4.2.5 Network-initiated Service change in the active state

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

When the visited MSC of either party can no longer support an ongoing multimedia call, for example due to degraded coverage conditions (including UTRAN to GERAN only transitions), the visited MSC of this party shall initiate a service-change from multimedia to speech, following the procedures described below.

If the visited MSC is again able to support the multimedia at a later point in time while the speech call is still ongoing, the same visited MSC may initiate a service change from speech to multimedia as stated in TS 22.101 [8]. The details for the service change from speech to multimedia are described in section 4.2.5.2.

For a downgrade from multimedia to speech the visited MSC shall initiate an In-Call Modification procedure towards the terminal it serves using the MODIFY message. The visited MSC shall also invoke the service change procedure (see clause 4.3.5) towards the remote side. The terminals on both sides will react as described in Clause 4.2.4.

The Visited MSC shall only initiate a Network Initiated Service Upgrade from speech to multimedia if the terminal has indicated support for Network Initiated Service Upgrade Capability during the call establishment phase, as detailed in 3GPP TS 24.008 [3]. When sending the Modify request to the local terminal the MSC shall include the Network-initiated Service Upgrade indicator. A visited MSC receiving an incoming Network Initiated Service Upgrade procedure from the core network shall also include the Network-initiated Service Upgrade indicator within the MODIFY request to the local terminal.

NOTE: If the visited MSC initiating the Network Initiated Service Upgrade uses the 3G-324.M codec in the core network signalling due to operator´s policy, the visited MSC receiving the incoming Service Upgrade procedure from the core network will not recognise that this procedure is network-initiated and thus will not include the Network-initiated Service Upgrade indicator within the MODIFY request to the local terminal.

Figure 4.14a: Network-Initiated Service change from multimedia to speech requested, accepted

Figure 4.14b: void

Figure 4.14c: void

Figure 4.14c1: Network-Initiated Service change from speech to multimedia requested, accepted

If the served terminal rejects the service change from speech to multimedia, the initiating MSC shall maintain the original service. If the remote side rejects the service change from speech to multimedia, the initiating MSC shall initiate a service change procedure towards the served terminal to revert to the original service.

Figure 4.14c2: Network-Initiated Service change from speech to multimedia requested, rejected by user A

Figure 4.14c3: Network-Initiated Service change from speech to multimedia requested, rejected by user B

4.2.5.1 Network-initiated Service change in the active state starting with multimedia in Iu mode

For a network initiated service change from multimedia in Iu mode to speech, the visited MSC shall use the following procedure.

In order to request a notification from the RNC when it detects a lack of sufficient resources or radio signal degradation, the visited MSC shall include an Alternative RAB Parameters IE in the RANAP RAB Assignment Request or RANAP Relocation Request message indicating the RAB configuration for speech in addition to the RAB configuration for multimedia, when it establishes or modifies the radio access bearer for multimedia at the Iu interface.

When the radio access network detects a lack of sufficient resources to sustain the multimedia RAB configuration, it shall inform the visited MSC by sending a RANAP Modify Request message (see 3GPP TS 25.413 [17]) to the visited MSC. The visited MSC shall then:

– initiate an In-Call Modification procedure to speech towards the terminal it serves using the MODIFY message; and

– invoke the service change procedure (see clause 4.3.5) towards the remote side,

– trigger the RAB modification by sending a RANAP RAB Assignment with the RAB requested to be Modified to the RNC.

Figure 4.14d: Network-Initiated Service change from UTRAN multimedia to speech requested, accepted

4.2.5.2 Network-initiated Service change in the active state starting with speech in Iu mode

The network initiated service change from speech to multimedia in Iu mode is an optional feature. If supported the MSC initiating the service upgrade to multimedia shall use the following procedure. However a service change from speech to multimedia shoud not be initiated unless a network initiated service change from multimedia to speech had previously taken place during the same user session. Furthermore a network initiated service upgrade to multimedia shall not be performed unless the terminal has indicated that it supports it by including the Enhanced Network-initiated ICM (ENICM) Capability at call establishment. If the 3G-324.M2 was not received in the available codec list, depending on operator policy, the visited MSC may or may not perform a Network-initiated Service change procedure from speech to multimedia.

NOTE: The 3G-324.M2 codec in the available codec list indicates that all nodes in the call support incoming request for the network initiated service change from speech to multimedia and thus collect charging information indicating that a network-initiated service change was performed. An operator could choose to perform a network-initiated service change even if the 3G-324.M2 codec was not received in the available codec list, for example if the operator applies a billing scheme where the initiator of the multimedia call pays for the call and mutual agreements with the peer´s operator allow this policy.

In order to request a notification about sufficient resources to sustain again the multimedia RAB configuration from the radio access network , the visited MSC shall include an Alternative RAB Parameters IE in the RANAP RAB Assignment Request or RANAP Relocation Request message indicating the RAB configuration for multimedia in addition to the RAB configuration for speech, when it establishes or modifies the radio access bearer for speech at the Iu interface during or after a network-initiated service change from multimedia to speech. In order to request a notification about sufficient resources from a target RNC after a subsequent relocation, the MSC shall pass the Alternative RAB Parameters IE in the RELOCATION REQUEST message to the target RNC.

NOTE: If the non-anchor RNC is a pre-Release 6 node then no notification about sufficient resources can be received and therefore the MSC cannot assume that it will receive the notification for upgrade if it did not receive a previous notification for downgrade from that RNC.

When the radio access network later detects that there are sufficient resources to sustain again the multimedia RAB configuration, it shall indicate the possibility of a service change to the alternative multimedia RAB configuration by sending a RANAP Modify Request message (see 3GPP TS 25.413 [17]) to the MSC.The MSC may then:

– initiate an In-Call Modification procedure to multimedia towards the terminal it serves using the MODIFY message. The visited MSC shall include the NISUid information element in the MODIFY message. The MSC initiating the service change shall not interrupt the user plane until the terminal accepts the modification with a MODIFY COMPLETE message. When the MODIFY COMPLETE message is received from the served terminal, the initiating MSC shall then:

– invoke the service change procedure (see clause 4.3.5) towards the remote side. The initiating MSC shall then;

– reconfigure the RAB to the multimedia bearer at the latest when receiving a confirmation about the successful service change procedure from the remote side.

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. After the radio bearer has been reconfigured by the network, the terminal shall send and receive data in the new mode.

Figure 4.2.5.2/1: Network-Initiated Service change from UTRAN speech to multimedia requested, accepted in case the RAB is modified on the initiating side after receiving the response to the service change request from the remote side

Figure 4.2.5.2/2: Network-Initiated Service change from UTRAN speech to multimedia requested, accepted in case the RAB is modified on the initiating side before receiving the response to the service change request from the remote side

Figure 4.2.5.2/3: Network-Initiated Service change from UTRAN speech to multimedia, RNC B failure in case the RAB on the initiating side is not modified before receiving the response to the service change request from the remote side

Figure 4.2.5.2/4: Network-Initiated Service change from UTRAN speech to multimedia, RNC B failure in case the RAB is modified on the initiating side before receiving the response to the service change request from the remote side

Figure 4.2.5.2/5: Network-Initiated Service change from UTRAN speech to multimedia requested, RNC A failure in case the RAB is modified on the initiating side after receiving the response to the service change request from the remote side

Figure 4.2.5.2/6: Network-Initiated Service change from UTRAN speech to multimedia requested, RNC A failure in case the RAB is modified on the initiating side before receiving the response to the service change request from the remote side

Figure 4.2.5.2/7: Alternative RAB Parameters delivery during the relocation