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DEFINITY ECS Release 8.2
Administrator’s Guide
555-233-506
Issue 1
April 2000
Features and technical reference
1413Look-Ahead routing
20
Look-Ahead routing
Look-Ahead Routing (LAR) allows the switch to reroute an outgoing ISDN call
that is not completing. The switch attempts to complete the call along a different
routing preference, or it tries the current routing preference a second time. If the
current preference fails twice, the next routing preference is tried.
LAR can be administered at an origination switch or a tandem switch. It can be
turned off at different points in the network to reduce network load. You use LAR
with AAR and ARS, GRS, UDP. You can also use it with a Feature Access Code
ISDN Access Code. A LAR field is administered on the Route Pattern screen.
NOTE:
When LAR is used in a mixed network of DEFINITY ECS and
pre-DEFINITY ECS switches, LAR ends at the pre-DEFINITY ECS switch
and calls are rejected the normal way. However, if a LAR-triggering cause
value is passed back in the network to a DEFINITY ECS that is enabled for
LAR, LAR is attempted from that switch again.
Detailed description
LAR can be administered for each ISDN route preference in each Pattern Number.
The maximum number of LAR attempts per call per switch is 2 times the number
of route preferences in the route pattern. LAR can be administered at each
intermediate node that the call may be tandemed through to allow the attempt of
all possible routes.
You can control LAR by:
■ administering it on a per route-preference basis
■ partitioning trunks
■ limiting the number of hop counts
LAR activation
LAR is active when a call is rejected with a cause value in the range of #34–#47
and #3 (no route to destination). The range of #34–#47 indicates congestion and
that resources are unavailable. The following cause values activate LAR:
Cause Value Cause Description
3 no route to destination
34 no circuit/channel available
38 network out of order