If the SETUP message has been delivered on a point-to-point data link and a RELEASE COMPLETE or DISCONNECT message is received before a CONNECT message has been received, the network shall stop timer T303, T304, T310 or T301 (if running); continue to clear the user as described in 5.3.3, and clear the call to the calling user with the cause received in the RELEASE COMPLETE or DISCONNECT message.
If the SETUP message has been delivered on a broadcast data link and a RELEASE COMPLETE message is received whilst timerT303 is running, the message cause shall be retained by the network. If timer T303 expires (i.e. if no valid message such as CALL PROCEEDING, ALERTING or CONNECT has been received) the cause previously retained when a RELEASE COMPLETE message was received is sent back to the calling user in a DISCONNECT message and the network shall enter the Call Abort state. When multiple RELEASE COMPLETE messages are received with different causes, the network shall:
1) ignore any cause No. 88, incompatible destination; and
2) give preference to the following causes (if received) in the order listed below:
(highest) No.17 user busy;
No.21 call rejected;
3) any other received cause may also be included in the clearing message sent to the originating user (see 5.3).
If the SETUP message has been delivered on a broadcast data link and a user which has previously sent a SETUP ACKNOWLEDGE, CALL PROCEEDING or ALERTING message sends a DISCONNECT message to the network, the actions taken by the network depend on whether timer T312 is running and whether other called users have responded to the SETUP message.
Case 1 - DISCONNECT received prior to expiry of timer T312
If timer T312 is running and the network receives a DISCONNECT message after having received a SETUP ACKNOWLEDGE, CALL PROCEEDING or ALERTING message from a called user (but before receiving a CONNECT message), timer T312, as well as timer T310 or T301 (if running), should continue to run. The network shall retain the cause in the DISCONNECT message and shall continue to clear the user as described in 5.3.3. The network shall stop timer T304 (if running) for this user.
Upon expiration of timer T312, if either
a) no other users have responded to the incoming call; or
b) all users that have responded to the incoming call have been cleared or are in the process of being cleared,
the network shall stop timer T310 or T301 (if running) and shall clear the call to the calling user. If an ALERTING message has been received, the cause sent to the calling user. shall be a cause received from the called user, giving preference to (in order of priority): No. 21, call rejected; any other cause sent by a called user. If only SETUP ACKNOWLEDGE, or CALL PROCEEDING messages have been received, the cause sent to the calling user shall be a cause received from the called user, giving preference to (in order of priority): No. 17, user busy; No. 21, call rejected; any other appropriate cause sent by a called user.
Case 2 - DISCONNECT received after expiry of timer T312
If timer T312 has expired and the network receives a DISCONNECT message from the called user after having received a SETUP ACKNOWLEDGE, CALL PROCEEDING or ALERTING message (but before receiving a CONNECT message), the network shall continue to clear the user as described in 5.3.3. The network shall stop timer T304(if running) for this user.
If other called users have responded to the SETUP message with a SETUP ACKNOWLEDGE, CALLPROCEEDING or ALERTING message, and still have the opportunity to accept the call by sending a CONNECT message, the network shall retain the cause in the DISCONNECT message. The network shall continue to process the incoming call for the remaining responding users (T310 or T301, if running, shall continue to run).
If either:
a) no other users have responded to the incoming call; or
b) all users that have responded to the incoming call have been cleared or are in the process of being cleared,
the network shall stop timer T310 or T301 (if running) and shall clear the call to the calling user. If an ALERTING message has been received, the cause sent to the calling user. shall be a cause received from the called user, giving preference to (in order of priority): No. 21, call rejected; or any other cause sent by a called user. If only SETUP ACKNOWLEDGE, or CALL PROCEEDING message have been received, the cause sent to the calling user shall be a cause received from the called user, giving preference to (in order of priority): No. 17, user busy; No. 21, call rejected; any other appropriate cause sent by a called user.