02.683GPPRelease 1999Stage 1TSVoice Group Call Service (VGCS)
The VGCS is defined in the following. Figure 1 gives an explanation of the logical concept of the VGCS.
a) The VGCS enables a calling service subscriber or calling dispatcher to establish a voice group call to destination subscribers belonging to a predefined group call area and group ID.
Applications for voice group call services typically involve multiple group members in a small group call area, for which the VGCS should provide spectrum efficient solutions.
- The calling service subscriber as well as the destination service subscribers may be any service subscriber which has subscribed to the related group ID. The calling dispatcher may be any dispatcher who is entitled to originate VGCS calls to the related call reference.
- Destination subscribers are all destination service subscribers or a group of destination service subscribers identified by the called group ID which have their present location in the group call area, and pre-registered destination dispatchers. Destination service subscribers shall be notified with the group ID, not by paging the subscriber individually. Destination dispatchers shall be called individually with their identity.
Service subscribers may become late destination subscribers when entering the group call area within 500 ms after reception of the first notification message related to the VGCS call. Service subscribers which leave the corresponding group call area during an on going VGCS call of which they are member cease to be destination subscribers.
d) The voice group call shall be established in a group call area which is comprised of one or a cluster of cells. Group call areas shall be predefined in the network by the service provider, co-ordinated by the network operator.
In case of a calling service subscriber initiating a VGCS, the group call area is uniquely identified by the actual cell in which the service subscriber resides at the moment of VGCS call initialization and by the group ID they issue.
A calling dispatcher initiating a VGCS call will be connected to a related predefined group call area. The entitlement of the dispatcher is checked by the network element responsible for the voice group call management by verification of the calling identity. Since a dispatcher may be registered to more than one group call area and group ID an indication of the wanted group call area and group ID has to be given in form of a dedicated address called by the dispatcher.
e) The service shall permit only one talking service subscriber at any moment; additionally up to five dispatcher can be talking simultaneously at one time. Dispatchers should hear all combinations of voices other than their own. Listening service subscribers shall hear the combination of all voices. The talking service subscriber shall be given some indication if any dispatchers are also talking.
NOTE 1: The indication may be just the dispatcher’s voice.
A dispatcher shall be able to talk at any moment , but the network operator may require him to signal the wish to talk to the network. If the network operator requires a dispatcher to indicate his wish to talk then a dispatcher in that network shall also indicate that he has finished speaking.
Service subscribers who wish to talk shall indicate this. They shall only be able to become talking subscribers if there is no other talking service subscriber. The right to be a talking service subscriber is allocated on a first come first served basis without queuing. Once a service subscriber has become a talking subscriber they shall eventually indicate their wish to become a listening subscriber, or the network may detect that they are no longer a talking subscriber due to time-out or other mechanisms.
SMS, CW and procedures for supplementary service management are not possible for a service subscriber.
f) The calling service subscriber or calling dispatcher shall be informed by the network with a suitable indication about the successful establishment of the voice group call so that he can start to speak.
NOTE 2: A successful establishment means that all voice group call downlink channels are allocated, with the restrictions mentioned in clause 6, whether somebody is listening or not, and the related dispatchers are alerted.
The system provides that for an established voice group call the uplink assignment to a service subscriber who wishes to talk is performed under normal conditions in <300 ms after a request to talk is made.
The mobile station of the talking service subscriber shall be requested to send its IMSI to the network in order so that the talker’s IMSI be stored in the event records.
g) Authentication is mandatory at GSM-call set up. To allow fast call set up in VGCS authentication of calling service subscribers or calling dispatchers at invocation may optionally be delayed. Similarly authentication of the talking service subscriber may optionally be delayed to allow fast access.
Confidentiality on the radio path is optional.
h) Different levels of priority and pre-emption shall be applied as defined in the stage 1 description on the enhanced Multi-Level Precedence and Pre-emption Service (eMLPP) in TS 02.67.
i) A number of voice group calls may exist simultaneously intended for different groups of destination users in the same group call area.
Parallel voice group calls are possible to the same group of destination subscribers in different, possibly overlapping, group call areas.
j) A voice group call shall be released on demand of the calling service subscriber or by an entitled dispatcher or by the network.
NOTE 3: The release by the calling service subscriber is only possible if the uplink is assigned to the calling service subscriber.
Automatic release of a voice group call after a selectable time of no voice activity is required.
j) If the mobile station having the uplink assigned leaves the group call area, it shall also leave the voice group call. However, the voice group call shall be maintained by the network.
This behaviour shall also apply if the mobile station is the calling service subscriber.
k) VGCS shall also be provided in case of roaming. For this, certain group IDs shall be defined as supra-PLMN group IDs which have to be co-ordinated between the network operators and which shall be known in the networks and in the SIM. A service subscriber which is entitled by his subscription to establish voice group calls while roaming shall only be able to use supra-PLMN group IDs in case of roaming.
l) For certain levels of priorities an acknowledgement of receipt of a voice group call can be required as an application option (e.g. for railways emergency calls) from all or from nominated destination service subscribers (nomination is recorded on the SIM). The acknowledgement itself shall be performed at the end of the voice group call. The acknowledgement shall indicate the time the reception started and the time the reception terminated. The acknowledgement has to be given to a predefined recipient.
m) It shall be possible for a service subscriber to activate or deactivate the voice group call reception for different group IDs. The selection list is stored on the SIM corresponding to the subscribed group IDs. It shall be possible to prohibit the deactivation of group IDs used for high priority calls.
Mobile users that are configured as dispatchers and which are registered in the network for a certain voice group call and which have also a subscription for VGCS with the same group ID as the voice group call for which they are dispatcher shall deactivate this group ID when they are located in the corresponding group call area in order to avoid conflicts between paging for the dispatcher and notifications for the group ID.
NOTE: VGCS1, VGCS2, VGCS3 = particular voice group calls with the attributes pre-registered in the network.
A, B, C, D = service subscriber with group ID a, b, c or d, respectively.
I. II, III, IV = group call areas.
w, x, y, z = dispatchers connected via normal GSM links or external networks.
Figure 1: Logical concept of the VGCS