Nortel Networks Circuit Card 311 - Manual (Page 244)

244 NT5D11 and NT5D14 Lineside T1 Interface cards
Descriptions of the excessive bit error rate and frame slip errors conditions
can be found in
"Configuring parameters" (page 235) . Bit errors may
activate either a level 1 or level 2 alarm. The remaining conditions, when
detected, always cause the system to activate a level 2 alarm.
An out of frame condition is declared if two out of four frame bits are in error.
If this condition occurs, the hardware immediately attempts to reframe.
During the reframe time, the T1 link is declared out of frame, and silence is
sent on all receive timeslots.
A loss of signal condition is declared if a full frame (192 bits) of consecutive
zeros has been detected at the receive inputs. If this condition occurs, the
T1 link automatically attempts to resynchronize with the distant end. If this
condition lasts for more than two seconds, a level 2 alarm is declared and
silence is sent on all receive timeslots. The alarm is cleared if, after two
seconds, neither a loss of signal, out of frame condition, nor blue alarm
condition occurs.
If a repeating device loses signal, it immediately begins sending an
unframed all 1’s signal to the far-end to indicate an alarm condition. This
condition is called a blue alarm, or an Alarm Indication Signal (AIS). If an
AIS is detected for more than two seconds, a level 2 alarm is declared, and
silence is sent on all receive timeslots. The alarm is cleared if, after two
seconds, neither a loss of signal, out of frame condition, nor blue alarm
condition occurs.
Alarm Disable
The Alarm Disable (A D) command disables the external alarm contacts.
When this command is typed, the MMI displays the message "Alarms
Disabled" and the MAINT LED turns on. In this mode, no yellow alarms are
sent and the Lineside T1 card does not enter line processing mode. Alarm
messages are still sent to the MMI terminal and the LED light continues
to indicate alarm conditions.
Alarm Enable
The Alarm Enable (A E) command set does the opposite of the Alarm
Disable command set. It enables the external alarm contacts. When this
command set is typed in, the MMI displays the message "Alarms Enabled."
In this mode, yellow alarms can be sent and the Lineside T1 card can enter
line processing mode.
Clear Alarm
The Clear Alarm (C A) command set clears all activity initiated by an alarm:
the external alarm hardware is deactivated (the contact normally open is
reopened), the LED light goes out, an entry is made in the alarm log of
the date and time when the alarm clears, and line processing ceases (for
Nortel Communication Server 1000
Circuit Card Reference
NN43001-311 01.04 Standard
Release 5.0 23 May 2008
Copyright © 2003-2008, Nortel Networks
.