When a user determines that a received SETUP message contains either:
a) no called number information; or
b) incomplete called number information;or
c) called number information which the user cannot determine to be complete; and
when the user
d) is compatible with other call characteristics (see Annex B); and
e) implements overlap receiving;
the user shall start timer T302; send a SETUP ACKNOWLEDGE message to the network; and enter the Overlap receiving state.
When the SETUP ACKNOWLEDGE message is received, the network shall: stop timer T303; start timer T304; enter the Overlap receiving state; and send the remainder of the call information (if any) in one or more INFORMATION messages, starting timer T304 when each INFORMATION message is sent.
The called party number information is provided in the Called party number information element.
The call address information may contain a sending complete indication (e.g. No. or, as a network option, the Sending complete information element) appropriate to the dialling plan being used.
Note 1 - If the network can determine that sufficient call set-up information will be received by the called user by sending the next INFORMATION message, it is recommended that the INFORMATION message contains the Sending complete information element.
The user shall start timer T302 on receipt of every INFORMATION message not containing a sending complete indication.
Following the receipt of a sending complete indication which the user understands, or the determination that sufficient call information has been received, the user shall stop timer T302 (if implemented) and send a CALL PROCEEDING message to the network. Alternatively,depending on internal events, the user may send an ALERTING or a CONNECT message to the network.
Note 2 - The CALL PROCEEDING message in this case will cause the originating exchange to send a CALL PROCEEDING message to the originating user, if not already sent.
At the expiration of timer T302 the user shall
a) initiate clearing in accordance with 5.3, with cause No. 28, invalid number format (incomplete number) if it determines that the call information is definitely incomplete; or
b) if sufficient information has been received, send a CALL PROCEEDING, ALERTING or CONNECT message as appropriate.
At the expiration of timer T304 the network initiates call clearing in accordance with 5.3, with cause No. 28, invalid number format (incomplete number) sent to the calling user, and cause No.102, recovery on timer expiry sent to the called user.
If, following the receipt of a SETUP message or during overlap receiving, the user determines that the received call information is invalid (e.g. invalid called party number), it shall initiate call clearing in accordance with 5.3 with a cause such as one of the following:
No. 1 - Unassigned (unallocated) number;
No. 3 - No route to destination;
No. 22 - Number changed;
No. 28 - Invalid number format(incomplete number).
Upon receipt of the complete call information the user may further perform some compatibility checking functions,as outlined in Annex B.
When the call is offered on point-to-point data link, only one SETUP ACKNOWLEDGE message can be received in response to the call offering.
When the call is offered to the user on a broadcast data link, multiple SETUP ACKNOWLEDGE messages may be received by the network which shall then complete as many overlap receiving procedures as such SETUP ACKNOWLEDGE messages were received. It is the network responsibility to limit the number of overlap receiving procedures to be completed for a given call. The default maximum is fixed to eight. Some networks will limit the call offering completion in overlap receiving to single data link and will therefore clear the subsequent responding users after the first SETUP ACKNOWLEDGE message has been received, in accordance with the non-selected user clearing procedures described in 5.2.9.