Local area network
From Wikipedia, the free encyclopedia
A local area network (LAN) is a computer network covering a local area, like a home, office, or group of buildings. Current LANs are most likely to be based on switched IEEE 802.3 Ethernet technology, running at 10, 100 or 1,000 Mbit/s, or on Wi-Fi technology. Each node or computer in the LAN has its own computing power but it can also access other devices on the LAN subject to the permissions it has been allowed. These could include data, the more expensive devices / less used resources that it would be impractical to have multiple copies of, and the ability to communicate or chat with other users in the network.
The defining characteristics of LANs, in contrast to WANs (wide area networks), are: their much higher data rates, smaller geographic range, and that they do not require leased telecommunication lines.
Although switched Ethernet is now the most common data link layer protocol (OSI 7-Layer Model), and IP as a network layer protocol, many different options have been used (see below), and some continue to be popular in niche areas. Smaller LANs consist of a few switches typically connected to each other and with one connected to a router, cable modem, or DSL modem. A traditional model of access, distribution, and core switches was popularized by Cisco Systems and has been in use for many years.
Larger LANs are characterized by distributing Ethernet traffic roles within the network. Each layer aggregates traffic of the layer below it and will typically maintain redundant links with switches capable of quality of service and spanning tree protocol to prevent loops and the recovery of failed uplinks.
While initially used for basic data or program sharing functionality the humble LAN has served as a catalyst for the indispensible role the intranet has come to play in modern government departments and businesses. The LAN based intranet has been a large contributor to the productivity increases in western economies during the early part of the 21st century. Initial implementations of LANs tended to revolve around the type of computers and devices attached to the LAN, and to the permissions they would be granted. Modern considerations include a carefully planned intranet strategy - to comply with legislative and other responsibilities - content management software, accessibility, scalability, audit requirements, document and information control and integration with telephone systems.
LANs may have connections to other LANs via routers and leased lines. Traditionally, the network connecting two or more LANs is referred to as the WAN (Wide Area Network). Recently, service providers have begun to offer additional services to link LANs together. These technologies, such as Metropolitan Area Networks (MANs), and MPLS/VPN services have diversified the standard model of interconnecting sites. There are also methods of connecting LANs together through the use of Internet connections, VPN software or hardware, and 'tunneling' across the Internet using VPN technologies.
Topology, protocols and media (The cables, like CAT5, or radio waves that connect devices in the LAN) are the characteristics that differentiate LANs.
With the proliferation of computers and IT devices in the modern home has come the frequent use of LANs to connect them together. Many of these home LANs are wireless and use the 802.11g wireless networking standard which transmits data at 2.4 GHz. 
In the days before personal computers, a site might have just one central computer, with users accessing this via computer terminals 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 computers 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 physical layer and network protocol implementations, and confusion over how best to share resources. Typically, each vendor would have their own type of network card, cabling, protocol, and network operating system. A solution appeared with the advent of Novell NetWare which gave: (a) even-handed support for the 40 or so competing card/cable types, and (b) a much more sophisticated operating system than most of its competitors. Netware dominated the personal computer LAN business from early after its introduction in 1983 until the mid 1990s when Microsoft introduced Windows NT 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 workstations 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, NETBEUI and other protocols used by the early PC LANs.
- SOHO network
- Campus area network
- Metropolitan area network
- Wireless LAN
- null modem
- LAN party
- Personal area network
- Home network
- Wide area network
- Demilitarized zone (computing)
- Category 5 cable
- Network-attached storage
- ^ Red Hat glossary
- ^ Webopedia
- ^ Intranet strategies and planning for deployment
- ^ http://www.howstuffworks.com/home-network.htm
- ^ http://www.varbusiness.com/sections/columns/columns.jhtml?articleId=18825403
- IEEE: The working group setting LAN standards
- Setting up a network using Linux
- Building a local area network