Local area network

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A local area network (LAN) is a computer network that interconnects computers within a limited area such as a home, school, computer laboratory, or office building using network media.1 The defining characteristics of LANs, in contrast to wide area networks (WANs), include their smaller geographic area, and non-inclusion of leased telecommunication lines.citation needed

ARCNET, Token Ring and other technology standards have been used in the past, but Ethernet over twisted pair cabling, and Wi-Fi are the two most common technologies currently used to build LANs.

History

A conceptual diagram of a local area network using 10BASE5 Ethernet

The increasing demand and use of computers in universities and research labs in the late 1960s generated the need to provide high-speed interconnections between computer systems. A 1970 report from the Lawrence Radiation Laboratory detailing the growth of their "Octopus" network23 gave a good indication of the situation.

Cambridge Ring was developed at Cambridge University in 19744 but was never developed into a successful commercial product.

Ethernet was developed at Xerox PARC in 1973–1975,5 and filed as U.S. Patent 4,063,220. In 1976, after the system was deployed at PARC, Metcalfe and Boggs published a seminal paper, "Ethernet: Distributed Packet-Switching for Local Computer Networks."6

ARCNET was developed by Datapoint Corporation in 1976 and announced in 1977.7 It had the first commercial installation in December 1977 at Chase Manhattan Bank in New York.8

Standards evolution

The development and proliferation of personal computers using the CP/M operating system in the late 1970s, and later DOS-based systems starting in 1981, meant that many sites grew to dozens or even hundreds of computers. The initial driving force for networking was generally to share storage and printers, which were both 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”.91011

In practice, the concept was marred by proliferation of incompatible physical layer and network protocol implementations, and a plethora of methods of sharing resources. Typically, each vendor would have its own type of network card, cabling, protocol, and network operating system. A solution appeared with the advent of Novell NetWare which provided even-handed support for dozens of competing card/cable types, and a much more sophisticated operating system than most of its competitors. Netware dominated12 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 - but none of these was particularly successful.

During the same period, 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, NBF, and other protocols used by the early PC LANs.

Cabling

Early LAN cabling had been based on various grades of coaxial cable. Shielded twisted pair was used in IBM's Token Ring LAN implementation. In 1984, StarLAN showed the potential of simple unshielded twisted pair by using Cat3 cable—the same simple cable used for telephone systems. This led to the development of 10Base-T (and its successors) and structured cabling which is still the basis of most commercial LANs today. In addition, fiber-optic cabling is increasingly used in commercial applications. Generally a LAN network uses Gigabit Ethernet cabling to the hub or switch (wired router, cannot be wireless), then the router connection is bridged to the wireless router.

As cabling is not always possible, Wi-Fi is now very common in residential premises, and elsewhere where support for laptops and smartphones is important.

Technical aspects

Network topology describes the layout of interconnections between devices and network segments. At the Data Link Layer and Physical Layer, a wide variety of LAN topologies have been used, including ring, bus, mesh and star, but the most common LAN topology in use today is switched Ethernet. At the higher layers, the Internet Protocol (TCP/IP) has become the standard, replacing NetBEUI, IPX/SPX, AppleTalk and others.

Simple LANs generally consist of one or more switches. A switch can be connected to a router, cable modem, or ADSL modem for Internet access. Complex 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 (QoS), and to segregate traffic with VLANs. A LAN can include a wide variety of network devices such as switches, firewalls, routers, load balancers, and sensors.13

LANs can maintain connections with other LANs via leased lines, leased services, or the Internet using virtual private network technologies. Depending on how the connections are established and secured in a LAN, and the distance involved, a LAN may also be classified as a metropolitan area network (MAN) or a wide area network (WAN).

See also

References

  1. ^ Gary A. Donahue (June 2007). Network Warrior. O'Reilly. p. 5. 
  2. ^ Samuel F. Mendicino (1970-12-01). "Octopus: The Lawrence Radiation Laboratory Network". Rogerdmoore.ca. Archived from the original on 2010-10-11. 
  3. ^ "THE LAWRENCE RADIATION LABORATORY OCTOPUS". Courant symposium series on networks (Osti.gov). 29 Nov 1970. OSTI 4045588. 
  4. ^ "A brief informal history of the Computer Laboratory". University of Cambridge. 20 December 2001. Archived from the original on 2010-10-11. 
  5. ^ "Ethernet Prototype Circuit Board". Smithsonian National Museum of American History. Retrieved 2007-09-02. 
  6. ^ "Ethernet: Distributed Packet-Switching For Local Computer Networks". Acm.org. Retrieved 2010-10-11. 
  7. ^ "ARCNET Timeline". ARCNETworks magazine. Fall 1998. Archived from the original on 2010-10-11. 
  8. ^ Lamont Wood (2008-01-31). "The LAN turns 30, but will it reach 40?". Computerworld.com. Retrieved 2010-10-11. 
  9. ^ "'The Year of The LAN' is a long-standing joke, and I freely admit to being the comedian that first declared it in 1982...", Robert Metcalfe, InfoWorld Dec 27, 1993
  10. ^ "...you will remember numerous computer magazines, over numerous years, announcing 'the year of the LAN.'", Quotes in 1999
  11. ^ "...a bit like the Year of the LAN which computer industry pundits predicted for the good part of a decade...", Christopher Herot
  12. ^ Wayne Spivak (2001-07-13). "Has Microsoft Ever Read the History Books?". VARBusiness. Archived from the original on 2010-10-11. 
  13. ^ "A Review of the Basic Components of a Local Area Network (LAN)". NetworkBits.net. Retrieved 2008-04-08. 

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