Administrator's Guide

Features and technical reference
555-233-5061942 Issue 5 October 2002
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
NxDS0 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 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 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 the switch receives and processes the SETUP message,
the switch selects the same B-channel for call origination. Since wideband calls
use more channels, the chances of glare are greater. Glare conditions can be
limited with proper channel administration, but they may never be eliminated and
some calls may still be dropped.
Some glare situations might not be resolvable. In one case, the network and the
user side may send SETUP messages simultaneously or nearly simultaneously.
Another glare scenario can occur in the brief window after the SETUP message
has been sent but before the first response is received from the switch at the other
side of the interface. If an incoming SETUP arrive during this window, the
incoming SETUP message is allowed to proceed and the outgoing call is dropped.
Various glare situations and their resolution are described in the following table.