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 4.5.5.2, 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"
Allow: INVITE, ACK, CANCEL, BYE, PRACK, UPDATE
Accept: application/sdp,application/vnd.3gpp.cw+xml
Content-Type: multipart/mixed;boundary="boundary1"
Content-Length: (…)
–boundary1
Content-Type: application/sdp
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
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=inactive
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
–boundary1
Content-Type: application/vnd.3gpp.cw+xml
<?xml version="1.0"?>
<ims-cw xmlns="urn:3gpp:ns:cw:1.0">
<communication-waiting-indication/>
</ims-cw>
–boundary1–
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 4.5.5.3.
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 1.2.3.4:1357;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
CSeq: 61 INVITE
Alert-Info:urn:alert:service:call-waiting
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.