A WAN is a data communications network that covers a relatively broad geographic area and that often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer.

The following are the various protocols and technologies used in WAN environments:

• Frame Relay
• High-Speed Serial Interface
• Integrated Services Digital Network
• Point-to-Point Protocol
• Switched Multimegabit Data Service
• Synchronous Data Link Control and Derivatives
• X.25
• Digital Subscriber Line

There are number of WAN technologies like point to point connection, circuit switching and packet switching. The WAN communication which is carried over a leased line is called point to point connection. In a point to point network the message from the customers end is traveled to the remote user via an ISP. Circuit switching is the data communication which is stared when there is need to communicate and it is terminated afterwards. It is like a telephone call. When the two users arte connected and identified, the data is transferred in other words voice is transferred. When the transmission of the data is complete the call is disconnected again. Packet switching data network is a WAN technology in which the network of the user is established in the carrier’s system. The examples of packet switching network include asynchronous transfer mode (ATM), switched multi megabyte data services (SMDS) and frame relay.