A.5.5 CAT diverting for CFNR using reINVITE request when UE#1, UE#2 and UE#3 have resources available

24.1823GPPIP Multimedia Subsystem (IMS) Customized Alerting Tones (CAT)Protocol specificationRelease 17TS

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

Figures A.5.5-1a and A.5.5-1b show an example CAT signalling flow for a successful communication forwarding on no reply based on a CDIV AS providing the forwarding.

Figure A.5.5-1a: CAT with CFNR, no resource reservation

Figure A.5.5-1b: CAT with CFNR, no resource reservation

1 INVITE request (UE#1 to S-CSCF) see example in table A.5.5-1

UE#1 sends a SIP INVITE request to the intermediate IM CN subsystem with UE#2 as the desired called UE. The URI-UE#2 is subscribed to the CFNR service.

Table A.5.5-1: INVITE request (UE#1 to CAT-AS)

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

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

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

Privacy: none

P-Early-Media: supported

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

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

Call-ID: cb03a0s09a2sdfglkj490333

Cseq: 127 INVITE

Require: sec-agree

Recv-Info: infoDtmf

Supported: precondition, 100rel, gruu, 199

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>;+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

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

a=tcap:1 RTP/AVPF

a=pcfg:1 t=1

b=AS:75

a=curr:qos local sendrecv

a=curr:qos remote none

a=des:qos mandatory local sendrecv

a=des:qos none remote sendrecv

a=rtpmap:98 H263

a=fmtp:98 profile-level-id=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; maxframes=2

a=rtpmap:96 telephone-event

Supported: The UE indicates support for GRUU, 199 responses, reliable provisional responses and preconditions.

P-Early-Media: The UE indicates support for the P-Early-Media header.

Recv-Info: The UE indicates willingness to receive DTMF Info Packages in INFO requests.

SDP The SDP offer (SDP_O) contains a set of codecs supported by UE#1 and desired by the calling user for this session. The local preconditions are indicated as fulfilled.

2 INVITE request (S-CSCF to CDIV AS)

The S-CSCF forwards the SIP INVITE request to the CDIV AS.

3-5 INVITE request (CDIV AS to CAT-AS)

Via the S-CSCF, the CDIV AS forwards the request to the CAT-AS serving UE#2.

The CAT-AS instructs the MRF to reserve CAT resources.

5-6 INVITE request (CAT-AS to UE#2)

The CAT-AS forwards the request to UE#2.

7-8 180 (Ringing) provisional response (UE#2 to CAT-AS)

The called party is alerted. UE#2 sends a SIP 180 (Ringing) provisional response for the INVITE request to the CAT-AS.

The CAT-AS terminates the provisional response.

9-12 180 (Ringing) provisional response (CAT-AS to UE#1) see example in table A.5.5-2

The CAT-AS sends a reliable SIP 180 (Ringing) provisional response to UE#1. The CDIV AS starts the no reply timer.

Table A.5.5-2: 180 (Ringing) response (CAT-AS to UE#1)

SIP/2.0 180 Ringing

Via: SIP/2.0/UDP scscf2.home2.net;branch=z9hG4bK764z87.1, SIP/2.0/UDP icscf2_s.home2.net;branch=z9hG4bK871y12.1, SIP/2.0/UDP scscf1.home1.net;branch=z9hG4bK332b23.1, SIP/2.0/UDP pcscf1.visited1.net;branch=z9hG4bK240f34.1, SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd]:1357;comp=sigcomp;branch=z9hG4bKnashds7

Record-Route: <sip:scscf2.home2.net;lr>, <sip:scscf1.home1.net;lr>, <sip:pcscf1.visited1.net;lr>

From:

To: <tel:+1-212-555-2222>;tag=2236

Call-ID:

Cseq:

Require: 100rel

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

RSeq: 9022

P-Early-Media: sendrecv

Contact: <sip:cat-as.home1.net>;+g.3gpp.icsi-ref="urn%3Aurn-7%3gpp-service.ims.icsi.mmtel"

Content-Type: application/sdp

Content-Length: (…)

v=0

o=- 29879336156 29879336156 IN IP6 5555::ccc:aaa:abc:abc

s=-

c=IN IP6 5555::ccc:aaa:abc:abc

t=0 0

m=video 340051372 RTP/AVPF 98

a=acfg:1 t=1

b=AS:75

a=curr:qos local sendrecv

a=curr:qos remote sendrecv

a=des:qos mandatory local sendrecv

a=des:qos mandatory remote sendrecv

a=rtpmap:98 H263

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

a=content:g.3gpp.cat

m=audio 49170 RTP/AVPF 97 96

a=acfg:1 t=1

b=AS:25.4

a=curr:qos local sendrecv

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

a=rtpmap:96 telephone-event

a=content:g.3gpp.cat

P-Early-Media: The CAT-AS requests authorization for early media.

SDP The SDP answer (SDP_A_cat) contains a set of codecs supported to be used for CAT and, in this example, includes a SDP "a=content" attribute with a "g.3gpp.cat" value for each media description. The SDP content is based on information received from the MRF. The local preconditions are indicated as fulfilled.

13 PRACK request (UE#1 to CAT-AS)

UE#1 sends a SIP PRACK request, which acknowledges the SIP 183 (Session Progress) provisional response, to the CAT-AS.

The CAT-AS instructs the MRF to play CAT media.

14 200 (OK) response to PRACK (CAT-AS to UE#1)

A SIP 200 (OK) response sent by the CAT-AS for the SIP PRACK request traverses through CDIV AS and S-CSCF to UE#1.

15 No reply timer expires

The no reply timer expires.

16-19 CANCEL request (CDIV AS to CAT-AS) and 200 (OK) response to CANCEL request (CAT-AS to CDIV AS)

The CDIV AS sends CANCEL request to the CAT-AS. The CAT AS instructs the MRF to stop CAT media. The CAT-AS sends 200 (OK) response for the CANCEL request to the CDIV AS.

20-23 CANCEL request (CAT-AS to UE#2) and 200 (OK) response to CANCEL request (UE#2 to CAT-AS)

The CAT-AS sends CANCEL request to UE#2. The UE#2 sends 200 (OK) response for the CANCEL request to the CAT-AS.

24 181 (Call Is Being Forwarded) response (CDIV AS to UE#1)

Depending on the value of CDIV subscription option "Originating user receives notification that his communication has been diverted (forwarded or deflected)", a 181 (Call Is Being Forwarded) response is sent towards UE#1 indicating that the communication is diverted.

25-28 487 (Request Terminated) response (CAT-AS to CDIV) and ACK request

A 487 (Request Terminated) response with a ACK request finalize the termination of the dialog between CDIV AS and CAT-AS.

29-32 487 (Request Terminated) response (UE#2 to CAT-AS) and ACK request

A 487 (Request Terminated) response with a ACK request finalize the termination of the dialog between CAT-AS and UE#2.

33 INVITE request (CDIV AS to S-CSCF) see example in table A.5.5-3

An INVITE request including URI-UE#3 as destination is sent towards the S-CSCF. Additional the History-Info header is included.

Table A.5.5-3: INVITE request (CDIV AS to UE#3)

SIP/2.0 200 OK

Via: SIP/2.0/UDP pcscf2.visited2.net:5088;comp=sigcomp;branch=z9hG4bK361k21.1, SIP/2.0/UDP scscf2.home2.net;branch=z9hG4bK764XC12.1, SIP/2.0/UDP catas.home2.net;branch=z9hG4bK764Q32.1, SIP/2.0/UDP scscf2.home2.net;branch=z9hG4bK764z87.1, SIP/2.0/UDP icscf2_s.home2.net;branch=z9hG4bK871y12.1, SIP/2.0/UDP scscf1.home1.net;branch=z9hG4bK332b23.1, SIP/2.0/UDP pcscf1.visited1.net;branch=z9hG4bK240f34.1, SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd]:1357;comp=sigcomp;branch=z9hG4bKnashds7

Record-Route: <sip:pcscf2.visited2.net:5088;lr;comp=sigcomp>, <sip:scscf2.home2.net;lr>, <sip:catas.home2.net;lr>, <sip:scscf2.home2.net;lr>, <sip:scscf1.home1.net;lr>, <sip:pcscf1.visited1.net;lr>

From:

To: <tel:+1-212-555-2222>;tag=2236

Call-ID:

Cseq:

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

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

Content-Type: application/sdp

Content-Length: (…)

v=0

o=- 29879336157 29879336157 IN IP6 6666::eee:fff:aaa:bbb

s=-

c=IN IP6 6666::eee:fff:aaa:bbb

t=0 0

m=video 7398 RTP/AVPF 98

b=AS:75

a=curr:qos local sendrecv

a=curr:qos remote sendrecv

a=des:qos mandatory local sendrecv

a=des:qos mandatory remote sendrecv

a=rtpmap:98 H263

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

m=audio 8386 RTP/AVPF 97 96

b=AS:25.4

a=curr:qos local sendrecv

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

a=rtpmap:96 telephone-event

SDP The SDP offer (SDP_O) contains a set of codecs to be used for the session. If preconditions are used, they are indicated as fulfilled.

34 INVITE request (S-CSCF to CAT-AS)

The S-CSCF forwards the INVITE request to the CAT-AS serving UE#3.

The CAT-AS instructs the MRF to reserve CAT resources.

35-36 INVITE request (CAT-AS to UE#3)

The CAT-AS forwards the request to UE#3.

37-38 180 (Ringing) provisional response (UE#3 to CAT-AS)

The called party is alerted. UE#3 sends a SIP 180 (Ringing) provisional response for the INVITE request to the CAT-AS.

The CAT-AS terminates the provisional response.

39-40 183 (Session Progress) provisional response (CAT-AS to CDIV AS) see example in table A.5.5-4

The CAT-AS sends a reliable SIP 183 (Session Progress) provisional response to CDIV AS.

Table A.5.5-4: 183 (Session Progress) response (CAT-AS to CDIV AS)

SIP/2.0 183 Session Progress

Record-Route: <sip:scscf2.home2.net;lr>, <sip:scscf1.home1.net;lr>, <sip:pcscf1.visited1.net;lr>

From:

To: <tel:+1-212-555-2222>;tag=2236

Call-ID:

Cseq:

Require: 100rel

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

RSeq: 9022

P-Early-Media: sendrecv

Contact: <sip:cat-as.home1.net>;+g.3gpp.icsi-ref="urn%3Aurn-7%3gpp-service.ims.icsi.mmtel"

Content-Type: application/sdp

Content-Length: (…)

v=0

o=- 29879336156 29879336156 IN IP6 5555::ccc:aaa:abc:abc

s=-

c=IN IP6 5555::ccc:aaa:abc:abc

t=0 0

m=video 51372 RTP/AVPF 98

a=acfg:1 t=1

b=AS:75

a=curr:qos local sendrecv

a=curr:qos remote sendrecv

a=des:qos mandatory local sendrecv

a=des:qos mandatory remote sendrecv

a=rtpmap:98 H263

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

m=audio 49170 RTP/AVPF 97 96

a=acfg:1 t=1

b=AS:25.4

a=curr:qos local sendrecv

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

a=rtpmap:96 telephone-event

P-Early-Media: The CAT-AS requests authorization for early media.

SDP The SDP answer (SDP_A_cat#3) contains a set of codecs supported to be used for CAT. The SDP content is based on information received from the MRF. The local preconditions are indicated as fulfilled.

41 UPDATE request (CDIV AS to UE#1) see example in table A5.5-5

The CDIV AS sends UPDATE request to UE#1.

Table A.5.5-5: UPDATE request (CDIV AS to UE#1)

SIP/2.0 183 Session Progress

Record-Route: <sip:scscf2.home2.net;lr>, <sip:scscf1.home1.net;lr>, <sip:pcscf1.visited1.net;lr>

From:

To: <tel:+1-212-555-2222>;tag=2236

Call-ID:

Cseq:

Require: 100rel

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

RSeq: 9022

P-Early-Media: sendrecv

Contact: <sip:cat-as.home1.net>;+g.3gpp.icsi-ref="urn%3Aurn-7%3gpp-service.ims.icsi.mmtel"

Content-Type: application/sdp

Content-Length: (…)

v=0

o=- 29879336156 29879336278 IN IP6 5555::ccc:aaa:abc:abc

s=-

c=IN IP6 5555::ccc:aaa:abc:abc

t=0 0

m=video 51372 RTP/AVPF 98

a=acfg:1 t=1

b=AS:75

a=curr:qos local sendrecv

a=curr:qos remote sendrecv

a=des:qos mandatory local sendrecv

a=des:qos mandatory remote sendrecv

a=rtpmap:98 H263

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

m=audio 49170 RTP/AVPF 97 96

a=acfg:1 t=1

b=AS:25.4

a=curr:qos local sendrecv

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

a=rtpmap:96 telephone-event

SDP The SDP offer (SDP_A_cat_#3) contains a set of codecs supported to be used for CAT. The SDP content is based on information received in previous 183 response.

42 200 (OK) response (UE#1 to CDIV AS) see example in table A5.5-6

The UE#1 sends 200 (OK) response for the UPDATE request to CDIV AS. UE#1 includes a SDP answer (SDP_O_cat_#3) in the 200 (OK) response to the corresponding SIP UPDATE request.

43-44 PRACK request (CDIV AS to CAT-AS)

The CDIV AS sends a SIP PRACK request, which acknowledges the SIP 183 (Session Progress) provisional response, to the CAT-AS. A SDP offer (SDP_O_cat_#3) is included.

45-46 200 (OK) response (CAT-AS to CDIV AS)

The CAT-AS sends a SIP 200 (OK) response for the PRACK request to CDIV AS. A SDP answer (SDP_A2_CAT_#3) is included in the 200(OK) response. The set of codecs supported to be used for CAT is based on information from MRF. The CAT-AS instructs the MRF to play the CAT media.

47-48 200 (OK) response to INVITE (UE#3 to CAT-AS) see example in table A.5.2-6

The called party answers the call. UE#3 sends a SIP 200 (OK) final response for the SIP INVITE request to the CAT-AS.

The CAT-AS instructs the MRF to stop CAT media.

Table A.5.2-6: 200 (OK) response (UE#3 to CAT-AS)

SIP/2.0 200 OK

Record-Route: <sip:pcscf2.visited2.net:5088;lr;comp=sigcomp>, <sip:scscf2.home2.net;lr>, <sip:catas.home2.net;lr>, <sip:scscf2.home2.net;lr>, <sip:scscf1.home1.net;lr>, <sip:pcscf1.visited1.net;lr>

From:

To: <tel:+1-212-555-2222>;tag=2236

Call-ID:

Cseq:

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

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

Content-Type: application/sdp

Content-Length: (…)

v=0

o=- 29879336157 29879336157 IN IP6 6666::eee:fff:aaa:bbb

s=-

c=IN IP6 6666::eee:fff:aaa:bbb

t=0 0

m=video 7398 RTP/AVPF 98

b=AS:75

a=curr:qos local sendrecv

a=curr:qos remote sendrecv

a=des:qos mandatory local sendrecv

a=des:qos mandatory remote sendrecv

a=rtpmap:98 H263

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

m=audio 8386 RTP/AVPF 97 96

b=AS:25.4

a=curr:qos local sendrecv

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

a=rtpmap:96 telephone-event

SDP The SDP answer (SDP_A_regular_#3) contains a set of codecs to be used for the session. If preconditions are used, they are indicated as fulfilled.

49-50 ACK request (CAT-AS to UE#3)

CAT-AS sends a SIP ACK request, which acknowledges the SIP 200 (OK) final response, to UE#3.

51-52 reINVITE request (CAT-AS to UE#3)

The CAT-AS sends a SIP reINVITE request without SDP to UE#3.

53-54 200 (OK) response to reINVITE request (UE#3 to CAT-AS) see example in table A.5.2-7

UE#3 sends a SIP 200 (OK) response for the SIP reINVITE request with SDP_O2_regular_#3 to the CAT-AS.

Table A.5.2-7: 200 (OK) response (UE#3 to CAT-AS)

SIP/2.0 200 OK

Record-Route: <sip:pcscf2.visited2.net:5088;lr;comp=sigcomp>, <sip:scscf2.home2.net;lr>, <sip:catas.home2.net;lr>, <sip:scscf2.home2.net;lr>, <sip:scscf1.home1.net;lr>, <sip:pcscf1.visited1.net;lr>

From:

To: <tel:+1-212-555-2222>;tag=2236

Call-ID:

Cseq:

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

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

Content-Type: application/sdp

Content-Length: (…)

v=0

o=- 29879336157 29879336157 IN IP6 6666::eee:fff:aaa:bbb

s=-

c=IN IP6 6666::eee:fff:aaa:bbb

t=0 0

m=video 7398 RTP/AVPF 98

b=AS:75

a=curr:qos local sendrecv

a=curr:qos remote sendrecv

a=des:qos mandatory local sendrecv

a=des:qos mandatory remote sendrecv

a=rtpmap:98 H263

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

m=audio 8386 RTP/AVPF 97 96

b=AS:25.4

a=curr:qos local sendrecv

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

a=rtpmap:96 telephone-event

SDP The SDP offer (SDP_O2_regular_#3) contains a set of codecs supported by UE#3 and desired by the called user for this session. The local preconditions are indicated as fulfilled.

55 UPDATE request (CAT-AS to UE#1) see example in table A.5.2-8

The CAT-AS sends an UPDATE request containing values received in the 200 (OK) response from UE#3.

Session between UE#1 and CAT-AS is replaced with session between UE#1 and UE#3.

Table A.5.2-8: UPDATE request (CAT-AS to UE#1)

UPDATE sip:user1_public1@home1.net;gr=urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6 SIP/2.0

Via: SIP/2.0/UDP [5555::ccc:aaa:abc:abc]:8805;branch=z9hG4bK182D87.1

Max-Forwards: 70

Route: <sip:scscf1.home1.net;lr>, <sip:pcscf1.visited1.net;lr>

From: <tel:+1-212-555-2222>;tag=2236

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

Call-ID:

Cseq: 12814111 UPDATE

Require:

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

Content-Type: application/sdp

Content-Length: (…)

v=0

o=- 29879336156 29879336389 IN IP6 5555::ccc:aaa:abc:abc

s=-

c=IN IP6 6666::eee:fff:aaa:bbb

t=0 0

m=video 7398 RTP/AVPF 98

b=AS:75

a=curr:qos local sendrecv

a=curr:qos remote sendrecv

a=des:qos mandatory local sendrecv

a=des:qos mandatory remote sendrecv

a=rtpmap:98 H263

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

m=audio 8386 RTP/AVPF 97 96

b=AS:25.4

a=curr:qos local sendrecv

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

a=rtpmap:96 telephone-event

SDP The SDP offer (SDP_O2_regular_#3) contains a set of codecs to be used for the session. The SDP content is based on information received from previous 200 (OK) response (step 52). The local preconditions are indicated as fulfilled.

56 200 (OK) response (UE#1 to CAT-AS)

UE#1 sends a SIP 200 (OK) response for the SIP UPDATE request to CAT-AS. UE#1 includes a SDP answer (SDP_A2_regular_#3) in the 200 (OK) response to the corresponding SIP UPDATE request.

57 200 (OK) response to INVITE request (CAT-AS to UE#1)

The CAT-AS sends the SIP 200 (OK) response for the (initial) SIP INVITE request to UE#1.

58 ACK request (UE#1 to CAT-AS)

UE#1 sends a SIP ACK request, which acknowledges the SIP 200 (OK) final response, to CAT-AS.

59-60 ACK request (CAT-AS to UE#2)

CAT-AS sends a SIP ACK request, which acknowledges the SIP 200 (OK) final response (step 54), with SDP answer (SDP_A2_regular_#3) to UE#2.