> For the complete documentation index, see [llms.txt](https://diameter.learn-telecom.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://diameter.learn-telecom.com/diameter-interfaces/epc-interfaces.md).

# EPC Interfaces

### Diameter EPC Interfaces

Diameter EPC (Evolved Packet Core) interfaces are used in LTE networks for signaling and control communications. Key interfaces include:

* **S6a**: Between MME and HSS, used for authentication and user profile management.
* **S6d**: Between SGSN and HSS for similar purposes in 2G/3G networks.
* **S13**: Between MME and EIR, for Equipment Identity Check.
* **Gx**: Between PCRF and PCEF, for policy control and charging rules.
* **Rx**: Between PCRF and AF, to transmit application-level session information.

These interfaces ensure seamless network operation and efficient management of user sessions and policies.

### Importance of Diameter EPC Interfaces

These interfaces facilitate critical functions such as:

* **Authentication**: Ensuring that only authorized users can access the network.
* **Policy Management**: Enforcing rules that define how data is prioritized and managed.
* **Roaming**: Allowing users to seamlessly switch between different network operators.
* **Billing**: Collecting data needed for accurate usage-based billing.

Understanding how to configure and troubleshoot these interfaces is essential for network engineers and administrators.