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| | Monday, April 13, 2009

WAN (Wide area Network)

Definition: A WAN spans a large geographic area, such as a state, province or country. WANs often connect multiple smaller networks, such as local area networks (LANs) or metro area networks (MANs).

The world's most popular WAN is the Internet. Some segments of the Internet, like extranets, are also WANs in themselves. Finally, many WANs are corporate or research networks that utilize leased lines.

WANs generally utilize different and much more expensive networking equipment than do LANs. Key technologies often found in WANs include SONET, Frame Relay, and ATM.

More about WAN---

The term Wide Area Network (WAN) usually refers to a network which covers a large geographical area, and use communications circuits to connect the intermediate nodes. A major factor impacting WAN design and performance is a requirement that they lease communications circuits from telephone companies or other communications carriers. Transmission rates are typically 2 Mbps, 34 Mbps, 45 Mbps, 155 Mbps, 625 Mbps (or sometimes considerably more).

Numerous WANs have been constructed, including public packet networks, large corporate networks, military networks, banking networks, stock brokerage networks, and airline reservation networks. Some WANs are very extensive, spanning the globe, but most do not provide true global coverage. Organisations supporting WANs using the Internet Protocol are known as Network Service Providers (NSPs). These form the core of the Internet.

By connecting the NSP WANs together using links at Internet Packet Interchanges (sometimes called "peering points") a global communication infrastructure is formed. NSPs do not generally handle individual customer accounts (except for the major corporate customers), but instead deal with intermediate organisations whom they can charge for high capacity communications. They generally have an agreement to exchange certain volumes of data at a certain "quality of service" with other NSPs. So practically any NSP can reach any other NSP, but may require the use of one or more other NSP networks to reach the required destination. NSPs vary in terms of the transit delay, transmission rate, and connectivity offered.

Typical "mesh" connectivity of a Wide Area Network

A typical network is shown in the figure above. This connects a number of End Systems (ES) (e.g. A, C, H, K) and a number of Intermediate Systems (IS) (e.g. B, D, E, F, G, I, J) to form a network over which data may be communicated between the End Systems (ES).

The characteristics of the transmission facilities lead to an emphasis on efficiency of communications techniques in the design of WANs. Controlling the volume of traffic and avoiding excessive delays is important. Since the topologies of WANs are likely to be more complex than those of LANs, routing algorithms also receive more emphasis. Many WANs also implement sophisticated monitoring procedures to account for which users consume the network resources. This is, in some cases, used to generate billing information to charge individual users.

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