The procedures in this clause and the following clauses are applicable only to 3GPP systems.
For IMS sessions that use CS media established by the non ICS UE, the MSC Server enhanced for ICS shall perform the necessary interworking between the I2 reference point and CS SCUDIF signalling described in
TS 23.172 and
TS 24.008 to add/remove the video media flow through SCUDIF if supported by the CS access network.
In the case that the non ICS UE is attached to the MSC Server not enhanced for ICS, the MGCF shall perform the service change procedures to add/remove the video media flow as specified in
TS 29.163.
The non ICS UE can also use the redial mechanism as defined in
TR 23.903 for switching between voice and video services.
Figure 7.9.1.2-1 describes how a video media flow is added to an ongoing speech session for the non ICS UE via the MSC Server enhanced for ICS. Change from multimedia (i.e. speech and video) to speech can be achieved in a similar way.
Step 1.
The non ICS UE A sends a MODIFY message requesting service change from speech to multimedia (i.e. video and voice) as specified in
TS 23.172.
Step 2.
The MSC Server initiates interaction with the MGW instructing it to modify bearer characteristics.
Step 3.
The MSC Server sends a re-INVITE message that offers the adding of the video media to the ongoing speech session to the S-CSCF.
Step 4.
The S-CSCF sends the re-INVITE to the SCC AS which has been inserted at session establishment.
Step 5.
The SCC AS sends the re-INVITE to the S-CSCF.
Step 6.
The S-CSCF forwards the re-INVITE to UE B.
Step 7.
Completion of the session and bearer setup procedures, where upon the establishment of the multimedia connection, the MSC Server shall perform the video codec negotiation and set up the multimedia bearer based on the procedures defined in
TS 29.163.
Figure 7.9.1.3-1 describes how a video media flow is added to an ongoing speech session for the non ICS UE via the MSC Server which is not enhanced for ICS. Change from multimedia (i.e. speech and video) to speech can be achieved in a similar way.
Step 1.
The non ICS UE A sends a MODIFY message requesting service change from speech to multimedia (i.e. video and voice) as specified in
TS 23.172.
Step 2.
The MSC Server sends the Modify Codec message to the MGCF indicating the change from speech to multimedia (i.e. video and voice).
Step 3.
The MGCF initiates interaction with the IMS-MGW instructing it to modify bearer characteristics.
Step 4.
The MGCF sends the re-INVITE that offers the adding of the video media to the ongoing speech session to the S-CSCF.
Step 5-7.
Step 8.
Completion of the session and bearer setup procedures, where upon the establishment of the multimedia connection, the MGCF/IMS-MGW shall perform the procedures as specified in
TS 29.163 to set up the multimedia bearer.