Only B-channels controlled by the same D-channel will be the subject of the selection procedure. The selection procedure is as follows:
a) The SETUP message will indicate one of the following:
1) channel is indicated, no accepTable alternative; or
2) channel is indicated, any alternative is acceptable.
b) In cases 1) and 2), if the indicated channel is accepTable and available, the recipient of the SETUP message reserve sit for the call. In case 2), if the recipient of the SETUP message cannot grant the indicated channel, it reserves any other available B-channel associated with the D-channel.
c) If the SETUP message included all information required to establish the call, the recipient of SETUP message indicates the selected B-channel in a CALL PROCEEDING message transferred across the interface and enters the Incoming Call Proceeding state.
d) If the SETUP message did not include all the information required to establish the call, B-channel is indicated in a SETUP ACKNOWLEDGE message sent across the interface. The additional call establishment information, if any, is sent in one or more INFORMATION messages transferred across the interface in the same direction as the SETUP message.When all call establishment information is received, a CALL PROCEEDING ALERTING or CONNECT message, as appropriate, is transferred across the interface.
e) In case 1) if the indicated B-channel is not available, or in case 2) if no B-channel is available, a RELEASE COMPLETE message with a cause value of No. 44, requested circuit/channel not available, or No. 34, no circuit/channel available, respectively, is returned to the initiator of the call. The sender of this message remains in the Null state.
f) If the channel indicated in the CALLPROCEEDING or SETUP ACKNOWLEDGE message is unaccepTable to the initiator of the call, it clears the call in accordance with 5.3.