Gmb (application id: 16777223)

Gmb interface in the GPRS network facilitates communication between the Gateway GPRS Support Node (GGSN) and the Broadcast-Multicast Service Center (BM-SC). This interface is specifically designed to support the delivery and management of MBMS (Multimedia Broadcast Multicast Services) bearer services. The Gmb interface ensures efficient signaling and resource allocation for multicast services.

Gmb interface workflow

1. User Authorization/Deactivation for Multicast MBMS Service
   • Authorization Request: The GGSN sends a request to the BM-SC to authorize a user for a multicast MBMS service. This request includes user identity and service-specific information.
   • Authorization Response: The BM-SC processes the request and responds with an authorization decision, indicating whether the user is allowed to access the service.
2. Registration/De-registration of GGSN for Multicast MBMS Service
   • Registration Request: The GGSN registers itself with the BM-SC to receive a specific multicast MBMS service. 
   • Registration Response: The BM-SC acknowledges the registration and includes the GGSN in the multicast service delivery.
3. Session Management
   • Session Start: The BM-SC sends a session start message to the GGSN, indicating the beginning of a multicast MBMS session. The GGSN, in coordination with the SGSN (Serving GPRS Support Node) and RAN (Radio Access Network), sets up the necessary resources for the service.
   • Session Update: The BM-SC may send session update messages to the GGSN to modify the parameters of an ongoing session. This ensures that any changes in the session are communicated, and resources are adjusted accordingly.
   • Session Stop: When the multicast MBMS session is to be terminated, the BM-SC sends a session stop message to the GGSN. The GGSN, SGSN, and RAN then tear down the resources allocated for the service.

For complete technical specification of Gmb interface in Diameter protocol please refer to: [3GPP TS 29.061]