4.2.4 User-initiated Service change in the active state

23.1723GPPRelease 17Stage 2Technical realization of Circuit Switched (CS) multimedia service UDI/RDI fallback and service modificationTS

At any given time, if either of the call parties wants to change from the current active mode to the other mode via MMI, the terminal shall activate an In-Call Modification procedure. Using this procedure, described in 3GPP TS 24.008 [3], clause, the UE shall send a MODIFY message containing the BC-IE to change to. This BC-IE shall be one of those already negotiated at call setup.

As a result, the MSC shall then invoke the service change procedure (see clause 4.3.5). If the request is accepted, the originating MSC sends a MODIFY COMPLETE message to the UE including the BC-IE of the mode to switch to (see figure 4.13). If the request is rejected, the MSC sends a MODIFY REJECT message to the UE including the BC-IE from the current active mode (see figure 4.14).

In the case the MSC has determined that the other mode is unavailable (e.g. a fallback to either mode has occurred), it shall reject the MODIFY request at once by replying with a MODIFY REJECT message.

On the remote side, the MSC shall initiate an In-Call Modification procedure towards the terminal using the MODIFY message. For a service change from speech to multimedia, the terminal shall request confirmation from the user unless configured differently. For a service change from multimedia to speech, the terminal shall accept the request without requesting confirmation from the user. If the change is accepted, the UE shall reply to the MSC with a MODIFY COMPLETE message, whereas a MODIFY REJECT message shall be sent if the change is rejected.

NOTE: Privacy concerns strongly advise that any change to multimedia mode, unless explicitly allowed by the user in the terminal configuration settings, triggers a question to the user in order to confirm or decline the change. The details on how to provide the user interaction are left for implementation.

When receiving a MODIFY message, a terminal shall not interrupt the data traffic and shall continue to send and receive data in the old mode, even after the terminal accepts the modification with a MODIFY COMPLETE message. The radio bearer will then be reconfigured by the network. After the radio bearer has been reconfigured, the terminal shall send and receive data in the new mode.

Figure 4.13: Service change requested, accepted

Figure 4.14: Service change requested, rejected