Gq (application id: 16777222)

Gq interface facilitates communication between the Application Function (AF) and the Policy Decision Function (PDF), enabling the dynamic enforcement of QoS policies that align with the service requirements of the application. It’s an important component within IP multimedia networks, particularly for managing Quality of Service (QoS) in scenarios where services like Voice over IP (VoIP), video streaming, or other real-time multimedia applications are involved.

Gq interface workflow

1. Session Establishment:
   • When a user initiates a session through the User Equipment (UE), the AF begins the process by signaling the session's QoS requirements to the PDF over the Gq interface. These requirements may include parameters like minimum bandwidth, latency thresholds, and packet loss tolerance, depending on the nature of the application.
2. QoS Policy Request:
   • The AF sends a detailed QoS request to the PDF via the Gq interface. This request is a critical input for the PDF, which considers multiple factors, such as the network's current load, subscriber data, and predefined QoS policies, before making a decision.
3. Policy Decision:
   • Upon receiving the QoS request, the PDF evaluates it against the network’s capabilities and policy rules. If the network can support the requested QoS, the PDF formulates a set of QoS policies to be enforced. 
4. Policy Enforcement:
   • The PDF then communicates its decision to the PEP within the GGSN via the Go interface. The PEP is responsible for enforcing the QoS policies on the data flows associated with the session. 
5. Session Management:
   • During the session, the Gq interface allows for dynamic adjustments to the QoS policies. If the AF detects changes in the session's requirements or network conditions, it can send updated QoS requests to the PDF, which in turn, can modify the policies in real-time.
6. Session Termination:
   • When the session ends, the AF notifies the PDF to terminate the QoS policies associated with the session. The PDF then instructs the PEP to release the resources allocated for that session.

For complete technical specification of Gq interface in Diameter protocol please refer to: [3GPP TS 29.209]
Signaling flows related to the Gq interface are specified in [3GPP TS 29.208]