Computer network is a set of devices connected together by media links for exchange of information and other applications. These devices can be a computer, printer or any other device which is capable of sending and receiving information. The links connecting these devices are called communication channels. Any computer network should meet at least following three criteria.

(i) Performance

(ii) Reliability

(iii) Security.

Broadly we can classify computer into three types.

(i) LAN (Local area network): Restricted to a building or an organization.

(ii) MAN (Metropolitan area network): Coverage area is restricted to a metro city.

(iii) WAN (Wide area network): It covers the whole world.