When the subscriber attribute or subscription data on a PCRF changes, the PCRF indicates a re-authorization request to update an IP-connectivity access network (IP-CAN) session. Figure 1 shows the message flow of PCRF-initiated IP-CAN session update.

1. The PCRF receives an internal or external trigger to re-evaluate policy decision for an IP-CAN session. If policy update is needed, the PCRF sends a Re-Auth Request message (RAR) message to the PCEF. The RAR message carries attribute value pairs (AVPs) such as Session-Id and Re-Auth-Request-Type (whose value is invalid to the Gx interface) and possibly Event-Trigger, Charging-Rule-Remove, Charging-Rule-Install, and QoS-Information. The QoS information AVP supports only the QoS Per IP-CAN Bearer rule. If the PCRF has delivered the QoS Per QCI rule, this AVP can be ignored.
2. The PCEF validates the RAR message, locates the IP-CAN session based on Session Id, and updates the authorized QoS of IP-CAN bearer1. Then, the PCEF sends an Update policy decision point (PDP) Context Request message to the SGSN. The Update PDP Context Request message carries IEs such as tunnel endpoint identifier (TEID), network service access point identifier (NSAPI), QoS Requested, Prohibit Payload Compression, and cell global identity (CGI)/service area identity (SAI)/routing area identity (RAI) change report indicator.
3. The SGSN validates the Update PDP Context Request message, initiates radio access bearer (RAB) modification, and sends a Modify PDP Context Request message to the user equipment (UE) if the validation is passed. The Modify PDP Context Request message carries parameters such as TI, PDP Address, QoS Profile, Radio Priority, Flow ID, and Protocol Configuration Options.
4. The UE returns a Modify PDP Context Accept message carrying TI to the SGSN.
5. The SGSN sends an Update PDP Context Response message to the PCEF after the SGSN receives the Modify PDP Context Accept message or the RAB modification is complete. The Update PDP Context Response message carries parameters such as TEID and QoS Negotiated.

6. The PCEF performs subsequent operations for IP-CAN bearer 1 after it receives the Update PDP Context Response message.

   In addition, the PCEF removes all PCC rules bound with IP-CAN bearer 2 according to instructions from the PCRF and sends a Delete PDP Context Request message to the SGSN. The Delete PDP Context Request message carries parameters such as TEID, NSAPI, and Teardown Indicator (which is set to 0).

   http://localhost:7904/pages/CEC1230A/01/CEC1230A/01/resources/public_sys-resources/icon-note.gif NOTE:

   Operations for IP-CAN bearer 1 and IP-CAN bearer 2 are performed simultaneously.

7. The SGSN validates the Delete PDP Context Request message and sends a Deactivate PDP Context Request message to the UE if the validation is passed. The Deactivate PDP Context Request message carries parameters such as TI and Cause.
8. The UE removes the indicated PDP context and sends a Deactivate PDP Context Accept message carrying TI to the SGSN.
9. The SGSN removes the indicated PDP context and sends a Delete PDP Context Response message carrying TEID to the PCEF. In addition, the RAB of IP-CAN bearer 2 is released.

10. The PCEF performs subsequent operations for IP-CAN bearer 2 after it receives the Delete PDP Context Response message. Entries associated with IP-CAN bearer 2 in the PDP context table are deleted, and the associations between entries in the PDP context table and the IP-CAN session are removed.

    The PCEF sends a Re-Auth Answer (RAA) message to the PCRF. The RAA message carries AVPs such as Session-Id and Result-Code/Experimental-Result.