Local area network

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

A local area network (LAN) is a computer network that interconnects computers within a limited area such as a residence, school, laboratory, university campus or office building^[1] and has its network equipment and interconnects locally managed. By contrast, a wide area network (WAN), not only covers a larger geographic distance, but also generally involves leased telecommunication circuits or Internet links.

Ethernet and Wi-Fi are the two most common transmission technologies in use for local area networks. Historical technologies include ARCNET, Token ring, and AppleTalk.

History

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" network gave a good indication of the situation.^[2][3]

A number of experimental and early commercial LAN technologies were developed in the 1970s. Cambridge Ring was developed at Cambridge University starting in 1974.^[4] 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, Robert Metcalfe and David 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]

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”.^[9][10][11]

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 dominated^[12] 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 workstations 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 generally been based on various grades of coaxial cable. Shielded twisted pair was used in IBM's Token Ring LAN implementation, but 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.

While fiber-optic cabling is common for links between switches, use of fiber to the desktop is rare.^[13]

Wireless media

Many LANs are now based partly or wholly on wireless technologies. Smartphones, tablet computers and laptops typically have wireless networking support built-in. In a wireless local area network, users may move unrestricted in the coverage area. Wireless networks have become popular in residences and small businesses, because of their ease of installation. Guests are often offered Internet access via a hotspot service.

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, NetBEUI, IPX/SPX, AppleTalk and others were once common, but the Internet Protocol Suite (TCP/IP) is now the standard.

Simple LANs generally consist of cabling and one or more switches. A switch can be connected to a router, cable modem, or ADSL modem for Internet access. A LAN can include a wide variety of other network devices such as firewalls, load balancers, and sensors;^[14] and more 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.

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

See also

• LAN messenger
• LAN party
• Network interface controller

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 (PDF) on 2010-10-11.
8. Lamont Wood (2008-01-31). "The LAN turns 30, but will it reach 40?". Computerworld.com. Retrieved 2016-06-02.
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. "Big pipe on campus: Ohio institutions implement a 10-Gigabit Ethernet switched-fiber backbone to enable high-speed desktop applications over UTP copper", Communications News, 2005-03-01, As alternatives were considered, fiber to the desk was evaluated, yet only briefly due to the added costs for fiber switches, cables and NICs. "Copper is still going to be a driving force to the desktop for the future, especially as long as the price for fiber components remains higher than for copper."
14. "A Review of the Basic Components of a Local Area Network (LAN)". NetworkBits.net. Retrieved 2008-04-08.

External links