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Token ring local area network (LAN) technology is a communications protocol for local area networks. It uses a special three-byte frame called a "token" that travels around a logical "ring" of workstations or servers. This token passing is a channel access method providing fair access for all stations, and eliminating the collisions of contention-based access methods. Introduced by IBM in 1984, it was then standardized with protocol IEEE 802.5 and was fairly successful, particularly in corporate environments, but gradually eclipsed by the later versions of Ethernet. (The main focus of this article is the IBM/IEEE 802.5 version, but there were several other earlier implementations of token rings). ==History== A wide range of different local area network technologies were developed in the early 1970s, of which one, the Cambridge Ring had demonstrated the potential of a token passing ring topology. At the IBM Zurich Research Laboratory Werner Bux and Hans Müller in particular worked on the design and development of IBM's token ring technology.〔("IEEE honors Zurich LAN pioneers" ), Zurich, Switzerland, 14 April 2003〕 Early work at MIT〔("Early Token Ring Work at MIT" ), J. Noel Chiappa, ieeexplore.ieee.org〕 led to the 1981, Proteon 10 Mbit/s ProNet-10 token ring network.〔("A History of Computer Communications 1968-1988" ), James Pelkey〕 In 1981, workstation vendor Apollo Computer introduced their proprietary 12 Mbit/s Apollo token ring (ATR) network running over 75 ohm RG-6U coaxial cabling. On October 15 1985, IBM launched their own proprietary IBM Token Ring products.〔("Local Area Networks" ), InfoWorld 24 Mar 1986〕 It ran at 4 Mbit/s, and attachment was possible from IBM PCs, midrange computers and mainframes. It used a convenient star-wired physical topology, and ran over shielded twisted-pair cabling - and shortly became the basis for the (ANSI)/IEEE standard 802.5.〔(IEEE Standards: P802.5 Working Group Area ). Ieee802.org. Retrieved on 2011-10-30.〕 In 1988 the faster 16 Mbit/s token ring was standardized by the 802.5 working group.〔(VS. TOKEN RING IN THE LOCAL AREA NETWORKING BUSINESS" ), URS VON BURG AND MARTIN KENNY, Industry and Innovation, Volume 10, Number 4, 351–375, December 2003〕 During this time, IBM argued strongly that token ring LANs were superior to Ethernet, especially under load,〔"IEEE 802.3 Local Area Network considerations", IBM document GG22-9422-0〕 but these claims were fiercely debated. Although an increase to 100 Mbit/s was standardized and marketed during the wane of token ring's existence, it was never widely used, (''"IBM does not view high-speed token ring as a requirement for the majority of its customers, and therefore the decision has been made not to provide 100 Mbps high-speed token ring uplinks on its products..."''),〔http://www.redbooks.ibm.com/redpapers/pdfs/redp0031.pdf〕 and while a 1000 Mbit/s was approved in 2001, no products were ever brought to market,〔(IEEE 802.5 activities ). Ieee802.org. Retrieved on 2011-10-30.〕 and standards activity came to a standstill as Fast Ethernet and Gigabit Ethernet dominated the local area networking market. 100 megabit token ring adapter.JPG|100 Mbit/s IBM Token Ring Management Adapter with Wake On LAN. Both UTP (RJ45) and STP (IBM Data Connector) interfaces are present. Token ring cards.JPG|Token Ring Network Interface Cards (NICs) with varying interfaces from: ISA, PCI and MicroChannel EISA TokenRing NIC.JPG|Madge 4/16Mbit/s TokenRing ISA NIC 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Token ring」の詳細全文を読む スポンサード リンク
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