COMPUTER NETWORKS - · PDF fileA popular example of a computer network is the ... Maninder Kaur ISO ... These topologies include: Bus Ring

Chapter 1

Introduction to

Computer Networks

14/10/2010 1 www.eazynotes.com

Computer Networks

A network consists of two or more computers that are linked in order to share resources (such as printers), exchange files, or allow electronic communications.

The computers on a network may be linked through cables, telephone lines, radio waves, satellites etc.

A popular example of a computer network is the Internet, which allows millions of users to share information.


Computer Network


Every Network Includes:

1. At least two computers that have something to share.

2. A cable or wireless, called Transmission Media, for computers to signal each other.

3. Rules, called Protocols, so that computers can use the unified principle of data communication.

4. Networking Interface Cards (NIC)


Advantages of Computer

Networks

File Sharing: Networks offer a quick and easy way to share files directly.

Resource Sharing: All computers in the network can share resources such as printers, fax machines, modems and scanners.

Communication: the network can communicate with each other via e-mail, messages, voice etc.


Advantages of Computer

Networks

Flexible Access: Networks allow their users

to access files from computers throughout the

network.

Sharing of Information: Computer networks

enable us to share data and information with

the computers that are located geographically

large distance apart.


Network Classification

Network Computing Models

Client / Server Centralized Computing

Peer-to-peer Distributed Computing


Client-Server Network (Centralized Computing)

◦ A client-server network is where every client is

connected to the server.

8

Server

Client/Server network

Nodes and servers share data roles

Nodes are called clients

Servers are used to control access

Access to database is controlled by server

Server is the most important computer

Client and Server computer role in networking

Server computer is a core component of the network, providing a link to the resources necessary to perform any task.

Server is the most important computer, store and process shared data, perform network activities, backup storage and user authentication.

Client computers normally request and receive information over the network and is normally a desktop or laptop computer.

Client computers also depends primarily on the central server for processing activities


Peer-to-Peer Network (Distributed Computing )

All nodes are equal.


Peer-to-peer network (P2PN)

A peer-to-peer network is a network where the computers act as both workstations and servers.

Small, simple, inexpensive networks and easy to install.

Each machine can have resources that are shared with any other machine.

There is no assigned role for any particular device, and each of the devices usually runs similar software.

They are popular as home networks and for use in small companies.

The maximum number of peers that can operate on a peer-to-peer network is ten (10) .

Simultaneous Access

Shared Peripheral Devices

Personal Communication

Easier Backup


Uses of Computer Network

ISO/OSI Model

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ISO/OSI Model

The International Standards Organization (ISO) Open Systems Interconnect (OSI) is a standard set of rules describing the transfer of data between each layer in a network operating system.

The OSI Model clearly defines the interfaces between each layer.

This allows different network operating systems and protocols to work together.

The application of the ISO OSI model has allowed the modern networks that exist today.

There are seven layers in the OSI model.

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ISO/OSI Model

Each layer should perform a well defined function.

Using the OSI Model

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Computer Network Protocols

A protocol is a set of rules that governs the communications between computers on a network

These rules include guidelines that regulate:

◦ The method of access,

◦ Types of cabling,

◦ Speed of data transfer.

PROTOCOL =

SET OF RULES

ABOUT

COMMUNICATIONS

BETWEEN

NETWORKS!

The most common protocols are:

1) Ethernet

2) Local Talk

3) Token Ring

4) FDDI

5) ATM

6) TCP/IP

Protocol = a formal

description of a set of

rules and conventions

that govern how devices

on a network exchange

information

1) Ethernet

Most widely used

Uses an access method

called CSMA/CD

(Carrier Sense Multiple

Access/Collision

Detection

The most common protocols

What does that mean?

Each computer in the network ‘listens’ to the cable before

sending anything through the network. If the network is clear,

the computer will transmit.

If another computer is already transmitting on the cable, the

computer will wait and try again when the line is clear.

Ethernet protocol allows transmission speed of 10 Mbps ,

100 Mbps (fast Ethernet) &, 1Gbps (Gigabit Ethernet).

A bit like waiting for some one to get off the telephone

Ethernet cont. .…

2) Local Talk

Local Talk is a network protocol that was developed by Apple for Macintosh computers.

Local Talk uses the CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance)

It is a lot slower than Ethernet (only 230 Kbps)


3) Token Ring

Token ring protocol

involves ‘token-passing’.

It is not as popular as

Ethernet protocol

A single electronic ‘token’

moves around the ring from

one computer to the next. If a

computer wishes to transmit

and receives an empty token, it

attaches data to the token

which then proceeds around

the ring until it comes to the

computer the data is meant for.


animation of the token ring

4) FDDI (Fiber Distributed Data Interface)

Is used mainly to connect two or more LANs, often over large distances.

Can operate over fiber optic cable at 100 Mbps.


5) ATM- Asynchronous Transfer Mode

Transmit data at a speed of 155 Mbps and higher

Works by transmitting all data in small packets of fixed size (other protocols transfer variable size packets)

Like FDDI , is most often used to connect two or more LANs.


6) TCP/IP

TCP/IP is the protocol that is used for the

transmission of information over the Internet.

TCP/IP reference model consists of four layers:

• Application layer

• Transport layer

• Internet layer

• Network interface layer


The Transmission Control Protocol/Internet Protocol (TCP/IP)

Reference Model

E-mail

Chatting

News Groups

Telnet

File Transfer Protocol (FTP)

Searchable Data (World Wide Web)

Internet Telephony (VoIP)

Virtual private network (VPN)


APPLICATIONS OF NETWOKS

• E-mail

Enables messages to be exchanged from computer to computer or

multiple recipients with attaching documents and multimedia files.

• Chatting

Enables two or more people connected simultaneously to interactive

conversations. Chat support voice, video and written conversations.

• News Groups

Are worldwide discussion group on which people share information

and ideas on a defined topic, such as pollution, communications .. Etc.


• Telnet

Logging to one computer system and doing work on another.

Telnet program runs on your computer and connects your PC to

a server on the network. This enables you to control the server

and communicate with other servers on the network.

• File Transfer Protocol (FTP)

Transferring files from computer to computer

• World Wide Web

Is a service provided by the Internet used for storing , retrieving,

formatting and displaying information in a page format on the

Internet including text, audio, graphics and voice.


• Voice over IP (VoIP)

Is a technology delivers voice information in digital form using

packet switching, avoiding the cost charged by local and long

distance telephone networks.

VoIP phone call convert a voice message into data packets that may

travel along different routes before being reassembled at the final

destination.

A processor nearest the call’s destination, called a gateway, arranges

the packets in the proper order and directs them to the telephone

number of the receiver or the IP address of the receiving computer.


How Voice over IP Works

An VoIP phone call digitizes and breaks up a voice message into data packets that may travel along different

routes before being reassembled at the final destination. A processor nearest the call’s destination, called a

gateway, arranges the packets in the proper order and directs them to the telephone number of the receiver

or the IP address of the receiving computer.


• Virtual private network (VPN)

• VPN is a secure , encrypted, private network that has

been configured within a public network such as Internet

to take advantage of the economies of scale and

management facilities of large networks.

• VPN also provide a network infrastructure for combining

voice and data networks.


A Virtual Private Network Using the Internet

This VPN is a private network of computers linked using a secure “tunnel” connection over the Internet. It protects data

transmitted over the public Internet by encoding the data and “wrapping” them within the Internet Protocol (IP). By

adding a wrapper around a network message to hide its content, organizations can create a private connection that

travels through the public Internet.

Types of Computer

Networks

Different Types of Networks

Depending upon the geographical area

covered by a network, it is classified as:

– Personal Area Network (PAN)

◦ Local Area Network (LAN)

◦ Metropolitan Area Network (MAN)

◦ Wide Area Network (WAN)

Personal Area Network (PAN)

A PAN is a network that is used for communicating among computers and computer devices (including telephones) in close proximity of around a few meters within a room

It can be used for communicating between the devices themselves, or for connecting to a larger network such as the internet.

PAN’s can be wired or wireless

Personal Area Network (PAN)

A LAN is a network that is used for communicating among computer devices, usually within an office, building or home.

LAN’s enable the sharing of resources such as files or hardware devices that may be needed by multiple users

Is limited in size, typically spanning a few hundred meters, and no more than a mile

Is fast, with speeds from 10 Mbps to 10 Gbps

Has lower cost compared to MAN’s or WAN’s

Local Area Network (LAN)


LAN’s can be either wired, wireless or both .

Every LAN uses a protocol – a set of rules that governs the communications between computers on a network.

Nodes in a LAN are linked together with a certain topology. These topologies include: ◦ Bus ◦ Ring ◦ Star ◦ Mesh


Advantages of LAN

High speed

Low cost

Security

E-mails sharing

Resource Sharing

Disadvantages of LAN

Expensive to Install

Requires Administrative Time

File Server May Fail

Cables May Break

Metropolitan Area Network (MAN)

Metropolitan Area Network (MAN) is a

large computer network that usually spans a city

or a large campus.

A MAN is optimized for a larger geographical

area than a LAN, ranging from several blocks

of buildings to entire cities.

A MAN might be owned and operated by a

single organization, but it usually will be used by

many individuals and organizations.

Metropolitan Area Network (MAN)

A MAN often acts as a high speed network

to allow sharing of regional resources.

A MAN typically covers an area of between

5 and 50 km diameter.

Examples of MAN: Telephone company

network that provides a high speed DSL

to customers.

Metropolitan Area Network

(MAN)

Wide Area Network (WAN)

WAN covers a large geographic area such as

country, continent or even whole of the

world.

To cover great distances, WANs may

transmit data over leased high-speed phone

lines or wireless links such as satellites.

Wide Area Network (WAN)

Multiple LANs can be connected together

using devices such as bridges, routers, or

gateways, which enable them to share data.

The world's most popular WAN is the

Internet.

Provides long-distance transmission of data, voice, image, and video information over large geographic areas

Wide-Area Networks (WAN)

Documents

COMPUTER NETWORKS - · PDF fileA popular example of a computer network is the ... Maninder Kaur ISO ... These topologies include: Bus Ring