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IMS MO SIP Signaling Flow with QoS
This document summarizes the SIP signaling flow for establishing a mobile originating call with QoS in an IMS network. It shows the steps for: 1) P-CSCF discovery via DHCP/DNS query after PDP context activation 2) The UE sending an INVITE message to the P-CSCF which is then forwarded to the S-CSCF to trigger application servers 3) The S-CSCF authorizing QoS resources after receiving a 183 Session Progress response 4) The call being established with an ACK and the exchange of media 5) The call being released with a BYE message which triggers removal of QoS reservations.
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IMS MO SIP Signaling Flow with QoS
- 1. IMS MO SIP SignalingFlow with QoS IP Multimedia Subsystem Series
- 2. P-CSCF Discovery Procedures(A) UE SGSN GGSN (1) Active PDP Context Request (2) Create PDP Context Request (4) Create PDP Context Response (+ P Address) (5) Activate PDP Context Accept (+ P Address) (3) Obtain P-CSCF Address from configuration database
- 3. P-CSCF Discovery Procedures(B) (1) PDP Context Activation Procedure （as in A) UE SGSN DHCP DNS GGSN (1) PDP Context Activation Procedure (as in A) (2) DHCP Query & Resp (3) DNS Query & Resp Default PDP Context
- 4. Mobile Originating P-CSCF (PDF) (3) Invite (4)100 Trying UE SGSN GGSN (1) Invite (2) 100Trying S-CSCF (6) Invite (7) 100 Trying AS (5)Trigger AS based on IFC
- 5. P-CSCF (PDF) (9) 183 Session Progress UE SGSN GGSN (11) 183Session Progress (+ MediaAuthorizationToken) S-CSCF (8) 183 Session Progress Mobile Originating (Cont’d) (10) Authorize QoS Resources
- 6. Mobile Originating (Cont’d) P-CSCF (PDF) (14)PRACK (17) 200 (OK) UE SGSN GGSN (12) PRACK (18) 200 (OK) S-CSCF (15) PRACK (16) 200 (OK) (13) Resource Reservation
- 7. Mobile Originating (Cont’d) P-CSCF (PDF)UE SGSN GGSNS-CSCF (a) Activate PDP Context (b) Create PDP Context (c) COPS: REQ (d) COPS: DEC (e) COPS: RPT (f) Response(g) Accept
- 8. Mobile Originating (Cont’d) P-CSCF (PDF) (20)Update (23) 200 (OK) UE SGSN GGSN (19) Update (24) 200 (OK) S-CSCF (21) Update (22) 200 (OK)
- 9. P-CSCF (PDF) (26) 180 Ringing UE SGSN GGSN (27) 180Ringing S-CSCF (25) 180 Ringing Mobile Originating (Cont’d)
- 10. Mobile Originating (Cont’d) P-CSCF (PDF) (29)PRACK (32) 200 (OK) UE SGSN GGSN (28) PRACK (33) 200 (OK) S-CSCF (30) PRACK (31) 200 (OK)
- 11. Mobile Originating (Cont’d) P-CSCF (PDF) (39)ACK UE SGSN GGSN (36) QoS Authorization S-CSCF (34) 200 (OK) (Invite) (40) ACK (35) 200 (OK) (Invite) (37) 200 (OK) (Invite) (38) ACK (a) COPS: DEC (b) COPS: RPT
- 12.
- 13. Mobile Originating (Cont’d) P-CSCF (PDF) (5)Bye (8) 200 (OK)UE SGSN GGSN (1) Bye (9) 200 (OK) S-CSCF (6) Bye (7) 200 (OK) (2) Release PDP (3) Rls Resp (4) Remove Res Rsrv
- 14.
Editor's Notes
- #13 Procedures: When the called party answers, the terminating endpoint sends a 200 (OK) final response to the INVITE request (6), as specified by the termination procedures and the S-CSCF to S-CSCF procedures, to the S-CSCF. The S-CSCF sends a 200 (OK) final response along the signalling path back to the P-CSCF. The P-CSCF approves the commitment of the QoS resources if it was not approved already in step (X). The P-CSCF forwards the 200 (OK) final response to the session originator. UE can start the media flow(s) for this session. The UE starts the media flow for this session, and responds to the 200 (OK) response (37) with an ACK request sent to the P-CSCF. The P-CSCF forwards the ACK request to the S-CSCF. The S-CSCF forwards the ACK request to the terminating endpoint, per the S-CSCF to S-CSCF procedure.
- #14 Procedures: One mobile party hangs up, which generates a SIP BYE request from the UE to the P-CSCF. Steps 2 and 3 may take place before or after Step 1 and in parallel with Step 4. The UE initiates the release of the bearer PDP context. The GPRS subsystem releases the PDP context. The IP network resources that had were reserved for the message receive path to the mobile for this session are now released. This is initiated from the GGSN. If RSVP was used to allocated resources, then the appropriate release messages for that protocol would invoked here. The GPRS subsystem responds to the UE. The P-CSCF removes the authorization for resources that had previously been issued for this endpoint for this session. This step will also result in a release indication to the GPRS subsystem to confirm that the IP bearers associated with the session have been deleted. The P-CSCF sends a SIP BYE request to the S-CSCF of the releasing party. The SIP BYE request is sent from the S-CSCF to the S-CSCF of the network of the other party. The S-CSCF of the other party forwards the 200 OK response to its local S-CSCF. The S-CSCF of the releasing party forwards the 200 OK response to the P-CSCF of the releasing party. The P-CSCF of the releasing party forwards the 200 OK response to the UE.