A wide-area network (WAN) is a data communications network spanning a large geographic area such as a state, province, or country. WANs often use transmission facilities provided by common carriers, for example, telephone companies.

These are the major characteristics of WANs:

• They connect devices that are separated by wide geographical areas.
• They use the services of carriers such as the Regional Bell Operating Companies (RBOCs), Sprint, MCI, VPM Internet Services, Inc., and Altantes.net.
• They use serial connections of various types to access bandwidth over large geographic areas.

A WAN differs from a LAN in several ways. For example, unlike a LAN, which connects workstations, peripherals, terminals, and other devices in a single building or other small geographic area, a WAN makes data connections across a broad geographic area. Companies use a WAN to connect various company sites so that information can be exchanged between distant offices.

A WAN operates at the physical layer and the data link layer of the OSI reference model. It interconnects LANs that are usually separated by large geographic areas. WANs provide for the exchange of data packets and frames between routers and switches and the LANs they support.

The following devices are used in WANs:

• Routers offer many services, including internetworking and WAN interface ports.
• Switches in the WAN provide connectivity for voice, data, and video communication.
• Modems include interface voice-grade services, channel service units/digital service units (CSU/DSUs) that interface T1/E1 services, and Terminal Adapters/Network Termination 1 (TA/NT1s) that interface Integrated Services Digital Network (ISDN) services.
• Communication servers concentrate dial-in and dial-out user communication.

WAN data link protocols describe how frames are carried between systems on a single data link. They include protocols designed to operate over dedicated point-to-point, multipoint, and multi-access switched services such as Frame Relay. WAN standards are defined and managed by a number of recognized authorities, including the following agencies:

• International Telecommunication Union-Telecommunication Standardization Sector (ITU-T), formerly the Consultative Committee for International Telegraph and Telephone (CCITT).
• International Organization for Standardization (ISO).
• Internet Engineering Task Force (IETF).
• Electronic Industries Association (EIA).

Interactive Media Activity Drag and Drop: Identifying Network Devices After completing this activity, the student will be able to understand WANs.