Data Communications: Wide Area Networks

Essay by murraysean5University, Bachelor's May 2004

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A Wide Area Network (WAN) is a computer network that spans across over a large geographical area. A wide area network typically is made up of two or more Local Area Networks (LANs). Computers connected to a wide area network are often connected through public networks, such as the telephone system. They can also be connected through leased lines or satellites. An example of a wide area network is the Internet, which is the biggest in existence. 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.

Types and Characteristics of WANs

Wide area networks are everywhere and there is a vast amount of different variations with regards to topologies, physical connection and what devices we use. WAN dialup services offer cost-effective methods for connectivity across WANs. Two popular dialup implementations are dial-on-demand routing (DDR) and dial backup.

DDR is a technique whereby a router can dynamically initiate a call on a switched circuit when it needs to send data. In a DDR set-up, the router is configured to initiate the call when certain criteria are met, such as a particular type of network traffic needing to be transmitted. When the connection is made, traffic passes over the line. The router configuration specifies an idle timer that tells the router to drop the connection when the circuit has remained idle for a certain period.

Dial backup is another way of configuring DDR. However, in dial backup, the switched circuit is used to provide backup service for another type of circuit, such as point-to-point or packet switching. The router is configured so that when a failure is detected on the primary circuit, the dial backup line is initiated. The dial backup line then supports the...