Data communication and networking by Md. Abdus Sobur Sikdar, Sylhet International University, Bangladesh.

1. 10/28/2014
Data Communication
and Networking
Submitted to:
Md. Abdus Sobur Sikdar
SYLHET INTERNATIONAL UNIVERSITY
Roll No.: 22065
Registration No.: 121101065
Mr. Sushanta Acharjee
Assistant Professor
Department of CSE
Sylhet International University
Submitted By:

2. 1
Table of Contents
Table of Contents ...................................................................................................................................1
Data Communications and Networking..................................................................................................3
Types of Computer Networking..............................................................................................................3
Personal Area Network (PAN): _____________________________________________________ 3
Local Area Network (LAN): ________________________________________________________ 3
Metropolitan Area Network (MAN):_________________________________________________ 3
Wide Area Network (WAN): _______________________________________________________ 3
Communication Model ...........................................................................................................................3
Source .............................................................................................................................................4
Transmitter .....................................................................................................................................4
Receiver...........................................................................................................................................4
Destination......................................................................................................................................4
Basic Element of a Communication System............................................................................................4
Tasks of communication system.............................................................................................................5
Basic terms in data communication........................................................................................................5
Analog Signal: __________________________________________________________________ 5
Digital Signal:___________________________________________________________________ 5
Analog Data: ___________________________________________________________________ 6
Digital Data:____________________________________________________________________ 6
Bandwidth: ____________________________________________________________________ 6
Bitrates:_______________________________________________________________________ 6
Data Transmission Modes.......................................................................................................................6
Types of Data Transmission Modes ........................................................................................................6
Simplex Mode __________________________________________________________________ 6
Half-Duplex Mode_______________________________________________________________ 6
Full-Duplex Mode _______________________________________________________________ 7
Advantage of digital transmission___________________________________________________ 7
Protocol...................................................................................................................................................7
Syntax..............................................................................................................................................7

3. 2
Transmission Impairment .......................................................................................................................8
Attenuation____________________________________________________________________ 8
Distortion _____________________________________________________________________ 8
Noise _________________________________________________________________________ 9
Data rate depends on?............................................................................................................................9
Formula to Calculate data rate .............................................................................................................10
Transmission Impulse ...........................................................................................................................10
Problem (1): __________________________________________________________________ 10
Problem (2): __________________________________________________________________ 11
Problem (3): __________________________________________________________________ 11
Problem (4): __________________________________________________________________ 12
Problem (5): __________________________________________________________________ 12
Questions..............................................................................................................................................13

4. 3
Data Communications and Networking
Data Communication is the process of transferring data (message) from one point to another.
Data communications refers to the transmission of this digital data between two or more
computers and a computer network or data network is a telecommunications network that
allows computers to exchange data. The physical connection between networked computing
devices is established using either cable media or wireless media. The best-known computer
network is the Internet.
Types of Computer Networking
Generally, networks are distinguished based on their geographical span. A network can be as
small as distance between your mobile phone and its Bluetooth headphone and as large as the
Internet itself, covering the whole geographical world, i.e. the Earth. There are four types of
computer network as given below.
a. PAN
b. LAN
c. MAN
d. WAN
Personal Area Network (PAN): A Personal Area Network or simply PAN, is smallest
network which is very personal to a user. This may include Bluetooth enabled devices or
infra-red enabled devices.
Local Area Network (LAN): A computer network spanned inside a building and operated
under single administrative system is generally termed as Local Area Network. Usually,
Local Area Network covers an organization’s offices, schools, college/universities etc.
Metropolitan Area Network (MAN): MAN, generally expands throughout a city such as
cable TV network. It can be in form of Ethernet, Token-ring, ATM or FDDI.
Wide Area Network (WAN): As name suggests, this network covers a wide area which
may span across provinces and even a whole country. Generally, telecommunication
networks are Wide Area Network. These networks provides connectivity to MANs and
LANs. Equipped with very high speed backbone, WAN uses very expensive network
equipment.
Communication Model

5. 4
The fundamental purpose of a communications system is the exchange of data between two
parties. I begin my study with a simple model of communications, illustrated by the block
diagram in Figure (1).
Figure (1): General block diagram
Source: This device generates the data to be transmitted; examples are telephones and
personal computers.
Transmitter: Usually, the data generated by a source system are not transmitted directly in
the form in which they were generated. Rather, a transmitter transforms and encodes the
information in such a way as to produce electromagnetic signals that can be transmitted
across some sort of transmission system. For example, a modem takes a digital bit stream
from an attached device such as a personal computer and transforms that bit stream into an
analog signal that can be handled by the telephone network. Transmission system. This can
be a single transmission line or a complex network connecting source and destination.
Receiver: The receiver accepts the signal from the transmission system and converts it into
a form that can be handled by the destination device. For example, a modem will accept an
analog signal coming from a network or transmission line and convert it into a digital bit
stream.
Destination: Takes the incoming data from the receiver. This simple narrative conceals a
wealth of technical complexity. 
Basic Element of a Communication System
The Basic Element of a Communication System are
The following are the basic requirements for working of a communication system.
Sender: A sender (source), which creates the message to be transmitted.
Source Transmitter Transmission
System
Receiver Destination
MediumSender Receiver
Figure (2): Communication System

6. 5
Medium: A medium that carries the message.
Receiver: A receiver (sink), which receives the message.
Example: A modem.
Tasks of communication system
Tasks of Communication System list are given below:
Transmission System Utilization (Multiplexing)
Interfacing
Signal Generation (Codding)
Synchronization between transmitter and receiver
Exchange Management (Connection Management)
Error Detection and Correction
Flow control
Addressing
Routing
Recovery
Message formatting
Security
Network Management
Basic terms in data communication
In data communication four basic terms are frequently used. They are
Data: A collection of facts in raw form that become information after processing.
Signals: Electric or electromagnetic encoding of data.
Signaling: Propagation of signals across a communication medium.
Transmission: Communication of data achieved by the processing of signals.
Analog Signal: A continues waveform that charge smoothly over time.
Digital Signal: A discrete signal with limited number of values.

7. 6
Analog Data: That is continuous and smooth and not limited to specific number of values.
Example: Audio, Video, Human voice.
Digital Data: That is representing by discrete values. Example: Text, String
Bandwidth: The range of frequencies that a medium can pass is called bandwidth. It is the
different between the highest and lowest frequency.
Bitrates: The number of bit transmitted per second is called bitrate.
Data Transmission Modes
The way in which data is transmitted from one place to another is called data transmission mode. It is
also called the data communication mode. It is indicates the direction of flow of information.
Sometimes, data transmission modes are also called directional modes.
Types of Data Transmission Modes
The types of data transmission modes are as follows:
a. Simplex Mode
b. Half-duplex Mode
c. Full-duplex Mode
Simplex Mode
In simplex mode, data can flow in only one direction. In this mode, a sender can only send
data and cannot receive it. Similarly, a receiver can only receive data but cannot send it. Data
sent from computer to printer is an example of simplex mode.
Half-Duplex Mode
In half-duplex mode, data can flow in both directions but only in one direction at a time. In
this mode, data is sent and received alternatively. It is like a one-lane bridge where two-way
traffic must give way in order to cross the other.
Sender Receiver
Figure (3): Simplex

8. 7
Full-Duplex Mode
In full duplex-mode, data can flow in both directions at the same time. It is the fastest
directional mode of data communication. The telephone communication system is an
example of full-duplex communication mode. Two persons can talk at the same time.
Another example of fully-duplex mode in daily life is automobile traffic on a two-lane road.
The traffic can move in both directions at the same time.
Advantage of digital transmission
a. Digital technology
b. Data integrity
c. Capacities utilization
d. Security and privacy
e. Integration
Protocol
A protocol is a set of rules that permit/govern data communication. Or a protocol define what
is communication how it is communicated & when it is communicated the key elements of a
protocol are.
The key elements of protocol are syntax, semantics and timing.
Syntax: Syntax relates to the structure or format of the data, meaning the order in which they are
presented. For example; a simple protocol may expect the first 8 bits of data to be the address of the
sender, the second 8 bits to be the address of receiver, and the rest of the stream to be the message
itself.
Semantics: Semantics relates to the meaning of each section of bits. How is a specified pattern to be
interpreted; and what action is to be taken based on that interpretation? For instance does an
address identify the route to be taken or the final destination of the message?
Sender/Receiver Receiver/Sender
Figure (4): Half-duplex
Sender/Receiver Receiver/Sender
Figure (5): Full-duplex

9. 8
Timing: Timing refers to two vital characteristics: when data should be sent and how fast they can
be sent. For example if a sender produces data at 100 Mbps but the receiver can process data at
only 1 Mbps, the transmission will overload the receiver and data will be largely lost.
Transmission Impairment
Signals travel through transmission media, which are not perfect. The imperfection causes
signal impairment. This means that the signal at the beginning of the medium is not the same
as the signal at the end of the medium. What is sent is not what is received. Three causes of
impairment are attenuation, distortion, and noise.
Attenuation: attenuation means a loss of energy. When a signal, simple or composite, travels
through a medium, it loses some of its energy in overcoming the resistance of the medium.
That is why a wire carrying electric signals gets warm, if not hot, after a while. Some of the
electrical energy in the signal is converted to heat. To compensate for this loss, amplifiers are
used to amplify the signal.
Distortion: Distortion means that the signal changes its form or shape. Distortion can occur
in a composite signal made of different frequencies. Each signal component has its own
propagation speed through a medium and, therefore, its own delay in arriving at the final
destination. Differences in delay may create a difference in phase if the delay is not exactly
the same as the period duration. In other words, signal components at the receiver have
phases different from what they had at the sender. The shape of the composite signal is
therefore not the same.
Figure (6)

10. 9
Noise: Noise is another cause of impairment. Several types of noise, such as thermal noise,
induced noise, crosstalk, and impulse noise, may corrupt the signal. Thermal noise is the
random motion of electrons in a wire which creates an extra signal not originally sent by the
transmitter. Induced noise comes from sources such as motors and appliances. These devices
act as a sending antenna, and the transmission medium acts as the receiving antenna.
Crosstalk is the effect of one wire on the other. One wire acts as a sending antenna and the
other as the receiving antenna. Impulse noise is a spike (a signal with high energy in a very
short time) that comes from power lines, lightning, and so on.
Data rate depends on?
A very important consideration in data communications is how fast we can send data, in bits
per second, over a channel.Data depends on three factors
i. The bandwidth available
Figure (7)
Figure (8)

11. 10
ii. The level of the signals we use
iii. The quality of the channel (the level of noise)
Formula to Calculate data rate
Formula to calculate data rate are
1. Nyquist bitrates for noiseless channel
Bitrate =2 × Bandwidth × log2 𝐿
2. Shannon capacity for noisy channel
Capacity = Bandwidth × log2(1 + 𝑆𝑁𝑅)
Transmission Impulse
The rules of transmission impulse
SNR (Signal to Noise Ratio)
SNR =
𝑆𝑖𝑔𝑛𝑎𝑙 𝑃𝑜𝑤𝑒𝑟
𝑁𝑜𝑖𝑠𝑒 𝑃𝑜𝑤𝑒𝑟
SNRdB= 10 log10 𝑆𝑁𝑅
Problem (1): We need to download text document at the rate of 100 pages per minute. What is
the required bitrates of the channel? (A page is an average of 24 lines with 80 characters in each
line?
Solution:
Character per page is 80×24=1920
Character 100 pages are 1920×100=192000
We know 1bit equal minimum 8byte
So 192000×8=1536000 bps
1536000÷1024=1500 kbps
1500÷1024=1.465 mbps
1.465 mbps bitrates is required.

12. 11
Problem (2): Consider a noiseless channel with a bandwidth of 3000Hz transmitting signal with
two signal levels. Find out the maximum bitrate?
Solution:
Here, Bandwidth B = 3000Hz
Signal Level L =2
Bitrate =?
By Nyquis bitrates formula we know,
Bitrate =2 × Bandwidth × log2 𝐿
Bitrate =2 ×3000 ×log2 2
Bitrate =2×3000×1
Bitrate =6000 bps
Problem (3): Consider a noiseless channel with a bandwidth of 30MHz transmitting signal with four
signal levels. Find out the maximum bitrate?
Solution:
Here, Bandwidth B = 30MHz
=30×1000×1000
=30×106
Hz
Signal Level L =4
Bitrate =?
By Nyquis bitrate formula we know,
Bitrate =2 × Bandwidth × log2 𝐿
Bitrate =2 ×30×106
×log2 4
Bitrate =120 ×106
bps
Bitrate =120 mbps

13. 12
Problem (4): We need to send 265 kbps over a noiseless channel with a bandwidth of 20 KHz. How
many signal level do we need?
Solution:
Here,
Bitrate = 265 kbps
= 265×103
bps
Bandwidth = 20 KHz
= 20 × 103
Hz
Level L =?
By Nyquis bitrates formula we know,
Bitrate =2 × Bandwidth × log2 𝐿
265×103
= 2×20 × 103
× log2 𝐿
log2 𝐿 =
265×103
20×103
log2 𝐿 = 6.625
L = 26.625
L = 98.7 Levels.
Since the result is not power of 2 we need to either increase the number of level or reduce the
bitrate. We have 128 levels the bitrate is 280 kbps. If we have 64 levels the bit rate is 240
kbps.
So level will be 64 or 128.
Problem (5): The spectrum of a channel is between 3MHz and 4MHz and SNRdB =24dB. How many
signaling levels are required?
Solution:
Here,
Bandwidth B = 4-3=1MHz
= 106
Hz
SNRdB = 24 dB
Signal level L =?
We Know that,
SNRdB= 10 log10 SNR
log10 SNR=
SNR 𝑑𝐵
10

14. 13
log10 SNR=
24
10
log10 SNR= 2.4
SNR = 102.4
SNR = 251
Again, Bitrate = Bandwidth × log2(1 + 𝑆𝑁𝑅)
Bitrate = 106
× log2(1 + 251)
Bitrate = 106
× log2 252
Bitrate = 106
× log2 28
Bitrate = 106
× 8 log2 2
Bitrate = 106
× 8 bps
From Nyquist bitrate we know,
Bitrate =2 × Bandwidth × log2 𝐿
log2 𝐿 =
Bitrate
2×Bandwidth
log2 𝐿 =
8×106
2×106
log2 𝐿 = 4
L = 24
L = 16 levels.
Questions
1. What is Protocol and Bandwidth? We need to download text document at the rate of 100
pages per minute. What is the required bitrates of the channel? (A page is an average of 24
lines with 80 characters in each line?
2. Write down the Basic Element of a Communication System. Describe the types of
data transmission modes.
3. Write down the formulas to calculate data rate. The spectrum of a channel is between
5MHz and 6MHz and SNRdB =24dB. How many signaling levels are required?
Answer to the Q no. 1:

15. 14
Protocol: A protocol is a set of rules that permit/govern data communication. Or a protocol
define what is communication how it is communicated & when it is communicated the key
elements of a protocol are.
Bandwidth: The range of frequencies that a medium can pass is called bandwidth. It is the
different between the highest and lowest frequency.
Solution:
Character per page is 80×24=1920
Character 100 pages are 1920×100=192000
We know 1bit equal minimum 8byte
So 192000×8=1536000 bps
1536000÷1024=1500 kbps
1500÷1024=1.465 mbps
1.465 mbps bitrates is required.
Answer to the Q no. 2:
The Basic Element of a Communication System are
The following are the basic requirements for working of a communication system.
Sender: A sender (source), which creates the message to be transmitted.
Medium: A medium that carries the message.
Receiver: A receiver (sink), which receives the message.
Example: A modem.
Types of Data Transmission Modes
The types of data transmission modes are as follows:
a. Simplex Mode
b. Half-duplex Mode
c. Full-duplex Mode
Simplex Mode
In simplex mode, data can flow in only one direction. In this mode, a sender can only send
MediumSender Receiver
Figure (2): Communication System

16. 15
data and cannot receive it. Similarly, a receiver can only receive data but cannot send it. Data
sent from computer to printer is an example of simplex mode.
Half-Duplex Mode
In half-duplex mode, data can flow in both directions but only in one direction at a time. In
this mode, data is sent and received alternatively. It is like a one-lane bridge where two-way
traffic must give way in order to cross the other.
Full-Duplex Mode
In full duplex-mode, data can flow in both directions at the same time. It is the fastest
directional mode of data communication. The telephone communication system is an
example of full-duplex communication mode. Two persons can talk at the same time.
Another example of fully-duplex mode in daily life is automobile traffic on a two-lane road.
The traffic can move in both directions at the same time.
Answer to the Q no. 3:
Formula to calculate data rate are
1. Nyquist bitrates for noiseless channel
Bitrate =2 × Bandwidth × log2 𝐿
2. Shannon capacity for noisy channel
Capacity = Bandwidth × log2(1 + 𝑆𝑁𝑅)
Solution:
Here,
Bandwidth B = 6-5=1MHz
Sender/Receiver Receiver/Sender
Figure (4): Half-duplex
Sender Receiver
Figure (3): Simplex
Sender/Receiver Receiver/Sender
Figure (5): Full-duplex

17. 16
= 106
Hz
SNRdB = 24 dB
Signal level L =?
We Know that,
SNRdB= 10 log10 SNR
log10 SNR=
SNR 𝑑𝐵
10
log10 SNR=
24
10
log10 SNR= 2.4
SNR = 102.4
SNR = 251
Again, Bitrate = Bandwidth × log2(1 + 𝑆𝑁𝑅)
Bitrate = 106
× log2(1 + 251)
Bitrate = 106
× log2 252
Bitrate = 106
× log2 28
Bitrate = 106
× 8 log2 2
Bitrate = 106
× 8 bps
From Nyquist bitrate we know,
Bitrate =2 × Bandwidth × log2 𝐿
log2 𝐿 =
Bitrate
2×Bandwidth
log2 𝐿 =
8×106
2×106
log2 𝐿 = 4
L = 24
L = 16 levels.