A wide area network (WAN) is a telecommunications network that extends over a large geographic area. Wide area networks are often established with leased telecommunication circuits. Businesses, as well as schools and government entities, use wide area networks to relay data to staff, students, clients, buyers and suppliers from various locations around the world. In essence, this mode of telecommunication allows a business to effectively carry out its daily function regardless of location. The Internet may be considered a WAN. Many WANs are, however, built for one particular organization and are private. WANs can be separated from local area networks (LANs) in that the latter refers to physically proximal networks. Design options The textbook definition of a WAN is a computer network spanning regions, countries, or even the world. However, in terms of the application of communication protocols and concepts, it may be best to view WANs as computer networking technologies used to transmit data over long distances, and between different networks. This distinction stems from the fact that common local area network (LAN) technologies operating at lower layers of the OSI model (such as the forms of Ethernet or Wi-Fi) are often designed for physically proximal networks, and thus cannot transmit data over tens, hundreds, or even thousands of miles or kilometres. WANs are used to connect LANs and other types of networks together so that users and computers in one location can communicate with users and computers in other locations. Many WANs are built for one particular organization and are private. Others, built by Internet service providers, provide connections from an organization's LAN to the Internet. WANs are often built using leased lines. At each end of the leased line, a router connects the LAN on one side with a second router within the LAN on the other. Because leased lines can be very expensive, instead of using leased lines, WANs can also be built using less costly circuit switching or packet switching methods. Network protocols including TCP/IP deliver transport and addressing functions. Protocols including Packet over SONET/SDH, Multiprotocol Label Switching (MPLS), Asynchronous Transfer Mode (ATM) and Frame Relay are often used by service providers to deliver the links that are used in WANs. Academic research into wide area networks can be broken down into three areas: mathematical models, network emulation, and network simulation. Performance improvements are sometimes delivered via wide area file services or WAN optimization. Private