A.6 Signalling flows for release of collaborative session for inter-UE transfer

24.3373GPPIP Multimedia (IM) Core Network (CN) subsystem IP Multimedia Subsystem (IMS) inter-UE transferRelease 17Stage 3TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

A.6.1 Introduction

The signalling flows for release of Collaborative Session demonstrate how the session is released by the Controller UE or by the remote party UE. The following signalling flows are included:

– subclause A.6.2 shows an example where the Controller UE initiates the release of a Collaborative Session. It demonstrates how the service control signalling and media path between the Controller UE and remote UE and the media path between the Controllee UE and the remote UE are released as a result of the session release; and

– subclause A.6.3 shows an example where the remote UE initiates the release of a Collaborative Session.

A.6.2 Controller UE releases collaborative session

In this example, session release is initiated by the Controller UE (UE 1), which is involved in the Collaborative Session with UE 2 and the remote UE (UE 3). The SCC AS ensures that all Controllee UEs involved in the Collaborative Session receive a request for session release in order to completely release the session ongoing with the remote UE.

Figure A.6.2-1: Release of Collaborative Session initiated by Controller UE

NOTE 1: For clarity, the SIP 100 (Trying) responses are not shown in the signalling flow.

1. Collaborative Session currently exists in a dialog with UE 3

A Collaborative Session involving UE 1 and UE 2 exists in a dialog with UE 3. Media paths exist between UE 1 and UE 3 and between UE 2 and UE 3. In this scenario, UE 1 is the Controller UE in the Collaborative Session and thus maintains service control signalling with the SCC AS.

2-3. SIP BYE request (UE 1 to SCC AS via intermediate IM CN subsystem entities)

UE 1, acting as the Controller UE, initiates session release by sending a SIP BYE request towards the SCC AS. There is no Inter UE transfer specific content in the SIP BYE request.

4-6. SIP BYE request (SCC AS to UE 3 via intermediate IM CN subsystem entities)

The SCC AS routes the SIP BYE request to UE 3 indicating to the remote UE that the Controller UE requests that the session is to be released.

7-9. SIP 200 (OK) response (UE 3 to SCC AS via intermediate IM CN subsystem entities)

UE 3 responds to the received SIP BYE request with a SIP 200 (OK) response.

10-11. SIP BYE request (SCC AS to UE 2 via intermediate IM CN subsystem entities)

The SCC AS, acting as a routing B2BUA, sends a SIP BYE request towards UE 2 to release the dialog it is involved in with UE 3 via the Collaborative Session. There is no Inter UE transfer specific content in the SIP BYE request.

NOTE 1: The SIP BYE request to UE 2 (step 10) can occur in parallel with the SIP BYE request to UE 3 (step 4). Alternatively, the SCC AS can send the SIP BYE request to UE 2 prior to sending the SIP BYE request to UE 3.

12-13. SIP 200 (OK) response (UE 2 to SCC AS via intermediate IM CN subsystem entities)

UE 2 responds to the received SIP BYE request with a SIP 200 (OK) response.

14-15 SIP 200 (OK) response (SCC AS to UE 1 via intermediate IM CN subsystem entities)

Upon receiving SIP 200 (OK) responses from UE 2 and UE 3, the SCC AS responds to the SIP BYE request from UE 1 with a SIP 200 (OK) response.

NOTE 2: The SIP 200 (OK) response in step 7 can be sent earlier by the SCC AS in response to the SIP BYE request received from UE 1(step 3). For example, the SCC AS can send the SIP 200 (OK) response to UE 1 after receiving the SIP 200 (OK) response from UE 3 (step 9).

A.6.3 Remote UE releases collaborative session

In this example, session release is initiated by the remote UE (UE 3). UE 1 and UE 2 are included in a Collaborative Session with the remote UE. The SCC AS ensures that all Controllee UEs involved in the Collaborative Session receive a request for session release in order to completely release the ongoing session.

Figure A.6.3-1: Release of Collaborative Session initiated by remote UE

NOTE 1: For clarity, the SIP 100 (Trying) responses are not shown in the signalling flow.

1. Collaborative Session currently exists in a dialog with UE 3

2-4. SIP BYE request (UE 3 to SCC AS via intermediate IM CN subsystem entities)

The remote UE, UE 3, initiates session release by sending a SIP BYE request towards the Controller UE via the SCC AS serving the Controller UE. There is no Inter UE transfer specific content in the SIP BYE request.

5-6. SIP BYE request (SCC AS to UE 1 via intermediate IM CN subsystem entities)

The SCC AS routes the SIP BYE request to UE 1, indicating to UE 1 that the remote UE requests that the session is to be released.

7-8. SIP BYE request (SCC AS to UE 2 via intermediate IM CN subsystem entities)

The SCC AS, acting as a routing B2BUA sends a SIP BYE request to UE 2 to release the dialog it is involved in with UE 3 via the Collaborative Session. There is no Inter UE transfer specific content in the SIP BYE request.

NOTE 1: Step 7 can occur in parallel with step 5. Alternatively, step 7 can occur prior to step 5. The order in which the SCC AS sends the SIP BYE requests is not considered to be important.

9-10. SIP 200 (OK) response (UE 1 to SCC AS via intermediate IM CN subsystems entities)

UE 1 responds to the received SIP BYE request with a SIP 200 (OK) response.

NOTE 2: Step 9 can occur immediately after UE1 has received the SIP BYE request in step 6.

11-12. SIP 200 (OK) response (UE 2 to SCC AS via intermediate IM CN subsystems entities)

UE 2 responds to the received SIP BYE request with a SIP 200 (OK) response.

13-15. SIP 200 (OK) response (SCC AS to UE 3 via intermediate IM CN subsystem entities)

Upon receiving SIP 200 (OK) responses from UE 1 and UE 2, the SCC AS responds to the SIP BYE request from UE 3 with a SIP 200 (OK) response.

NOTE 3: Step 13 can occur after the SCC AS has received the SIP BYE request step 4 since it is not necessary to wait for SIP BYE requests to UE1 and UE2.