Content for &nbsp; TS 23.237 &nbsp; Word version:&nbsp; 18.0.0

A Collaborative Session is established between UE-1 and UE-2 and a remote party with UE-1 acting as the Controller UE and UE-2 acting as a Controllee UE. Each UE has a media flow with the remote party.

UE-1 wishes to transfer the Collaborative Session Control to UE-2. However, none of the existing media flows are affected. UE-1 sends a Collaborative Session Control transfer request to the SCC AS to relinquish Collaborative Session Control. This request includes a registered Public User Identity or public GRUU of UE-2.

If the SCC AS does not have the list of Public User Identities that share the service profile with the Public User Identity used by UE-1 for the Collaborative Session, the SCC AS retrieves this information. If the Collaborative Session Control transfer request indicates that UE-2 has the same Public User Identity (but different public GRUU) as UE-1, this step is skipped.

Figure 6a.4a.2-1: Controller UE initiated transfer of Collaborative Session Control with transfer of media flow

The SCC AS performs authorization as specified in clause 6a.12, ensures that UE-2 can act as the Controller UE for this Collaborative Session, and that the Public User Identity used by UE-2 shares the service profile with the Public User Identity used by UE-1 for the Collaborative Session. The SCC AS then sends a message to UE-2 requesting UE-2 to assume the role of Controller UE for this on-going Collaborative Session. Included in the request to UE-2 is session information associated with the Collaborative Session that UE-2 is requested to assume the role of Controller UE for.

Step 5.

UE-2 accepts the role of Controller UE for this Collaborative Session and indicates its acceptance to the SCC AS.

Step 6.

The SCC AS in turn provides an acknowledgement to UE-1 confirming that UE-2 is the new Controller UE for the Collaborative Session, and removes Collaborative Session Control from UE-1.

Step 7.

UE-2 has become the Controller UE and UE-1 has become a Controllee UE.

6a.4a.2 Controller UE transfers Collaborative Session Control to another UE with Media Transfer p. 136

UE-1 and UE-3 are involved in a Collaborative Session with a remote party. The Collaborative Session is anchored at the SCC AS. UE-1 is the Controller UE of the Collaborative Session. UE-1 wishes to transfer the Collaborative Session Control to UE-2 along with the media flow on UE-1. The media flow to UE-3 from the remote party remains unaffected. Following is an information flow for this procedure.

Reproduction of 3GPP TS 23.237, Fig. 6a.4a.2-1: Controller UE initiated transfer of Collaborative Session Control with transfer of media flow

A Collaborative Session is established between UE-1 and UE-3 and a remote party with UE-1 acting as the Controller UE and the UE-3 acting as a Controllee UE. Each UE has a media flow with the remote party.

UE-1 wishes to transfer the Collaborative Session Control along with media flow A to UE-2. UE-1 sends a request to SCC AS to transfer media flow A and relinquish Collaborative Session Control. This request includes a registered Public User Identity or public GRUU of UE-2.

Figure 6a.4a.3-1: Collaborative Session handling upon loss of Collaborative Session Control

The SCC AS performs authorization as specified in clause 6a.12, ensures that UE-2 can act as the Controller UE for this Collaborative Session, and that the Public User Identity used by UE-2 shares the service profile with the Public User Identity used by UE-1 for the Collaborative Session. The SCC-AS then sends a message to UE-2 requesting UE-2 to transfer media flow A and assume the role of Controller UE for this on-going Collaborative Session. Included in the request to UE-2 is session information associated with the Collaborative Session that UE-2 is requested to assume the role of Controller UE for.

Step 5.

UE-2 accepts transfer of media flow A and accepts the role of Controller UE for this Collaborative Session and indicates its acceptance to the SCC AS.

Step 6.

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.

Step 7.

SCC AS in turn provides an acknowledgement to UE-1 confirming that UE-2 has accepted the media transfer and is the new Controller UE for the Collaborative Session.

Step 8.

UE-2 has become the Controller UE and UE-1 has become the Controllee UE and media flow A is now transferred to UE-2. If there is no media flow remaining on UE-1, UE-1 is released from the Collaborative Session.

6a.4a.3 Transfer of Collaborative Session Control upon loss of Controller UE p. 137

The Controller UE can lose the Collaborative Session Control as a result of, for example, losing underlying network connectivity. The Figure below shows an information flow where the SCC AS has pre-configured Collaborative Session Control loss preferences, and acts upon the loss of Collaborative Session Control based on these preferences. There is no media on UE-1.

Reproduction of 3GPP TS 23.237, Fig. 6a.4a.3-1: Collaborative Session handling upon loss of Collaborative Session Control

A Collaborative Session is established between UE-1, UE-2, UE-3 and a remote party. UE-1 is the Controller UE, and UE-2 and UE-3 are Controllee UEs. Collaborative Session Control loss preference is sent/updated to SCC AS at any time before or during the Collaborative Session, including:

the Public User Identity/ies or public GRUUs of the UE(s) which may be the successive Controller UE (in priority order), or
criteria on how to select the successive Controller UE.

The SCC AS detects that the Collaborative Session Control has been lost during the session.

The loss of Collaborative Session Control triggers the activation of Collaborative Session Control loss preference. SCC AS performs authorization as specified in clause 6a.12, then selects a Controllee UE as the new Controller UE based on Collaborative Session Control loss preference.

Figure 6a.4a.3a-1: Transfer of Collaborative Session Control with media flow(s) upon loss of Collaborative Session control

SCC AS offers Collaborative Session Control to the selected Controllee UE, UE-3. Included in the request to UE-3 is session information associated with the Collaborative Session that UE-3 is requested to assume the role of Controller UE for.

Step 5a is for the case where UE-3 accepts to become Controller UE.

Step 5a.

The Controllee UE-3 accepts the offer to become the new Controller UE.

Steps 5b-5d are for the case that the Controllee UE refuses to be a new Controller UE.

Step 5b.

Control transfer is not accepted by the Controllee UE.

Step 5c.

If there is other candidate Controller UEs to which Collaborative Session control could be but has not yet been offered, the SCC AS offers them control of the collaborative session (repeat step 4) according to their priority order in user preference.

Step 5d.

If no candidate Controller UE accepts to take over the control of the collaborative session, SCC AS releases the Collaborative Session associated with lost Controller UE as specified in steps 2 to 4 of clause 6a.5.1.

6a.4a.4 Transfer of Collaborative Session Control with media flows upon loss of Controller UE p. 138

If the Collaborative Session Control is lost in the Controller UE and there was/were media flow(s) as part of the Collaborative Session in the old Controller UE, the media flow(s) may be transferred together with the Collaborative Session Control to the new Controller UE based on user preferences.

Figure 6a.4a.3a-1 shows an information flow of transferring the Collaborative Session Control with the media flows upon loss of the Controller UE. A Collaborative Session is established between UE-1, UE-2, UE-3 and the remote party. UE-1 is the Controller UE, and UE-2 and UE-3 are Controllee UEs. Media Flow-A, Media Flow-B and Media Flow-C are established respectively between UE-1, UE-2, UE-3 and the Remote Party.

Reproduction of 3GPP TS 23.237, Fig. 6a.4a.3a-1: Transfer of Collaborative Session Control with media flow(s) upon loss of Collaborative Session control

The SCC AS detects the loss of Controller UE-1.

Figure 6a.4a.5-1: Transfer of Collaborative Session Control initiated by the target UE

Based on user preferences, the SCC AS performs authorization as specified in clause 6a.12, then sends a Collaborative Session Control transfer with media transfer request to Controllee UE-2, which is capable of being a Controller UE and has a Public User Identity sharing the same service profile with UE-1. The request indicates the Collaborative Session Control and Media Flow-A are to be transferred to UE-2 due to loss of Controller UE-1. Included in the request to UE-2 is session information associated with the Collaborative Session that UE-2 is requested to assume the role of Controller UE for.

Steps 3a - 4a are for the case of UE-2 accepting both the Collaborative Session Control and media transfer:

Step 3a.

UE-2 accepts the role of Collaborative Session Controller UE as well as the transfer of Media Flow-A, and sends a Collaborative Session Control transfer and media transfer confirmation to the SCC AS.

Step 4a.

The SCC AS performs Remote Leg Update procedure towards the remote party as specified in clause 6a.1.2.

Steps 3b - 5b are for the case of UE-2 accepting only the Collaborative Session Control transfer:

Step 3b.

UE-2 only accepts the role of Collaborative Session Controller UE, and sends a Collaborative Session Control transfer confirmation to the SCC AS.

Step 4b.

UE-2, the new Controller UE, initiates one of the following procedures, in order to transfer Media Flow-A to another UE, or to remove it from the Collaborative Session:

Controller UE initiated media transfer from Controllee UE to another Controllee UE, specified in clause 6a.3.3;
Controller UE initiated release media (media flow on the Controllee UE), specified in clause 6a.4.4;
Controller UE initiated release Collaborative Session, specified in clause 6a.5.1.

Step 5b.

The SCC AS performs Remote Leg Update procedure towards the remote party as specified in clause 6a.1.2.

6a.4a.5 Transfer of Collaborative Session Control initiated by the target UE p. 140

UE-1 and UE-2 are involved in a Collaborative Session with a remote party. The Collaborative Session is anchored at the SCC AS. UE-1 is the Controller UE of the Collaborative Session. UE-2 wishes to transfer the Collaborative Session Control from UE-1 to itself. The media flows to UE-1 and UE-2 from the remote party remain unaffected. The following information flow shows this procedure. If UE-2 is not involved in the Collaborative Session controlled by UE-1 before the transfer of Collaborative Session Control, there is at least another Controllee UE involved in the Collaborative Session before the transfer of Collaborative Session Control, which is not shown in the information flow.

Reproduction of 3GPP TS 23.237, Fig. 6a.4a.5-1: Transfer of Collaborative Session Control initiated by the target UE

UE-2 obtains information about the existing sessions and UE-1's control of Collaborative Session which UE-2 is participating in according to procedure defined in clause 6a.8.3.2.

UE-2 wishes to transfer the Collaborative Session Control from UE-1 to itself. However, none of the existing media flows are affected. UE-2 sends a Collaborative Session Control transfer request to the SCC AS to obtain Collaborative Session Control. This request includes a registered Public User Identity or public GRUU of UE-1.