13.20.2 Talker change in Voice group call (1 channel model)

23.2053GPPBearer-independent circuit-switched core networkRelease 17Stage 2TS

If the MSC server decides that the talker shall use the uplink associated to the downlink of the ASCI broadcast (common group call) channel (1 channel model, see 3GPP TS 43.068 [39] or 3GPP TS 48.008 [27] (for AoIP)), the talker’s speech is transferred via the uplink channel of the ASCI broadcast channel of the cell. The stream arrives within the MGW on the termination of the traffic channel serving the cell or BSS (enhanced A-interface) and is transferred to the conference function where the summarized conference signal is calculated. The resulting stream is then transferred to all conference terminations. The normal behaviour of a conference bridge is to subtract for each conference member its own speech (incoming stream) from the summarized signal, otherwise it hears itself (outgoing stream). Therefore the Talker context need to be modified by adding a new termination to the context which is connected to the listener context (see figure 13.20.5/3 and 13.20.5/5). The topology within the talker context is set oneway from uplink of the ASCI broadcast channel in direction to Conference bridge (old termination of the talker context) and the topology is set to Oneway from the new added termination towards the termination connected to the downlink of the ASCI broadcast channel. This is performed using establish bearer procedure and change flowdirection. To avoid, that the talker hears himself, the UE internally switches off the loudspeaker (muting/unmuting functionality, 3GPP TS 43.068 [39]) on request of the MSC server.