Token Ring is a Local Area Network (LAN) technology that was developed by IBM but one that is overshadowed by its more widely known rival-Ethernet. After the United States Patents and Trademarks Office granted the technology the patent in 1980’s, the technology was standardized as IEEE 802.5 by the Institute of Electrical and electronic Engineers and it gained some modicum of success at least initially. But the technology never really gained wide acceptance among the top tier vendors apart from its developer, IBM, almost all of whom preferred the 10BASE-T for Ethernet, a LAN technology that emerged in the 1990’s. IBM did try to promote the reliability and better performance due to its deterministic access methods, but the availability of less costly Ethernet switching dealt a heavy blow to Token Ring technology, as today most vendors go for Ethernet.

Token Ring employs a ring topology (hence the name) in which data is sent from one machine to the next and the process is repeated until the information gets back to where it originated from. The use of Token Control Passing ensures that only the machine that has control over the token can use the network and this works to avoid collisions as only one machine may use the network at a given time. The mode of operation involves a free token going around the network. A token is basically a vessel which can be used to transmit data. In order for a machine to use the network, it first has to capture the free token and replace the data inside with its message. The message includes the address of the recipient. Hen the token is passed around the network. The next machine then considers the contents of the token (without reading the contents) and if the token is not meant for that machine (from the address), then it will pass the token to the next machine. The process is repeated until the token is passed to the correct machine which then reads the message. However, the recipient machine will not release the free token into the network to be used by another machine until the token is sent back to the message originator, which is the machine which sent out the message. So the token will be passes on to the next machine until it goes back to where the process began. The token will then be released into the ring once again for the next machine to use it.

When the Token Ring network starts up, the machines in the network deliberate on which one among them takes control of the ring. The machine with the highest MAC (Media Access Control) address is the one that is usually chosen to take control of the ring, and thus becomes the “Active Monitor” while the other machines are referred to as the “standby monitors”. The active monitor primary role is to ensure that none of the standby monitors are causing trouble in the network. It performs a ring polling every seven seconds to see which machine is participating in the ring. Active Monitor also performs a “Ring Purge” to reset the ring if interruption or data loss is reported.

For more information on Token Ring read What is Token Ring?

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