Computer Networks

Computer Networks

Why Computer Networks ?- Sharing Resources

- Sharing Data & Software

- Efficient Communication

- Using one database

- Saving time

Disadvantages of a Computer Networks

- High cost to establish

- Spreading virus soon

- Need experts to maintain the network

- Server down effect the whole network

Aims of a Computer Networks

- Resource Sharing

- Remote Computability

- High Reliability

- Ensure the data consistency

- Message Passing

- Data Security

- Save money

Classification Of Network

- Wide Area Network – (WAN)

By Geographical Setup

Spread to unlimited

area

Eg:- Internet

Classification Of Network

- Metropolitan Area Network – (MAN)

By Geographical Setup

Spread in a City or Country Eg:- Network within town

- Campus Area Network – (CAN)

By Geographical Setup

Spread in a site like School,

Campus Eg:-

Network within a school

Classification Of Network

- Local Area Network – (LAN)

By Geographical Setup

Spread in a Building

Eg:- Network within a Building

Classification Of Network

- Home Area Network – (HAN)

By Geographical Setup

Spread in a House

Eg:- Network within a home

Classification Of Network

- Personal Area Network – (PAN)

By Geographical Setup

Computer and its components

Classification Of Network

- Client Sever

By Functional Relationship

Clients work under Server

Classification Of Network

- Peer to Peer (P2P)

By Functional Relationship

All the Computer have same capabilities

Classification Of Network

- Bus Network

By Network Topology Classification Of Network

- Star Network

By Network Topology Classification Of Network

- Ring Network

By Network Topology Classification Of Network

- Tree Network

By Network Topology Classification Of Network

- Mesh Network

By Network Topology Classification Of Network

- Hybrid Network

By Network Topology Classification Of Network

Server – Manages all the other computers in the network..

Common Network Elements

Client – Work under the server

Communication Media – Trough which computers are connected.

Network Operating System (NOS) – Software installed to the server

Shared Resources – Devices shared among network clients

Modem – Device used to get the internet

Hub/ Switch – Device used to connect all the computer

Common Network Elements

Server

Clients

Communication Media

Network Operating

Shared Resources

Modem

Hub/ Switch

Hub

Hub sends messages to all computers

Hub Vs Switch

A B C D

Switch sends messages to destination computer only

Switch

1. Dedicated Line

Line Connections

2. Lease Line

3. Switch line (Dial Up connection)

Simplex

Transmission Modes

Duplex

Half Duplex

Guided Media

Communication Media

Radiated Media

Guided Media

Coaxial Cables Guided Media

Twisted pair cables Guided Media

Fiber Optic Cables Guided Media

Radiated Media

Radio Transmission Radiated Media Media

Infrared Transmission Radiated Media Media

Microwave Transmission Radiated Media Media

Satellite Transmission Radiated Media Media

Data Transmission Types

Serial Transmission

Parallel Transmission

0 1 1 0 0 0

0110

Network Interface Card

Make the physical Connection between the computer and network wire

What is a Network Protocol ?

It is an agreement on transferring Data between computers in a network

Eg:-

TCP/IP, IPX/SPX, X.25

Backbone Network Components Components that several networks link together.

TCP/IP TCP/IP

Devices

Hub Bridge

Backbone Network Components Components that several networks link together.

TCP/IP IPX/SPX

Devices

Router Gateway

InternetWide Network spread all over the world to transfer electronic data.

Today Internet is used for….

Business, Education, communication

Resources in the internet

Information, Pictures, Sounds, Vedio, on line exams, Games, Chatting

Necessaries for Getting Internet

A Computer, Modem, Telephone line, internet browser

Why a modem is needed….

To convert digital signals Analog and vise versa

Analog Signals

Digital Signals

DAC - Modulation

ADC - Demodulation

Internet Browsers

The Application Software through which we access to the internet Eg :-

Internet explorer Netscape Navigator

Fire Fox

Safari

World Wide Web (WWW)

Collection of Web pages throughout the world

WWW. Rupavahini.lk WWW. Defence.lk

www.Rupavahini.lk

Web Address = URL (Uniform Resource Locator)

It is essential to separate web pages each other

http: // WWW. Defence.lk /News

Protocol

Hyper Text Transfer Protocol

The server

Where this information is?

Path name

Location of an item on the server

Domain Name

www.Rupavahini.lk

www.Youtube.com

www.Wickipedia.org

www. Carrer.edu

Classification of web sites according to their contents.

Domain Type What it Means

.com a commercial business, organization, or company

.edu an educational institution

.int an international organization

.gov a nonmilitary government entity

.mil a military organization

.net a network administration, often Internet-related

.org other organizations: nonprofit, nonacademic

.uk, .au, ca, jp, nz, etc. country codes denoting servers found in other countries

Search Engines

A web page that helps us to find information on web pages when we don’t know the exact name of the Web.

Eg:- WWW. Google.com, Yahoo.com ….

Popularity of Search Engines

What is download & Upload

Internet SeversHome Computer

Downloading…

Uploading

Computer Virus

Computer Virus

It is a software that is very harm to computer.

• Replicate itself

• Join with another programs

• Do unintended actions

Why Virus ?

• Hacking

• Avoid of copying software

• Revenge

• To break security systems

• to defeat competitors

Etc…..

How Virus enter ?

Characteristics of Virus ?

• If computer take long time than normal to open a program

• If it Read the hard disks, Floppy disks often

• If Unknown files are visible• If unnecessary beep codes activate• If Unnecessary messages & pictures visible

Kinds of Virus ?

• Boot virus

• File Virus

• Macro Virus

• Trojan horse

• Warms

• Spyware

+

Format Fonts

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• Spam Unsolicited email, often of a commercial nature, sent indiscriminately to multiple mailing lists or individuals.

• Spyware This is software that secretly gathers information about a user while he/she navigates the Internet. This information is normally used for advertising purposes. Spyware can also gather information about email addresses and even passwords and credit card numbers.

• Trojan horse This is a program that disguises itself as another program. Similar to a virus, these programs are hidden and cause an unwanted effect. They differ from viruses because they are normally not designed to replicate like a virus.

• Virus A computer virus is a piece of code that is secretly introduced into a system in order to corrupt it or destroy data. Often viruses are hidden in other programs or documents and when opened, the virus is let loose.

• Worm This is a special type of virus that spreads without any user interaction, typically by exploiting a flaw in popular software.

Prevent from virus ?

• Use Anti virus Software

Prevent from virus ?

• Use Firewalls

Prevent from virus ?

• Avoiding of using unexamined CD, Floppy, Software

Virus G

uard

E-mail (Electronic Mail)

• Sending electronic data by using a network

E-mail Addresses

samantha perera@gmail.com - wrong (Space between username)

samantha#?perera@gmail.com - wrong (Special Symbols)

samantha@perera@gmail.com - duplicated @ sign

SAMANTHAPERERA@gmail.com - wrong (Capital Letters)

samantha_ perera@gmail.com - Correct (Underscore can be use)

samanthaperera1981@gmail.com - Correct (numbers can be use)

E-mail Addresses

samantha@gmail.com

We can create email accounts through….

www.google.com – username@gmail.com

www.yahoo.com – username@yahoo.com

www.esrilanka.lk – username@esrilanka.lk

Through Telecom – username@slt.lk