As an enterprise grows beyond a single location, it becomes necessary to interconnect LANs in various locations to form a WAN. Several technologies are involved in the functioning of WANs, including hardware devices and software functions. This lesson describes the functions and characteristics of WANs and contrasts them with LANs. The lesson also explores how WANs relate to the Open Systems Interconnection (OSI) reference model in their design and function, which major hardware components are typically seen in WAN environments, and how data is managed in a WAN through multiplexing.
What Is a WAN?
A WAN is a data communications network that operates beyond the geographical scope of a LAN.
WANs use facilities provided by a service provider, or carrier, such as a telephone or cable company. They connect the locations of an organization to each other, to locations of other organizations, to external services, and to remote users. WANs generally carry a variety of traffic types, such as voice, data, and video. Figure 5-1 shows how the WAN provides interconnectivity between the campus LAN and remote sites.
Here are the three major characteristics of WANs:
■ WANs connect devices that are separated by wide geographical areas.
■ WANs use the services of carriers, such as telephone companies, cable companies, satellite systems, and network providers.
■ WANs use serial connections of various types to provide access to bandwidth over large geographical areas.
Why Are WANs Necessary?
LAN technologies provide both speed and cost-efficiency for the transmission of data in organizations in relatively small geographical areas. However, other business needs require communication among remote users, including the following:
■ People in the regional or branch offices of an organization need to be able to communicate and share data.
■ Organizations often want to share information with other organizations across large distances. For example, software manufacturers routinely communicate product and promotion information to distributors that sell their products to end users.
■ Employees who travel on company business frequently need to access information that resides on their corporate networks.
In addition, home computer users need to send and receive data across increasingly larger distances. Here are some examples:
■ It is now common in many households for consumers to communicate with banks, stores, and a variety of providers of goods and services via computers.
■ Students do research for classes by accessing library indexes and publications located in other parts of their country and in other parts of the world.
Figure 5-2 shows the variety of ways that WAN users connect to corporate resources.
Because it is obviously not feasible to connect computers across a country or around the world with cables, different technologies have evolved to support this need to connect these geographically diverse devices. WANs allow organizations and individuals to meet their wide-area communication needs.
How Is a WAN Different from a LAN?
WANs are different from LANs in several ways. Whereas a LAN connects computers, peripherals, and other devices in a single building or other small geographical area, a WAN enables the transmission of data across broad geographical distances. In addition, a company or organization must subscribe to an outside WAN service provider to use WAN carrier network services. LANs are typically owned by the company or organization that uses them. Table 5-1 compares the differences between the WAN and LAN.
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