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Maintenance Object Repair Procedures
555-233-123 10-980 Issue 4 May 2002
DS1 ISDN Trunk Service States
This section defines the possible service states of a DS1 ISDN trunk, explains the
reason for each service state, and provides the recommended recovery
procedures (when required).
Service States
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In-Service (INS)
The B-channel is in its normal operating state.
■
Out-of-Service/Far-end (OOS/FE)
A B-channel is initialized to this state when administered and it may also be
in this state if there is a failure on the B-channel attributed to a problem on
the far-end switch. The switch sends messages to the far-end to negotiate
the B-channel into service. If the far-end does not respond to the messages
within a certain time period, then the service state remains out-of-service
and maintenance will periodically resend the messages. The trunk is
unusable for outgoing calls. On US interfaces, the trunk is unusable for
incoming calls, but on non-US interfaces, incoming calls will be accepted.
■
Out-of-Service/Near-end (OOS/NE)
This is the state of the trunk when a hardware failure exists on the link, the
NPE Crosstalk Test fails, or when the trunk is busied out by system
technician. In this state, the trunk is unusable for incoming or outgoing
calls. No messages are sent to the far-end until the signaling link comes
back into service or the trunk is released by system technician.
■
Maintenance/Far-end (MTC/FE)
This state is reached when the far-end does not respond to messages sent
over the signaling link for a particular trunk after a certain amount of time.
This state is different from OOS/FE since the signaling link must have
initially been up and the B-channels in-service. The switch will periodically
send messages to the far-end to try to negotiate the trunk (B-channel) into
service. The trunk is unusable for outgoing calls but will service incoming
call requests from the far-end. Note that transitions into MTC/FE do not
drop stable calls. Therefore, if the service state changes from in-service to
MTC/FE, then stable calls are unaffected.