Nortel Circuit Card 311 Reference page 307

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Descriptions of the excessive bit error rate and frame slip errors conditions
are found in
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 3 consecutive frame bits are in error.
If this condition occurs, the hardware immediately attempts to reframe.
During the reframe time, the E1 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 (255 bits) of consecutive
zeros has been detected at the receive inputs. If this condition occurs, the
E1 link automatically attempts to resynchronize with the far-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, or blue alarm
condition occurs.
If a repeating device loses signal, it immediately begins sending an
unframed signal of all ones 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, or 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 lights. In this mode, no yellow
alarms are sent and the LEI does not enter line processing mode. Alarm
messages are sent on the MMI terminal and the LED continues to indicate
alarm conditions.
Alarm Enable
The Alarm Enable (A E) command does the reverse of the Alarm
Disable (A D) command. It enables the external alarm contacts.
When this command is typed in, the MMI displays the message Alarms
Enabled. In this mode, yellow alarms can be sent and the LEI can enter
line processing mode.
Copyright © 2003-2008, Nortel Networks
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Out of frame condition
Loss of signal condition
Blue alarm (AIS) condition
"Configuring parameters" (page
Nortel Communication Server 1000
Circuit Card Reference
NN43001-311 01.04 Standard
Release 5.0 23 May 2008
Man-Machine E1 maintenance interface software 307
297). Bit errors activate either