Wide Area Networking (WAN)
The technologies studied earlier are effective for setting up networks on rather small distances. However frequently for building of a network, there is a necessity to connect among them computers removed from each other on large geographical distance. A typical example - connection of the user of Internet services with remote provider. In given case it is perfect other world - world of technologies WAN. Wide area network is data communications network that serves users across a broad geographic area and uses transmission devices provided by common carriers.
One more difference of a WAN consists that the LAN can simply be constructed by own strength. For construction of a WAN the huge material input are required, which include: cost of cable works, expense for the communication equipment and intermediate intensifying equipment, and also operational expenses for constant maintenance of services of all network. Therefore, as a rule, there is a necessity to subscribe to an outside WAN service provider, such as a regional Bell operating of company (RBOC). A choice of provider is the very important part of competent construction of a WAN, as just provider defines WAN technology for connection of the subscribers and main function a network will depend on it. Less often WAN is completely created by the company independently for own needs. As creation of WAN is a very expensive task, more often company rents the central channels of communication, based on which independently builds own territorial networks.
WANs generally carry a variety of traffic types, such as voice, data, and video as just multi-service networks is a priority direction for creation of new and development old networks, because the association of different kinds of the traffic in one channel allows reducing expenses of creation and purchasing of the equipment.
WAN technologies function at the three layers of the OSI model: the physical layer, the data link layer, and the network layer.201
201. Vendors point of view for WAN: http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/introwan.htm
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