3com 7000 Manual De Usuario

 

 

 

 

installation and rental of ISDN lines has dropped to the point where it is 

 

extremely attractive as regards cost and performance.

 

 

ISDN provides an ideal service to connect remote LANs. To be effective, 

 

the connecting bandwidth needed is at least 56 Kbps to achieve a realistic 

 

throughput. Slower speed links can be used but usually only when usage 

 

is low and infrequent, or if higher speed circuits cannot be provided.

 

Leased digital point-to-point circuits can still be cost effective if usage 

 

spans many hours per day. However as ISDN tariffs reduce, this balance 

 

also changes. ISDN can be used to provide effective backup of these 

 

point-to-point WAN circuits in two ways.

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Firstly, if the point-to-point circuit fails, an ISDN channel can be 

 

dialled-up automatically and quickly, to provide an alternative path to 

 

the remote unit.

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Secondly, if the leased circuit becomes heavily loaded due to peaks in 

 

the traffic between remote bridges or routers, additional bandwidth 

 

can be automatically dialled-up to supplement the bandwidth of the 

 

leased circuit. The interconnected bridges would then treat the leased 

 

line and ISDN channel as parallel links, sharing the load across the two.