Nortel NT1R20 Description page 143

NT5D11 Line-side T1 Interface Card Page 119 of 290
Descriptions of the excessive bit error rate and frame slip errors conditions
can be found in "Configuring parameters" on page 114. 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 occurs 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 will immediately begin sending an
unframed all ones signal to the distant 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 in the MMI will display the message "Alarms
Disabled" and the MAINT LED will light. In this mode, no yellow alarms are
sent and the line-side T1 card will not enter line processing mode. Alarm
messages will still be to be sent on the MMI terminal and the LED light will
still continue to indicate alarm conditions.
Alarm Enable
The Alarm Enable (A E) command set does the reverse 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
mode, yellow alarms can be sent and the line-side T1 card can enter line
processing mode.
Line cards Description