Introduction to WANS

A WAN is a data communications network that spans a large geographic area such as a state, province, or country. WANs often use transmission facilities provided by common carriers such as 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, and VPM Internet Services, Inc. to establish the link or connection between sites.
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, 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.
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)

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