"LAN" redirects here. For other uses, see
LAN (disambiguation).
A local area network (LAN) is a
computer network covering a small physical area, like a home, office, or small group of buildings, such as a school, or an airport. The defining characteristics of LANs, in contrast to
wide-area networks (WANs), include their usually 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.
Contents
[
hide]
1 History1.1 Early systems1.2 The personal computer1.3 Cabling2 Technical aspects3 See also4 References5 External links//
[
edit] History
As larger universities and research labs obtained more computers during the late 1960s, there was increasing pressure to provide high-speed interconnections. A report in 1970 from the
Lawrence Radiation Laboratory detailing the growth of their "Octopus" network
[1][2], gives a good indication of the situation.
[
edit] Early systems
Cambridge University's
Cambridge Ring was started in 1974
[3] but was never developed into a successful commercial product.
Ethernet was developed at
Xerox PARC in 1973–1975,
[4] and filed as
U.S. Patent 4,063,220 . In 1976, after the system was deployed at PARC, Metcalfe and Boggs published their seminal paper - "Ethernet: Distributed Packet-Switching For Local Computer Networks"
[5]ARCNET was developed by
Datapoint Corporation in 1976 and announced in 1977
[6] - and had the first commercial installation in December 1977 at Chase Manhattan Bank in New York
[7][
edit] The personal computer
The development and proliferation of
CP/M-based personal computers from the late 1970s and then
DOS-based
personal computers a from 1981 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 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 the 40 or so competing card/cable types, and a much more sophisticated operating system than most of its competitors. Netware dominated
[8] 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,
NBF and other protocols used by the early PC LANs.
[
edit] Cabling
Early LAN cabling had always been based on various grades of
co-axial cable, but IBM's
Token Ring used shielded
twisted pair cabling of their own design, and in 1984
StarLAN showed the potential of simple
Cat3 unshielded
twisted pair—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 LANs today.
[
edit] 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 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 (QoS), and to segregate traffic via
VLANs. Larger LANS also contain a wide variety of network devices such as switches, firewalls, routers, load balancers, sensors and so on.
[9]LANs may have connections with other LANs via leased lines, leased services, or by 'tunneling' across the
Internet using
VPN technologies. Depending on how the connections are made and secured, and the distance involved, they become a Metropolitan Area Network (MAN), a Wide Area Network (WAN), or a part of the internet.