Voice Group Call Service

The Voice Group Call Service ( VGCS, engl. For group call service ) is a service in GSM networks, which allows participants to communicate with several other participants at the same time.

Description

The service allows a voice-based communication to a predefined group of users in half-duplex mode, which means that more and can only speak a participant in a group call. Only certain members of the group have permission to build VGCS calls. There are special mobile phones needed to support the VGCS. The VGCS works fundamentally different push-to- talk over cellular and should not be confused with this.

First practical application was this service in the networks of the European rail network operators.

Function

Each call group has a unique identifier. The terminal lead in the SIM list of call groups in which the user is a member, as well as a list of identifiers of the group calls to be accepted. This list can be edited in the terminal.

For the information of network devices over a group call a special channel is needed, the Notification Channel ( NCH ).

The MSC maintains a list of subscribers who are eligible to participate in a special group call. In addition, it is decided at MSC, in which cells a certain group call is sent out. The MSC continues to decide on first-come- first-served basis to award the uplinks.

The network can handle a group call very resource friendly, as always can only speak a participant in the group call. Therefore, regardless of the number of call participants, only one uplink and one downlink channel per radio cell needs.

In addition to the mobile users can be defined in the fixed network for each call group a limited number of participants.

Once a terminal is located in a cell in which a group call is transmitted, the terminal device checks the identifier of the group call. Is this identifier included in the list of the likely group calls, the terminal establishes a connection and starts to reproduce the data transmitted in the downlink voice data. The user is informed of the active group call.

If the user currently on a call, the presence of a group call will be signaled. If it is implemented in the mobile network eMLPP, can be displaced depending on the configuration, the another call.