A warning alarm is logged against a DS1 ISDN B-Channel trunk when it is placed in the Maintenance/Far-End or Out-Of-Service/Far-End states, during which the trunk is unusable for outgoing calls. When a warning alarm is present, use the status trunk grp#/mem# command to determine the exact state. Other alarms can be diagnosed by using the short and/or long test sequences.

An ISDN B-Channel trunk can be placed in a Far-End service state by either action taken by the far-end switch or by failure of the far-end switch to respond. For example, if the far end does not respond to a Remote Layer 3 Query test (#637) for ISDN-SGR, the associated DS1 ISDN trunk B-Channels will be placed in the Maintenance/Far-End service state.

As a port on a DS1 Media Module (MG-DS1), and as part of a signaling group dependent on a D-Channel (ISDN-PLK) for signaling, operation of the ISDN-TRK is dependent on the health of these other MOs. In turn, the ISDN D-Channel depends on the packet bus (PKT-BUS) for transmission through the system. Keep this hierarchy of dependencies in mind when diagnosing problems.