Avaya Communication Manager Administrator's Manual page 467

Note that a D-channel is considered a busy trunk and results in the top most quadrant of a T1, B-channels
19 to 24, always being partially contaminated. This is not true for NFAS.
If this H0 optioned trunk group is also administered to support H11, H12, or N x DS0, then the system
also attempts to preserve idle facilities. In other words, when offered a narrowband, H0, or N x DS0 call,
the system searches partially-contaminated facilities before it searches to idle facilities.
N x DS0
For the N x DS0 multi-rate service, a trunk group parameter determines whether a floating or a flexible
trunk allocation scheme is to be used. The algorithm to satisfy an N x DS0 call is either floating or
flexible.
•
Floating (Contiguous) — In the floating scheme, an N x DS0 call is placed on a contiguous group
of B-channels large enough to satisfy the requested bandwidth without any constraint being put on
the starting channel (that is, no fixed starting point trunk).
•
Flexible — In the flexible scheme, an N x DS0 call is placed on any set of B-channels as 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.
Administrator's Guide for Avaya Communication Manager
November 2003
Managing Data Calls
Wideband Switching
467