B.2 IMS Session Establishment
29.2133GPPPolicy and charging control signalling flows and Quality of Service (QoS) parameter mappingRelease 17TS
B.2.1 Provisioning of service information at Originating P-CSCF and PCRF
This clause covers the PCC procedures at the originating P-CSCF and PCRF at IMS session establishment.
In figure B.2.1.1 the P-CSCF derives the provisioning of service information to the PCRF from the SDP offer/answer exchange.
Figure B.2.1.1: PCC Procedures for IMS Session Establishment at originating P-CSCF and PCRF
1. The P-CSCF receives the SDP parameters defined by the originator within an SDP offer in SIP signalling.
2. The P-CSCF identifies the connection information needed (IP address of the down link IP flow(s), port numbers to be used etc…).
3. The P-CSCF forwards the SDP offer in SIP signalling.
4. The P-CSCF gets the negotiated SDP parameters from the terminating side through SIP signalling interaction.
5. The P-CSCF identifies the connection information needed (IP address of the up-link media IP flow(s), port numbers to be used etc…).
6. The P-CSCF forwards the derived session information to the PCRF by sending a Diameter AAR over a new Rx Diameter session.
7. The PCRF stores the received session information, and performs session binding.
8. The PCRF replies to the P-CSCF with a Diameter AAA.
9. Upon reception of the acknowledgement from the PCRF, the SDP parameters are passed to the UE in SIP signalling.
10. The PCRF executes interactions according to figure 4.3.1.1.1 . This step implies provisioning of PCC/QoS rules and is executed in parallel with steps 8 and 9.
11. If the P-CSCF requested access network information in step 6, the PCRF forwards the access network information received in step 10 in a Diameter RAR.
12. If step 11 occurs, the P-CSCF acknowledges the receipt of Diameter RAR.
13. If step 11 occurs, the P-CSCF forwards the access network information as the network provided location information when a suitable SIP message is received.
Optionally, the provisioning of service information may be derived already from the SDP offer to enable that a possible rejection of the service information by the PCRF is obtained by the P-CSCF in time to reject the service with appropriate SIP signalling, to allow the P-CSCF to request network provided location information for inclusion in the SDP offer, to support authentication of roaming users in deployments with no IMS-level roaming interfaces or to support PSAP callback functionality for anonymous IMS emergency sessions. This is described in figure B.2.1.2.
Figure B.2.1.2: PCC Procedures for IMS Session Establishment at originating P-CSCF and PCRF, provisioning of service information derived from SDP offer and answer
1. The P-CSCF receives the first SDP offer for a new SIP dialogue within a SIP INVITE request.
2. The P-CSCF extracts service information from the SDP offer (IP address of the down link IP flow(s), port numbers to be used etc…).
3. The P-CSCF forwards the derived service information to the PCRF by sending a Diameter AAR over a new Rx Diameter session. It indicates that only an authorization check of the service information is requested.
4. The PCRF checks and authorizes the service information, performs session binding, but does not provision PCC/QoS rules at this stage.
5. The PCRF replies to the P-CSCF with a Diameter AAA.
6. If the P-CSCF did not request access network information in step 3, or if the P-CSCF requested access network information but does not require the access network information for inclusion in the SDP offer, or the P-CSCF requested EPC-level user information in step 3 the P-CSCF forwards the SDP offer in SIP signalling.
7. If the P-CSCF requested access network information in step 3, the PCRF executes interactions according to Figure 4.3.1.1.1. This step implies provisioning of PCC/QoS rules.
8. If the P-CSCF requested access network information in step 3, the PCRF forwards the access network information received in step 7 in a Diameter RAR.
9. If step 8 occurs, the P-CSCF acknowledges the receipt of Diameter RAR.
10a. If step 8 occurs, and if the P-CSCF requires the access network information for inclusion in the SDP offer, the P-CSCF forwards the SDP offer and adds the access network information as the network provided location information to the corresponding SIP message.
10b. If step 8 occurs, and if the P-CSCF does not require the access network information for inclusion in the SDP offer, the P-CSCF forwards the access network information as the network provided location information in a suitable SIP message. This step normally occurs only after step 17.
11. The P-CSCF receives the negotiated SDP parameters from the terminating side within a SDP answer in SIP signalling.
12. The P-CSCF extracts service information from the SDP answer (IP address of the up-link media IP flow(s), port numbers to be used etc…).
13. The P-CSCF forwards the derived service information to the PCRF by sending a Diameter AAR over the existing Rx Diameter session. Access network information is not requested if done in step 7.
14. The PCRF stores the received session information.
15. The PCRF replies to the P-CSCF with a Diameter AAA.
16. The PCRF authorizes the session information. The PCRF executes interactions according to Figure 4.3.1.1.1. This step implies provisioning of PCC/QoS rules and authorized QoS.
17. Upon successful authorization of the session, the SDP parameters are passed to the UE in SIP signalling. This step is executed in parallel with step 16.
B.2.2 Provisioning of service information at terminating P-CSCF and PCRF
This clause covers the PCC procedures at the terminating P-CSCF and PCRF at IMS session establishment.
In figure B.2.2.1 the P-CSCF derives the provisioning of service information to the PCRF from the SDP offer/answer exchange.
Figure B.2.2.1: PCC Procedures for IMS Session Establishment at terminating P-CSCF and PCRF
1. The P-CSCF receives the SDP parameters defined by the originator.
2. The P-CSCF identifies the connection information needed (IP address of the up-link IP flow(s), port numbers to be used etc…).
3. The P-CSCF sends the SDP offer to the UE.
4. The P-CSCF receives the negotiated SDP parameters from the UE.
5. The P-CSCF identifies the connection information needed (IP address of the down-link IP flow(s), port numbers to be used etc…).
6. The P-CSCF forwards the derived service information to the PCRF by sending a Diameter AAR over a new Rx Diameter session.
7. The PCRF stores the received session information, and performs session binding.
8. The PCRF sends a Diameter AAA to the P-CSCF.
9. If the P-CSCF did not request access network information in step 6, upon reception of the acknowledgement from the PCRF, the SDP parameters in the SDP answer are passed to the originator.
10. The PCRF executes interactions according to clause 4.3.1.1.1. This step implies provisioning of PCC/QoS rules and is executed in parallel with steps 8 and 9.
11. If the P-CSCF requested access network information in step 6, the PCRF forwards the access network information received in step 10 in a Diameter RAR.
12. If step 11 occurs, the P-CSCF acknowledges the receipt of Diameter RAR.
13. If step 11 occurs, the P-CSCF forwards the SDP answer and adds the access network information as the network provided location information to the corresponding SIP message.
Optionally, the provisioning of service information may be derived already from the SDP offer to enable that a possible rejection of the service information by the PCRF is obtained by the P-CSCF in time to reject the service with appropriate SIP signalling or to enable pre-authorization for a UE terminated IMS session establishment with UE initiated resource reservation. This is described in figure B.2.2.2.
Figure B.2.2.2: PCC Procedures for IMS Session Establishment at terminating P-CSCF and PCRF, provisioning of service information derived from SDP offer and answer
1. The P-CSCF receives the first SDP offer for a new SIP dialogue within SIP signalling, e.g. within a SIP INVITE request.
2. The P-CSCF extracts the service information from the SDP offer (IP address of the up-link IP flow(s), port numbers to be used etc…).
3. The P-CSCF forwards the derived session information to the PCRF by sending a Diameter AAR over a new Rx Diameter session. It indicates that the service information that the AF has provided to the PCRF is preliminary and needs to be further negotiated between the two ends.
4. The PCRF checks and authorizes the session information, performs session binding, but does not provision PCC/QoS Rules at this stage.
5. The PCRF replies to the P-CSCF with a Diameter AAA.
6. The P-CSCF sends the SDP offer to the UE.
7. If the UE initiates a bearer resource modification request, the PCRF provides the PCEF/BBERF with PCC/QoS rules according to figure 4.3.1.1.1 based on the SDP offer.
NOTE: Step 7 is not applicable for IMS Emergency Sessions.
8. The P-CSCF receives the negotiated SDP parameters from the UE within an SDP answer in SIP signalling.
9. The P-CSCF extracts service information from the SDP answer (IP address of the down-link IP flow(s), port numbers to be used etc…).
10. The P-CSCF forwards the derived service information to the PCRF by sending a Diameter AAR over the existing Rx Diameter session.
10a. The PCRF stores the received session information.
11. The PCRF sends a Diameter AAA to the P-CSCF.
12. The PCRF authorizes the session information. The PCRF executes interactions according to Figure 4.3.1.1.1. This step implies provisioning of PCC/QoS rules and authorized QoS.
13. If the P-CSCF did not request access network information in step 3 or 10, upon successful authorization of the session the SDP parameters in the SDP answer are passed to the originator. This step is executed in parallel with step 12.
14. If the P-CSCF requested access network information in step 3 or 10, the PCRF forwards the access network information received in step 12 in a Diameter RAR.
15. If step 14 occurs, the P-CSCF acknowledges the receipt of Diameter RAR.
16. If step 14 occurs, the P-CSCF forwards the SDP answer and adds the access network information as the network provided location information to the corresponding SIP message.