Description
The Mission Critical MBMS subchannel Control Protocol (MCMC) is a control-plane protocol specified in 3GPP TS 24.380. It operates within the framework of Mission Critical Services (MCS), specifically for Mission Critical Push-to-Talk (MCPTT) over MBMS (Multimedia Broadcast Multicast Service). Its primary function is to manage the establishment, modification, and release of MBMS subchannels that are allocated for MCPTT group communication sessions. An MBMS subchannel is a logical channel within an MBMS bearer service, used to carry media and control information for a specific MCPTT group. The protocol enables the MCPTT server to request the BM-SC (Broadcast Multicast Service Centre) to activate or deactivate these dedicated subchannels based on the dynamic needs of group calls.
Architecturally, MCMC resides between the MCPTT application server and the BM-SC in the core network. It defines specific procedures and messages for subchannel control. For instance, when an MCPTT group call is initiated, the MCPTT server uses MCMC to send a subchannel activation request to the BM-SC. This request includes parameters such as the TMGI (Temporary Mobile Group Identity), session description, and QoS requirements for the subchannel. The BM-SC, upon receiving this request, coordinates with the LTE or 5G NR network to establish the necessary MBMS radio bearers and allocate resources for broadcasting the media to all subscribed users within the service area.
The protocol ensures that MBMS resources are used efficiently for mission-critical group communications. Instead of establishing multiple unicast connections, a single MBMS broadcast stream serves all members of an MCPTT group, conserving radio and core network resources, especially in scenarios with many listeners. MCMC handles the lifecycle of these subchannels, including modifications during a session (e.g., adding a new talker, changing QoS) and timely release when the group call ends. This management is crucial for maintaining service continuity, prioritizing critical traffic, and ensuring that network capacity is optimally utilized for public safety operations where reliable, low-latency group communication is paramount.
Purpose & Motivation
MCMC was introduced to address the specific requirements of Mission Critical Services (MCS) for efficient, one-to-many group communications. Traditional MCPTT over unicast paths can strain network resources when serving large groups, as it requires individual data streams to each user. This is inefficient for public safety scenarios where many first responders need to receive the same voice transmission simultaneously. The purpose of MCMC is to leverage the broadcast/multicast capabilities of MBMS to offload this traffic, but a dedicated control mechanism was needed to integrate MBMS with the MCPTT application layer.
Prior to MCMC, MBMS control was more generalized and not optimized for the dynamic, session-based nature of mission-critical group calls. The creation of MCMC solved the problem of how an MCPTT application server could directly and dynamically control MBMS subchannels. It provides the necessary signaling interface to request broadcast resources on-demand, align them with specific MCPTT group sessions, and manage their QoS parameters. This enables network operators to support large-scale mission-critical communications with predictable latency and high reliability while making efficient use of limited radio spectrum, a critical consideration during major incidents or disasters.
Key Features
- Dynamic activation and deactivation of MBMS subchannels for MCPTT groups
- Signaling interface between MCPTT Application Server and BM-SC (Broadcast Multicast Service Centre)
- Support for QoS parameter negotiation for mission-critical broadcast bearers
- Management of subchannel lifecycle (establishment, modification, release)
- Association of subchannels with specific TMGIs (Temporary Mobile Group Identities) and MCPTT group IDs
- Enables efficient one-to-many media distribution for public safety communications
Evolution Across Releases
Initial introduction of MCMC in 3GPP TS 24.380. Defined the basic protocol procedures for MBMS subchannel control to support Mission Critical Push-to-Talk (MCPTT) services over LTE-based MBMS. Established the signaling messages for activation, modification, and deactivation of subchannels between the MCPTT server and the BM-SC.
Defining Specifications
| Specification | Title |
|---|---|
| TS 24.380 | 3GPP TS 24.380 |