A.2 Terminal based CW flows
24.6153GPPCommunication Waiting (CW) using IP Multimedia (IM) Core Network (CN) subsystemProtocol specificationRelease 17TS
A.2.1 Successful communication establishment
Figure A.2.1: Communication Waiting signalling flow at the terminating side, successful communication establishment
Explanation Figure A.2.1:
NOTE: only the most relevant messages are shown.
1. – 5. A communication invitation arrives at UE-B.
1a. Evaluation of initial filter criteria (CW is subscribed 🡪 forwarding to CW AS).
6. – 10. UE-B sends back a provisional response to the communication origin.
11. – 15. UE-B sends back a 180 (Ringing) response. UE-B optionally inserts a Alert-Info with a "service:call-waiting" urn into the 180 (Ringing) response, see Table A.2-1.
Table A.2-1: 180 (Ringing) response (UE-B to P-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:user2_public1@home2.net;gr=urn:uuid:2ad8950e-48a5-4a74-8d99-ad76cc7fc74>;+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
[11a. out of scope: user B uses the HOLD service or releases a session in order to free resources]
13a. A CW timer is started.
[14a. 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].]
16. – 20. UE-B sends a 200 OK to the communication origin with the SDP offer of UE-B.
18a. The CW timer stops.
A.2.2 Timer expires
Figure A.2.2: Communication Waiting signalling flow at the terminating side, CW timer expires
Explanation Figure A.2.2:
NOTE: Only the most relevant messages are shown.
1. – 5. A communication invitation arrives at UE-B.
1a. Evaluation of initial filter criteria (CW is subscribed 🡪 forwarding to CW AS).
6. – 10. UE-B sends back a provisional response to the communication origin.
11. – 15. UE-B sends back a 180 (Ringing) response. UE-B optionally inserts a Alert-Info with a "service:call-waiting" urn into the 180 (Ringing) response, see Table A.2-2.
Table A.2-2: 180 (Ringing) response (UE-B to P-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:user2_public1@home2.net;gr=urn:uuid:2ad8950e-48a5-4a74-8d99-ad76cc7fc74>;+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
[11a. out of scope: user B uses the HOLD service or releases a session in order to free resources]
13a. A CW timer is started.
[14a. 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].]
14b. The CW timer expires.
16. – 18. The CW AS sends a CANCEL request to to UE-B.
19. – 20. The CW AS sends a 480 (Temporarily unavailable) response to the communication origin.
Annex B (informative):
Example of Filter Criteria
This annex provides an example of a filter criterion that triggers SIP requests that are subject to initial filter criteria evaluation.
An example of an IFC when the CW service is active at the terminating S-CSCF is:
Method: INVITE.
Editor’s note: It’s needed to consider if further clarification is needed for Filter Criteria in cases where additional services based upon INVITE are also deployed.
Annex C (informative):
IANA Registration templates