Gxx (application id: 16777266)

Gxx interface facilitates communication between the Policy and Charging Rules Function (PCRF) and the Bearer Binding and Event Reporting Function (BBERF). The Gxx interface is particularly important in scenarios involving Access Network Gateways, such as the Serving Gateway (S-GW) in LTE networks, or in trusted non-3GPP access networks.
BBERF is implemented within the Access Network Gateway, such as the S-GW in LTE networks or a similar gateway in non-3GPP networks. The BBERF enforces the QoS policies and charging rules received from the PCRF, managing bearer binding and reporting events related to bearer management, such as establishment, modification, and release.

• In a non-roaming scenario, the PCRF directly communicates with the BBERF within the same network. The Gxx interface is used to enforce policies based on the decisions made by the PCRF.
• In the Roaming with Home Routed Access scenario, the V-PCRF (Visiting PCRF) in the visited network communicates with the H-PCRF (Home PCRF) in the home network. The H-PCRF makes the policy decisions, and the Gxx interface is used to enforce these decisions at the BBERF in the visited network.
• In the Roaming with Visited Access scenario, the V-PCRF in the visited network is responsible for making policy decisions. The Gxx interface in the visited network is used to enforce the policies locally.

Gxx interface workflow

1. Session Initialization:
   • When a user initiates a session, the PCRF determines the necessary QoS policies based on input from the Application Function (AF) and user subscription data. These policies are communicated to the BBERF via the Gxx interface.
2. QoS Rule Provisioning:
   • The PCRF sends QoS rules to the BBERF using the Gxx interface. The BBERF enforces these rules by applying them to the relevant bearers, ensuring that the session's traffic adheres to the specified QoS parameters.
3. Bearer Binding:
   • The BBERF binds the bearers to the appropriate QoS rules as instructed by the PCRF. This binding ensures that the traffic for each session is managed according to the specified policies.
4. Event Reporting:
   • The BBERF reports significant events, such as the establishment, modification, or release of bearers, to the PCRF via the Gxx interface. 
5. Session Modification:
   • If there are changes in the session requirements (e.g., an upgrade in service quality), the PCRF sends updated QoS rules to the BBERF via the Gxx interface. 
6. Session Termination:
   • When the session ends, the PCRF instructs the BBERF to release the resources associated with the session and stop enforcing the QoS rules.

For complete technical specification of Gxx interface in Diameter protocol please refer to: [3GPP TS 29.212]