6a.4.6a Controllee UE initiated add new media on another Controllee UE
23.2373GPPIP Multimedia Subsystem (IMS) Service ContinuityRelease 17Stage 2TS
This information flow shows the Controllee UE-2 adding a media flow to another Controllee (UE-3). As a pre-requisite, there exists a Collaborative Session with a media flow, Media–A, on the Controllee UE (UE-2). UE-3 might or might not be part of the Collaborative Session before the media addition. Furthermore, Controller UE 1 and Controllee UE-2 profiles are served by different IUT SCC AS: SCC AS-1 and SCC AS-2, which are in turn attached to S-CSCF-1 and S-CSCF-2 respectively. For simplicity, these S-CSCFs are not shown in the following figure.
Figure 6a.4.6a-1: Controllee initiated addition of media to another Controllee UE (Controller and Controllees belong to different IMS subscriptions)
1. UE-2 sends a Collaborative session request to SCC AS-2 to add Media-B to UE-3. The Collaborative Session request includes enough information for the network to:
– identify that the media to be added is Media-B;
– identify that the target for the media to be added to is UE-3;
– identify the session that contains of the media flow to be added;
– Controller of the Collaborative Session is UE-1.
2. SCC AS-2 authorizes the request from UE-2 as specified in clause 6a.12 and identifies that the session is a Collaborative Session anchored at SCC AS-1.
3. SCC AS-2 then forwards the Collaborative session request to SCC AS-1 which is the SCC AS for the Controller UE in order to add Media-B to UE-3.
4-6. SCC AS-1 sends a Collaborative session request to the Controller UE-1, and the Controller UE-1 authorizes the media addition request.
NOTE 1: SCC AS-1 may be configured to authorize the request on behalf of UE-1.
7. SCC AS-1 sends Session request to add Media-B to UE-3 via S-CSCF‑3. The Session request includes enough information for the network to:
– identify the source of the addition request as UE-1;
– identify the remote party;
– identify that the media flow to be added is Media-B;
– identify that the target of the media flow to be added is UE-3;
8. S-CSCF-3 forwards the Session request to UE-3.
9. UE-3 sends a Session response to S-CSCF-3.
10. S-CSCF-3 forwards Session response to SCC AS-1.
11. SCC AS-1 updates remote leg with Remote Leg Update Procedure.
12. SCC AS-2 sends the Collaborative session response to UE-2.
When the Inter-UE Transfer is completed, UE-1 keeps the Collaborative Session Control.