Apart from the exceptions identified in 5.3.2 and 5.8, the user shall initiate clearing by sending a DISCONNECT message; starting timer T305 (the value of timer T305 is specified in 9.2); disconnecting the B-channel and entering the disconnect request state.
Note 1 - When a user initiates call clearing by sending a RELEASE message, the procedures described in 5.3.4 are then followed.
The network shall enter the Disconnect Request state upon receipt of a DISCONNECT message. This message then prompts the network to disconnect the B-channel, and to initiate procedures for clearing the network connection to the remote user. Once the B-channel used for the call has been disconnected, the network shall send a RELEASE message to the user; start timer T308 (the value of a timer T.308 is specified in 9.1), and enter the Release Request state.
Note 2 - The RELEASE message has only local significance and does not imply an acknowledgement of clearing from the remote user.
On receipt of the RELEASE message the user shall cancel timer T305; release the B-channel; send a RELEASE COMPLETE message; release the call reference and return to the Null state. Following the receipt of a RELEASE COMPLETE message from the user, the network shall stop timer T308; release both the B-channel and the call reference, and return to the Null state.
If timer T305 expires, the user shall send a RELEASE message to the network with the cause number originally contained in the DISCONNECT message; start timer T308 and enter the Release Request state.In addition, the user may indicate a second Cause information element with cause No. 102, recovery on timer expiry.
If timer T308 expires for the first time,the network shall retransmit the RELEASE message and timer T308 shall be restarted. In addition, the network may indicate a second Cause information element with cause No. 102, recovery on timer expiry. If no RELEASECOMPLETE message is received from the user before timer T308 expires a second time, the network shall place the B-channel in a maintenance condition, release the call reference, and return to the Null state.
Note 3 - The restart procedures contained in 5.5 may be used on B-channels in the maintenance condition.
Note 4 - Other actions which could be taken by the network upon receipt of a DISCONNECT message are for further study.
The actions to be taken with regard to the maintenance condition are network dependent.