Rx (application id: 16777236)

The Rx interface facilitates communication between the Application Function (AF) and the Policy and Charging Rules Function (PCRF). The primary purpose of the Rx interface is to exchange application-level session information, enabling the PCRF to make informed policy and charging decisions that align with the specific needs of a service session and the subscriber's profile.

Architecture of the Rx Interface:

• Application Function (AF):
  • The AF is a network element that handles the signaling and control of specific application services, such as voice over IP (VoIP), video streaming, or other data services. The AF interacts with the PCRF via the Rx interface to request policy control and resource allocation for these services.
  • The AF provides critical session information, including media types, QoS requirements, and event triggers, which are necessary for the PCRF to enforce appropriate policies.
• Policy and Charging Rules Function (PCRF):
  • The PCRF is the central decision-making element in the PCC architecture. It is responsible for determining the policy and charging rules that apply to each service session based on the information received from the AF.
  • The PCRF makes decisions regarding QoS enforcement, resource allocation, and charging rules, and communicates these decisions back to the AF. The PCRF also coordinates with other network elements like the Policy and Charging Enforcement Function (PCEF) to ensure that policies are enforced on the data path.

Rx interface workflow:

1. Session Initiation:
   • When a service session begins, the AF sends an AA-Request (AAR) message to the PCRF over the Rx interface. This message includes details such as the type of media being used, the required QoS, and any other session-specific parameters.
2. Policy Decision:
   • Upon receiving the AAR message, the PCRF evaluates the request against predefined policies, which may include subscriber profiles, service-level agreements (SLAs), and current network conditions.
   • Based on this evaluation, the PCRF formulates a response that specifies the QoS parameters, resource allocation, and charging rules to be applied to the session. This information is sent back to the AF in an AA-Answer (AAA) message.
3. Session Management:
   • During the session, the AF may send additional AAR messages to the PCRF if there are changes in the session's parameters, such as a change in media type or a handover event. The PCRF re-evaluates the policies and may adjust the QoS or charging rules accordingly.
   • The PCRF can also send unsolicited Re-Auth-Request (RAR) messages to the AF if there is a need to modify the ongoing session due to changes in network conditions or updated policies.
4. Session Termination:
   • At the conclusion of the session, the AF sends a Session-Termination-Request (STR) message to the PCRF, indicating that the session is ending.
   • The PCRF processes the termination request, finalizes any charging data, and ensures that all resources allocated for the session are released. The PCRF then sends a Session-Termination-Answer (STA) message back to the AF to confirm the session's closure.

For complete technical specification of Rx interface in Diameter protocol please refer to: [3GPP TS 29.214]