Voice Group Call » History » Revision 3
Revision 2 (laforge, 11/20/2022 06:25 PM) → Revision 3/4 (laforge, 11/20/2022 07:03 PM)
h1. Voice Group Call (VGCS)
Voice Group Calls are part of the [[ASCI]] features introduced primarily for GSM-R. They're basically the _bigger brother_ of [[Voice_Broadcast_Call]] (VBS). So if you're unfamiliar with the former, it is suggested to first read up on VBS.
While VBS calls are unidirectional, VGCS calls are bi-directional between multiple parties. There's always one _talker_ and many _listeners_. The talker can change dynamically over time, basically creating a user experience of a classic two-way radio. There is always only one talker active at any moment.
Like VBS, VGCS works with the concept of _groups_. Eachs subscriber can be part of up to 50 groups, and calls are made to a specific group. There can be any number of parallel groups active in parallel next to each other. Each group has an _area_ describing a list of cells in which subscribers can participate in the group call.
* notification works via NCH, like VBS
* there still is only one TCH per BTS, like VBS
** however, that TCH has uplink: For voice, in case the talker is in the current cell
** for all listeners, the TCH is downlink-only, like in VBS
h2. Seizure of the uplink
* the NCH contains information if the uplink of a given group is currently free
** if it is, a subscriber wanting to talk can send an uplink request on the group TCH uplink
** if it is not free, the subscriber must request via RACH
h2. Arbitration
A subscriber who wishes to talk signals this to the network. The right to talk is allocated on a first-come-first-serve basis without queuing.
h2. Specifications
For more information, see
* 3GPP TS 42.068 (Stage 1)
* 3GPP TS 43.068 (Stage 2)
* 3GPP TS 44.068 (Stage 3; GCC Layer 3 Protocol)