Data Communication/ Transmission and Computer Networks

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Data Communication/ Transmission and Computer Networks

What is data transmission?

Physical movement of data from one place to another place (Physical exchange of data) is called

data transmission.

What is data communication?

This is the meaningful exchange of information after the relevant receiver gets transmitted

information.

Elements of Data Communication

1 Sender / Source

2 Data Communication Medium

3 Receiver



Data Transmission Media

There are 2 main types of media that transmit data from one place to another place.

(1) Guided Media

(2) Radiated Media / Unguided Media

(1) Guided Media

I. Twisted Pair Cable (TP)

a) Unshielded Twisted Pair (UTP)

b) Shielded Twisted Pair (STP)

II. Co - axial Cable

III. Fiber Optics Cable

I. Twisted Pair Cable (TP)

This cable can transmit data from 100m to 200m without any obstacle. The costs of

these are less. There are two types, one is UTP and the other is STP. The jacks RJ45 and RJ11

are used to connect these to any device. Generally these are named as telephone cables and

these cables are spun to minimize the destruction which is caused by outside magnetic fields. UTP

STP

II. Co - axial Cable Generally these are called Antenna cables. They transmit data far about 500m without

any obstacle. These are more expensive than TP cable and less than Fiber optics. These are

connected to any device by BNC connector and used for CCTV camera systems.

Conductor (copper)

Insulating Jacket

Outer Jacket

Conductor (copper)

Insulating Jacket

Outer Jacket

Pair Shield



Conductor (copper)

Insulating Jacket

Outer Jacket (Outer Cylindrical Shell)

Shield Second Conductor

Fiber Core

Cladding

Outer Jacket

III. Fiber Optics Cable

These cables can transmit data far about 2km without any obstacle and price is more than the

other cables. This is the guided media with low resistance and the speed of data transmission

is highest. These are connected with ST and SC connectors and transmit data by reflecting

light. It is called light reflection.

(2) Radiated Media / Un guided Media

I. Radio Waves

II. Infrared light beams

III. Micro Waves

I. Radio Wave These types of waves are used for radio telecast and television transmission. And also

radio waves are used for Wi-Fi and blue tooth technologies.

II. Infrared light beam

These are used to transmit data to short distance and mostly used in remote controls.

Also these are used in wireless keyboard and wireless mouse.

III. Micro Wave

This is used for transmit data long distance and also used in satellite technology.



Blue tooth

This technology transmits data far about 100m and uses radio waves. This is used in

mobile phones, Laptops, Notebooks, Tablet computers, etc…….

Wi-Fi

This technology transmits data far about 150m using radio waves. Commonly this is

used to get wireless internet facilities.

Wi – max

This can transmit data far about 10 km and this is used for WAN. And also it is used for data

transmission among telephone exchanges.

Data Transmission Types

1. Serial Data Transmission

2. Paralleled Data Transmission

Serial Data Transmission

This is introduced as the way of data transmission one by one through any data transmission

media. As the fewer amounts of media are needed for this, the expense is less. And this gets a long

time for data transmission the speed is low. This is suitable for long distance data transmission.



Parallel Data Transmission

This is introduced as the way of data transmission parallel once through several data

transmission media. As more media is needed for this, the expense is more and the data

transmission speed is high. This is suitable for short distance data transmission.

Data Transmission Modes

The direction of data transmission' There are 3 types of data transmission modes.

1. Simplex Data Transmission

Transmit data to only one direction

Ex :- Television Transmission

Radio Transmission

Sender Receiver

2. Half Duplex Data Transmission

Transmit data both directions, but not simultaneously

Ex :- Wolki - Toki Conversation

Sender Receiver

3. Full Duplex Data Transmission

Transmit data both direction simultaneously

Ex :- Telephone Conversation

Video Conferencing

Online Voice Chat

Sender Receiver

Computer Networks

A computer network consists of two or more computers that are link in order to shire

resources (Printers, scanners, CD drive), exchange files or folders or electronic communication

(Online chat, Video conferencing) among users.

Classification of Computer Network

1. Classification of Computer Networks According to Geographical area

Local Area Network /LAN

Metropolitan Area Network /MAN

Wide Area Network/WAN

Medium

Medium

Medium



Local Area Network (LAN)

A small area limited for a room, a house, a building, several buildings, a school or a campus

is called LAN. In such network mostly cables are used to connect the computers each other. So in

every computer, a Network Interface Card (NIC) can be seen. A LAN expands for several miles

occasionally. LAN can be seen in three types

Personal Area Network (PAN)

The connection of the digital devices around one person.

Home Area Network (HAN)

The connection of the computers in a house.

Campus Area Network (CAN)

The connection of the computers in an area such as campus.

Example for LAN: - Computer network in your school

Metropolitan Area Network (MAN)

The connection of the computers with same technology which expanded in a large city is

called MAN. Personal computers as well as LAN can be in such network.

Ex :- Network built by connecting branches in several places in Colombo city.

Wide Area Network (WAN)

The network spread in all over the world or in a country is called WAN. In such network to

connect the computers each other, under grounded cables or satellite technology is used. LAN,

MAN and personal computers can be in a WAN. The Internet is the best example for WAN.

Eg :- Internet, School net

2. Classification of Computer networks according to Relationship

Peer To Peer (P2P)

Client Server

Peer To Peer (P2P)

Every computer in this network has similar privileges. There’s not a main computer

(Server).



Client Server

The connection of main computer that supplies a resource to the network (Server) and a

client that asks for a resource from the network is called as Client – Server network

Eg :- Internet

Network in a bank

3. Classification of computer Networks according to opening to the external environment

Intranet

Extranet

Internet

Intranet

A network that limited to selected people only

Eg :- A network limited to an office

Extranet

This is also an Intranet but it is open to the environment, protecting through the username

and password

Eg :- A computer network in a bank (ATM)

Internet

This is a common network open to anyone in the environment

Eg :- Internet

Advantages of Computer Networking Hardware resource can be shared between computers.

Electronic communication between uses. (Online Chat, Video Conferencing)

Files, Folders can be shared between users.

Duplicating data is avoided

Communication cost can be reduced

Server

Client 3

Client 2

Client 1



Disadvantages of Computer Networking

Computer viruses can easily accessed to the computer

Doesn’t have security for files and software in the computer or network.

System open to the hackers

Network management can become difficult

Sometimes error in one computer or hardware it may cause to functioning of other

computer.

Network Topology

Physical layout of a computer network is called as its topology I. Main Topologies i. Star Network Topology ii. Ring Network Topology iii. Bus Network Topology II. Hybrid Topologies iv. Tree Network Topology v. Mesh Network Topology

i. Star Network Topology

In a star network topology all computers and other communication devices are connected

to a central point such as Hub, Switch or Central Host Computer. Such a network topology can

be prepared easily and low cost. The disadvantage of this network topology is when central

point is not functioning the whole network will be broken down.

ii. Ring Network Topology

In a ring network topology all communication devices are connected in a continuous Ring.

Such a network topology can be prepared easily and low cost. The disadvantage of this

network topology is the low speed of data transmission and also when one computer is not

functioning the whole network will be broken down. Only the computer which owns the token

transmits data and the data transmission is done to only one direction.

Node ^A physical device of a network (Computer

/Printer/Server)



iii. Bus Network Topology

Such a layout can be created by connecting the computers to the common channel with the

help of byways. Here the obstacles for the data transmission are minimum. The main

disadvantage is the high expense for the preparation. The high expense for the common

channel is the reason. Also the depending of the whole network on the main cable is another

disadvantage.

Hybrid Topologies

iv. Tree Network Topology

This is a network like a tree with branches. This can be introduced as a developed stage of

star topology. Controlling separately only one branch is an advantage. However establishing

and maintaining the network is a difficult task.

Node

Terminator

Nodes

Common Channel

(Backbone Cable)



v. Mesh Network Topology

This is a developed stage of Ring network topology. Creating and maintaining is very

complex. Data transmission speed is high.

Network Hardware / Communication Devices

Hub

This is the centralized device that connect all the

computers each other in Star and tree Topology. As this

device transmits the data obtained from a computer to all

the computers, there will be a bustling. It is a powerful

disadvantage. Also the security of the data and

information is minimum.

Switch

This is also used as centralized device to connect all he

computers in Star and Tree topology. When data transmit

through this device as the data transmits to only relevant

computer, the data transmission speed is high. Also the

security of the data and information is high.

Modem

(MOdulation and DEModulation)

A modem is a device that converts digital signal into analog (Modulation) and analog signal

into digital (Demodulation) There are 2 types of modem

i. Internal Modem

ii. External Modem

A

B

C

D

E

F

G

H

Hub

F to C

A

B

C

D

E

F

G

H

Hub

F to C >>

E to A >



Analog Signal

Digital Signals

Bridge

Bridge is used to connect 2 or more similar

networks

Router

A major function of router is that chooses the beat route between networks that may have

multiple paths between them.

Repeater

Any electrical signal reaching the repeater from one segment, will be amplified and

retransmitted to the other segment.

Gateway

Gateway is used to connect 2 or more different network that used to different

technology.

LAN ISDN = Integrated Services Digital Network

Network Interface Card (NIC)

NIC provides the physical connection between the computers and computer cables of a

network

Digital

Signal

Analog

Signal

Modulation

Demodulation

ISDN Gateway

Bridge

0 0 0 0 0 0

1 1 1 1 1 1 1



Common Network Elements Client

Server

Modem

Shared Resources

Communication Media

Hub

Switch

Internet The Internet is a collection of computers and computer networks. It was started in 70’s from

USA developing ARPANET (Advanced Research Project Agency) The Internet was introduced to

Sri Lanka in 1995. Internet is the world’s biggest Wide Area Network. The computers are

connected to the internet is resource full and therefore internet is a massive collection of

information.

In general terms of internet are collection of computers, networks, Hardware, Software and

people. The internet consists of web pages and web pages are developed using web language

(HTML, XML and PHP)

Layout of the Internet

Web

Server

Web

Server

Web

Server



Needs to access to the Internet A Computer

A Modem

A Telephone Line (SL Telecom, Mobitel, Dialog, Suntel, Lankabel…etc)

A Web Browser/An Internet Browser (Software)

Microsoft Internet Explorer

Mozilla Firefox

Opera

Safari

Google chrome

Netscape Navigator

An Internet Service Provider (ISP)

Sri Lanka Telecom

Mobitel

Dialog

ITMIN

PAN Lanka

Eureka

Suntel

Lankabel

Lanka Internet

Internet Facilities (Advantages of the Internet)

E-mail

Online Chat

Video conferencing

E-commerce

E-banking

E-learning

E-medicine (E-channelling)

Downloading

Uploading



Disadvantages of the Internet Computer viruses can easily access to the computers through the Internet

Children mind are corrupted

Hacking

Doesn’t have security and can’t control

No owner for the Internet

Web Address

Uniform Resource Locater (URL)

http://www.host name. Sub level domain name. Top level domain name

Domain Name

Eg:-

http://www.google.com

http://www.doenets.lk

http://www.saman.kamal.com Host Name – Name of the website

Domain Name – Common sub name that can be used for many websites

Domain Name – Common top level name that can be used for many websites

IP Address (Internet Protocol Address)

IP address is the number which is to identify each node uniquely connected to the computer

network

EX 192.248.9.33

123.45.6.4

This IP address should be in four numbers.

Top Level Domain Names

com - Commercial

edu - Education

org - Organization

gov - Government

mil - Military

uk - United Kingdom

lk - Sri Lanka

http://www.host/

http://www.google.com/

http://www.doenets.lk/

http://www.saman.kamal.com/



Protocol Common rule of a network is called as a protocol

Eg:- http - Hyper Text Transfer Protocol

ftp - File Transfer Protocol

pop - Post Office Protocol

smtp - Simple Mail Transfer Protocol

DNS Server (Domain Name Server)

Converting web address into IP address is done by the DNS server.

E-Mail E-mail is a sending message from one computer to another computer (One e-mail account to

another e-mail account) via internet. To use e-mail both sender and recipient should have e-mail

accounts. The message has to be typed in to e-mail software (Outlook express). The massage will

be sent to your e-mail service provider and will be saved in the user’s mail box. When the receiver

logs into the system the service provider sends the mail saved in the system and the receiver read

the mail and replies.

E-mail Address

Username @ email service . Sub level domain name. Top level domain name

providers

hostname

Eg:- [email protected]

[email protected]

[email protected]

Advantages of e-mail over normal post

1 High speed for anywhere of the world

2 Low cost for anywhere of the world

3 Video, Audio, Picture files can be attached

4 Security of the message

5 No paper are used

Documents

Data Communication/ Transmission and Computer Networks