A computer network is a telecommunications network which allows different computers to exchange data between them. All the computers which are intended to share data are linked using the data connections. In computer networks, networked computing devices pass data to each other along data connections. These connections or network links are established using either cable media or wireless media between the nodes. There are many types of computer networks including Local area networks (LANs), Wide area networks (WANs), Metropolitan-area networks (MANs) etc. Internet is one of the best known computer network and it is the world largest WAN. Computer devices in the network which can originate, route and terminate the data are called network nodes. Nodes can be any devices such as personal computers, phones, servers as well as networking hardware. These kinds of devices are said to be networked together when one device is in a position to exchange information with the other device, independent of a direct connection to each other. A computer network can also be simply termed as Networking. Computer networks support many applications such as World Wide Web access, shared use of application and storage servers, printers, and fax machines, use of email and instant messaging applications. Computer networks differ many ways like physical media which is used to transmit their signals, the communications protocols which are used to organize network traffic, Size of the network, and topology. Computer network is built combining the computer hardware and software. Computer networks exist in two different basic forms called client/server networks and Peer to peer networks. Network topology represent computer networks structure from data flow point of view.