Content for  TS 23.172  Word version:  18.0.0

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. 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. 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 TS 25.413) 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.