A computer network is a communication network which allows nodes to share resources. In computer networks, computing devices exchange data with each other using connections between nodes. These data links are established over guided media and unguided media. Network computer devices that originate, route and terminate the data are called network nodes. Nodes are generally identified by network IP addresses, and can include hosts such as personal computers, phones, and servers, as well as networking hardware such as routers and switches. Two such devices can be said to be networked together when one device is able to exchange information with the other device through wired or wireless, whether or not they have a direct connection to each other. Computer networks support an enormous number of applications and services such as access to the WWW, Audio and Video shared use of application and storage servers, printers, and scanners, and use of email and instant messaging applications as well as many others. Computer networks differ in the transmission medium used to carry their signals