Nortel NT1R20 Description page 197

NT5D33 and NTRB34 Line-side E1 Interface Cards Page 173 of 290
The alarm indications (LEDs and external alarm contacts) will clear
automatically after the specified period, or duration, has expired if the Set
Clearing (S C) "Enable Self Clearing" option has been set. Otherwise,
the alarm will continue until the command Clear Alarm
(C A) has been entered. When an alarm is cleared, all activity caused by
the alarm indications will be cleared: the external alarm hardware will be
deactivated (the contact normally open will be reopened), the LED will go
out, an entry will be made in the alarm log of the date and time the alarm was
cleared, and carrier-fail line supervision will cease (for alarm level 2 only). If
self-clearing alarm indications have been disabled, carrier-fail line
supervision will terminate when the alarm condition has ceased, but the
external alarm contact and faceplate LED will remain active until the alarm
is cleared.
A heavy bit-error rate can cause 200 bit errors to occur much more quickly
than100 seconds. This will cause the alarm to be declared sooner.
An alarm condition will not be automatically cleared until the system no
longer detects the respective bit error threshold during the corresponding
duration period. For example, if AL1 threshold of 6 (representing 10-6) is
specified, and a duration period of 100 seconds is specified, an alarm will be
activated if more than 200 bit errors occur in any 100 second period. As soon
as the alarm is activated, the bit counter will be reset to 0. If the next 100
seconds pass, and less than 200 bit errors are detected, then the alarm will
clear after the alarm's duration period. However, if more than 200 bit errors
are detected in the next 100 seconds, the alarm condition will continue for the
designated time period. The alarm will finally clear when the alarm condition
is no longer detected for the designated period either by self-clearing (if this
function is enabled), or when the Clear Alarm (C A) command is
entered.
In addition to bit errors, the Set Alarm function sets parameters for detecting
frame-slip errors by establishing a threshold necessary to activate an alarm. If
the threshold value is exceeded, a level 2 alarm will be activated. The frame
slip threshold can be specified from 1 to 255 frame slips per time period. The
duration time period can be specified from 1 to 24 hours.
Line cards Description