SGmb (application id: 16777292)

The SGmb interface in the Diameter protocol is used for communication between the Multimedia Broadcast Multicast Service Gateway (MBMS-GW) and the Broadcast Multicast Service Center (BM-SC). This interface is crucial for managing and controlling MBMS sessions in E-UTRAN/UTRAN networks.

The primary purpose of the SGmb interface is to facilitate the following key functions:

• Session Management: It manages the start, update, and stop of MBMS sessions. When the BM-SC decides to initiate an MBMS session, it uses the SGmb interface to signal the MBMS-GW, which then sets up the necessary resources across the network to deliver the service. Similarly, the BM-SC uses the SGmb interface to update ongoing sessions (e.g., adjusting service areas or attributes) or terminate sessions once the service is no longer needed.
• Path Failure Detection: The interface allows the BM-SC and MBMS-GW to monitor the integrity of the MBMS data paths. If a failure is detected on the SGmb path, such as a loss of connection between the BM-SC and MBMS-GW, the SGmb interface enables the detection and appropriate response to restore service continuity.
• M1 Interface Information Transfer: The SGmb interface is also used for transferring local MBMS information related to the M1 interface, which is crucial for synchronizing and managing MBMS services across the network.

SGmb interface workflow:

1. Session Initiation:
   • When the BM-SC decides to start an MBMS session, it sends a message over the SGmb interface to the MBMS-GW, indicating the session parameters such as QoS requirements, service area, and control nodes involved (e.g., MME, SGSN).
   • The MBMS-GW receives this message and proceeds to allocate the necessary network resources to support the session.
2. Session Update:
   • During an active MBMS session, if there is a need to update session parameters (e.g., extending the service area or modifying QoS), the BM-SC sends an update message over the SGmb interface to the MBMS-GW.
   • The MBMS-GW updates the session according to the new parameters and ensures that all relevant network elements are informed of the changes.
3. Session Termination:
   • When the MBMS service is no longer required, the BM-SC sends a session stop message over the SGmb interface to the MBMS-GW.
   • The MBMS-GW then deallocates the resources and informs all involved nodes to terminate the session.
4. Heartbeat Procedure:
   • The SGmb interface supports a heartbeat mechanism that enables the BM-SC and MBMS-GW to detect any failures in the communication path between them.
   • This procedure involves the periodic exchange of heartbeat messages, allowing the detection of path failures or restarts of the MBMS nodes.

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