Nortel DMS-100 Series Reference Manual page 61

OAS alarm and Control Circuits 6-3
The Enhanced DSA alarm is active when you set office parameter
ENHANCED_DEAD_SYSTEM_ALARM in table OFCENG to YES. You
do not require a restart to change the setting of this office parameter. Note
that dead system alarms can occur during the change.
Note 1: The Enhanced DSA does not function on some international
switches. These switches have SD points MTMFAIL and OAUFAIL on
MTM or ISM that require the IMTMEX exec lineup.
Note 2: Office parameter ENHANCED_DEAD_SYSTEM_ALARM is
available in all types of alarms systems.
Common Channel Interoffice Signaling (CCIS) dead system
alarm
When an office in a CCIS network experiences a critical failure, the office
sends a broadcast dynamic overload control level 3 (BDOC3) message to the
rest of the network. This message is a network management message that
causes the system to reroute traffic intended for the failed office.
The system can detect a dead system condition at the near end and inform
the CCIS network. The system monitors the sanity of the CC in the message
switch and buffer (MSB) peripheral. If the CC in the MSB does not operate,
a BDOC3 message is sent from the MSB outward.
When the signaling transfer point (STP) receives a BDOC3 from the failed
office, it sends the BDOC3 to other offices that use the same signaling link
the BCDO3 arrived on. Transmission of the BDOC3 must occur on each
link connected to the affected MSB.
This process ensures that the failed office does not have to send BDOC3
messages to all the offices connected to the failed office.
Dead system alarm and network management
Offices have a hardware link between the network management control and
DSA that permits level 3 dynamic overload control signalling (SDOC3).
For more information refer to Network Management System Reference
Manual, 297-1001-453. The system automatically activates this link when
the office loses call processing capability. This condition can occur when
the operating company performs warm, cold, and reload restarts (See
Figure 6-1).
To avoid a situation in which the alarm system sends dead system signals to
network management (NWM), the following events occur.
1 When you test one side of the DSA or operate a DSA-related scan point,
a link break occurs.
DMS-100 Family Alarm System Description Reference Manual BASE12