11.3.2 Call release

3GPP43.068Release 17Stage 2TSVoice Group Call Service (VGCS)

The voice group call can be terminated by the calling service subscriber or the calling dispatcher clearing it down, or by any dispatcher nominated in the GCR allowed to terminate the call.

11.3.2.1 Call termination by the calling subscriber

The calling service subscriber will need to gain the uplink before he can issue a termination request.

If the mobile station uses the uplink with a talker priority different from "normal subscriber" it shall include this talker priority in the termination request message. If the network supports uplink access option (i) as defined in subclause 7.2 and A-interface link sharing applies, the MSC shall compare the talker priority included in the termination request message with the talker priority stored for the current talker. If they are equal, the termination request is processed further; otherwise the MSC discards the termination request message.

The MSC has to store the identity of the calling service subscriber and to check it against the identity of the service subscriber which sends the voice group call termination request. If they are equal, the MSC shall accept the termination request and release all resources. On the radio interface a channel release message shall be sent on the FACCH of all cells in the group call area and then all resources are freed.

11.3.2.2 Call termination by dispatchers

A dispatcher entitled to terminate the call can be a mobile subscriber or a fixed line subscriber. The dispatcher may use out-of-band DTMF messages as a means for the control of the call termination, if it is a mobile dispatcher. The dispatcher may use , or DTMF tones or the signalling option specified in ETSI TS 103 389 [19], if it is a fixed line dispatcher.

If the call is terminated by a mobile dispatcher using DTMF, the out-of-band messages START_DTMF(X) and STOP_DTMF are sent via the radio interface towards the network. If the out-of-band DTMF messages are sent by a mobile dispatcher who is not controlled by the anchor MSC, the DTMF messages will be converted by the controlling MSC (e.g. relay MSC or visited MSC) into DTMF tones and these DTMF tones will be sent through the network to the anchor MSC.

If a fixed dispatcher initiates DTMF tones, the DTMF tones will be sent through the network to the anchor MSC.

Both in case of a mobile and a fixed line dispatcher the anchor MSC is responsible for the detection and collection of the out-of-band DTMF messages or in-band signals. After the evaluation of the received information, the anchor MSC shall trigger the appropriate function (see the figures 7b to 7d in 11.3.8).

In order to avoid the erroneous detection of the specific DTMF tone sequence for call termination by the MSC, this sequence shall consist of at least three DTMF digits.

11.3.2.3 Call termination on expiry of no activity timer

A time-out mechanism is required such that, if the anchor MSC does not detect any activity (as specified in subclause 8.1.2.3) within a pre-set time, the call is terminated by the anchor MSC. For this a timer shall be provided with a length as defined in the group call attributes in the GCR.

The network may provide an in-band indication, e.g. a tone, to inform the participants of the group call about the forthcoming expiry of the "no activity" timer.