The Policy Control and Charging (PCC) Rules Function (PCRF) is a centralized policy decision point that deploys business policy rules to allocate network resources and manages flow-based charges for subscribers and services. Gx is the policy interface between the PCRF and the Policy and Charging Enforcement Function (PCEF), providing control over policy and flow-based charges for subscribers. Reference: TS 29.212
Resource Allocation Message Flow
The Gx interface includes support for:
- Service provisioning, activation, and deactivation;
- Threshold triggers for service statistics processing;
- Accounting;
- Subscriber session maintenance (activation, updating and termination);
- Event notifications.
One important part of provisioning PCC rules is ascertaining that the requested resources associated with a PCC rule are successfully allocated. The PCRF can request this verification from the PCEF with a CCA or RAR message that includes the Event-Trigger AVP with the value SUCCESSFUL_RESOURCE_ALLOCATION. The PCRF installs the rules that require resource allocation confirmation by including the Resource-Allocation-Notification AVP with the value ENABLE_NOTIFICATION within the corresponding Charging-Rule-Install AVP.
Message Exchange 1: CCR-I/CCA-I Initial Request/Answer
CCR-I/CCA-I Initial Request/Answer
The PCEF establishes a Gx Session with the PCRF with a Credit-Control-Request Initialization (CCR-I) message. The PCRF responds to the PCEF with a Credit-Control-Answer (CCA-I) in which the PCRF requests that the PCEF confirm that the resources associated with a PCC rule are successfully allocated. This request by the PCRF is accomplished by the inclusion of an Event-Trigger AVP with the value of SUCCESSFUL_RESOURCE_ALLOCATION.
Message Exchange 2: AAR/AAA: Establish Rx session between CSCF and PCRF
AAR/AAA: Establish Rx session between CSCF and PCRF
The CSCF establishes a Rx Session with the PCRF with a Authorize/Authenticate-Request (AAR) message. The PCRF responds to the CSCF with an AA-Answer (AAA).
Message Exchange 3: RAR/RAA Gx Re-Auth Request
The establishment of a Rx session triggers a Gx Re-Authorization Request from the PCRF to the PCEF. Using the Charging-Rule-Install AVP, the PCRF reauthorizes the installed PCC rules at the PCEF. The PCRF indicates which rules require notification by including the Resource-Allocation-Notification AVP with a value of ENABLE_NOTIFICATION
Message Exchange 4: CCR-U/CCA-U Gx Update
CCR-U/CCA-U Exchange
The RAR/RAA exchange triggers a Gx CCR Update (CCR-U) from the PCEF to the PCRF, based upon the initial CCR-I/CCA-I exchange with the Event-Trigger AVP with the value of SUCCESSFUL_RESOURCE_ALLOCATION from the PCRF (Message Exchange 1). The PCEF includes the Charging-Rule-Report AVP in the CCR-U which contains the Charging-Rule-Name AVP for each of the rules installed.
Message Exchange 5: STR/STA
The Rx session is terminated.
Message Exchange 6: RAR/RAA
Gx reauthorization request/answer exchange as a result of the Rx session termination.
Message Exchange 7: CCR-T/CCA-T
The Gx session is terminated.
dsTest
Developing Solutions’ dsTest supports this behavior of Policy Control by allowing a service to be configured with “Resource_Allocation_Notification” element. See the dsTest schema for more information.