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What is the interface between PGW and PCRF?

In LTE (Long-Term Evolution) networks, the interface between the PGW (Packet Data Network Gateway) and the PCRF (Policy and Charging Rules Function) is known as the Gx interface. This interface serves as a crucial link for communication and coordination between these two essential elements in the Evolved Packet Core (EPC) architecture. Let’s delve into the detailed functions, protocols, and interactions on the Gx interface:

1. Definition of Gx Interface:

  • The Gx interface is the interface that connects the PGW to the PCRF in LTE networks. It facilitates the exchange of policy and charging-related information between the evolved packet core network elements.

2. Functions of the Gx Interface:

  • Policy Control: The Gx interface enables policy control functions, allowing the PCRF to define and enforce policies related to the quality of service (QoS) for data services. This includes decisions on bandwidth allocation, traffic prioritization, and other policy rules.
  • Charging Control: Gx supports charging control functions, allowing the PCRF to provide instructions to the PGW regarding charging parameters for data services. This includes information related to data usage, charging rates, and billing details.
  • Bearer and QoS Management: Gx facilitates the exchange of information related to bearers and QoS parameters between the PGW and PCRF. This ensures that the network can provide the desired level of service to subscribers based on policy decisions.
  • Dynamic Policy Enforcement: The Gx interface allows for dynamic enforcement of policies based on real-time network conditions and subscriber behavior. Policies can be adjusted in real-time to adapt to changing circumstances and optimize resource utilization.
  • Flow-Based Charging: Gx supports flow-based charging, allowing the PCRF to provide instructions to the PGW on how to handle and charge for specific data flows. This is crucial for accurate billing and charging based on the actual usage patterns of subscribers.
  • Subscriber and Session Context Transfer: Gx facilitates the transfer of subscriber and session context information between the PGW and PCRF. This ensures that the PCRF has up-to-date information to make informed policy and charging decisions.

3. Protocols Used on Gx Interface:

  • Diameter Protocol: The Diameter protocol is widely used on the Gx interface for communication between the PGW and PCRF. It is an authentication, authorization, and accounting (AAA) protocol that supports secure and reliable information exchange.
  • Gx Interface Extensions: The Gx interface extends the Diameter protocol to include specific messages and Attribute-Value Pairs (AVPs) relevant to policy control and charging functions. These extensions ensure that the Gx interface can handle the unique requirements of LTE networks.

4. Key Procedures on Gx Interface:

  • Credit-Control Application: The Gx interface supports the Credit-Control Application within the Diameter protocol, allowing the PCRF to interact with the PGW for credit control decisions. This includes initiating credit-control sessions and updating credit-related information.
  • Policy Decision and Enforcement: Gx enables the PCRF to make policy decisions and enforce them at the PGW. Policies may include rules for traffic prioritization, bandwidth allocation, and other parameters impacting the quality and delivery of data services.
  • Charging Information Exchange: The Gx interface facilitates the exchange of charging-related information between the PGW and PCRF. This includes details about data usage, charging rates, and other billing-related information essential for accurate billing.
  • Dynamic Policy Updates: Gx supports dynamic policy updates, allowing the PCRF to send real-time instructions to the PGW based on changing network conditions or subscriber behavior. This ensures adaptive and efficient policy enforcement.

5. Redundancy and Resilience:

  • To enhance network reliability, the Gx interface may implement mechanisms for redundancy, load balancing, and failover. Redundant paths and backup connections help maintain service continuity in the event of network failures or disruptions.


The Gx interface between the PGW and PCRF in LTE networks is a critical component for policy control and charging functions. Its protocols and procedures contribute to the efficient and accurate enforcement of policies and charging mechanisms, ensuring a seamless and responsive user experience within the LTE ecosystem.

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