Wide Area Networks


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 Wide Area Networks  

 

 

 

 

Wide area networks (WANs) connect computers and other devices separated by very large distances. WANs support data transmission between cities, states, and/or countries. For example, a multinational corporation with offices in New York and Seattle might use a WAN to connect two or more LANs. Although WANs support transmission of many of the same types of applications as MANs, they typically do so at a much lower speed. For example, two of the more common line speeds used in WANs are 1.544 Mbps (T1)17 and 44.746 Mbps (T3).18


17 T1 — United States digital communication line operating at 1.544 Mbps.
18 T3 — United States digital communication line operating at 44 Mbps.


Private19 WANs have steadily grown in popularity because they offer flexibility, security, and control over internal data communications. During the late 1960s through the 1970s, WANs based on IBM’s SNA, and TCP/IP or X.25 packet switching dominated the corporate scene. WANs built at this time were comprised of such components as terminals, processors, modems, multiplexers,20 concentrators,21 and communications links. Efficiency and speed were less important in these early WANs than cost-effective connectivity. The most common applications involved connecting users to remote resources to perform tasks like database retrieval and maintenance, batch file processing, on-line data entry, and so on. These applications are much less time sensitive than the demanding applications of today (e.g., videoconferencing). The most commonly used communication link was the T1, which was used to build large corporate WAN backbone networks. A “backbone” typically consists of a collection of high-speed lines — i.e., T1s — that transmit and consolidate traffic from a number of other lines operating at lower speeds. The lower-speed, dedicated lines were typically used to transmit data to and from mainframes and dumb terminals, at a rate of 9.6 Kbps or 19.2 Kbps. The consolidation of traffic onto lines with a larger capacity offered many throughput and cost advantages over many lines with smaller capacity. WAN networks such as these flourished as T1 costs steadily declined over the years.


19 Private — Communications facilities that are used exclusively by the organization that owns or leases them.
20 Multiplexer — Also known as a “mux,” this is a device that allows more than one signal to be sent over a channel simultaneously.
21 Concentrator — A device that consolidates traffic coming from a number of circuits onto a smaller number of circuits; used to reduce costs.

 

 

 

 

 
 
 
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