The status trunk command displays the following possible service states for ISDN trunks. Table 213 gives recommended procedures for each state.
The B-channel is in its normal operating state.
A B-Channel is initialized to this state when administered. 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 incoming and outgoing calls.
This is the state of the trunk when 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.
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.
The trunk (B-channel) is in this state if the signaling channel (ISDN-LNK) is busied out by system technician. The trunk (B-channel) is also temporarily in this state if system technician has issued a test trunk trunk group/trunk member long command. This command will execute the ISDN-PRI test call. This test will change 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.
In addition to one of the above 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.
The near-end is waiting for a response from the far-end to a B-channel maintenance message requesting that the B-channel be transitioned to in-service.
This state is supported only by systems using country protocol 1 (including US). The near-end is waiting for a response from the far-end to a maintenance message requesting that the B-channel be transitioned to the maintenance service state.
The in-service service state also has a call activity component.