Description
MCPTT Emergency Group Call (MEGC) is the actual service invocation and session establishment procedure that utilizes an MCPTT Emergency Group (MEG). It represents the end-to-end process of initiating, authorizing, establishing, and maintaining a real-time, typically half-duplex voice, group communication session targeted at a specific MEG. The service is a cornerstone of the 3GPP Mission Critical Services suite. Architecturally, it involves the MCPTT client on the user's device, the MCPTT application server, and the underlying 3GPP access and core networks (E-UTRAN/EPC or NG-RAN/5GC).
The workflow begins when an authorized MCPTT user activates the emergency group call function, specifying the target MEG identifier. The MCPTT client sends a service request to the MCPTT application server over the established signaling connection (using protocols like SIP over IMS). This request is marked as an emergency request. The MCPTT server performs several critical checks: it authenticates the user, verifies their authorization to initiate a call to the requested MEG, and retrieves the current member list for that MEG. Upon validation, the server initiates the media session establishment. A key differentiator of MEGC is its interaction with the network's policy and charging control (PCC) framework. The MCPTT server communicates with the Policy Control Function (PCF) to request the establishment of a dedicated, prioritized bearer (in 4G) or QoS Flow (in 5G) for the media stream. This bearer is assigned a high-priority QoS Class Identifier (QCI) or 5QI, often with pre-emption capabilities, to ensure the call is not blocked by congestion.
Simultaneously, the server signals to the MCPTT clients of all MEG members (except the initiator), alerting them to the incoming emergency group call. These alerts are typically intrusive and may override other device activities. Once the media path is established via the network's user plane functions (UPF in 5G, PGW in 4G), a one-to-many media distribution tree is formed, with the initiator's audio stream replicated to all group members. The server manages the floor control for the call, granting the right to speak according to MCPTT rules, which for emergency calls may involve pre-emptive or prioritized floor granting. The call persists until explicitly terminated, providing a stable channel for crisis coordination.
Purpose & Motivation
MEGC was created to fulfill the stringent requirement for instantaneous, guaranteed, and group-wide communication during public safety and emergency response operations. While general MCPTT group calls provide efficient team communication, they may not have the absolute priority and resource guarantees required for life-or-death situations. MEGC addresses this gap by defining a specialized, highest-priority service class within MCPTT. The problem it solves is the potential failure or delay of a critical group call due to network congestion, contention with other services, or complex setup procedures.
Historically, first responders used push-to-talk on LMR systems, where an emergency group call often meant switching to a dedicated, pre-allocated "emergency" channel or using a channel-grabbing feature. The purpose of standardizing MEGC in 3GPP (starting in Release 13) was to replicate and improve upon this capability in broadband LTE and 5G networks. It addresses the limitations of best-effort IP communication by mandating network-enforced priority end-to-end, from the radio interface through the core to the application server. This ensures that emergency communications from authorized personnel can pre-empt other network traffic, a critical capability during major incidents where public networks become congested. Its creation was motivated by the need for a standardized, interoperable, and carrier-grade emergency group call feature that could be deployed globally on commercial networks, enabling seamless cooperation between different agencies and across geographical boundaries.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (212 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-13, normative work from Rel-15.
In Release 15, the MEGC function was enhanced with new procedures for remotely initiated group calls by both client and server, along with mechanisms for managing functional aliases between the serving and owning MCPTT servers. It also introduced capabilities for subscribing to group dynamic data and defined specific triggering criteria for MCPTT emergency location. Furthermore, the release provided clarifications and corrections for broadcast group call control and SIP usage in group call scenarios.
- Remotely initiated group call client procedures TS 24.379CR0354
- Remotely initiated group call server procedures TS 24.379CR0355
- Managing functional alias – MCPTT server serving the user TS 24.379CR0390
- Managing functional alias – MCPTT server owning the functional alias TS 24.379CR0391
- Enter-Exit emergency alert area TS 24.379CR0411
- Subscription to group dynamic data TS 24.379CR0432
+ 6 more changes
In Release 16, the MEGC function was enhanced with support for functional aliases in emergency alerts and broadcast group calls, and introduced the capability for automatic group affiliation and deaffiliation based on location or functional alias. It also added new procedures for preconfigured regroup using an XML schema and allowed for automatic triggering of an emergency group call following an emergency alert. Furthermore, updates were made to service authorization procedures to limit the number of authorized clients per MCPTT user and to restrict the number of accepted emergency group calls based on the calling functional alias.
- Support of functional aliases in broadcast group calls TS 24.379CR0484
- Triggering an emergency group call after an emergency alert automatically TS 24.379CR0485
- List of MCPTT group members who did not acknowledge the group call request TS 24.379CR0486
- Support of functional aliases in emergency alerts TS 24.379CR0500
- Preconfigured regroup – XML schema for regroup using preconfigured group TS 24.379CR0529
- Additional commencement modes for group calls TS 24.379CR0542
+ 19 more changes
In Release 17, the MEGC function was enhanced with new interconnect procedures to enable emergency group calls across different MCPTT systems, including specific procedures for pre-arranged groups, emergency alerts, and private calls. The release also introduced the ability for an authorized user to perform a remote change of another MCPTT user's selected group. Furthermore, location reporting for emergencies was improved by adding altitude, timestamp, and accuracy attributes to the MCPTT location XML schema.
- Add altitude, timestamp to MCPTT location XML schema TS 24.379CR0625
- Check for Preconfigured Group Use Only TS 24.379CR0626
- Call transfer for MCPTT private call, call control part TS 24.379CR0673
- Add accuracy to MCPTT location XML schema TS 24.379CR0698
- Call forwarding for MCPTT private call, call control part TS 24.379CR0709
- Interconnect - MCPTT Gateway Server functional entity TS 24.379CR0720
+ 57 more changes
In Release 18, enhancements for MCPTT Emergency Group Call (MEGC) included new procedures for emergency alerts within ad-hoc group calls and support for location information requests from an MCPTT client using functional aliases. The release also introduced mechanisms for group-regroup notifications to clients affiliating after a regroup operation and enabled QoS support for clients behind MC gateway UEs. Furthermore, it defined procedures for emergency alerts to clients performing late affiliation to ensure comprehensive emergency call handling.
- MCPTT Chat group join to group regroup TS 24.379CR0855
- Addition of 5G MBS inter-RAT information in MCPTT signalling TS 24.379CR0873
- MC GW UE functions in MCPTT TS 24.379CR0901
- General adhoc group call procedures in single system - Protoc impl for MCPTT TS 24.379CR0902
- Add the description of 5MBS in MCPTT TS 24.379CR0899
- Support MCPTT over 5G ProSe TS 24.379CR0905
+ 69 more changes
In Release 19, the MCPTT Emergency Group Call (MEGC) function was enhanced with new procedures for emergency remote floor requests and refined criteria for determining participants during ongoing ad hoc group emergency alerts. It also introduced the ability for an authorized user to release an ad hoc group call and added an option to apply automatic commencement for such calls. Furthermore, corrections and clarifications were made to ad hoc group call setup, group regroup procedures, and the handling of criteria for ad hoc group communications.
- Modify list of participants by changing the criteria during an ongoing MCPTT ad hoc group call TS 24.379CR1004
- Adhoc group emergency alert add criteria to the SIP message containing the participant lists sent to the authorised users TS 24.379CR1014
- MCPTT adhoc group call to migrated user TS 24.379CR1015
- Adding option to apply automatic commencement for adhoc group calls TS 24.379CR1021
- Modifying the criteria for determining the participants during an ongoing ad hoc group emergency alert TS 24.379CR1018
- Adhoc group call release by an authorized user (MCPTT) TS 24.379CR1022
+ 31 more changes
Explore further
Broader topics and technologies where MEGC plays a role.
Defining Specifications
3GPP specifications that define or reference MEGC, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 24.379 vj50 | Mission Critical Push To Talk (MCPTT) call control | Rel-19 |
| TS 36.579 | 3GPP TR 36.579 | Rel-13 |
| TS 37.579 vi40 | Mission Critical services conformance testing | Rel-18 |