Link Failure - Nortel DMS-100 Series Maintenance Manual

1-54 Maintenance overview

Link failure

Link failures include the following:
DS-1 links
Link failures are usually associated with the DS-1 interface cards in the host
controller, DS-1 link, or DS-1 interface cards in the RLCM-EDC.
Monitoring is performed through operational measurements (OM) that
indicate when maintenance or out-of-service thresholds have been exceeded.
The host controller maintains and tests the DS-1 links, generates alarms for
link faults, and reassigns channels when faults occur on these links.
Operating company personnel can obtain the bipolar violation (BpV) count
at the RLCM-EDC either by posting the host LTC+ at the carrier level of the
MAP display and observing the counts from NT6X50AB card in the host
LTC+ or by issuing the DETAIL command with the REM option on each
individual link and observing the counts from NT6X50AB card in the
RLCM-EDC. BpVs, although not severe enough to raise an alarm, can
signal deterioration of a DS-1 link.
Because the signals on a DS-1 link travel in two directions, either the host
controller or the RLCM-EDC can detect faults (such as BpVs). The
RLCM-EDC notifies the host controller when the BpV count exceeds the
3
threshold of 1 BpV per 10 bits. The RLCM-EDC also monitors the loss of
frame indicator for the DS-1 links. RLCM-EDC, due to ESF settings, looks
for loss of signal (red alarm) in addition to loss of frame (loss of more than
2.5 seconds). That is, if the line is broken, ESF mode does not show loss of
frame, indicating only loss of signal (red alarm). The outgoing alarm is
removed when the signal or frame has been restored for 10 seconds. These
timings, typically 2.5 and 10 seconds, reflect the same values datafilled for
each link as datafilled for the host LTC.
If the RLCM-EDC detects loss of the framing pattern for 2.5 seconds or
more, or if the host LTC+ detects loss of the framing pattern for 220
milliseconds (ms), frame loss at the out-of-service limit has occurred. A
local carrier group alarm (LCGA) occurs at the carrier level of the MAP
display if the host LTC+ detects loss of frame; a remote carrier group alarm
(RCGA) appears if the RLCM-EDC detects the loss of frame. For
information on standard troubleshooting procedures to clear these faults,
refer to the chapter "Troubleshooting chart."
DS30A links
DS30A links on the P-side of the RLCM-EDC can experience failure.
These links connect to an RMM. Faults on these links can affect the
associated modules as well.
297-8381-550 Standard 02.02 April 1999