Data Communications Networking Devices - 4th Ed.pdf

676 _________________________ WIDE AREA NETWORK DATA CONCENTRATION EQUIPMENTpower supplies as well as redundant common logic and spare voice and data adaptercards. Doing so may minimize downtime in the event of a component failure asmany multiplexers are designed to enable technicians to easily replace failedcomponents.Maximum number of hops and nodes supportedAs T1 and E1 multiplexers are interconnected to form a networkeach multiplexercan be considered as a networknode. When a DS0 channel is routed through amultiplexer that multiplexer is known as a hop. Thus, the maximum number ofhops refers to the maximum number of internodal devices a DS0 channel cantraverse to complete an end-to-end connection.In addition to the maximum number of hops users must also consider themaximum number of nodes that can be networked together. The maximumnumber of addressable nodes that can be managed as a single networkis normallymuch greater than the maximum number of hops supported since the latter isconstrained by the delay to voice as DS0 channels are switched and routed throughhops.DiagnosticsMost T1 and E1 multiplexers provide both local and remote channel loop-backcapability to facilitate fault isolation. Some multiplexers have built-in test patterngeneration capability which may alleviate the necessity of obtaining additional testequipment for isolating networkfaults.Con®guration rulesFigure 6.34 illustrates a typical T1 multiplexer cabinet layout which is similar to themanner in which a multiplexer would be installed in an industry standard 19-inchrack. In examining multiplexer con®guration rules, a variety of constraints mayFigure 6.34Typical T1 or E1 multiplexer cabinet