Nortel Networks Circuit Card - Manual (Page 237)

NT5D11 and NT5D14 Lineside T1 Interface cards Page 237 of 906
Circuit Card Description and Installation
Descriptions of the excessive bit error rate and frame slip errors conditions
can be found in “Configuring parameters” on
page 232 . Bit errors may
activate either a level 1 or level 2 alarm. The remaining conditions, when
detected, will always cause the system to activate a level 2 alarm.
An out of frame condition will be declared if two out of four frame bits are in
error. If this condition occurs, the hardware will immediately attempt to
reframe. During the reframe time, the T1 link will be declared out of frame,
and silence will be 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 will automatically attempt to resynchronize with the distant end. If this
condition lasts for more than two seconds, a level 2 alarm will be declared,
and silence will be sent on all receive timeslots. The alarm will be 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 will be declared, and silence will
be sent on all receive timeslots. The alarm will be 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 will display the message “Alarms
Disabled” and the MAINT LED will light. In this mode, no yellow alarms are
sent and the lineside T1 card will not enter line processing mode. Alarm
messages will still be sent to the MMI terminal and the LED light will
continue 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 will display the message “Alarms Enabled.” In this