Table of Contents
Advertisement
8-12 Dialable Wideband Service
Fragmentation
Fragmentation occurs when the total of B-channels over all the T1 spans is
enough to accommodate a request for wideband services, but there are not
enough B-channels on any single T1 to accommodate the request. If a call
requires more channels than are available on the first T1 of the route list, the
call advances to the next T1 of the list. If the call exhausts all the T1s of the
route list, the call is released and a GNCT is applied.
Fragmentation not only increases call time as the route list is searched for a
T1 with enough idle B-channels; it also can cause more calls to be released
if no T1 of the route list can accommodate the request.
Dense datafill
To avoid fragmentation, datafill B-channels densely on each T1 span, rather
than distribute them over many T1 spans. This method of datafilling
prevents wideband calls from having to check the next element in the route
list.
When wideband and narrowband traffic are routed over the same T1 span,
fragmentation becomes a problem, particularly for calls that require
H0-channels. H-0 channels are six contiguous channels in one of four
timeslots: 1–6, 7–12, 13–18, or 19–24.
Separate wideband and narrowband traffic
Keeping wideband traffic and narrowband traffic on separate T1s also helps
prevent fragmentation. When a single channel on a wideband T1 (channel 1,
for example) is carrying narrowband traffic, a call requiring an H0-channel
cannot use the first timeslot, even if the other five channels (channels 2–6)
are idle.
For the T1s to work as efficiently as possible, route single B-channel calls
on T1s that do not support wideband services. Only route a single B-channel
call over a wideband trunk as a last resort.
Glare
Glare occurs when the switches at each end of the trunk seize the trunk at
the same time and cause a call to be blocked. The following can occur in
relation to glare:
297-2521-106 Standard 23.01 March 2001
If a glare condition occurs during a narrowband call, the call will try to
reselect another member from the same trunk group.
If the termination is set to YIELD and glare occurs at the terminator, a
terminating trunk group is selected from the valid route list element.
If the route list is exhausted, a REL message with a cause of "resource
unavailable" is returned.
Advertisement
Table of Contents
