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The Ethernet network is a collaborative development, but Token Ring is an IBM (International Business Machine) development that is now covered by the IEEE 802.5 standard. Its basic premise is that the network's primary cable (backbone) is arranged in a ring (or at least in a loop). The control mechanism used in a ring structure is called token passing. Picture a group of people in a circle, the only way one person can talk is when they have the token. When they want to communicate with the person accross from them, they send them the token by passing it along the circle. They were the only person allowed to talk to the other, due to the fact that they had sole possession of the token. Nodes connect to the loop through devices called multistation access units (MAUs). MAUs are most commonly found on large corporate mainframe sites. Token ring networks are actually configured more like a star with the MAU used as the clustering device. Multiple MAUs are linked together with patch cords to create a logical ring. Because of its physical star configuration, any single station that breaks down has little effect on the ring, as long as the MAU can omit it from the loop. Token ring networks work at 4 Mbps and 16 Mbps. |