WAN, which stands for Wireless Area Network, is a computer network that spans a wide geographical range, crossing metropolitan, regional or national boundaries using routers and public communications links.

A WAN is used to connect local area networks (LAN), as well as other types of networks such as campus area networks (CAN), personal area networks (PAN) and metropolitan area networks (MAN) together in order for users and computers in various locations to be able to communicate with each other.

WANs are often private and built for individual organizations, although there are WANs built by Internet service providers (ISP) that are able to provide connections from an organization’s LAN to the Internet, which is the largest and most popular example of a WAN.

There are several options available to be used for building WANs. These options are leased lines, circuit-switching, packet-switching and cell relay. Leased lines are commonly used for WAN connectivity, since this option offers the best security.

On one end of a leased line is a router that connects to the LAN. On the other end of the leased line is a hub within the WAN. Since leased lines tend to be costly, WANs may be built using circuit-switching or packet-switching methods, which are inexpensive in comparison.

The disadvantages of these are call setup for circuit-switching, and sharing media across a link for packet-switching. Cell relay is the ideal option for simultaneous use of voice and data, however, it experiences a significant amount of overhead.

Transport and addressing functions in a WAN are delivered by network protocols such as TCP/IP. Links that are used in WANs are delivered by such protocols as Packet over Synchronous Optical Networking (SONET) or Synchronous Digital Hierarchy (SDH), Multiprotocol Label Switching (MPLS), Asynchronous Transfer Mode (ATM) and Frame Relay, chosen by service providers.

There are three areas of interest for academic research into wide area networks. The first of these, mathematical models, is the creation of an abstract model using mathematical language in order to describe the behavior of a system.

The second, network emulation, is the technique of simulating the properties of an existing, planned or non-ideal network in order to assess the performance of the network or predict the impact of any changes made to it, among other things.

The third, network simulation, is the technique of using a program to model the behavior of a network through either of two methods: using mathematical formulas to calculate the interaction between the various network entities such as hosts or routers, data links and packets, or playing back observations that have been captured from a production network.

Wide area file services (WAFS) or WAN Optimization are two product types that may be used to deliver performance improvements to WANs.