PDCA - 05

VARDHAMAN MAHAVEER OPEN UNIVERSITY, KOTA

Post Graduate Diploma in Computer Application

(PGDCA)

Computer Networking and Internet

Course Development Committee

Chaiman
Prof. (Dr.) Naresh Dadhich
Vice-Chancellor
Vardhaman Mahaveer Open University Kota
Convener / Coordinator Members
Prof. (Dr.) D.S. Chauhan 1. Prof. (Dr.) S.C. Jain
Department of Mathematics Engineering College Ajmer
University of Rajasthan Jaipur
2. Prof. (Dr.) M.C. Govil
Member Secretary / Coordinator M.N.I.T. Jaipur
Sh. Rakesh Sharma
Assistant Professor (Computer Application) 3. Dr. (Mrs.) Madhavi Sinha
V.M. Open University Kota A.I.M. & A.C.T. Jaipur
Editing and Course Writing
Editor
Sh. Rajeev Srivastava
HOD (Computer Science)
LBS PG College Jaipur

Writers
1. Dr. S.B. Sharma 4. Ms. Poonam Kshatriya
Director, Dau Dayal Vocational Institute Sr. Lecturer (Computer
Science)
Dr. B.R. Ambedkar University Agra A.I.M. & A.C.T. Jaipur

2. Dr. D.K. Paliwal 5. Ms. Shweta Sharma

Lecturer (Institute of Basic Sciences) Lecturer (Computer

Engineering)
Dr. B.R. Ambedkar University Agra Modi Institute of Technology
Kota
3. Sh. Manoj Kumar
Asstt. Professor (Computer Engineering)
Rajasthan Technical University Kota

Course Supervision and Production

Director (Academic) Director (Material Production &
Distribution)
Prof. (Dr.) Anam Jaitly Prof. (Dr.) P.K. Sharma
Vardhaman Mahaveer Open University, Vardhaman Mahaveer Open
Kota University, Kota

Production July 2007

All rights reserved. No, part of this book may be reproduced in any form by mimeograph or any
other means, without permission in writing from the V.M. Open University, Kota.
Printed and published on behalf of V.M. Open University, Kota by Director (Academic).
 Index
Unit Number Unit Name Page Number

UNIT - I COMPUTER NETWORK FUNDAMENTALS 1 - 22

UNIT II COMPUTER NETWORK CONTD. 23-40

UNIT- III COMPUTER NETWORK CONTD. 41 - 65

UNIT - IV INTERNET 66 - 75

UNIT - V INTERNET FEATURES 76 - 101

UNIT - VI INTERNET CONNECTIVITY 102 - 137

UNIT - VII WORLD WIDE WEB 138 - 156

UNIT - VIII APPLICATION OF INTERNET 157 - 164

UNIT - IX E-COMMERCE 165 - 179

UNIT - X CREATING AND MAINTAINING WEB SITES 180 - 194

UNIT - XI FORMATTING FEATURES 195 - 204

UNIT - XII WEBSITE FEATURES 205 - 216

UNIT - XIII JAVASCRIPT 217 - 234

UNIT - XIV ACTIVE SERVER PAGES (ASP) 235 - 249

UNIT - XV ACTIVE SERVER PAGES (ASP) CONTD. 250 - 267

UNIT - I COMPUTER NETWORK FUNDAMENTALS 1

UNIT - I
COMPUTER NETWORK FUNDAMENTALS
STRUCTURE OF THE UNIT
1.0 Objective
1.1 Introduction
1.2 Definitions
1.3 Applications
1.4 Transmission media
1.4.1 Magnetic Media
1.4.2 Twisted pair
1.4.3 Co-axial cable
1.4.4 Fiber Optics
1.5 Networking essentials
1.5.1 Repeaters
1.5.2 Hubs
1.5.3 Switches
1.5.4 Routers
1.5.5 Gateways
1.5.6 NIC
1.6 Summary
1.7 Glossary
1.8 Further Readings
1.9 Answers to the self learning exercises
1.10 Unit end questions
1.0 OBJECTIVE:
Students who complete this unit should be able to understand the following tasks:
w Evolution of Networking
w Various types of transmission media
w Various types of inter-network connecting devices
1.1 INTRODUCTION
Data networks developed as a result of business applications that were written for
microcomputers. The microcomputers were not connected so there was no efficient way to
share data among them. It was not efficient or cost-effective for businesses to use floppy
disks to share data known as Sneaker net. Sneaker net created multiple copies of the data.
Each time a file was modified it would have to be shared again with all other people who
needed that file. If two people modified the file and then tried to share it, one of the sets of
changes would be lost. Businesses needed a solution that would successfully address the
following three problems:
UNIT - I COMPUTER NETWORK FUNDAMENTALS 2

w How to avoid duplication of equipment and resources

w How to communicate efficiently
w How to set up and manage a network
Businesses realized that computer networking could increase productivity and save money.
Networks were added and expanded almost as rapidly as new network technologies and
products were introduced. The early development of networking was disorganized. However,
a tremendous expansion occurred in the early 1980s.
1.2 DEFINITIONS
LAN (Local Area Network)
A high-speed, low-error data network covering a relatively small geographic area, up to a
few thousand meters. LANs connect workstations, peripherals, terminals, and other devices
in a single building or other geographically limited area. LANs allow businesses to locally
share computer files and printers efficiently and make internal communications possible.
LANs manage data, local communications, and computing equipment. LAN standards
specify cabling and signaling at the physical and data link layers of the OSI model. Ethernet,
FDDI, and Token Ring are widely used LAN technologies.
LANs consist of the following components:
w Computers
w Network interface cards
w Peripheral devices
w Networking media
w Network devices
MAN (Metropolitan Area Network)
A MAN usually consists of two or more LANs in a common geographic area. A network
that spans a metropolitan area. Generally, a MAN spans a larger geographic area than a
LAN, but a smaller geographic area than a WAN. For example, a bank with multiple branches
may utilize a MAN. Typically, a service provider is used to connect two or more LAN sites
using private communication lines or optical services. A MAN can also be created using
wireless bridge technology by beaming signals across public areas. Wireless bridge
technologies that send signals across public areas can also be used to create a MAN.
WAN (Wide Area Network)
A WAN is a data communications network that serves users across a broad geographic area
and often uses transmission devices provided by common carriers. Frame Relay, SMDS,
and X.25 are examples of WANs. WANs interconnect LANs, which then provide access to
computers or file servers in other locations. Because WANs connect user networks over a
large geographical area, they make it possible for businesses to communicate across great
distances. WANs allow computers, printers, and other devices on a LAN to be shared with
distant locations. WANs provide instant communications across large geographic areas.
Collaboration software provides access to real-time information and resources and
allows meetings to be held remotely. WANs have created a new class of workers called
telecommuters. These people never have to leave their homes to go to work.
WANs are designed to do the following:
w Operate over a large and geographically separated area
UNIT - I COMPUTER NETWORK FUNDAMENTALS 3

w Allow users to have real-time communication capabilities with other users

w Provide full-time remote resources connected to local services
w Provide e-mail, Internet, file transfer, and e-commerce services
Some common WAN technologies include the following:
w Integrated Services Digital Network (ISDN)
w Digital subscriber line (DSL)
w Frame Relay
w T1, E1, T3, and E3
w Synchronous Optical Network (SONET)
The Internet and Beyond
More than just a technology, the Internet has become a way of life for many people, and it
has spurred a revolution of sorts for both public and private sharing of information. The
most popular source of information about almost anything, the Internet is used daily by
technical and non-technical users alike.
The Internet: The Largest Network of All
With the meteoric rise in demand for connectivity, the Internet has become a major
communications highway for millions of users. It is a decentralized system of linked
networks that are worldwide in scope. It facilitates data communication services such as
remote log-in, file transfer, electronic mail, the World Wide Web and newsgroups. It consists
of independent hosts of computers that can designate which Internet services to use and
which of their local services to make available to the global community.
Initially restricted to military and academic institutions, the Internet now operates on a
three-level hierarchy composed of backbone networks, mid-level networks and stub
networks. It is a full-fledged conduit for any and all forms of information and commerce.
Internet websites now provide personal, educational, political and economic resources to
virtually any point on the planet.
Intranet: A Secure Internet-like Network for Organizations
With advancements in browser-based software for the Internet, many private organizations
have implemented intranets. An intranet is a private network utilizing Internet-type tools,
but available only within that organization. For large organizations, an intranet provides
easy access to corporate information for designated employees.
Extranet: A Secure Means for Sharing Information with Partners
While an intranet is used to disseminate confidential information within a corporation, an
extranet is commonly used by companies to share data in a secure fashion with their business
partners. Internet-type tools are used by content providers to update the extranet. Encryption
and user authentication means are provided to protect the information, and to ensure that
designated people with the proper access privileges are allowed to view it.
Self learning Exercises :
1. The performance of a data communication network depends on:
(a) the number of users (b) the transmission media
(c) the hardware and software (d) all of the above
UNIT - I COMPUTER NETWORK FUNDAMENTALS 4

2. The information to be communicated in a data communication system is the:

(a) medium (b) protocol
(c) message (d) transmission
3. The world’s largest network that provides communication to people around the
world:
(a) LAN (b) Intranet
(c) Internet (d) WAN
1.3 APPLICATIONS
Computer Networking has become more and more a part of our daily lives. The exchange
of information and sharing of devices in this digital world can only be accomplished by
networking. It has evolved from being something only useful to businesses, to being a
necessity to home users. Computer networking has expanded it uses in many positive
ways and continues to do so.
Interactive Multimedia Networking
Applications that require real-time interaction among their users are gaining importance
and diffusion as computer networks become more powerful and ubiquitous. Many such
applications impose very stringent requirements on the network; among the applications
today widely deployed, video-conferencing is the most demanding. In order for the
participants in a videoconference call to interact naturally, the end-to-end delay should be
below human perception; even though an objective and unique figure cannot be set, 100
ms is widely recognized as the desired one way delay requirement for interaction. Since
the global propagation delay can be about 100 ms, the actual end-to-end delay budget
available to the system designer (excluding propagation delay) can be no more than 10 ms.
E-Com (Electronic Commerce)
This covers the electronic business transactions over network Electronic Commerce (EC)
conducted on the Internet and World Wide Web (WWW). After an introduction to the
Internet and WWW, during which the benefits of using these infrastructures for EC are
highlighted, the importance of authentication, confidentiality, integrity and non-repudiability
in any business transaction will be handled and extrapolated to EC on the Internet/WWW.
The importance of digital signatures and digital identities are major issues, as well as the
public key infrastructure on which such signatures and identities are based. The role of
Certification Authorities in certifying digital identities is an important issue. Several Internet
security protocols like Secure Sockets Layer (SSL) and Secure Hyper Text Transport protocol
(SHTTP) as well as the secure payment protocol SET participates, showing how the
discussed security technologies are used in these protocols. Different implementations for
electronic cash as well as some legal and policy aspects concludes the EC.
Today, E-mail and Internet access are as important to your business as your phone, or any
other revenue-producing asset. Innovative network peripherals, powerful administrative
tools and thorough management of these growing networks are a requirement to keep your
networks available, reliable and secure. Many companies offer for industry-leading solutions
from building the backbone of your workgroup or enterprise WAN to connectivity from
your home offices or between your satellite sites.
UNIT - I COMPUTER NETWORK FUNDAMENTALS 5

Enterprise Management
Enterprise management solutions generally do more than optimize infrastructure, availability
and performance. Companies provide solutions that put you in control and allow you to
focus on improving your business’ efficiency and increasing customer satisfaction. This
allows you a greater (ROI) return on investment.
Network Systems
In today’s challenging economic environment, IT managers increasingly have to do more
with constrained resources. For the enterprise network manager, this means looking for
smarter ways to use the network while managing the demands of users, applications and
limited budgets. Companies offer a unique blend of practical and innovative technologies
and way of combining them that provides you with high-value, leading-edge solutions
designed for the realities of business and the Internet.
1.4 TRANSMISSION MEDIA
Whatever type of network is used, some type of network media is needed to carry signals
between computers. Two types of media are used in networks: cable-based media, such as
twisted pair, and the media types associated with wireless networking, such as radio waves,
microwaves and Infrared waves.
In networks using cable-based media, there are three basic choices:
w Twisted pair
w Coaxial
w Fiber-optic
Twisted-pair and coaxial cables both use copper wire to conduct the signals electronically;
fiber-optic cable uses a glass or plastic conductor and transmits the signals as light.
For many years, coaxial was the cable of choice for most LANs. Today, however (and for
the past 10 years), twisted pair has proved to be far and away the cable media of choice,
thus retiring coax to the confines of storage closets. Fiber-optic cable has also seen its
popularity rise but because of cost has been primarily restricted to use as a network back-
bone where segment length and higher speeds are needed. That said, fiber is now increas-
ingly common in server room environments as a server to switch connection method, and
in building to building connections in what are termed as metropolitan area networks
(MANs).
Copper cable is used in almost every LAN. Many different types of copper cable are avail-
able. Each type has advantages and disadvantages. Proper selection of cabling is key to
efficient network operation. Since copper uses electrical currents to transmit information,
it is important to understand some basics of electricity.
1.4.1 Magnetic Media
All matter is composed of atoms. The Periodic Table of Elements lists all known types of
atoms and their properties. The atom is comprised of three basic particles:
w Electrons – Particles with a negative charge that orbit the nucleus
w Protons – Particles with a positive charge
w Neutrons – Neutral particles with no charge
UNIT - I COMPUTER NETWORK FUNDAMENTALS 6

The protons and neutrons are combined together in a small group called a nucleus. Atoms,
are groups of atoms called molecules, can be referred to as materials. Materials are classi-
fied into three groups based on how easily free electrons flow through them.
The basis for all electronic devices is the knowledge of how insulators, conductors, and
semiconductors control the flow of electrons and work together. The materials through
which current flows vary in their resistance to the movement of the electrons. The materi-
als that offer very little or no resistance are called conductors. Those materials that do not
allow the current to flow, or severely restrict its flow, are called insulators. The amount of
resistance depends on the chemical composition of the materials.
All materials that conduct electricity have a measure of resistance to the flow of electrons
through them. These materials also have other effects called capacitance and inductance
that relate to the flow of electrons. Impedance includes resistance, capacitance, and induc-
tance and is similar to the concept of resistance.
Attenuation is important in relation to networks. Attenuation refers to the resistance to the
flow of electrons and explains why a signal becomes degraded as it travels along the con-
duit.
Electrical insulators are materials that are most resistant to the flow of electrons through
them. Examples of electrical insulators include plastic, glass, air, dry wood, paper, rubber,
and helium gas. These materials have very stable chemical structures and the electrons are
tightly bound within the atoms.
Electrical conductors are materials that allow electrons to flow through them easily. The
outermost electrons are bound very loosely to the nucleus and are easily freed. At room
temperature, these materials have a large number of free electrons that can provide con-
duction. The introduction of voltage causes the free electrons to move, which results in a
current flow.
Semiconductors are materials that allow the amount of electricity they conduct to be pre-
cisely controlled. Examples include carbon (C), germanium (Ge), and the alloy gallium
arsenide (GaAs). Silicon (Si) is the most important semiconductor because it makes the
best microscopic-sized electronic circuits. Silicon is very common and can be found in
sand, glass, and many types of rocks.
Voltage is sometimes referred to as electromotive force (EMF). EMF is related to an elec-
trical force, or pressure, that occurs when electrons and protons are separated. The force
that is created pushes toward the opposite charge and away from the like charge. This
process occurs in a battery, where chemical action causes electrons to be freed from the
negative terminal of the battery. The electrons then travel to the opposite, or positive,
terminal through an external circuit. The electrons do not travel through the battery. Re-
member that the flow of electricity is really the flow of electrons. Voltage can also be
created in three other ways. The first is by friction, or static electricity. The second way is
by magnetism, or an electric generator. The last way that voltage can be created is by light,
or a solar cell.
The purpose of the physical layer is to transport a raw bit stream from one machine to
another. Various physical media can be used for the actual transmission. Each one has its
own niche in terms of bandwidth, delay, cost, and ease of installation and maintenance.
Media are roughly grouped into guided media, such as copper wire and fiber optics, and
unguided media, such as radio and lasers through the air.
UNIT - I COMPUTER NETWORK FUNDAMENTALS 7

Magnetic media, commonly called as copper wire media, is term referring to the transmis-
sion of audio/video, analog/digital data on a magnetised medium, in form of voltage pulses.
Cables have different specifications and expectations. Important considerations related to
performance are as follows:
w What speeds for data transmission can be achieved? The speed of bit transmission
through the cable is extremely important. The speed of transmission is affected by
the kind of conduit used.
w Will the transmissions be digital or analog? Digital or baseband transmission and
analog or broadband transmission require different types of cable.
w How far can a signal travel before attenuation becomes a concern? If the signal is
degraded, network devices might not be able to receive and interpret the signal.
The distance the signal travels through the cable affects attenuation of the signal.
Degradation is directly related to the distance the signal travels and the type of
cable used.
The following Ethernet specifications relate to cable type:
w 10BASE-T
w 10BASE5
w 10BASE2
10BASE-T refers to the speed of transmission at 10 Mbps. The type of transmission is
baseband, or digitally interpreted. The T stands for twisted pair.
10BASE5 refers to the speed of transmission at 10 Mbps. The type of transmission is
baseband, or digitally interpreted. The 5 indicates that a signal can travel for approxi-
mately 500 meters before attenuation could disrupt the ability of the receiver to interpret
the signal. 10BASE5 is often referred to as Thicknet. Thicknet is a type of network and
10BASE5 is the cable used in that network.
10BASE2 refers to the speed of transmission at 10 Mbps. The type of transmission is
baseband, or digitally interpreted. The 2, in 10BASE2, refers to the approximate maxi-
mum segment length being 200 meters before attenuation could disrupt the ability of the
receiver to appropriately interpret the signal being received. The maximum segment length
is actually 185 meters. 10BASE2 is often referred to as Thinnet. Thinnet is a type of net-
work and 10BASE2 is the cable used in that network.
1.4.2 Twisted Pair
Twisted pair is the ordinary copper wire that connects home and many business computers
to the telephone company. To reduce crosstalk or electromagnetic induction between pairs
of wires, two insulated copper wires are twisted around each other. Each connection on
twisted pair requires both wires. Since some telephone sets or desktop locations require
multiple connections, twisted pair is sometimes installed in two or more pairs, all within a
single cable. For some business locations, twisted pair is enclosed in a shield that func-
tions as a ground. This is known as shielded twisted pair (STP). Ordinary wire to the home
is unshielded twisted pair (UTP).
UNIT - I COMPUTER NETWORK FUNDAMENTALS 8

UTP :

UTP cables are made up of pairs of copper wires twisted together. The twisting serves an
important purpose – it helps to eliminate electromagnetic interference (EMI). EMI is a
common problem on networks using copper wire. Signals from one wire pair might inter-
fere with another (referred to as crosstalk), while powerful external electrical devices may
also impact transmission capabilities. When using UTP cables, a common mistake is to
unravel the twisting too far – this will certainly degrade signal strength and make the wires
more prone to interference.
UTP cable has many advantages. It is easy to install and is less expensive than other types
of networking media. In fact, UTP costs less per meter than any other type of LAN cabling.
However, the real advantage is the size. Since it has such a small external diameter, UTP
does not fill up wiring ducts as rapidly as other types of cable. This can be an extremely
important factor to consider, particularly when a network is installed in an older building.
When UTP cable is installed with an RJ-45 connector, potential sources of network noise
are greatly reduced and a good solid connection is almost guaranteed.
There are some disadvantages of twisted-pair cabling. UTP cable is more prone to electri-
cal noise and interference than other types of networking media, and the distance between
signal boosts is shorter for UTP than it is for coaxial and fiber optic cables. Twisted pair
cabling was once considered slower at transmitting data than other types of cable. This is
no longer true. In fact, today, twisted pair is considered the fastest copper-based media..
The category of the cabling defines how many wire pairs you’ll find in a given cable. Voice
grade cable, also known as Category (or simply ‘Cat’) 3, uses only two pairs and is used
for telephone service and 10Mb Ethernet. Cat 5 wiring, on the other hand, uses 4 wire pairs
and is the minimum required for 100Mb Fast Ethernet. For the most part, buildings today
are usually pre-wired for Cat 5, although Cat 3 may still be found in older environments.
You may also come across what is known as Cat 5E – this version of Cat 5 simply has more
twists per inch of wiring, providing better resistance to EMI and higher transmission capa-
bilities.
UNIT - I COMPUTER NETWORK FUNDAMENTALS 9

STP :
Twisted pair cables are often shielded in attempt to prevent electromagnetic interference
(EMI). Because the shielding is made of metal, it may also serve as a ground. However,
usually a shielded or a screened twisted pair(ScTP) cable has a special grounding wire
added called a drain wire. This shielding can be applied to individual pairs, or to the col-
lection of pairs. When shielding is applied to the collection of pairs, this is referred to as
screening. The shielding must be grounded for the shielding to work.

STP cable combines the techniques of cancellation, shielded, and twisted wires. Each pair
of wires is wrapped in metallic foil. The two pairs of wires are wrapped in an overall
metallic braid or foil. It is usually 150-ohm cable. As specified for use in Token Ring
network installations, STP reduces electrical noise within the cable such as pair to pair
coupling and crosstalk. STP also reduces electronic noise from outside the cable such as
electromagnetic interference (EMI) and radio frequency interference (RFI). STP cable shares
many of the advantages and disadvantages of UTP cable. STP provides more protection
from all types of external interference. However, STP is more expensive and difficult to
install than UTP. A variation of STP, known as ScTP for “screened twisted pair” or FTP for
“foil twisted pair,” uses only the overall shield and provides more protection than UTP, but
not as much as STP.
1.4.3 Coaxial Cable
Coaxial cable (or “coax) is the most common cable used for transmitting video signals.
The name “coaxial” refers to the common axis of the two conductors.

The dielectric is surrounded by foil shield/s and/or copper braid/s which form the outer
conductor and also shield against The outer conductor/shield is encased in a PVC jacket.
Most coaxial cables for video applications have a nominal impedance of 75 ohms. Their
differing electrical and physical characteristics make it important to select the correct type
of cable to suit the application.
UNIT - I COMPUTER NETWORK FUNDAMENTALS 10

A coaxial cable has a solid copper or copper-clad-steel centre conductor surrounded by a

non-conductive dielectric insulating material. The center conductor can also be made of
tin plated aluminium cable allowing for the cable to be manufactured inexpensively. Over
this insulating material is a woven copper braid or metallic foil that acts as the second wire
in the circuit and as a shield against for the inner conductor. This second layer, or shield
also reduces the amount of outside electromagnetic interference. Covering this shield is
the cable jacket.
For LANs, coaxial cable offers several advantages. It can be run longer distances than
shielded twisted pair, STP, unshielded twisted pair, UTP, and screened twisted pair, ScTP,
cable without the need for repeaters. Repeaters regenerate the signals in a network so that
they can cover greater distances. Coaxial cable is less expensive than fiber-optic cable and
the technology is well known. It has been used for many years for many types of data
communication such as cable television.
It is important to consider the size of a cable. As the thickness increases, it becomes more
difficult to work with a cable. Remember that cable must be pulled through conduits and
troughs that are limited in size. Coaxial cable comes in a variety of sizes. The largest
diameter was specified for use as Ethernet backbone cable since it has greater transmission
lengths and noise rejection characteristics. This type of coaxial cable is frequently referred
to as Thicknet. This type of cable can be too rigid to install easily in some situations.
Generally, the more difficult the network media is to install, the more expensive it is to
install. Coaxial cable is more expensive to install than twisted-pair cable.
In the past, Thinnet coaxial cable with an outside diameter of only 0.35 cm was used in
Ethernet networks. It was especially useful for cable installations that required the cable to
make many twists and turns. Since Thinnet was easier to install, it was also cheaper to
install. This led some people to refer to it as Cheapernet. The outer copper or metallic braid
in coaxial cable comprises half the electric circuit. A solid electrical connection at both
ends is important to properly ground the cable. Poor shield connection is one of the biggest
sources of connection problems in the installation of coaxial cable. Connection problems
result in electrical noise that interferes with signal transmission. For this reason Thinnet is
no longer commonly used nor supported by latest standards, 100 Mbps and higher, for
Ethernet networks.
UNIT - I COMPUTER NETWORK FUNDAMENTALS 11

Types of Coax :
Coaxial cables that conform to U.S. Government specifications are identified with an RG
designation. The meaning of the individual components of the designation are:

Radio Frequency

Government

Government-assigned approval number

Universal specification

R G 8 /U

If the letters A, B or C appear before the slash (/) it indicates a specification-modification

or revision. As an example, RG 8/U is superseded by RG 8A/U.
The three most commonly used coaxial cable types for video applications are RG59/U,
RG6/U and RG11/U.

RG59/U is available with either solid copper or copper-clad-steel centre

conductor. It's suitable for basic analog TV antenna feeds in residential
applications and for basic CCTV systems over short cable runs. The copper-
clad-steel type has high tensile strength and should be used when terminating
the cable with F-Type connectors.
RG6/U Quad-shield is the minimum requirement under the latest
Australian Standard for digital TV antenna cabling and for all TV antenna
cabling for apartments/units (MATV). It is also used for the distribution of
Cable TV (CATV) and Satellite TV (SATV) in residential or commercial
premises. It features a copper-clad-steel inner conductor. Single-shield,
dual-shield and tri-shield versions of RG6/U are available but do not
provide adequate EMI shielding.
RG11/U Quad-shield is used for the same applications as RG6/U for
either backbone cabling or for long distribution runs. It features a copper-
clad-steel inner conductor.
UNIT - I COMPUTER NETWORK FUNDAMENTALS 12

Choosing the correct cable :

Use the table below to determine which cable should be used for your application.

Analog TV RG59/U Acceptable performance on cable runs <225

metres

RG6/U Gives superior performance on cable runs <225

metres.Used for cable runs >225 metres but <545
metres.
RG11/U For cable runs greater than 545 metres.

CCTV RG59/U Acceptable performance on cable runs <225 metres

RG6/U Gives for superior performance on cable runs <225

metres.Used for cable runs >225 metres but <545
metres.

RG11/U For cable runs greater than 545 metres.

DTV, CATV, SATV, RG6/U Standard cable for these applications

MATV RG11/U Recommended for long cable runs and for backbone
cabling.

Coaxial Connectors
BNC connector are bayonet type connectors, commonly used
in CCTV systems. They are the most suitable connector for use
with RG59/U cable. BNC connectors are specified by IEC
standard IEC60169-8. The argument, over what the “BNC” in
“BNC connector” means, will go on forever. It has been variously
defined as: British Navy Connector, Bayonet Node Connector,
Bayonet Nut Coupling, Baby Neil Connector, etc. The two
Amphenol engineers who invented the BNC connector were
named Paul Neil and Carl Concelman. It therefore seems logical
that the “true” meaning of the “BNC” acronym is perhaps
“Bayonet Neil-Concelman”.
F-Type connectors are used for CATV, SATV and Digital TV in
conjunction with either RG6 or RG11 cables. The copper-clad-
steel inner conductor of the cable forms the inner “pin” of the
connector. Although “twist-on” type connectors are available,
they do not produce a reliable connection in comparison to a
crimp-type connector that has been terminated with a good-quality
ratchet crimping tool. F-type connectors are also known as F-81
connectors and are specified by IEC standard IEC60169-24.
F-type connectors are named according to the type of cable or
the application that they have been designed for as shown in the
table below.
UNIT - I COMPUTER NETWORK FUNDAMENTALS 13

Connector Name Application / Description

F-59A male F-connector that seizes the outer braid and
F-6 (F-56) jacket of an RG-59, RG-6 (RG-56) or RG-
F-11 11 coaxial cable. The cable’s centre
conductor extends through the connector
to form the centre contact.

F-61 An equipment or panel-mounted F-con-

nector (usually female) with
soldered cable connections. A 3/8" ( 32
pitch) thread is provided
to accept the connector nut of the male
connector.
F-71 A male/male F-connector.
F-81A female/female F-connector used to couple
two male-ended cables together for in-line
or wall-plate applications.

PAL (Belling Lee) connectors are a push-on connector that have

been traditionally used for TV antenna wall plates and connec-
tions. With the exception of TV/VCR hook-ups, PAL connec-
tors are being replaced by F-Type connectors as required for
CATV, SATV and DTV. PAL connectors are specified by IEC
standard IEC60169-2.

Adaptors. Where BNC connectors are required with RG6/U

coaxial cable, it is recommended that an F-Type plug be crimped
to the RG6/U and an F-Type to BNC adaptor used.

1.4.4 Fiber Optics

Optical fiber is the most frequently used medium for the longer, high bandwidth, point-to-
point transmissions required on LAN backbones and on WANs. Optical media uses light
to transmit data through thin glass or plastic fiber. Electrical signals cause a fiber-optic
transmitter to generate the light signals sent down the fiber. The receiving host receives the
light signals and converts them to electrical signals at the far end of the fiber. However,
there is no electricity in the fiber-optic cable. In fact, the glass used in fiber-optic cable is a
very good electrical insulator.
The part of an optical fiber through which light rays travel is called the core of the fiber.
Light rays can only enter the core if their angle is inside the numerical aperture of the fiber.
Likewise, once the rays have entered the core of the fiber, there are a limited number of
optical paths that a light ray can follow through the fiber. These optical paths are called
modes. If the diameter of the core of the fiber is large enough so that there are many paths
UNIT - I COMPUTER NETWORK FUNDAMENTALS 14

that light can take through the fiber, the fiber is called “multimode” fiber. Single-mode
fiber has a much smaller core that only allows light rays to travel along one mode inside
the fiber.

Properties of light rays:

When electromagnetic waves travel out from a source, they travel in straight lines. These
straight lines pointing out from the source are called rays. Think of light rays as narrow
beams of light like those produced by lasers. In the vacuum of empty space, light travels
continuously in a straight line at 300,000 kilometers per second. However, light travels at
different, slower speeds through other materials like air, water, and glass. When a light ray
called the incident ray, crosses the boundary from one material to another, some of the
light energy in the ray will be reflected back. That is why you can see yourself in window
glass. The light that is reflected back is called the reflected ray.
The light energy in the incident ray that is not reflected will enter the glass. The entering
ray will be bent at an angle from its original path. This ray is called the refracted ray. How
much the incident light ray is bent depends on the angle at which the incident ray strikes
the surface of the glass and the different rates of speed at which light travels through the
two substances.
The bending of light rays at the boundary of two substances is the reason why light rays are
able to travel through an optical fiber even if the fiber curves in a circle.
The optical density of the glass determines how much the rays of light in the glass bends.
Optical density refers to how much a light ray slows down when it passes through a sub-
stance. The greater the optical density of a material, the more it slows light down from its
speed in a vacuum. The index of refraction is defined as the speed of light in vacuum
divided by the speed of light in the medium. Therefore, the measure of the optical density
of a material is the index of refraction of that material. A material with a large index of
refraction is more optically dense and slows down more light than a material with a smaller
index of refraction.
For a substance like glass, the Index of Refraction, or the optical density, can be made
larger by adding chemicals to the glass. Making the glass very pure can make the index of
refraction smaller. The next lessons will provide further information about reflection and
refraction, and their relation to the design and function of optical fiber
An overview of reflection:
When a ray of light (the incident ray) strikes the shiny surface of a flat piece of glass, some
of the light energy in the ray is reflected. The angle between the incident ray and a line
perpendicular to the surface of the glass at the point where the incident ray strikes the glass
is called the angle of incidence. The perpendicular line is called the normal. It is not a light
ray but a tool to allow the measurement of angles. The angle between the reflected ray and
the normal is called the angle of reflection. The Law of Reflection states that the angle of
reflection of a light ray is equal to the angle of incidence. In other words, the angle at which
UNIT - I COMPUTER NETWORK FUNDAMENTALS 15

a light ray strikes a reflective surface determines the angle that the ray will reflect off the
surface.
These principles are depicted in the diagram below.

An overview of refraction:
When a light strikes the interface between two transparent materials, the light divides into
two parts. Part of the light ray is reflected back into the first substance, with the angle of
reflection equaling the angle of incidence. The remaining energy in the light ray crosses
the interface and enters into the second substance.
UNIT - I COMPUTER NETWORK FUNDAMENTALS 16

If the incident ray strikes the glass surface at an exact 90-degree angle, the ray goes straight
into the glass. The ray is not bent. However, if the incident ray is not at an exact 90-degree
angle to the surface, then the transmitted ray that enters the glass is bent. The bending of
the entering ray is called refraction. How much the ray is refracted depends on the index of
refraction of the two transparent materials. If the light ray travels from a substance whose
index of refraction is smaller, into a substance where the index of refraction is larger, the
refracted ray is bent towards the normal. If the light ray travels from a substance where the
index of refraction is larger into a substance where the index of refraction is smaller, the
refracted ray is bent away from the normal.
Consider a light ray moving at an angle other than 90 degrees through the boundary be-
tween glass and a diamond. The glass has an index of refraction of about 1.523. The dia-
mond has an index of refraction of about 2.419. Therefore, the ray that continues into the
diamond will be bent towards the normal. When that light ray crosses the boundary be-
tween the diamond and the air at some angle other than 90 degrees, it will be bent away
from the normal. The reason for this is that air has a lower index of refraction, about 1.000
than the index of refraction of the diamond.
Total internal reflection as it relates to optical media
A light ray that is being turned on and off to send data (1s and 0s) into an optical fiber must
stay inside the fiber until it reaches the far end. The ray must not refract into the material
wrapped around the outside of the fiber. The refraction would cause the loss of part of the
light energy of the ray. A design must be achieved for the fiber that will make the outside
surface of the fiber act like a mirror to the light ray moving through the fiber. If any light
ray that tries to move out through the side of the fiber were reflected back into the fiber at
an angle that sends it towards the far end of the fiber, this would be a good “pipe” or “wave
guide” for the light waves.
The laws of reflection and refraction illustrate how to design a fiber that guides the light
waves through the fiber with a minimum energy loss. The following two conditions must
be met for the light rays in a fiber to be reflected back into the fiber without any loss due to
refraction:
w The core of the optical fiber has to have a larger index of refraction (n) than the
material that surrounds it. The material that surrounds the core of the fiber is called
the cladding.
w The angle of incidence of the light ray is greater than the critical angle for the core
and its cladding.
When both of these conditions are met, the entire incident light in the fiber is reflected
back inside the fiber. This is called total internal reflection, which is the foundation upon
which optical fiber is constructed. Total internal reflection causes the light rays in the fiber
to bounce off the core-cladding boundary and continue its journey towards the far end of
the fiber. The light will follow a zigzag path through the core of the fiber.
A fiber that meets the first condition can be easily created. In addition, the angle of inci-
dence of the light rays that enter the core can be controlled. Restricting the following two
factors controls the angle of incidence:
w The numerical aperture of the fiber – The numerical aperture of a core is the
range of angles of incident light rays entering the fiber that will be completely
reflected.
UNIT - I COMPUTER NETWORK FUNDAMENTALS 17

w Modes – The paths which a light ray can follow when traveling down a fiber.
By controlling both conditions, the fiber run will have total internal reflection. This gives
a light wave guide that can be used for data communications.
Self Learning Exercises :
4 Why are pairs of wires twisted together in UTP cable :
(a) twisting of wires makes it less expensive
(b) twisting of wires makes it thinner
(c) twisting of reduces noise problems
(d) makes six pairs fit in space of four pairs
5 Which material is considered electrical semiconductor :
(a) Air (b) Silicon
(c) Glass (d) Gold
6 Which of the following are the parts of fiber optic cable :
(a) Clad (b) Braid
(c) Core (d) All of the above
1.5 NETWORKING ESSENTIALS
1.5.1 Repeaters
A repeater connects two segments of your network cable. It retimes and regenerates the
signals to proper amplitudes and sends them to the other segments. When talking about,
ethernet topology, you are probably talking about using a hub as a repeater. Repeaters
require a small amount of time to regenerate the signal. This can cause a propagation delay
which can affect network communication when there are several repeaters in a row. Many
network architectures limit the number of repeaters that can be used in a row. Repeaters
work only at the physical layer of the OSI network model.
1.5.2 Hubs
Hubs are actually multiport repeaters. The difference between hubs and repeaters is usu-
ally the number of ports that each device provides. A typical repeater usually has two ports.
A hub generally has from 4 to 24 ports. Hubs are most commonly used in Ethernet 10BASE-
T or 100BASE-T networks.
Hubs come in three basic types:
w Passive – A passive hub serves as a physical connection point only. It does not
manipulate or view the traffic that crosses it. It does not boost or clean the signal. A
passive hub is used only to share the physical media. A passive hub does not need
electrical power.
w Active – An active hub must be plugged into an electrical outlet because it needs
power to amplify a signal before it is sent to the other ports.
w Intelligent – Intelligent hubs are sometimes called smart hubs. They function like
active hubs with microprocessor chips and diagnostic capabilities. Intelligent hubs
are more expensive than active hubs. They are also more useful in troubleshooting
situations.
UNIT - I COMPUTER NETWORK FUNDAMENTALS 18

Devices attached to a hub receive all traffic that travels through the hub. If many devices
are attached to the hub, collisions are more likely to occur. A collision occurs when two or
more workstations send data over the network wire at the same time. All data is corrupted
when this occurs. All devices that are connected to the same network segment are mem-
bers of the same collision domain.
Sometimes hubs are called concentrators since they are central connection points for Ethernet
LANs.
1.5.3 Switches
Switches occupy the same place in the network as hubs. Unlike hubs, switches examine
each packet and process it accordingly rather than simply repeating the signal to all ports.
Switches map the Ethernet addresses of the nodes residing on each network segment and
then allow only the necessary traffic to pass through the switch. When a packet is received
by the switch, the switch examines the destination and source hardware addresses and
compares them to a table of network segments and addresses. If the segments are the same,
the packet is dropped (“filtered”); if the segments are different, then the packet is “for-
warded” to the proper segment. Additionally, switches prevent bad or misaligned packets
from spreading by not forwarding them.
Filtering of packets, and the regeneration of forwarded packets enables switching technol-
ogy to split a network into separate collision domains. Regeneration of packets allows for
greater distances and more nodes to be used in the total network design, and dramatically
lowers the overall collision rates. In switched networks, each segment is an independent
collision domain. In shared networks all nodes reside in one, big shared collision domain.
Easy to install, most switches are self learning. They determine the Ethernet addresses in
use on each segment, building a table as packets are passed through the switch. This “plug
and play” element makes switches an attractive alternative to hubs.
Switches can connect different networks types (such as Ethernet and Fast Ethernet) or
networks of the same type. Many switches today offer high-speed links, like Fast Ethernet
or FDDI, that can be used to link the switches together or to give added bandwidth to
important servers that get a lot of traffic. A network composed of a number of switches
linked together via these fast uplinks is called a “collapsed backbone” network.
Dedicating ports on switches to individual nodes is another way to speed access for critical
computers. Servers and power users can take advantage of a full segment for one node, so
some networks connect high traffic nodes to a dedicated switch port.
Full duplex is another method to increase bandwidth to dedicated workstations or servers.
To use full duplex, both network interface cards used in the server or workstation, and the
switch must support full duplex operation. Full duplex doubles the potential bandwidth on
that link, providing 20 Mbps for Ethernet and 200 Mbps for Fast Ethernet.
Bridge
A bridge reads the outermost section of data on the data packet, to tell where the message
is going. It reduces the traffic on other network segments, since it does not send all packets.
Bridges can be programmed to reject packets from particular networks. Bridging occurs at
the data link layer of the OSI model, which means the bridge cannot read IP addresses, but
only the outermost hardware address of the packet. In our case the bridge can read the
ethernet data which gives the hardware address of the destination address, not the IP ad-
UNIT - I COMPUTER NETWORK FUNDAMENTALS 19

dress. Bridges forward all broadcast messages. Only a special bridge called a translation
bridge will allow two networks of different architectures to be connected. Bridges do not
normally allow connection of networks with different architectures. The hardware address
is also called the MAC (media access control) address. To determine the network segment
a MAC address belongs to, bridges use one of:
w Transparent Bridging - They build a table of addresses (bridging table) as they
receive packets. If the address is not in the bridging table, the packet is forwarded
to all segments other than the one it came from. This type of bridge is used on
Ethernet networks.
w Source route bridging - The source computer provides path information inside
the packet. This is used on Token Ring networks.
1.5.4 Router
A router is used to route data packets between two networks. It reads the information in
each packet to tell where it is going. If it is destined for an immediate network it has access
to, it will strip the outer packet, readdress the packet to the proper Ethernet address, and
transmit it on that network. If it is destined for another network and must be sent to another
router, it will re-package the outer packet to be received by the next router and send it to
the next router. The section on routing explains the theory behind this and how routing
tables are used to help determine packet destinations. Routing occurs at the network layer
of the OSI model. They can connect networks with different architectures such as Token
Ring and Ethernet. Although they can transform information at the data link level, routers
cannot transform information from one data format such as TCP/IP to another such as IPX/
SPX. Routers do not send broadcast packets or corrupted packets. If the routing table does
not indicate the proper address of a packet, the packet is discarded.
There is a device called a brouter which will function similar to a bridge for network
transport protocols that are not routable, and will function as a router for routable proto-
cols. It functions at the network and data link layers of the OSI network model.
1.5.5 Gateways
A gateway can translate information between different network data formats or network
architectures. It can translate TCP/IP to AppleTalk so computers supporting TCP/IP can
communicate with Apple brand computers. Most gateways operate at the application layer,
but can operate at the network or session layer of the OSI model. Gateways will start at the
lower level and strip information until it gets to the required level and repackage the infor-
mation and work its way back toward the hardware layer of the OSI model. To confuse
issues, when talking about a router that is used to interface to another network, the word
gateway is often used. This does not mean the routing machine is a gateway as defined
here, although it could be.
1.5.6 NIC (Network interface Card)
Each network card, called a network interface card (NIC) has a built in hardware address
programmed by its manufacturer. This is a 48 bit address and should be unique for each
card. This address is called a media access control (MAC) address.
Network Interface Cards, commonly referred to as NICs, are used to connect a PC to a
network. The NIC provides a physical connection between the networking cable and the
computer’s internal bus. Different computers have different bus architectures. PCI bus
UNIT - I COMPUTER NETWORK FUNDAMENTALS 20

slots are most commonly found on 486/Pentium PCs and ISA expansion slots are com-
monly found on 386 and older PCs. NICs come in three basic varieties: 8-bit, 16-bit, and
32-bit. The larger the number of bits that can be transferred to the NIC, the faster the NIC
can transfer data to the network cable. Most NICs are designed for a particular type of
network, protocol, and medium, though some can serve multiple networks.
Many NIC adapters comply with plug-and-play specifications. On these systems, NICs are
automatically configured without user intervention, while on non-plug-and-play systems,
configuration is done manually through a set-up program and/or DIP switches.
Cards are available to support almost all networking standards. Fast Ethernet NICs are
often 10/100 capable, and will automatically set to the appropriate speed. Gigabit Ethernet
NICs are 10/100/1000 capable with auto negotiation depending on the user’s Ethernet
speed. Full duplex networking is another option where a dedicated connection to a switch
allows a NIC to operate at twice the speed.
Self learning exercises:
7 What is the function of router?
(a) It routes traffic from one LAN segment to another
(b) It regenerates the data
(c) It transforms the data from one format to another
(d) None of the above
8 What is multiport repeater called as?
(a) Hub (b) Switch
(c) Router (d) Gateway
9 What is the Gateway?
(a) It is used to connect two totally dissimilar networks
(b) It regenerates and retransmits signals from one network to another
(c) It acts as a bridge between two networks
(d) It is used to change the format of the message
1.6 SUMMARY
Computer networks developed in response to business and government computing needs.
Applying standards to network functions provided a set of guidelines for creating network
hardware and software and provided compatibility among equipment from different com-
panies. Information could move within a company and from one business to another.
Network devices, such as repeaters, hubs, bridges, switches and routers connect host de-
vices together to allow them to communicate. Protocols provide a set of rules for commu-
nication.
The amount of information that can flow through a network connection in a given period
of time is referred to as bandwidth. Network bandwidth is typically measured in thousands
of bits per second (kbps), millions of bits per second (Mbps), billions of bits per second
(Gbps) and trillions of bits per second (Tbps). The theoretical bandwidth of a network is an
important consideration in network design. If the theoretical bandwidth of a network con-
nection is known, the formula T=S/BW (transfer time = size of file / bandwidth) can be
UNIT - I COMPUTER NETWORK FUNDAMENTALS 21

used to calculate potential data transfer time. However the actual bandwidth, referred to as
throughput, is affected by multiple factors such as network devices and topology being
used, type of data, number of users, hardware and power conditions.
Intranets are only available to users who have access privileges to the internal network of
an organization. Extranets are designed to deliver applications and services that are Intranet
based to external users or enterprises.
1.7 GLOSSARY
w Attenuation - signal loss due to impedance
w Backbone - Main cable used to connect computers on a network.
w Bandwidth - Indicates the amount of data that can be sent in a
time period. Measured in Mbps which is one mil-
lion bits per second.
w Baseband - Data bits are defined by discrete signal changes.
w Bridge - Read the outermost section of data on the data packet,
to tell where the message is going. It reduces the
traffic on other network segments, since it does not
send all packets but only sends packets intended for
that segment they are attached to.
w Broadband - Uses analog signals to divide the cable into several
channels with each channel at its own frequency.
Each channel can only transmit one direction.
w Broadcast - A transmission to all interface cards on the network.
w Brouter - Will function similar to a bridge for network trans-
port protocols that are not routable, and will func-
tion as a router for routable protocols.
w EMI - Interference by electromagnetic signals that can cause
interference) reduced data integrity (electromagnetic and
increased error rates on transmission channels.
w Media - The hardware method used to connect computers
over a network. The three main types are copper
cable, fiber optic cable, and wireless.
w Protocol - A set of standards sets of standards that define all
operations within a network. There are various pro-
tocols that operate at various levels of the OSI net-
work model such as transport protocols include TCP,
SPX.
w Repeater - Used on a network to regenerate signals to be sent
over long distances or tie computers together on a
network.
w Router - Routes data packets between two networks. It reads
the information in each packet to tell where it is go-
ing.
w Thicknet - Half inch rigid cable. Maximum cable length is 500
meters. Transmission speed is 10Mbps. Expensive
and is not commonly used. (RG-11 or RG-8).
UNIT - I COMPUTER NETWORK FUNDAMENTALS 22

w Thinnet - Thinnet uses a British Naval Connector (BNC) on

each end. Thinnet is part of the RG-58 family of
cable*. Maximum cable length is 185 meters. Trans-
mission speed is 10Mbps.
w Token Ring - A network architecture developed by IBM which
sends tokens around a ring of computers to allow
media access. Standardized to IEEE 802.5
w Topology - The shape of the physical connection of a network
with regard to repeaters and networked computers.
The three main types are ring, bus, and star.
w VPN - Virtual Private Networking. The function of VPN is
to allow two computers or networks to talk to each
other over a transport media that is not secure, but
the network is made secure by VPN security proto-
cols.
1.8 FURTHER READINGS
1. Data Communication & Networking - Behrouz Forouzan
2. CCNA (Cisco Certified Network Associate) First year Companion Guide -
Cisco Press
3. Computer Networks – Andrew Tanenbaum; Prentice Hall India(PHI)
1.9 ANSWERS TO THE SELF LEARNING EXERCISES
1. d
2. c
3. c
4. c
5. b
6. d
7. a
8. a
9. a
1.10 UNIT END QUESTIONS
1. How do guided media differ from unguided media.
2. Name the advantages of optical fiber over twisted-pair and coaxial cable.
3. Why is coaxial cable superior to twisted pair cable?
4. What is reflection? How is total internal reflection used in fiber optics for
communication?
5. What is major advantage of shielded twisted pair over un-shielded twisted
Pair?
6. What is the device Router used for?
7. What is the function of Repeater?
8. Differentiate between Switch and Bridge?
9. What is the significance of NIC?
10. List out various Internet applications.