Calling service subscriber

Description

The term "Calling service subscriber" is defined in 3GPP TS 42.068 and TS 42.069 as the service subscriber which originates the Voice Group Call Service (VGCS) call. VGCS is a feature that allows a calling subscriber to establish a group call to a predefined group of subscribers in a specific area. The calling service subscriber is the initiator of such a call, and their role is distinct from that of the called service subscribers who are the recipients of the group call.

In the context of VGCS, the calling service subscriber is typically a dispatcher or a user with the authority to initiate group communications. The VGCS call is established by the calling subscriber dialing a specific group identity (Group ID) and possibly a service code. The network then sets up the call to all group members located in the group call area. The calling service subscriber becomes the talker in the group call, and other participants can request to talk using the uplink access procedure.

The calling service subscriber is identified by their IMSI or TMSI, and their subscription profile includes the necessary VGCS permissions. The network ensures that only authorized subscribers can initiate group calls. The calling service subscriber may also have priority levels assigned, which can affect the handling of the call in case of network congestion or pre-emption.

The term is used in the context of VGCS service descriptions and technical realization. It helps to differentiate between the various roles in a group call: the calling service subscriber (originator), the called service subscribers (recipients), and the dispatchers (who may also initiate calls). The calling service subscriber is responsible for initiating the call and may also control the call, such as ending it or changing the group.

This term has been present since Release 8, when VGCS specifications were updated to include this definition. It has remained unchanged through Release 19, indicating stability in the VGCS service definition. The calling service subscriber concept is essential for understanding the operation of VGCS and for implementing the service in GSM and UMTS networks.

Purpose & Motivation

The term "Calling service subscriber" was introduced to clearly identify the originator of a Voice Group Call Service (VGCS) call within the 3GPP specifications. VGCS is a service that enables group communication in cellular networks, primarily for professional users such as public safety, transportation, and utilities. In such systems, it is crucial to distinguish between the different roles: the one who initiates the call (calling service subscriber), the ones who receive it (called service subscribers), and dispatchers who may have special privileges.

Before the explicit definition, the term "calling subscriber" was used in some contexts, but it was ambiguous because it could refer to the originator of any call, not specifically a VGCS call. The introduction of "Calling service subscriber" in Release 8 provided clarity and precision, especially as VGCS specifications were refined. This distinction is important for charging, authorization, and call control procedures. For example, the network must know who initiated the call to apply the correct charging and to enforce group membership policies.

The term also helps in describing the technical realization of VGCS, as it appears in stage 2 and stage 3 specifications. It ensures that the roles are consistently understood across different network entities, such as the MSC, VLR, and Group Call Register (GCR). The calling service subscriber is the entity that requests the group call, and the network uses this information to set up the call and manage the group call area.