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A local area network (LAN) is a Computer Network covering a small geographic area, like a home, office, or group of buildings. The defining characteristics of LANs, in contrast to Wide Area Networks (WANs) , include their much higher data transfer rates, smaller geographic range, and lack of a need for Leased Telecommunication Lines . Ethernet over Unshielded Twisted Pair cabling, and Wi-Fi are the two most common technologies currently, but ARCNET , Token Ring and many others have been used in the past. HISTORY In the days before personal computers, a site might have just one central computer, with users accessing this via Computer Terminal s over simple low-speed cabling. Networks such as IBM's SNA ( Systems Network Architecture ) were aimed at linking terminals or other mainframes at remote sites over leased lines—hence these were wide area networks. The first LANs were created in the late 1970s and used to create high-speed links between several large central computers at one site. Of many competing systems created at this time, Ethernet and ARCNET were the most popular. The development and proliferation of CP/M and then DOS -based Personal Computer s meant that a single site began to have dozens or even hundreds of computers. The initial attraction of networking these was generally to share disk space and laser printers, which were both very expensive at the time. There was much enthusiasm for the concept and for several years, from about 1983 onward, computer industry pundits would regularly declare the coming year to be “ The Year Of The LAN ”. In reality, the concept was marred by proliferation of incompatible Advanced Server and Windows For Workgroups . Of the competitors to NetWare, only Banyan Vines had comparable technical strengths, but Banyan never gained a secure base. Microsoft and 3Com worked together to create a simple network operating system which formed the base of 3Com's 3+Share, Microsoft's LAN Manager and IBM's LAN Server . None of these were particularly successful. In this same timeframe, Unix Computer Workstation s from vendors such as Sun Microsystems , Hewlett-Packard , Silicon Graphics , Intergraph , NeXT and Apollo were using TCP/IP based networking. Although this market segment is now much reduced, the technologies developed in this area continue to be influential on the Internet and in both Linux and Apple Mac OS X networking—and the TCP/IP protocol has now almost completely replaced IPX , AppleTalk , NBF and other protocols used by the early PC LANs. TECHNICAL ASPECTS Although switched Ethernet is now the most common Data Link layer protocol and IP as a Network Layer Protocol , many different options have been used, and some continue to be popular in niche areas. Smaller LANs generally consist of a one or more switches linked to each other - often with one connected to a Router , Cable Modem , or DSL Modem for Internet access. Larger LANs are characterized by their use of redundant links with switches using the Spanning Tree Protocol to prevent loops, their ability to manage differing traffic types via Quality Of Service , and to segregate traffic via VLAN ing. LANs may have connections with other LANs via leased lines, leased services, or by 'tunneling' across the Internet using VPN technologies. SEE ALSO
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