A.1 Network based CW flows

24.6153GPPCommunication Waiting (CW) using IP Multimedia (IM) Core Network (CN) subsystemProtocol specificationRelease 17TS

Figure A.1.1: CW signalling flow using an AS

Figure A.1.1 shows a basic signalling flow for Communication Waiting.

Call flows

1 to 2 The communication is initiated by UE-A by sending an INVITE request. The Request URI will include the URI of UE-B. After IFC evaluation in the S-CSCF the INVITE request is routed to the CW AS.

2a. The AS detects the CW condition and inserts a 3GPP IM CN Subsystem XML body into the INVITE request per procedures in subclause, see Table A.1-1.

Table A.1-1: SIP INVITE request (CW AS to S-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.home1.net:7531;lr;comp=sigcomp>, <sip:orig@scscf1.home1.net;lr>

Privacy: none

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

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

Call-ID: cb03a0s09a2sdfglkj490333

Cseq: 127 INVITE

Supported: 100rel; precondition, gruu, 199

Require: sec-agree; replaces

Replaces: me03a0s09a2sdfgjkl491777; to-tag=774321; from-tag=64727891

Proxy-Require: sec-agree

Security-Verify: ipsec-3gpp; q=0.1; alg=hmac-sha-1-96; spi=87654321; port1=7531

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

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

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


Accept: application/sdp,application/vnd.3gpp.cw+xml

Content-Type: multipart/mixed;boundary="boundary1"

Content-Length: (…)


Content-Type: application/sdp


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


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

t=0 0

m=audio 3456 RTP/AVP 97 96

a=tcap:1 RTP/AVPF

a=pcfg:1 t=1


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



Content-Type: application/vnd.3gpp.cw+xml

<?xml version="1.0"?>

<ims-cw xmlns="urn:3gpp:ns:cw:1.0">




3. – 4. The INVITE request is routed to UE-B.

5. UE-B recognizes the 3GPP IM CN Subsystem XML body per procedures in subclause

6. UE-B sends back a 180 (Ringing) response.

[6a. out of scope: user B uses the HOLD service or releases a session in order to free resources]

7. – 8. The 180 (Ringing) response is routed back to the AS.

8a. The AS optionally inserts a Alert-Info with a ‘CW’ urn into the 180 (Ringing) response.

Table A.1-2: 180 (Ringing) response (CW AS to S-CSCF)

SIP/2.0 180 Ringing

Via: SIP/2.0/UDP pcscf1.visited1.net;branch=z9hG4bk120f34.1

Via: SIP/2.0/UDP;branch=z9hG4bKnashds7

From: <sip:user1_public1@home1.net>;tag=31415

To: <tel:+1-212-555-2222>;tag=24615

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

Call-ID: b89rjhnedlrfjflslj40a222



Content-Length: 0

9. – 10. The 180 (Ringing) response is routed back to the communication origin.

[9a. The AS may initiate an announcement to the calling user that the communication is a waiting communication, in accordance with 3GPP TS 24.628 [4].]

11. – 15. UE-B sends back a 200 (OK) response to the communication origin.