Gq’ (application id: 16777222)

The Gq' interface is specifically designed for service-based policy setup and resource reservation in fixed broadband access networks. It facilitates the exchange of policy-related information between two key functional entities: the Service-Based Policy Decision Function (SPDF) and the Application Function (AF).
While both Gq and Gq' interfaces serve the purpose of service-based policy setup and resource reservation, they are used in different contexts. The Gq interface is generally used for IMS-based services, specifically for the interaction between the P-CSCF (as an AF) and the Policy and Charging Rules Function (PCRF). In contrast, the Gq' interface is utilized primarily for fixed broadband access networks, and involves communication between the AF and the SPDF.
Another key difference is the entities involved in the communication. The Gq interface is associated with the PCRF, which is a more comprehensive entity managing both policy control and charging rules. The Gq' interface, however, involves the SPDF, which is more focused on policy decisions and resource reservations without directly handling charging rules.

Gq’ interface workflow:

1. Initiation of Resource Request:
   • The AF initiates a request to reserve resources for a specific service or session by sending a message over the Gq' interface to the SPDF. This request contains the necessary session information and resource requirements.
2. Policy Decision Making:
   • Upon receiving the request, the SPDF evaluates it against the predefined policy rules. The SPDF determines whether the requested resources can be allocated based on the current network conditions, policies, and available resources.
3. Resource Allocation and Policy Enforcement:
   • If the SPDF approves the request, it sends the necessary policy rules and session information back to the AF. The AF then proceeds to establish the session based on the approved resources.
4. Border Gateway Function (BGF) Instantiation:
   • If required by the session, the SPDF may trigger the instantiation of a Border Gateway Function (BGF) via the Ia interface. The BGF handles the border gateway functions necessary for the session's operation.
5. SPDF Notifications:
   • The SPDF can send unsolicited Resource Allocation Request (RA-Request) messages to the AF over the Gq' interface. These messages are used to notify the AF of significant events, such as the revocation of established resource reservations.

For complete technical specification of Gq’ interface in Diameter protocol please refer to: [ETSI TS 183 017]