A.5.3 Signalling flows for termination to an ICS UE with CS media using Gm reference point when using an MSC server enhanced for ICS

24.2923GPPIP Multimedia (IM) Core Network (CN) subsystem Centralized Services (ICS)Release 17Stage 3TS

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

Figure A.5.3-1 shows the termination of a call to an ICS UE using CS bearers controlled through the IM CN subsystem. In this example the MSC Server is enhanced for ICS and is capable of translating NAS signalling received from the ICS UE to SIP and vice versa.

Figure A.5.3-1: ICS UE termination with CS media using Gm reference point when using an MSC Server enhanced for ICS

The details of the signalling flows are as follows:

1. SIP INVITE request (originating IM CN subsystem to intermediate IM CN subsystem entities in terminating network) – see example in table A.5.3-1 In this example, the originating UE initiates a voice call though its home IM CN subsystem (home2) with a terminating UE which is ICS capable which is in a different network (home1).

Table A.5.3-1: SIP INVITE request (originating IM CN subsystem to intermediate IM CN subsystem entities in terminating network)

INVITE sip:user2_public1@home1.net SIP/2.0

Via: SIP/2.0/UDP icscf1.home1.net;branch=z9hG4bK871y12.1, SIP/2.0/UDP scscf1.home2.net;branch=z9hG4bK332b23.1, SIP/2.0/UDP pcscf1.visited2.net;branch=z9hG4bK431h23.1, SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd]:1357;comp=sigcomp;branch=z9hG4bKnashds7

Max-Forwards: 67

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

Record-Route: <sip:scscf1.home2.net;lr>, <sip:pcscf1.visted2.net;lr>

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

P-Asserted-Identity: "John Doe" <sip:user1_public1@home2.net>, <tel:+1-212-555-1111>

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

P-Asserted-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

From: <sip:user1_public1@home2.net>;tag=171828

To: <sip:user2_public1@home1.net>

Call-ID: cb03a0s09a2sdfglkj490333

Cseq: 127 INVITE

Supported: 100rel, precondition, gruu, 199

Contact: <sip:user1_public1@home2.net;gr=urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf7>;+g.3gpp.icsi-ref="urn%3Aurn-7%3gpp-service.ims.icsi.mmtel">

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

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 0 96

b=AS:25.4

a=curr:qos local sendrcv

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

NOTE 1: This example assumes the session was originated from a 3GPP Release 8 IMS UE and thus includes the ICSI value defined for MMTel in the Contact header field and Accept Contact header field. However, termination procedures for ICS do not rely upon the MMTel ICSI value being present in the incoming request.

2. SIP 100 (Trying) response (intermediate IM CN subsystem entities to originating IM CN subsystem)

The intermediate IM CN subsystem entities respond to the originating IM CN subsystem with a SIP 100 (Trying) response. There is no ICS specific content in this response.

3. Evaluation of initial filter criteria

The S-CSCF evaluates initial filter criteria for the served ICS user and as a result routes the SIP INVITE request towards the SCC AS.

NOTE 2: for terminating scenario, the SCC AS is configured as the last AS in the terminating iFC chain.

4. SIP INVITE request (intermediate IM CN subsystem entities to SCC AS) – see example in table A.5.3-4

As a result of iFC evaluation, the S-CSCF routes the INVITE request to the SCC AS.

Table A.5.3-4: SIP INVITE request (intermediate IM CN subsystem entities to SCC AS)

INVITE sip:user2_public1@home1.net SIP/2.0

Via: SIP/2.0/UDP scscf1.home1.net;branch=z9hG4bK332b33.1,SIP/2.0/UDP icscf1.home1.net;branch=z9hG4bK871y12.1, SIP/2.0/UDP scscf1.home2.net;branch=z9hG4bK332b23.1, SIP/2.0/UDP pcscf1.visited2.net;branch=z9hG4bK431h23.1, SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd]:1357;comp=sigcomp;branch=z9hG4bKnashds7

Max-Forwards: 66

Route: <sip:sccas.home1.net;lr>, <sip:cb03a0s09a2sdfglkj490333@scscf1.home1.net;lr>;orig-dialog-id="O:73935718_92645110-712786jd246395302d-zKE"

Record-Route: <sip:scscf1.home1.net;lr>, <sip:scscf1.home2.net;lr>, <sip:pcscf1.visited2.net;lr>

P-Access-Network-Info:

P-Asserted-Identity:

P-Charging-Vector:

P-Asserted-Service:

Accept-Contact:

Privacy:

From:

To:

Call-ID:

Cseq:

Supported:

Accept:

Contact:

Allow:

Content-Type:

Content-Length:

v=0

o=-

s=-

5. SIP 100 (Trying) response (SCC AS to intermediate IM CN subsystem entities)

The SCC AS responds to the intermediate IM CN subsystem entities with a SIP 100 (Trying) response. There is no ICS specific content in this response.

6. Terminating Access Domain Selection

The SCC AS performs Terminating Access Domain Selection and chooses the CS domain for the setup of the media.

7. SIP INVITE request (SCC AS to intermediate IM CN subsystem entities) – see example in Table A.5.3-7.

The SCC AS, acting as a routing B2BUA, generates a SIP INVITE request based upon the received SIP INVITE request and send it to the intermediate subsystem entities. The SDP indicates that the ICS UE B should establish a CS media bearer.

Table A.5.3-7: SIP INVITE request (SCC AS to intermediate IM CN subsystem entities)

INVITE sip:user2_public1@home1.net SIP/2.0

Via: SIP/2.0/UDP sccas2.home2.net;branch=z9hG4bKnas34r5

Max-Forwards: 65

Route: <sip:cb03a0s09a2sdfglkj490333@scscf1.home1.net;lr>;orig-dialog-id="O:73935718_92645110-712786jd246395302d-zKE"

Record-Route:<sip:sccas.home1.net;lr>

P-Access-Network-Info:

P-Asserted-Identity:

P-Charging-Function-Addresses: ccf=[5555::b99:c88:d77:e66]; ccf=[5555::a55:b44:c33:d22]; ecf=[5555::1ff:2ee:3dd:4ee]; ecf=[5555::6aa:7bb:8cc:9dd]

P-Charging-Vector:

P-Asserted-Service:

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

Accept-Contact:+*;g.3gpp.ics="principal";explicit;require

Privacy:

From:<sip:user1_public1@home2.net>;tag=274890

To:

Call-ID:

Cseq:

Supported:

Accept:

Contact:

Allow:

Content-Type:

Content-Length:

v=0

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

s=-

c=PSTN E164 +12125556666

t=0 0

m=audio 9 PSTN –

a=setup:passive

a=connection:new

a=cs-correlation:callerid

a=curr: qos local none

a=curr: qos remote none

a=des: qos mandatory local sendrcv

a=des: qos mandatory remote sendrcv

a=inactive

8. SIP 100 (Trying) response (intermediate IM CN subsystem entities to SCC AS)

The intermediate IM CN subsystem entities respond to the SCC AS with a SIP 100 (Trying) response. There is no ICS specific content in this response.

9. SIP INVITE request (intermediate IM CN subsystem entties to ICS UE B)

The SIP INVITE request is routed towards the called party ICS UE B since further iFC evaluation is not necessary.

10. SIP 100 (Trying) response (ICS UE B to intermediate IM CN subsystem entities)

The ICS UE B responds to the intermediate IM CN subsystem entities with a SIP 100 (Trying) response. There is no ICS specific content in this response.

11 SIP 183 (Session Progress) response (ICS UE B to intermediate IM CN subsystem entities) – see example in table A.5.3-11

The ICS UE generates a SIP 183 (Session Progress) response based upon the received SIP INVITE request and indicates in the SDP that the CS media bearer is used.

Table A.5.3-11: SIP 183 (Session Progress) response (ICS UE to intermediate IM CN subsystem entities)

SIP/2.0 183 Session Progress

Via: SIP/2.0/UDP pcscf1.home1.net;branch=z9hG4bK240f34.1,

SIP/2.0/UDP scscf1.home1.net;branch=z9hG4bK332b23.1,

SIP/2.0/UDP sccas.home1.net;branch=z9hG4bKnas34r5,

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

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

P-Charging-Vector: icid-value="AyretyU0dm+6O2IrT5tAFrbHLso=023551024"

Privacy: none

From: <sip:user1_public1@home2.net>;tag=171828

To: <sip:user2_public1@home1.net>;tag=171820

Call-ID:

CSeq:

Require: 100rel

Contact: <sip:user2_public1@home1.net;gr=urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6>;+g.3gpp.icsi-ref="urn%3Aurn-7%3gpp-service.ims.icsi.mmtel";+g.3gpp.ics="principal"

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

t=0 0

m=audio 9 PSTN –

c=PSTN – –

a=setup:active

a=connection:new

a=cs-correlation:callerid:+12125552222

a=curr:qos local none

a=curr:qos remote none

a=des:qos mandatory local sendrecv

a=des:qos mandatory remote sendrecv

12. SIP 183 (Session Progress) response (intermediate IM CN subsystem entities to SCC AS)

The SIP 183 (Session Progress) response is routed towards the SCC AS.

13. SETUP message (ICS UE B to MSC Server enhanced for ICS)

The ICS UE B inititates bearer setup in the CS domain by sending a SETUP message to the MSC Server enhanced for ICS.

Specifically for this signalling flow, the SETUP message includes:

– Called Party Number information element = = [(Numbering plan identifier = ISDN/telephony numbering plan), (type of number = international number ), (Number digits = 1212556666)]. The Called Party Number information element is set to the SCC AS PSI DN.

– Bearer Capability information element = [(information transfer capability = speech), (speech versions = FR AMR, GSM EFR, GSM FR)]

– Supported Codec List information element = {[(SysID 1 = UMTS), (Codec Bitmap for SysID 1 = UMTS AMR 2)], [(SysID 2 = GSM), (Codec Bitmap for SysID 2 = FR AMR, GSM EFR, GSM FR)]}

The MSC Server enhanced for ICS knows the calling party number corresponding to the ICS UE B.

14. CALL PROCEEDING message (MSC Server enhanced for ICS to ICS UE B)

Upon receipt of the SETUP message from the ICS UE B, the MSC Server enhanced for ICS responds with a CALL PROCEEDING message. There is no ICS specific content in this message.

15. SIP INVITE request (MSC Server enhanced for ICS to intermediate IM CN subsystem entities) – see example in table A.5.3-15.

The MSC Server enhanced for ICS maps the received SETUP message to a SIP INVITE request which is routed towards the intermediate IM CN subsystem entities. The INVITE request is addressed to the SCC AS PSI DN in the Request-URI.

Table A.5.3-15: SIP INVITE request (MSC Server enhanced for ICS to intermediate IM CN subsystem entities)

INVITE tel:+1-212-555-6666 SIP/2.0

Via: SIP/2.0/UDP msc2.home1.net;branch=z9hG4bKnashds7

Max-Forwards: 70

Route: <sip:icscf1.home1.net:lr>

P-Asserted-Identity: <sip:user2_public1@home1.net>,<tel:+1-212-555-2222>

P-Charging-Vector: icid-value="AyretyU0dm+6O2IrT5tAFrbHLso=023551024"; orig-ioi=home2.net

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

P-Access-Network-Info:

Privacy: none

From: <sip:user2_public1@home1.net>;tag=171828

To: <tel:+1-212-555-6666>

Call-ID: f81d4fae-7dec-11d0-a765-00a0c91e6bf6

Cseq: 127 INVITE

Supported: 100rel, precondition, gruu, 199

Contact: <sip:user2_public1@home1.net;gr=urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6>; +g.3gpp.icsi-ref="urn%3Aurn-7%3gpp-service.ims.icsi.mmtel";+g.3gpp.ics="server"

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

Content-Type: application/sdp

Content-Length: (…)

v=0

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

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

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; mode-change-period=2

a=rtpmap:96 telephone-event

a=maxptime:20

Request-URI: SCC AS PSI DN as received in the SETUP message.

P-Asserted-Identity: The MSC Server enhanced for ICS inserts the tel-URI containing the subscriber number, as received from the ICS UE B.

Accept-Contact: The MSC Server enhanced for ICS includes the mmtel media feature tag in the INVITE request .

Contact: The MSC Server enhanced for ICS includes the GRUU received at registration, the media feature tag g.3gpp.icsi-ref set to "urn%3Aurn-7%3gpp-service.ims.icsi.mmtel" and the media feature tag g.3gpp.ics set to "server".

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

16. SIP 100 (Trying) response (intermediate IM CN subsystem entities to MSC Server enhanced for ICS)

The intermediate IM CN subsystem entities respond to the MSC Server enhanced for ICS with a SIP 100 (Trying) response. There is no ICS specific content in this response.

17. SIP INVITE request (intermediate IM CN subsystem entities to SCC AS) – see example in Table A.5.3-17

The SIP INVITE request is sent to the SCC AS.

Table A.5.3-17: SIP INVITE request (intermediate IM CN subsystem entities to SCC AS)

INVITE tel:+1-212-555-6666 SIP/2.0

Via: SIP/2.0/UDP scscf1.home1.net;branch=z9hG4bK332b33.1,SIP/2.0/UDP icscf1.home1.net;branch=z9hG4bK871y12.1, SIP/2.0/UDP msc2.home1.net;branch=z9hG4bKnashds7

Max-Forwards: 68

Route: <sip:sccas .home1.net:lr>, <sip:scscf1.home1.net;lr>;orig-dialog-id="yuflsae80r3rb3fh31ondyr829cnyr381cn932YDWref0w0-wwtg374"

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

P-Asserted-Identity:

P-Charging-Vector:

P-Access-Network-Info:

Accept-Contact:

Privacy:

From:

To:

Call-ID:

Cseq:

Supported:

Require:

Proxy-Require:

Security-Verify:

Contact:

Allow:

Content-Type:

Content-Length: (…)

o=-

18. SIP 100 (Trying) response (SCC AS to intermediate IM CN subsystem entities)

The SCC AS responds to the intermediate IM CN subsystem entities with a SIP 100 (Trying) response. There is no ICS specific content in this response.

19. SIP 200 (OK) response (SCC AS to intermediate IM CN subsystem entities) – see example in table A.5.3-19.

The SCC AS responds to the SIP INVITE request with a SIP 200 (OK) response that includes an SDP answer.

Table A.5.3-19: SIP 200 (OK) response (SCC AS to intermediate IM CN subsystem entities)

SIP/2.0 200 OK

Via: SIP/2.0/UDP scscf2.home2.net;branch=z9hG4bK332b33.1,SIP/2.0/UDP icscf2.home2.net;branch=z9hG4bK871y12.1, SIP/2.0/UDP msc2.home2.net;branch=z9hG4bKnashds7

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

P-Access-Network-Info:

Privacy: none

From: <tel: +1-212-555-2222>;tag=171828

To: <tel:+1-212-555-6666>;tag=378959

Call-ID: f81d4fae-7dec-11d0-a765-00a0c91e6bf6

CSeq:

Require: 100rel, precondition

Contact: <sip:user1_public1@home2.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

Content-Type: application/sdp

Content-Length: (…)

v=0

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

s=-

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

t=0 0

m=audio 3456 RTP/AVP 97 96

b=AS:25.4

a=curr:qos local sendrcv

a=curr:qos remote sendrcv

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; mode-change-period=2

a=maxptime:20

20. SIP 200 (OK) response (intermediate IM CN subsystem to MSC Server enhanced for ICS)

The intermediate IM CN subsystem entities route the SIP 200 (OK) response to the MSC Server enhanced for ICS.

21. CONNECT message (MSC Server enhanced for ICS to ICS UE B)

The enhance MSC Server maps the received SIP 200 (OK) response to a CONNECT message. There is no ICS specific content in this message.

22. CONNECT ACKNOWLEDGEMENT message (ICS UE B to MSC Server enhanced for ICS)

The ICS UE A sends a CONNECT ACKNOWLEDGMENT message upon receiving the CONNECT message. There is no ICS specific content in this message.

23-24. SIP ACK request (MSC Server enhanced for ICS to SCC AS via intermediate IM CN subsystem entities)

The MSC Server enhanced for ICS interworks the received CONNECT ACKNOWLEDGEMENT message to a SIP ACK request which is routed to the SCC AS via the intermediate IM CN subsystem entities. There is no ICS specific content in this response.

25-26. SIP 180 (Ringing) response (ICS UE B to SCC AS via intermediate IM CN subsystem entities)

The ICS UE B responds to the received SIP INVITE request with a SIP 180 (Ringing) response. The response contains no SDP body and contains no ICS specific content. The SIP 180 (Ringing) response is routed to the SCC AS.

27-28. SIP 180 (Ringing) response (SCC AS to originating IM CN subsystem via intermediate IM CN subsystem entities)

The SCC AS routes the received SIP 180 (Ringing) response towards the originating network and the calling party.

29. SIP 200 (OK) response (ICS UE B to intermediate IM CN subsystem entities) – see example in Table A.5.3-29

The ICS UE B responds to the received initial SIP INVITE request with a SIP 200 (OK) response. This SIP 200 (OK) response includes an SDP answer from the ICS UE and indicates resources have been reserved and the dialog can be established.

Table A.5.3-29: SIP 200 (OK) response (ICS UE B to intermediate IM CN subsystem entities)

SIP/2.0 200 OK

Via: SIP/2.0/UDP pcscf2.home2.net;branch=z9hG4bKfeh9083, SIP/2.0/UDP scscf2.home2.net;branch=z9hG4bK332b44.1, SIP/2.0/UDP sccas2.home2.net;branch=z9hG4bKnas34r5

Record-Route: <sip:pcscf2.visited2.net;lr>, <sip:scscf2.home2.net;lr>

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

Privacy: none

From: <tel: +1-212-555-1111>;tag=171828

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

Call-ID: cb03a0s09a2sdfglkj490333

CSeq:

Require: 100rel, precondition

Contact:

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

Content-Type: application/sdp

Content-Length: (…)

v=0

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

s=-

c=PSTN – –

t=0 0

m=audio 9 PSTN –

a=setup:active

a=connection:new

a=cs-correlation:callerid:+358504821437

a=curr:qos local sendrcv

a=curr:qos remote sendrcv

a=des:qos mandatory local sendrecv

a=des:qos mandatory remote sendrecv

30. SIP 200 (OK) response (intermediate IM CN subsystem entities to SCC AS)

The SIP 200 (OK) response and final SDP answer from the ICS UE is routed towards the SCC AS.

31. SIP 200 (OK) response (SCC AS to intermediate IM CN subsystem entities) – see example in Table A.5.3-31

The SCC AS, acting as a B2BUA, generates a SIP 200 (OK) response based upon the SIP 200 (OK) response reeceived and is routed towards the intermediate IM CN subsystem entities. This SIP 200 (OK) response includes an answer SDP in response to the offer SDP that was received by the SCC AS in the original SIP INVITE request. The answer SDP indicates the IP addressed and codecs of the MGW as received by the SCC AS during CS bearer setup.

Table A.5.3-31: SIP 200 (OK) response (SCC AS to intermediate IM CN subsystem entities)

SIP/2.0 200 OK

Via: SIP/2.0/UDP pcscf2.home2.net;branch=z9hG4bKfeh9083, SIP/2.0/UDP scscf2.home2.net;branch=z9hG4bK332b44.1, SIP/2.0/UDP sccas2.home2.net;branch=z9hG4bKnas34r5

Record-Route: <sip:pcscf2.visited2.net;lr>, <sip:scscf2.home2.net;lr>

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

Privacy: none

From: <tel: +1-212-555-1111>;tag=171828

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

Call-ID: cb03a0s09a2sdfglkj490333

CSeq:

Require: 100rel, precondition

Contact:

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

Content-Type: application/sdp

Content-Length: (…)

v=0

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

s=-

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

t=0 0

m=audio 3456 RTP/AVP 97 96

a=curr:qos local sendrcv

a=curr:qos remote sendrcv

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; mode-change-period=2

a=maxptime:20

32. SIP 200 (OK) response (intermediate IM CN subsystem entities to originating IM CN subsystem via)

The SIP 200 (OK) response is routed towards the originating UE via the originating IM CN subsystem.

33-34. SIP ACK request (originating IM CN subsystem to SCC AS via intermediate IM CN subsystem entities and SCC AS)

The originating IM CN subsystem sends a SIP ACK request to the SCC AS via the intermediate IM CN subsystem entities. There is no ICS specific content in this response.

35-36. SIP ACK request (SCC AS to ICS UE B via intermediate IM CN subsystem entities and SCC AS)

The SCC AS sends a SIP ACK request to the ICS UE B via the intermediate IM CN subsystem entities. There is no ICS specific content in this response.