A.17.6 Session transfer for originating call is in alerting phase with forked responses using PS to CS SRVCC procedure: PS to CS

24.2373GPPIP Multimedia (IM) Core Network (CN) subsystem IP Multimedia Subsystem (IMS) service continuityRelease 17Stage 3TS

In the example flow at the figure A.17.6-1, SC UE A initiates an originating session with speech media component which has received several forked responses. The call is anchored at SCC AS and in alerting phase. Based upon measurement reports sent from the UE to E-UTRAN, the source E-UTRAN decides to trigger a PS to CS SRVCC handover to CS access.

Figure A.17.6-1: PS-CS SRVCC, originating call in alerting phase with forked responses

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

1-4. SIP INVITE request (SC UE A to Terminating network Intermediate IM CN subsystem entities) – see example in table A.17.6-1

SC UE A sends an outgoing call to the terminating party. The call has been anchored at the SCC AS.

Table A.17.6-1: SIP INVITE request (UE to Intermediate IM CN subsystem entities)

INVITE tel:+1-212-555-2222 SIP/2.0

Via: SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd]:1357;comp=sigcomp;branch=z9hG4bKnashds7

Max-Forwards: 70

Route: <sip:pcscf1.visited2.net:7531;lr;comp=sigcomp>, <sip:orig@scscf1.home1.net;lr>

P-Preferred-Identity: "John Doe" <sip:user1_public1@home1.net>

P-Preferred-Service: urn:urn-7:3gpp-service.ims.icsi.mmtel

P-Access-Network-Info: 3GPP-UTRAN-TDD; utran-cell-id-3gpp=234151D0FCE11

Privacy: none

From: <sip:user1_public1@home1.net>;tag=171828

To: <tel:+1-212-555-2222>

Call-ID: cb03a0s09a2sdfglkj490333

Cseq: 127 INVITE

Require: sec-agree

Supported: precondition, 100rel, gruu, norefersub

Proxy-Require: sec-agree

Security-Verify: ipsec-3gpp; q=0.1; alg=hmac-sha-1-96; spi-c=98765432; spi-s=87654321; port-c=8642; port-s=7531

Contact: <sip:user1_public1@home1.net;gr=urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6;comp=sigcomp>;+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel"

Accept-Contact: *;+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel"

Allow: INVITE, ACK, CANCEL, BYE, PRACK, UPDATE, REFER, MESSAGE

Content-Type: application/sdp

Content-Length: (…)

v=0

o=- 2987933615 2987933615 IN IP6 5555::aaa:bbb:ccc:ddd

s=-

c=IN IP6 5555::aaa:bbb:ccc:ddd

t=0 0

m=audio 3456 RTP/AVP 97 96

b=AS:25.4

a=curr:qos local sendrecv

a=curr:qos remote none

a=des:qos mandatory local sendrecv

a=des:qos none remote sendrecv

a=rtpmap:97 AMR

a=fmtp:97 mode-set=0,2,5,7; maxframes=2

a=rtpmap:96 telephone-event

5. SIP INVITE request (Terminating network Intermediate IM CN subsystem entities to UE B)

The Terminating network Intermediate IM CN subsystem entities, i.e. S-CSCF serving for remote UE, determine that the SIP INVITE request should be forked, and send the SIP INVITE request to UE B.

6. SIP INVITE request (Terminating network Intermediate IM CN subsystem entities to UE C)

The Terminating network Intermediate IM CN subsystem entities, i.e. S-CSCF serving for remote UE, determine that the SIP INVITE request should be forked, and send the SIP INVITE request to UE C.

7-11. SIP 180 (Ringing) response to SIP INVITE request (UE B to UE A though SCC AS)

The remote UE B responds with SIP 180 (Ringing) response. And a dialog (dialog 1) has been established between UE A and UE B.

Table A.17.6-7: SIP 180 (Ringing) response (UE B to Terminating network Intermediate IM CN subsystem entities)

SIP/2.0 180 Ringing

Record-Route: <sip:pcscf1.visited1.net;lr>

Via:

Max-Forwards: 60

P-Asserted-Identity: <tel:+1-212-555-2222>

Privacy:

From:

To: <tel:+1-212-555-2222>; tag=aaa

Call-ID:

Cseq:

Require:

Supported:

Contact: <sip:user2_public1@home2.net;gr=urn:uuid:2ad8950e-48a5-4a74-8d99-ad76cc7fc74>;+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel"

Allow:

Content-Type:

Content-Length:

v=0

o=- 462346 5654 IN IP6 1234::55:66:77:88

s=-

c=IN IP6 1234::55:66:77:88

t=0 0

m=audio 4456 RTP/AVP 97 96

b=AS:25.4

a=curr:qos local none

a=curr:qos remote sendrecv

a=des:qos mandatory local sendrecv

a=des:qos mandatory remote sendrecv

a=rtpmap:97 AMR

a=fmtp:97 mode-set=0,2,5,7; maxframes=2

a=rtpmap:96 telephone-event

12-16. SIP 180 (Ringing) response to SIP INVITE request (UE C to UE A though SCC AS)

The remote UE C responds with SIP 180 (Ringing) response. And a dialog (dialog 2) has been established between UE A and UE B.

Table A.17.6-12: SIP 180 (Ringing) response (UE B to Terminating network Intermediate IM CN subsystem entities)

SIP/2.0 180 Ringing

Record-Route: <sip:pcscf1.visited1.net;lr>

Via:

Max-Forwards: 60

P-Asserted-Identity: <tel:+1-212-555-2222>

Privacy:

From:

To: <tel:+1-212-555-2222>; tag=bbb

Call-ID:

Cseq:

Require:

Supported:

Contact: <sip:user2_public1@home2.net;gr=urn:uuid:2ad8950e-48a5-4a74-8d99-ad76cc7fc74>;+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel"

Allow:

Content-Type:

Content-Length:

v=0

o=- 462346 5654 IN IP6 1234::55:66:77:88

s=-

c=IN IP6 1234::55:66:77:88

t=0 0

m=audio 4456 RTP/AVP 97 96

b=AS:25.4

a=curr:qos local none

a=curr:qos remote sendrecv

a=des:qos mandatory local sendrecv

a=des:qos mandatory remote sendrecv

a=rtpmap:97 AMR

a=fmtp:97 mode-set=0,2,5,7; maxframes=2

a=rtpmap:96 telephone-event

17. SC UE A attaches to the CS domain

UE A sends the measurement reports to E-UTRAN, and the source E-UTRAN decides to trigger an PS to CS SRVCC handover to CS access. The MSC server initiates the session transfer with the STN-SR, refer to 3GPP TS 23.237 [9]. The UE continues ringing.

18. SIP INVITE request transferring the session (MSC server to originating network intermediate IM CN subsystem entities) – see example in table A.17.6-18

The MSC server sends an initial SIP INVITE request with STN-SR

Table A.17.6-18: SIP INVITE request (MSC server to intermediate IM CN subsystem entities)

INVITE tel: +1-237-555-3333 SIP/2.0

Via: SIP/2.0/UDP msc1.visit1.net;branch=z9hG4bk731b87

Max-Forwards: 70

Route: <sip:icscf1.visit1.net;lr>

P-Asserted-Identity: <tel:+1-237-555-1111>

P-Charging-Vector: icid-value="AyretyU0dm+6O2IrT5tAFrbHLso=023551024";orig-ioi=visit1.net

Privacy: none

From: <tel:+1-237-555-1111>;tag=171828

To: <tel:+1-237-555-3333>

Call-ID: cb03a0s09a2sdfglkj490334

Cseq: 127 INVITE

Supported: 100rel, precondition, gruu, norefersub

Accept-Contact: *;+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel"

P-Asserted-Service: urn:urn-7:3gpp-service.ims.icsi.mmtel

Contact: <sip: msc1.visit1.net:1357>;+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel"

Allow: INVITE, ACK, CANCEL, BYE, PRACK, UPDATE, REFER

Recv-Info: g.3gpp.state-and-event

Content-Type: application/sdp

Content-Length: (…)

P-Early-Media: supported

v=0

o=- 2987933615 2987933615 IN IP6 5555::aaa:bbb:ccc:eee

s=

c=IN IP6 5555::aaa:bbb:ccc:eee

t=0 0

m=audio 3456 RTP/AVP 97 96

a=tcap:1 RTP/AVPF

a=pcfg:1 t=1

b=AS:25.4

a=curr:qos local sendrecv

a=curr:qos remote none

a=des:qos mandatory local sendrecv

a=des:qos none remote sendrecv

a=rtpmap:97 AMR

a=fmtp:97 mode-set=0,2,5,7; mode-change-period=2

a=rtpmap:96 telephone-event

a=maxptime:20

Request-URI: contains the STN-SR.

SDP: The SDP contains set of codecs supported by the MGW.

19. SIP INVITE request transferring the session (intermediate IM CN subsystem entities to SCC AS)

The SIP INVITE is routed towards the SCC AS, based on filter criteria in S-CSCF.

20. Remote Leg Update

The SCC AS correlates SIP INVITE request to the local and remote call legs of the existing session between the UE A and the remote end. Since the existing session has forked responses, more than one dialog can be correlated to the SIP INVITE due to STN-SR The SCC AS performs the Remote Leg update towards all the correlated dialogs.

21-23. SIP UPDATE request (SCC AS to UE B through Intermediate IM CN subsystem entities)

The SCC AS acting as a B2BUA generates a SIP UPDATE request towards dialog 1 to remote UE B based upon the received SIP INVITE request in step 19.

24-26. SIP 200 (OK) response (Remote UE B to SCC AS through Intermediate IM CN subsystem entities)

Upon receiving the SIP UPDATE request containing the SDP offer for the leg to the MSC, the remote UE B sends SIP 200 (OK).

27-28. SIP 183 (Session Progress) response (SCC AS to MSC server through Intermediate IM CN subsystem entities)

The SCC AS sends a 183 (Session Progress) containing the SDP answer as received from the remote UE B to the MSC server. The SDP answer indicates that resources are available

29-30. SIP PRACK request (MSC server to SCC AS through Intermediate IM CN subsystem entities)

The MSC acknowledges the receipt of the 183 Session Progress by sending SIP PRACK request to the SCC AS.

31-32. SIP 200 (OK) response (SCC AS to MSC server through Intermediate IM CN subsystem entities)

The SCC AS acknowledges the SIP PRACK request with the SIP 200 (OK) response to the MSC server.

33. SIP INFO request (SCC AS to Originating network intermediate IM CN subsystem entities) – see example in table A.17.6-33

Table A.17.6-33: INFO request (SCC AS to intermediate IM CN subsystem entities)

INFO sip: msc1.visit1.net:1357 SIP/2.0

Via SIP/2.0/UDP sip:sccas1.home1.net;branch=z9hG4bK332b23.1

Max-Forwards: 68

Route: <sip:scscf1.home1.net;lr>

From: <tel: +1-237-555-3333>;tag=314159

To: <tel:+1-237-555-1111>;tag=171828

Call-ID: cb03a0s09a2sdfglkj490334

Cseq: 129 INFO

Info-Package: g.3gpp.state-and-event

Content-Disposition: Info-Package

Content-Type: application/vnd.3gpp.state-and-event-info+xml

Content-Length:

<?xml version="1.0" encoding="UTF-8"?>

<state-and-event-info>

<state-info>early</state-info>

<direction>initiator</direction>

</state-and-event-info>

34. SIP INFO request (Intermediate IM CN subsystem entities to MSC server)

The intermediate IM CN subsystem entities forward the SIP INFO request to the MSC server. The MSC server is aware that the call that is transferred is in originating alerting phase.

35. SIP 200 (OK) response (MSC server to Intermediate IM CN subsystem entities)

The MSC Server acknowledges the receipt of the SIP INFO request.

36. SIP 200 (OK) response (Intermediate IM CN subsystem entities to SCC AS)

The intermediate IM CN subsystem entities forwards the SIP 200 (OK) response to the SCC AS.

37-39. SIP UPDATE request (SCC AS to UE C through Intermediate IM CN subsystem entities)

In parallel with step 21, the SCC AS acting as a B2BUA generates a SIP UPDATE request towards dialog 2 to remote UE C based upon the received SIP INVITE request in step 19.

40-42. SIP 200 (OK) response (Remote UE C to SCC AS through Intermediate IM CN subsystem entities)

Upon receiving the SIP UPDATE request containing the SDP offer for the leg to the MSC, the remote UE C sends a SIP 200 (OK) response.

43-44. SIP 183 (Session Progress) response (SCC AS to MSC server through Intermediate IM CN subsystem entities)

The SCC AS sends a SIP 183 (Session Progress) containing the SDP answer as received from the remote UE C to the MSC server. The SDP answer indicates that resources are available

45-46. SIP PRACK request (MSC server to SCC AS through Intermediate IM CN subsystem entities)

The MSC acknowledges the receipt of the 183 Session Progress by sending SIP PRACK request to the SCC AS.

47-48. SIP 200 (OK) response (SCC AS to MSC server through Intermediate IM CN subsystem entities)

The SCC AS acknowledges the SIP PRACK request with the SIP 200 (OK) response to the MSC server.

49. SIP 200 (OK) response (UE B to intermediate IM CN subsystem entities)

In this example, the remote UE B accepts the call first and sends a SIP 200 (OK) response.

50-51. SIP 200 (OK) response (Intermediate IM CN subsystem entities to SCC AS)

The SIP 200 (OK) response is forwarded to SCC AS.

52-53 SIP 200 (OK) response (SCC AS to MSC server through Intermediate IM CN subsystem entities)

The SIP 200 (OK) response is forwarded to the MSC server based on the route established during step 24-28.

54 CC CONNECT message (MSC server to SC UE A)

The MSC server indicates to the SC UA A that the remote UE B has accepted the call.

55-59. SIP ACK request (MSC server to remote UE B through intermediate IM CN subsystem entities)

The MSC server acknowledges the SIP 200 (OK) response by sending The SIP ACK request to remote UE B.

60 SIP CANCEL request (Terminating network intermediate IM CN subsystem entities to remote UE C)

The intermediate IM CN subsystem entities send the SIP CANCEL request to remote UE C to release the call towards remote UE C.

61 SIP 200 (OK) response to SIP CANCEL request (UE-3 to Intermediate IM CN subsystem entities)

Remote UE C responds SIP 200 (OK) response to the SIP CANCEL request.

62 CC CONNECT ACKNOWLEDGE message (MSC server to SC UE A)

SC UE A acknowledges the CC CONNECT message.

63–66 The SCC AS releases the original source leg towards the SC UE A

The SCC AS sends a SIP 404 (Not Found) response in order to release to original source dialog towards the SC UE A

NOTE: Steps 64-65 are performed only if the SC UE A Gm after the PS-CS access transfer in alerting phase is completed; otherwise, the SC UE A and the network release the source access leg locally, without any signalling between the SC UE A and the network