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ISDN-TRK (DS1 ISDN Trunk)
Issue 1 June 2005 1449
● Maintenance/Far-End (MTC/FE)
This state is reached when the far end does not respond after a certain amount of time to
messages sent over the signaling link for a particular trunk. 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.
● Maintenance/Near-End (MTC/NE)
The trunk (B channel) is in this state if the signaling channel (ISDN-LNK) is busied out by
the system technician. The trunk (B channel) is also temporarily in this state if the system
technician enters test trunk grp#/mem# long. This command executes the ISDN-PRI
test call. This test changes the state of the trunk member to MTC/NE for the duration of the
test unless a call request comes in from the far end. In that case, the test would abort. Note
that transitions into MTC/NE do not drop stable calls. In this state, the B channel is not
usable for new incoming or outgoing calls.
● Pending States
In addition to one of the previous components, the service state may have a pending
component, indicating that the switch is waiting for a reply from the far end. These service
states remain in effect until either a response is received or the allotted waiting time expires.
- Pending-in-Service
The near end is awaiting a far-end response to a B-channel maintenance message
requesting that a B channel be transitioned to in service.
The far-end has a certain amount of time to respond to the message. The service state
will be PINS until either a response is received or the timer expires.
- Pending-Maintenance
This state is supported only by systems using country protocol 1 (including US). The near
end is awaiting a far-end response to a maintenance message requesting that a B
channel be transitioned to the maintenance service state. The far-end has a certain
amount of time to respond to the message. The service state will be PMTC until either a
response is received or the timer expires.
● Call Activity States
The in-service state also has a call activity component.
-Active
A call is connected over the B channel (for example, in service active).
-Idle
There is no call currently on the B channel (for example, in serviced).
The following diagram of the DS1 ISDN Trunk service states shows the common progression
from one service state to another and the event that caused the change of state.