Using Isdn To Support Leased Line Wan Circuits - 3Com Access Builder 7000 User Manual

Introduction 1-3
installation and rental of ISDN lines has dropped to the point where it is
extremely attractive as regards cost and performance.

Using ISDN to Support Leased Line WAN Circuits

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.