A.15 Signalling flows for collaborative session handling upon loss of collaborative session control
24.3373GPPIP Multimedia (IM) Core Network (CN) subsystem IP Multimedia Subsystem (IMS) inter-UE transferRelease 17Stage 3TS
A.15.1 Introduction
The signalling flows in this subclause demonstrate how a control from controller UE-1 that is lost from the collaborative session can be transferred to UE-2.
A.15.2 Session handling upon controller lost
1. Collaborative session controlled by UE-1
A collaborative session is established between UE-1 and UE-2 and the remote UE with UE-1 acting as the controller UE and UE-2 acting as a controllee UE. For simplicity, other UEs participating in the session are not shown in this flow and only controllee UEs have media flows with the remote UE.
2. SIP BYE (IMS CN to SCC AS)
The S-CSCF receives a SIP BYE message with a reason header 503 (Service Unavailable) from P-CSCF that detecting the lost of UE, it routes this SIP BYE message to SCC AS of the session.
3. SCC AS checks the controller loss preference user preference
The SCC AS checks the controller loss preference user preference and selects a candidate UE as new controller. Otherwise the session is released.
4. SIP re-INVITE request (SCC AS to intermediate IM CN subsystem entities) – see example in table A.15.2-4
The SCC AS sends a SIP re-INVITE request towards the Controllee UE (UE-2). The re-INVITE request contains the XML body from the URI in the Refer-To header field from the SIP REFER request.
Table A.15.2-4: SIP re-INVITE request (SCC-AS to IM CN subsystem entities)
INVITE sip:user2_public1@home1.net;gr=urn:uuid:f 81d4fae-7dec-11d0-a765-00a0c91e6bf6 SIP/2.0
Via:
Route:
To: sip:user2_public1@home1.net;abcdef
From: sip:user3_public3@home3.net;tag=123456
Call-ID:
CSeq:
Max-Forwards:
Require:
Contact: sip:user3_public3@home3.net;gr=urn:uuid:f81d4fae-17oct-11a1-a678-0054c91eabcd
Allow:
Accept: application/vnd.3gpp.iut+xml
Content-Type: multipart/mixed;boundary="boundary1"
Content-Length: {…}
–boundary1
Content-Type: application/sdp
v=0
o=- 1027933615 1027933615 IN 132.54.76.98
s=-
c=IN IP4 132.54.76.98
t=0 0
m=audio 0 RTP/AVP 97
m=video 3002 RTP/AVP 98 99
b=AS:75
a=rtpmap:98 H263
a=fmtp:98 profile-level-id=0
a=rtpmap:99 MP4V-ES
–boundary1
Content-Type: application/vnd.3gpp.iut+xml;handling=optional
<controlTransfer>
<targetController=<sip:user2_public2@home2.net;gr=urn:uuid:f81d4fae-7dec-11d0-a762-00a0c91e6bf6>/>
</ControlTansfer>
–boundary1
5. SIP re-INVITE request (intermediate IM CN subsystem entities to UE-2)
6-7. SIP 200 (OK) response (UE-2 to SCC AS through intermediate IM CN subsystem entities)
UE-2 accepts the transfer of control and indicates this by including a g.3gpp.current-iut-controller media feature tag set to Active in the SIP 200 (OK) response it sends to the SCC AS.
Table A.15.2-6: SIP 200 (OK) response (UE-2 to SCC-AS)
SIP/2.0 200 OK
Via:
To: sip:user1_public2@home1.net;tag=xyzwv
From: sip:interUEtransfer@example.net; tag = 12486
Call-ID:
CSeq:
P-Preferred-Identity:
Contact: sip:user1_public2@home1.net;gr=urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6;+g.3gpp current-iut-controller=Active
Allow:
Content-Type: application/sdp
Content-Length: (…)
v=0
o=- 1027933615 1027933615 IN IP4 145.23.77.88
s=-
c=145.23.77.88
t=0 0
m=audio 0 RTP/AVP 97
m=video 1302 RTP/AVP 98 99
b=AS:75
a=rtpmap:98 H263
a=fmtp:98 profile-level-id=0
a=rtpmap:99 MP4V-ES
8-9. SIP ACK request (from SCC-AS to UE-2)
10. Collaborative session controlled by UE-2