3com 500 Manual De Usuario

 

 

 

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.

■

 

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.

■

 

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.