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Content for  TS 23.237  Word version:  18.0.0

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6a.9 Inter-UE Transfer Initiated by Target UE  6a.9.1 Controller UE and Controllee UE belong to same IMS subscription  6a.9.1.1 Initiated by UE not participating in ongoing Collaborative Session  6a.9.1.2 Initiated by Controllee UE in ongoing Collaborative Session  6a.9.1.3 IUT solicited by a target UE without prior information about the existing sessions  6a.9.2 Controller UE and Controllee UE belong to different IMS subscriptions  6a.9.2.1 Initiated by UE not participating in the session - Collaborative Session established  6a.9.2.2 Initiated by UE not participating in ongoing Collaborative Session - media on Controllee UE 
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6a.9  Inter-UE Transfer Initiated by Target UE |R10|  p. 151

6a.9.1  Controller UE and Controllee UE belong to same IMS subscription  p. 151

6a.9.1.1  Initiated by UE not participating in ongoing Collaborative Session  p. 151

UE-1, UE-2 and UE-3 are under the same IMS subscription. UE-1 and UE-2 are involved in Collaborative Session with remote party. The Figure below shows media flow transfer from UE-1 to UE-3 requested by UE-3.
Reproduction of 3GPP TS 23.237, Fig. 6a.9.1.1-1: Inter-UE Transfer initiated by UE not participating in the Collaborative Session
Figure 6a.9.1.1-1: Inter-UE Transfer initiated by UE not participating in the Collaborative Session
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Step 1.
UE-3 obtains information about the existing sessions and their media flows.
Step 2.
UE-3 sends IUT media transfer request to transfer the Media-A from UE-1 to UE-3. The request shall include the enough information for the network to:
  • identify the targeted Collaborative Session;
  • identify that the transferred media flow is Media-A;
  • identify that the target of the transferred media flow is UE-3;
  • keep the control of the Collaborative Session in UE-1;
  • other information.
Step 3.
The SCC AS performs authorization as specified in clause 6a.12; in particular, the SCC AS requests the Controller UE-1 to authorize the pull request or the SCC AS authorizes the request on behalf of UE-1 (e.g. pre-configured). The SCC AS will also authorize that the target UE is of the same subscription. If the request is authorized, SCC AS continues in accordance with step 2 of clause 6a.3.1.1, i.e. SCC AS establishes a session with UE-3 for the Media-A, removes Media-A from UE-1, and updates the Remote Leg using the Remote Leg Update procedure. The UE-1 remains the Controller UE and UE-3 becomes a new Controllee UE.
Step 4.
The SCC AS sends IUT media transfer response to UE-3.
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6a.9.1.2  Initiated by Controllee UE in ongoing Collaborative Session  p. 152

UE-1 and UE-2 are under the same IMS subscription. UE-1 and UE-2 are involved in a Collaborative Session with remote party, in which UE-1 is the Controller UE and UE-2 is the Controllee UE. The Figure below shows media flow transfer from UE-1 to UE-2 requested by UE-2.
Reproduction of 3GPP TS 23.237, Fig. 6a.9.1.2-1: Inter-UE Transfer initiated by Controllee UE in ongoing Collaborative Session
Figure 6a.9.1.2-1: Inter-UE Transfer initiated by Controllee UE in ongoing Collaborative Session
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Step 1.
UE-2 obtains the information about the media flows in its current participating Collaborative Session.
Step 2.
UE-2 sends IUT media transfer request to transfer the Media-A from UE-1 to UE-2. The request shall include enough information for the network to:
  • identify that the transferred media flow is Media-A;
  • identify that the target of the transferred media flow is UE-2;
  • keep the control of the Collaborative Session in UE-1;
  • other information.
Step 3.
The SCC AS performs authorization as specified in clause 6a.12; in particular, the SCC AS requests the Controller UE-1 to authorize the pull request or the SCC AS authorizes the request on behalf of UE-1 (e.g. pre-configured). If the request is authorized, SCC AS continues in accordance with step 2 of clause 6a.3.1.1 to transfer Media-A to UE-2, removes Media-A from UE-1, and updates the Remote Leg using the Remote Leg Update procedure. The UE-1 remains the Controller UE and UE-2 remains a Controllee UE.
Step 4.
The SCC AS sends IUT media transfer response to UE-2.
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6a.9.1.3  IUT solicited by a target UE without prior information about the existing sessions  p. 153

This realization of pull mode is particularly applicable to the cases where the UE to be target of an IUT operation does not have information about ongoing sessions, e.g. because of privacy restrictions.
It is based on extending the information provided in the event package used for the discovery of status and capabilities of potential target UEs, with information on the wish to be the target of an IUT operation.
The following information flow shows a UE in control of an IMS session or Collaborative Session, subscribing to a device info event to be notified of availability and capabilities of potential target UEs, this event package being extended with additional information on the wish to be the target of an IUT operation. The end user subsequently requests the transfer of a video to UE-2 by interacting with UE-2. UE-2 then updates its status to inform the network that it solicits an IUT to be performed to itself. In this example, the notification includes the type of media that UE-2 expects to be transferred. Alternatively, any other kind of IUT could be requested the same way, e.g. transfer of Collaborative Session Control.
Reproduction of 3GPP TS 23.237, Fig. 6a.9.1.3-1: IUT solicited by a target UE without prior information about existing sessions
Figure 6a.9.1.3-1: IUT solicited by a target UE without prior information about existing sessions
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Step 1.
An IMS session or a Collaborative Session is set-up, involving at least UE-1 and a remote party. In case of a Collaborative Session, UE-1 is the Controller UE. Two media are established: audio (Media Flow-A) and video (Media Flow-B).
Step 2.
UE-1 performs IUT target discovery and discovers UE-2 as specified in clause 6a.8.
Step 3.
By interacting with UE-2, the user requests the transfer of a video media to UE-2.
Step 4.
UE-2 updates its status, indicating that it solicits an IUT of a video media.
Step 5 - 6.
This status update is notified to UE-1.
Step 7.
UE-1 identifies that it controls Media Flow-B which corresponds to the solicitation (video) and decides whether to initiate the IUT solicited by UE-2 or not.
Step 8.
UE-1 uses the relevant IUT procedure to transfer Media Flow-B to UE-2.
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6a.9.2  Controller UE and Controllee UE belong to different IMS subscriptions  p. 155

6a.9.2.1  Initiated by UE not participating in the session - Collaborative Session established  p. 155

The information flow below illustrates a transfer of media flow scenario in which a UE belonging to one subscription (UE-2) requests a media flow from a UE that belongs to another subscription (UE-1). At this time, the control of the transferred media flow remains at UE-1. After the transfer, a Collaborative Session is established, in which the UE-1 is Controller UE, and UE-2 is Controllee UE. It is assumed that, prior to the scenario, User-2 has discovered that there is an ongoing session between UE-1 and the remote party.
Reproduction of 3GPP TS 23.237, Fig. 6a.9.2.1-1: Establish Collaborative Session by target UE initiated transferring media
Figure 6a.9.2.1-1: Establish Collaborative Session by target UE initiated transferring media
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There are Media-A and Media-B between UE-1 and remote party.
Step 1.
UE-2 sends a request towards UE-1 to transfer Media-B from UE-1 to UE-2. The request includes enough information for the network to:
  • identify that the media flow to be transferred is Media-B;
  • identify that the source of the media flow to be transferred is UE-1;
  • identify the session that contains the media flow to be transferred;
  • identify that the target of the transferred media flow is UE-2;
  • give control of the Collaborative Session to UE-1.
Step 2.
S-CSCF-2 forwards the request to SCC AS-2.
Step 3.
SCC AS-2 authorizes the request from UE-2.as specified in clause 6a.12
Step 4.
SCC AS-2 sends a request to S-CSCF-2 towards UE-1 to transfer Media-B from UE-1 to UE-2. The Collaborative Session request includes enough information for the network to:
  • identify the source of the transfer request as UE-2;
  • identify that the media flow to be transferred is Media-B;
  • identify that the target of the transferred media flow is UE-2;
  • give control of the Collaborative Session to Controller UE-1.
Step 4a.
S-CSCF-2 forwards the request towards UE-1.
Step 4b.
S-CSCF-1 forwards the request to SCC AS-1.
Step 5.
SCC AS-1 authorizes the request from UE-2.
Step 6.
SCC AS-1 removes Media-B from UE-1, updates Remote Leg and finishes Access Leg establishment for setting up Media-B between remote party and UE-2, and updates the media information in Controller UE-1.
After the above operation, 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.
This information flow is also applicable to the cases where a UE not participating in an ongoing Collaborative Session joins the Collaborative Session by initiating the transfer of media flow(s) from Controller UE which belongs to the different IMS subscription to itself.
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6a.9.2.2  Initiated by UE not participating in ongoing Collaborative Session - media on Controllee UE  p. 156

UE-1 and UE-2 are involved in Collaborative Session with remote party. UE-1 and UE-2 belong to different subscriptions and SCC AS-1 serves the user of UE-1, SCC AS-2 serves the user of UE-2. UE-3 which is not in the Collaborative Session can belong to the same subscription as UE-1 or UE-2 or neither. The Figure below shows the media flow transfer procedure from UE-2 to UE-3 requested by UE-3. For simplification, in the flow UE-3 belongs to the same subscription with UE-2.
Reproduction of 3GPP TS 23.237, Fig. 6a.9.2.2-1: Inter UE Transfer initiated by target UE not participating in the Collaborative Session - media on the Controllee UE
Figure 6a.9.2.2-1: Inter UE Transfer initiated by target UE not participating in the Collaborative Session - media on the Controllee UE
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Step 1.
UE-3 obtains information about the existing sessions and their media flows of UE-2.
Step 2.
UE-3 sends an IUT media transfer request towards UE-2 to transfer the Media-B from UE-2 to UE-3. The request shall include the enough information for the network to:
  • identify the targeted Collaborative Session;
  • identify that the transferred media flow is Media-B;
  • identify that the target of the transferred media flow is UE-3;
  • other information.
Step 3.
Based on the identifier of the targeted Collaborative Session, SCC AS-2 knows itself to be the SCC AS serving the Controllee UE of the collaborative session, and relays the media transfer request via S-CSCF2/1 to the SCC AS-1 which serves the Controller UE of the collaborative session.
Step 4-6.
SCC AS-1 sends a media transfer request to the Controller UE-1, and the Controller UE-1 authorizes the media transfer request. If SCC AS-1 is configured to authorize the request on behalf of UE-1, steps 4-6 are skipped.
Step 7.
After obtaining authorization as specified in clause 6a.12, SCC AS-1 establishes a session with UE-3 for the Media-B, removes Media-B from UE-2, and updates the Remote Leg using the Remote Leg Update procedure as specified in clause 6a.1.2. The UE-3 becomes a new Controllee UE.
Step 8.
SCC AS-1 sends the media transfer response via S-CSCF1/2 towards UE-3.
Step 9.
SCC AS-2 sends the media transfer response towards UE-3.
Step 10.
SCC AS-1 sends the Collaborative Session information to the Controller UE-1 to inform UE-1 of the change of the Collaborative Session.
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