Avaya Communication Manager Administrator's Manual page 554

Managing Data Calls
Flexible — In the flexible scheme, an N x DS0 call is placed on any set of B-channels as
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long as the requested bandwidth is satisfied. There is absolutely no constraint such as
contiguity of B-channels or fixed starting points. Of course, as with all wideband calls, all
the B-channels comprising the wideband call must reside on the same ISDN facility.
Regardless of the allocation scheme employed, the N x DS0 algorithm, like the H11 and
H12 algorithms, attempts to preserve idle facilities when offered B, H0, and N x DS0 calls.
This is important so that N x DS0 calls, for large values of N, have a better chance of being
satisfied by a given trunk group. However, if one of these calls cannot be satisfied by a
partially-contaminated facility and an idle facility exists, a trunk on that idle facility is
selected, thus contaminating that facility.
There are additional factors to note regarding specific values of N and the N x DS0 service:
- N = 1 — this is considered a narrowband call and is treated as any other voice or
narrowband-data (B-channel) call.
- N = 6 — if a trunk group is optioned for both H0 and N x DS0 service, a 384-kbps call
offered to that trunk group is treated as an H0 call and the H0 constraints apply. If the H0
constraints cannot be met, then the call is blocked.
- N = 24 — if a trunk group is optioned for both H11 and N x DS0 service, a 1,536-kbps call
offered to that trunk group is treated as an H11 call and the H11 trunk allocation
constraints apply.
- N = 30 — if a trunk group is optioned for both H12 and N x DS0 service, a 1,920-kbps call
offered to that trunk group is treated as an H12 call and the H12 trunk allocation
constraints apply.
Glare and blocking
Glare prevention
Glare occurs when both sides of an ISDN interface select the same B-channel for call initiation.
For example, a user side of an interface selects the B-channel for an outgoing call and, before
Communication Manager receives and processes the SETUP message, the server also selects
the same B-channel for call origination. Since any single wideband call uses more channels, the
chances of glare are greater. With proper and careful administration, glare conditions can be
reduced.
To reduce glare probability, the network needs to be administered so both sides of the interface
select channels from opposite ends of facilities. This is called linear hunting, ascending or
descending. For example, on a 23B+D trunk group, the user side could be administered to
select B-channels starting at channel 23 while the network side would be administered to start
selecting at channel 1. Using the same example, if channel 22 is active but channel 23 is idle,
the user side should select channel 23 for re-use.
554 Administrator Guide for Avaya Communication Manager