Cabletron Systems MMAC-5FNB Networking Manual

Also see for MMAC-5FNB: Overview and setup guide

Contents

Cabletron Systems MMAC-5FNB Networking Manual Manual pdf 124 page image

Token Ring6-4DescriptionFault IsolationDue to the very orderly fashion in which Token Ring networks operate, a numberof fault location and recovery features can be incorporated into the Token Ringdesign. These fault recovery processes can locate a hardware or cable error andeliminate it, hopefully returning a faulty ring to an operating condition. The faultisolation and recovery features rely on the operational structure of Token Ringnetworks and on the ability of Token Ring devices to bypass station connections.While Token Ring networks treat stations as though they were part of a ringtopology, the stations themselves are cabled in a point-to-point, usually star,topology (see Chapter 2, Overview of Networking). Stations are connectedthrough single lengths of cabling to Token Ring concentrator devices. The basicconcentrator unit for Token Ring networks is the Multistation Access Unit, orMAU (pronounced like the Hawaiian island of Maui, minus the final “i”). TheMAU may also be called a concentrator, and it provides much the same networkconnection function as an Ethernet concentrator. The MAU allows networkstations to attach to the Token Ring at a central point which providesinterconnection between the stations. A MAU also insures that a station beingremoved from the network will not destroy the continuity of the Token Ring andprevent the network from functioning.Figure 6-6. MAU and Port StatesSince connections to the stations are made through the MAU, a connection that isnot active or is suffering an error condition can be bypassed. This bypassoperation closes a relay which keeps the flow of electrical impulses past the portcontiguous (see Figure 6-6). When a station is removed from the ring, the relaycloses. When the MAU senses that the station is attempting to reattach, the relayopens. Token Ring stations may also remove themselves from the ring, closing thebypass at the MAU.At times, however, a Token Ring network may suffer difficulties without thestations or MAUs ever losing the flow of electrical impulses which keep the portsof the MAU active. These errors are usually higher-level difficulties than a cut ordisconnected cable, and result in what is known as “beaconing.”on offRing TrunkMultistation Access UnitBypassedStationPortsOpenStationConnection1706n34