Data communication and network Chapter -1

(zafar_ayub@hotmail.com)
Copyright revised for Zafar Ayub
DATA COMMUNICATION AND
NETWORK
CHAPTER - 1
1 Compile by Zafar Ayub

WHAT IS DATA COMMUNICATION?
 Electronic transmission of information that has been encoded
digitally with some standard from one network (systems) to
other network (systems) via certain medium, knows as Data
Communication.
Elements of Data Communication;



 Information / Data
 Digital encoded
 Transfer of data / sender and receiver
 Specific medium

2

WHAT IS NETWORK?
 A computer network often simply referred to as a network, is
a collection of hardware components, which are
interconnected by communication channels that allow sharing
of resources and information with respect to certain set of
rules / protocols via OS / software.

 Elements of Network;
 Hardware equipments
 Network OS / software
 Communication channel
 Information / Data / Recourse
 Protocols

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TERMINOLOGIES
 Data transmission process between sender and receiver is
refer to data communication, and deployed physical
environment (hardware / software / protocols / channel ) is
network.

 Data: digital information over computer / network, which may
define with certain type of file extension; like .doc, .ppt, .pdf,
.exe, and etc. File extension dominate nature of data
file

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Resource: all sharable / accessible items over network, which
may physical / virtual, knows as resource.
physical resource - may be hard drive, printer, servers and
etc.
virtual resource - may be data files, online application, web
site, internet and etc.

Share Resource: a shared resource or network share is a
device / piece of information means file / software or
application, on a computer that can be remotely accessed
from another computer.

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Channel: communication channel is a medium on which
resource can be access over network and establish
connectivity between sender and receiver. Channel speed /
network speed is depends upon bandwidth.
bandwidth - channel capacity known as bandwidth.
There are two types of channels;

physical channel like; network cable, fiber optic,
electrical wire, and etc.
logical or virtual channel like; wireless, radio
frequency, Wi-Fi, Wi-Max, and Bluetooth

6

Protocols: a communications protocol is a system of digital
message formats and rules for exchanging those messages in
or between computer systems and in network /
telecommunications.
Protocols regulate the following characteristics of a network:
access method, allowed physical topologies, types of cabling,
and speed of data transfer.

Protocols may include signaling, authentication, error
detection method, and network policies.
A protocol can be implement at hardware or software or both,
and with respect to assignment these are implemented like;
for web http, for security SSL, for email POP3 / SMTP, for LAN
network Ethernet, for routing BGP / RIP, etc.

7

Digital Encryption: in encryption is the process of transforming
information / data using an algorithm to make it unreadable to
anyone (except those possessing special knowledge, usually
referred to as a key).
The result of the process is encrypted information and the
reverse process, i.e. to make the encrypted information
readable again is referred to as decryption.

algorithm – set of steps for assembling / reassembling of data
with respect to define network technology.

Types of digital encryption;
Software Based Encryption – a software program to facilitate
encryption process on data / file with respect to 256-bit AES /
448-bit Blowfish algorithms. Hardware is only responsible to
deliver encrypted file to other end computer where again via
software program file may be decrypt for original data / file.

8

Drawbacks
all encryption perform on data / file during file transfer.
data / file size is also increase with addition of certain
algorithms.
security risk for confidentiality documents.
Hardware Based Encryption – all data intensive encryption
tasks are done onboard storage device, rather than on file, by

this file size remain standard with maximum speed. Most
important factor is hardware security protocols which are only
configure same end device
Hardware encryption is also apply with specialize network
equipment.
Drawbacks
higher cost of equipments

9

Network Hardware: all equipments / devices which may used
on network and facilitate for resource sharing and data
connectivity like; router, switch, firewall, and servers etc.
Network Software: specialize software / OS which may
establish logical connectivity, authentication, and management
of network, commonly built-in with operating system. Some
are like; teamviewer, skype, etc

10

Sender: a computer / device from which data / files are send
to specific destination.

Receiver a computer / device at which data / files are received
by source.

11

DATA TRANSMISSION
 Data transmission is the physical transfer of data over a point-
to-point or point-to-multipoint channel.
Data transmission is a subset of the field of data
communications, which also includes computer networking or
computer communication applications and networking

protocols, for example routing and switching.
 Point – to –point : In telecommunications a point-to-point
connection refers to a communications connection between
two nodes or endpoints.
 Point – to –multipoint : refers to communication which is
accomplished via a specific and distinct type of one-to-many
connection

12

DATA COMMUNICATION TECHNIQUES
Serial Transmission - is the process of sending data one bit at a
time, in sequentially, over a communication channel / computer
bus. A data channel that transfers digital data in a serial mode,
one bit after the other over one wire, with start and stop bit.

Serial interfaces may have multiple lines, but only one line is
used for data. On earlier PCs, the serial port was a serial
interface for attaching modems and data acquisition terminals,
and sometimes mouse.

13

Parallel Transmission - is a method of sending several data
signals simultaneously over several parallel channels.

In parallel transmission, multiple bits (usually 8 bits or a
byte/character) are sent simultaneously on different channels
(wires, frequency channels) within the same cable, or radio
path, and synchronized to a clock. Due to multi channels lines in

parallel transmission, it may comparatively fast as serial
transmission.

14

Transmission Characteristic - The advantages, limitations and
typical applications of parallel and serial transmission
methodologies are summarized in chart;

Transmission Serial Parallel
Characteristic

Transmission One bit comes after another, one by All bits in a single character and
description one transmit simultaneously

Comparative Speed Slower Faster

Distance Limitation Farther Shorter

Application Between two computer, from Within a computer the along
computer to external devices, and computer buses, between drive
local and wide network controller to hard drive
Cable Description All bits travel down in single wire, Each bit travel down its own wire
one bit at one time simultaneously with other bits

15

DATA COMMUNICATION CHANNELS
There are three data communication channels like;
Simplex communication- refers to communication that occurs in
one direction only. Examples radio broadcast, keyboard / mouse
inputs to CPU, internet multicast, and one – lane and one side
road only.

Half duplex communication - system provides communication in
both directions, but only one direction at a time (not
simultaneously). Typically, once a party begins receiving a
signal, it must wait for the transmitter to stop transmitting, before
replying. Examples walkie-talkie, one-lane road with traffic
controllers at each end.
16

Full duplex communication- sometimes called double-duplex
system allows communication in both directions simultaneously.
Virtually no collisions take place on a full-duplex transmission.
Perhaps a bigger benefit is the increase in overall throughput-
since we are sending and receiving on two different
channels, we just theoretically doubled our data transfer rate.
Examples landline / mobile phone, two way double side road.

17

DATA COMMUNICATION MODES
Data communication modes define behavior of data flow during
communication which is based on interval of time.

When devices are communicating, they must be know when
ever data has to send or receive (in period of time). The two

devices must establish and maintain some type of timing
between them so that signals are produced, transmitted, and
detected accurately.

There are two main alternatives to establishing and maintaining
the timing for the sampling of the signals. These two timing
alternatives are known as asynchronous and synchronous, also
known as data communication modes.

Data Link Layer : all synchronization occurs on the data link
layer (2nd layer of TCP/IP), where the data in form of frame.
18

Asynchronous communication- The transmission of data in
which each character is a self-contained unit with its own start
and stop bits. Intervals between characters may be irregular.

19

 Start bit inform that transmission has to start with binary value
of “0”.
 Stop bit inform to equipment that transmission has been stop
with binary value of “1”.
 When no character is being transmitted, the line between
transmitter and receiver is in an idle state (binary 1 level).
 A minimum length for the stop element is specified, and this is

usually 1, 1.5, or 2 times the duration of an ordinary bit.
 Data contain may be 5 -8 character bits.

Parity bit : Character bit may include parity bit, set by the
transmitter such that the total number of ones in the
character, including the parity bit, is even (even parity) or odd
(odd parity). The receiver uses this bit for error detection.

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 There are two types of parity bit
even parity bit
odd parity bit
Even parity bit - when using even parity, the parity bit is set to 1 if
the number of ones in a given set of bits (not including the parity
bit) is odd, making the number of ones in the entire set of bits
(including the parity bit) even. If the number of ones in a given

set of bits is already even, it is set to a 0.
an even parity bit will be set to "1" if the number of 1s + 1 is even
Odd parity bit - when using odd parity, the parity bit is set to 1 if
the number of ones in a given set of bits (not including the parity
bit) is even, keeping the number of ones in the entire set of bits
(including the parity bit) odd. And when the number of set bits is
already odd, the odd parity bit is set to 0.
an odd parity bit will be set to "1" if the number of 1s +1 is odd

21

 at end of transmission no maximum value is
specified, because the stop element is the same as the idle
state, the transmitter will continue to transmit the stop element
until it is ready to send the next character.

Synchronous communication- The transmission of data in block
set and time intervals between characters may be regular.

 each block of data is formatted as a frame that includes a
starting and an ending flag, and is transmitted in a steady stream
without start and stop codes.

Clock speed : time interval (clock speed) must be
synchronized, to prevent timing drift between transmitter and
receiver;
can use separate clock line
embed clock signal in data 22

By adding clock line – add specific time of break between sender
and receiver.
By adding clock signal – add clock information in frame.

 In synchronous transmission, there is another level of
synchronization required, to allow the receiver to determine the
beginning and end of a block of data.

 each block begins with a preamble bit pattern (opening flag)
and generally ends with a post-amble bit pattern (closing flag).

23

preamble bit – The preamble is a 64-bit (8 byte) field that
contains a synchronization pattern consisting of alternating ones
and zeros and ending with two consecutive ones. After
synchronization is established, the preamble is used to locate
the first bit of the packet. The preamble is generated by the LAN
interface card.

post-amble bit – commonly used end of synchronous
transmission.

Control bit : start control bit contain destination MAC, source
MAC, and protocol; and similar stop control bit contain CRC
information.

24

Comparison - some comparison between asynchronous
communication and Synchronous communication as follow;

Characteristic Asynchronous Synchronous

Transmission techniques Used serial communication Used parallel communication

Comparative capacity Data transmit one character at Data transmit block (bunch of
one time character) at one time
Distance limitation Farther (long) Shorter

Sync method Start and stop bit Clock speed

Comparative speed Low speed due to serial More efficient due to parallel
transmission transmission
Costing Simple and cheap Much cost due to mechanism

Bandwidth loss 20% to 30% over capacity 5% over capacity

25

DATA COMMUNICATION PORTS
For interconnection with other device every data communication
device have specific port / interface, by data communication
mechanism two types of ports are available;

Serial port- a serial port is a serial communication physical

interface through which information transfers in or out one bit at
a time.
Serial port available in DB-9, DB-25 and Mini Din-8 (apple
format);
DB-9 DB-25 Mini Din-8
male male male

female female female
26

DB- 9 – DB-9 also known as RS-422, pin configuration as
follows;

DB- 25 – DB -25 also know as RS-232, pin configuration as
follows;

27

Mini Din -8 – Din-8 also known as RS-422, pin configuration as
follows;

Note : serial port commonly used in old mouse port, game controller,
modem port and some old printers.
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Parallel port- a parallel port is a parallel communication physical
interface. It is also known as a printer port or centronics port.

Parallel port is standard of IBM known as (DB-25) 25-pin
combinations. Some available speed of parallel ports;
oBi-directional – 150 Kbps
oEPP – 1.5 Mbps

oECP – 2.5 Mbps
oEPP PCI – 4.5 Mbps

Before the advent of USB, the parallel interface was adapted to
access a number of peripheral devices other than printers. List
are bellow here;
Hardware dongles, Zip drives, Scanners, Webcam, External
modem, Sound card, External HDD and CD Rom

29

DB- 25 – DB-25 standard of IEEE 1284 as printer port;

Centronics – port with 36-pins interface;

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USB - Universal Serial Bus is also serial port with high speed
data flow.

USB 1.0 with speed of 1.5 Mbps
USB 1.1 with speed of 12 Mbps
USB 2.0 with speed of 480 Mbps
USB 3.0 with speed of 5 Gbps (Super Speed)

USB 1 USB 2 USB 3

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USB - Data Transfer Rate Comparison

USB Revision USB1.0 USB2.0 USB3.0

Media (Data Size) Transfer Time

Song / Pic (4 MB) 5.3 sec 0.1 sec 0.01 sec

256 Flash (256 MB) 5.7 min 8.5 sec 0.8 sec

USB Flash (1 GB) 22 min 33 sec 3.3 sec

SD-Movie (6 GB) 2.2 hr 3.3 min 20 sec

USB Flash (16 GB) 5.9 hr 8.9 min 53.3 sec

HD-Movie (25GB) 9.3 hr 13.9 min 70 sec 32

SIGNALS AND SYSTEM
A signal is an electric current or electromagnetic field used to
convey data from one place to another.

The simplest form of signal is a direct current (DC) that is
switched on and off; this is the principle by which the early

telegraph worked. More complex signals consist of an
alternating-current (AC) or electromagnetic carrier that contains
one or more data streams.

Data is superimposed on a carrier current or wave by means of
a process called modulation. Signal modulation can be done in
either of two main ways: analog and digital.

Note : In recent years, digital modulation has been getting more
common, while analog modulation methods have been used less
and less. There are still plenty of analog signals
33
around, however, and they will probably never become totally
extinct.

There are three data transmissions core aspect;

Data – Actual information being sent / received, possibly Analog
(continuous) or digital (discrete).
Analog Data – Takes on continuous values. Ex. Voice or video
Digital Data – Takes on discrete values. Ex. Text and integers

Signal - Electronic or electromagnetic representation of
data, possibly Analog or digital.
Analog Signal – Continuously varying electromagnetic wave
representing data carried over a variety of medium.
Digital Signal – Sequence of voltage pulses representing data
transmitted over a wire medium

Transmission – Communication of data by sending /
receiving, and processing data.
Analog Transmission – Communication of analog signals
Digital Transmission – Communication of digital signals
34

Analog Signals - An analog signal is any continuous signals for
which the time is variable of the signal.

Digital Signals - A digital signal is a physical signal that is a
representation of a sequence of discrete values.

35

Comparison - some comparison between analog and digital
signals as follow;

Characteristic Analog Digital

Number of range Analog signals can have an Digital signals can have only a
infinite number of values in a limited number of values (1 / 0)

range
Type of data Continuous Discrete

Value of data More exact values, but more Not as exact as analog, but
difficult to work with easier to work with
Wave types Sing waves Square waves
Type of value Negative / positive Positive
Medium Wire / un-wire Wire
Device Amplifier for signals boosting Repeater for signals regenerating
(noise also be amplify) (noise isn’t boost)
Security Non-encryption Encryption
Capacity / Bandwidth Low High

Examples Voice, video, file format on Text, integers, images, computer
36
tape, Radio / TV transmission format files (CD, HDD)
waves

Analog Signal Example - Telephones take sound vibrations and
turn them into electrical vibrations of the same shape before they
are transmitted over traditional telephone lines. Radio wave
transmissions work in the same way. Computers, which handle
data in digital form, require modems to turn signals from digital
to analog before transmitting those signals over communication
lines such as telephone lines that carry only analog signals. The

signals are turned back into digital form (demodulated) at the
receiving end so that the computer can process the data in its
digital format.

Digital Signal Example - This is the principle behind compact
discs (CDs). The music itself exists in an analog form, as waves
in the air, but these sounds are then translated into a digital form
that is encoded onto the disk. When you play a compact disc,
the CD player reads the digital data, translates it back into its
original analog form, and sends it to the amplifier and eventually
the speakers.
37

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