PC4a (application id: 16777336)

The PC4a interface within the 3GPP Proximity Services (ProSe) architecture, specifically designed for communication between the ProSe Function and the Home Subscriber Server (HSS). This interface manages Diameter-based signaling for ProSe services, focusing on message prioritization and load control. The PC4a interface ensures that ProSe-related messages are processed efficiently, maintaining service quality even under varying network loads.
The PC4a interface facilitates the exchange of Diameter messages, enabling the ProSe Function to query and update subscriber data as needed for ProSe operations.

PC4a interface workflow:

1. Message Prioritization: When the ProSe Function sends a Diameter message to the HSS, it includes the DRMP AVP to indicate the required priority level. The HSS processes the message according to this priority, ensuring that higher-priority messages are handled first.
2. Load Reporting: The HSS monitors its load and includes a Load AVP in its Diameter responses over the PC4a interface. This AVP provides the ProSe Function with information about the current load, allowing it to adjust its message processing and routing strategies accordingly.
3. Load-Controlled Routing: When selecting the next hop for Diameter messages, the ProSe Function considers the load information provided by the HSS. This helps to distribute the load evenly across the network, preventing bottlenecks and ensuring that critical ProSe services are delivered without delay.
4. Service Execution: With the priority and load considerations managed, the ProSe Function can execute the required ProSe services, such as user discovery or direct communication, with the necessary resources allocated efficiently by the HSS.

For complete technical specification of PC4a interface in Diameter protocol please refer to: [3GPP TS 29.344].