Voice Group Call Member

Description

A Voice group call member is defined in 3GPP TS 23.068 and TS 43.068 as any group member or dispatcher who is currently participating in an ongoing voice group call. This term is fundamental to the Voice Group Call Service (VGCS), a feature originally specified for GSM and later adapted for LTE and 5G mission-critical services. VGCS allows multiple users to communicate in a group call using a push-to-talk mechanism, where only one member speaks at a time while others listen. The service is designed for professional users such as police, fire brigades, and ambulance services, who require efficient one-to-many communication.

In the architecture, a voice group call is established within a group call area, which is a set of cells where the call is active. The network maintains a list of group members and dispatchers. A dispatcher is a special user, often in a control room, who can monitor and participate in multiple group calls. When a group call is ongoing, any group member or dispatcher who joins becomes a voice group call member. The network ensures that these members receive the downlink voice stream and can request the uplink channel to speak. The group call is managed by the Group Call Register (GCR) and the Group Call Service Center (GCSC) in the core network, which handle call setup, resource allocation, and mobility.

From a technical perspective, VGCS uses a combination of point-to-multipoint downlink and point-to-point uplink. The downlink is typically broadcast in the cells of the group call area, allowing all members to receive the voice without individual connections. The uplink is granted to one member at a time, based on a talker arbitration mechanism. This efficient use of radio resources is crucial in bandwidth-constrained environments. In LTE, the equivalent service is known as Mission Critical Push-to-Talk (MCPTT), which builds on the IP Multimedia Subsystem (IMS) and uses unicast or multicast bearers. However, the concept of a voice group call member remains similar: an active participant in a group communication session.

The term has been stable across releases, with only minor editorial changes in capitalization. This stability reflects the maturity of the service and its continued relevance. Even as networks evolve to 5G, group communication services are being standardized under the Mission Critical Services (MCS) framework, where the voice group call member is a key role. Understanding this term is essential for engineers working on public safety networks, as it defines the user plane and control plane interactions for group calls.

In summary, a voice group call member is an active participant in a voice group call, which is a critical service for professional users. The term encompasses both regular group members and dispatchers, and its definition has remained consistent across 3GPP releases, underscoring the stability of the underlying service.

Purpose & Motivation

The concept of a voice group call member exists to facilitate efficient group communication in professional mobile radio (PMR) systems. Traditional cellular networks were designed for one-to-one calls, but public safety and professional users require one-to-many communication with fast call setup and efficient resource usage. The Voice Group Call Service (VGCS) was created to address this need, allowing a group of users to share a single call. The term 'voice group call member' identifies the active participants in such a call, distinguishing them from passive group members who are not currently in the call.

Before VGCS, group communication was achieved through separate calls or conference bridges, which were inefficient and slow. VGCS introduced a more efficient mechanism by using broadcast downlink and shared uplink, reducing the load on the network and enabling rapid call setup. The definition of a voice group call member helps in specifying the behavior of the network and the terminals: only members are entitled to receive the call and request the uplink. This clarity is essential for interoperability and for ensuring that resources are allocated correctly.

As networks evolved, the concept was carried forward into LTE and 5G mission-critical services, where the term is still used to denote active participants in group calls. The purpose remains the same: to enable reliable, efficient, and scalable group communication for users who need to coordinate in real-time.