Wide Area Network

A wide area network is a digital communication system, which interconnects different sites, computer installation and user terminals and may also enable LANs to communicate with each other. This type of communication network may be developed to operate nationwide or worldwide. In a WAN the transmission medium used are normally public systems such as telephone lines, microwave and satellite links.
In WAN different LANs and other types of network are connected together, so that users and computers in one location can communicate with users and computers in other locations.
Many WANs are built for one particular organization and are private. Others, built by internet service providers, provide connections from an organization's LANto the internet.
WANs are often built using leased lines. At each end of the leased line, a router connects to the LAN on one side and a hub within the WAN on the other. Leased lines can be very expensive. Instead of using lines, WANs can also be built using less costly circuit switching public systems. Network protocols including TCP/IP deliver transport and addressing functions. X.25 was an important early WAN protocol, and is often considered to be the "grandfather" of Frame Relay as many of the underlying protocols and functions of X.25 are still in use today by frame relay.