6 Exception procedures or unsuccessful outcome
22.0913GPPExplicit Call Transfer (ECT) supplementary serviceStage 1TS
If a mobile subscriber tries to invoke the call transfer service while not subscribed to or the network cannot provide ECT supplementary service for some other reason, an indication shall be provided to the mobile subscriber to notify the mobile subscriber with the reason of failure.
The call state is not affected and the established connection shall remain in the state prior to the request.
In the case where:
– the two calls are incompatible with the ECT request, i.e. either one of them or both are not belonging to the service TS:11 (telephony);
– if the network option is not supported and the call state is not compatible with the request, e.g. one call is not answered
the request shall be rejected by the network and the subscriber shall be notified with the reason.
The call state is not affected and the established connection shall remain in the state prior to the request.
The request for the ECT supplementary service shall be rejected if, as a network option, the network can determine that the resulting connection would contain no subscriber who is able to terminate the call.
NOTE: It may not be possible to decide if the resulting connection would have such a subscriber, e.g. when interworking between different versions of signalling systems occurs. In such cases, as a network option, the request for the ECT supplementary service may be accepted, or rejected. If the request for the ECT supplementary service is accepted in this case, the network may employ other means to control this situation (e.g. time supervision). The procedures for this are outside the scope of the present document.