Description
The Binding Revocation Acknowledgement (BRA) is a Diameter Answer message, specifically a Diameter Answer command, defined within the 3GPP Gx application (specified in 3GPP TS 29.212). It operates on the Gx interface, which connects the Policy and Charging Rules Function (PCRF) and the Policy and Charging Enforcement Function (PCEF), typically located in the Packet Data Network Gateway (PGW) in the EPC. The BRA is the direct response to a Binding Revocation Request (BRR) command. When a user's IP Connectivity Access Network (IP-CAN) session is terminated (e.g., due to user detachment, network failure, or administrative action), the PCEF must inform the PCRF so that all associated policy and charging rules can be cleaned up. The PCEF sends a BRR to the PCRF. Upon successfully processing this request and removing all PCC rules and session context for that IP-CAN session, the PCRF sends a BRA back to the PCEF to confirm the operation.
The message structure of the BRA follows the Diameter base protocol (RFC 6733) and includes the standard Diameter header with the Command-Code set to the value assigned for BRA. It must contain the Session-Id Attribute-Value Pair (AVP), which uniquely identifies the IP-CAN session being revoked, ensuring the acknowledgement is matched to the correct request. The Result-Code AVP is mandatory and indicates the outcome of the revocation request; a value of DIAMETER_SUCCESS (2001) confirms successful revocation, while other error codes indicate failures that may require retransmission or alternative handling. The BRA may also include optional AVPs for vendor-specific extensions or additional diagnostic information.
From a network operation perspective, the BRA completes a critical signaling transaction for session management. Its reliable delivery, ensured by the underlying Diameter protocol's failover and transport mechanisms, guarantees that the PCRF's policy state is synchronized with the PCEF's bearer state. This prevents scenarios where the PCEF believes a session is closed but the PCRF continues to hold resources and charging contexts, which could lead to incorrect billing, policy rule conflicts for reused IP addresses, and inefficient use of network and memory resources in both network functions. The BRA, therefore, is a fundamental element in maintaining the integrity of the PCC architecture.
Purpose & Motivation
The BRA was introduced to provide a formal, reliable acknowledgement mechanism for the binding revocation procedure within the 3GPP Policy and Charging Control (PCC) architecture. Prior to its standardization, session termination signaling between the gateway enforcing policies (PCEF) and the entity managing them (PCRF) was less explicit or relied on implicit session timeouts, which could lead to state desynchronization. This desynchronization posed significant operational problems, including resource leaks within the PCRF, inaccurate charging records, and potential policy conflicts when IP addresses were reassigned to new sessions.
The creation of the BRA, alongside the BRR, addressed these limitations by establishing a clean, transactional dialog for session termination. It was motivated by the need for robust, stateful policy management in the all-IP Evolved Packet System (EPS) defined from 3GPP Release 8 onwards. As networks moved to support more complex, real-time services with fine-grained QoS and charging rules, the cost of incorrect policy state became higher. The BRA ensures that the PCRF can definitively confirm the release of all rules associated with a session, providing a clear audit trail and enabling accurate resource accounting. This is essential for both network efficiency and commercial billing accuracy in modern mobile broadband services.
Key Features
- Defined as a Diameter Answer command (Answer) on the Gx interface
- Mandatory response to a Binding Revocation Request (BRR) command
- Carries a Result-Code AVP to indicate success or failure of the revocation
- Includes the Session-Id AVP to uniquely identify the terminated IP-CAN session
- Ensures synchronization of policy state between PCRF and PCEF
- Prevents resource leaks and billing inaccuracies by confirming context removal
Evolution Across Releases
Introduced as part of the initial Gx interface specification for the Evolved Packet Core (EPC). Defined the BRA command as the mandatory acknowledgement from the PCRF to the PCEF in response to a BRR, establishing the foundational two-message procedure for explicit binding revocation. This provided a reliable mechanism to clean up PCC rules upon IP-CAN session termination.
Defining Specifications
| Specification | Title |
|---|---|
| TS 29.275 | 3GPP TS 29.275 |