Group call

Description

A Group Call is a core service in 3GPP group communication, allowing a user to transmit data (typically voice) to multiple recipients simultaneously. It is defined as the relationship that exists between the members of a group for the purpose of transferring data. More than one group call may exist in a group, and a group call establishes an active group. This means that when a group call is initiated, the group becomes active, and the network sets up the necessary resources to deliver the call to all participating members.

Group calls are used in various applications, including public safety (e.g., police, fire, ambulance), commercial dispatch, and mission-critical communications. The service enables efficient use of network resources by multicasting the call to multiple users in a given area, rather than setting up individual connections for each recipient. The group call can be voice, data, or video, depending on the service.

In GSM/UMTS, the Voice Group Call Service (VGCS) and Voice Broadcast Service (VBS) provide group call capabilities. VGCS allows bidirectional communication among group members, while VBS is unidirectional (broadcast). The network uses the Group Call Register (GCR) to store group definitions and call-related data. The group call anchor MSC manages the call, and relay MSCs handle distribution to cells in their areas.

In LTE and 5G, group call services are part of the Mission Critical Services (MCS) framework, specifically MCPTT (Mission Critical Push-to-Talk). The architecture includes functional entities like the Group Management Server (GMS), which manages groups and their members, and the MCPTT Server, which handles call control. Group calls can be pre-arranged or chat-based, and can involve floor control to manage who speaks when.

The group call concept has evolved with technology. In Rel-20, the definition was updated to focus on MCPTT: 'A mechanism by which an MCPTT user can make a one-to-many MCPTT transmission to other users that are members of MCPTT group(s).' This reflects the shift towards IP-based mission-critical services. Despite changes in wording, the fundamental purpose remains: to enable efficient one-to-many communication among a defined set of users.

Purpose & Motivation

Group calls exist to provide efficient one-to-many communication in cellular networks. Traditional voice calls are point-to-point, which is inefficient for disseminating information to a large number of users simultaneously. In scenarios like public safety, dispatch, and emergency response, it is essential to communicate with a group of responders at once. Group calls solve this by allowing a single call instance to serve multiple recipients, reducing signaling overhead and radio resource usage.

Before group call services, users had to establish multiple individual calls or use conference bridges, which were cumbersome and not optimized for mobile networks. The introduction of group calls in Rel-4 (with VGCS/VBS) provided a native mechanism for group communication, leveraging multicast capabilities in the radio access network. This allowed the network to deliver the call only to cells where group members are located, optimizing resource usage.

With the evolution to LTE and 5G, group calls have been adapted to IP-based mission-critical services. The MCPTT standard (3GPP Release 13 onwards) defines group calls over LTE, supporting features like floor control, priority, and pre-emption. The Rel-20 definition update reflects the integration of group calls into the MCPTT framework, ensuring that the concept remains relevant in modern networks.