Wide Area Network
WAN or Wide Area Network is a data communications network in which computers, separated by a distance of more than half a mile, can be connected. A WAN can consist of several Local Area Networks (LANs) or Metro Area Networks (MANs). The largest WAN in existence is the Inetrnet itself.
Generally WANs are built by collaboration of different corporations, banks, military or ISPs. Local stores or corporations may use a WAN to connect with their customers. WANs are an effective way of communication between companies, or within a single company's own divisions and locations.
WAN may seem a bigger version of LAN but in reality its structure is quite different. Two LANs must exist in order to create a WAN. The WANs built by ISPs provide connectivity from LAN to Internet. WANs do not directly connect one computer to another, which is the role of LAN. Local Area Networks are connected by a device named router which then connects them to WAN. In WAN the data transmission is generally provided by telephone lines. However it can also be connected through Packet Switching, Circuit Switching, Cell Relay or leased lines. The main features of each connectivity option are given below:
Leased Lines provide Point-to-Point connection between Local Area Networks.
Circuit switching creates a dedicated circuit path between end points as used in Dial-Up connections.
Packet switching creates packets of data which are then transferred through different variable length virtual circuits.
Cell relay also creates packets but these packets are tranferred through fixed length virtual circuits. 
Several technologies and protocols can be used in Deployment of WAN. Some of these include:
- Frame Relay
- High-Speed Serial Interface
- Integrated Services Digital Network
- Point-to-Point Protocol
- Switched Multimegabit Data Service
- Synchronous Data Link Control and Derivatives
- Digital Subscriber Line