Cellular Network Infrastructure

h1. Voice Broadcast Call (VBCS)

Voice Broadcast Calls are part of the [[ASCI]] features introduced primarily for GSM-R.

They allow the distribution of speech (or other signals which can be transmitted via the speech codec), generated by a service subscriber, into a predefined geographical area to all or a group of service subscribers located in this area.

VBS is an uni-directional service.

Voice can originate from any subscriber (with related privileges).

VBS contains the notion of a _VBS group_.  Subscribers are either part of a group or not. Each subscriber can be part of up to 50 groups. Every group is identified by a _Group ID_.  Every group is realted to a _Group Call Area_ (a group of cells in).

Only subscribers that are members of the _Group ID_ which are currently within the _Group Call Area_ will receive the voice information.  If they leave the area, they loose the call.

Subscribers can activate/deactivate their group membership; that information is stored on the SIM card.

h2. Security

Normal GSM authentication is only performed for the calling subscriber, but not for the called (receiving) subscribers; those have uni-directional downlink signals only with no return channel.

Before Release 6, VBS calls were always in cleartext.

Release 6 introduced the optional ciphering of VBS.  The group specific key material are stored on the USIM (e.g. via OTA).

h2. Specifications

For more information, see

* 3GPP TS 42.069 (Stage 1)

* 3GPP TS 43.069 (Stage 2)

* 3GPP TS 44.069 (Stage 3; BCC Layer 3 Protocol)