| 单词 | Token Ring (TR) |
| 释义 | Token Ring (TR) A local area network (LAN) technology invented in 1967 by Swedish inventor Olof Soderblom (1940–), who worked for IBM at the time. Soderblom subsequently filed for a patent that was finally awarded in 1981. IBM developed and heavily promoted the technology, a variation of which was standardized by the IEEE as 802.5.The 802.5 standard is for a token-passing ring access method and Physical Layer specifications supporting data rates of 4 Mbps and 16 Mbps.Through a multistation access unit (MSAU or MAU), as many as 250 stations can connect in a physical star topology that operates as a logical ring, and multiple MAUs can be interconnected in a physical ring topology.Token Ring specifies differential Manchester coding and a deterministic access method known as token passing.As is the case with token-based networks, in general, Token Ring offers a high level of access control, which is centralized. Access delay is measured and ensured, with priority access supported. Throughput is very close to raw bandwidth, as data collisions are avoided and retransmissions, therefore, are avoided. Throughput also improves under load, although absolute overhead is higher than with nondeterministic access techniques. A Token Ring network elects one active monitor (AM), which is the node with the highest medium access control (MAC) address. The AM is responsible for ring administration, including clocking, token management, and removal of circulating frames. All other nodes are standby monitors (SMs), and can assume control in the event of an AM failure. If a station detects a network problem, it invokes a beaconing process that involves the continuous transmission of small control frames that identify the transmitting 74570c20.qxd 9/12/07 12:44 AM Page 491 |
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