Data communications and networking(DCN)

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Unit 1. Introduction to data
communications and networking
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NETWORKING FUNDAMENTALS
Unit Structure
1.0 Objectives
1.1 Introduction
1.2 Data & Information
1.3 Data Communication
1.3.1 Characteristics of Data Communication
1.3.2 Components of Data Communication
1.4 Data Representation
1.5 Data Flow
1.5.1. Simplex
1.52. Half Duplex
1.5.3. Full Duplex
1.6 Computer Network
1.6.1 Categories of a network
1.7 Protocol
1.7.1 Elements of a Protocol
1.8 Standards In Networking
1.8.1 Concept of Standard
1.8.2 Standard Organizations in field of Networking
1.9 Review Questions
1.10 References
1.0 OBJECTIVES:
 Introduce the readers to data communication and its
fundamentals
 Define networks
 Define protocols
 Standards in networking

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1.1 INTRODUCTION
This chapter provides an introduction to Computer networks and
covers fundamental topics like data, information to the definition
of communication and computer networks.
The main objective of data communication and networking is to
enable seamless exchange of data between any two points in
the world.
This exchange of data takes place over a computer network.
1.2 DATA & INFORMATION
Data refers to the raw facts that are collected while information
refers to processed data that enables us to take decisions.
Ex. When result of a particular test is declared it contains data
of all students, when you find the marks you have scored you
have the information that lets you know whether you have
passed or failed.
The word data refers to any information which is presented in a
form that is agreed and accepted upon by is creators and users.
1.3 DATA COMMUNICATION
Data Communication is a process of exchanging data or
information
In case of computer networks this exchange is done between
two devices over a transmission medium.
This process involves a communication system which is made
up of hardware and software. The hardware part involves the
sender and receiver devices and the intermediate devices
through which the data passes. The software part involves
certain rules which specify what is to be communicated, how it
is to be communicated and when. It is also called as a Protocol.
The following sections describes the fundamental
characteristics that are important for the effective working of
data communication process and is followed by the components
that make up a data communications system.
1.3.1 Characteristics of Data Communication
The effectiveness of any data communications system depends
upon the following four fundamental characteristics:

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1. Delivery: The data should be delivered to the correct
destination and correct user.
2. Accuracy: The communication system should deliver the data
accurately, without introducing any errors. The data may get
corrupted during transmission affecting the accuracy of the
delivered data.
3. Timeliness: Audio and Video data has to be delivered in a
timely manner without any delay; such a data delivery is called
real time transmission of data.
4. Jitter: It is the variation in the packet arrival time. Uneven Jitter
may affect the timeliness of data being transmitted.
1.3.2 Components of Data Communication
A Data Communication system has five components as
shown in the diagram below:
Fig. Components of a Data Communication System
1. Message
Message is the information to be communicated by the sender to
the receiver.
2. Sender
The sender is any device that is capable of sending the data
(message).
3. Receiver
The receiver is a device that the sender wants to communicate the
data (message).
4. Transmission Medium
It is the path by which the message travels from sender to receiver.
It can be wired or wireless and many subtypes in both.

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5. Protocol
It is an agreed upon set or rules used by the sender and
receiver to communicate data.
A protocol is a set of rules that governs data communication.
A Protocol is a necessity in data communications without
which the communicating entities are like two persons trying
to talk to each other in a different language without know the
other language.
1.4 DATA REPRESENTATION
Data is collection of raw facts which is processed to deduce
information.
There may be different forms in which data may be represented.
Some of the forms of data used in communications are as follows:
1. Text
Text includes combination of alphabets in small case as well
as upper case.
It is stored as a pattern of bits. Prevalent encoding system :
ASCII, Unicode
2. Numbers
Numbers include combination of digits from 0 to 9.
It is stored as a pattern of bits. Prevalent encoding system :
ASCII, Unicode
3. Images
―An image is worth a thousand words‖ is a very famous saying.
In computers images are digitally stored.
A Pixel is the smallest element of an image. To put it in simple
terms, a picture or image is a matrix of pixel elements.
The pixels are represented in the form of bits. Depending upon
the type of image (black n white or color) each pixel would
require different number of bits to represent the value of a pixel.
The size of an image depends upon the number of pixels (also
called resolution) and the bit pattern used to indicate the value
of each pixel.
Example: if an image is purely black and white (two color) each
pixel can be represented by a value either 0 or 1, so an image
made up of 10 x 10 pixel elements would require only 100 bits in
memory to be stored.
On the other hand an image that includes gray may require 2
bits to represent every pixel value (00 - black, 01 – dark gray, 10

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– light gray, 11 –white). So the same 10 x 10 pixel image would
now require 200 bits of memory to be stored.
Commonly used Image formats : jpg, png, bmp, etc
4. Audio
Data can also be in the form of sound which can be recorded
and broadcasted. Example: What we hear on the radio is a
source of data or information.
Audio data is continuous, not discrete.
5. Video
Video refers to broadcasting of data in form of picture or movie
1.5 DATA FLOW
wo devices communicate with each other by sending and
receiving data. The data can flow between the two devices in the
following ways.
1. Simplex
2. Half Duplex
3. Full Duplex
1.5.1 Simplex
Figure: Simplex mode of communication
In Simplex, communication is unidirectional
Only one of the devices sends the data and the other one
only receives the data.
Example: in the above diagram: a cpu send data while a
monitor only receives data.
1.5.2 Half Duplex

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Figure: Half Duplex Mode of Communication
In half duplex both the stations can transmit as well as receive
but not at the same time.
When one device is sending other can only receive and vice-
versa (as shown in figure above.)
Example: A walkie-talkie.
1.5.3 Full Duplex
Figure: Full Duplex Mode of Communication
In Full duplex mode, both stations can transmit and receive
at the same time.
Example: mobile phones
1.6 COMPUTER NETWORK
Computer Networks are used for data communications
Definition:
A computer network can be defined as a collection of nodes.
A node can be any device capable of transmitting or
receiving data.
The communicating nodes have to be connected by
communication links.
A Compute network should ensure
reliability of the data communication process, should c
security of the data

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performance by achieving higher throughput and smaller
delay times
1.6.1 Categories of Network
Networks are categorized on the basis of their size. The
three basic categories of computer networks are:
A.Local Area Networks (LAN) is usually limited to a few
kilometers of area. It may be privately owned and could be
a network inside an office on one of the floor of a building
or a LAN could be a network consisting of the computers in
a entire building.
B.Wide Area Network (WAN) is made of all the networks in a
(geographically) large area. The network in the entire state
of Maharashtra could be a WAN
C.Metropolitan Area Network (MAN) is of size between
LAN & WAN. It is larger than LAN but smaller than WAN. It
may comprise the entire network in a city like Mumbai.
1.7 PROTOCOL
A Protocol is one of the components of a data
communications system. Without protocol communication
cannot occur. The sending device cannot just send the data
and expect the receiving device to receive and further
interpret it correctly.
When the sender sends a message it may consist of text,
number, images, etc. which are converted into bits and
grouped into blocks to be transmitted and often certain
additional information called control information is also
added to help the receiver interpret the data.
For successful communication to occur, the sender and
receiver must agree upon certain rules called protocol.
A Protocol is defined as a set of rules that governs data
communications.
A protocol defines what is to be communicated, how it is to
be communicated and when it is to be communicated.
1.7.1 Elements of a Protocol
There are three key elements of a protocol:

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A. Syntax
It means the structure or format of the data.
It is the arrangement of data in a particular order.
B. Semantics
It tells the meaning of each section of bits and
indicates the interpretation of each section.
It also tells what action/decision is to be taken based
on the interpretation.
C. Timing
It tells the sender about the readiness of the receiver to
receive the data
It tells the sender at what rate the data should be sent
to the receiver to avoid overwhelming the receiver.
1.7 STANDARDS IN NETWORKING
Standards are necessary in networking to ensure
interconnectivity and interoperability between various
networking hardware and software components.
Without standards we would have proprietary products
creating isolated islands of users which cannot interconnect.
1.7.1 Concept of Standard
Standards provide guidelines to product manufacturers and
vendors to ensure national and international
interconnectivity.
Data communications standards are classified into two
categories:
1. De facto Standard
o These are the standards that have been traditionally
used and mean by fact or by convention
o These standards are not approved by any organized
body but are adopted by widespread use.
2. De jure standard
o It means by law or by regulation.
o These standards are legislated and approved by
an body that is officially recognized.
1.7.2 Standard Organizations in field of Networking

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oStandards are created by standards creation committees,
forums, and government regulatory agencies.
oExamples of Standard Creation Committees :
1. International Organization for Standardization(ISO)
2. International Telecommunications Union –
Telecommunications Standard (ITU-T)
3. American National Standards Institute (ANSI)
4. Institute of Electrical & Electronics Engineers
(IEEE)
5. Electronic Industries Associates (EIA)
o Examples of Forums
1. ATM Forum
2. MPLS Forum
3. Frame Relay Forum
o Examples of Regulatory Agencies:
1. Federal Communications Committee (FCC)
1.8 REVIEW QUESTIONS
1. Differentiate between data & information. What are the different
forms in which data can be represented?
2. What are the characteristics of data communication?
3. What are the components of a data communication system?
4. Define computer network and categorize.
5. Explain protocols in details
1.9 REFERENCES
1. Data Communication & Networking – Behrouz Forouzan
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Unit 1 Introduction to data
communications and networking
2
Signals
Unit Structure
2.0 Objectives
2.1 Introduction
2.2 Data & Signals
2.2.1 Data –types
2.2.2 Signal – types
2.2.3 Periodic & Non Periodic Signals
2.3 Analog Signal
2.3.1 Characteristics of Analog Signal
2.3.1.1 Peak Amplitude
2.3.1.2 Frequency
2.3.1.3 Phase
2.3.2 Relation between Frequency & Period
2.3.3 Wavelength
2.3.4 Time & Frequency Domain Representation of a signal
2.3.5 Composite Signal
2.4 Digital Signal
2.4.1 Definition
2.4.2 Level
2.4.3 Bit lenght or Bit Interval
2.4.4 Bit Rate
2.4.5 Baud Rate
2.5 Types of Channel
2.5.1 Lowpass Channel
2.5.2 Bandpass Channel
2.6 Transmission of Digital signal
2.6.1 Baseband Transmission
2.6.2 Broadband Transmission
2.8 References

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2.0 OBJECTIVES
 Introduce the readers to fundamentals of data & signal
 Types of data & signal
 Characteristics and nature of analog & digital signal
 Representation of signal
 Transmission of digital signals
2.1 INTRODUCTION
Computer networks are designed to transfer data from one
point to another. During transit data is in the form of
electromagnetic signals. Hence it is important to study data and
signals before we move to further concepts in data communication.
2.2 DATA & SIGNALS
To be transmitted, data must be transformed to
electromagnetic signals.
2.2.1. Data can be Analog or Digital.
1. Analog data refers to information that is continuous; ex.
sounds made by a human voice
2. Digital data refers to information that has discrete states.
Digital data take on discrete values.
3. For example, data are stored in computer memory in the
form of Os and 1s
2.2.2. Signals can be of two types:
1. Analog Signal: They have infinite values in a range.
2. Digital Signal: They have limited number of defined
values
Figure: a. Analog Signal b. Digital Signal*
2.2.3. Periodic & Non Periodic Signals

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Signals which repeat itself after a fixed time period are called
Periodic Signals.
Signals which do not repeat itself after a fixed time period
are called Non-Periodic Signals.
In data communications, we commonly use periodic
analog signals and non-periodic digital signals.
2.3 ANALOG SIGNAL
An analog signal has infinitely many levels of intensity over a
period of time.
As the wave moves from value A to value B, it passes
through and includes an infinite number of values along its
path as it can be seen in the figure below.
A simple analog signal is a sine wave that cannot be further
decomposed into simpler signals.
Fig. Sine wave
A sine wave is characterized by three parameters:
1. Peak Amplitude
2. Frequency
3. Phase
2.3.1 Characteristics of an Analog Signal
2.3.1.1 Peak Amplitude
The amplitude of a signal is the absolute value of its
intensity at time t
The peak amplitude of a signal is the absolute value of
the highest intensity.

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The amplitude of a signal is proportional to the energy
carried by the signal
Fig. Amplitude of a sine wave
2.3.1.2. Frequency
Frequency refers to the number of cycles completed by the
wave in one second.
Period refers to the time taken by the wave to complete one
second.
Fig: Frequency & Period of a sine wave

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2.3.1.3. Phase
Phase describes the position of the waveform with respect to time
(specifically relative to time O).
Fig: Phase of a sine wave*
Phase indicates the forward or backward shift of the
waveform from the axis
It is measured in degrees or radian
The figure above shows the sine waves with same amplitude
and frequency but different phases
2.3.2 Relation between Frequency & Period
Frequency & Period are inverse of each other.
It is indicated by the following formula:

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Example1. A wave has a frequency of 100hz. Its period(T) is given
by
T = 1/ F = 1/ 100 = 0.01 sec
Example2. A wave completes its one cycle in 0.25 seconds. Its
frequency is given by
F = 1 / T = 1 / 0.25 = 4 Hz
2.3.3 Wavelength
The wavelength of a signal refers to the relationship between
frequency (or period) and propagation speed of the wave
through a medium.
The wavelength is the distance a signal travels in one
period.
It is given by
Wavelength = Propagation Speed X Period
OR
Wavelength =Propagation Speed X 1 a
Frequency
It is represented by the symbol : λ (pronounced as lamda)
It is measured in micrometers
It varies from one medium to another.
2.3.4. Time Domain and Frequency domain representation of
signals
A sine wave can be represented either in the time domain or
frequency domain.
The time-domain plot shows changes in signal amplitude
with respect to time. It indicates time and amplitude relation
of a signal.
The frequency-domain plot shows signal frequency and
peak amplitude.
The figure below show time and frequency domain plots of
three sine waves.

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Fig: Time domain and frequency domain plots of three sine
waves*
A complete sine wave in the time domain can be
represented by one single spike in the frequency domain
2.3.5. Composite Signal
A composite signal is a combination of two or more simple
sine waves with different frequency, phase and amplitude.
If the composite signal is periodic, the decomposition gives a
series of signals with discrete frequencies; if the composite
signal is non-periodic, the decomposition gives a
combination of sine waves with continuous frequencies.
Fig: A Composite signal with three component signals

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For data communication a simple sine wave is not useful,
what is used is a composite signal which is a combination of
many simple sine waves.
According to French Mathematician, Jean Baptist, any
composite signal is a combination of simple sine waves with
different amplitudes and frequencies and phases.
Composite signals can be periodic or non periodic.
A periodic composite signal can be decomposed into a
series of signals with discrete frequencies.
A non-periodic signal when decomposed gives a
combination of sine waves with continuous frequencies.
Fig The time and frequency domains of a non-periodic
composite analog signal
2.4 Digital Signal
Information can also be explained in the form of a digital
signal.
A digital signal can be explained with the help of following
points:
2.4.1 Definition:-
A digital is a signal that has discrete values.
The signal will have value that is not continuous.
2.4.2 LEVEL
Information in a digital signal can be represented in the
form of voltage levels.
Ex. In the signal shown below, a ‗1‘ is represented by a
positive voltage and a ‗0‘ is represented by a Zero voltage.

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Fig: A digital signal with Two levels. „1‟ represented by a
positive voltage and „0‟ represented by a negative voltage
A Signal can have more than two levels
11 10 01 00 00 01 10 10
LEVEL
4
LEVEL
3
LEVEL
2
LEVEL
1
Fig: A digital signal with four levels
In general, if a signal has L levels then, each level need
Log2L bits
Example: Consider a digital Signal with four levels, how
many bits are required per level?
Answer: Number of bits per level = Log2L
= Log24
= 2
Hence, 2 bits are required per level for a signal with four
levels.
2.4.3 BIT LENGTH or Bit Interval (Tb)
It is the time required to send one bit.
It is measured in seconds.

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2.4.4 BIT RATE
It is the number of bits transmitted in one second.
It is expressed as bits per second (bps).
Relation between bit rate and bit interval can be as follows
Bit rate = 1 / Bit interval
2.4.5 Baud Rate
It is the rate of Signal Speed, i.e the rate at which the signal
changes.
A digital signal with two levels ‗0‘ & ‗1‘ will have the same
baud rate and bit rate & bit rate.
The diagram below shows three signal of period (T) 1
second
a) Signal with a bit rate of 8 bits/ sec and baud rate of 8
baud/sec
b) Signal with a bit rate of 16 bits/ sec and baud rate of 8
baud/sec
c) Signal with a bit rate of 16 bits/ sec and baud rate of 4
baud/sec
Fig: Three signals with different bit rates and baud rates

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2.5 TYPES OF CHANNELS:
Each composite signal has a lowest possible(minimum)
frequency and a highest possible (maximum) frequency.
From the point of view of transmission, there are two types of
channels:
2.5.1 Low pass Channel
This channel has the lowest frequency as ‗0‘ and highest
frequency as some non-zero frequency ‗f1‘.
This channel can pass all the frequencies in the range 0 to f1.
2.5.2 Band pass channel
This channel has the lowest frequency as some non-zero
frequency ‗f1‘ and highest frequency as some non-zero
frequency ‗f2‘.
This channel can pass all the frequencies in the range f1 to f2.
Fig: Lowpass Channel & Bandpass Channel
2.6 Transmission of Digital signal
Digital signal can be transmitted in the following two ways:
2.6.1 Baseband Transmission
The signal is transmitted without making any change to it
(ie. Without modulation)

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In baseband transmission, the bandwidth of the signal to
be transmitted has to be less than the bandwidth of the
channel.
Ex. Consider a Baseband channel with lower frequency
0Hz and higher frequency 100Hz, hence its bandwidth is
100 (Bandwidth is calculated by getting the difference
between the highest and lowest frequency).
We can easily transmit a signal with frequency below
100Hz, such a channel whose bandwidth is more than
the bandwidth of the signal is called Wideband channel
Logically a signal with frequency say 120Hz will be
blocked resulting in loss of information, such a channel
whose bandwidth is less than the bandwidth of the signal
is called Narrowband channel
2.6.2 Broad band Transmission
Given a bandpass channel, a digital signal cannot be
transmitted directly through it
In broadband transmission we use modulation, i.e we
change the signal to analog signal before transmitting it.
The digital signal is first converted to an analog signal,
since we have a bandpass channel we cannot directly
send this signal through the available channel. Ex.
Consider the bandpass channel with lower frequency
50Hz and higher frequency 80Hz, and the signal to be
transmitted has frequency 10Hz.
To pass the analog signal through the bandpass channel,
the signal is modulated using a carrier frequency. Ex.
The analog signal (10Hz) is modulated by a carrier
frequency of 50Hz resulting in an signal of frequency
60Hz which can pass through our bandpass channel.
The signal is demodulated and again converted into an
digital signal at the other end as shown in the figure
below.

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Fig: Broadband Transmission Involving Modulation &
Demodulation
1. Define analog and digital signals
2. Explain Composite analog signals.
3. Explain Time and Frequency Domain Representation of
signals
4. Explain the characteristics of an Analog signal
5. Explain the characteristics of an Digital signal
6. Explain the difference between
1. Lowpass and Bandpass channel
2. Narrowband and wideband channel
7. Explain why a digital signal requires to undergo a change
before transmitting it through a bandpass channel.
2.8 REFERENCES & FURTHER READING
Data Communication & Networking – Behrouz Forouzan
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3
BANDWIDTH
Unit Structure
3.0 Objectives
3.1 Introduction
3.2 Fourier Analysis
3.3 Bandwidth of a signal
3.3.1 Bandwidth of an analog signal
3.3.2 Bandwidth of a digital signal
3.4 Bandwidth of a channel
3.5 The Maximum Data Rate of a Channel
3.5.1 Nyquist Bit Rate
3.5.2 Shanno Capacity
3.7 References & Further Reading
3.0 OBJECTIVES
To understand
 Concept of bandwidth
 Bandwidth of Analog signal
 Bandwidth of Digital signal
 Bandwidth of Channel
 Maximum Data rate of a channel : noisy & noiseless
3.1 INTRODUCTION
This chapter gives insights to the concept of bandwidth. It
tells about bandwidth of signal and medium. Also explains how to
calculate the bandwidth for a noisy and noiseless channel
3.2 FOURIER ANALYSIS
In the 19th
century, French mathematician Jean-Baptiste
Fourier proved that any composite signal is a combination of
simple sine waves with different frequencies, amplitudes,
and phases.

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A Composite signal can be periodic as well as non periodic.
A periodic composite signal when decomposed gives a
series of simple sine waves with discrete frequencies i.e.
frequencies that have integer values (1, 2, 3, etc).
A non-periodic composite signal when decomposed gives a
combination of an infinite number of simple sine waves with
continuous frequencies i.e. frequencies that have real
values.
3.3 BANDWIDTH OF A SIGNAL
Bandwidth can be defined as the portion of the
electromagnetic spectrum occupied by the signal
It may also be defined as the frequency range over which a
signal is transmitted.
Different types of signals have different bandwidth. Ex. Voice
signal, music signal, etc
Bandwidth of analog and digital signals are calculated in
separate ways; analog signal bandwidth is measured in
terms of its frequency (hz) but digital signal bandwidth is
measured in terms of bit rate (bits per second, bps)
Bandwidth of signal is different from bandwidth of the
medium/channel
3.3.1 Bandwidth of an analog signal
Bandwidth of an analog signal is expressed in terms of its
frequencies.
It is defined as the range of frequencies that the composite
analog signal carries.
It is calculated by the difference between the maximum
frequency and the minimum frequency.
Consider the signal shown in the diagram below:

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Fig: Bandwidth of a signal in time domain and frequency
domain
The signal shown in the diagram is an composite analog
signal with many component signals.
It has a minimum frequency of F1 = 30Hz and maximum
frequency of F2 = 90Hz.
Hence the bandwidth is given by F2 – F1 = 90 – 30 = 60 Hz
3.3.2 Bandwidth of a digital signal
It is defined as the maximum bit rate of the signal to be
transmitted.
It is measured in bits per second.

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3.4 BANDWIDTH OF A CHANNEL
A channel is the medium through which the signal carrying
information will be passed.
In terms of analog signal, bandwidth of the channel is the
range of frequencies that the channel can carry.
In terms of digital signal, bandwidth of the channel is the
maximum bit rate supported by the channel. i.e. the
maximum amount of data that the channel can carry per
second.
The bandwidth of the medium should always be greater than
the bandwidth of the signal to be transmitted else the
transmitted signal will be either attenuated or distorted or
both leading in loss of information.
The channel bandwidth determines the type of signal to be
transmitted i.e. analog or digital.
3.5 THE MAXIMUM DATA RATE OF A CHANNEL
Data rate depends on three factors:
1. The bandwidth available
2. The level of the signals we use
3. The quality of the channel (the level of noise)
The quality of the channel indicates two types:
a) A Noiseless or Perfect Channel
An ideal channel with no noise.
The Nyquist Bit rate derived by Henry Nyquist
gives the bit rate for a Noiseless Channel.
b) A Noisy Channel
A realistic channel that has some noise.
The Shannon Capacity formulated by Claude
Shannon gives the bit rate for a Noisy Channel
3.5.1 Nyquist Bit Rate
The Nyquist bit rate formula defines the theoretical maximum
bit rate for a noiseless channel
Bitrate = 2 x Bandwidth x Log2 L

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Where,
Bitrate is the bitrate of the channel in bits per second
Bandwidth is the bandwidth of the channel
L is the number of signal levels.
Example
What is the maximum bit rate of a noiseless channel with a
bandwidth of 5000 Hz transmitting a signal with two signal
levels.
Solution:
The bit rate for a noiseless channel according to Nyquist Bit
rate can be calculated as follows:
BitRate = 2 x Bandwidth x Log2 L
= 2 x 5000 x log2 2 =10000 bps
3.5.2 Shannon Capacity
The Shannon Capacity defines the theoretical maximum bit
rate for a noisy channel
Capacity=bandwidth X log2 (1 +SNR)
Where,
Capacity is the capacity of the channel in bits per
second
Bandwidth is the bandwidth of the channel
SNR is the Signal to Noise Ratio
Shannon Capacity for calculating the maximum bit rate for a
noisy channel does not consider the number of levels of the
signals being transmitted as done in the Nyquist bit rate.
Example:
Calculate the bit rate for a noisy channel with SNR 300 and
bandwidth of 3000Hz
Solution:
The bit rate for a noisy channel according to Shannon
Capacity can be calculated as follows:
Capacity=bandwidth X log2 (1 +SNR)
= 3000 x log2 (1 + 300)
= 3000 x log2 ( 301)
= 3000 x 8.23
= 24,690bps

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1. Explain the term bandwidth of a signal
2. Explain the term bandwidth of a channel.
3. Write short note on maximum data rate of a channel.
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4
NETWORK MODELS
Unit Structure
4.0 Objectives
4.1 Introduction
4.2 Concept of Layered task
4.3 OSIRM
4.3.1 Introduction to OSI Model & its layers
4.3.2 Layered Architecture of OSI Model
4.3.3 Communication & Interfaces
4.3.4 Encapsulation of Data
4.3.5 Description of Layers in the OSI Model
4.4 Summary
4.0 OBJECTIVES
 Understand concept of dividing a job into layered tasks
 Get introduced to the OSIRM
 Understand the functions of the various layers of the OSI
Mode.
4.1 INTRODUCTION
In the study of computer networks it is essential to study the
way our networks work. Computer networks are operated by
network models; most prominently the OSIRM and the TCP/ IP
Model. This chapter gives the understanding of the OSI reference
model.
4.2 CONCEPT OF LAYERED TASK
i. The main objective of a computer network is to be able to
transfer the data from sender to receiver. This task can be
done by breaking it into small sub tasks, each of which are
well defined.

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ii. Each subtask will have its own process or processes to do
and will take specific inputs and give specific outputs to the
subtask before or after it. In more technical terms we can call
these sub tasks as layers.
iii. In general, every task or job can be done by dividing it into
sub task or layers. Consider the example of sending a letter
where the sender is in City A and receiver is in city B.
iv. The process of sending letter is shown below:
Fig: Concept of layer task: sending a letter
v. The above figure shows
a. Sender, Receiver & Carrier
b. Hierarchy of layers
vi. At the sender site, the activities take place in the following
descending order:
a. Higher Layer: The sender writes the letter along with the
sender and receivers address and put it in an envelope
and drop it in the mailbox.
b. Middle Layer: The letter is picked up by the post man and
delivered to the post office
c. Lower Layer: The letters at the post office are sorted and
are ready to be transported through a carrier.

31
vii. During transition the letter may be carried by truck, plane or
ship or a combination of transport modes before it reaches
the destination post office.
viii. At the Receiver site, the activities take place in the following
ascending order:
a. Lower Layer: The carrier delivers the letter to the
destination post office
b. Middle Layer: After sorting, the letter is delivered to the
receivers mail box
c. Higher Layer: The receiver picks up the letter, opens the
envelope and reads it.
ix. Hierarchy of layers: The activities in the entire task are
organized into three layers. Each activity at the sender or
receiver side occurs in a particular order at the hierarchy.
x. The important and complex activities are organized into the
Higher Layer and the simpler ones into middle and lower
layer.
4.3 OPEN SYSTEMS INTER CONNECTION
REFERENCE MODEL (OSIRM )
4.3.1 Introduction to OSI Model & its layers
The Open Systems Interconnection (OSI) Model was
developed by International Organization for
Standardization (ISO).
ISO is the organization, OSI is the model
It was developed to allow systems with different platforms
to communicate with each other. Platform could mean
hardware, software or operating system.
It is a network model that defines the protocols for
network communications.
It is a hierarchical model that groups its processes into
layers. It has 7 layers as follows: (Top to Bottom)
1. Application Layer
2. Presentation Layer
3. Session Layer
4. Transport Layer
5. Network Layer
6. Data Link Layer
7. Physical Layer
Each layer has specific duties to perform and has to co-
operate with the layers above and below it.

32
4.3.2 Layered Architecture of OSI Model
The OSI model has 7 layers each with its own dedicated
task.
A message sent from Device A to Device B passes has to
pass through all layers at A from top to bottom then all layers
at B from bottom to top as shown in the figure below.
At Device A, the message is sent from the top layer i.e
Application Layer A then all the layers till it reaches its
physical layer and then it is transmitted through the
transmission medium.
At Device B, the message received by the physical layer
passes through all its other layers and moves upwards till it
reaches its Application Layer.
Fig: Flow of Data from Device A to Device B through various
layers
As the message travels from device A to device B, it may
pass through many intermediate nodes. These intermediate
nodes usually involve only the first three layers of the OSI
model as shown below.

33
Fig: Data Transfer through Intermediate nodes
The Data Link layer determines the next node where the
message is supposed to be forwarded and the network layer
determines the final recipient.
4.3.3 Communication & Interfaces
For communication to occur, each layer in the sending
device adds its own information to the message it receives
from the layer just above it and passes the whole package to
the layer just below it. Each layer in the receiving device
removes the information added at the corresponding layer
and sends the obtained data to the layer above it.
Every Layer has its own dedicated function or services and
is different from the function of the other layers.
On every sending device, each layer calls upon the service
offered by the layer below it.
On every receiving device, each layer calls upon the service
offered by the layer above it.
Between two devices, the layers at corresponding levels
communicate with each other .i.e layer 2 at receiving end
can communicate and understand data from layer 2 of
sending end. This is called peer –to – peer communication.
For this communication to be possible between every two
adjacent layers there is an interface. An interface defines the
service that a layer must provide. Every layer has an
interface to the layer above and below it as shown in the
figure below

34
Fig: Communication & Interfaces in the OSI model
4.3.4 Encapsulation of Data
Fig: Encapsulation

35
As shown in the figure above the data at layer 7 i.e the
Application layer along with the header added at layer 7 is
given to layer 6, the Presentation layer. This layer adds Its
header and passed the whole package to the layer below.
The corresponding layers at the receiving side removes the
corresponding header added at that layer and sends the
remaining data to the above layer.
The above process is called encapsulation
4.3.5 Description of Layers in the OSI Model
4.3.5.1 Physical Layer
I. The Physical Layer provides a standardized interface to
physical transmission media, including :
a. Mechanical specification of electrical connectors
and cables, for example maximum cable length
b. Electrical specification of transmission line
c. Bit-by-bit or symbol-by-symbol delivery
II. On the sender side, the physical layer receives the data from
Data Link Layer and encodes it into signals to be transmitted
onto the medium. On the receiver side, the physical layer
receives the signals from the transmission medium decodes
it back into data and sends it to the Data Link Layer as
shown in the figure below:
Fig: Transmission of data to and from Physical Layer
III. Interface
The Physical Layer defines the characteristics of interfaces
between the devices & transmission medium.

36
IV. Representation of bits
The physical layer is concerned with transmission of signals
from one device to another which involves converting data
(1‘s & 0‘s) into signals and vice versa. It is not concerned
with the meaning or interpretation of bits.
V. Data rate
The physical layer defines the data transmission rate i.e.
number of bits sent per second. It is the responsibility of the
physical layer to maintain the defined data rate.
VI. Synchronization of bits
To interpret correct and accurate data the sender and
receiver have to maintain the same bit rate and also have
synchronized clocks.
VII. Line configuration
The physical layer defines the nature of the connection .i.e. a
point to point link, or a multi point link.
VIII. Physical Topology
The physical layer defines the type of topology in which the
device is connected to the network. In a mesh topology it
uses a multipoint connection and other topologies it uses a
point to point connection to send data.
IX. Transmission mode
The physical layer defines the direction of data transfer
between the sender and receiver. Two devices can transfer
the data in simplex, half duplex or full duplex mode
X. Main responsibility of the physical layer
Transmission of bits from one hop to the next.
4.3.5.2 Data Link Layer
I. The Data Link layer adds reliability to the physical layer by
providing error detection and correction mechanisms.
II. On the sender side, the Data Link layer receives the data
from Network Layer and divides the stream of bits into
fixed size manageable units called as Frames and sends
it to the physical layer. On the receiver side, the data link
layer receives the stream of bits from the physical layer
and regroups them into frames and sends them to the
Network layer. This process is called Framing. It is
shown in the figure below:

37
Fig: Data Link Layer: The process of Framing
III. Physical Addressing (inside / outside senders
network)
a. The Data link layer appends the physical address in
the header of the frame before sending it to physical
layer.
b. The physical address contains the address of the
sender and receiver.
c. In case the receiver happens to be on the same
physical network as the sender; the receiver is at only
one hop from the sender and the receiver address
contains the receiver‘s physical address.
d. In case the receiver is not directly connected to the
sender, the physical address is the address of the
next node where the data is supposed to be
delivered.
IV. Flow control
a. The data link layer makes sure that the sender
sends the data at a speed at which the receiver can
receive it else if there is an overflow at the receiver
side the data will be lost.
b. The data link layer imposes flow control mechanism
over the sender and receiver to avoid overwhelming
of the receiver.
V. Error control
a. The data link layer imposes error control mechanism
to identify lost or damaged frames, duplicate frames
and then retransmit them.
b. Error control information is present in the trailer of a
frame.

38
VI. Access Control
a. The data link layer imposes access control
mechanism to determine which device has right to
send data in an multipoint connection scenario.
VII. Main Responsibility
i. The main responsibility of the data link layer is hop to
hop transmission of frames.
4.3.5.3 Network Layer
I. The network layer makes sure that the data is delivered to
the receiver despite multiple intermediate devices.
II. The network layer at the sending side accepts data from the
transport layer, divides it into packets, adds addressing
information in the header and passes it to the data link layer.
At the receiving end the network layer receives the frames
sent by data link layer, converts them back into packets,
verifies the physical address (verifies if the receiver address
matches with its own address) and the send the packets to
the transport layer.
Fig: Network Layer
III. The network layer is responsible for source to destination of
delivery of data. Hence it may have to route the data through
multiple networks via multiple intermediate devices. In order
to achieve this the network layer relies on two things:
a. Logical Addressing
b. Routing
IV. Logical Addressing
The network layer uses logical address commonly known
as IP address to recognize devices on the network.

39
An IP address is a universally unique address which
enables the network layer to identify devices outside the
sender‘s network.
The header appended by the network layer contains the
actual sender and receiver IP address.
At every hop the network layer of the intermediate node
check the IP address in the header, if its own IP address
does not match with the IP address of the receiver found
in the header, the intermediate node concludes that it is
not the final node but an intermediate node and passes
the packet to the data link layer where the data is
forwarded to the next node.
V. Routing
VI. The network layer divides data into units called
packets of equal size and bears a sequence number for
rearranging on the receiving end.
Each packet is independent of the other and may travel
using different routes to reach the receiver hence may
arrive out of turn at the receiver.
Hence every intermediate node which encounters a
packet tries to compute the best possible path for the
packet. The best possible path may depend on several
factors such as congestion, number of hops, etc
This process of finding the best path is called as Routing.
It is done using routing algorithms.
VI. The Network layer does not perform any flow control or error
control
The main responsibility of Network Layer is
transmission of packets from source to destination
4.3.5.4 Transport Layer
I. A logical address at network layer facilitates the
transmission of data from source to destination device.
But the source and the destination both may be having
multiple processes communicating with each other.
Hence it is important to deliver the data not only from
the sender to the receiver but from the correct process
on the sender to the correct process on the receiver.
The transport layer takes care of process to process
delivery of data and makes sure that it is intact and in
order.

40
II. At the sending side, the transport layer receives data
from the session layer, divides it into units called
segments and sends it to the network layer. At the
receiving side, the transport layer receives packets
from the network layer, converts and arranges into
proper sequence of segments and sends it to the
session layer.
Fig: Transport Layer
III. To ensure process to process delivery the transport
layer makes use of port address to identify the data
from the sending and receiving process. A Port
Address is the name or label given to a process. It is a
16 bit address. Ex. TELNET uses port address 23,
HTTP uses port address 80. Port address is also
called as Service Point Address
IV. The data can be transported in a connection oriented
or connectionless manner. If the connection is
connection oriented then all segments are received in
order else they are independent of each other and are
received out of order and have to be rearranged.
V. The Transport layer is responsible for segmentation
and reassembly of the message into segments which
bear sequence numbers. This numbering enables the
receiving transport layer to rearrange the segments in
proper order.
VI. Flow Control & Error control: the transport layer also
carries out flow control and error control functions; but
unlike data link layer these are end to end rather than
node to node.

41
The main responsibility of the transport layer is
process to process delivery of the entire message.
4.3.5.5 Session Layer
I. The session layer establishes a session between the
communicating devices called dialog and
synchronizes their interaction. It is the responsibility of
the session layer to establish and synchronize the
dialogs. It is also called the network dialog controller.
II. The session layer at the sending side accepts data
from the presentation layer adds checkpoints to it
called syn bits and passes the data to the transport
layer. At the receiving end the session layer receives
data from the transport layer removes the checkpoints
inserted previously and passes the data to the
presentation layer.
III. The checkpoints or synchronization points is a way of
informing the status of the data transfer. Ex. A
checkpoint after first 500 bits of data will ensure that
those 500 bits are not sent again in case of
retransmission at 650th
bit.
IV. Main responsibility of session layer is dialog
control and synchronizatoin
4.3.5.6 Presentation Layer
I. The communicating devices may be having different
platforms. The presentation layer performs translation,
encryption and compression of data.

42
II. The presentation layer at sending side receives the data
from the application layer adds header which contains
information related to encryption and compression and
sends it to the session layer. At the receiving side, the
presentation layer receives data from the session layer
decompresses and decrypts the data as required and
translates it back as per the encoding scheme used at the
receiver.
Fig : Presentation Layer
III. Translation
The sending and receiving devices may run on different
platforms (hardware, software and operating system). Hence
it is important that they understand the messages that are
used for communicating. Hence a translation service may be
required which is provided by the Presentation layers
IV. Compression
Compression ensures faster data transfer. The data
compressed at sender has to be decompressed at the
receiving end, both performed by the Presentation layer.
V. Encryption
It is the process of transforming the original message to
change its meaning before sending it. The reverse process
called decryption has to be performed at the receiving end to
recover the original message from the encrypted message.
VI. Main responsibility
The main responsibility of the Presentation layer is
translation, compression and encryption.
4.3.5.7Application Layer
I. The application layer enables the user to
communicate its data to the receiver by providing

43
certain services. For ex. Email is sent using X.400
service.
Fig : Application Layer
II. X500 is a directory service used to provide
information and access to distributed objects
III. X400 is services that provides basis for mail storage
and forwarding
IV. FTAM (File transfer, access and management)
provides access to files stored on remote computers
and mechanism for transfer and manage them locally.
V. Main Responsibility
Main Responsibility of Application layer is to provide
access to network resources.
4.4 SUMMARY
The responsibilities of the 7 layers of OSI model can be
summarized as follows:
1. Application Layer : To provide the users access to network
resources
2. Presentation Layer: To provide the functions of translation,
encryption and compression.
3. Session Layer: To establish, manage and terminate sessions

44
4. Transport Layer: To provide process to process delivery of
message
5. Network Layer: To provide source to destination delivery of
packets.
6. Datalink Layer: To provide hop to hop delivery of frames
7. Physical Layer: To transmit data over a bit stream from one hop
to the next and provide electrical and mechanical
specification.
1. Explain the concept of layered task.
2. What is the OSI model? List its layers and explain their
responsibility in exactly one line.
3. Explain how the communication takes place between layers
of OSI model.
4. Write a short note on encapsulation of data in OSI model.
5. Differentiate between the working of Data link layer, Network
layer and Transport layer.
4.6 REFERENCE & FURTHER READING
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5
TCP/IP MODEL, ADDRESSING IN
TCP/IP – IPV4
Unit Structure
5.0 Objectives
5.1 Introduction
5.2 TCP/IP Model,
5.3 Addressing In TCP/IP
5.4 IPv4
5.4.1 IP addresses
5.4.2 Address Space
5.4.3 Notations used to express IP address
5.4.4 Classfull Addressing
5.4.5 Subnetting
5.4.6 CIDR
5.4.7 NAT
5.4.8 IPv4 Header Format
5.5 Summary
5.0 OBJECTIVES
 Understand the basics of TCP/IP model
 Understand the functions of the different layers and
protocols involved
 Understand the Addressing mechanisms used under the
TCP/IP
 Understand IPv4 and importantly IP address and IP
header format
5.1 INTRODUCTION
After an understand of the concept of layered task and then
understanding the OSI model we introduce the TCP/IP model. This
model is currently being used on our systems. TCP/IP model is a
collection of protocols often called a protocol suite. It offers a rich
variety of protocols from which we can choose from.

46
5.2 TCP/IP MODEL
It is also called as the TCP/IP protocol suite. It is a collection
of protocols.
IT is a hierarchical model, ie. There are multiple layers and
higher layer protocols are supported by lower layer
protocols.
It existed even before the OSI model was developed.
Originally had four layers (bottom to top):
1. Host to Network Layer
2. Internet Layer
3. Transport Layer
4. Application Layer
The figure for TCP/IP model is as follows:
Application
Transport
Network or IP
Host to Network
Fig: Layers of TCP/IP Reference Model
The structure TCP/IP model is very similar to the structure of
the OSI reference model. The OSI model has seven layers
where the TCP/IP model has four layers.
The Application layer of TCP/IP model corresponds to the
Application Layer of Session, Presentation & Application
Layer of OSI model.
The Transport layer of TCP/IP model corresponds to the
Transport Layer of OSI model
The Network layer of TCP/IP model corresponds to the
Network Layer of OSI model
The Host to network layer of TCP/IP model corresponds to
the Physical and Datalink Layer of OSI model.
The diagram showing the comparison of OSI model and
TCP/IP model along with the protocols is as shown below:

47
Fig: Comparison of OSI model and TCP/IP model
Functions of the Layers of TCP/IP model:
A. Host to Network Layer
This layer is a combination of protocols at the physical and
data link layers.
It supports all standard protocols used at these layers.
B. Network Layer or IP
Also called as the Internetwork Layer (IP). It holds the IP
protocol which is a network layer protocol and is
responsible for source to destination transmission of
data.
The Internetworking Protocol (IP) is an connection-less
& unreliable protocol.

48
It is a best effort delivery service. i.e. there is no error
checking in IP, it simply sends the data and relies on its
underlying layers to get the data transmitted to the
destination.
IP transports data by dividing it into packets or
datagrams of same size. Each packet is independent of
the other and can be transported across different routes
and can arrive out of order at the receiver.
In other words, since there is no connection set up
between the sender and the receiver the packets find the
best possible path and reach the destination. Hence, the
word connection-less.
The packets may get dropped during transmission along
various routes. Since IP does not make any guarantee
about the delivery of the data its call an unreliable
protocol.
Even if it is unreliable IP cannot be considered weak and
useless; since it provides only the functionality that is
required for transmitting data thereby giving maximum
efficiency. Since there is no mechanism of error detection
or correction in IP, there will be no delay introduced on a
medium where there is no error at all.
IP is a combination of four protocols:
1. ARP
2. RARP
3. ICMP
4. IGMP
1. ARP – Address Resolution Protocol
I. It is used to resolve the physical address of a device
on a network, where its logical address is known.
II. Physical address is the 48 bit address that is
imprinted on the NIC or LAN card, Logical address is
the Internet Address or commonly known as IP
address that is used to uniquely & universally identify
a device.
2. RARP– Reverse Address Resolution Protocol
I. It is used by a device on the network to find its
Internet address when it knows its physical address.
3. ICMP- Internet Control Message Protocol
I. It is a signaling mechanism used to inform the sender
about datagram problems that occur during transit.

49
II. It is used by intermediate devices.
III. In case and intermediate device like a gateway
encounters any problem like a corrupt datagram it
may use ICMP to send a message to the sender of
the datagram.
4. IGMP- Internet Group Message Protocol
I. It is a mechanism that allows to send the same
message to a group of recipients.
C. Transport Layer
Transport layer protocols are responsible for
transmission of data running on a process of one
machine to the correct process running on another
machine.
The transport layer contains three protocols:
1. TCP
2. UDP
3. SCTP
1. TCP – Transmission Control Protocol
I. TCP is a reliable connection-oriented, reliable
protocol. i.e. a connection is established between the
sender and receiver before the data can be
transmitted.
II. It divides the data it receives from the upper layer into
segments and tags a sequence number to each
segment which is used at the receiving end for
reordering of data.
2. UDP – User Datagram Protocol
I. UDP is a simple protocol used for process to process
transmission.
II. It is an unreliable, connectionless protocol for
applications that do not require flow control or error
control.
III. It simply adds port address, checksum and length
information to the data it receives from the upper
layer.
3. SCTP – Stream Control Transmission Protocol
I. SCTP is a relatively new protocol added to the
transport layer of TCP/IP protocol suite.
II. It combines the features of TCP and UDP.
III. It is used in applications like voice over Internet and
has a much broader range of applications

50
D. Application Layer
I. The Application Layer is a combination of Session,
Presentation & Application Layers of OSI models and
define high level protocols like File Transfer (FTP),
Electronic Mail (SMTP), Virtual Terminal (TELNET),
Domain Name Service (DNS), etc.
5.3 ADDRESSING IN TCP/IP
The TCP/IP protocol suited involves 4 different types of
addressing:
1. Physical Address
2. Logical Address
3. Port Address
4. Specific Address
Fig: Addressing in TCP/IP model
APPLICATION
LAYER
Processes
SPECIFIC
ADDRESS
TRANSPORT
LAYER
TCP UDP SCTP
PORT
ADDRESS
NETWORK
LAYER
IP and other
associated
protocols
LOGICAL
ADDRESS
Protocols of underlying network used
at physical & data link layer
HOST TO
NETWORK
LAYER
PHYSICAL
ADDRESS

51
Each of these addresses are described below:
1. Physical Address
i. Physical Address is the lowest level of addressing, also
known as link address.
ii. It is local to the network to which the device is connected
and unique inside it.
iii. The physical address is usually included in the frame and is
used at the data link layer.
iv. MAC is a type of physical address that is 6 byte (48 bit) in
size and is imprinted on the Network Interface Card (NIC) of
the device.
v. The size of physical address may change depending on the
type of network. Ex. An Ethernet network uses a 6 byte MAC
address.
2. Logical Address
i. Logical Addresses are used for universal communication.
ii. Most of the times the data has to pass through different
networks; since physical addresses are local to the network
there is a possibility that they may be duplicated across
multiples networks also the type of physical address being
used may change with the type of network encountered. For
ex: Ethernet to wireless to fiber optic. Hence physical
addresses are inadequate for source to destination delivery
of data in an internetwork environment.
iii. Logical Address is also called as IP Address (Internet
Protocol address).
iv. At the network layer, device i.e. computers and routers are
identified universally by their IP Address.
v. IP addresses are universally unique.
vi. Currently there are two versions of IP addresses being used:
a. IPv4: 32 bit address, capable of supporting 232
nodes
b. IPv6: 128 bit address, capable of supporting 2128
nodes
3. Port Address
VIII.A logical address facilitates the transmission of data
from source to destination device. But the source and
the destination both may be having multiple processes
communicating with each other.

52
Ex. Users A & B are chatting with each other using
Google Talk, Users B & C are exchanging emails
using Hotmail. The IP address will enable transmitting
data from A to B, but still the data needs to be
delivered to the correct process. The data from A
cannot be given to B on yahoo messenger since A & B
are communicating using Google Talk.
IX. Since the responsibility of the IP address is over here
there is a need of addressing that helps identify the
source and destination processes. In other words, data
needs to be delivered not only on the correct device
but also on the correct process on the correct device.
X. A Port Address is the name or label given to a
process. It is a 16 bit address.
XI. Ex. TELNET uses port address 23, HTTP uses port
address 80
4. Specific Address
i. Port addresses address facilitates the transmission of data
from process to process but still there may be a problem with
data delivery.
For Ex: Consider users A, B & C chatting with each other
using Google Talk. Every user has two windows open, user
A has two chat windows for B & C, user B has two chat
windows for A & C and so on for user C
Now a port address will enable delivery of data from user A
to the correct process ( in this case Google Talk) on user B
but now there are two windows of Google Talk for user A &
C available on B where the data can be delivered.
ii. Again the responsibility of the port address is over here and
there is a need of addressing that helps identify the different
instances of the same process.
iii. Such address are user friendly addresses and are called
specific addresses.
iv. Other Examples: Multiple Tabs or windows of a web browser
work under the same process that is HTTP but are identified
using Uniform Resource Locators (URL), Email
addresses.

53
5.4 IP PROTOCOL – IPV4
Packets in the IPv4 format are called datagram. An IP
datagram consists of a header part and a text part (payload). The
header has a 20-byte fixed part and a variable length optional part.
It is transmitted in big-endian order: from left to right, with the high-
order bit of the Version field going first.
IPv4 can be explained with the help of following points:
1. IP addresses
2. Address Space
3. Notations used to express IP address
4. Classfull Addressing
5. Subnetting
6. CIDR
7. NAT
8. IPv4 Header Format
5.4.1 IP addresses
Every host and router on the Internet has an IP address,
which encodes its network number and host number.
The combination is unique: in principle, no two machines on
the Internet have the same IP address.
An IPv4 address is 32 bits long
They are used in the Source address and Destination
address fields of IP packets.
An IP address does not refer to a host but it refers to a
network interface.
5.4.2 Address Space
An address space is the total number of addresses used by
the protocol. If a protocol uses N bits to define an address,
the address space is 2N
because each bit can have two
different values (0 or 1) and N bits can have 2N
values.
IPv4 uses 32-bit addresses, which means that the address
space is 232
or 4,294,967,296 (more than 4 billion).
5.4.3 Notations
There are two notations to show an IPv4 address:
1. Binary notation
The IPv4 address is displayed as 32 bits.
ex. 11000001 10000011 00011011 11111111

54
2. Dotted decimal notation
To make the IPv4 address easier to read, Internet
addresses are usually written in decimal form with a
decimal point (dot) separating the bytes.
Each byte (octet) is 8 bits hence each number in
dotted-decimal notation is a value ranging from 0 to
255.
Ex. 129.11.11.239
5.4.4 Classful addressing
In classful addressing, the address space is divided into five
classes: A, B, C, D, and E.
Figure: Classful addressing : IPv4
Netid and Hostid
In classful addressing, an IP address in class A, B, or C is
divided into netid and hostid.
These parts are of varying lengths, depending on the class
of the address as shown above.

55
Information on the Number of networks and host in each
class is given below:
The IP address 0.0.0.0 is used by hosts when they are being
booted.
All addresses of the form 127.xx.yy.zz are reserved for
loopback testing, they are processed locally and treated as
incoming packets.
5.4.5 Subnetting
It allows a network to be split into several parts for internal
use but still act like a single network to the outside world.
To implement subnetting, the router needs a subnet mask
that indicates the split between network + subnet number
and host. Ex. 255.255.252.0/22. A‖/22‖ to indicate that the
subnet mask is 22 bits long.
Consider a class B address with 14 bits for the network
number and 16 bits for the host number where some bits are
taken away from the host number to create a subnet
number.
4Fig: A Class B network subnetted into 64 subnets.

56
If 6 bits from the host Id are taken for subnet then available
bits are :
14 bits for network + 6 bits for subnet + 10 bits for host
With 6 bits for subnet the number of possible subnets is 26
which is 64.
With 10 bits for host the number of possible host are 210
which is 1022 (0 & 1 are not available)
5.4.6 CIDR
A class B address is far too large for most organizations and
a class C network, with 256 addresses is too small. This leads to
granting Class B address to organizations who do not require all
the address in the address space wasting most of it.
This is resulting in depletion of Address space.
A solution is CIDR (Classless InterDomain Routing) The
basic idea behind CIDR, is to allocate the remaining IP addresses
in variable-sized blocks, without regard to the classes.
5.4.7 NAT (Network Address Translation)
The scarcity of network addresses in IPv4 led to the
development of IPv6.
IPv6 uses a 128 bit address, hence it has 2128
addresses in
its address space which is larger than 232
addresses
provided by IPv4.
Transition from IPv4 to IPv6 is slowly occurring, but will take
years to complete, because of legacy hardware and its
incompatibility to process IPv6 address.
NAT (Network Address Translation) was used to speed up
the transition process
The only rule is that no packets containing these addresses
may appear on the Internet itself. The three reserved ranges
are:
10.0.0.0 – 10.255.255.255/8 (16,777,216 hosts)
172.16.0.0 – 172.31.255.255/12 (1,048,576 hosts)
192.168.0.0 – 192.168.255.255/16 (65,536 hosts)
Operation:
Within the Organization, every computer has a unique
address of the form 10.x.y.z. However, when a packet
leaves the organization, it passes through a NAT box that
converts the internal IP source address, 10.x.y.z, to the
organizations true IP address, 198.60.42.12 for example.

57
5.4.8 IP Header
Figure: The IPv4 (Internet Protocol) header
The description of the fields shown in the diagram is as
follows:
No Field Name Description
1 Version Keeps track of the version of the protocol the
datagram belongs to (IPV4 or IPv6)
2 IHL Used to indicate the length of the Header.
Minimum value is 5 Maximum value 15
3 Type of service Used to distinguish between different classes
of service
4 Total length It includes everything in the datagram—both
header and data. The maximum length is
65,535 bytes
5 Identification Used to allow the destination host to identify
which datagram a newly arrived fragment
belongs to. All the fragments of a datagram
contain the same Identification value

58
6 DF 1 bit field. It stands for Don't Fragment.
Signals the routers not to fragment the
datagram because the destination is
incapable of putting the pieces back together
again
7 MF MF stands for More Fragments. All fragments
except the last one have this bit set. It is
needed to know when all fragments of a
datagram have arrived.
8 Fragment offset Used to determine the position of the
fragment in the current datagram.
9 Time to live It is a counter used to limit packet lifetimes. It
must be decremented on each hop. When it
hits zero, the packet is discarded and a
warning packet is sent back to the source
host.
10 Header
checksum
It verifies Header for errors.
11 Source address IP address of the source
12 Destination
address
IP address of the destination
13 Options The options are variable length. Originally,
five options were defined:
1. Security : specifies how secret the
datagram is
2. Strict source routing : Gives complete
path to be followed
3. Loose source routing : Gives a list of
routers not to be missed
4. Record route: Makes each router
append its IP address
5. Timestamp: Makes each router
append its IP address and timestamp
5.5 SUMMARY
1. TCP/IP has 4 layers: host to network, IP, Transport & Application
2. It uses 4 levels of address: physical, logical, port & specific

59
3. IP address uniquely identifies a device on the Internet.
6. Explain the structure of TCP/IP protocol
7. Explain in short the functions of every layer of TCP/IP
8. Explain the function of every protocol of the IP layer
9. Explain the concept of IP addresses in detail
10.Why do we use subnetting?
11.What Is NAT? why is it used for?
12.Explain the header of and IPv4 Packet.
5.7 REFERENCE & FURTHER READING
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60
6
INFORMATION ENCODING
Unit Structure
6.0 Objective
6.1 Introduction
6.2 Representing different symbols
6.3 Minimizing Errors
6.4 Multimedia
6.5 Multimedia and Data Compression
6.6 review questions
6.7 References
1. Data Communication & Networking – BehrouzForouzan
6.0 OBJECTIVES
 Introduce representing different symbols
 Introduction to error
 Multimedia
 Sampling
 Quantization
6.1 INTRODUCTION
In communications and information processing, encoding is
the process by which information from a source is converted into
symbols to be communicated.
In computer system we have to use encoding to represent
the Information in the format that computer understand i.e. ―binary‖
language.
Encoding enables us to improve the communication in
places where written languages is difficult to use or impossible.

61
6.2 REPRESENTING DIFFERENT SYMBOLS
In information theory and computer science, a code is
usually considered as an algorithm which uniquely represents
symbols from some source alphabet, by encoded strings, which
may be in some other target alphabet.
The purpose of the symbols is to communicate the idea or
meaning. We use the different symbols to represent the Information
in computer understandable format.
There are different symbols available e.g. in English
language we have 26 capital letters from ―A to Z‖ and same way we
have small letters from ―a to z‖, we have numeric symbols like
(0,1,…9) and special symbols like (!,@,#,$,%,^,&,*, etc.)
6.3 MINIMIZING ERRORS
One way to represent the information is to use sound beep.
The different sound intensities can be utilized to represent the
around 162 different symbols.
Practically we won‘t be able to distinguish between all 162
sound levels. So it will lead to errors in identifying a symbol
correctly. We should follow the representation that minimizes the
errors.
So another way of doing work is just use two states OFF or
ON. With sound beep we get some sound or none at all. When it is
no sound then the value must be 0. When we hear some sound
then value must be 1.
With this beep and no-beep we can represent only two
symbols correctly. We call this system as binary system.
We can have the following table to represent our symbols:
Sound Represented
symbols
Code
No-beep A 0
Beep B 1
We must note that the system which is explained
above, even though the error in representation of symbols is
minimized, is restricted with two symbols. So let us see how to
represent more symbols using the binary system.

62
6.3.1 Representing more symbols:
Now we see what happens when we use two sound devices.
As shown in the following table we get the different combinations
like 00, 01, 10 and 11. And now we can represent four different
symbols.
Sound device
1
Sound
device 2
Represented
symbols
Code
No-beep No-beep A 0 0
No-beep Beep B 0 1
Beep No-beep C 1 0
Beep Beep D 1 1
Thus with the pair of sound devices, we get four ON/OFF
combinations and hence we can represent four symbols.
If we extend the same technique with three sound devices
then we can get eight different codes to represent our symbols like
(000,001,010,011,100,101,110 and 111)
The generalized we can say that with N number of sound
devices we can have 2N
symbols to be represented.
Number of states : 2N
Where N is number of sound devices.
6.4 Multimedia:
Now a day the computers that we use have additional
facilities such as:
1. Drawing, capturing, storing and viewing pictures of different
formats.
2. Recording, storing the sound/songs and playing them back.
3. Capturing, editing, storing the video information and playing them
back.
Since video, pictures are not made of alphabets; we cannot
represent them with the help of the character codes like ASCII
(American Standard Code for Information Interchange) or EBCDIC
(Extended Binary Coded Decimal Interchange Code) etc.
So we use the concept of multimedia in order to code the
picture or videos.
With the help of multimedia technique it‘s possible to use the
computer system to store, play and process the audio, video and
picture information along with the textual data.

63
6.4.1 Pictures/Images:
We can represent the data in the form of Images / Pictures.
Images are represented by the pixels i.e. the smallest element in
the picture.
The basic idea is shown in the following figure:
(a) (b)
Figure (a) shows the computer screen made up of number of
dots (pixels). Figure (b) shows the letter W by illuminating specific
dots.
We can use a large number of pixels for better resolution.
Higher resolution gives better quality to the picture.
When we divide a picture into pixels, each pixel is
represented by a unique pattern.
If Image is black and white then we can use only one bit per
pattern. Bit 1 is used to represent white and bit 0 is used to
represent black.
If the image is having gray shade then we can use 2 bit
pattern to represent each pixel. So 00 is black, 01 is dark gray, 10
is light gray and 11 will represent white.
If the image is colored then it is to be represented by the
pixels that are constituted of the three primary colorsnamely red,
green and blue (RGB).
It means that any picture can be drawn on screen by
illuminating or darkening specific pixels.
We know that computer can understand on binary values (0
and 1). So it is important that the way in which we make computer
understand the concept of pixels.

64
We can consider the coding scheme where illuminated pixel
is considered to be binary 1 and darkened pixel is considered to be
binary 0. We can imagine that any picture that we draw on screen
can be mapped first to a series of pixels. Which in turn, get mapped
to a series of zeros and ones.
We can show this idea in following figure:
Computer screen Computer memory
6.4.2 Video:
Animation is used as a basic technique for creating videos.
We get the animation if we show set of pictures rapidly, the
human eye gets an illusion that the picture is in motion.
The above pictures show the idea behind the video. It shows
the movements of the horse and his rider. If you were shown these
four pictures one after the other very fast, you would believe that
the horse is actually running.
We use the same principle to store pictures in the disk /
memory of the computer in their binary form and show them rapidly
at the rate of 24 such pictures or images per second on the screen.
6.4.3 Sound:
A sound wave in its most basic form continuous in nature. It
is continuous in two aspects:
First, the strength (the amplitude) and time.
A typical sound signal takes the form of sine wave as shown
in following figure:
0 1 0 1 0 1 1 1 1 0 1 0 1 0
1 0 1 1 1 0 1 0 1 1 0 1 1 0
0 1 1 0 1 0 1 0 1 1 1 1 0 1
1 0 0 0 0 1 1 1 0 1 0 1 0 1
0 1 1 1 0 1 0 1 1 0 1 0 1 1
1 1 0 1 0 1 0 1 0 1 1 1 0 1
0 1 1 0 1 1 0 0 1 1 0 1 0 1
0 1 1 1 1 0 1 1 0 0

65
Amplitude
Time
The sound needs to be converted into the digital form in order to
store it in the computer system. Thus if we have to show the zeros
and ones inside a computer‘s memory graphically, then we get the
following figure:
Amplitude
1
0 time
In order to convert the sound into digital form, we have carry
out the following processes on the analog sound signal:
1. Sampling
2. Quantization
3. Encoding
These processes are collectively called as Pulse Code
Modulation (PCM). The following figure shows all the processes:
Analog sound Digital sound
6.4.3.1 Sampling:
When we transfer the signal using pulse code modulation
and digital modulation the signal must be in the discrete time form.
Sampling Quantization Encoding

66
If the message is generated from the computer system or
any other digital source then it is in the proper form for processing
by the digital communication system.
But in real life the signal can be of analog type (e.g. voice).
In such a case it has to be first converted into discrete time signal.
For this we use ―Sampling‖ method. Thus using the sampling
process we convert the continuous time signal (analog) into the
discrete time signal (digital).
The sampling process should satisfy the following
requirements:
1. Sampled signal should represent the original signal.
2. It should be possible to reconstruct the original signal from its
sampled form.
The following figure explains the sampling process:
amplitude
time
6.4.3.2 Quantization:
Quantization is the process in which we assign the numbers
to the discrete values depending upon their amplitude values.
Quantizer converts the sampled signal into an approximate
quantized signal which consists of only finite number of predecided
voltage levels.
Each sampled value at the input of the quantizer is
approximated or rounded to the nearest standard predecided
voltage level (Quantization levels).

67
The following figure shows the overview of the process:
amplitude
quantized signal
input signal
time
We can show the sampling and quantization process as follows:
Original signal Sampling Measuring
for the signal
5
4
3
2
0
Stored on the disk as a numbers
Quantization
1 4 2 3 1 3 4 1

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6.5 MULTIMEDIA AND DATA COMPRESSION
When we store the information in the form of pictures, videos
and sounds there would be lot of repetition that can be observed.
Storing such repeated information would cause the wastage
of computer memory.
We must find the better schemes that eliminate the
duplication of the data or redundant information.
There are various multimedia file formats available which
allow storage of multimedia files in more efficient manner by getting
rid of duplication/ redundancy by means of the process called as
Data Compression.
8. Define multimedia
9. What is quantization
10.What is sampling and explain it‘s importance
6.7 REFERENCES
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7
ERRORS, DETECTION & CORRECTION
Unit Structure
7.0 Objective
7.1 Introduction
7.2 Error Classification
7.3 Types of errors
7.4 Redundancy
7.5 Detection versus correction
7.6 Hamming distance
7.7 Cyclic Redundancy Check
7.8 Review questions
7.9 References
7.0 OBJECTIVE
 Understand error classification
 Types of error
 Understand concept redundancy
 Hamming code concept
 CRC concept
 Checksum technic
7.1 INTRODUCTION:
Errors in the data are basically caused due to the various
impairments that occur during the process of transmission.
When there is an imperfect medium or environment exists in
the transmission it prone to errors in the original data.
Errors can be classified as follows:
Attenuation
Noise
Distortion

70
7.2 ERRORS CLASSIFICATION
Following are the categories of the errors:
1. Attenuation:
As signal travels through the medium, its strength decreases
as distance increases, as shown in the figure 7.1, the example is
voice, it becomes weak over the distance and loses its contents
beyond a certain distance. As the distance increases attenuation
also increases.
Strength
Distance
Figure 7.1
2. Noise:
Noise is defined as an unwanted data. When some
electromagnetic signal gets inserted during the transmission, it is
generally called as a Noise. Due to Noise it is difficult to retrieve the
original data or information.
3. Distortion:
When there is an interference of the different frequencies
who travel across the medium with the different speed, Distortion
occurs. So it is important to have a space (guard space) between
the different frequencies.
7.3 TYPES OF ERRORS:
If the signal comprises of binary data there can be two types
of errors which are possible during the transmission:
1. Single bit errors
2. Burst Errors

71
Figure 7.2
1. Single-bit errors:
In single-bit error, a bit value of 0 changes to bit value 1 or
vice versa. Single bit errors are more likely to occur in parallel
transmission. Figure 7.3 (a)
2. Burst errors:
In Burst error, multiple bits of the binary value changes.
Burst error can change any two or more bits in a transmission.
These bits need not be adjacent bits. Burst errors are more likely to
occur in serial transmission. Figure 7.3 (b)
Original data Received data
0 1 0 0 1 1 0 1 1 1
Figure 7.3 (a) Single bit error
Original data Received data
0 1 0 0 1 1 0 1 1 1
Figure 7.3 (b) Burst error
7.4 REDUNDANCY
In order to detect and correct the errors in the data
communication we add some extra bits to the original data. These
extra bits are nothing but the redundant bits which will be removed
by the receiver after receiving the data.
Their presence allows the receiver to detect or correct
corrupted bits. Instead of repeating the entire data stream, a short
group of bits may be attached to the entire data stream.This
technique is called redundancy because the extra bits are
redundant to the information: they are discarded as soon as the
accuracy of the transmission has been determined.
0 0 0 0 1 1 0 1 1 1
0 0 0 1 1 1 0 0 1 1

72
Receiver Sender
Figure 7.4
There are different techniques used for transmission error detection
and correction.
Figure 7.5
2. Parity Check:
In this technique, a redundant bit called a parity bit is
addedto every data unit so that the total number of 1‘s in the
unit(including the parity bit) becomes even (or odd). Following
0 1 1 0 1 1 0
0 1 1 0 1 1 0 0 1 1 0
Data and Redundancy
0 1 1 0 1 1 0
Rejected
Data
0 1 1 0 1 1 0 0 1 1 0
Data and Redundancy
Data
Data
Medium
OK ?
Yes
No

73
Figure shows this concept when transmit the binary data
unit110101.
Receiver Sender
Simple parity check can detect all single-bit errors. It canalso
detect burst errors as long as the total number of bitschanged is
odd. This method cannot detect errors where thetotal number of
bits changed is even.
Two-Dimensional Parity Check:
A better approach is the two dimensional parity checks. In
this method, a block of bits is organized in a table (rows and
columns). First we calculate the parity bit for each data unit. Then
we organize them into a table. We then calculate the parity bit for
eachcolumn and create a new row of 8 bits.
Consider the following example; we have four data units to
send. They are organized in the tabular form as shown below.
Drop parity bit and accept the data 1 0 0 1 0 1
1 0 0 1 0 1 1
Data
Calculate
Parity bit
Medium
Calculate
Parity bit
Bits
Even
?
Yes
No
Rejected
Data

74
Original Data
Data and Parity bits
We then calculate the parity bit for eachcolumn and create a
new row of 8 bits; they are the parity bits for the whole block. Note
that the first parity bit in thefifth row is calculated based on all first
bits: the secondparity bit is calculated based on all second bits: and
so on.We then attach the 8 parity bits to the original data andsend
them to the receiver.
Two-dimensional parity check increases the likelihood
ofdetecting burst errors.A burst error of more than ‗n‘bits is also
detected by thismethod with a very high probability.
3. Cyclic Redundancy Check (CRC)
Most powerful of the redundancy checkingtechniques is the
cyclic redundancy check (CRC). This method is based on the
binary division. In CRC, the desired sequence of redundant bits are
generated and is appended to the end of data unit. It is also called
as CRC reminder. So that the resulting data unit becomes exactly
divisible by a predetermined binary number.
At its destination, theincoming data unit is divided by the
same number. If at thisstep there is no remainder then the data unit
0110110 1101001 1110011 0001110
0 1 1 0 1 1 0 0
1 1 0 1 0 0 1 0
1 1 1 0 0 1 1 1
0 0 0 1 1 1 0 1
0 1 0 0 0 1 0 0
Row
parities
Column
parities
01101100 11010010 11100111 00011101 01000100

75
is assumed to be correct and is therefore accepted.A remainder
indicates thatthe data unit has been damaged in transit and
thereforemust be rejected.
The redundancy bits used by CRC are derived by dividingthe
data unit by a predetermined divisor; the remainder isthe CRC.To
be valid, a CRC must have two qualities: It musthave exactly one
less bit than the divisor, and appending itto the end of the data
string must make the resulting bitsequence exactly divisible by the
divisor.
The following figure shows the process:
Receiver Sender
Step1: A string of 0‘s is appended to the data unit. It is n bits long.
The number n is 1 less if-number of bits in the predetermined
divisor which is n + 1 bits.
Step 2: The newly generated data unit is divided by the divisor,
using a process called as binary division. The remainder resulting
from this division is the CRC.
Step 3: the CRC of n bits derived in step 2 replaces the appended
0‘s at the data unit. Note that the CRC may consist of all 0‘s.
The data unit arrives at the receiver data first, followed by
the CRC. The receiver treats the whole string as a unit and divides
it by the same divisor that was used the CRC remainder. If the
string arrives without error, the CRC checker yields a remainder of
zero, the data unit passes. If the string has been changed in transit,
the division yields zero remainder and the data unit does not pass.
Data 00…0
n bits
n+1 bits
remainder
n bits
Divisor
CRC
Data CRC
Zero, accept
Non- zero, Reject
Divisor
Remainde
r
Data CRC

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Following figure shows the process of generating CRC
reminder:
Figure :
Quotient
___1 1 1 1 0 1________
Divisor 1 1 0 1 1 0 0 1 0 0 0 0 0 Extra bits
1 1 0 1
_________
1 000
1 1 0 1
_______
1 0 1 0
1 1 0 1
______
1 1 1 0
1 1 0 1
________
0 1 1 0
0 0 0 0
_______
1 1 0 0
1 1 0 1
________
0 0 1 Remainder
A CRC checker functions does exactly as the generator
does. After receiving the data appended with the CRC, it does the
samemodulo-2 division. If the remainder is all 0‘s, the CRC
isdropped and the data is accepted: otherwise, the receivedstream
of bits is discarded and data is resent.

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Following Figure shows the same process of division in the
receiver.
Figure:
Quotient
___1 1 1 1 0 1________
Divisor 1 1 0 1 1 0 0 1 0 0 0 0 1 CRC
1 1 0 1
_________
1 000
1 1 0 1
_______
1 0 1 0
1 1 0 1
______
1 1 1 0
1 1 0 1
________
0 1 1 0
0 0 0 0
_______
1 1 0 1
1 1 0 1
________
0 0 0 Result
Performance:
CRC is a very effective error detection method. If the divisoris
chosen according to the previously mentioned rules,
1.CRC can detect all burst errors that affect an odd numberof bits.
2.CRC can detect all burst errors of length less than or equalto the
degree of the polynomial
3.CRC can detect, with a very high probability, burst errorsof length
greater than the degree of the polynomial.
3. Checksum
A checksum is fixed length data that is the result of
performing certain operations on the data to be sent from sender to
the receiver. The sender runs the appropriate checksum algorithm
to compute the checksum of the data, appends it as a field in the

78
packet that contains the data to be sent, as well as various
headers.
When the receiver receives the data, the receiver runs the
same checksum algorithm to compute a fresh checksum. The
receiver compares this freshly computed checksum with the
checksum that was computed by the sender. If the two checksum
matches, the receiver of the data is assured that the data has not
changed during the transit.
Hamming Code:
The Hamming code can be applied to data units of any
length and uses the relationship between data and redundancy bits
discussed above. For example, a 7-bit ASCII code requires 4
redundancy bits that can be added 10 the end of the data unit or
interspersed with the original data bits. In following Figure,these
bits are placed in positions 1, 2,4, and 8 (the positions in an 11-bit
sequence that are powers of 2). For clarity in the examples below,
we refer to these bits as r1, r2, r4, and r8.
11 10 9 8 7 6 5 4 3 2 1
In the Hamming code, each r bit is the parity bit for
onecombination of data bits, is shown below:
r1 : bits 1,3,5,7,9,11
r2 : bits 2,3,6,7,10,11
r3 : bits 4,5,6,7
r4 : bits 8,9,10,11
d d d r8 d d d r4 d r2 r1

79
r1will be assigned to these bits position:
11 9 7 5 3
1
11 10 7 6 3 2
7 6 5 4
11 10 9 8
Now suppose we have 1001101 data to be sent, then the
redundant bits are calculated by the following method:
Data is: 1 0 0 1 1 0 1
11 10 9 8 7 6 5 4 3 2 1
Adding r1:
11 10 9 8 7 6 5 4 3 2 1
1 0 0 1 1 0 1
1 0 0 1 1 0 1 1

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Adding r2:
11 10 9 8 7 6 5 4 3 2 1
Adding r4:
11 10 9 8 7 6 5 4 3 2 1
Adding r8:
11 10 9 8 7 6 5 4 3 2 1
Code: 10011100101
Now imagine that by the time the above transmission
isreceived, the number 7 bit has been changed from 1 to 0.The
receiver takes the transmission and recalculates 4 newparity bits,
using the same sets of bits used by the senderplus the relevant
parity r bit for each set (see following Fig.). Thenit assembles the
new parity values into a binary number inorder of r position (r8 r4,
r2, r1). In our example, this stepgives us the binary number 0111 (7
in decimal), which is theprecise location of the bit in error.
1 0 0 1 1 0 1 0 1
1 0 0 1 1 0 0 1 0 1
1 0 0 1 1 1 0 0 1 0 1

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Corrupted bit
Error bit position 7 : 01 1 1
Once the bit is identified, the receiver can reverse itsvalue
and correct the error. The beauty of the technique isthat it can
easily be implemented in hardware and the codeis corrected before
the receiver knows about it.
1. Explain error classification?
2. Explain error type with example?
3. Discuss Hamming code?
4. explain CRC.
5. write a short note on Checksum?
7.9 REFERENCES
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1 0 0 1 0 1 0 0 1 0 1
1 0 0 1 0 1 0 0 1 0 1
1 0 0 1 0 1 0 0 1 0 1

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8
SIGNAL ENCODING
Unit Structure
8.0 Objectives
8.1 Introduction to Signal Encoding
8.2 Synchronization
8.3 Digital Data to Digital Signal
8.3.1 Line EnCoding
8.3.2 Classification of Line Coding Schemes
8.3.2.A Unipolar - NRZ
8.3.2.B Polar-NRZ, NRZ-L, NRZ-I, RZ, Biphase
8.3.2.C Bipolar - AMI, Pseudoternary
8.3.2.D Multilevel - mBnL, 4D-PAMS
8.3.2.E MultiTransision- MLT-3
8.3.3 Block Coding
8.4 (Analog data to analog signal conversion)
8.4.1. Modulation
8.4.2 Types of Modulation
8.4.2.1 Analog Modulation types
8.4.2.1.1 AM
8.4.2.1.2 FM
8.4.2.1.3 PM
8.4.2.2 Digital Modulation Types(Digital to Analog
signal conversion)
8.4.2.2.1 ASK
8.4.2.2.2 FSK
8.4.2.2.3 PSK
8.4.2.2.4 QAM
8.4.2.3 Analog to Digtal conversion using modulation)
8.4.2.3.1 PAM
8.4.2.3.2 PCM
8.4.2.3.3 PWM

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8.0 OBJECTIVES
The objectives of this chapter are:
1. Understand what is signal encoding
2. Different ways of converting analog signal to digital
3. Different ways of converting digital signal to analog
4. Modulation
8.1 INTRODUCTION TO SIGNAL ENCODING
Data can be analog or digital, so can be the signal that
represents it.
Signal encoding is the conversion from analog/digital data
to analog / digital signal.
Figure: Signal Encoding
In the Figure above,
A) Demonstrates Digital Signaling where data from an
analog/digital source is encoded into Digital Signal
B) Demonstrates Analog signaling in which the analog/digital
source modulates a continuous carrier signal to produce an
analog signal.

84
The possible encodings are:
1. Digital data to Digital Signal
2. Digital data to Analog Signal
3. Analog data to Digital Signal
4. Analog data to Analog Signal
8.2 SYNCHRONIZATION
In order to receive the signals correctly, the receivers bit
intervals must correspond exactly to the senders bit
intervals.
The clock frequency of the transmitter and receiver should
be the same.
If the clock frequency at the receiver is slower or faster than
the bit intervals are not matched and the received signal is
different than the transmitted one.
Figure : Synchronization

85
In the above figure, the receiver clock frequency is twice that
of the transmitter frequency. Hence the received data is
totally different than the transmitted one
To avoid this, receiver and transmitter clocks have to be
synchronized.
To achieve this the transmitted digital signal should include
timing information which forces synchronization
8.3 Digital Data to Digital Signal
Coding methods Coding methods are used to convert digital
data into digital signals.
There are two types of coding methods:
1 Line Coding
2 Block Coding
Scrambling is also one of the ways to convert digital data to digital
signals but is not used.
8.3.1 Line Encoding
It is the process of converting Digital data into digital
signal.
In other words, it is converting of binary data(i.e. A sequence of
bits) into digital signal (i.e. a sequence of discrete,
discontinuous voltage pulses)
Figure: Line Coding
8.3.2 Classification of Line Codes
The following figure shows the classification of Line coding
schemes:

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Figure : Classification of line coding schemes
8.3.2.A Unipolar
All signal levels are either above or below the time axis.
NRZ - Non Return to Zero scheme is an example of this
code. The signal level does not return to zero during a
symbol transmission.
8.3.2.B Polar
NRZ-voltages are on both sides of the time axis.
Polar NRZ scheme can be implemented with two voltages.
E.g. +V for 1 and -V for 0.
There are two variations:
o NZR - Level (NRZ-L) - positive voltage for one
symbol and negative for the other
o NRZ - Inversion (NRZ-I) - the change or lack of
change in polarity determines the value of a symbol.
E.g. a ―1‖ symbol inverts the polarity a ―0‖ does not.
Polar – RZ
 The Return to Zero (RZ) scheme uses three voltage
values. +, 0, -.

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 Each symbol has a transition in the middle. Either from
high to zero or from low to zero
 More complex as it uses three voltage level. It has no
error detection capability
Figure : Unipolar(NRZ) & Polar(RZ & NRZ) Encoding
Polar - Biphase: Manchester and Differential Manchester
Manchester coding is a combination of NRZ-L and RZ
schemes.
Every symbol has a level transition in the middle: from
high to low or low to high.
It uses only two voltage levels.
Differential Manchester coding consists of combining
the NRZ-I and RZ schemes.
Every symbol has a level transition in the middle. But
the level at the beginning of the symbol is determined
by the symbol value. One symbol causes a level
change the other does not.

88
Figure : Polar biphase: Manchester and differential Manchester
coding schemes
8.3.2.C Bipolar - AMI and Pseudoternary
This coding scheme uses 3 voltage levels: - +, 0, -, to
represent the symbols
Voltage level for one symbol is at ―0‖ and the other
alternates between + & -.
Bipolar Alternate Mark Inversion (AMI) - the ―0‖ symbol
is represented by zero voltage and the ―1‖ symbol
alternates between +V and -V.
Pseudoternary is the reverse of AMI
Figure: Bipolar coding scheme - AMI and Pseudoternary

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8.3.2.D Multilevel
Here the number of data bits is increased per symbol to
increase the bit rate.
2 types of data element a 1 or a 0 are available, it can be
combined into a pattern of n elements to create 2m
symbols.
Using L signal levels we can have n signal elements to
create Ln
signal elements. The following possibilities can
occur:
With 2m
symbols and Ln
signals:
If 2m
> Ln
then we cannot represent the data elements,
we don‘t have enough signals.
If 2m
= Ln
then we have an exact mapping of one symbol
on one signal.
If 2m
< Ln
then we have more signals than symbols and
we can choose the signals that are more distinct to
represent the symbols and therefore have better noise
immunity and error detection as some signals are not
valid
These types of codings are classified as mBnL schemes. In
mBnL schemes, a pattern of m data elements is encoded as
a pattern of n signal elements in which 2m
≤ Ln
.
2B1Q (two binary, one quaternary)
Here m = 2; n = 1 ; Q = 4. It uses data patterns of size 2 and
encodes the 2-bit patterns as one signal element belonging
to a four-level signal.
Figure: Multilevel coding scheme : 2B1Q

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8B6T(eight binary, six ternary)
Here a pattern of 8 bits is encoded a pattern of 6 signal
elements, where the signal has three levels
Here m = 8; n = 6 ; T = 3
So we can have 28
=256 different data patterns and 36
=478 different signal patterns.
Figure : Multilevel coding scheme : 8B6T
4D-PAM5 (Four Dimensional Five-Level Pulse Amplitude
Modulation)
4D -means that data is sent over four channels at the
same time.
It uses five voltage levels, such as -2, -1, 0, 1, and 2.
8.3.2.E Multitransition
Because of synchronization requirements we force
transitions. This can result in very high bandwidth
requirements -> more transitions than are bits (e.g. mid bit
transition with inversion).
Codes can be created that are differential at the bit level
forcing transitions at bit boundaries. This results in a
bandwidth requirement that is equivalent to the bit rate.
In some instances, the bandwidth requirement may even be
lower, due to repetitive patterns resulting in a periodic signal.
MLT-3
o Signal rate is same as NRZ-I
o Uses three levels (+v, 0, and - V) and three transition
rules to move between the levels.
 If the next bit is 0, there is no transition.
 If the next bit is 1 and the current level is not 0,
the next level is 0.
 If the next bit is 1 and the current level is 0, the
next level is the opposite of the last nonzero
level.

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8.3.3 Block Coding
Block coding adds redundancy to line coding so that error
detection can be implemented.
Block coding changes a block of m bits into a block of n bits,
where n is larger than m.
Block coding is referred to as an mB/nB encoding
technique.
The additional bits added to the original ―m bits‖ are called
parity bits or check bits
m : message bits
Figure : Block Coding
Example: 4B/5B encoding
Here a 4 bit code is converted into a 5 bit code
8.4 Analog data to analog signal
8.4.1 Modulation
The Process of converting analog data to analog signal is
called Modulation.
Modulation is used to send an information bearing signal
over long distances.
Modulation is the process of varying some characteristic
of a periodic wave with an external signal called carrier
signal.
These carrier signals are high frequency signals and can
be transmitted over the air easily and are capable of
traveling long distances.
The characteristics (amplitude, frequency, or phase) of
the carrier signal are varied in accordance with the
information bearing signal(analog data).
The information bearing signal is also known as the
modulating signal.

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The modulating signal is a slowly varying – as opposed
to the rapidly varying carrier frequency.
8.4.2 Types of Modulation:
Signal modulation can be divided into two broad categories:
 Analog modulation and
 Digital modulation.
Analog or digital refers to how the data is modulated
onto a sine wave.
If analog audio data is modulated onto a carrier sine
wave, then this is referred to as analog modulation.
Digital modulation is used to convert digital data to
analog signal. Ex ASK, FSK, PSK.
8.4.2.1 Analog Modulation can be accomplished in three ways:
1. Amplitude modulation (AM)
2. Frequency modulation (FM)
3. Phase modulation (PM).
8.4.2.1.1 Amplitude modulation (AM)
Amplitude modulation is a type of modulation where the
amplitude of the carrier signal is varied in accordance
with modulating signal.
The envelope, or boundary, of the amplitude modulated
signal embeds modulating signal.
Amplitude Modulation is abbreviated AM.
Figure : Amplitude modulation (AM)

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8.4.2.1.2 Frequency modulation (FM)
Frequency modulation is a type of modulation where the
frequency of the carrier is varied in accordance with the
modulating signal. The amplitude of the carrier remains
constant.
The information-bearing signal (the modulating signal)
changes the instantaneous frequency of the carrier.
Since the amplitude is kept constant, FM modulation is a
low-noise process and provides a high quality modulation
technique which is used for music and speech in hi-
fidelity broadcasts.
Frequency Modulation is abbreviated FM.
Figure : Frequency modulation (FM)
8.4.2.1.3 Phase modulation (PM).
In phase modulation, the instantaneous phase of a
carrier wave is varied from its reference value by an

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amount proportional to the instantaneous amplitude of
the modulating signal.
Phase Modulation is abbreviated PM.
Figure : Phase modulation (PM).
Figure : Comparison of AM, FM & PM

95
8.4.2.2 Digital Modulation Types(Digital to Analog signal
conversion)
Digital modulation is used to convert digital data to
analog signal.
It can be accomplished in the following ways:
1. ASK
2. FSK
3. PSK
4. QAM
8.4.2.2.1 Amplitude Shift Keying (ASK)
In amplitude shift keying, the amplitude of the carrier signal is
varied to create signal elements.
Both frequency and phase remain constant while the
amplitude changes.
Binary ASK (BASK)
ASK is normally implemented using only two levels and is
hence called binary amplitude shift keying.
Bit 1 is transmitted by a carrier of one particular amplitude.
To transmit Bit 0 we change the amplitude keeping the
frequency is kept constant
Figure : Amplitude Shift Keying (ASK
8.4.2.2.2 Frequency Shift Keying (FSK)
In Frequency shift keying, we change the frequency of the
carrier wave.
Bit 0 is represented by a specific frequency, and bit 1 is
represented by a different frequency.
In the figure below frequency used for bit 1 is higher than
frequency used for bit 0

96
Figure : Frequency Shift Keying (FSK)
8.4.2.2.3. Phase Shift Keying (PSK)
Phase shift keying (PSK) is a method of transmitting and
receiving digital signals in which the phase of a transmitted
signal is varied to convey information.
Both amplitude and frequency remain constant as the phase
changes.
The simplest from of PSK has only two phases, 0 and 1.
If the phase of the wave does not change, then the signal
state stays the same (low or high).
If the phase of the wave changes by 180 degrees, that is, if
the phase reverses, then the signal state changes (from low
to high or from high to low)

97
Figure: Phase Shift Keying (PSK)
8.4.2.2.4 QAM
The concept of Quadrature Amplitude Modulation (QAM)
involves use of two carriers, one for phase and the other for
quadrature, with different amplitude levels for each carrier.
It is a combination of ASK & PSK.
8.4.2.2 Analog to Digital Conversion using modulation
The definition of the term modulation is described in the
next section. Here we discuss 3 modulation techniques:
1. PAM
2. PCM
3. PWM
8.4.2.3.1 PAM (Pulse Amplitude Modulation)
Pulse Amplitude Modulation refers to a method of
carrying information on a train of pulses, the information
being encoded in the amplitude of the pulses.
8.4.2.3.2 PCM (Pulse Code Modulation)
PCM is a general scheme for transmitting analog data
in a digital and binary way, independent of the
complexity of the analog waveform. With PCM all
forms of analog data like video, voice, music and
telemetry can be transferred.
To obtain PCM from an analog waveform at the
source (transmitter), the analog signal amplitude is

98
sampled at regular time intervals. The sampling rate
(number of samples per second), is several times the
maximum frequency of the analog waveform. The
amplitude of the analog signal at each sample is
rounded off to the nearest binary level (quantization).
The number of levels is always a power of 2 (4, 8, 16,
32, 64, ...). These numbers can be represented by
two, three, four, five, six or more binary digits (bits)
respectively.
At the destination (receiver), a pulse code
demodulator converts the binary numbers back into
pulses having the same quantum levels as those in
the modulator. These pulses are further processed to
restore the original analog waveform.
8.4.2.3.3 PWM (Pulse Width Modulation)
Pulse Width Modulation refers to a method of carrying
information on a train of pulses, the information being
encoded in the width of the pulses. In applications to
motion control, it is not exactly information we are
encoding, but a method of controlling power in motors
without (significant) loss.
There are several schemes to accomplish this technique.
One is to switch voltage on and off, and let the current
recirculate through diodes when the transistors have
switched off. Another technique is to switch voltage
polarity back and forth with a full-bridge switch
arrangement, with 4 transistors.
This technique may have better linearity, since it can go
right down to an cycles, and may jitter between
minimum duty cycles of positive and negative polarity.
In battery systems PWM is the most effective way to
achieve a constant voltage for battery charging by
switching the system controller's power devices on and
off.
The generation of exact working PWM circuitry is
complicated, but it is extremely conceptually important since
there is good reason to believe that neurons transmit
information using PWM spike trains.

99
1. Explain the different ways of converting data to signal and
viceversa.
2. Eplain in detail what is signal encoding
3. What are the different ways of converting analog data to digital
data?
4. What is modulation? What are its two types?
1. Data Communication & Networking – Behrouz Forouzan.
2. Computer Networks – Andrew Tannenbaum
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9
TRANSMISSION MODES & IMPAIRMENTS
Unit Structure
9.0 Objectives
9.1 Introduction
9.2 Transmission Modes & Types
9.2.1 Parallel Transmission
9.2.2 Serial Transmission
9.2.2.1 Synchronous Transmission
9.2.2.2 Asynchronous Transmission
9.2.2.3 Comparison of serial and parallel
Transmission
9.3 Transmission Impairments & Types
9.3.1 Attenuation
9.3.2 Distortion
9.3.3 Noise
9.0 OBJECTIVES
After reading this chapter you will understand:
Transmission Modes and their types
Parallel transmission mode
Serial Transmission mode.
Asynchronous and synchronous transmission mode
Transmission Impairment
9.1 INTRODUCTION
This chapter gives an understanding about the way in which
data can be transmitted between two devices (parallel & Serial) and
the impairments in transmission due to imperfections of the
transmission medium.

101
9.2 TRANSMISSION MODES
Data is transmitted between two digital devices on the
network in the form of bits.
Transmission mode refers to the mode used for transmitting
the data. The transmission medium may be capable of
sending only a single bit in unit time or multiple bits in unit
time.
When a single bit is transmitted in unit time the transmission
mode used is Serial Transmission and when multiple bits are
sent in unit time the transmission mode used is called
Parallel transmission.
Types of Transmission Modes:
There are two basic types of transmission modes Serial
and Parallel as shown in the figure below.
Serial transmission is further categorized into
Synchronous and Asynchronous Serial transmission.
Fig. Types of Transmission Modes
9.2.1 Parallel Transmission
It involves simultaneous transmission of N bits over N
different channels
Parallel Transmission increases transmission speed by a
factor of N over serial transmission
Disadvantage of parallel transmission is the cost involved, N
channels have to be used, hence, it can be used for short
distance communication only

102
Fig. Parallel Transmission of Data over N = 8 channels
Example of Parallel Transmission is the communication
between CPU and the Projector.
9.2.2 Serial Transmission
In Serial Transmission, as the name suggests data is
transmitted serially, i.e. bit by bit, one bit at a time.
Since only one bit has to be sent in unit time only a single
channel is required.
Fig. Serial Transmission of Data over N = 8 channels
Types of Serial Transmission:
Depending upon the timing of transmission of data there are
two types of serial transmission as described below

103
9.2.2.1 ASynchronous Transmission
In asynchronous serial transmission the sender and receiver
are not synchronized.
The data is sent in group of 8 bits i.e. in bytes.
The sender can start data transmission at any time instant
without informing the receiver.
To avoid confusing the receiver while receiving the data,
―start‖ and ―stop‖ bits are inserted before and after every
group of 8 bits as shown below
0 1 BYTE 1
Fig: Start and Bit before and after every data byte
The start bit is indicated by ―0‖ and stop bit is indicated by
―1‖.
The sender and receiver may not be synchronized as seen
above but at the bit level they have to be synchronized i.e.
the duration of one bit needs to be same for both sender and
receiver for accurate data transmission.
There may be gaps in between the data transmission
indication that there is no data being transmitted from
sender. Ex. Assume a user typing at uneven speeds, at
times there is no data being transmitted from Keyboard to
the CPU.
Following is the Diagram for Asynchronous Serial
Transmission.
Fig: Asynchronous Serial Transmission

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Advantages
1. Cheap and Effective implementation
2. Can be used for low speed communication
Disadvantages
Insertion of start bits, stop bits and gaps make asynchronous
transmission slow.
Application
Keyboard
9.2.2.2 Synchronous Transmission
In Synchronous Serial Transmission, the sender and
receiver are highly synchronized.
No start, stop bits are used.
Instead a common master clock is used for reference.
The sender simply send stream of data bits in group of 8 bits
to the receiver without any start or stop bit.
It is the responsibility of the receiver to regroup the bits into
units of 8 bits once they are received.
When no data is being transmitted a sequence of 0‘s and 1‘s
indicating IDLE is put on the transmission medium by the
sender.
Fig: Asynchronous Serial Transmission
Advantage
1. There are no start bits, stop bits or gaps between data
units
2. Since the above are absent data transmission is
faster.
3. Due to synchronization there are no timing errors.

105
9.2.2.3 Comparison of serial and parallel transmission
Sr.no Parameter Parallel
transmission
Serial transmission
1 Number of wire
required to
transmit N bits
N wire 1 wire
2 Number of bits
transmitted
simultaneously
N bits 1 bit
3 Speed of data
transfer
False Slow
4 Cost Higher due to
more number of
conductor
Low, since only one
wire is used
5 Application Short distance
communication
such as computer
to printer
communication
Long distance
computer to
computer
communication.
9.3 Transmission Impairments & Types
Data is transmitted through transmission medium which are
not perfect.
The imperfection causes signal impairment.
Due to the imperfection error is introduced in the transmitted
data i.e. the original signal at the beginning of the
transmission is not the same as the signal at the Receiver.
There are three causes of impairment: attenuation,
distortion, and noise as shown below:
Fig: Transmission Impairment Types

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9.3.1 Attenuation
• Attenuation results in loss of energy. When a signal travels
through a medium, it loses some of its energy in overcoming
the resistance of the medium.
• The electrical energy in the signal may converted to heat.
• To compensate for this loss, amplifiers are used to amplify
the signal. Figure below shows the effect of attenuation and
amplification.
Fig. Attenuation
9.3.2 Distortion
Distortion changes the shape of the signal as shown
below
Fig. Distortion
9.3.3 Noise
Noise is any unwanted signal that is mixed or combined
with the original signal during transmission.
Due to noise the original signal is altered and signal
received is not same as the one sent.

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1. What is data transmission? What are the different possible
ways of transmitting data?
2. Explain Parallel transmission mode
3. Explain Serial transmission mode and list its types
4. Explain Asynchronous serial transmission
5. Explain Synchronous Serial Transmission
6. Write a short note on transmission impairments
7. Differentiate between serial and parallel Transmission
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10
TRANSMISSION MEDIUM
Unit Structure
10.0 Objectives
10.1 Introduction
10.2 Transmission Medium
10.2.1 Categories of Transmission Medium
10.3 Guided Transmission Media
10.3.1 Twisted Pair Cable
10.3.1.1 Unshielded & Shielded Twisted Pair Cable
10.3.2 Co-axial Cable
10.3.3 Fiber Optic Cable
10.4 Unguided (wireless) Transmission Medium
10.4.1 Propagation Method of wireless signals
10.4.2. Types of wireless transmission
10.4.2.1. Radio waves
10.4.2.2. Microwaves
10.4.2.3. Infrared
10.5 Comparison between wired and wireless media
10.6 Comparison between twisted pair cable, co-axial cable and
optical fiber
10.0 OBJECTIVES
In this chapter, you will understand:
Definition of Transmission Medium and its types
Different types of Guided Transmission medium
Different types of UnGuided Transmission medium
Different ways in which wireless signals are transmitted
10.1 INTRODUCTION
In Data Communication networking, it is worth understanding
the medium through which data passes and what are the available

109
mediums and their types. This chapter give a thorough
understanding of the different types of transmission medium used
for data communication
10.2 TRANSMISSION MEDIA
• Transmission media is ameans by which a communication
signal is carried from one system to another
• A transmission medium can be defined as anything that can
carry information from a source to a destination.
• The transmission medium is usually free space, metallic
cable or fiber – optic cable.
Figure: Transmission of data from sender to receiver through
a medium
10.2.1 Categories of transmission media
Figure : Categories of Transmission Medium

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10.3 GUIDED MEDIA
• Guided Transmission media uses a cabling system that
guides the data signals along a specific path.
• Guided media also known as Bounded media, which are
those that provide a conduit from one device to another,
include twisted-pair cable, coaxial cable, and fiber-optic
cable.
• Out of these twisted-pair cable, coaxial cable transport
signals in the form of electric signals and fiber-optic cable
transport signals in the form of light.
• Types:
1. Twisted-Pair Cable
2. Coaxial Cable
3. Fiber-OpticCable
10.3.1 Twisted-pair cable
Figure: Twisted Pair Cable
• The wires is twisted twisted together in pairs.
• Each pair would consist of wire used for the +ve data signal
and a wire used for the —ve data signal. Any noise that
appears on +ve/—ve wire of the pair would occur on
the other wire.
• Because the wires are opposite polarities, they are 180
degrees out of phase (180 degree phases or definition of
opposite polarity) when the noise appears on both wires, it
cancels or nulls itself out at the receiving used.
• Twisted pair cables are most effectively used in a system
that uses a balanced line method of transmission.

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10.3.1.1 Unshielded Twisted Pair Cable (UTP)& Shielded
Twisted Pair Cable (STP)
Fig. Unshielded Twisted Pair Cable
Fig. Shielded Twisted Pair Cable
• Cables with the shield are called shielded twisted pair and
commonly abbreviated STP.
• Cables without a shield are called unshielded twisted pair or
UTP.
• Twisting the wires together results in characteristics
impedance for the cable.
• UTP or unshielded twisted pair cable is used on Ethernet
• UTP cables are used for Ethernet cabling where 4 twisted pair
cables (a total of 8 wires are used)
• 10.3.2 Co-Axial Cable
Figure: Co-axial cable
• Coaxial cable consists of 2 conductors.
• The inner conductor is contained inside the insulator with the
other conductor weaves around it providing a shield.
• An insulating protective coating called a jacket covers the
outer conductor.

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• The outer shield protects the inner conductor from outside
electrical signals.
• The distance between the outer conductor (Shield) and inner
conductor plus the type of material used for insulating the
inner conductor determine the cable properties or
impedance. The excellent control of the impedance
characteristics of the cable allow higher data rates to be
transferred than twisted pair cable.
10.3.3 Fibre Optic Cable
Figure Fiber Optic Cable
• Optical fiber consists of thin glass fiber that can carry
information at frequencies in the visible light spectrum.
• The typical optical fiber consists of a very narrow strand of glass
called the cladding.
• A typical core diameter is 62.5 microns.
• Typically cladding has a diameter of 125 minors. Coating the
cladding is a protective coating consisting of plastic, it is called
the jacket.
• The device generating the message has it in electromagnetic
form (electrical signal); this has to be converted into light (i.e.
optical signal) to send it on optic fiber cable. The process of
converting light to electric signal is done on the receiving side.
Advantages:
1. Small size and light weight: The size of the optical fibers is
very small.Therefore a large number of optical fibers can fit into
a cable of small diameter.
2. Easy availability and low cost: The material used for the
manufacturing of optical fibers is ―Silica glass‖. this material is
easily available. So the optical fibers cost lower than the cables
with metallic conductors.

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3. No electrical or electromagnetic interference: Since the
transmission takes place in the form of light rays the signal is
not affected due to any electrical or electromagnetic
Interference.
4. Large Bandwidth: As the light rays have a very high frequency
in GHz range, the bandwidth of the optical fiber is extremely
large.
5. Other advantages: - No cross talk inside the optical fiber cable.
Signal can be sent up to 100 times faster.
10.4 UNGUIDED (WIRELESS) TRANSMISSION
MEDIUM
• Unguided media transport data without using a physical
conductor. This type of communication is often referred to as
wireless communication.
• It uses wireless electromagnetic signals to send data.
• There are three types of Unguided Media
(i) Radio waves
(ii) Micro waves
(iii) Infrared.
• Before understanding the different types of wireless
transmission medium, let us first understand the ways in which
wireless signals travel. These signals can be sent or propagated
in the following three ways:
1. Ground-wave propagation
2. Sky-wave propagation
3. Line-of-sight propagation
1. Ground-wave propagation
Figure : Ground Propagation of waves

114
Characteristics of Ground-wave propagation are as follows:
i. Follows contour of the earth
ii. Can Propagate considerable distances
iii. Frequencies up to 2 MHz
iv. Example
a. AM radio
2. Sky-wave propagation
Figure :of waves
Characteristics of Sky Propagation are as follows:
i. Signal reflected from ionized layer of atmosphere back down
to earth
ii. Signal can travel a number of hops, back and forth between
ionosphere and earth‘s surface
iii. Reflection effect caused by refraction
iv. Examples
a. Amateur radio
b. CB radio
3. Line-of-sight propagation
Figure : Line of Sight Propagation of waves
Characteristics of Line of Sight Propagation are as follows:

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i. Transmitting and receiving antennas must be within line of
sight
a. Satellite communication – signal above 30 MHz not
reflected by ionosphere
b. Ground communication – antennas within effective
line of site due to refraction
1. Radio waves:
• Electromagnetic wave ranging in frequencies between 3 KHz
and 1GHz are normally called radio waves.
• Radio waves are omni-directional when an antenna transmits
radio waves they are propagated in all directions. This means
that sending and receiving antenna do not have to he aligned. A
sending antenna can send waves that can be received by any
receiving antenna.
• Radio waves particularly those waves that propagate in sky
mode, can travel long distances. This makes radio waves a
good candidate for long-distance broadcasting such as AM
radio.
• Radio waves particularly those of low and medium frequencies
can penetrate walls. It is an advantage because; an AM radio
can receive signals inside a building. It is the disadvantage
because we cannot isolate a communication to first inside or
outside a building.
2. Microwaves:
• Electromagnetic waves having frequencies between 1 and 300
GHz are called microwaves.
• Microwaves are unidirectional; when an antenna transmits
microwaves they can be narrowly focused. This means that the
sending and receiving antennas need to be aligned. The
unidirectional property has an obvious advantage. A pair of
antennas can be aligned without interfering with another pair of
aligned antennas.
• Microwaves propagation is line-of-sight. Since the towers with
the mounted antennas needs to be in direct sight of each other,
towers that are far apart need to be very tall, the curvature of
the earth as well as other blocking obstacles do not allow two
short towers to communicate using microwaves, Repeaters are
often needed for long distance communication very high
frequency microwaves cannot penetrate walls.
• Parabolic dish antenna and horn antenna are used for this
means of transmission

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3. Infrared
• Infrared signals with frequencies ranges from 300 GHz to 400
GHz can be used for short range communication.
• Infrared signals, having high frequencies, cannot penetrate
walls. This helps to prevent interference between one system
and another. Infrared Transmissionin one room cannot be
affected by the infrared transmission in another room.
• Infrared band, has an excellent potential for data transmission.
Transfer digital data is possible with a high speed with a very
high frequency. There are number of computer devices which
are used to send the data through infrared medium e.g.
keyboard mice, PCs and printers. There are some
manufacturers provide a special part called the IrDA port that
allows a wireless keyboard to communicate with a PC.
10.5 COMPARISON BETWEEN WIRED AND
WIRELESS MEDIA
Wired media Wireless media
The signal energy is contained
and guided within a solid
medium
The signal energy propagates
in the form of unguided
electromagnetic waves.
Twisted pair wires, coaxial
cable, optical fiber cables are
the examples of wired media.
Radio and infrared lights are
the examples of wireless
media.
Used for point to point
communication
Used for radio broadcasting in
all direction
Wired media lead to discrete
network topology
Wireless media leads to
continuous network topology
Additional transmission capacity
can be procured by adding more
wire
It is not possible procure
additional capacity.
Installation is costly and time
consuming
Installation needs less time
and money
Attenuation depends
exponentially on the distance
Attenuation is proportional to
square of the distance.

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10.6 COMPARISON BETWEEN TWISTED PAIR
CABLE, CO-AXIAL CABLE AND OPTICAL FIBER
Twisted pair cable Co-axial cable Optical fiber
Transmission of
signals take place in
the electrical form
over the metallic
conducting wires.
Transmission of
signals take place in
the inner conductor
of the cable
Signal transmission
takes place in an
optical form over a
glass fiber.
Noise immunity is
low. Therefore more
distortion
Higher noise
immunity than the
twisted pair cable
due to the presence
of shielding
conductor
Higher noise
immunity as the light
rays are unaffected
by the electrical
noise.
Affected due to
external magnetic
field
Less affected due to
external magnetic
field
Not affected by the
external magnetic
field.
Short circuit
between the two
conductor is
possible
Short circuit
between the two
conductor is
possible
Short circuit is not
possible
Cheapest Moderately
expensive
Expensive
Can support low
data rates
Moderately high
data rate
Very high data
rates.
Low bandwidth Moderately high
bandwidth
Very high bandwidth
Easy to installed Installation is fairly
easy
Installation is difficult
1. Write short note on transmission medium and explain its different
types.
2. Explain Twisted Pair Cables in detail
3. Explain Fiber Optic Cables with its advantages
4. Explain the different ways is which wireless signals propogate.

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5. Write short notes on :
a) Radio waves
b) Microwaves
c) Infrared
a) Data Communication & Networking – BehrouzForouzan
b) Computer Networks – Andrew Tannenbaum
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11
NETWORK TOPOLOGIES
Unit Structure
11.0 Objectives
11.1 Introduction
11.2 An Overview of network
11.3 Types of network
11.3.1 Local Area Network
11.3.2 Wide Area Network
11.4 Comparing types of network coverage
11.5 An Illustrated Example of a University Network
11.6 What is a Topology?
11.6.1 The Technical Connotation of Topology
11.6.2 What are the Basic Types of Topology?
11.6.3 How Is the Physical Topology Classified?
11.7 Summary and exercise
11.8 Review Question
11.9 References
11.0 OBJECTIVES

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 To understand various network strategies and topologies,
you will:
 Examine three common strategies used to connect nodes on
a network.
 Explore network processing strategies and establish the
differences between centralized and distributed processing.
 Identify and compare three common network classifications.
 Identify and define three common network topologies.
11.1 INTRODUCTION
This chapter presents an outline on Network topology is the
layout pattern of interconnections of the various elements
(links, nodes, etc.) of a computer or biological network. Network
topologies may be physical or logical.
Physical topology refers to the physical design of a network
including the devices, location and cable installation. Logical
topology refers to how data is actually transferred in a network as
opposed to its physical design. In general physical topology relates
to a core network whereas logical topology relates to basic network.
This chapter also presents an insight into the various networking
strategies and the platform needed for networking.
11.2 AN OVERVIEW OF NETWORK
A network consists of two or more computers that are linked
in order to share resources (such as printers and CDs), exchange
files, or allow electronic communications. The computers on a
network may be linked through cables, telephone lines, radio
waves, satellites, or infrared light beams.
Two very common types of networks include:
Local Area Network (LAN)
Wide Area Network (WAN)
You may also see references to a Metropolitan Area Networks
(MAN), a Wireless LAN (WLAN), or a Wireless WAN (WWAN).

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11.3 WHAT IS A NETWORK TYPE
11.3.1 Local Area Network
A Local Area Network (LAN) is a network that is confined to
a relatively small area. It is generally limited to a geographic area
such as a writing lab, school, or building.
Computers connected to a network are broadly categorized
as servers or workstations. Servers are generally not used by
humans directly, but rather run continuously to provide "services" to
the other computers (and their human users) on the network.
Services provided can include printing and faxing, software hosting,
file storage and sharing, messaging, data storage and retrieval,
complete access control (security) for the network's resources, and
many others.
Workstations are called such because they typically do have
a human user which interacts with the network through them.
Workstations were traditionally considered a desktop, consisting of
a computer, keyboard, display, and mouse, or a laptop, with with
integrated keyboard, display, and touchpad. With the advent of the
tablet computer, and the touch screen devices such as iPad and
iPhone, our definition of workstation is quickly evolving to include
those devices, because of their ability to interact with the network
and utilize network services.
Servers tend to be more powerful than workstations,
although configurations are guided by needs. For example, a group
of servers might be located in a secure area, away from humans,
and only accessed through the network. In such cases, it would be
common for the servers to operate without a dedicated display or
keyboard. However, the size and speed of the server's
processor(s), hard drive, and main memory might add dramatically
to the cost of the system. On the other hand, a workstation might
not need as much storage or working memory, but might require an
expensive display to accommodate the needs of its user. Every
computer on a network should be appropriately configured for its
use.
11.3.2 Wide Area Network

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Wide Area Networks (WANs) connect networks in larger
geographic areas, such as Maharashtra, India, or the world.
Dedicated transoceanic cabling or satellite uplinks may be used to
connect this type of global network.
Using a WAN, schools in Maharashtra can communicate
with places like Tokyo in a matter of seconds, without paying
enormous phone bills. Two users a half-world apart with
workstations equipped with microphones and a webcams might
teleconference in real time. A WAN is complicated. It uses
multiplexers, bridges, and routers to connect local and metropolitan
networks to global communications networks like the Internet. To
users, however, a WAN will not appear to be much different than a
LAN.
11.4Comparing types of network coverage
The table below compares the three types of networks:
LAN MAN WAN
Relatively small.
Can incorporate multiple
LANs.
Uses data
transmission
Contained within a
single building or
campus.
Contained within a single city
or metropolitan area.
networks to
incorporate LANs
and MANs.
Generally inexpensive
to implement and
maintain.
Expensive to implement and
maintain.
Essentially
unlimited
geographic area.
Typically owned
privately.
Typically owned by private
providers.
Cost varies widely,
depending on how
it is configured.
11.5 AN ILLUSTRATED EXAMPLE OF A UNIVERSITY
NETWORK
Advantages of Installing a Network
User access control.
Modern networks almost always have one or more servers
which allows centralized management for users and for
network resources to which they have access. User
credentials on a privately-owned and operated network may
be as simple as a user name and password, but with ever-
increasing attention to computing security issues, these
servers are critical to ensuring that sensitive information is
only available to authorized users.

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Information storing and sharing.
Computers allow users to create and manipulate information.
Information takes on a life of its own on a network. The
network provides both a place to store the information and
mechanisms to share that information with other network
users.
Connections.
Administrators, instructors, and even students and guests
can be connected using the campus network.
Services.
The institution can provide services, such as registration,
college directories, course schedules, access to research,
and email accounts, and many others. (Remember, network
services are generally provided by servers).
Internet.
The institution can provide network users with access to the
internet, via an internet gateway.
Computing resources.
The institution can provide access to special purpose
computing devices which individual users would not normally
own. For example, an institution network might have high-
speed high quality printers strategically located around a
campus for instructor or student use.
Flexible Access.
Institution networks allow students to access their
information from connected devices throughout the school.
Students can begin an assignment in their classroom, save
part of it on a public access area of the network, then go to
the media center after school to finish their work. Students
can also work cooperatively through the network.
Workgroup Computing.

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Collaborative software allows many users to work on a
document or project concurrently. For example, educators
located at various institution within a county could
simultaneously contribute their ideas about new curriculum
standards to the same document, spreadsheets, or website.
Disadvantages of Installing a Network
Expensive to Install.
Large campus networks can carry hefty price tags. Cabling,
network cards, routers, bridges, firewalls, wireless access
points, and software can get expensive, and the installation
would certainly require the services of technicians. But, with
the ease of setup of home networks, a simple network with
internet access can be setup for a small campus in an
afternoon.
Requires Administrative Time.
Proper maintenance of a network requires considerable time
and expertise. Many schools have installed a network, only
to find that they did not budget for the necessary
administrative support.
Servers Fail.
Although a network server is no more susceptible to failure
than any other computer, when the files server "goes down"
the entire network may come to a halt. Good network design
practices say that critical network services (provided by
servers) should be redundant on the network whenever
possible.
Cables May Break.
The Topology chapter presents information about the
various configurations of cables. Some of the configurations
are designed to minimize the inconvenience of a broken
cable; with other configurations, one broken cable can stop
the entire network.
Security and compliance.
Network security is expensive. It is also very important. An
institution network would possibly be subject to more

125
stringent security requirements than a similarly-sized
corporate network, because of its likelihood of storing
personal and confidential information of network users, the
danger of which can be compounded if any network users
are minors. A great deal of attention must be paid to network
services to ensure all network content is appropriate for the
network community it serves.
11.6 WHAT IS A TOPOLOGY?
A topology is a description of the layout of a specific region
or area. A network topology is a description of the layout of the
region or area covered by that network.
There are two types of connections that describe how many
devices connect to a single cable or segment of transmission
media. They are: point-to-point and multi-point.
Point-to-point connections provide a direct link between two
devices; for example, a computer connected directly to a printer, or
a modem to a mainframe.
Multi-point connections provide a link between three or more
devices on a network. All computer networks rely upon point-to-
point and multi-point connections.
11.6.1 The Technical Connotation of Topology
The virtual shape or structure of a network is referred as
topology.
The pattern or layout of interconnections of different
elements or nodes of a computer network is a network topology
that might be logical or physical.
However, the complete physical structure of the cable (or
transmission media) is called the physical topology. The physical
topology of a network refers to the configuration of cables,
computers, and other peripherals.
The way data flows through the network (or transmission
media) is called the logical topology. A logical topology is the
method used to pass information between workstations.

126
11.6.2What are the Basic Types of Topology?
There are seven basic topologies in the study of network topology:
1. Point-to-point topology,
2. Bus (point-to-multipoint) topology,
3. Ring topology,
4. Star topology,
5. Hybrid topology,
6. Mesh topology and
7. Tree topology.
The interconnections between computers whether logical or
physical are the foundation of this classification.
Logical topology is the way a computer in a given network
transmits information, not the way it looks or connected, along with
the varying speeds of cables used from one network to another.
On the other hand the physical topology is affected by a number
of factors:
Troubleshooting technique,
Installation cost,
Office layout and
Cables‘ types.
The physical topology is figured out on the basis of a
network‘s capability to access media and devices, the fault
tolerance desired and the cost of telecommunications circuits.
The classification of networks by the virtue of their physical span is
as follows: Local Area Networks (LAN), Wide Area Internetworks
(WAN) and Metropolitan Area Networks or campus or building
internetworks.
11.6.3 How Is the Physical Topology Classified?
Point-to-Point Network Topology
It is the basic model of typical telephony. The simplest
topology is a permanent connection between two points. The value

127
of a demanding point-to-point network is proportionate to the
number of subscribers‘ potential pairs. It is possible to establish a
permanent circuit within many switched telecommunication
systems: the telephone present in a lobby would always connect to
the same port, no matter what number is being dialed. A switch
connection would save the cost between two points where the
resources could be released when no longer required.
Bus Network Topology
LANs that make use of bus topology connects each node to
a single cable. Some connector connects each computer or server
to the bus cable. For avoiding the bouncing of signal a terminator is
used at each end of the bus cable. The source transmits a signal
that travels in both directions and passes all machines unless it
finds the system with IP address, the intended recipient. The data is
ignored in case the address is unmatched. The installation of one
cable makes bus topology an inexpensive solution as compared to
other topologies; however the maintenance cost is high. If the cable
is broken all systems would collapse.
o Linear Bus: If all network nodes are connected to a combine
transmission medium that has two endpoints the Bus is Linear. The
data transmitted between these nodes is transmitted over the
combine medium and received by all nodes simultaneously.
o Distributed Bus: If all network nodes are connected to a
combine transmission medium that has more than two endpoints
created by branching the main section of the transmitting medium.
A linear bus topology consists of a main run of cable with a
terminator at each end (See fig. 1). All nodes (file server,
workstations, and peripherals) are connected to the linear cable. A
bus topology uses one long cable (backbone) to which network

128
devices are either directly attached or are attached by using short
drop cables. Because all workstations share this bus, a workstation
checks for any information that might be coming down the
backbone before sending their messages. All messages pass the
other workstations on the way to their destinations. Each
workstation then checks the address of each message to see if it
matches its own. Note that bus network topologies, the backbone
must be terminated at both ends to remove the signal from the wire
after it has passed all devices on the network.
Fig. 1. Linear Bus topology
Advantages of a Linear Bus Topology
Easy to connect a computer or peripheral to a linear bus.
Requires less cable length than a star topology.
Disadvantages of a Linear Bus Topology
Entire network shuts down if there is a break in the main
cable.
Terminators are required at both ends of the backbone
cable.
Difficult to identify the problem if the entire network shuts
down.
Not meant to be used as a stand-alone solution in a large
building.

129
Star Network Topology
The topology when each network host is connected to a
central hub in LAN is called Star. Each node is connected to the
hub with a point-to-point connection. All traffic passes through the
hub that serves as a repeater or signal booster. The easiest
topology to install is hailed for its simplicity to add more nodes but
criticized for making hub the single point of failure. The network
could be BMA (broadcast multi-access) or NBMA (non-broadcast
multi-access) depending on whether the signal is automatically
propagated at the hub to all spokes or individually spokes with
those who are addressed.
o Extended Star: A network that keeps one or more than one
repeaters between the central node or hub and the peripheral or
the spoke node, supported by the transmitter power of the hub and
beyond that supported by the standard of the physical layer of the
network.
o Distributed Star: The topology is based on the linear
connectivity that is Daisy Chained with no top or centre level
connection points.
Advantages of a Star Topology
Easy to install and wire.
No disruptions to the network when connecting or removing
devices.
Easy to detect faults and to remove parts.

130
Disadvantages of a Star Topology
Requires more cable length than a linear topology.
If the hub, switch, or concentrator fails, nodes attached are
disabled.
More expensive than linear bus topologies because of the
cost of the hubs, etc.
Ring Network Topology
Ring topology is one of the old ways of building computer
network design and it is pretty much obsolete. FDDI, SONET or
Token Ring technologies are used to build ring technology. It is not
widely popular in terms of usability but incase if you find it
anywhere it will mostly be in schools or office buildings.
Such physical setting sets up nodes in a circular manner
where the data could travel in one direction where each device on
the right serves as a repeater to strengthen the signal as it moves
ahead.
Mesh Network Topology
The exponent of the number of subscribers is proportionate to the
value of the fully meshed networks.
o Fully Connected: For practical networks such topology is
too complex and costly but highly recommended for small number
of interconnected nodes.

131
o Partially Connected: This set up involves the connection of
some nodes to more than one nodes in the network via point-to-
point link. In such connection it is possible to take advantage of the
redundancy without any complexity or expense of establishing a
connection between each node.
Hybrid Topology
Hybrid topologies are a combination of two or more different
topologies. WANs sometimes have hybrid topologies because they
connect a variety of LAN topologies. The big advantage of hybrid
topologies is that they connect disparate topologies. However, the
disadvantage of hybrid topologies is that they are potentially
complex to establish and manage.
Tree Network Topology
The top level of the hierarchy, the central root node is connected to
some nodes that are a level low in the hierarchy by a point-to-point
link where the second level nodes that are already connected to
central root would be connected to the nodes in the third level by a
point-to-point link. The central root would be the only node having
no higher node in the hierarchy. The tree hierarchy is symmetrical.
The BRANCHING FACTOR is the fixed number of nodes
connected to the next level in the hierarchy. Such network must
have at least three levels. Physical Linear Tree Topology would be
of a network whose Branching Factor is one.

132
Advantages of a Tree Topology
Point-to-point wiring for individual segments.
Supported by several hardware and software venders.
Disadvantages of a Tree Topology
Overall length of each segment is limited by the type of
cabling used.
If the backbone line breaks, the entire segment goes down.
More difficult to configure and wire than other topologies.
Considerations When Choosing a Topology
Money. A linear bus network may be the least expensive
way to install a network; you do not have to purchase
concentrators.
Length of cable needed. The linear bus network uses
shorter lengths of cable.
Future growth. With a star topology, expanding a network is
easily done by adding another concentrator.

133
Cable type. The most common cable in schools is
unshielded twisted pair,
11.7 SUMMARY
Knowledge of networking topologies is of core importance of
computer networking design. Computer networks can only
be developed using the knowledge about these topologies
and decide to which topology design is best suited according
to the requirement.
A computer network consists of nodes and communication
links whichimplement its protocols. It interconnects a set of
hosts which conform to thenetwork protocols.
A network may be classified as a LAN, MAN, or WAN,
depending on itsgeographic spread, and as private or
public, depending on its accessrestrictions.
It may employ a point-to-point or a broadcast
communication model. A point-to-point model may be based
on circuit switching or packetswitching.
Exercises:
1. Classify the networks operated and/or utilized by your
organization as LAN, MAN,WAN, private, public, point-to-
point, broadcast, circuit-switched, or packetswitched.
2. Discuss and compare the advantages and disadvantages of
circuit switching versuspacket switching. Name at least one
well-known network which is based on eithertype of
switching.
11.8 REVIEW QUESTION
1. What is a Network?
2. Explain Lan, Man, Wan?
3. Write a short note on Network coverage?

134
4. ExplainAn Illustrated Example of a University Network
5. What is a Topology?
6.What are the Basic Types of Topology?
7.How Is the Physical Topology Classified?
11.9 REFERENCES
http://www.garymgordon.com/misc/tutorials/networking/Lesson2.pdf
http://networkworld.com/ns/books/ciscopress/samples/0735700745.
pdf
http://pages.cs.wisc.edu/~tvrdik/7/html/Section7.html
http://fcit.usf.edu/network/chap2/chap2.htm
www.pragsoft.com Chapter 4: The Network Layer 57
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12
INTRODUCTION TO ROUTING
Unit Structure
12.0 Objective
12.1 What Is Routing?
12.1.1 Components
12.1.2 Path Determination
12.2Switching
12.3 Introduction to algorithm
12.3.1 Design Goals
12.3.2 Routing Algorithm Types
12.4 Routing Metrics
12.5 Summary
12.6 Review question
12. References
12.0 OBJECTIVE
Introduction to switches and router
Routing concept
Concept of switching
Routing algorithms
Static and dynamic routing
Routing metrics

136
12.0 WHAT IS ROUTING?
Routing is the act of moving information across an
internetwork from a source to a destination. Along the way, at least
one intermediate node typically is encountered. Routing is often
contrasted with bridging, which might seem to accomplish precisely
the same thing to the casual observer. The primary difference
between the two is that bridging occurs at Layer 2 (the link layer) of
the OSI reference model, whereas routing occurs at Layer 3 (the
network layer). This distinction provides routing and bridging with
different information to use in the process of moving information
from source to destination, so the two functions accomplish their
tasks in different ways.
12.1.1 Routing Components
Routing involves two basic activities: determining optimal
routing paths and transporting information groups (typically called
packets) through an internetwork. In the context of the routing
process, the latter of these is referred to as packet switching.
Although packet switching is relatively straightforward, path
determination can be very complex.
12.1.2 Path Determination
Routing protocols use metrics to evaluate what path will be
the best for a packet to travel. A metric is a standard of
measurement, such as path bandwidth, that is used by routing
algorithms to determine the optimal path to a destination. To aid the
process of path determination, routing algorithms initialize and
maintain routing tables, which contain route information. Route
information varies depending on the routing algorithm used.
Routing algorithms fill routing tables with a variety of
information. Destination/next hop associations tell a router that a
particular destination can be reached optimally by sending the
packet to a particular router representing the ―next hop‖ on the way
to the final destination. When a router receives an incoming packet,
it checks the destination address and attempts to associate this
address with a next hop.

137
Fig. Destination/Next Hop Associations Determine the Data’s
Optimal Path
Routing tables also can contain other information, such as
data about the desirability of a path. Routers compare metrics to
determine optimal routes, and these metrics differ depending on the
design of the routing algorithm used.
Routers communicate with one another and maintain their
routing tables through the transmission of a variety of messages.
The routing update message is one such message that generally
consists of all or a portion of a routing table. By analyzing routing
updates from all other routers, a router can build a detailed picture
of network topology. A link-state advertisement, another example of
a message sent between routers, informs other routers of the state
of the sender‘s links. Link information also can be used to build a
complete picture of network topology to enable routers to determine
optimal routes to network destinations.
12.2 SWITCHING
Switching algorithms is relatively simple; it is the same for
most routing protocols. In most cases, a host determines that it
must send a packet to another host. Having acquired a router‘s
address by some means, the source host sends a packet
addressed specifically to a router‘s physical (Media Access Control
[MAC]-layer) address, this time with the protocol (network layer)
address of the destination host.
As it examines the packet‘s destination protocol address, the
router determines that it either knows or does not know how to
forward the packet to the next hop. If the router does not know how
to forward the packet, it typically drops the packet. If the router
knows how to forward the packet, however, it changes the
destination physical address to that of the next hop and transmits
the packet. The next hop may be the ultimate destination host. If
not, the next hop is usually another router, which executes the
same switching decision process. As the packet moves through the

138
internetwork, its physical address changes, but its protocol address
remains constant.
The preceding discussion describes switching between a
source and a destination end system. The International
Organization for Standardization (ISO) has developed a
hierarchical terminology that is useful in describing this process.
Using this terminology, network devices without the capability to
forward packets between subnetworks are called end systems
(ESs), whereas network devices with these capabilities are called
intermediate systems (ISs). ISs are further divided into those that
can communicate within routing domains (intradomain ISs) and
those that communicate both within and between routing domains
(interdomain ISs). A routing domain generally is considered a
portion of an internetwork under common administrative authority
that is regulated by a particular set of administrative guidelines.
Routing domains are also called autonomous systems.With certain
protocols, routing domains can be divided into routing areas, but
intradomain routing protocols are still used for switching both within
and between areas.
Fig.of switching

139
12.3 INTRODUCTION TO ALGORITHM
Routing Algorithms- Introduction
Routing algorithms can be differentiated based on several
key characteristics. First, the particular goals of the algorithm
designer affect the operation of the resulting routing protocol.
Second, various types of routing algorithms exist, and each
algorithm has a different impact on network and router resources.
Finally, routing algorithms use a variety of metrics that affect
calculation of optimal routes. The following sections analyze these
routing algorithm attributes.
12.3.1Design Goals
Routing algorithms often have one or more of the following
design goals:
• Optimality
• Simplicity and low overhead
• Robustness and stability
• Rapid convergence
• Flexibility
 Optimality refers to the capability of the routing algorithm to
select the best route, which depends on the metrics and
metric weightings used to make the calculation.
For example, one routing algorithm may use a number of
hops and delays, but it may weigh delay more heavily in the
calculation. Naturally, routing protocols must define their metric
calculation algorithms strictly.
 Routing algorithms also are designed to be as simple as
possible. In other words, the routing algorithm must offer its
functionality efficiently, with a minimum of software and
utilization overhead. Efficiency is particularly important when
the software implementing the routing algorithm must run on
a computer with limited physical resources.
 Routing algorithms must be robust, which means that they
should perform correctly in the face of unusual or unforeseen
circumstances, such as hardware failures, high load
conditions, and incorrect implementations. Because routers
are located at network junction points, they can cause
considerable problems when they fail. The best routing

140
algorithms are often those that have withstood the test of
time and that have proven stable under a variety of network
conditions.
 In addition, routing algorithms must converge rapidly.
Convergence is the process of agreement, by all routers, on
optimal routes. When a network event causes routes to
either go down or become available, routers distribute
routing update messages that permeate networks,
stimulating recalculation of optimal routes and eventually
causing all routers to agree on these routes. Routing
algorithms that converge slowly can cause routing loops or
network outages.
 Routing algorithms should also be flexible, which means that
they should quickly and accurately adapt to a variety of
network circumstances. Assume, for example, that a network
segment has gone down. As many routing algorithms
become aware of the problem, they will quickly select the
next-best path for all routes normally using that segment.
Routing algorithms can be programmed to adapt to changes
in network bandwidth, router queue size, and network delay,
among other variables.
 12.3.2 Routing Algorithm Types
Routing algorithms can be classified by type. Key
differentiators include these:
1. Static versus dynamic
2. Single-path versus multipath
3. Flat versus hierarchical
4. Host-intelligent versus router-intelligent
5. Intradomain versus interdomain
6. Link-state versus distance vector
1. Static Versus Dynamic
Static routing algorithms are hardly algorithms at all, but are
table mappings established by the network administrator before the
beginning of routing. These mappings do not change unless the
network administrator alters them. Algorithms that use static routes
are simple to design and work well in environments where network
traffic is relatively predictable and where network design is
relatively simple.

141
Because static routing systems cannot react to network
changes, they generally are considered unsuitable for today‘s large,
constantly changing networks. Most of the dominant routing
algorithms today are
Dynamic routing algorithms, which adjust to changing
network circumstances by analyzing incoming routing update
messages. If the message indicates that a network change has
occurred, the routing software recalculates routes and sends out
new routing update messages. These messages permeate the
network, stimulating routers to rerun their algorithms and change
their routing tables accordingly.
Dynamic routing algorithms can be supplemented with static
routes where appropriate. A router of last resort (a router to which
all unroutable packets are sent), for example, can be designated to
act as a repository for all unroutable packets, ensuring that all
messages are at least handled in some way.
2. Single-Path Versus Multipath
Some sophisticated routing protocols support multiple paths
to the same destination. Unlike single-path algorithms, these
multipath algorithms permit traffic multiplexing over multiple lines.
The advantages of multipath algorithms are obvious: They can
provide substantially better throughput and reliability. This is
generally called load sharing.
3. Flat Versus Hierarchical
Some routing algorithms operate in a flat space, while others
use routing hierarchies.
In a flat routing system, the routers are peers of all others. In
a hierarchical routing system, some routers form whatamounts to a
routing backbone. Packets from nonbackbone routers travel to the
backbone routers, wherethey are sent through the backbone until
they reach the general area of the destination. At this point,
theytravel from the last backbone router through one or more
nonbackbone routers to the final destination.Routing systems often
designate logical groups of nodes, called domains, autonomous
systems, or areas.
In hierarchical systems, some routers in a domain can
communicate with routers in other domains, while others can
communicate only with routers within their domain. In very large
networks, additional hierarchical levels may exist, with routers at
the highest hierarchical level forming the routing backbone.

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The primary advantage of hierarchical routing is that it mimics
the organization of most companies and therefore supports their
traffic patterns well. Most network communication occurs within
small company groups (domains). Because intradomain routers
need to know only about other routers within their domain, their
routing algorithms can be simplified, and, depending on the routing
algorithm being used, routing update traffic can be reduced
accordingly.
4. Host-Intelligent Versus Router-Intelligent
Some routing algorithms assume that the source end node
will determine the entire route. This is usually referred to as source
routing. In source-routing systems, routers merely act as store-and-
forward devices, mindlessly sending the packet to the next stop.
Other algorithms assume that hosts know nothing about routes. In
these algorithms, routers determine the path through the
internetwork based on their own calculations. In the first system,
the hosts have the routing intelligence. In the latter system, routers
have the routing intelligence.
5. Intradomain Versus Interdomain
Some routing algorithms work only within domains; others
work within and between domains. The nature of these two
algorithm types is different. It stands to reason, therefore, that an
optimal intradomain-routing algorithm would not necessarily be an
optimal interdomain-routing algorithm.
6. Link-State Versus Distance Vector
Link-state algorithms (also known as shortest path first
algorithms) flood routing information to all nodes in the
internetwork. Each router, however, sends only the portion of the
routing table that describes the state of its own links. In link-state
algorithms, each router builds a picture of the entire network in its
routing tables.
Distance vector algorithms (also known as Bellman-Ford
algorithms) call for each outer to send all or some portion of its
routing table, but only to its neighbors. In essence, link-state
algorithms send small updates everywhere, while distance vector
algorithms send larger updates only to neighboring routers.
Distance vector algorithms know only about their neighbors.
Because they converge more quickly, link-state algorithms are
somewhat less prone to routing loops than distance vector
algorithms. On the other hand, link-state algorithms require more
CPU power and memory than distance vector algorithms. Link-state
algorithms, therefore, can be more expensive to implement and
support. Link-state protocols are generally more scalable than
distance vector protocols.

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12.4 ROUTING METRICS
Routing tables contain information used by switching
software to select the best route. Routing algorithms have used
many different metrics to determine the best route. Sophisticated
routing algorithms can base route selection on multiple metrics,
combining them in a single (hybrid) metric. All the following metrics
have been used:
• Path length
• Reliability
• Delay
• Bandwidth Load
• Communication cost
 Path length is the most common routing metric. Some routing
protocols allow network administrators to assign arbitrary costs
to each network link. In this case, path length is the sum of the
costs associated with each link traversed. Other routing
protocols define hop count, a metric that specifies the number of
passes through internetworking products, such as routers, that a
packet must take en route from a source to a destination.
 Reliability, in the context of routing algorithms, refers to the
dependability (usually described in terms of the bit-error rate) of
each network link. Some network links might go down more
often than others. After a network fails, certain network links
might be repaired more easily or more quickly than other links.
Any reliability factors can be taken into account in the
assignment of the reliability ratings, which are arbitrary numeric
values usually assigned to network links by network
administrators.
 Routing delay refers to the length of time required to move a
packet from source to destination through the internetwork.
Delay depends on many factors, including the bandwidth of
intermediate network links, the port queues at each router along
the way, network congestion on all intermediate network links,
and the physical distance to be travelled. Because delay is a
conglomeration of several important variables, it is a common
and useful metric.

144
 Bandwidth refers to the available traffic capacity of a link. All
other things being equal, a 10-Mbps Ethernet link would be
preferable to a 64-kbps leased line. Although bandwidth is a
rating of the maximum attainable throughput on a link, routes
through links with greater bandwidth do not necessarily provide
better routes than routes through slower links. For example, if a
faster link is busier, the actual time required to send a packet to
the destination could be greater.
 Load refers to the degree to which a network resource, such as
a router, is busy. Load can be calculated in a variety of ways,
including CPU utilization and packets processed per second.
Monitoring these parameters on a continual basis can be
resource-intensive itself.
 Communication cost is another important metric, especially
because some companies may not care about performance as
much as they care about operating expenditures. Although line
delay may be longer, they will send packets over their own lines
rather than through the public lines that cost money for usage
time.
12.5 SUMMARY
Routing is the act of moving information across an
internetwork from a source to a destination.
Routing involves two basic activities: determining optimal
routing paths and transporting information groups (typically
called packets) through an internetwork.
the best for a packet to travel.
the best for a packet to travel.
Switching algorithms is relatively simple; it is the same for
most routing protocols.
Routing algorithms often have one or more of the following
design goals:
• Optimality
• Simplicity and low overhead
• Robustness and stability
• Rapid convergence
• Flexibility

145
Routing tables contain information used by switching
software to select the best route.
1. Explain routing concept?
2. Explain switching concept?
3. Discuss design goal?
4. Explain routing algorithms?
5. Explain Routing metrics?
12.6 LIST OF REFERENCES
Stamper, D. (1993) Local Area Networks, Addison-Wesley,
Reading, MA.
Stamper, D. (1991) Business Data Communications, Third
Edition, Addison-Wesley, Reading, MA.
Stone, H. (1982), Microcomputer Interfacing, Addison-Wesley,
Reading, MA.
Tanenbaum, A. (1989), Computer Networks, Second Edition,
Prentice Hall, Englewood Cliffs, NJ.
Van Duuren, J., Schoute, F., and Kastelein, P. (1992)
Telecommunications
Networks and Services, Addison-Wesley, Reading, MA.
Viniotis Y. and Onvural R. (editors) (1993) Asynchronous
Transfer Mode, Networks, Plenum, New York, NY.
White, G. (1992) Internetworking and Addressing, McGraw-Hill,
NY.
Zitsen, W. (1990) ‗Metropolitan Area Networks: Taking LANs
into the Public, Network,‘ Telecommunications, pp. 53-60.
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13
SWITCHING CONCEPTS
Unit Structure
13.0 Objective
13.1 Introduction
13.2 Switching Methods
 13.2.1 Circuit Switching
 13.2.2Switching Node
 13.2.3 Time Division Switching
 13.2.4 Packet Switching
 13.2.5 Switching Modes
13.3 Summary
13.4Review Questions
13.5References
13.0 OBJECTIVE
 Introduce switching concept
 Define switching node
 Define packet switching
 Switching mode
13.1 INTRODUCTION
Switching is the generic method for establishing a path for
point-to-point communication in a network. It involves the nodes in

147
the network utilizing their direct communication lines to other nodes
so that a path is established in a piecewise fashion. Each node has
the capability to ‗switch‘ to a neighbouring node (i.e., a node to
which it is directly connected) to further stretch the path until it is
completed.
One of the most important functions of the network layer is to
employ theswitching capability of the nodes in order to route
messages across the network.There are two basic methods of
switching circuit switching and packet switching.
13.2.1. Circuit Switching
Figure 13.2.1 A „switched‟ path.
In circuit switching, two communicating stations are
connected by a dedicated communication path which consists of
intermediate nodes in the network and thelinks that connect these
nodes.
Figure 13.2.1 shows a simple circuit switch which consists of a 3×3
matrix, capable of connecting any of its inlets (a, b, and c) to any of
its outlets (d, e, and f). Each crosspoint appears as a circle. A
hollow circle means that the crosspoint is off (i.e., the two crossing
wires are not connected). A solid circles means that the crosspoint
is on (i.e., the crossing wires are connected).

148
Switches may also have more inlets than outlets, or more outlets
than inlets.)
Figure 13.2.2 A simple circuit switch.
When the two hosts shown in the figure initiate a connection,
the network determines a path through the intermediate switches
and establishes a circuit which is maintained for the duration of the
connection. When the hosts disconnect, the network releases the
circuit.
Fig 13.2.3 Circuit switching.
Communication via circuit switching implies that there is a
dedicated communication path between the two stations. The path
is a connected through a sequence of links between network
nodes. On each physical link, a logical channel is dedicated to the
connection. Circuit switching is commonly used technique in
telephony, where the caller sends a special message with the
address of the callee (i.e. by dialling a number) to state its
destination. It involved the following three distinct steps, as shown
in Fig. 13.2.3
Circuit Establishment: To establish an end-to-end connection
before any transfer of data.

149
Some segments of the circuit may be a dedicated link, while some
other segments may be shared.
Data transfer:
Transfer data is from the source to the destination.
The data may be analog or digital, depending on the nature
of the network.
The connection is generally full-duplex.
Circuit disconnect:
Terminate connection at the end of data transfer.
• Signals must be propagated to deallocate the dedicated
resources.
Fig: 13.2.4 Circuit Switching technique
13.2.2 Switching Node
Let us consider the operation of a single circuit switched node
comprising a collection of stations attached to a central switching
unit, which establishes a dedicated path between any two devices
that wish to communicate.
Major elements of a single-node network are summarized below:
Digital switch: That provides a transparent (full-duplex) signal path
between any pair of attached devices.

150
Network interface:That represents the functions and hardware
needed to connect digital devices to the network (like telephones).
Control unit:That establishes, maintains, and tears down a
connection.
An important characteristic of a circuit-switch node is
whether it is blocking or non-blocking.
A blocking network is one, which may be unable to connect
two stations because all possible paths between them are already
in use. A non-blocking network permits all stations to be connected
(in pairs) at once and grants all possible connection requests as
long as the called party is free. For a network that supports only
voice traffic, a blocking configuration may be acceptable, since
most phone calls are of short duration. For data applications, where
a connection may remain active for hours, non-blocking
configuration is desirable.
Fig 13.2.5 Schematic Diagram of a Switching node
Circuit switching uses any of the three technologies: Space-
division switches, Time-division switches or a combination of
both. In Space-division switching, the paths in the circuit are
separated with each other spatially, i.e. different ongoing
connections, at a same instant of time, uses different switching
paths, which are separated spatially. This was originally developed

151
for the analog environment, and has been carried over to the digital
domain. Some of the space switches are crossbar switches, Multi-
stage switches (e.g. Omega Switches). A crossbar switch is shown
in Fig. Fig 13.2.6 . Basic building block of the switch is a metallic
crosspoint or semiconductor gate that can be enabled or disabled
by a control unit.
Fig 13.2.6 Schematic diagram of a crossbar switch
Limitations of crossbar switches are as follows:
• The number of crosspoints grows with the square of the number
of attached stations.
• Costly for a large switch.
• The failure of a crosspoint prevents connection between the two
devices whose lines intersect at that crosspoint.
• The crosspoints are inefficiently utilized.
• Only a small fraction of crosspoints are engaged even if all of
the attached devices are active.
Some of the above problems can be overcome with the help
of multistage space division switches. By splitting the crossbar
switch into smaller units and interconnecting them, it is possible to
build multistage switches with fewer crosspoints.

152
Fig 13.2.6 A three-stage space division
switch
Fig 13.2.7 Block nature of the switch
Figure Fig 13.2.6 shows a three-stage space division switch. In
this case the number of crosspoints needed goes down from 64 to
40. There is more than one path through the network to connect
two endpoints, thereby increasing reliability. Multistage switches
may lead to blocking. The problem may be tackled by increasing
the number or size of the intermediate switches, which also
increases the cost. The blocking feature is illustrated in Fig. Fig
13.2.7 . As shown in Fig. Fig 13.2.7 , after setting up connections
for 1-to-3 and 2-to-4, the switch cannot establish connections for 3-
to-6 and 4-to-5.

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13.2.3 Time Division Switching
Both voice and data can be transmitted using digital signals
through the same switches. All modern circuit switches use digital
time-division multiplexing (TDM) technique for establishing and
maintaining circuits. Synchronous TDM allows multiple low-speed
bit streams to share a high-speed line.
13.2.8 TIME Division Multiplexing
Time-division switching uses time-division multiplexing to
achieve switching, i.e. different ongoing connections can use same
switching path but at different interleaved time intervals.
13.2.4 Packet Switching
Packet switching was designed to address the shortcomings
of circuit switching in dealing with data communication. Unlike
circuit switching where communication is continuous along a
dedicated circuit, in packet switching, communication is discrete in
form of packets. Each packet is of a limited size and can hold up to
a certain number of octets of user data. Larger messages are
broken into smaller chunks so that they can be fitted into packets.
In addition to user data, each packet carries additional information

154
(in form of a header) to enable the network to route it to its final
destination.
A packet is handed over from node to node across the
network. Each receiving node temporarily stores the packet, until
the next node is ready to receive it, and then passes it onto the next
node. This technique is called store-and-forward and overcomes
one of the limitations of circuit switching. A packet-switched
network has a much higher capacity for accepting further
connections. Additional connections are usually not blocked but
simply slow down existing connections, because they increase the
overall number of packets in the network and hence increase the
delivery time of each packet. Figure 13.2.9 shows a simple packet
switch with six I/O channels (a through f). Each channel has an
associated buffer which it uses to store packets in transit. The
operation of the switch is controlled by a microprocessor. A packet
received on anynof the channels can be passed onto any of the
other channels by the microprocessor moving it to the
corresponding buffer.
Figure 13.2.9 A simple packet switch.
Two variations of packet switching exist: virtual circuit and
datagram. The virtual circuit method (also known as connection-
oriented) is closer to circuit switching. Here a complete route is
worked out prior to sending data packets. The route is established
by sending a connection request packet along the route to the
intended destination. This packet informs the intermediate nodes
about the connection and the established route so that they will
know how to route subsequent packets. The result is a circuit
somewhat similar to those in circuit switching, except that it uses
packets as its basic unit of communication. Hence it is called a
virtual circuit.
Each packet carries a virtual circuit identifier which enables a
node to determine to which virtual circuit it belongs and hence how

155
it should be handled. (The virtual circuit identifier is essential
because multiple virtual circuits may pass through the same node
at the same time.) Because the route is fixed for the duration of the
call, the nodes spend no effort in determining how to route packets.
Fig 13.2.10 illustrates the virtual circuit method using the switch.
When the two hosts initiate a connection, the network layer
establishes a virtual circuit (denoted by shaded switches) which is
maintained for the duration of the connection. When the hosts
disconnect, the network layer releases the circuit. The packets in
transit are displayed as dark boxes within the buffers. These
packets travel only along the designatedvirtual circuit.
Figure 13.2.10 Packet switching with virtual circuits.
The datagram method (also known as connectionless)
does not rely on a pre-established route, instead each packet is
treated independently. Therefore, it ispossible for different packets
to travel along different routes in the network to reach the same
final destination. As a result, packets may arrive out of order, or
even never arrive (due to node failure). It is up to the network user
to deal with lost packets, and to rearrange packets to their original
order. Because of the absence of a preestablishedcircuit, each
packet must carry enough information in its header to enable the
nodes to route it correctly.

156
Figure 13.2.11 illustrates the datagram method. Note how the
packets exercise different routes.
13.2.11 Packet switching with datagrams.
The advantage of the datagram approach is that because
there is no circuit, congestion and faulty nodes can be avoided by
choosing a different route. Also, connections can be established
more quickly because of reduced overheads. This makes
datagrams better suited than virtual circuits for brief connections.
For example, database transactions in banking systems are of this
nature, where each transaction involves only a few packets.
The advantage of the virtual circuit approach is that because
no separate routing is required for each packet, they are likely to
reach their destination more quickly; this leads to improved
throughput. Furthermore, packets always arrive in order.
Virtual circuits are better suited to long connections that
involve the transfer of large amounts of data (e.g., transfer of large
files). Because packet switching is the more dominant form of
switching for data communication, we will focus our attention on
this form of switching from now on.
13.2.5 Switching Modes

157
Any delay in passing traffic is known as latency. Switches
offer three ways to switch the traffic depending upon how
thoroughly you want the frame to be checked before it is passed
on. The more checking you want, the more latency you will
introduce to the switch.
The three switching modes to choose from are:
Cut-through
Store-and-forward
Fragment-free
 Cut-through Mode
Cut-through switching is the fastest switching method
meaning it has the lowest latency. The incoming frame is read up to
the destination MAC address. Once it reaches the destination MAC
address, the switch then checks its CAM table for the correct port to
forward the frame out of and sends it on its way. There is no error
checking, so this method gives you the lowest latency. The price,
however, is that the switch will forward any frames containing
errors.
The process of switching modes can best be described by
using a metaphor.
 Store-and-forward Mode
Here the switch reads the entire frame and copies it into its
buffers. A cyclic redundancy check (CRC) takes place to check the
frame for any errors. If errors are found, the frame is dropped.
Otherwise the switching table is examined and the frame
forwarded.
 Fragment-free (modified cut-through/runt-free) Mode
Since cut-through can ensure that all frames are good and
store-and-forward takes too long, we need a method that is both
quick and reliable. Using our example of the nightclub security,
imagine you are asked to make sure that everyone has an ID and
that the picture matches the person. With this method you have
made sure everyone is who they say they are, but you do not have
to take down all the information. In switching we accomplish this by
using the fragment-free method of switching.
13.3 SUMMARY
The generic method for establishing a path for point-to-point
communication in anetwork is called switching. There are two
general switching methods: circuitswitching and packet switching.
In circuit switching two communicating stations are connected by
a dedicatedcommunication path.

158
In packet switching communication is discrete in form of
packets. The packetsare handled by the intermediate nodes in a
store-and-forward fashion. Packetswitching is either based on
virtual circuits or on datagrams.
The task of selecting a path for the transport of packets across
the network iscalled routing. The three classes of routing
algorithms are: flooding, staticrouting, and dynamic routing.
1. Define Circuit Switching
2. Explain Switching Node
3. Explain Time Division Switching
13.5 LIST OF REFERENCES
Black, U. (1989), Data Networks: Concepts, Theory, and
Practice, Prentice
Hall, Englewood Cliffs, NJ.
Gitlin, R. D., Hayes, J. F., and Weinstein, S. B. (1992) Data
Communication
Principles, Plenum, New York, NY.
Hughes, L. (1992) Data Communications, McGraw-Hill, NY.
Kessler, G. and Train, D. (1992) Metropolitan Area
Networks: Concepts,
Standards, and Service, McGraw-Hill, NY.
Martin, J. and Leben, J. (1988), Principles of Data
Communication, Prentice
Hall, Englewood Cliffs, NJ.
Spohn, D. (1993) Data Network Design, McGraw-Hill, NY.
Stallings, W. (1990), Handbook of Computer
Communications Standards, Volumes I and II, Howard Sams
and Company, Carmel.
Stallings, W. (1992), ISDN and Broadband ISDN, Second
Edition, Macmillan, NY.
Stallings, W. (1994), Data and Computer Communications,
Fourth Edition, Macmillan, NY.
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14
INTRODUCTION TO IP Version 6 ( IPv6)
Unit Structure
14.0 OBJECTIVES
14.1 INTRODUCTION
14.2 An Overview
14.2.1 IPv6 Introduction
14.2.2IPv6 Packet Format
14.2.3IPv6 Extension Headers
14.2.4Fragmentation in IPv6
14.2.5IPv6 Addressing
14.3 Summary
14.5 References
14.0 OBJECTIVES:
To briefly understand the major functions of addresses in the
Internetworking arena
To discusses the problems and the drawbacks of IPv4
addressing.
It discusses how IPv6 can be used in the future of
internetworking
It reviews the areas that IPv6 technology covers the
technologies and design approaches used when used with the
latest technology.
14.0 INTRODUCTION
This chapter provides a brief introduction on the IP
networking Protocol that uses the internet to connect to Learn the
characteristics of IPv6 routing Learn the properties of IPSec
security, It emphasises on the the various standards and optional
headers supported by IPv6 packets.

160
14.2 AN OVERVIEW
14.2.1 IPv6 Introduction
Definition : What is IPv6?
Internet Protocol version 6 (IPv6) is a networking protocol
that allows Windows users to communicate with other users over
the Internet. It interacts with Windows naming services such as
Domain Name System (DNS) and uses security technologies such
as Internet Protocol security (IPSec), because they help facilitate
the successful andsecure transfer of IP packets between
computers.IPv6 supplants IPv4, pure IPv6 across the Internet will
become more prevalent and will eventually replace IPv4.
Specifically, IPv6 contains addressing and control
information to route packets for the next generation Internet.We
believe that the expansion of the Internet is important and upgrades
are sometimes warranted. Gathering information concerning every
aspects of IPv6 we would hope to provide knowledge about this
technology so everyone can benefit. It is therefore also called the
Next Generation Internet Protocol or IPng .
Why we need IPv6 Addressing
IPv6 addresses the main problem of IPv4, that is, the
exhaustion of addresses to connect computers or host in a packet-
switched network. IPv6 has a very large address space and
consists of 128 bits as compared to 32 bits in IPv4. The extended
address length offered by IPv6 eliminates the need to use
techniques such as network address translation to avoid running
out of the available address space. IPv6 contains addressing and
control information to route packets for the next generation Internet.
Therefore, it is now possible to support 2^128 unique IP
addresses, a substantial increase in number of computers that can
be addressed with the help of IPv6 addressing scheme.
14.2.2IPv6 Packet
Like IPv4, IPv6 is a connectionless, unreliable datagram
protocol that is primarily responsible for addressing and routing
packets between hosts. An IPv6 packet consists of an IPv6 header
and an IPv6 payload. The IPv6 payload consists of zero or more
IPv6 extension headers and an upper layer protocol data unit, such
as an ICMPv6 message, a TCP segment, or a UDP message. The
following figure shows the structure of an IPv6 packet.

161
IPv4 Header vs. IPv6 Header
Structure of an IPv6 Packet
Key Fields in the IPv6 Header
IP HEADER FIELD FUNCTION
Source Address: Identifies the IPv6 address of the original
source of the packet.
Destination Address: Identifies the IPv6 address of the
intermediate or final destination of the packet.
Next Header: Identifies either the extension header
immediately following the IPv6 header or an upper layer
protocol, such as ICMPv6, TCP, or UDP.
Hop Limit: Designates the number of subnets, or network
segments, on which the packet is allowed to travel before
being discarded by a router. The sending host sets the Hop
• The IPv4 header
has 20 octets
containing 12
basic header
fields.
• The IPv6 header
has 40 octets
containing 8
fields.
• Three of these fields are identical in
nature.
• Other fields serve similar functions as in
IPv4.
• The remaining IPv4 fields no longer exist
in IPv6.

162
Limit, which prevents packets from endlessly circulating on
an IPv6 internetwork. When forwarding an IPv6 packet,
routers decrement the Hop Limit by one.
14.2.3 IPv6 Extension Headers
Zero or more extension headers of varying lengths can be
present. If any extension headers are present, a Next Header field
in the IPv6 header indicates the first extension header. In a typical
IPv6 packet, no extension headers are present. The sending host
adds one or more extension headers only if either an intermediate
router or the destination requires special handling.
Within each extension header is another Next Header field
that indicates the next extension header. The last extension header
indicates the upper layer protocol (such as TCP, UDP, or ICMPv6)
contained within the upper layer protocol data unit.
The IPv6 header and extension headers replace the
existing IPv4 header with options. The new extension header
format allows IPv6 to be augmented to support future needs and
capabilities. Unlike options in the IPv4 header, IPv6 extension
headers have no maximum size and can expand to accommodate
all the extension data needed for IPv6 communication.

163
Following extension headers, which all IPv6 nodes must support:
Hop-by-Hop Options header
Destination Options header
Routing header
Fragment header
Authentication header
Encapsulating Security Payload header
14.2.4 Fragmentation in IPv6
If an IPv4 router receives a packet that is too large for
the network segment to which the packet is being forwarded and
fragmentation of the packet is allowed, IPv4 fragments the original
packet into smaller packets that fit on the downstream network
segment. In IPv6, only the sending host performs fragmentation. If
an IPv6 router cannot forward a packet because it is too large, the
router sends an ICMPv6 Packet Too Big message to the sending
host and discards the packet.
Use of the Fragment extension header facilitates sending
host fragmentation and destination host reassembly.
14.2.5 IPv6 Addressing
IPv6 Address Syntax
Types of IPv6 Addresses
The most obvious distinguishing feature of IPv6 is its use of
much larger addresses. The size of an address in IPv6 is 128 bits,
which is four times larger than an IPv4 address. A 32-bit address
space includes 232 or 4,294,967,296 possible addresses. A 128-bit
address space includes 2128
or 340,282, 366, 920, 938, 463, 463,
374, 607, 431, 768, 211, 456 (or 3.4×1038
) possible addresses.

164
It is even harder to conceive that the IPv6 address space
will be consumed. A 128-bit address space provides 655, 570, 793,
348, 866, 943, 898, 599 (6.5×1023
) addresses for every square
meter of the Earth‘s surface.
It is important to remember that the decision to make the
IPv6 address 128 bits long was not so that every square meter of
the Earth could have 6.5×1023
addresses. Rather, the relatively
large size of the IPv6 address is designed to be subdivided into
hierarchical routing domains that reflect the topology of the modern
Internet. The use of 128 bits allows multiple levels of hierarchy and
flexibility in designing hierarchical addressing and routing that is
currently lacking in the IPv4-based Internet.
IPv6 Address Syntax
IPv4 addresses are represented in dotted-decimal format.
These 32-bit addresses are divided along 8-bit boundaries. Each
set of 8 bits is converted to its decimal equivalent and separated
from the other sets by periods. For IPv6, the 128-bit address is
divided along 16-bit boundaries. Each 16-bit block is converted to a
4-digit hexadecimal number and separated by colons. The resulting
representation is known as colon-hexadecimal.
The following is an IPv6 address in binary form:
00100001110110100000000011010011000000000000000000101
11100111011
00000010101010100000000011111111111111100010100010011
10001011010
The 128-bit address is divided along 16-bit boundaries:
0010000111011010 0000000011010011 0000000000000000
0010111100111011 0000001010101010 0000000011111111
1111111000101000 1001110001011010
Each 16-bit block is converted to hexadecimal and delimited with
colons. The result is:
21DA:00D3:0000:2F3B:02AA:00FF:FE28:9C5A
IPv6 representation can be further simplified by removing the
leading zeros within each 16-bit block. However, each block must
have at least a single digit. With leading zero suppression, the
address representation becomes:
21DA:D3:0:2F3B:2AA:FF:FE28:9C5A

165
Compressing Zeros
Some types of addresses contain long sequences of zeros. To
further simplify the representation of IPv6 addresses, a contiguous
sequence of 16-bit blocks set to 0 in the colon-hexadecimal format
can be compressed to ―::,‖ known as double-colon.
For example, the link-local address of
FE80:0:0:0:2AA:FF:FE9A:4CA2 can be compressed to
FE80::2AA:FF:FE9A:4CA2. The multicast address
FF02:0:0:0:0:0:0:2 can be compressed to FF02::2.
Zero compression can be used to compress only a single
contiguous series of 16-bit blocks expressed in colon-hexadecimal
notation. You cannot use zero compression to include part of a 16-
bit block. For example, you cannot express FF02:30:0:0:0:0:0:5 as
FF02:3::5.
To determine how many 0 bits are represented by the
double colon, you can count the number of blocks in the
compressed address, subtract this number from 8, and then
multiply the result by 16. For example, the address FF02::2 has two
blocks (the ―FF02‖ block and the ―2‖ block.) The number of 0 bits
expressed by the double colon is 96 (96 = (8 – 2)×16).
Zero compression can be used only once in a given address.
Otherwise, you could not determine the number of 0 bits
represented by each double colon.
Types of IPv6 Addresses
IPv6 supports three types of addresses:
Unicast
A unicast address identifies a single interface within the
scope of the type of unicast address. With the appropriate
unicast routing topology, packets addressed to a unicast
address are delivered to a single interface. To accommodate
load-balancing systems, allows multiple interfaces to use the
same address as long as they appear as a single interface to
the IPv6 implementation on the host.
Multicast
A multicast address identifies multiple interfaces. With the
appropriate multicast routing topology, packets addressed to
a multicast address are delivered to all interfaces that are
identified by the address. A multicast address is used for
one-to-many communication, with delivery to multiple
interfaces.

166
Anycast
An anycast address identifies multiple interfaces. With the
appropriate routing topology, packets addressed to an
anycast address are delivered to a single interface, the
nearest interface that is identified by the address. The
nearest interface is defined as being closest in terms of
routing distance. An anycast address is used for one-to-one-
of-many communication, with delivery to a single interface.
ADDRESS
TYPE
DESCRIPTION TOPOLOGY
UNICAST “One to One‖
An address
destined for a
single interface.
A packet sent to a
unicast address is
delivered to the
interface identified
by that address.
MULTICAST “One to Many”
An address for a
set of interfaces
(typically
belonging to
different nodes).
A packet sent to a
multicast address
will be delivered to
all interfaces
identified by that
address.
ANYCAST ―One to Nearest‖
(Allocated from Unicast)
• An address for a
set of interfaces.
• In most cases
these interfaces
belong to different
nodes.
• A packet sent to
an anycast
address is
delivered to the

167
closest interface
as determined by
the IGP.
14.3 SUMMARY
In this chapter we have examined the future of the Internet
Protocol (IP) as embodied by IPv6, which is the next-generation IP.
The areas in which IPv6 introduces the greatest changes are the
areas of security, addressing, routing, and quality of service. Much
of the detail in IPv6 differs from IPv4, and these changes were
covered in detail in this chapter.
The chapter focused on the following topics:
 The issues associated with IPv4.
 The features of IPv6, including: larger address space,
elimination of NAT and broadcast addresses, simplified
header for improved router efficiency, support for mobility
and security, and transition richness
 The features of IPv6 addresses, including: stateless
autoconfiguration, prefix renumbering, multiple addresses
per interface, link-local addresses, and the ability to use
provider-dependent or provider-independent addressing.
• The 40-octet IPv6 header, with its 8 fields plus
extension headers to handle options
• The 128-bit IPv6 addresses written in the format
x:x:x:x:x:x:x:x
• The IPv6 address interface ID
 The IPv6 address types including unicast (including global,
link-local, and the deprecated site-local), multicast (for one-

168
to-many), and anycast (for one-to-nearest). There are no
broadcast addresses.
 The ability to summarize IPv6 addresses, similar to IPv4
address summarization.
1. Explain IP6 protocol?
2. Define IP6 Packet Format ?
3. IPv6 Addressing ?
14.5 REFERENCES
Davies, J. Understanding IPv6. Redmond, WA: Microsoft Press,
2002.
Huitema, C. IPv6: The New Internet Protocol. Second edition.
Upper Saddle River, NJ: Prentice Hall, 1998.
Miller, M. Implementing IPv6: Supporting the Next Generation of
Protocols. Second edition. Foster City, CA: M&T Books, 2000.
[RFC1884] R. Hinden and S. Deering, 1995, IP version 6
addressing architecture.
[RFC1886] S. Thomson and C. Huitema, 1995, DNS Extensions
to support IP version 6.
[RFC2463] S. Thomson and T. Narten, 1998, IPv6 Stateless
Address Autoconfiguration.
[ngtrans-broker-05] Alain Durand, Paolo Fasano, and Domenico
Lento, 2000, IPv6 Tunnel broker, draft-ietf-ngtrans-broker-05.
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169
15
IP Version 6 (IPv6) CONFIGURATIONS
AND TRANSISTIONS
Unit Structure
15.0 OBJECTIVES
15.1 INTRODUCTION
15.2 An Overview
15.2.1 Address Auto configuration
15.2.2 Types of Auto configuration
15.2.3 Auto Configuration Process
15.2.4 IPv6 Transition Technologies
15.2.5 IPv6 - Auto Configuration vs DHCPv6
15.2.6 DHCPv6
15.2.7 Summary of Benefits of IPv6 in a nutshell:
15.3 Review question
15.4 Summary
15.5 references
15.0 CHAPTER OBJECTIVES:
List and describe the different types of IPv4 and IPv6 nodes.
List and describe the types of tunneling configurations.
Define the differences between configured and automatic
tunneling.

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15.1 CHAPTER INTRODUCTION
The IPv6/IPv4 nodes with a dual stack or dual
IP architecture, DNS infrastructure, and IPv6 over IPv4
tunneling are used to coexist with an IPv4 infrastructure and
to provide eventual migration to anIPv6-only infrastructure.
The chapter presents the IPv6 address configuration and
verification commands. It also lists and describe the different
types of IPv4 and IPv6 nodes, mechanisms for IPv4 to
IPv6 transition, types of tunneling configurations.
15.2.1 Address Auto configuration
A highly useful aspect of IPv6 is its ability to automatically
configure itself without the use of a stateful configuration protocol,
such as Dynamic Host Configuration Protocol for IPv6 (DHCPv6).
By default, an IPv6 host can configure a link-local address for each
interface. By using router discovery, a host can also determine the
addresses of routers, additional addresses, and other configuration
parameters. The Router Advertisement message indicates whether
a stateful address configuration protocol should be used.
Address autoconfiguration can be performed only on multicast-
capable interfaces.
Autoconfigured Address States
Autoconfigured addresses are in one or more of the following
states:
Tentative
The address is in the process of being verified as unique.
Verification occurs through duplicate address detection.
Preferred
An address for which uniqueness has been verified. A node
can send and receive unicast traffic to and from a preferred
address. Router Advertisement messages include the period
of time that an address can remain in the tentative and
preferred states.
Deprecated
An address that is still valid but whose use is discouraged for
new communication. Existing communication sessions can
continue to use a deprecated address. Nodes can send and
receive unicast traffic to and from deprecated addresses.

171
Valid
An address from which unicast traffic can be sent and
received. The valid state covers both the preferred and
deprecated states. Router Advertisement messages include
the amount of time that an address remains in the valid
state. The valid lifetime must be longer than or equal to the
preferred lifetime.
Invalid
An address for which a node can no longer send or receive
unicast traffic. An address enters the invalid state after the
valid lifetime expires.
The following figure shows the relationship between the
states of an autoconfigured address and the preferred and valid
lifetimes.
With the exception of link-local addresses, address
autoconfiguration is specified only for hosts. Routers must obtain
address and configuration parameters through another means (for
example, manual configuration).
15.2.2 Types of Autoconfiguration
Autoconfiguration falls into three types:
1. Stateless
Configuration is based on Router Advertisement messages.
These messages include stateless address prefixes and require
that hosts not use a stateful address configuration protocol.
2. Stateful
Configuration is based on a stateful address configuration
protocol, such as DHCPv6, to obtain addresses and other
configuration options. Hosts use stateful address configuration
when they receive Router Advertisement messages that do not
include address prefixes and that require the hosts to use a
stateful address configuration protocol. A host will also use a

172
stateful address configuration protocol when no routers are
present on the local link.
3. Both
Configuration is based on Router Advertisement messages.
These messages include stateless address prefixes but require
hosts to use a stateful address configuration protocol.
For all autoconfiguration types, a link-local address is always
configured.
15.2.3 Autoconfiguration Process
Address autoconfiguration for an IPv6 node occurs as follows:
1. A tentative link-local address is derived, based on the link-
local prefix of FE80::/64 and the 64-bit interface identifier.
2. Duplicate address detection is performed to verify the
uniqueness of the tentative link-local address. If the address
is already in use, the node must be configured manually.
3. If the address is not already in use, the tentative link-local
address is assumed to be unique and valid. The link-local
address is initialized for the interface. The corresponding
solicited-node multicast link-layer address is registered with
the network adapter.
4. The host sends a Router Solicitation message.
5. If the host receives no Router Advertisement messages,
then it uses a stateful address configuration protocol to
obtain addresses and other configuration parameters.
Windows Server 2003 does not support the use of a stateful
address configuration protocol for IPv6.
6. If the host receives a Router Advertisement message, the
host is configured based on the information in the message
7. For each stateless address prefix that the message
includes:
A tentative address is derived from the address prefix and
the appropriate 64-bit interface identifier.

173
8. The uniqueness of the tentative address is verified.
If the tentative address is in use, the address is not initialized
for the interface.
If the tentative address is not in use, the address is
initialized. Initialization includes setting the valid and
preferred lifetimes based on information in the Router
Advertisement message. Initialization also includes
registering the corresponding solicited-node multicast link-
layer address with the network adapter.
9. If specified in the Router Advertisement message, the host
uses a stateful address configuration protocol to obtain
additional addresses or configuration parameters.
15.2.4IPv6 Transition Technologies
1. Node Types
2. Address Compatibility
Protocol transitions are not easy, and the transition from
IPv4 to IPv6 is no exception. Protocol transitions are typically
deployed by installing and configuring the new protocol on all nodes
within the network and verifying that all node and router operations
work. Although this might be possible in a small- or medium-sized
organization, the challenge of making a rapid protocol transition in a
large organization is very difficult. Additionally, given the scope of
the Internet, rapid protocol transition becomes an impossible task.
The transition from IPv4 to IPv6 will take years, and
organizations or hosts within organizations might continue to use
IPv4 indefinitely. Therefore, although migration is the long-term
goal, equal consideration must be given to the interim coexistence
of IPv4 and IPv6 nodes.
It defines the following transition criteria:
1. Existing IPv4 hosts can be upgraded at any time,
independent of the upgrade of other hosts or routers.
2. Hosts that use only IPv6 can be added at any time, without
dependencies on other hosts or routing infrastructure.
3. IPv4 hosts on which IPv6 is installed can continue to use
their IPv4 addresses and do not need additional addresses.
4. Little preparation is required to either upgrade IPv4 nodes to
IPv6 or deploy new IPv6 nodes.

174
The inherent lack of dependencies between IPv4 and IPv6 hosts,
IPv4 routing infrastructure, and IPv6 routing infrastructure requires
several mechanisms that allow seamless coexistence.
1. Node Types
Defines the following node types:
IPv4-only Node
A node that implements only IPv4 (and has only IPv4
addresses). This node does not support IPv6. Most hosts and
routers installed today are IPv4-only nodes.
IPv6-only Node
A node that implements only IPv6 (and has only IPv6
addresses). This node is able to communicate only with IPv6 nodes
and applications. This type of node is not common today, but it
might become more prevalent as smaller devices such as cellular
phones and handheld computing devices include the IPv6 protocol.
IPv6/IPv4 Node
A node that implements both IPv4 and IPv6. This node is
IPv6-enabled if it has an IPv6 interface configured.
For coexistence to occur, the largest number of nodes (IPv4
or IPv6 nodes) can communicate using an IPv4 infrastructure, an
IPv6 infrastructure, or an infrastructure that is a combination of IPv4
and IPv6. True migration is achieved when all IPv4 nodes are
converted to IPv6-only nodes. However, for the foreseeable future,
practical migration is achieved when as many IPv4-only nodes as
possible are converted to IPv6/IPv4 nodes. IPv4-only nodes can
communicate with IPv6-only nodes only through an IPv4-to-IPv6
proxy or translation gateway.
2. Address Compatibility
The following addresses are defined to help IPv4 and IPv6 nodes
coexist:
IPv4-compatible Addresses
IPv6/IPv4 nodes that are communicating with IPv6 over an IPv4
infrastructure use IPv4-compatible addresses, 0:0:0:0:0:0:w.x.y.z or
::w.x.y.z (where w.x.y.z is the dotted decimal representation of a
public IPv4 address). When an IPv4-compatible address is used as
an IPv6 destination, IPv6 traffic is automatically encapsulated with
IPv4 headers and sent to their destinations using the IPv4
infrastructure.

175
IPv4-mapped Addresses
The IPv4-mapped address, 0:0:0:0:0:FFFF:w.x.y.z or
::FFFF:w.x.y.z, is used to represent an IPv4-only node to an IPv6
node. It is used only for internal representation. The IPv4-mapped
address is never used as a source or destination address of an
IPv6 packet. The IPv6 protocol for Windows Server 2003 does not
support IPv4-mapped addresses. Some IPv6 implementations use
IPv4-mapped addresses when translating traffic between IPv4-only
and IPv6-only nodes.
6over4 Addresses
Each 6over4 address comprises a valid 64-bit unicast address
prefix and the interface identifier ::WWXX:YYZZ (where
WWXX:YYZZ is the colon-hexadecimal representation of w.x.y.z, a
unicast IPv4 address assigned to an interface). An example of a
link-local 6over4 address based on the IPv4 address of
131.107.4.92 is FE80::836B:45C. 6over4 addresses represent a
host that use the automatic tunneling mechanism.
6to4 Addresses
6to4 addresses are based on the prefix 2002:WWXX:YYZZ::/48
(where WWXX:YYZZ is the colon-hexadecimal representation of
w.x.y.z, a public IPv4 address assigned to an interface). 6to4
addresses represent sites that use the automatic tunneling
mechanism
ISATAP Addresses
Each Intra-site Automatic Tunnel Addressing Protocol (ISATAP)
addresses comprise a valid 64-bit unicast address prefix and the
interface identifier ::0:5EFE:w.x.y.z (where w.x.y.z is a unicast IPv4
address assigned to an interface). An example of a link-local
ISATAP address is FE80::5EFE:131.107.4.92. ISATAP addresses
represent hosts that use the automatic tunneling mechanism
Teredo Addresses
Teredo addresses use the prefix 3FFE:831F::/32. An
example of a Teredo address is
3FFE:831F:CE49:7601:8000:EFFF:62C3:FFFE. Beyond the first 32
bits, Teredo addresses encode the IPv4 address of a Teredo
server, flags, and the encoded version of the external address and
port of a Teredo client. Teredo addresses represent hosts that use
the automatic tunnellingmechanism .
15.2.5 IPv6 - Auto Configuration vs DHCPv6
Introduction
A growing number of IPv6 experts are apprehensive about
the adoption of the auto-configuration feature offered by IPv6 in
contrast to the services offered by the existing DHCPv6 protocol in

176
the task of configuration of connected devices over an IP network.
There are concerns over the potential disadvantages of auto-
configuration in IPv6 such as its focus on configuration of IP
address while overlooking the configuration of other parameters
such as the DNS domain, DNS server, time servers, legacy WINS
servers etc.
Using DHCP to supply this information and using IPv6 auto-
configuration in its present form only for IP addressing does not
make sense. The enterprises could as well use the DHCPv6 to
configure the IP addresses too. Apart from the IP addresses, the
additional information supplied by DHCPv6 offers the audit, tracking
and management capabilities as required by the business
enterprises. Despite its present shortcomings, IPv6 offers the most
comprehensive long-term solution for the future networking
requirements of the business enterprises. Every network
administration policy maker across different business enterprises
faces the dilemma of using IPv6 auto-configuration versus
DHCPv6.
15.2.5IPv6Auto-Configuration
An important feature of IPv6 is that it allows plug and play
option to the network devices by allowing them to configure
themselves independently. It is possible to plug a node into an IPv6
network without requiring any human intervention. This feature was
critical to allow network connectivity to an increasing number of
mobile devices.
The proliferation of network enabled mobile devices has
introduced the requirements of a mobile device to arbitrarily change
locations on an IPv6 network while still maintaining its existing
connections. To offer this functionality, a mobile device is assigned
a home address where it remains always reachable. When the
mobile device is at home, it connects to the home link and makes
use of its home address. When the mobile device is away from
home, a home agent (router) acts as a conduit and relays
messages between the mobile device and other devices on the
network to maintain the connection.
Types of auto-configuration:
 Stateful auto configuration and
 Stateless auto configuration.

177
IPv6 offers two types of auto-configuration: Stateful auto
configuration and stateless auto configuration.
Stateful auto-configuration: This configuration requires some
human intervention as it makes use of the Dynamic Host
Configuration Protocol for IPv6 (DHCPv6) for installation and
administration of nodes over a network. The DHCPv6 server
maintains a list of nodes and the information about their state to
know the availability of each IP address from the range specified by
the network administrator.
Stateless auto-configuration: This type of configuration is
suitable for small organizations and individuals. It allows each host
to determine its address from the contents of received user
advertisements
15.2.6 DHCPv6
The Dynamic Host Configuration Protocol (DHCP) facilitates
the addition of new machines in a network. Around October 1993,
DHCP began to take shape as a standard network protocol. The
protocol allows the network devices to obtain the different
parameters that are required by the clients to operate in an Internet
Protocol (IP) network. The DHCP protocol significantly reduces the
system administration workload as the network devices can be
added to the network with little or no change in the device
configuration.
DHCP also allows network parameter assignment at a
single DHCP server or a group of such server located across the
network. The dynamic host configuration is made possible with the
automatic assignment of IP addresses, default gateway, subnet
masks and other IP parameters. On connecting to a network, a
DHCP configured node sends a broadcast query to the DHCP
server requesting for necessary information. Upon receipt of a valid
request, the DHCP server assigns an IP address from its pool of IP
addresses and other TCP/IP configuration parameters such as the
default gateway and subnet mask. The broadcast query is initiated
just after booting and must be completed before the client initiates
IP-based communication with other devices over the network.
DHCP allocates IP addresses to the network devices in
three different modes: dynamic mode, automatic mode and manual
mode. In the dynamic mode, the client is allotted an IP address for
a specific period of time ranging from a few hours to a few months.
At any time before the expiry of the lease, a DHCP client can
request a renewal of the current IP address. Expiry of the lease

178
during a session leads to a dynamic renegotiation with the server
for the original or a new IP address. In the automatic (also called as
DHCP Reservation) mode, an IP address is chosen from the range
defined by the network administrator and permanently assigned to
the client. In the manual mode, the client manually selects the IP
address and uses the DHCP protocol messages to inform the
server of the choice of the IP address.
15.2.7 Summary of Benefits of IPv6 in a nutshell:
1) Increased address space
2) More efficient routing
3) Reduced management requirement
4) Improved methods to change ISP
5) Better mobility support
6) Multi-homing
7) Security
8) Scoped address: link-local, site-local and global-address space
1) Explain IP6 auto configuration
2) Explain DHCP using IP6
15.4 SUMMARY
The chapter includes the following pieces of key information:
 IPv6 address configuration and verification commands
 The neighbor discovery or solicitation phase.
 Stateless autoconfiguration.
 The processes used to connect IPv6 devices on:
• Broadcast multiaccess connections
• Point-to-point connections
• point-to-multipoint connections.
A configured tunnel requires manual configuration of
the tunnel endpoints.
An automatic tunnel is a tunnel that does not require manual
configuration. Tunnel endpoints are determined from routes
and tunneling interfaces.

179
ISATAP is an address assignment and host-to-host, host-to-
router, and router-to-host automatic tunneling technology
that provides unicast IPv6 connectivity between IPv6 hosts
across an IPv4 intranet.
ISATAP addresses are composed of a valid 64-bit unicast
address prefix and the interface
identifier::0:5EFE:w.x.y.z (w.x.y.z is a unicast IPv4 address
assigned to an interface).
Teredo is an address assignment and host-to-host or host-
to-router automatic tunneling technology that provides
unicast IPv6 connectivity across the IPv4 Internet when
IPv6/IPv4 hosts are located behind one or multiple IPv4
NATs.
15.5 REFERENCES:
 IPv6 Main Page
www.cisco.com/go/ipv6
 IPv6 Headers At-a-Glance
http://www.cisco.com/en/US/technologies/tk648/tk872/technolog
ies_white_paper0900aecd80260042.pdf
 The Cisco IOS Software Releases 12.4 Mainline Command
References, available at:
http://www.cisco.com/en/US/products/ps6350/prod_command_r
eference_list.html
 The Cisco IOS IPv6 Command Reference, available at:
http://www.cisco.com/en/US/docs/ios/ipv6/command/reference/i
pv6_book.html
 The Cisco IOS IPv6 Configuration Guide, Release 12.4,
available at:
http://www.cisco.com/en/US/docs/ios/ipv6/configuration/guide/1
2_4/ipv6_12_4_book.html
 Cisco IOS IPv6 Multicast Introduction, available at:
http://www.cisco.com/en/US/tech/tk828/technologies_white_pap
er09186a0080203e90.shtml
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180
F.Y.B.Sc. (IT) (Semester II)
Data Communication & Network Standards
Unit - I Introduction to data communications and networking
Introduction, Fundamental concepts, Data
communications, Protocol, standards, standard
organizations, signal propagation, analog and digital
signals, bandwidth of signal and a medium, Fourier
analysis and the concept of bandwidth of a signal. The
data transmission rate and bandwidth.
Unit - II Network Models
Layered Tasks, The OSI reference model, Layers in the
OSI reference model.
TCP/IP protocol suite, Addressing IPv4
Unit - III Information Encoding, Errors Detection and Correction
Introduction, representing different symbols, Minimizing
errors, Multimedia, Multimedia and Data compression.
Error classification, types of errors, redundancy, detection
versus correction, hamming distance, cyclic redundancy
check.
Unit - IV Media and Transmission modes
Data and signals, Periodic analog signals, Digital signals,
Transmission impairment, Data rate limits, Performance,
Digital to digital, Analog to digital conversion, Transmission
modes, Digital to analog conversion, Analog to analog
conversion, Guided media and Unguided media
Unit - V Network topologies, Switching and routing algorithms
Mesh, star, tree, ring, bus, hybrid, switching basics, circuit
switching, packet switching and Message switching,
routing algorithms
Unit - VI IP version 6
Overview, Terminology, IPv6 addresses, Special
addresses, IPv6 header formats, IPv6 extension headers,
IPv6 auto configuration via DHCP v6, IPv6 transition
Books :

181
Behrouz A Forouzan, ―Data communications and Networking‖, Fourth
Edition, Mc-Graw Hill Achyut Godbole, ―Data communications and
Networks, TMH
Dr. Sidnie Feit, ―TCP/IP‖, Second Edition, TMH
Reference
W. Stallings, ―Data and Computer Communications‖, Eight Edition,
Pearson Education.
Term Work and Tutorial
Should contain minimum 10 assignments and two class tests. (One case
study in lieassignments)
Practical
None
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Data communications and networking(DCN)

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