1

Data Communication & Computer Networks

Lecture #5

Mrs. Vasanthi Muniasamy Department of Information System

King Khalid university

2

Data Communication

The transfer of data/messages from

one point to another point.

3

Basic Elements of Communication System

Three basic elements of communication

system are:-

1. A sender (source) which creates the message

to transmitted.

2. A medium which carries the message.

3. A receiver (destination) which receives the

message.

4

Basic Elements of Communication System

Sender (source)

Receiver (destination)

Medium

5

Data Transmission Modes

There are three ways, modes for

transmitting data from one point to

another. These are simplex, half-

duplex and full-duplex.

6

Data Transmission Modes

Simplex:

If transmission is simplex, communication can take place in only

one direction. For example, radio & T.V. etc.

Half-Duplex:

A half-duplex system can transmit data in both directions, but only

in one direction at a time. For example, wireless etc.

Full-Duplex:

A full-duplex system is used that allows information to flow

simultaneously in both directions on the transmission path. For

example, telephone etc.

7

Data Transmission Modes

Sender

Sender orReceiver

Sender &Receiver

Sender & Receiver

Receiver orSender

ReceiverSimplex

Half-Duplex

or

Full-Duplex

and

8

Digital & Analog Transmission

Digital transmission sends data as distinct

pulses, either on or off, in much the same

way that data travels through the

computer.

Analog transmission, a continuous

electrical signal in the form of a wave.

9

Digital & Analog Transmission

10

Digital & Analog Transmission

Frequency: It is the rate (cycles/sec or HZ) at which

the signals repeat.

Bandwidth: It is the range of frequencies that is

available for the transmission of data.

Channel: A channel is a portion of the

communications medium allocated to the sender and

receiver for conveying information between them.

Modems: A modem is a device that converts a

digital signal to an analog signal and vice versa.

11

12

Transmission Media

There are several types of physical

channels (communication media) through

which data can be transmitted from one

point to another. Some of the most

common data transmission medium are

as under:-

13

Wire Pairs: It is also known as twisted pair. Wire

pairs are wires twisted together to form a cable, which is

thin insulated. Wire pairs are inexpensive.

Application: Telephone networks, within buildings & LAN

etc.

Benefits & Drawbacks: Cheap

Low data rate

Short range

Easy to work with

Transmission Media

14

Transmission Media

Coaxial Cable: are groups of specially

wrapped and insulated wire lines that are

able to transmit data at very high rates.

These cables can transmit data much

faster than wire pairs.

Application: Long distance telephone

transmission, Local Area Networks etc.

15

Transmission Media

Fiber Optics: Instead of using electricity to send

data, fiber optics uses light.

Application: Long haul trunks, Metropolitan trunks,

LAN & WAN etc.

Benefits & Drawbacks:

Greater capacity

Smaller size & weight

Lower attenuation

16

Protocol

A protocol is a set of rules and procedures

established to control transmission

between two points.

Some common protocols are:-

TCP/IP (Transmission Control Protocol/Internet

protocol)

IPX (Internet Packet Exchange) etc.

17

Computer Networks

Network: A computer system that uses communications equipment to

connect two or more computers and their resources.

Network Interface Card (NIC): A circuit board that can be inserted into a

slot inside a personal computer to allow it to send and receive

messages on a LAN.

Node: A device, usually a personal computer, that is connected to a

computer.

Topology: The physical layout of a network is called a topology.

Some common network topologies are as under:-

18

Network Topologies

Star Topology: A star network has a

hub computer that is

responsible for

managing the network.

All messages are routed

through the central

computer, which acts as

a traffic cop to prevent

collision.

19

Network Topologies

Star Topology:

Any connection failure

between a node and the

hub will not affect the

overall system.

However, if the hub

computer fails, the

network fails.

20

Network Topologies

Ring Topology:

A ring network links all

nodes together in a circular

chain.

Data messages travel in

only one direction around

the ring.

Any data passes by, is

examined by the node to

see if it is addressee; if not,

the

21

Network Topologies

Ring Topology:

Data is passed on to the

next node in the ring..

Since data travels in

only one direction,

there is no danger of

data collision.

However, if one node

fails, the entire network

fails.

22

Network Topologies

Bus Topology: A bus network has a single line to

which all the network nodes are

attached.

Computers on the network

transmit data in the hope that it

will not collide with data

transmitted by other Nodes.

If this happens, the sending node

simply tries again.

Furthermore, if one node fails, it

does not affect the rest of the

network.

23

Computer Networks

There are two ways to organize the

resources in networking, which

are :-

Peer to Peer Networking

Client/Server Networking

24

Computer Networks

Peer to Peer Networking: In which, a group of

computers communicate directly with each other,

rather than through a central server.

Client/Server Networking: A client/server

arrangement involves a server, the computer that

controls the networks.

25

Kinds of Networks

There are different kinds of

networks, for example,

LAN (Local Area Networks)

WAN (Wide Area Networks)

MAN (Metropolitan Area Network)

26

Kinds of Networks

Local Area Networks: A network which

spreads over limited geographical area is

called as LAN.

Wide Area Networks: A WAN is a network

of geographically distant computers. (e.g.

Internet)

27

Local Area Networks

LAN refers to a network with the following

characteristics:-

The network is confined to a small area,

typically a single building.

The network consists of a shared transmission

medium.

The data rate on the network is high, anywhere

from 1 Mbps to 100 Mbps.

28

Local Area Networks

LAN Protocols: The two most common network protocols for

LANs are Ethernet & Token Ring network.

Ethernet – The network protocol which uses the high speed

network cable.

Ethernet uses a bus topology, inexpensive and relatively simple to

set up.

Since all the computers in a LAN use the same cable to transmit

and receive data, they must follow a set of rules about when to

communicate; otherwise two or more computers could transmit at

the same time,

29

Local Area Networks

Ethernet – Causing lost messages. So, if the

cable is in use, the computer must wait.

When the cable is free from other

transmissions, the computer can begin

transmitting immediately.

This transmission method is called by the

fancy name of carrier sense multiple access

with collision detection (CSMA/CD).

30

Local Area Networks

Token Ring – which is closely associated with IBM, works on the

concept of a ring network topology, using a token, a kind of

electronic signal.

Only one token is available on the network. When a computer

on a network wishes to transmit, it first captures the token;

only then can it transmit data.

When the computer has sent its message, it releases the

token back to the network.

Since only one token is circulating around the network, only

one device is able to access the network at a time.

31

Network Applications

Electronic Mail

Voice Mail

Facsimile Technology (FAX)

Electronic Data Interchange (EDI)

E–Commerce

Instant Banking

Video Conferencing etc.

32

Internet – & its use…

ISP - An internet service provider provides the facility to

connect the internet.

Browser – is a software on the user’s computer that allows the

user to access the internet, for example, Internet explorer &

Netscape communicator etc.

Domain Name – Which is the address of the specific web page.

Search Engine – is a software that lets a user specify search

terms; the search engine then finds sites that fit those terms.