MB2-C (application id: 16777335)

The MB2-C interface serves as a control-plane interface facilitating communication between the Group Communication Service Application Server (GCS AS) and the Broadcast-Multicast Service Centre (BM-SC). 
The GCS AS is responsible for managing group communication services, such as those provided by MBMS and V2X. It initiates and controls the delivery of multicast or broadcast content to the users through the BM-SC.
MB2-C interface reuses many of the Diameter Base Protocol commands, such as Capabilities-Exchange-Request (CER) and Capabilities-Exchange-Answer (CEA), with modifications specific to MBMS and V2X services.

MB2-C interface workflow

1. Session Initialization:
   • When the GCS AS decides to start a broadcast or multicast session, it sends a request via the MB2-C interface to the BM-SC to activate a new MBMS bearer. This request includes the Temporary Mobile Group Identity (TMGI) and other relevant parameters.
2. Bearer Activation:
   • The BM-SC processes the activation request and allocates the necessary network resources. It then confirms the activation of the MBMS bearer to the GCS AS, allowing the session to proceed.
3. Content Delivery:
   • With the MBMS bearer active, the BM-SC is responsible for delivering the broadcast or multicast content to the UEs. The content flows from the GCS AS to the BM-SC, which then disseminates it according to the specified parameters.
4. Bearer Modification:
   • If the GCS AS needs to adjust the MBMS bearer parameters (e.g., change the broadcast area or modify the content), it sends a modification request via the MB2-C interface. The BM-SC implements these changes and continues the session with the updated settings.
5. Session Termination:
   • At the end of the session, the GCS AS sends a deactivation request to the BM-SC via the MB2-C interface. The BM-SC releases the network resources and confirms the deactivation, effectively ending the session.

For complete technical specification of MB2-C interface in Diameter protocol please refer to: [3GPP TS 29.468]