This TS specifies the stage two description of the Voice Group Call Service (VGCS) which allows speech conversation of a predefined group of service subscribers in half duplex mode on the radio link taking into account multiple subscribers involved in the group call per cell.
Service subscribers can become group members on a PLMN wide basis to one or more groups pre-defined in the
network by a corresponding group identification (group ID). The membership enables them to initiate or receive voice group calls associated with that group ID. Certain dispatchers connected to external networks also require the capability to initiate or receive voice group calls.
A prefix can be used together with the group ID to define a subset of the group members and to restrict the group of service subscribers able to receive a voice group call to this subset.
In addition to subscriber details in the HLR, it is necessary for the mobile station to be aware of its group membership by storing details on the SIM/USIM. This is required because it shall respond to notification messages which include only the group ID (i.e. no IMSI or TMSI details).
Having become a group member, each service subscriber can set to active state or deactive state the group ID or any one out of his several group IDs on the SIM/USIM. In active state the subscriber can initiate voice group calls to that group. When in deactive state the subscriber can not make voice group calls to the group and the mobile station ignores any notification for that group.
If no NCH (Notification Channel) is defined in the cell, mobiles shall assume VGCS service is not available on that cell.