6a.2 Information flows for Collaborative Session establishment

23.2373GPPIP Multimedia Subsystem (IMS) Service ContinuityRelease 17Stage 2TS

6a.2.1 Establish Collaborative Session by transferring media

There is an ongoing session between UE-1 and a remote party, which is anchored at the SCC AS. UE-1 transfers the media flow from UE-1 to UE-2 to establish a Collaborative Session. Following is an information flow for the Collaborative Session establishment procedure when UE-1 initiates media transfer from UE-1 to UE-2. After the transfer, the UE-1 becomes Controller UE, and UE-2 becomes Controllee UE.

Figure 6a.2.1-1: Establish Collaborative Session by transferring media

1. UE-1 sends an IUT media transfer request to the SCC AS to transfer Media Flow-A from UE-1 to UE-2. The IUT media transfer request shall include the enough information for the SCC AS to:

– identify that the transferred media flow is Media Flow-A;

– identify that the target of the transferred media flow is UE-2;

– keep the control of the Collaborative Session in UE-1.

2. The SCC AS performs authorization as specified in clause 6a.12, then sends request to establish Access Leg at UE-2 for Media Flow-A. The SCC AS removes Media Flow-A from UE-1, and updates the Remote Leg using the Remote Leg Update procedure as specified in clause 6a.1.2.

3. The SCC AS sends an IUT media transfer response to UE-1. A Collaborative Session is established, for which UE-1 becomes the Controller UE and UE-2 becomes a Controllee UE.

When the above transfer is completed the SCC AS retains the service state (e.g. media flows status) of UE-1 and UE-2, and UE-1 retains the control of the Collaborative Session.

NOTE 1: UE-1 can transfer other media flows from UE-1 by repeating the above steps 1-3.

NOTE 2: If, besides Media Flow-A, there are other media flows between UE-1 and the remote party, these other media flows shall not be impacted by the above Inter‑UE Transfer operation, i.e. these other media flows remain on UE‑1.

6a.2.2 Establish Collaborative Session with new media

The following information flow shows the Collaborative Session establishment procedure. There is an ongoing IMS session with Media Flow-A between UE-1 and a remote party, which is anchored at the SCC AS. UE-1 wants to add a new Media Flow-B on another UE-2 to the current ongoing IMS session to establish a Collaborative Session.

Figure 6a.2.2-1: Flow for Collaborative Session establishment with new media flow on another UE

1. UE-1 decides to add a new Media Flow-B to UE-2. It sends an IUT add media request to the SCC AS, indicating that a new Media Flow-B will be added to UE-2. The request shall include enough information for the SCC AS to:

– identify that the added media flow is Media Flow-B;

– identify that the target of the added media flow is UE-2;

– keep the control of the Collaborative Session in UE-1;

2. The SCC AS performs authorization as specified in clause 6a.12, then sends the IUT add media request to UE-2, indicating that a new Media Flow-B will be created on UE-2. Media Flow-B between UE-2 and remote party is established. The Remote Leg is updated accordingly.

3. After the successful establishment of the Media Flow-B on UE-2, the SCC AS sends an IUT add media response back to UE-1. A Collaborative Session is established, for which UE-1 becomes the Controller UE and UE-2 becomes a Controllee UE and Media Flow-A and Media Flow-B become part of the Collaborative Session under the control of UE‑1..

6a.2.3 Establish Collaborative Session at originating IMS session setup

The following information flow shows the Collaborative Session establishment procedure when there is no ongoing IMS session. Concurrent with a normal session set-up towards a remote party, UE-1 wants to establish a Collaborative Session, which is anchored at the SCC AS, with a new Media Flow-A on itself and a new Media Flow-B on another UE-2.

Figure 6a.2.3-1: Establishment of Collaborative Session upon Originating IMS Session Setup

1. UE-1 sends an IUT request to the SCC AS in order to set up a Collaborative Session to remote party with Media‑A in UE-1, and with Media-B in UE-2. The session setup request shall include enough information for the SCC AS to:

– identify the remote party of the session setup request;

– identify that Media-A shall be established in UE-1;

– identify that Media-B shall be established in UE-2 and the requested media type associated with Media-B (e.g. video);

– keep the control of the Collaborative Session in UE-1.

2. The SCC AS performs authorization as specified in clause 6a.12, then sends a request to establish an Access Leg at UE-2 for Media-B.

NOTE: In order to obtain the full media description of Media-B, it is necessary to establish the Access Leg at UE‑2 prior to engaging the remote party so that the SCC AS can send a proper (complete) SDP offer towards the remote party in step 3.

3. The SCC AS sends a session setup request to the remote party.

4. The remote party sends a response with the SDP answer of Media-A and Media-B to the SCC AS.

5. The SCC AS sends a response with the SDP answer of Media-A to UE-1 to establish Media-A in UE‑1.

6. The SCC AS sends a response with the SDP answer of Media-B to UE-2 to establish Media-B in UE‑2.

After the above operation, a Collaborative Session is established, for which UE-1 becomes the Controller UE and UE‑2 becomes a Controllee UE. Media-A is established between Controller UE-1 and the remote party, and Media-B is established between Controllee UE-2 and the remote party.

6a.2.4 Establish Collaborative Session at terminating IMS session setup

The following information flow shows the Collaborative Session establishment procedure when there is no ongoing IMS session. Concurrent with the response to a normal session invitation received from a remote party, UE-1 wants to establish a Collaborative Session, which is anchored at the SCC AS, with the requested Media Flow-A on itself and the requested Media Flow-B on another UE-2.

Figure 6a.2.4-1: Establishment of Collaborative Session upon Terminating IMS Session Setup

1. The remote party sends a session setup request to the SCC AS to set up Media-A and Media-B with UE‑1.

2. The SCC AS forwards the session setup request to UE‑1.

3. UE-1 sends a Collaborative Session request to the SCC AS to setup Media-B in UE-2. The session setup request includes enough information for the network to:

– identify that Media-B shall be established in UE-2 and the requested media type associated with Media‑B (e.g. video);

– keep the control of the Collaborative Session in UE‑1.

4. The SCC AS performs authorization as specified in clause 6a.12, then sends a request to establish an Access Leg at UE-2 for Media‑B.

5. The SCC AS sends a response to the remote party. The response carries the SDP answer of Media-A in UE‑1 and Media‑B in UE-2.

After the above operation, a Collaborative Session is established, for which UE-1 becomes the Controller UE and UE‑2 becomes a Controllee UE. Media-A is established between Controller UE-1 and the remote party, and Media‑B is established between Controllee UE-2 and the remote party.