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token ring

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Definition: Token Ring is a data link technology for local area networks (LANs). It operates at layer 2 of the OSI model.

How Token Ring Works

Unlike all other standard forms of LAN interconnects, Token Ring maintains one or more common data frames that continuously circulates through the network. These frames are shared by all connected devices on the network as follows:
  • a frame (packet) arrives at the next device in the ring sequence
  • that device checks whether the frame contains a message addressed to it. If so, the device removes the message from the frame. If not, the frame is empty (called a token frame).
  • the device holding the frame decides whether to send a message. If so, it inserts message data into the token frame and issues it back onto the LAN. If not, the device releases the token frame for the next device in sequence to pick up
  • the above steps are repeated continuosly for all devices in the token ring

Characteristics of Token Ring Networks

Token Ring was developed by IBM during the 1980s as an alternative to Ethernet. Starting in the 1990s, it significantly decreased in popularity and gradually was phased out of business networks as Ethernet technology began to dominate LAN designs.

Standard Token Ring supports only up to 16 Mbps. In the 1990s, an industry initiative called High Speed Token Ring developed technology for extending Token Ring to 100 Mbps equal to Ethernet, but insufficient interest in the marketplace existed for HSTR products and the technology was abandoned.

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