets
Your organization’s' efficiency can be improved by using your intranet for:

• publishing - delivering information and business news as directories and web
documents
• document management - viewing, printing and working collaboratively on
office documents such as spreadsheets
• training - accessing and delivering various types of e-learning to the user's
desktop
• workflow - automating a range of administrative processes
• front-end to corporate systems - providing a common interface to corporate
databases and business information systems
• email - integrating intranet content with email services so that information can be
distributed effectively

The main benefits of an intranet are:

• better internal communications - corporate information can be stored centrally
and accessed at any time
• sharing of resources and best practice - a virtual community can be created to
facilitate information sharing and collaborative working
• improved customer service - better access to accurate and consistent information
by your staff leads to enhanced levels of customer service
• reduction in paperwork - forms can be accessed and completed on the desktop,
and then forwarded as appropriate for approval, without ever having to be printed
out, and with the benefit of an audit trail

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It is a good idea to give your intranet a different image and structure from your customer-
facing website. This will help to give your internal communications their own identity
and prevent employees confusing internal and external information.

BENEFITS OF INTERNET IN RELATION TO:
ECONOMICS: The most often cited reasons for communities establishing their
own local access networks are for reasons of economic development and the
requirement for local businesses to have high-speed Internet services. The system
requirements were that it must provide broadband virtual private networks (VPN)
and high-speed Internet access for municipal facilities, emergency and public
services, businesses and industrial spaces.

One of the more recent studies on the economic impact of mass market broadband was
conducted on a range of communities across the United States comparing indicators of
economic activity that included employment wages and industry mix (Lehr, Osorio,
Gillett and Sirbu, 2004). In those U.S. communities where broadband had been deployed
since December 1999, the researchers found that between 1998 and 2002, these
communities experienced more rapid growth in employment, number of businesses
overall, and businesses in IT- intensive sectors.

As noted by the authors, “… the early results presented here suggest that the assumed
(and oft-touted) economic impacts of broadband are both real and measurable.”[7]

The major reason that access to high-speed Internet access is believed to benefit local
communities, particularly in rural areas, is the impact that it has on increasing the
competitiveness of businesses by increasing productivity, extending their market reach
and reducing costs. Until recently, there has been little research done on attempting to
analyse and document the underlying reasons why businesses are positively impacted by
high-speed Internet access. There are two studies, one from Cornwall, England and the
other from British Columbia, Canada, which have shown remarkably similar results.

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Cornwall is a relatively isolated area that is provided with high-speed Internet access by
actnow, a public-private partnership that was established in 2002 by Cornwall Enterprise
to promote economic development in the region. In April 2005, an online survey of
companies that were served by actnow was undertaken. The main findings of the study
were:

“Their answers suggest that broadband is generally benefiting enterprises, individuals,
the Cornish economy, society and the natural environment by, for example, extending
market reach and impact, making organisational working practices more efficient,
enabling staff to work flexibly, and substituting travel and meetings with electronic
communication. In particular:

• Over 94% of respondents report positive overall impacts from broadband, with
68% stating that they are highly positive.
• A large majority of respondents feel that broadband has positive impacts on
business performance (91%), relationships with customers (87%), and the job
satisfaction and skills of staff (74%).
• 90% of respondents expect to get continued benefits – and 45% considerable
benefits - from broadband.” [8]

The Peace River and South Silmilkameen regions are located in remote parts of British
Columbia, Canada. The area is served by the Peace Region Internet Society which is a
not for profit organisation established in 1994 to provide affordable access to the Internet
for individuals, businesses, and organizations in the Peace Region of Northern British
Columbia. In 2005, an online survey of customers was undertaken to measure the
economic impact of high-speed Internet access in these communities. The major findings
were:

“For most businesses in the communities we studied, broadband is an important factor
in remaining competitive. Broadband allows businesses to be more productive, to
identify and respond to opportunities faster, and to meet the expectations of customers,
partners, and suppliers.

• Over 80 per cent of business respondents reported that broadband positively
affected their businesses. Over 18 per cent stated they could not operate without
broadband;
• 62 per cent of businesses say productivity has gone up with a majority citing an
increase of more than 10 per cent;

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• Many businesses reported increased revenue and/or decreased costs due to
broadband connectivity.”[9]

The two studies show a high degree of similarity in the responses with businesses in both
areas demonstrating that high-speed Internet access has positively impacted their
businesses, through increased productivity and overall efficiencies. The research
demonstrates that high-speed Internet connectivity is important to ensure that businesses
in rural and remote areas remain competitive and without it, they would be at a severe
competitive disadvantage.

POLITICAL: Theoretical Background: Inclusion in or Exclusion from the
Political System? Some years ago Dick Morris, one of Bill Clintons spin doctors, saw the
United States on the way from James Madison towards Thomas Jefferson, from
representative democracy to direct democracy, with the Internet serving as a catalyst
(Morris 1999). Al Gore and others tried to "re-invent governance" by means of the
Internet, thus creating some sort of "new Athenian age" of democracy (Gore 1995).
Today such enthusiasm seems somehow exaggerated. The Internet fell short of many
expectations not only economically. Now we have the chance to take a restrained look at
the Internet to calculate costs and benefits from online communication - even in the field
of politics. First we want to specify the three levels on which an impact of the Internet in
this field may be considered: • a macro-level approach considers the use of the Internet
by states ("e-governance"). • a meso-level approach considers the use of the Internet by
political organizations ("virtual parties") • a micro-level approach considers the use of the
Internet by individual citizens ("e- democracy") In our presentation we deal only with
micro-level consequences of Internet usage. Our focus is on the individual activities
people take to communicate politically. This includes reception of political media as well
as talks about politics and showing of ones own opinion in public (in a demonstration for
example). What are the common assumptions about consequences of internet usage on
political communication? The literature provides a first position that ascribes a
"mobilizing function" to the Internet (Schwartz 1996; Rheingold 1994, Grossman 1995).
This position expects a higher frequency and a higher intensity in political
communication among Internet users than among non-users. It expects also that the
Internet may include even those parts of the population who can’t be reached by

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traditional channels of political communication. The public and scientific discussion is
dominated by this "hypothesis of inclusion": The Internet intensifies political
communication and thus leads to a growing integration of citizens into the political
system.

EDUCATIONAL: The internet provides a powerful resource for learning, as
well as an efficient means of communication. Its use in education can provide a number
of specific learning benefits, including the development of:
• independent learning and research skills, such as improved access to subject learning
across a wide range of learning areas, as well as in integrated or cross-curricular
studies; and
• communication and collaboration, such as the ability to use learning technologies to
access resources, create resources and communicate with others.
Access to resources
The internet is a huge repository of learning material. As a result, it significantly expands
the resources available to students beyond the standard print materials found in school
libraries. It gives students access to the latest reports on government and non-government
websites, including research results, scientific and artistic resources in museums and art
galleries, and other organisations with information applicable to student learning. At
secondary schooling levels, the internet can be used for undertaking reasonably
sophisticated research projects.
The internet is also a time-efficient tool for a teacher that expands the possibilities for
curriculum development.
Learning depends on the ability to find relevant and reliable information quickly and
easily, and to select, interpret and evaluate that information. Searching for information
on the internet can help to develop these skills. Classroom exercises and take-home
assessment tasks, where students are required to compare and contrast website content,
are ideal for alerting students to the requirements of writing for different audiences, the
purpose of particular content, identifying bias and judging accuracy and reliability. Since
many sites adopt particular views about issues, the internet is a useful mechanism for

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developing the skills of distinguishing fact from opinion and exploring subjectivity and
objectivity.
Communication and collaboration
The internet is a powerful tool for developing students’ communication and collaboration
skills. Above all, the internet is an effective means of building language skills.
Through email, chat rooms and discussion groups, students learn the basic principles
of communication in the written form. This gives teachers the opportunity to incorporate
internet-based activities into mainstream literacy programs and bring diversity to their
repertoires of teaching strategies. For example, website publishing can be a powerful
means of generating enthusiasm for literacy units, since most students are motivated by
the prospect of having their work posted on a website for public access.
Collaborative projects can be designed to enhance students’ literacy skills, mainly
through email messaging with their peers from other schools or even other countries.
Collaborative projects are also useful for engaging students and providing meaningful
learning experiences. In this way, the internet becomes an effective means of advancing
intercultural understanding. Moderated chat rooms and group projects can also provide
students with opportunities for collaborative learning.
Numerous protocols govern use of the internet. Learning these protocols and how to
adhere to them helps students understand the rule-based society in which they live and to
treat others with respect and decency. The internet also contributes to students’ broader
understanding of information and communication technologies (ICT) and its centrality to
the information economy and society as a whole.

Culture: Two definitions
1: High culture
The best literature, art, music, film that exists. Societies are often ‘defined’ by their high
culture.
Problem: who decides what is best – are there any timeless rules?
2: Culture as lived experience
Culture is the ordinary, everyday social world around us.
Is there a single culture?
• In the early part of the 20th century people would talk about “national culture”

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• With the rise of global media and the deregulation of information flows people
are more likely to talk about “cultures” within a nation based on age, ethnicity, interests,
gender.
• There are many cultures and an individual may belong to more than one….
• A key issue is that some groups may have more “power” than others to effect
people’s lives...

HARDWARE REQUIREMENT FOR INTERNET
CONNECTIVITY
The term modem is an acronym of “modulator-demodulator”. In simple words, a modem
enables users to connect their computer to internet. It also enables to transmit and receive
data across the internet. It is the key that unlocks doors of the world of the Internet for the
user. The modems can be of various types. They may be hardware, software or controller
less. The most widely used modems are hardware modems. There are mainly three types
of hardware modems. All three types of modems work the same way. However, each has
its advantages and disadvantages. Here, we discuss them…
The oldest and simplest type of hardware modems are external modems. In fact, they are
the earliest modems that have been in use for more then 25 years. As the name suggest,
they reside outside the main computer. Therefore, they are easy to install, as the computer
need not be opened. They connect to a computer's serial port through a cable. On other
hand, the telephone line is plugged in a socket on the modem. Advantage of an external
modem is that the external modems have their own power supply. The modem can be
turned off to break an online connection quickly without powering down the computer.
Another advantage is that by having a separate power supply is that it does not drain any
power from the computer. The Main disadvantage is that the external modems are more
expensive then the internal modems.
On other hand, Internal modems come installed in the computer you buy. Internal
modems are integrated into the computer system mostly installed in the motherboard.
Hence, do not need any special attention. Internal modems are activated when you run a
dialer program to access internet. The internal modem can be turned off when you exit
the program. This can be very convenient. The major disadvantage with internal modems

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is their location. When you want to replace an internal modem you have to go inside the
computer case to change it. Internal modems usually cost less than external modems, but
the price difference is usually small.
The third significant type of hardware modem is the PC Card modem. These modems are
mainly designed for portable computers. They come in size of a credit card and could be
fitted into the PC Card slot on notebook and handheld computers. These modem cards are
removable when the modem is no longer needed. Most notably, except for their size, PC
Card modems combine the characteristics of both external and internal modems. The PC
card modems are plugged directly into an external slot in the portable computer. There is
no cable requirement like external modems. The only other requirement is the telephone
line connection. The only disadvantage is that running a PC Card modem while the
portable computer is operating on battery power drastically decreases the life of your
batteries. The portable computer need tp power the PC card modems. This is fine unless
the computer is battery operated.
Overall, you may have an external, an internal modem or a PC modem card as per your
requirements. The modem you choose should be depend upon how your computer is
configured and your preferences on accessing internet.

History
News wire services in 1920s used multiplex equipment that met the definition, but the
modem function was incidental to the multiplexing function, so they are not commonly
included in the history of modems.
Modems grew out of the need to connect teletype machines over ordinary phone lines
instead of more expensive leased lines which had previously been used for current loop-
based teleprinters and automated telegraphs. George Stibitz connected a New Hampshire
teletype to a computer in New York City by a subscriber telephone line in 1940.

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Anderson-Jacobsen brand Bell 101 dataset 110 baud RS-232 modem, in original wood
chassis
Mass-produced modems in the United States began as part of the SAGE air-defense
system in 1958, connecting terminals at various airbases, radar sites, and command-and-
control centers to the SAGE director centers scattered around the U.S. and Canada.
SAGE modems were described by AT&T's Bell Labs as conforming to their newly
published Bell 101 dataset standard. While they ran on dedicated telephone lines, the
devices at each end were no different from commercial acoustically coupled Bell 101,
110 baud modems.
In the summer of 1960, the name Data-Phone was introduced to replace the earlier term
digital subset. The 202 Data-Phone was a half-duplex asynchronous service that was
marketed extensively in late 1960. In 1962, the 201A and 201B Data-Phones were
introduced. They were synchronous modems using two-bit-per-baud phase-shift keying
(PSK). The 201A operated half-duplex at 2000 bit/s over normal phone lines, while the
201B provided full duplex 2400 bit/s service on four-wire leased lines, the send and
receive channels running on their own set of two wires each.
The famous Bell 103A dataset standard was also introduced by Bell Labs in 1962. It
provided full-duplex service at 300 baud over normal phone lines. Frequency-shift keying
was used with the call originator transmitting at 1070 or 1270 Hz and the answering
modem transmitting at 2025 or 2225 Hz. The readily available 103A2 gave an important
boost to the use of remote low-speed terminals such as the KSR33, the ASR33, and the
IBM 2741. AT&T reduced modem costs by introducing the originate-only 113D and the
answer-only 113B/C modems.
The Carterfone decision

The Novation CAT acoustically coupled modem

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For many years, the Bell System (AT&T) maintained a monopoly in the United States on
the use of its phone lines, allowing only Bell-supplied devices to be attached to its
network. Before 1968, AT&T maintained a monopoly on what devices could be
electrically connected to its phone lines. This led to a market for 103A-compatible
modems that were mechanically connected to the phone, through the handset, known as
acoustically coupled modems. Particularly common models from the 1970s were the
Novation CAT and the Anderson-Jacobson, spun off from an in-house project at the
Lawrence Livermore National Laboratory. Hush-a-Phone v. FCC was a seminal ruling in
United States telecommunications law decided by the DC Circuit Court of Appeals on
November 8, 1956. The District Court found that it was within the FCC's authority to
regulate the terms of use of AT&T's equipment. Subsequently, the FCC examiner found
that as long as the device was not physically attached it would not threaten to degenerate
the system. Later, in the Carterfone decision, the FCC passed a rule setting stringent
AT&T-designed tests for electronically coupling a device to the phone lines. AT&T
made these tests complex and expensive, so acoustically coupled modems remained
common into the early 1980s.
In December 1972, Vadic introduced the VA3400. This device was remarkable because it
provided full duplex operation at 1200 bit/s over the dial network, using methods similar
to those of the 103A in that it used different frequency bands for transmit and receive. In
November 1976, AT&T introduced the 212A modem to compete with Vadic. It was
similar in design to Vadic's model, but used the lower frequency set for transmission. It
was also possible to use the 212A with a 103A modem at 300 bit/s. According to Vadic,
the change in frequency assignments made the 212 intentionally incompatible with
acoustic coupling, thereby locking out many potential modem manufacturers. In 1977,
Vadic responded with the VA3467 triple modem, an answer-only modem sold to
computer center operators that supported Vadic's 1200-bit/s mode, AT&T's 212A mode,
and 103A operation.

20

The Smartmodem and the rise of BBSes

US Robotics Sportster 14, 400 Fax modem (1994)
The next major advance in modems was the Smartmodem, introduced in 1981 by Hayes
Communications. The Smartmodem was an otherwise standard 103A 300-bit/s modem,
but was attached to a small controller that let the computer send commands to it and
enable it to operate the phone line. The command set included instructions for picking up
and hanging up the phone, dialing numbers, and answering calls. The basic Hayes
command set remains the basis for computer control of most modern modems.
Prior to the Hayes Smartmodem, modems almost universally required a two-step
process to activate a connection: first, the user had to manually dial the remote number on
a standard phone handset, and then secondly, plug the handset into an acoustic coupler.
Hardware add-ons, known simply as dialers, were used in special circumstances, and
generally operated by emulating someone dialing a handset.
With the Smartmodem, the computer could dial the phone directly by sending the modem
a command, thus eliminating the need for an associated phone for dialing and the need
for an acoustic coupler. The Smartmodem instead plugged directly into the phone line.
This greatly simplified setup and operation. Terminal programs that maintained lists of
phone numbers and sent the dialing commands became common.
The Smartmodem and its clones also aided the spread of bulletin board systems (BBSs).
Modems had previously been typically either the call-only, acoustically coupled models
used on the client side, or the much more expensive, answer-only models used on the
server side. The Smartmodem could operate in either mode depending on the commands
sent from the computer. There was now a low-cost server-side modem on the market, and
the BBSs flourished.

21

Softmodem (dumb modem)
Main article: Softmodem
Apple's GeoPort modems from the second half of the 1990s were similar. Although a
clever idea in theory, enabling the creation of more-powerful telephony applications, in
practice the only programs created were simple answering-machine and fax software,
hardly more advanced than their physical-world counterparts, and certainly more error-
prone and cumbersome. The software was finicky and ate up significant processor time,
and no longer functions in current operating system versions.
Almost all modern modems also do double-duty as a fax machine as well. Digital faxes,
introduced in the 1980s, are simply a particular image format sent over a high-speed
(commonly 14.4 kbit/s) modem. Software running on the host computer can convert any
image into fax-format, which can then be sent using the modem. Such software was at
one time an add-on, but since has become largely universal.

A PCI Winmodem/Softmodem (on the left) next to a traditional ISA modem (on the
right). Notice the less complex circuitry of the modem on the left.
A Winmodem or Softmodem is a stripped-down modem that replaces tasks traditionally
handled in hardware with software. In this case the modem is a simple digital signal
processor designed to create sounds, or voltage variations, on the telephone line.
Softmodems are cheaper than traditional modems, since they have fewer hardware
components. One downside is that the software generating the modem tones is not
simple, and the performance of the computer as a whole often suffers when it is being
used. For online gaming this can be a real concern. Another problem is lack of portability
such that other OSes (such as Linux) may not have an equivalent driver to operate the
modem. A Winmodem might not work with a later version of Microsoft Windows, if its
driver turns out to be incompatible with that later version of the operating system.

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Narrowband/phone-line dialup modems
A standard modem of today contains two functional parts: an analog section for
generating the signals and operating the phone, and a digital section for setup and
control. This functionality is actually incorporated into a single chip, but the division
remains in theory. In operation the modem can be in one of two "modes", data mode in
which data is sent to and from the computer over the phone lines, and command mode in
which the modem listens to the data from the computer for commands, and carries them
out. A typical session consists of powering up the modem (often inside the computer
itself) which automatically assumes command mode, then sending it the command for
dialing a number. After the connection is established to the remote modem, the modem
automatically goes into data mode, and the user can send and receive data. When the user
is finished, the escape sequence, "+++" followed by a pause of about a second, is sent to
the modem to return it to command mode, and the command ATH to hang up the phone
is sent.
The commands themselves are typically from the Hayes command set, although that term
is somewhat misleading. The original Hayes commands were useful for 300 bit/s
operation only, and then extended for their 1200 bit/s modems. Faster speeds required
new commands, leading to a proliferation of command sets in the early 1990s. Things
became considerably more standardized in the second half of the 1990s, when most
modems were built from one of a very small number of "chip sets". We call this the
Hayes command set even today, although it has three or four times the numbers of
commands as the actual standard.

23

Increasing speeds (V.21 V.22 V.22bis)

A 2400 bit/s modem for a laptop.
The 300 bit/s modems used frequency-shift keying to send data. In this system the stream
of 1s and 0s in computer data is translated into sounds which can be easily sent on the
phone lines. In the Bell 103 system the originating modem sends 0s by playing a
1070 Hz tone, and 1s at 1270 Hz, with the answering modem putting its 0s on 2025 Hz
and 1s on 2225 Hz. These frequencies were chosen carefully, they are in the range that
suffer minimum distortion on the phone system, and also are not harmonics of each other.
In the 1200 bit/s and faster systems, phase-shift keying was used. In this system the two
tones for any one side of the connection are sent at the similar frequencies as in the 300
bit/s systems, but slightly out of phase. By comparing the phase of the two signals, 1s and
0s could be pulled back out, for instance if the signals were 90 degrees out of phase, this
represented two digits, "1, 0", at 180 degrees it was "1, 1". In this way each cycle of the
signal represents two digits instead of one. 1200 bit/s modems were, in effect, 600
symbols per second modems (600 baud modems) with 2 bits per symbol.
Voiceband modems generally remained at 300 and 1200 bit/s (V.21 and V.22) into the
mid 1980s. A V.22bis 2400-bit/s system similar in concept to the 1200-bit/s Bell 212
signalling was introduced in the U.S., and a slightly different one in Europe. By the late
1980s, most modems could support all of these standards and 2400-bit/s operation was
becoming common.

24

For more information on baud rates versus bit rates, see the companion article List of
device bandwidths.
Increasing speeds (one-way proprietary standards)
Many other standards were also introduced for special purposes, commonly using a high-
speed channel for receiving, and a lower-speed channel for sending. One typical example
was used in the French Minitel system, in which the user's terminals spent the majority of
their time receiving information. The modem in the Minitel terminal thus operated at
1200 bit/s for reception, and 75 bit/s for sending commands back to the servers.
Three U.S. companies became famous for high-speed versions of the same concept.
Telebit introduced its Trailblazer modem in 1984, which used a large number of 36 bit/s
channels to send data one-way at rates up to 18,432 bit/s. A single additional channel in
the reverse direction allowed the two modems to communicate how much data was
waiting at either end of the link, and the modems could change direction on the fly. The
Trailblazer modems also supported a feature that allowed them to "spoof" the UUCP "g"
protocol, commonly used on Unix systems to send e-mail, and thereby speed UUCP up
by a tremendous amount. Trailblazers thus became extremely common on Unix systems,
and maintained their dominance in this market well into the 1990s.
U.S. Robotics (USR) introduced a similar system, known as HST, although this supplied
only 9600 bit/s (in early versions at least) and provided for a larger backchannel. Rather
than offer spoofing, USR instead created a large market among Fidonet users by offering
its modems to BBS sysops at a much lower price, resulting in sales to end users who
wanted faster file transfers. Hayes was forced to compete, and introduced its own 9600-
bit/s standard, Express 96 (also known as "Ping-Pong"), which was generally similar to
Telebit's PEP. Hayes, however, offered neither protocol spoofing nor sysop discounts,
and its high-speed modems remained rare.
4800 and 9600 (V.27ter, V.32)
Echo cancellation was the next major advance in modem design. Local telephone lines
use the same wires to send and receive, which results in a small amount of the outgoing
signal bouncing back. This signal can confuse the modem. Is the signal it is "hearing" a
data transmission from the remote modem, or its own transmission bouncing back? This
was why earlier modems split the signal frequencies into answer and originate; each

25

modem simply didn't listen to its own transmitting frequencies. Even with improvements
to the phone system allowing higher speeds, this splitting of available phone signal
bandwidth still imposed a half-speed limit on modems.
Echo cancellation got around this problem. Measuring the echo delays and magnitudes
allowed the modem to tell if the received signal was from itself or the remote modem,
and create an equal and opposite signal to cancel its own. Modems were then able to send
at "full speed" in both directions at the same time, leading to the development of 4800
and 9600 bit/s modems.
Increases in speed have used increasingly complicated communications theory. 1200 and
2400 bit/s modems used the phase shift key (PSK) concept. This could transmit two or
three bits per symbol. The next major advance encoded four bits into a combination of
amplitude and phase, known as Quadrature Amplitude Modulation (QAM). Best
visualized as a constellation diagram, the bits are mapped onto points on a graph with the
x (real) and y (quadrature) coordinates transmitted over a single carrier.
The new V.27ter and V.32 standards were able to transmit 4 bits per symbol, at a rate of
1200 or 2400 baud, giving an effective bit rate of 4800 or 9600 bits per second. The
carrier frequency was 1650 Hz. For many years, most engineers considered this rate to be
the limit of data communications over telephone networks.
Error correction and compression
Operations at these speeds pushed the limits of the phone lines, resulting in high error
rates. This led to the introduction of error-correction systems built into the modems,
made most famous with Microcom's MNP systems. A string of MNP standards came out
in the 1980s, each increasing the effective data rate by minimizing overhead, from about
75% theoretical maximum in MNP 1, to 95% in MNP 4. The new method called MNP 5
took this a step further, adding data compression to the system, thereby increasing the
data rate above the modem's rating. Generally the user could expect an MNP5 modem to
transfer at about 130% the normal data rate of the modem. MNP was later "opened" and
became popular on a series of 2400-bit/s modems, and ultimately led to the development
of V.42 and V.42bis ITU standards. V.42 and V.42bis were non-compatible with MNP
but were similar in concept: Error correction and compression.

26

Another common feature of these high-speed modems was the concept of fallback,
allowing them to talk to less-capable modems. During the call initiation the modem
would play a series of signals into the line and wait for the remote modem to "answer"
them. They would start at high speeds and progressively get slower and slower until they
heard an answer. Thus, two USR modems would be able to connect at 9600 bit/s, but,
when a user with a 2400-bit/s modem called in, the USR would "fall back" to the
common 2400-bit/s speed. This would also happen if a V.32 modem and a HST modem
were connected. Because they used a different standard at 9600 bit/s, they would fall
back to their highest commonly supported standard at 2400 bit/s. The same applies to
V.32bis and 14400 bit/s HST modem, which would still be able to communicate with
each other at only 2400 bit/s.
Breaking the 9.6k barrier
In 1980 Gottfried Ungerboeck from IBM Zurich Research Laboratory applied powerful
channel coding techniques to search for new ways to increase the speed of modems. His
results were astonishing but only conveyed to a few colleagues. Finally in 1982, he
agreed to publish what is now a landmark paper in the theory of information coding. By
applying powerful parity check coding to the bits in each symbol, and mapping the
encoded bits into a two dimensional "diamond pattern", Ungerboeck showed that it was
possible to increase the speed by a factor of two with the same error rate. The new
technique was called "mapping by set partitions" (now known as trellis modulation).
Error correcting codes, which encode code words (sets of bits) in such a way that they are
far from each other, so that in case of error they are still closest to the original word (and
not confused with another) can be thought of as analogous to sphere packing or packing
pennies on a surface: the greater two bit sequences are from one another, the easier it is to
correct minor errors.
The industry was galvanized into new research and development. More powerful coding
techniques were developed, commercial firms rolled out new product lines, and the
standards organizations rapidly adopted to new technology. The "tipping point" occurred
with the introduction of the SupraFAXModem 14400 in 1991. Rockwell had introduced a
new chipset supporting not only V.32 and MNP, but the newer 14, 400 bit/s V.32bis and
the higher-compression V.42bis as well, and even included 9600 bit/s fax capability.

27

Supra, then known primarily for their hard drive systems, used this chipset to build a low-
priced 14, 400 bit/s modem which cost the same as a 2400 bit/s modem from a year or
two earlier (about US$300). The product was a runaway best-seller, and it was months
before the company could keep up with demand.
V.32bis was so successful that the older high-speed standards had little to recommend
them. USR fought back with a 16, 800 bit/s version of HST, while AT&T introduced a
one-off 19, 200 bit/s method they referred to as V.32ter (also known as V.32 terbo), but
neither non-standard modem sold well.
V.34 / 28.8k and 33.6k

An ISA modem manufactured to conform to the V.34 protocol.
Any interest in these systems was destroyed during the lengthy introduction of the 28,
800 bit/s V.34 standard. While waiting, several companies decided to "jump the gun" and
introduced modems they referred to as "V.FAST". In order to guarantee compatibility
with V.34 modems once the standard was ratified (1994), the manufacturers were forced
to use more "flexible" parts, generally a DSP and microcontroller, as opposed to purpose-
designed "modem chips".
Today the ITU standard V.34 represents the culmination of the joint efforts. It employs
the most powerful coding techniques including channel encoding and shape encoding.
From the mere 4 bits per symbol (9.6 kbit/s), the new standards used the functional
equivalent of 6 to 10 bits per symbol, plus increasing baud rates from 2400 to 3429, to
create 14.4, 28.8, and 33.6 kbit/s modems. This rate is near the theoretical Shannon limit.

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When calculated, the Shannon capacity of a narrowband line is Bandwidth * log2(1
+ Pu / Pn), with Pu / Pn the signal-to-noise ratio. Narrowband phone lines have a
bandwidth from 300-3100 Hz, so using Pu / Pn = 10,000: capacity is approximately
36 kbit/s.
Without the discovery and eventual application of trellis modulation, maximum
telephone rates would have been limited to 3429 baud * 4 bit/symbol == approximately
14 kilobits per second using traditional QAM.
Using digital lines and PCM (V.90/92)
In the late 1990s Rockwell and U.S. Robotics introduced new technology based upon the
digital transmission used in modern telephony networks. The standard digital
transmission in modern networks is 64 kbit/s but some networks use a part of the
bandwidth for remote office signaling (eg to hang up the phone), limiting the effective
rate to 56 kbit/s DS0. This new technology was adopted into ITU standards V.90 and is
common in modern computers. The 56 kbit/s rate is only possible from the central office
to the user site (downlink) and in the United States, government regulation limits the
maximum power output to only 53.3 kbit/s. The uplink (from the user to the central
office) still uses V.34 technology at 33.6k.
Later in V.92, the digital PCM technique was applied to increase the upload speed to a
maximum of 48 kbit/s, but at the expense of download rates. For example a 48 kbit/s
upstream rate would reduce the downstream as low as 40 kbit/s, due to echo on the
telephone line. To avoid this problem, V.92 modems offer the option to turn off the
digital upstream and instead use a 33.6 kbit/s analog connection, in order to maintain a
high digital downstream of 50 kbit/s or higher. (See November and October 2000 update
at http://www.modemsite.com/56k/v92s.asp ) V.92 also adds two other features. The first
is the ability for users who have call waiting to put their dial-up Internet connection on
hold for extended periods of time while they answer a call. The second feature is the
ability to "quick connect" to one's ISP. This is achieved by remembering the analog and
digital characteristics of the telephone line, and using this saved information to reconnect
at a fast pace.

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Using compression to exceed 56k
Today's V.42, V.42bis and V.44 standards allow the modem to transmit data faster than
its basic rate would imply. For instance, a 53.3 kbit/s connection with V.44 can transmit
up to 53.3*6 == 320 kbit/s using pure text. However, the compression ratio tends to vary
due to noise on the line, or due to the transfer of already-compressed files (ZIP files,
[2]
JPEG images, MP3 audio, MPEG video). At some points the modem will be sending
compressed files at approximately 50 kbit/s, uncompressed files at 160 kbit/s, and pure
text at 320 kbit/s, or any value in between. [3]
In such situations a small amount of memory in the modem, a buffer, is used to hold the
data while it is being compressed and sent across the phone line, but in order to prevent
overflow of the buffer, it sometimes becomes necessary to tell the computer to pause the
datastream. This is accomplished through hardware flow control using extra lines on the
modem–computer connection. The computer is then set to supply the modem at some
higher rate, such as 320 kbit/s, and the modem will tell the computer when to start or stop
sending data.
Compression by the ISP
As telephone-based 56k modems began losing popularity, some Internet Service
Providers such as Netzero and Juno started using pre-compression to increase the
throughput & maintain their customer base. As example, the Netscape ISP uses a
compression program that squeezes images, text, and other objects at the server, just prior
to sending them across the phone line. The server-side compression operates much more
efficiently than the "on-the-fly" compression of V.44-enabled modems. Typically website
text is compacted to 4% thus increasing effective throughput to approximately 1300
kbit/s. The accelerator also pre-compresses Flash executables and images to
approximately 30% and 12%, respectively.
The drawback of this approach is a loss in quality, where the graphics become heavily
compacted and smeared, but the speed is dramatically improved such that web pages load
in less than 5 seconds, and the user can manually choose to view the uncompressed
images at any time. The ISPs employing this approach advertise it as "DSL speeds over
regular phone lines" or simply "high speed dial-up".

30

FUNCTIONS
In addition to converting digital signals into analog signals, the modems carry out
many other tasks. Modems minimize the errors that occur while the transmission of
signals. They also have the functionality of compressing the data sent via signals.
Modems also do the task of regulating the information sent over a network.
• Error Correction: In this process the modem checks if the information they
receive is undamaged. The modems involved in error correction divide the
information into packets called frames. Before sending this information, the
modems tag each of the frames with checksums. Checksum is a method of
checking redundancy in the data present on the computer. The modems that
receive the information, verify if the information matches with checksums, sent
by the error-correcting modem. If it fails to match with the checksum, the
information is sent back.
• Compressing the Data: For compressing the data, it is sent together in many bits.
The bits are grouped together by the modem, in order to compress them.
• Flow Control: Different modems vary in their speed of sending signals. Thus, it
creates problems in receiving the signals if either one of the modems is slow. In
the flow control mechanism, the slower modem signals the faster one to pause, by
sending a 'character'. When it is ready to catch up with the faster modem, a
different character is sent, which in turn resumes the flow of signals.

WiFi and WiMax
Wireless data modems are used in the WiFi and WiMax standards, operating at
microwave frequencies.
WiFi is principally used in laptops for Internet connections (wireless access point) and
wireless application protocol (WAP).
Mobile modems and routers
Modems which use mobile phone lines (GPRS,UMTS,HSPA,EVDO,WiMax,etc.), are
known as Cellular Modems. Cellular modems can be embedded inside a laptop or
appliance, or they can be external to it. External cellular modems are datacards and

31

cellular routers. The datacard is a PC card or ExpressCard which slides into a
PCMCIA/PC card/ExpressCard slot on a computer. The most famous brand of cellular
modem datacards is the AirCard made by Sierra Wireless. (Many people just refer to all
makes and models as "AirCards", when in fact this is a trademarked brand name.)
Nowadays, there are USB cellular modems as well that use a USB port on the laptop
instead of a PC card or ExpressCard slot. A cellular router may or may not have an
external datacard ("AirCard") that slides into it. Most cellular routers do allow such
datacards or USB modems, except for the WAAV, Inc. CM3 mobile broadband cellular
router. Cellular Routers may not be modems per se, but they contain modems or allow
modems to be slid into them. The difference between a cellular router and a cellular
modem is that a cellular router normally allows multiple people to connect to it (since it
can "route"), while the modem is made for one connection.
Most of the GSM cellular modems come with an integrated SIM cardholder (i.e, Huawei
E220, Sierra 881, etc.) The CDMA (EVDO) versions do not use SIM cards, but use
Electronic Serial Number (ESN) instead.
The cost of using a cellular modem varies from country to country. Some carriers
implement "flat rate" plans for unlimited data transfers. Some have caps (or maximum
limits) on the amount of data that can be transferred per month. Other countries have "per
Megabyte" or even "per Kilobyte" plans that charge a fixed rate per Megabyte or
Kilobyte of data downloaded; this tends to add up quickly in today's content-filled world,
which is why many people are pushing for flat data rates. See : flat rate.
The faster data rates of the newest cellular modem technologies
(UMTS,HSPA,EVDO,WiMax) are also considered to be "Broadband Cellular Modems"
and compete with other Broadband modems below.

DATA RATE TRANSFER
The speed at which a modem can transfer information, usually given in bits per second
(bps). The higher the data transfer rate, the faster the modem, but the more it costs.
A faster modem can save you money by cutting down on your long-distance
charges. Three common speeds for modems are 9,600 bps, 14,400 bps, and 28,800
bps.

32

Modems are distinguished primarily by the maximum data rate they support. Data rates
can range from 75 bits per second up to 56000 and beyond. Data from the user (i.e.
flowing from the local terminal or computer via the modem to the telephone line) is
sometimes at a lower rate than the other direction, on the assumption that the user
cannot type more than a few characters per second.

Various data compression and error correction algorithms are required to support
the highest speeds. Other optional features are auto-dial (auto-call) and auto-answer
which allow the computer to initiate and accept calls without human intervention.
Most modern modems support a number of different protocols, and two modems,
when first connected, will automatically negotiate to find a common protocol (this
process may be audible through the modem or computer's loudspeakers). Some
modem protocols allow the two modems to renegotiate ("retrain") if the initial
choice of data rate is too high and gives too many transmission errors.

A modem may either be internal (connected to the computer's bus) or external
("stand-alone", connected to one of the computer's serial ports). The actual speed of
transmission in characters per second depends not just the modem-to-modem data
rate, but also on the speed with which the processor can transfer data to and from
the modem, the kind of compression used and whether the data is compressed by
the processor or the modem, the amount of noise on the telephone line (which
causes retransmissions), the serial character format (typically 8N1: one start bit,
eight data bits, no parity, one stop bit).

WIRELESS TRANSMISSION AND BANDWIDTH
The term "wireless" has become a generic and all-encompassing word used to describe
communications in which electromagnetic waves or RF (rather than some form of wire)
carry a signal over part or the entire communication path. Common examples of wireless
equipment in use today include:

33

• Professional LMR (Land Mobile Radio) and SMR (Specialized Mobile Radio)
typically used by business, industrial and Public Safety entities
• Consumer Two Way Radio including FRS (Family Radio Service), GMRS
(General Mobile Radio Service) and Citizens band ("CB") radios
• The Amateur Radio Service (Ham radio)
• Consumer and professional Marine VHF radios
• Cellular telephones and pagers: provide connectivity for portable and mobile
applications, both personal and business.
• Global Positioning System (GPS): allows drivers of cars and trucks, captains of
boats and ships, and pilots of aircraft to ascertain their location anywhere on
earth.
• Cordless computer peripherals: the cordless mouse is a common example;
keyboards and printers can also be linked to a computer via wireless.
• Cordless telephone sets: these are limited-range devices, not to be confused with
cell phones.
• Satellite television: allows viewers in almost any location to select from hundreds
of channels.
• Wireless gaming: new gaming consoles allow players to interact and play in the
same game regardless of whether they are playing on different consoles. Players
can chat, send text messages as well as record sound and send it to their friends.
Controllers also use wireless technology. They do not have any cords but they can
send the information from what is being pressed on the controller to the main
console which then processes this information and makes it happen in the game.
All of these steps are completed in milliseconds.
Wireless networking (i.e. the various types of unlicensed 2.4 GHz WiFi devices) is used
to meet many needs. Perhaps the most common use is to connect laptop users who travel
from location to location. Another common use is for mobile networks that connect via
satellite. A wireless transmission method is a logical choice to network a LAN segment
that must frequently change locations. The following situations justify the use of wireless
technology:
• To span a distance beyond the capabilities of typical cabling,

34

• To avoid obstacles such as physical structures, EMI, or RFI,
• To provide a backup communications link in case of normal network failure,
• To link portable or temporary workstations,
• To overcome situations where normal cabling is difficult or financially
impractical, or
• To remotely connect mobile users or networks.
Wireless communication can be via:
• radio frequency communication,
• microwave communication, for example long-range line-of-sight via highly
directional antennas, or short-range communication, or
• infrared (IR) short-range communication, for example from remote controls or via
IRDA.
Applications may involve point-to-point communication, point-to-multipoint
communication, broadcasting, cellular networks and other wireless networks.
The term "wireless" should not be confused with the term "cordless", which is generally
used to refer to powered electrical or electronic devices that are able to operate from a
portable power source (e.g. a battery pack) without any cable or cord to limit the mobility
of the cordless device through a connection to the mains power supply. Some cordless
devices, such as cordless telephones, are also wireless in the sense that information is
transferred from the cordless telephone to the telephone's base unit via some type of
wireless communications link. This has caused some disparity in the usage of the term
"cordless", for example in Digital Enhanced Cordless Telecommunications.
In the last fifty years, wireless communications industry experienced drastic changes
driven by many technology innovations.

Early wireless work
David E. Hughes, eight years before Hertz's experiments, induced electromagnetic waves
in a signaling system. Hughes transmitted Morse code by an induction apparatus. In
1878, Hughes's induction transmission method utilized a "clockwork transmitter" to
transmit signals. In 1885, T. A. Edison used a vibrator magnet for induction transmission.
In 1888, Edison deploys a system of signaling on the Lehigh Valley Railroad. In 1891,

35

Edison obtained the wireless patent for this method using inductance (U.S. Patent
465,971).
The demonstration of the theory of electromagnetic waves by Heinrich Rudolf Hertz in
1888 was important. The theory of electromagnetic waves were predicted from the
research of James Clerk Maxwell and Michael Faraday. Hertz demonstrated that
electromagnetic waves could be transmitted and caused to travel through space at straight
lines and that they were able to be received by an experimental apparatus. The
experiments were not followed up by Hertz. The practical applications of the wireless
communication and remote control technology were implemented by Nikola Tesla.
Bandwidth (Speed)
Wireless Network uses Transmitted signal rather then Wire (CAT5e/CAT6). There
are few parameters that are affecting Wireless Network communication that are not
an issue when using Wired Network. The two most important variables are Signal
Strength, Signal Stability.
Signal Strength is mainly depending on the Distance and the number and nature of
obstructions. Stability is affected by the presence of other signals in the air +
temporal changes in the environment. As an example Computer movement and
orientation, people movement, electrical appliances “kinking in and out”, and other
interferences are constantly changing and affecting the signal in a temporal manner.
The general results are that Wireless Bandwidth (Speed) and Latency becomes
“None Stop” changeable variables.
Wireless Bandwidth (or “Speed”) of Wireless depends on what standard in use
(802.11b. 802.11g, etc.) and how much of the signal is available for processing. The
smaller the signal the less bandwidth.

- VSAT

Short for very small aperture terminal, an earthbound station used in satellite
communications of data, voice and video signals, excluding broadcast television. A
VSAT consists of two parts, a transceiver that is placed outdoors in direct line of sight to
the satellite and a device that is placed indoors to interface the transceiver with the end
user's communications device, such as a PC. The transceiver receives or sends a signal to

36

a satellite transponder in the sky. The satellite sends and receives signals from a ground
station computer that acts as a hub for the system. Each end user is interconnected with
the hub station via the satellite, forming a star topology. The hub controls the entire
operation of the network. For one end user to communicate with another, each
transmission has to first go to the hub station that then retransmits it via the satellite to the
other end user's VSAT. VSAT can handle up to 56 Kbps.

- RADIO

Direct broadcast satellite, WiFi, and mobile phones all use modems to communicate, as
do most other wireless services today. Modern telecommunications and data networks
also make extensive use of radio modems where long distance data links are required.
Such systems are an important part of the PSTN, and are also in common use for high-
speed computer network links to outlying areas where fibre is not economical.
Even where a cable is installed, it is often possible to get better performance or make
other parts of the system simpler by using radio frequencies and modulation techniques
through a cable. Coaxial cable has a very large bandwidth, however signal attenuation
becomes a major problem at high data rates if a digital signal is used. By using a modem,
a much larger amount of digital data can be transmitted through a single piece of wire.
Digital cable television and cable Internet services use radio frequency modems to
provide the increasing bandwidth needs of modern households. Using a modem also
allows for frequency-division multiple access to be used, making full-duplex digital
communication with many users possible using a single wire.
Wireless modems come in a variety of types, bandwidths, and speeds. Wireless modems
are often referred to as transparent or smart. They transmit information that is modulated
onto a carrier frequency to allow many simultaneous wireless communication links to
work simultaneously on different frequencies.
Transparent modems operate in a manner similar to their phone line modem cousins.
Typically, they were half duplex, meaning that they could not send and receive data at the
same time. Typically transparent modems are polled in a round robin manner to collect
small amounts of data from scattered locations that do not have easy access to wired

37

infrastructure. Transparent modems are most commonly used by utility companies for
data collection.
Smart modems come with a media access controller inside which prevents random data
from colliding and resends data that is not correctly received. Smart modems typically
require more bandwidth than transparent modems, and typically achieve higher data
rates. The IEEE 802.11 standard defines a short range modulation scheme that is used on
a large scale throughout the world.

OBSTACLES TO EFFECTIVE TRANSMISSION
While a message source may be able to deliver a message through a transmission
medium, there are many potential obstacles to the message successfully reaching the
receiver the way the sender intends. The potential obstacles that may affect good
communication include:
• Poor Encoding – This occurs when the message source fails to create the right

sensory stimuli to meet the objectives of the message. For instance, in person-to-
person communication, verbally phrasing words poorly so the intended
communication is not what is actually meant, is the result of poor encoding. Poor
encoding is also seen in advertisements that are difficult for the intended audience
to understand, such as words or symbols that lack meaning or, worse, have totally
different meaning within a certain cultural groups. This often occurs when
marketers use the same advertising message across many different countries.
Differences due to translation or cultural understanding can result in the message
receiver having a different frame of reference for how to interpret words, symbols,
sounds, etc. This may lead the message receiver to decode the meaning of the
message in a different way than was intended by the message sender.
• Poor Decoding – This refers to a message receiver’s error in processing the

message so that the meaning given to the received message is not what the source
intended. This differs from poor encoding when it is clear, through comparative
analysis with other receivers, that a particular receiver perceived a message
differently from others and from what the message source intended. Clearly, as we
noted above, if the receiver’s frame of reference is different (e.g., meaning of

38

words are different) then decoding problems can occur. More likely, when it
comes to marketing promotions, decoding errors occur due to personal or
psychological factors, such as not paying attention to a full television
advertisement, driving too quickly past a billboard, or allowing one’s mind to
wonder while talking to a salesperson.
• Medium Failure – Sometimes communication channels break down and end up

sending out weak or faltering signals. Other times the wrong medium is used to
communicate the message. For instance, trying to educate doctors about a new
treatment for heart disease using television commercials that quickly flash highly
detailed information is not going to be as effective as presenting this information in
a print ad where doctors can take their time evaluating the information.
• Communication Noise – Noise in communication occurs when an outside force in

someway affects delivery of the message. The most obvious example is when loud
sounds block the receiver’s ability to hear a message. Nearly any distraction to the
sender or the receiver can lead to communication noise. In advertising, many
customers are overwhelmed (i.e., distracted) by the large number of advertisements
they encountered each day. Such advertising clutter (i.e., noise) makes it difficult
for advertisers to get their message through to desired customers.

STEPS REQUIRED TO CONNECT PC TO INTERNET
General Guidelines
Use a Firewall
The most important step when setting up a new computer is to install a firewall
BEFORE you connect it to the Internet. Whether this is a hardware router/firewall or a
software firewall it is important that you have immediate protection when you are
connecting to the Internet. This is because the minute you connect your computer to the
Internet there will be remote computers or worms scanning large blocks of IP addresses
looking for computers with security holes. When you connect your computer, if one of
these scans find you, it will be able to infect your computer as you do not have the latest
security updates. You may be thinking, what are the chances of my computer getting
scanned with all the millions of computers active on the Internet. The truth is that your

39

chances are extremely high as there are thousands, if not more, computers scanning at
any given time. The best scolution is if you have a hardware router/firewall installed..
This is because you will be behind that device immediately on turning on your computer
and there will be no lapse of time between your connecting to the Internet and being
secure. If a hardware based firewall is not available then you should use a software based
firewall. Many of the newer operating systems contain a built-in firewall that you should
immediately turn on. If your operating system does not contain a built-in firewall then
you should download and install a free firewall as there are many available. If you have a
friend or another computer with a cd rom burner, download the firewall and burn it onto a
CD so that you can install it before you even connect your computer to the Internet. We
have put together a tutorial on firewalls that you can read by clicking on the link below:
Disable services that you do not immediately need
Disable any non-essential services or applications that are running on your computer
before you connect to the Internet. When an operating system is not patched to the latest
security updates there are generally a few applications that have security holes in them.
By disabling services that you do not immediately need or plan to use you minimize the
risk of these security holes being used by a malicious user or piece of software.
Download the latest security updates
Now that you have a firewall and non-essential services disabled, it is time to connect
your computer to the Internet and download all the available security updates for your
operating system. By downloading these updates you will ensure that your computer is up
to date with all the latest available security patches released for your particular operating
system and therefore making it much more difficult for you to get infected with a piece of
malware.
Use an Antivirus Software
Many of the programs that will automatically attempt to infect your computer are worms,
trojans, and viruses. By using a good and up to date antivirus software you will be able to
catch these programs before they can do much harm. You can find a listing of some free
antivirus programs at the below link:

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Browse through the various free antivirus programs at the above list and install one
before you connect to the Internet. Download it from another computer and burn it onto a
CD so that it is installed before you connect.

Specific Steps for Windows 2000
Windows 2000 does not contain a full featured firewall, but does contain a way for you to
get limited security until you update the computer and install a true firewall. Windows
2000 comes with a feature called TCP filtering that we can use as a temporary measure.
To set this up follow these steps:
1. Click on Start, then Settings and then Control Panel to enter the control panel.
2. Double-click on the Network and Dial-up Connections control panel icon.
3. Right-click on the connection icon that is currently being used for Internet access
and click on properties. The connection icon is usually the one labeled Local
Area Connection
4. Double-click on Internet Protocol (TCP/IP) and then click on the Advanced
button.
5. Select the Options tab
6. Double-click on TCP/IP Filtering.
7. Put a checkmark in the box labeled Enable TCP/IP Filtering (All Adapters) and
change all the radio dial options to Permit Only.
8. Press the OK button.
9. If it asks to reboot, please do so.
After it reboots your computer will now be protected from the majority of attacks from
the Internet. Now immediately go to http://www.windowsupdate.com/ and download and
install all critical updates and service packs available for your operating system. Keep
going back and visiting this page until all the updates have been installed.
Once that is completed install an antivirus software and free firewall, and disable the
filtering we set up previously.

Specific Steps for Microsoft Windows XP

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If you have recently purchased a computer and it came with XP Service Pack 2 installed,
then the firewall will be enabled by default and you will not have to do anything but
install a antivirus software and check for any new updates at
http://www.windowsupdate.com/.
On the other hand, if this is an older computer, or you are re-installing one, then you
should follow these steps before you connect to the Internet:
1. Log into Windows XP with an administrator account.
2. Enable the Internet Connection Firewall by following the steps found in the
following tutorial link: Configuring Windows XP Internet Connection
Firewall
3. Once the firewall has been turned immediately go to www.windowsupdate.com
and download and install all critical updates and service packs available for your
operating system. Keep going back and visiting this page until all the updates
have been installed.
4. Once that is completed install an antivirus software and free firewall.
5. Disable the built in XP firewall.

Specific Steps for MAC OSX
Mac OSX has a built-in firewall that should be used before connecting to the Internet. To
turn this firewall on follow these steps:
1. Open up the System Preferences
2. Click on the Sharing icon
3. Click on the Firewall tab
4. Click on the Start button
5. Now the screen should show the status of the Firewall as On.
Now that the firewall is configured you should connect to the Internet and immediately
check for new updates from Apple by following these steps:
1. Choose System Preferences from the Apple Menu.
2. Choose Software Update from the View menu.
3. Click Update Now.

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4. Select the items you want to install, then click Install.
5. Enter an Admin user name and password.
6. After the update is complete, restart the computer if necessary
Now install an antivirus software on your computer if one is not already.

Specific Steps for Linux/UNIX
Almost all Linux distributions come with a built in firewall which is usually iptables.
Make sure that the firewall is starting automatically at boot up and is configured to deny
all traffic inbound to your computer except for the services you require like SSH.
Unfortunately iptables would require a tutorial all in its own, so I will refer you to this
already created tutorial:
Installing and Configuring iptables
Once the firewall is configured, go to the respective site for your Linux distribution and
immediately download and install any of the latest security updates that are available.
Windows is not the only operating system with security vulnerabilities and it is just as
important for Linux users to have an up to date operating system.

Conclusion
As you can see the most important step that should be done before connecting to the
Internet is to install a firewall and block all ports that you do not need open. This will
assure us that your computer will not become hacked by many of the worms and bots out
on the Internet. Once a firewall is installed, updating your computer and installing an
antivirus software are the next steps. Please follow these steps, as if it is not done, your
computer will ultimately get compromised and then further proliferate the infection of
others..

PROBLEMS OF TELECOMMUNICATION
Information technology is continually developing and in the last few years there has been
a rapid growth in electronic telecommunications to provide Internet and other
network-based services. Interest in using telecommunications to provide services to
the public is growing, with a number of pilot services being set up across the

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country to explore market potential and/or stimulate demand.Administrations
across Europe are now using telecommunications technology to provide citizens
with information (Hoare, 1998). The British Government, for instance, has issued a
directive that 25% of all civil service communications must be on-line by 2002.
This is intended to provide savings in paperwork and a streamlined service.An area
of possible government assistance is to provide the public with on-line information
about welfare benefit entitlement. This may have benefits for all members of
society but could be of particular value for retired and older members of the public,
many of whom do not always claim their entitlement. It is estimated in the UK, for
example, that one million pensioners could be entitled to Income Support that they
are not claiming (Benefits Agency, 1998). To provide information to the public, the
Benefits Agency produces a website of over 1,000 pages for customers to browse
through which can be viewed at http://www.dss.gov.uk/ba. Yet while many people
are now connected to the Internet, and the EU average is 25 computers connected
per thousand people, (Lennon, 1999) the number of older or retired people using it
is still quite small. An indication of this is given by the results of the worldwide
10th Georgia Tech web survey (GVU, 1999). The survey, conducted in 1998,
received 5,022 responses of which only 2.7% were from people who were 66 years
of age and over.This raises the key question of whether older people will be able to
benefit from the promise of the connected future, with information available
electronically on tap, or whether they will get left behind. This also represents a lost
opportunity for suppliers as, according to Oftel (the UK telephone watchdog
organisation) and disability campaign groups, A growing grey market containing
millions of potential customers is being ignored in the telecoms boom, Dawe
(1998).

Domain Name System
The Domain Name System (DNS) is a hierarchical naming system for computers,
services, or any resource connected to the Internet or a private network. It associates
various information with domain names assigned to each of the participants. Most
importantly, it translates domain names meaningful to humans into the numerical (binary)
identifiers associated with networking equipment for the purpose of locating and
addressing these devices worldwide. An often-used analogy to explain the Domain Name

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System is that it serves as the "phone book" for the Internet by translating human-friendly
computer hostnames into IP addresses. For example, www.example.com translates to
192.0.32.10.

The Domain Name System makes it possible to assign domain names to groups of
Internet users in a meaningful way, independent of each user's physical location. Because
of this, World Wide Web (WWW) hyperlinks and Internet contact information can
remain consistent and constant even if the current Internet routing arrangements change
or the participant uses a mobile device. Internet domain names are easier to remember
than IP addresses such as 208.77.188.166 (IPv4) or
2001:db8:1f70::999:de8:7648:6e8 (IPv6). People take advantage of this when they
recite meaningful URLs and e-mail addresses without having to know how the machine
will actually locate them.

The Domain Name System distributes the responsibility of assigning domain names and
mapping those names to IP addresses by designating authoritative name servers for each
domain. Authoritative name servers are assigned to be responsible for their particular
domains, and in turn can assign other authoritative name servers for their sub-domains.
This mechanism has made the DNS distributed, fault tolerant, and helped avoid the need
for a single central register to be continually consulted and updated.

In general, the Domain Name System also stores other types of information, such as the
list of mail servers that accept email for a given Internet domain. By providing a
worldwide, distributed keyword-based redirection service, the Domain Name System is
an essential component of the functionality of the Internet.

Other identifiers such as RFID tags, UPC codes, International characters in email
addresses and host names, and a variety of other identifiers could all potentially utilize
DNS.[1]

The Domain Name System also defines the technical underpinnings of the functionality
of this database service. For this purpose it defines the DNS protocol, a detailed
specification of the data structures and communication exchanges used in DNS, as part of
the Internet Protocol Suite (TCP/IP).

Overview
The Internet maintains two principal namespaces, the domain name hierarchy and the
Internet Protocol (IP) address system.[3] The Domain Name System maintains the domain
namespace and provides translation services between these two namespaces. Internet
name servers and a communications protocol, implement the Domain Name System. [4] A
DNS name server is a server that stores the DNS records, such as address (A) records,
name server (NS) records, and mail exchanger (MX) records for a domain name and
responds with answers to queries against its database.

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History
The practice of using a name as a humanly more meaningful abstraction of a host's
numerical address on the network dates back to the ARPANET era. Before the DNS was
invented in 1983, each computer on the network retrieved a file called HOSTS.TXT from
a computer at SRI (now SRI International).[5][6] The HOSTS.TXT file mapped names to
numerical addresses. A hosts file still exists on most modern operating systems, either by
default or through explicit configuration. Many operating systems use name resolution
logic that allows the administrator to configure selection priorities for available DNS
resolution methods.

The rapid growth of the network required a scalable system that recorded a change in a
host's address in one place only. Other hosts would learn about the change dynamically
through a notification system, thus completing a globally accessible network of all hosts'
names and their associated IP addresses.

At the request of Jon Postel, Paul Mockapetris invented the Domain Name System in
1983 and wrote the first implementation. The original specifications appeared in RFC
882 and RFC 883 which were superseded in November 1987 by RFC 1034[2] and RFC
1035.[4] Several additional Request for Comments have proposed various extensions to
the core DNS protocols.

In 1984, four Berkeley students—Douglas Terry, Mark Painter, David Riggle and
Songnian Zhou—wrote the first UNIX implementation, which was maintained by Ralph
Campbell thereafter. In 1985, Kevin Dunlap of DEC significantly re-wrote the DNS
implementation and renamed it BIND—Berkeley Internet Name Domain. Mike Karels,
Phil Almquist and Paul Vixie have maintained BIND since then. BIND was ported to the
Windows NT platform in the early 1990s.

BIND was widely distributed, especially on Unix systems, and is the dominant DNS
software in use on the Internet. [7] With the heavy use and resulting scrutiny of its open-
source code, as well as increasingly more sophisticated attack methods, many security
flaws were discovered in BIND. This contributed to the development of a number of
alternative nameserver and resolver programs. BIND itself was re-written from scratch in
version 9, which has a security record comparable to other modern Internet software.

The DNS protocol was developed and defined in the early 1980s and published by the
Internet Engineering Task Force.

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Structure
The domain name space

The hierarchical domain name system, organized into zones, each served by a name
server.

The domain name space consists of a tree of domain names. Each node or leaf in the tree
has zero or more resource records, which hold information associated with the domain
name. The tree sub-divides into zones beginning at the root zone. A DNS zone consists of
a collection of connected nodes authoritatively served by an authoritative nameserver.
(Note that a single nameserver can host several zones.)

Administrative responsibility over any zone may be divided, thereby creating additional
zones. Authority is said to be delegated for a portion of the old space, usually in form of
sub-domains, to another nameserver and administrative entity. The old zone ceases to be
authoritative for the new zone.

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Domain name formulation

The definitive descriptions of the rules for forming domain names appear in RFC 1035,
RFC 1123, and RFC 2181. A domain name consists of one or more parts, technically
called labels, that are conventionally concatenated, and delimited by dots, such as
example.com.

• The right-most label conveys the top-level domain; for example, the domain name
www.example.com belongs to the top-level domain com.
• The hierarchy of domains descends from right to left; each label to the left
specifies a subdivision, or subdomain of the domain to the right. For example: the
label example specifies a subdomain of the com domain, and www is a subdomain
of example.com. This tree of subdivisions may consist of 127 levels.
• Each label may contain up to 63 characters. The full domain name may not
exceed a total length of 253 characters.[8] In practice, some domain registries may
have shorter limits.
• DNS names may technically consist of any character representable in an octet
(RFC 3696). However, the allowed formulation of domain names in the DNS root
zone, and most other subdomains, uses a preferred format and character set. The
characters allowed in a label are a subset of the ASCII character set, and includes
the characters a through z, A through Z, digits 0 through 9, and the hyphen. This
rule is known as the LDH rule (letters, digits, hyphen). Domain names are
interpreted in case-independent manner. Labels may not start or end with a
hyphen, nor may two hyphens occur in sequence.
• A hostname is a domain name that has at least one IP address associated. For
example, the domain names www.example.com and example.com are also
hostnames, whereas the com domain is not.

Internationalized domain names
Main article: Internationalized domain name

The permitted character set of the DNS prevented the representation of names and words
of many languages in their native alphabets or scripts. ICANN has approved the
Punycode-based Internationalized domain name (IDNA) system, which maps Unicode
strings into the valid DNS character set. In 2009 ICANN approved the installation of IDN
country code top-level domains. In addition, many registries of the existing TLDs have
adopted IDNA.

Name servers

The Domain Name System is maintained by a distributed database system, which uses
the client-server model. The nodes of this database are the name servers. Each domain
has at least one authoritative DNS server that publishes information about that domain
and the name servers of any domains subordinate to it. The top of the hierarchy is served
by the root nameservers, the servers to query when looking up (resolving) a top-level
domain name (TLD).

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Authoritative name server

An authoritative name server is a name server that gives answers that have been
configured by an original source, for example, the domain administrator or by dynamic
DNS methods, in contrast to answers that were obtained via a regular DNS query to
another name server. An authoritative-only name server only returns answers to queries
about domain names that have been specifically configured by the administrator.

An authoritative name server can either be a master server or a slave server. A master
server is a server that stores the original (master) copies of all zone records. A slave
server uses an automatic updating mechanism of the DNS protocol in communication
with its master to maintain an identical copy of the master records.

Every DNS zone must be assigned a set of authoritative name servers that are installed in
NS records in the parent zone.

When domain names are registered with a domain name registrar their installation at the
domain registry of a top level domain requires the assignment of a primary name server
and at least one secondary name server. The requirement of multiple name servers aims
to make the domain still functional even if one name server becomes inaccessible or
inoperable.[9] The designation of a primary name server is solely determined by the
priority given to the domain name registrar. For this purpose generally only the fully
qualified domain name of the name server is required, unless the servers are contained in
the registered domain, in which case the corresponding IP address is needed as well.

Primary name servers are often master name servers, while secondary name server may
be implemented as slave servers.

An authoritative server indicates its status of supplying definitive answers, deemed
authoritative, by setting a software flag (a protocol structure bit), called the Authoritative
Answer (AA) bit in its responses.[4] This flag is usually reproduced prominently in the
output of DNS administration query tools (such as dig) to indicate that the responding
name server is an authority for the domain name in question.[4]

Recursive and caching name server

In principle, authoritative name servers are sufficient for the operation of the Internet.
However, with only authoritative name servers operating, every DNS query must start
with recursive queries at the root zone of the Domain Name System and each user system
must implement resolver software capable of recursive operation.

To improve efficiency, reduce DNS traffic across the Internet, and increase performance
in end-user applications, the Domain Name System supports DNS cache servers which
store DNS query results for a period of time determined in the configuration (time-to-
live) of the domain name record in question. Typically, such caching DNS servers, also
called DNS caches, also implement the recursive algorithm necessary to resolve a given

49

name starting with the DNS root through to the authoritative name servers of the queried
domain. With this function implemented in the name server, user applications gain
efficiency in design and operation.

The combination of DNS caching and recursive functions in a name server is not
mandatory, the functions can be implemented independently in servers for special
purposes.

Internet service providers typically provide recursive and caching name servers for their
customers. In addition, many home networking routers implement DNS caches and
recursors to improve efficiency in the local network.

DNS resolvers
See also: resolv.conf

The client-side of the DNS is called a DNS resolver. It is responsible for initiating and
sequencing the queries that ultimately lead to a full resolution (translation) of the
resource sought, e.g., translation of a domain name into an IP address.

A DNS query may be either a non-recursive query or a recursive query:

• A non-recursive query is one in which the DNS server provides a record for a
domain for which it is authoritative itself, or it provides a partial result without
querying other servers.
• A recursive query is one for which the DNS server will fully answer the query (or
give an error) by querying other name servers as needed. DNS servers are not
required to support recursive queries.

The resolver, or another DNS server acting recursively on behalf of the resolver,
negotiates use of recursive service using bits in the query headers.

Resolving usually entails iterating through several name servers to find the needed
information. However, some resolvers function simplistically and can communicate only
with a single name server. These simple resolvers (called "stub resolvers") rely on a
recursive name server to perform the work of finding information for them.

Operation
Address resolution mechanism

Domain name resolvers determine the appropriate domain name servers responsible for
the domain name in question by a sequence of queries starting with the right-most (top-
level) domain label.

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A DNS recursor consults three nameservers to resolve the address www.wikipedia.org.

The process entails:

1. A system that needs to use the DNS is configured with the known addresses of the
root servers. This is often stored in a file of root hints, which are updated
periodically by an administrator from a reliable source.
2. Query one of the root servers to find the server authoritative for the top-level
domain.
3. Query the obtained TLD DNS server for the address of a DNS server authoritative
for the second-level domain.
4. Repeating the previous step to process each domain name label in sequence, until
the final step which would, rather than generating the address of the next DNS
server, return the IP address of the host sought.

The diagram illustrates this process for the host www.wikipedia.org.

The mechanism in this simple form would place a large operating burden on the root
servers, with every search for an address starting by querying one of them. Being as
critical as they are to the overall function of the system, such heavy use would create an
insurmountable bottleneck for trillions of queries placed every day. In practice caching is
used in DNS servers to overcome this problem, and as a result, root nameservers actually
are involved with very little of the total traffic.

Circular dependencies and glue records

Name servers in delegations appear listed by name, rather than by IP address. This means
that a resolving name server must issue another DNS request to find out the IP address of
the server to which it has been referred. Since this can introduce a circular dependency if
the nameserver referred to is under the domain for which it is authoritative, it is
occasionally necessary for the nameserver providing the delegation to also provide the IP
address of the next nameserver. This record is called a glue record.

For example, assume that the sub-domain en.wikipedia.org contains further sub-domains
(such as something.en.wikipedia.org) and that the authoritative name server for these
lives at ns1.something.en.wikipedia.org. A computer trying to resolve

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something.en.wikipedia.org will thus first have to resolve
ns1.something.en.wikipedia.org. Since ns1 is also under the
something.en.wikipedia.org subdomain, resolving
ns1.something.en.wikipedia.org requires resolving something.en.wikipedia.org
which is exactly the circular dependency mentioned above. The dependency is broken by
the glue record in the nameserver of en.wikipedia.org that provides the IP address of
ns1.something.en.wikipedia.org directly to the requestor, enabling it to bootstrap the
process by figuring out where ns1.something.en.wikipedia.org is located.

Record caching

Because of the large volume of requests generated in the DNS for the public Internet, the
designers wished to provide a mechanism to reduce the load on individual DNS servers.
To this end, the DNS resolution process allows for caching of records for a period of time
after an answer. This entails the local recording and subsequent consultation of the copy
instead of initiating a new request upstream. The time for which a resolver caches a DNS
response is determined by a value called the time to live (TTL) associated with every
record. The TTL is set by the administrator of the DNS server handing out the
authoritative response. The period of validity may vary from just seconds to days or even
weeks.

As a noteworthy consequence of this distributed and caching architecture, changes to
DNS records do not propagate throughout the network immediately, but require all
caches to expire and refresh after the TTL. RFC 1912 conveys basic rules for determining
appropriate TTL values.

Some resolvers may override TTL values, as the protocol supports caching for up to 68
years or no caching at all. Negative caching, i.e. the caching of the fact of non-existence
of a record, is determined by name servers authoritative for a zone which must include
the Start of Authority (SOA) record when reporting no data of the requested type exists.
The value of the MINIMUM field of the SOA record and the TTL of the SOA itself is
used to establish the TTL for the negative answer.

Reverse lookup

The term reverse lookup refers to performing a DNS query to find one or more DNS
names associated with a given IP address.

The DNS stores IP addresses in form of specially formatted names as pointer ( PTR)
records using special domains. For IPv4, the domain is in-addr.arpa. For IPv6, the
reverse lookup domain is ip6.arpa. The IP address is represented as a name in reverse-
ordered octet representation for IPv4, and reverse-ordered nibble representation for IPv6.

When performing a reverse lookup, the DNS client converts the address into these
formats, and then queries the name for a PTR record following the delegation chain as for
any DNS query. For example, the IPv4 address 208.80.152.2 is represented as a DNS

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name as 2.152.80.208.in-addr.arpa. The DNS resolver begins by querying the root
servers, which point to ARIN's servers for the 208.in-addr.arpa zone. From there the
Wikimedia servers are assigned for 152.80.208.in-addr.arpa, and the PTR lookup
completes by querying the wikimedia nameserver for 2.152.80.208.in-addr.arpa,
which results in an authoritative response.

Client lookup

DNS resolution sequence.

Users generally do not communicate directly with a DNS resolver. Instead DNS
resolution takes place transparently in applications programs such as web browsers, e-
mail clients, and other Internet applications. When an application makes a request that
requires a domain name lookup, such programs send a resolution request to the DNS
resolver in the local operating system, which in turn handles the communications
required.

The DNS resolver will almost invariably have a cache (see above) containing recent
lookups. If the cache can provide the answer to the request, the resolver will return the
value in the cache to the program that made the request. If the cache does not contain the
answer, the resolver will send the request to one or more designated DNS servers. In the
case of most home users, the Internet service provider to which the machine connects will
usually supply this DNS server: such a user will either have configured that server's
address manually or allowed DHCP to set it; however, where systems administrators
have configured systems to use their own DNS servers, their DNS resolvers point to
separately maintained nameservers of the organization. In any event, the name server thus
queried will follow the process outlined above, until it either successfully finds a result or
does not. It then returns its results to the DNS resolver; assuming it has found a result, the
resolver duly caches that result for future use, and hands the result back to the software
which initiated the request.

Broken resolvers

An additional level of complexity emerges when resolvers violate the rules of the DNS
protocol. A number of large ISPs have configured their DNS servers to violate rules

53

(presumably to allow them to run on less-expensive hardware than a fully compliant
resolver), such as by disobeying TTLs, or by indicating that a domain name does not
exist just because one of its name servers does not respond.[10]

As a final level of complexity, some applications (such as web-browsers) also have their
own DNS cache, in order to reduce the use of the DNS resolver library itself. This
practice can add extra difficulty when debugging DNS issues, as it obscures the freshness
of data, and/or what data comes from which cache. These caches typically use very short
caching times — on the order of one minute. Internet Explorer offers a notable exception:
recent versions cache DNS records for half an hour.[11]

Other applications

The system outlined above provides a somewhat simplified scenario. The Domain Name
System includes several other functions:

• Hostnames and IP addresses do not necessarily match on a one-to-one basis.
Many hostnames may correspond to a single IP address: combined with virtual
hosting, this allows a single machine to serve many web sites. Alternatively a
single hostname may correspond to many IP addresses: this can facilitate fault
tolerance and load distribution, and also allows a site to move physical location
seamlessly.
• There are many uses of DNS besides translating names to IP addresses. For
instance, Mail transfer agents use DNS to find out where to deliver e-mail for a
particular address. The domain to mail exchanger mapping provided by MX
records accommodates another layer of fault tolerance and load distribution on
top of the name to IP address mapping.

• E-mail Blacklists: The DNS system is used for efficient storage and distribution
of IP addresses of blacklisted e-mail hosts. The usual method is putting the IP
address of the subject host into the sub-domain of a higher level domain name,
and resolve that name to different records to indicate a positive or a negative. A
hypothetical example using blacklist.com,
o 102.3.4.5 is blacklisted => Creates 5.4.3.102.blacklist.com and resolves to
127.0.0.1
o 102.3.4.6 is not => 6.4.3.102.blacklist.com is not found, or default to
127.0.0.2
o E-mail servers can then query blacklist.com through the DNS mechanism
to find out if a specific host connecting to them is in the blacklist. Today
many of such blacklists, either free or subscription-based, are available
mainly for use by email administrators and anti-spam software.

• Software Updates: many anti-virus and commercial software now use the DNS
system to store version numbers of the latest software updates so client computers
do not need to connect to the update servers every time. For these types of
applications, the cache time of the DNS records are usually shorter.

54

• Sender Policy Framework and DomainKeys, instead of creating their own record
types, were designed to take advantage of another DNS record type, the TXT
record.
• To provide resilience in the event of computer failure, multiple DNS servers are
usually provided for coverage of each domain, and at the top level, thirteen very
powerful root servers exist, with additional "copies" of several of them distributed
worldwide via Anycast.
• Dynamic DNS (also referred to as DDNS) provides clients the ability to update
their IP address in the DNS after it changes due to mobility, e.g.

Protocol details
DNS primarily uses User Datagram Protocol (UDP) on port number 53[12] to serve
requests. DNS queries consist of a single UDP request from the client followed by a
single UDP reply from the server. The Transmission Control Protocol (TCP) is used
when the response data size exceeds 512 bytes, or for tasks such as zone transfers. Some
operating systems, such as HP-UX, are known to have resolver implementations that use
TCP for all queries, even when UDP would suffice.

DNS resource records
Further information: List of DNS record types

A Resource Record (RR) is the basic data element in the domain name system. Each
record has a type (A, MX, etc.), an expiration time limit, a class, and some type-specific
data. Resource records of the same type define a resource record set. The order of
resource records in a set, returned by a resolver to an application, is undefined, but often
servers implement round-robin ordering to achieve load balancing. DNSSEC, however,
works on complete resource record sets in a canonical order.

When sent over an IP network, all records use the common format specified in RFC 1035
and shown below.

RR (Resource record) fields

Field Description Length

55

(octets)

NAME Name of the node to which this record pertains. (variable)

TYPE Type of RR. For example, MX is type 15. 2

CLASS Class code. 2

Unsigned time in seconds that RR stays valid, maximum is
TTL 4
2147483647.

RDLENGTH Length of RDATA field. 2

RDATA Additional RR-specific data. (variable)

NAME is the fully qualified domain name of the node in the tree. On the wire, the name
may be shortened using label compression where ends of domain names mentioned
earlier in the packet can be substituted for the end of the current domain name.

TYPE is the record type. It indicates the format of the data and it gives a hint of its
intended use. For example, the A record is used to translate from a domain name to an
IPv4 address, the NS record lists which name servers can answer lookups on a DNS zone,
and the MX record specifies the mail server used to handle mail for a domain specified in
an e-mail address (see also List of DNS record types).

RDATA is data of type-specific relevance, such as the IP address for address records, or
the priority and hostname for MX records. Well known record types may use label
compression in the RDATA field, but "unknown" record types must not (RFC 3597).

The CLASS of a record is set to IN (for Internet) for common DNS records involving
Internet hostnames, servers, or IP addresses. In addition, the classes CH (Chaos) and HS
(Hesiod) exist. Each class is a completely independent tree with potentially different
delegations of DNS zones.

In addition to resource records defined in a zone file, the domain name system also
defines several request types that are used only in communication with other DNS nodes

56

(on the wire), such as when performing zone transfers (AXFR/IXFR) or for EDNS
(OPT).

Wildcard DNS records
Main article: Wildcard DNS record

The domain name system supports wildcard domain names which are names that start
with the asterisk label, '*', e.g., *.example.[2][13] DNS records belonging to wildcard
domain names specify rules for generating resource records within a single DNS zone by
substituting whole labels with matching components of the query name, including any
specified descendants. For example, in the DNS zone x.example, the following
configuration specifies that all subdomains (including subdomains of subdomains) of
x.example use the mail exchanger a.x.example. The records for a.x.example are needed to
specify the mail exchanger. As this has the result of excluding this domain name and its
subdomains from the wildcard matches, all subdomains of a.x.example must be defined
in a separate wildcard statement.

X.EXAMPLE. MX 10 A.X.EXAMPLE.
*.X.EXAMPLE. MX 10 A.X.EXAMPLE.
*.A.X.EXAMPLE. MX 10 A.X.EXAMPLE.
A.X.EXAMPLE. MX 10 A.X.EXAMPLE.
A.X.EXAMPLE. AAAA 2001:db8::1

The role of wildcard records was refined in RFC 4592, because the original definition in
RFC 1034 was incomplete and resulted in misinterpretations by implementers.[13]

Protocol extensions
The original DNS protocol had limited provisions for extension with new features. In
1999, Paul Vixie published in RFC 2671 an extension mechanism, called Extension
mechanisms for DNS (EDNS) that introduced optional protocol elements without
increasing overhead when not in use. This was accomplished through the OPT pseudo-
resource record that only exists in wire transmissions of the protocol, but not in any zone
files. Initial extensions were also suggested (EDNS0), such as increasing the DNS
message size in UDP datagrams.

Dynamic zone updates
Dynamic DNS updates use the UPDATE DNS opcode to add or remove resource records
dynamically from a zone data base maintained on an authoritative DNS server. The
feature is described in RFC 2136. This facility is useful to register network clients into
the DNS when they boot or become otherwise available on the network. Since a booting
client may be assigned a different IP address each time from a DHCP server, it is not
possible to provide static DNS assignments for such clients.

57

Security issues
DNS was not originally designed with security in mind, and thus has a number of security
issues.

One class of vulnerabilities is DNS cache poisoning, which tricks a DNS server into
believing it has received authentic information when, in reality, it has not.

DNS responses are traditionally not cryptographically signed, leading to many attack
possibilities; The Domain Name System Security Extensions (DNSSEC) modifies DNS
to add support for cryptographically signed responses. There are various extensions to
support securing zone transfer information as well.

Even with encryption, a DNS server could become compromised by a virus (or for that
matter a disgruntled employee) that would cause IP addresses of that server to be
redirected to a malicious address with a long TTL. This could have far-reaching impact to
potentially millions of Internet users if busy DNS servers cache the bad IP data. This
would require manual purging of all affected DNS caches as required by the long TTL
(up to 68 years).

Some domain names can spoof other, similar-looking domain names. For example,
"paypal.com" and "paypa1.com" are different names, yet users may be unable to tell the
difference when the user's typeface (font) does not clearly differentiate the letter l and the
numeral 1. This problem is much more serious in systems that support internationalized
domain names, since many characters that are different, from the point of view of ISO
10646, appear identical on typical computer screens. This vulnerability is often exploited
in phishing.

Techniques such as Forward Confirmed reverse DNS can also be used to help validate
DNS results.

Domain name registration
The right to use a domain name is delegated by domain name registrars which are
accredited by the Internet Corporation for Assigned Names and Numbers (ICANN), the
organization charged with overseeing the name and number systems of the Internet. In
addition to ICANN, each top-level domain (TLD) is maintained and serviced technically
by an administrative organization, operating a registry. A registry is responsible for
maintaining the database of names registered within the TLD it administers. The registry
receives registration information from each domain name registrar authorized to assign
names in the corresponding TLD and publishes the information using a special service,
the whois protocol.

ICANN publishes the complete list of TLD registries and domain name registrars.
Registrant information associated with domain names is maintained in an online database

58

accessible with the WHOIS service. For most of the more than 240 country code top-
level domains (ccTLDs), the domain registries maintain the WHOIS (Registrant, name
servers, expiration dates, etc.) information. For instance, DENIC, Germany NIC, holds
the DE domain data. Since about 2001, most gTLD registries have adopted this so-called
thick registry approach, i.e. keeping the WHOIS data in central registries instead of
registrar databases.

For COM and NET domain names, a thin registry model is used: the domain registry (e.g.
VeriSign) holds basic WHOIS (registrar and name servers, etc.) data. One can find the
detailed WHOIS (registrant, name servers, expiry dates, etc.) at the registrars.

Some domain name registries, often called network information centers (NIC), also
function as registrars to end-users. The major generic top-level domain registries, such as
for the COM, NET, ORG, INFO domains and others, use a registry-registrar model consisting
of hundreds of domain name registrars (see lists at ICANN or VeriSign). In this method
of management, the registry only manages the domain name database and the relationship
with the registrars. The registrants (users of a domain name) are customers of the
registrar, in some cases through additional layers of resellers.

ISP (Internet Service Provider)
Stands for "Internet Service Provider." In order to connect to the Internet, you need an
ISP. It is the company that you (or your parents) pay a monthly fee to in order to
use the Internet. If you use a dial-up modem to connect to your ISP, a point-to-
point protocol (PPP) connection is established with another modem on the ISP's
end. That modem connects to one of the ISP's routers, which routes you to the
Internet "backbone." From there, you can access information from anywhere
around the world. DSL and cable modems work the same way, except after you
connect the first time, you are always connected.

ICT SPECIALISED TRAINING – WEB-TECH
SEARCH ENGINE
A web search engine is designed to search for information on the World Wide Web. The
search results are generally presented in a line of results often referred to as search
engine results pages (SERPs). The information may be a specialist in web pages, images,
information and other types of files. Some search engines also mine data available in
databases or open directories. Unlike web directories, which are maintained only by
human editors, search engines also maintain real-time information by running an
algorithm on a web crawler.

59

A search engine operates in the following order:
1. Web crawling
2. Indexing
3. Searching
Web search engines work by storing information about many web pages, which they
retrieve from the HTML itself. These pages are retrieved by a Web crawler (sometimes
also known as a spider) — an automated Web browser which follows every link on the
site. Exclusions can be made by the use of robots.txt. The contents of each page are
then analyzed to determine how it should be indexed (for example, words can be
extracted from the titles, page content, headings, or special fields called meta tags).
Data about web pages are stored in an index database for use in later queries. A query
can be a single word. The purpose of an index is to allow information to be found as
quickly as possible. Some search engines, such as Google, store all or part of the source
page (referred to as a cache) as well as information about the web pages, whereas
others, such as AltaVista, store every word of every page they find. This cached page
always holds the actual search text since it is the one that was actually indexed, so it can
be very useful when the content of the current page has been updated and the search
terms are no longer in it. This problem might be considered to be a mild form of linkrot,
and Google's handling of it increases usability by satisfying user expectations that the
search terms will be on the returned webpage. This satisfies the principle of least
astonishment since the user normally expects the search terms to be on the returned
pages. Increased search relevance makes these cached pages very useful, even beyond
the fact that they may contain data that may no longer be available elsewhere.

60

High-level architecture of a standard Web crawler
When a user enters a query into a search engine (typically by using keywords), the
engine examines its index and provides a listing of best-matching web pages according
to its criteria, usually with a short summary containing the document's title and
sometimes parts of the text. The index is built from the information stored with the data
and the method by which the information is indexed. As early as 2007 the Google.com
search engine has allowed one to search by date by clicking 'Show search tools' in the
leftmost column of the initial search results page, and then selecting the desired date
range. Most search engines support the use of the boolean operators AND, OR and NOT
to further specify the search query. Boolean operators are for literal searches that allow
the user to refine and extend the terms of the search. The engine looks for the words or
phrases exactly as entered. Some search engines provide an advanced feature called
proximity search which allows users to define the distance between keywords. There is
also concept-based searching where the research involves using statistical analysis on
pages containing the words or phrases you search for. As well, natural language queries
allow the user to type a question in the same form one would ask it to a human. A site
like this would be ask.com.
The usefulness of a search engine depends on the relevance of the result set it gives
back. While there may be millions of web pages that include a particular word or phrase,
some pages may be more relevant, popular, or authoritative than others. Most search
engines employ methods to rank the results to provide the "best" results first. How a
search engine decides which pages are the best matches, and what order the results
should be shown in, varies widely from one engine to another. The methods also change
over time as Internet usage changes and new techniques evolve. There are two main
types of search engine that have evolved: one is a system of predefined and
hierarchically ordered keywords that humans have programmed extensively. The other
is a system that generates an "inverted index" by analyzing texts it locates. This first
form relies much more heavily on the computer itself to do the bulk of the work.

61

Most Web search engines are commercial ventures supported by advertising revenue
and, as a result, some employ ,the practice of allowing advertisers to pay money to have
their listings ranked higher in search results. Those search engines which do not accept
money for their search engine results make money by running search related ads
alongside the regular search engine results. The search engines make money every time
someone clicks on one of these ads.

References
1. ^ "Core Characteristics of Web 2.0 Services". http://www.techpluto.com/web-20-
services/.
2. ^ DiNucci, D. (1999). "Fragmented Future". Print 53 (4): 32.
a b c
3. ^ Paul Graham (November 2005). "Web 2.0".
http://www.paulgraham.com/web20.html. Retrieved on 2006-08-02. ""I first
heard the phrase 'Web 2.0' in the name of the Web 2.0 conference in 2004.""
4. ^ a b c d e f Tim O'Reilly (2005-09-30). "What Is Web 2.0". O'Reilly Network.
http://www.oreillynet.com/pub/a/oreilly/tim/news/2005/09/30/what-is-web-
20.html. Retrieved on 2006-08-06.
5. ^ Tim O'Reilly (2006-12-10). "Web 2.0 Compact Definition: Trying Again".
http://radar.oreilly.com/archives/2006/12/web_20_compact.html. Retrieved on
2007-01-20.
6. ^ a b c "developerWorks Interviews: Tim Berners-Lee". 2006-07-28.
http://www.ibm.com/developerworks/podcast/dwi/cm-int082206txt.html.
Retrieved on 2007-02-07.

7. Lehr, W., Osorio, C., Gillett, S., and Sirbu, M, (2005) “Measuring Broadband’s
Economic Impact”, paper presented at the 33rd Research Conference on
Communication, Information, and Internet Policy (TPRC), Arlington, VA, and
revised as of October 4, 2005.
http://itc.mit.edu/itel/docs/2005/MeasuringBB_EconImpact.pdf

8. James, P. and Hopkinson, P., “SUSTAINABLE BROADBAND? -The
Economic, Environmental and Social Impacts of Cornwall’s actnow Project, May
2005.http://www.sustainit.org/publications/files/87-EnvironmentalStudy-
finalfullreport.doc

9. Zilber, J., Schneider, D., and Djwa, P. “ You Snooze, You Lose: The Economic
Impact of Broadband in the Peace River and South Similkameen Regions,
September 2005. http://www.7thfloormedia.com/broadbandimpact

62

10. http://en.wikipedia.org/wiki/Domain_Name_System

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