Description
The Temporary Multicast Group Identifier (TMGI) is a critical identifier within the 3GPP Multimedia Broadcast Multicast Service (MBMS) architecture. It uniquely identifies a specific MBMS session within a PLMN (Public Land Mobile Network) or across PLMNs. A TMGI is not a permanent address but is temporarily assigned for the duration of a specific MBMS service session. Its structure, defined in 3GPP TS 23.003, typically includes a Mobile Country Code (MCC), a Mobile Network Code (MNC), and a service-specific group ID, allowing for global or network-specific uniqueness.
The TMGI's primary function is to act as a handle for the entire MBMS service delivery chain. Service announcement procedures, which inform User Equipment (UE) about available MBMS content, include the TMGI. When a UE wishes to receive a service, it uses the TMGI to initiate a join procedure towards the network, indicating its interest in the specific multicast group. Within the core network, the BM-SC (Broadcast Multicast Service Center) allocates the TMGI and uses it to identify the bearer and session towards the access network. In the radio access network (RAN), the TMGI is used to identify the common radio resources (like an MBMS Point-to-Multipoint Control Channel) allocated for that session, enabling multiple UEs to efficiently receive the same data stream.
From a protocol perspective, the TMGI is carried in multiple layers. It appears in NAS (Non-Access Stratum) signaling messages for session management, in RRC (Radio Resource Control) messages for multicast group management in the RAN, and is integral to the IP multicast addressing scheme used for the data plane. The network uses the TMGI to map the MBMS service to a specific IP multicast address and port combination for data distribution. This end-to-end binding ensures that from the service originator (BM-SC) to the receiving UE, all network elements can correctly identify and process the data flow associated with a particular broadcast or multicast session.
Purpose & Motivation
The TMGI was created to solve the fundamental problem of identifying and managing multicast sessions in a cellular environment. Unlike unicast, where a connection is unique to a single UE, multicast involves delivering the same content to potentially millions of devices. A unique, session-specific identifier was needed to allow UEs to signal their interest (join/leave), for the network to allocate shared resources efficiently, and to distinguish between multiple concurrent MBMS services.
It addresses the limitations of using only IP multicast addresses for this purpose in a mobile context. An IP multicast group address alone does not contain the necessary network routing context (e.g., home network) and is not ideal for signaling in mobile-specific control planes. The TMGI provides a structured, mobile-network-friendly identifier that incorporates PLMN identity, enabling network-based service discovery, access control, and roaming support. Its creation was motivated by the introduction of MBMS in Release 6, which aimed to enable efficient mass content delivery (like mobile TV) over 3GPP networks, requiring a robust session management and identification mechanism tailored for cellular architectures.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (575 CRs across 6 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-6, normative work from Rel-15.
In Release 15, the TMGI function was enhanced to support new server-initiated procedures and interconnection capabilities. Specifically, it introduced the MC server initiated group de-affiliation procedure, support for group regrouping with an MC system, and group configuration for interconnection. Furthermore, new capabilities like header compression for MC services over MBMS and subscription to group dynamic data were added.
- Introduction of MC server initiated group de-affiliation procedure TS 23.280CR0026
- Enhancement on group regrouping with an MC system TS 23.280CR0052
- MC server initiated group de-affiliation from group(s) in partner system TS 23.280CR0053
- MBMS bearer event notification TS 23.280CR0025
- Header compression for MC services over MBMS TS 23.280CR0058
- Group configuration for interconnection TS 23.280CR0074
+ 84 more changes
In Release 16, the TMGI function was enhanced to support **"regroup using preconfigured group"** and **"broadcast group regroup"** procedures, enabling more dynamic multicast group management. New capabilities were introduced for **"criteria based automatic group affiliation and de-affiliation"** and for providing a **"list of MCPTT group members who did not acknowledge the group call request"**. Furthermore, support for **"functional aliases"** was extended to broadcast, emergency, and imminent peril group calls.
- Regroup group configuration TS 23.280CR0171
- Broadcast group regroup TS 23.280CR0174
- Group status notification over MBMS TS 23.280CR0178
- MBMS listening status report TS 23.280CR0181
- Interconnection chat group call TS 23.379CR0143
- Regroup using preconfigured group TS 23.379CR0164
+ 79 more changes
In Release 17, enhancements for TMGI-related functions focused on expanding interconnect procedures for MCPTT and MCVideo services, including pre-arranged group originating/controlling and remote change of selected group. The release also introduced new capabilities for handling functional aliases, such as providing lists of aliases used by affiliated members and associating them with MCVideo groups. Furthermore, it added clarifications and procedures for group area configuration, geographic area entry/exit handling for MCVideo, and checks for preconfigured group use.
- Providing activated functional alias information to the group controlling server TS 23.280CR0207
- Providing the list of functional aliases used by affiliated group members TS 23.280CR0208
- Clarification on setting the MBMS broadcast areas when activating MBMS bearer TS 23.280CR0255
- Dynamic data associated with a group at GMS TS 23.280CR0260
- Clarification on user subscription, group policy and functional alias policy TS 23.280CR0258
- Handling the originating side of functional alias for group calls TS 23.379CR0238
+ 120 more changes
In Release 18, the TMGI function was enhanced to support multicast MBS data reception by UEs in the RRC_INACTIVE state, including new mobility procedures for these sessions. It also introduced comprehensive support for ad hoc group emergency alerts, defining new procedures for initiation, participant notification, and subsequent communications across multiple MC systems. Furthermore, new group management procedures were specified, such as group de-affiliation for specific UEs and updates to group message delivery.
- Group Message Delivery TS 23.247CR0143
- Support of MBS multicast reception by UEs in RRC_INACTIVE state TS 23.247CR0149
- Support RRC_INACTIVE UE receiving multicast MBS data TS 23.247CR0159
- On the Update of Group Message Delivery TS 23.247CR0163
- Mobility procedures for UEs receiving multicast MBS session data in RRC Inactive state TS 23.247CR0179
- Update group message delivery procedure TS 23.247CR0220
+ 153 more changes
In Release 19, the TMGI function was enhanced to support dynamic modification of participant lists during ongoing ad hoc group calls and emergency alerts by changing the selection criteria, both within single and across multiple MC systems. New procedures were also introduced for the migration of users during an ad hoc group call and for authorizing specific users to modify the criteria for emergency alert participants.
- Modify list of participants by changing the criteria during an ongoing ad hoc group emergency alert (single MC system) TS 23.280CR0413
- Changing the criteria during an ongoing ad hoc group emergency alert (multiple MC systems) TS 23.280CR0432
- Add the regroup group member update during MCX session TS 23.280CR0441
- Distribute criteria of an ad hoc group emergency alert request to authorised users TS 23.280CR0464
- ACM Group configuration management TS 23.280CR0466
- ACM providing interconnection MC service group ID TS 23.280CR0506
+ 100 more changes
In Release 20, the TMGI function was enhanced to support new procedures for Ad hoc Group calls, specifically for call forwarding scenarios both within a single MCPTT system and across multiple MCPTT systems. Furthermore, the concept of a "preconfigured ad hoc group regroup" was introduced and integrated into the existing regroup procedures and information elements. These updates extended TMGI management to better handle dynamic group communications for MCPTT and MCData services.
- Adding MCData to generic procedure for migration during an ongoing group communication TS 23.280CR0658
- Preconfigured ad hoc group regroup procedure TS 23.280CR0705
- Call forwarding for Ad hoc Group calls (information flows) TS 23.379CR0488
- Call forwarding for Ad hoc Group calls single MCPTT system (procedures) TS 23.379CR0489
- Call forwarding for Ad hoc Group calls involving multiple MCPTT systems (procedures) TS 23.379CR0490
- Updating preconfigured regroup IE to include ad hoc groups TS 23.280CR0706
+ 3 more changes
Explore further
Broader topics and technologies where TMGI plays a role.
Defining Specifications
3GPP specifications that define or reference TMGI, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 23.246 vj00 | MBMS Bearer Service Stage 2 Description | Rel-19 |
| TS 23.247 vj30 | 5G Multicast/Broadcast Service Architecture | Rel-19 |
| TS 23.280 vk10 | Common Architecture for Mission Critical Services | Rel-20 |
| TS 23.379 vk00 | MCPTT Functional Architecture | Rel-20 |
| TS 23.468 vj00 | Group Communication System Enablers for LTE | Rel-19 |
| TS 23.479 vj00 | MBMS API for Mission Critical Services | Rel-19 |
| TS 23.768 vc10 | Group Communication System Enablers for LTE | Rel-12 |
| TR 23.780 ve00 | MBMS for Mission Critical Communication Services | Rel-14 |
| TS 23.792 vg00 | MBMS API for Mission Critical Services | Rel-16 |
| TS 23.795 vg10 | V2X Application Architecture Study | Rel-16 |
| TS 24.008 vj50 | 3GPP TS 24008: Core Network Protocols | Rel-19 |
| TS 24.281 vj40 | MCVideo Signalling Control Specification | Rel-19 |
| TS 24.334 vj00 | ProSe Protocols and Procedures | Rel-19 |
| TS 24.379 vj50 | Mission Critical Push To Talk (MCPTT) call control | Rel-19 |
| TS 24.380 vj10 | MCPTT Media Plane Control Protocol | Rel-19 |
| TS 24.501 vj50 | 5G NAS Protocols Specification | Rel-19 |
| TS 24.575 vj00 | UE Pre-configuration for MBS | Rel-19 |
| TS 24.578 vj00 | UE policies for A2X services in 5GS | Rel-19 |
| TS 24.581 vj00 | MCVideo Media Plane Control Protocol Specification | Rel-19 |
| TS 24.587 vj30 | V2X Services Protocols for 5G System | Rel-19 |
| TS 24.588 vj00 | UE Policies for V2X Services in 5GS | Rel-19 |
| TS 25.304 vj00 | UTRA Idle Mode Procedures Specification | Rel-19 |
| TS 25.367 vj00 | Home NodeB Mobility Procedures | Rel-19 |
| TS 25.401 vj00 | UTRAN Overall Architecture | Rel-19 |
| TS 25.413 vj00 | Radio Access Network Application Part (RANAP) | Rel-19 |
| TS 25.423 vj00 | UTRAN RNSAP Specification | Rel-19 |
| TR 25.931 vj00 | UTRAN Signalling Procedures Examples | Rel-19 |
| TS 26.346 vj20 | MBMS User Services Media Codecs & Protocols | Rel-19 |
| TS 26.517 vj10 | 5G MBS User Service Protocols and Formats | Rel-19 |
| TS 26.802 vj20 | Multicast Enhancements for 5G Media Streaming | Rel-19 |
| TS 26.804 vj10 | 5G Media Streaming Extensions Study | Rel-19 |
| TS 26.849 vc10 | MBMS Operation on Demand (MooD) | Rel-12 |
| TS 26.852 ve20 | MBMS user service profiles, APIs and transport enabler study | Rel-14 |
| TS 26.880 ve00 | MBMS Enhancements for Mission Critical Video | Rel-14 |
| TR 26.946 vj00 | MBMS User Services Overview | Rel-19 |
| TR 26.981 vj00 | MBMS Provisioning & Content Ingestion Interface Study | Rel-19 |
| TS 29.061 vj00 | Packet Domain Interworking for PLMN | Rel-19 |
| TS 29.116 vj00 | REST-based protocol for xMB reference point | Rel-19 |
| TS 29.244 vj40 | PFCP Specification for Control/User Plane Separation | Rel-19 |
| TS 29.468 vj00 | MB2 Reference Point Protocol Definition | Rel-19 |
| TS 29.522 vj40 | 5G NEF Northbound APIs Stage 3 | Rel-19 |
| TS 29.532 vj30 | MB-SMF Service Based Interface Protocol | Rel-19 |
| TS 29.549 vj40 | SEAL API Specification for Vertical Applications | Rel-19 |
| TS 29.580 vj30 | 5G MBSF Service Interface Stage 3 Specification | Rel-19 |
| TS 31.102 vj40 | USIM Application Specification | Rel-19 |
| TS 32.273 vj00 | MBMS Charging Management | Rel-19 |
| TS 33.880 vf10 | Security Study for Enhanced Mission Critical Services | Rel-15 |
| TR 33.883 vi01 | Technical Report on 5G Multicast-Broadcast Services Security | Rel-18 |
| TS 36.300 vj00 | E-UTRAN Radio Interface Protocol Architecture Overview | Rel-19 |
| TS 36.579 | 3GPP TR 36.579 | Rel-6 |
| TS 36.868 vc00 | Study on Group Communication for E-UTRA | Rel-12 |
| TS 37.579 vi40 | Mission Critical services conformance testing | Rel-18 |
| TS 38.331 vj00 | NR Radio Resource Control (RRC) Protocol Specification | Rel-19 |
| TS 43.246 vj00 | MBMS in GERAN Stage 2 Specification | Rel-19 |
| TS 48.018 vj00 | BSS-SGSN Interface for GPRS Control | Rel-19 |