A.1 CONF interworking signalling flow in case of an active communication between IMS and PSTN

24.6053GPPConference (CONF) using IP Multimedia (IM) Core Network (CN) subsystemProtocol specificationRelease 18TS

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

Figure A.1 depictures a flow where two UEs are engaged in a call, and one of the users is located in the PSTN. At some point in time, UE A decides to activate the CONF service and move the call to a centralized conference. UE A creates the conference, and provides instructions to the conference server to contact UE B and replace the initial communication with a communication to the conference server.

Figure A.1: CONF interworking signalling flow in case of an active communication
between IMS and PSTN

– Description figure A.1

NOTE: Only the most relevant messages are shown in figure A.1

UE-A is in an active voice session with a PSTN/ISDN TE (SIP dialog with Call-ID, to-tag and from-tag between UE-A and MGCF). It then creates a conference and invites the PSTN/ISDN TE to the conference by sending a REFER to the conference focus, which invites the PSTN/ISDN TE to the conference by sending an INVITE which includes the Replaces header to the MGCF. The MGCF confirms the session, switches the existing bearer channel to the new RTP session, and terminates the session which is replaced.

1. to 3. UE-A initiates a voice session with a PSTN/ISDN TE by sending an INVITE request to the MGCF.

Table A.1: 1.INVITE (UE-A to P-CSCF)

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.visited1.net:7531;lr;comp=sigcomp>, <sip:scscf1.home1.net;lr>

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

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

Proxy-Require: sec-agree

Supported: precondition, 100rel, gruu, 199

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%3gpp-service.ims.icsi.mmtel"

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

Accept:application/sdp,.application/3gpp-ims+xml

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

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

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=video 3400 RTP/AVP 98 99a=tcap:1 RTP/AVPF

a=pcfg:1 t=1

b=AS:75

a=curr:qos local none

a=curr:qos remote none

a=des:qos mandatory local sendrecv

a=des:qos none remote sendrecv

a=inactive

a=rtpmap:98 H263

a=fmtp:98 profile-level-id=0

a=rtpmap:99 MP4V-ES

m=audio 3456 RTP/AVP 97 96a=tcap:1 RTP/AVPF

a=pcfg:1 t=1

b=AS:25.4

a=curr:qos local none

a=curr:qos remote none

a=des:qos mandatory local sendrecv

a=des:qos none remote sendrecv

a=inactive

a=rtpmap:97 AMR

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

a=rtpmap:96 telephone-event

4: Interaction to reserve resources.

5: SS7: IAM.

7: SS7: ANM.

8: Interaction for session establishment.

9 to 11: The MGCF sends a final response back to the session originator.

Table A.2: 9. 200 OK (MGCF to S-CSCF)

SIP/2.0 200 OK

Via: SIP/2.0/UDP bgcf1.home1.net;branch=z9hG4bK6546q2.1, SIP/2.0/UDP scscf1.home1.net;branch=z9hG4bK332b23.1, SIP/2.0/UDP pcscf1.home1.net;branch=z9hG4bK431h23.1, SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd]:1357;comp=sigcomp;branch=z9hG4bKnashds7

Record-Route: <sip:scscf1.home1.net;lr>, <sip:pcscf1.home1.net;lr>

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

P-Charging-Vector:

Privacy: none

From:

To: <tel:+1-212-555-2222>;tag=314159

Call-ID:

CSeq:

Require: 100rel, precondition

Contact: <sip:mgcf1.home1.net;gr>

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

RSeq: 9021

Content-Type: application/sdp

Content-Length: (…)

v=0

o=- 2987933623 2987933623 IN IP6 5555::eee:fff:aaa:bbb

s=-

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

t=0 0

m=video 0 RTP/AVP 98 99

m=audio 6544 RTP/AVPF 97 96a=acfg:1 t=1

b=AS:25.4

a=curr:qos local none

a=curr:qos remote none

a=des:qos mandatory local sendrecv

a=des:qos none remote sendrecv

a=inactive

a=conf:qos remote sendrecv

a=rtpmap:97 AMR

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

a=rtpmap:96 telephone-event

12 to 14: The Calling party acknowledges the final response with an ACK request.

15 to 24: UE-A creates a conference by sending an INVITE request to the Conference Factory URI and connects to the conference.

Table A.3: 15. INVITE request (UE-A to P-CSCF)

INVITE sip:conference-factory1@mrfc1.home1.net SIP/2.0

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

Max-Forwards: 70

Route: <sip:pcscf1.visited1.net:7531;lr;comp=sigcomp>, <sip:orig@scscf1.home1.net;lr>

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

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

Privacy: none

From: <sip:user1_public1@home1.net>; tag=171829

To: <sip:conference-factory1@mrfc1.home1.net>

Call-ID: cb03a0s09a2sdfglkj490444

Cseq: 127 INVITE

Require: sec-agree

Proxy-Require: sec-agree

Supported: precondition, 100rel, gruu, 199

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%3gpp-service.ims.icsi.mmtel"

Accept:application/sdp,.application/3gpp-ims+xml

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

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

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

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=video 3400 RTP/AVP 98 99a=tcap:1 RTP/AVPF

a=pcfg:1 t=1

b=AS:75

a=curr:qos local none

a=curr:qos remote none

a=des:qos mandatory local sendrecv

a=des:qos none remote sendrecv

a=inactive

a=rtpmap:98 H263

a=fmtp:98 profile-level-id=0

a=rtpmap:99:MPVMP4V-ES

m=audio 3456 RTP/AVP 97 96a=tcap:1 RTP/AVPF

a=pcfg:1 t=1

b=AS:25.4

a=curr:qos local none

a=curr:qos remote none

a=des:qos mandatory local sendrecv

a=des:qos none remote sendrecv

a=inactive

a=rtpmap:97 AMR

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

a=rtpmap:96 telephone-event

25 to 27: UE-A invites the PSTN/ISDN TE to the conference by sending a REFER request to the conference focus, the "method" parameter set to "INVITE". The Refer-To header of the REFER request includes the Replaces parameter with Call-ID, to-tag and from‑tag from the existing SIP dialog.

Table A.4: 25. REFER request (UE-A to P-CSCF)

REFER sip: conference1@mrfc1.home1.net SIP/2.0

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

Max-Forwards: 70

Route: <sip:pcscf1.visited1.net:7531;lr;comp=sigcomp>, <sip:orig@scscf1.home1.net;lr>

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

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

Privacy: none

From: <sip:user1_public1@home1.net>; tag=171829

To: <sip:conference1@mrfc1.home1.net>

Call-ID: cb03a0s09a2sdfglkj490555

Cseq: 127 REFER

Require: sec-agree

Refer-To: <sip:mgcf1.home1.net; method=INVITE?Replaces=cb03a0s09a2sdfglkj490333%3Bto-tag%3D314159%3Bfrom-tag%3D171828&Requrie=replaces >

Referred-By: <sip:user1_public1@home1.net>

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%3gpp-service.ims.icsi.mmtel"

Content-Length: 0

27a: Interactions to reserve resources for an additional participant in the conference.

28 to 30: The conference focus sends a NOTIFY request containing information about the progress of the REFER request processing. The Subscription-State is set to "active".

31 to 32: The conference focus invites the PSTN/ISDN TE by sending an INVITE request to the MGCF. The INVITE request includes the Replaces header with Call-ID, to-tag and from-tag from the existing SIP dialog.

Table A.5: 31. INVITE request (MRFC/AS to S-CSCF)

INVITE sip:mgcf1.home1.net SIP/2.0

Via: SIP/2.0/UDP mrfc1.home1.net;branch=z9hG4bK23273846

Max-Forwards: 70

P-Asserted-Identity: <sip:conference1@mrfc1.home1.net>

P-Charging-Vector: icid-value="AyretyU0dm+6O2IrT5tAFrbHLso=023551024"; orig-ioi=home1.net

Privacy: none

From: <sip:conference1@mrfc1.home1.net>;tag=171123

To: <sip:mgcf1.home1.net>

Call-ID: bc03a0s09a2sdfglkj490333

Cseq: 127 INVITE

Require: replaces

Replaces: cb03a0s09a2sdfglkj490333;to-tag=314159;from-tag=171828

Supported: precondition, 100rel

Referred-By: <sip:user1_public1@home1.net>

Contact: <sip:conference1@mrfc1.home1.net>;isfocus

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

Allow-Events: conference

Content-Type: application/sdp

Content-Length: (…)

v=0

o=- 2987933615 2987933615 IN IP6 5555::abc:def:abc:abc

s=-

c=IN IP6 5555::abc:def:abc:def

t=0 0

m=video 10001 RTP/AVP 98

a=tcap:1 RTP/AVPF

a=pcfg:1 t=1

b=AS:75

a=curr:qos local none

a=curr:qos remote none

a=des:qos mandatory local sendrecv

a=des:qos none remote sendrecv

a=inactive

a=rtpmap:98 H263

a=fmtp:98 profile-level-id=0

m=audio 6544 RTP/AVP 97 96a=tcap:1 RTP/AVPF

a=pcfg:1 t=1

b=AS:25.4

a=curr:qos local none

a=curr:qos remote none

a=des:qos mandatory local sendrecv

a=des:qos none remote sendrecv

a=inactive

a=rtpmap:97 AMR

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

a=rtpmap:96 telephone-event

33: Interaction for switching existing bearer channel to new RTP.

34 to 35: The MGCF sends a final response back to the session originator.

35a: Interaction to add the participant to the conference.

36 to 37: The Calling party acknowledges the final response with an ACK request.

38 to 40: The conference focus sends a NOTIFY request containing information about the progress of the REFER request processing. The Subscription-State is set to "terminated".

41: The MGCF replaces the existing RTP stream to UE-A with the new RTP stream to the conferencefocus.

42 to 44: The MGCF releases the session with UE-A by sending a BYE request to UE-A.

45 to 47: UE-A responds with a 200 OK response.