ETSI ETS 300 933 ed.4 (1998-06)
Digital cellular telecommunications system (Phase 2+) (GSM); Voice Group Call Service (VGCS); Stage 2 (GSM 03.68 version 5.4.1)
Digital cellular telecommunications system (Phase 2+) (GSM); Voice Group Call Service (VGCS); Stage 2 (GSM 03.68 version 5.4.1)
RE/SMG-030368QR3
Digitalni celični telekomunikacijski sistem (faza 2+) – Storitev govornega skupinskega klica (VGCS) – Stopnja 2 (GSM 03.68, različica 5.4.1)
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
01-december-2003
'LJLWDOQLFHOLþQLWHOHNRPXQLNDFLMVNLVLVWHP ID]D ±6WRULWHYJRYRUQHJD
VNXSLQVNHJDNOLFD 9*&6 ±6WRSQMD *60UD]OLþLFD
Digital cellular telecommunications system (Phase 2+) (GSM); Voice Group Call Service
(VGCS); Stage 2 (GSM 03.68 version 5.4.1)
Ta slovenski standard je istoveten z: ETS 300 933 Edition 4
ICS:
33.070.50 Globalni sistem za mobilno Global System for Mobile
telekomunikacijo (GSM) Communication (GSM)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EUROPEAN ETS 300 933
TELECOMMUNICATION July 1998
STANDARD Fourth Edition
Source: SMG Reference: RE/SMG-030368QR3
ICS: 33.020
Key words: Digital cellular telecommunications system, Global System for Mobile communications (GSM)
R
GLOBAL SYSTEM FOR
MOBILE COMMUNICATIONS
Digital cellular telecommunications system (Phase 2+);
Voice Group Call Service (VGCS) - Stage 2
(GSM 03.68 version 5.4.1)
ETSI
European Telecommunications Standards Institute
ETSI Secretariat
Postal address: F-06921 Sophia Antipolis CEDEX - FRANCE
Office address: 650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCE
Internet: secretariat@etsi.fr - http://www.etsi.fr - http://www.etsi.org
Tel.:+33 4 92 94 42 00 - Fax: +33 4 93 65 47 16
Copyright Notification: No part may be reproduced except as authorized by written permission. The copyright and the
foregoing restriction extend to reproduction in all media.
© European Telecommunications Standards Institute 1998. All rights reserved.
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ETS 300 933 (GSM 03.68 version 5.4.1): July 1998
Whilst every care has been taken in the preparation and publication of this document, errors in content,
typographical or otherwise, may occur. If you have comments concerning its accuracy, please write to
"ETSI Editing and Committee Support Dept." at the address shown on the title page.
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ETS 300 933 (GSM 03.68 version 5.4.1): July 1998
Contents
Foreword .5
1 Scope .7
2 Normative references.7
3 Definitions and abbreviations .8
3.1 Definitions .8
3.2 Abbreviations .8
4 Main concepts .9
4.1 Group definition.9
4.2 Group conversations.9
4.2.1 Group call initiation.9
4.2.1.1 Normal operation with successful outcome.9
4.2.1.2 Exceptional procedures .10
4.2.2 On-going group calls .10
4.2.2.1 Normal operation with successful outcome.10
4.2.2.2 Exceptional procedures .11
4.2.3 Leaving of a group call without termination .11
4.2.4 Group call termination .12
4.2.5 Acknowledgements .12
4.2.6 Transactions between the mobile station and the network .12
5 General architecture.12
5.1 Group Call Register (GCR).12
5.2 Voice group call responsibility.14
6 Compatibility issues.15
7 Transmission.15
7.1 Transmission architecture.15
7.2 Radio channels .15
7.3 Data confidentiality.16
8 Information storage .17
8.1 Information stored in the GCR.17
8.1.1 Information used for routing of service subscriber originated voice group
calls .17
8.1.2 Group call attributes .17
8.1.2.1 Group call area .18
8.1.2.2 Dispatcher identities .18
8.1.2.3 No activity time .18
8.1.2.4 Priorities.18
8.2 Information managed per subscriber.19
8.2.1 Stored in the HLR.19
8.2.2 Stored in the VLR .19
8.2.3 Stored in the SIM.19
8.3 Information used for routing of dispatcher originated voice group calls .19
9 Identities .20
9.1 Elementary identities for group calls.20
9.2 Use of identities in the network.20
10 Operation and maintenance aspects .21
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ETS 300 933 (GSM 03.68 version 5.4.1): July 1998
11 Function and information flows. 21
11.1 Group management . 21
11.2 Group membership management . 21
11.3 Call management . 22
11.3.1 Call establishment . 22
11.3.1.1 Service subscriber call establishment. 22
11.3.1.1.1 Initial stage . 22
11.3.1.1.2 Establishment of the transmission
means . 23
11.3.1.1.3 Release of the dedicated transmission
means of the calling service
subscriber. 23
11.3.1.1.4 Release of the dedicated transmission
means of mobile stations responding
to a notification . 23
11.3.1.1.5 Transfer of a talking service
subscriber to a dedicated connection. 23
11.3.1.2 Dispatcher call establishment . 24
11.3.1.3 Notification procedures . 24
11.3.1.4 Destination subscribers. 26
11.3.1.5 Called dispatchers. 26
11.3.2 Call release. 26
11.3.3 Leaving of a dispatcher. 27
11.3.4 Leaving and returning to a voice group call . 27
11.3.5 Cell change. 27
11.3.5.1 Listening subscriber . 27
11.3.5.2 Talking subscriber. 27
11.3.5.3 Dispatcher. 27
11.3.6 New calls . 28
11.3.7 Uplink transmission management . 28
11.3.8 Overview of signalling. 28
11.4 Functional requirement of Anchor MSC. 46
11.5 Functional requirement of Relay MSC . 53
11.6 Functional requirement of GCR . 61
11.7 Functional requirement of VLR . 64
12 Content of messages. 66
12.1 Messages on the B-interface (MSC-VLR). 66
12.1.1 Allocate Group Call Number. 66
12.1.2 Allocate Group Call Number ack . 66
12.1.3 Allocate Group Call Number negative response. 66
12.1.4 Release Group Call Number. 67
12.2 Messages on the E-interface (MSC-MSC). 67
12.2.1 Prepare Group Call. 67
12.2.2 Prepare Group Call ack . 67
12.2.3 Prepare Group Call negative response . 67
12.2.4 Send Group Call End Signal. 67
12.2.5 Forward Group Call Signalling. 68
12.2.6 Process Group Call Signalling . 68
12.3 Messages on the I-interface (MSC-GCR) . 69
12.3.1 GCR Interrogation. 69
12.3.2 GCR Interrogation ack. 70
12.3.3 GCR interrogation negative response . 70
12.3.4 Call released. 70
Annex A (informative): Status of GSM 03.68. 71
History. 72
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Foreword
This European Telecommunication Standard (ETS) has been produced by the Special Mobile Group
(SMG) of the European Telecommunications Standards Institute (ETSI).
This ETS specifies the stage two description of the voice group call service (VGCS) within the digital
cellular telecommunications system.
The contents of this ETS is subject to continuing work within SMG and may change following formal SMG
approval. Should SMG modify the contents of this ETS, it will be resubmitted for UAP by ETSI with an
identifying change of release date and an increase in version number as follows:
Version 5.x.y
where:
y the third digit is incremented when editorial only changes have been incorporated in the
specification;
x the second digit is incremented for all other types of changes, i.e. technical enhancements,
corrections, updates, etc.
Transposition dates
Date of adoption of this ETS: 3 July 1998
Date of latest announcement of this ETS (doa): 31 October 1998
Date of latest publication of new National Standard
or endorsement of this ETS (dop/e): 30 April 1999
Date of withdrawal of any conflicting National Standard (dow): 30 April 1999
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1 Scope
This European Telecommunication Standard (ETS) 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.
2 Normative references
This ETS incorporates by dated and undated references, provisions from other publications. These
normative references are cited at the appropriate places in the text and the publications are listed
hereafter. For dated references, subsequent amendments to or revisions of any of these publications
apply to this ETS only when incorporated in it by amendment or revision. For undated references the latest
edition of the publication referred to applies.
[1] GSM 01.04 (ETR 350): "Digital cellular telecommunications system (Phase 2+);
Abbreviations and acronyms".
[2] GSM 02.68 (ETS 300 925): "Digital cellular telecommunications system
(Phase 2+); Voice Group Call Service (VGCS) - stage 1".
[3] GSM 03.22 (ETS 300 930): "Digital cellular telecommunications system;
Functions related to Mobile Station (MS) in idle mode".
[4] GSM 03.67 (ETS 300 932): "Digital cellular telecommunications system
(Phase 2+); enhanced Multi-Level Precedence and Pre-emption service
(eMLPP) - Stage 2".
[5] GSM 04.08 (ETS 300 940): "Digital cellular telecommunications system
(Phase 2+); Mobile radio interface layer 3 specification".
[6] GSM 05.08 (ETS 300 911): "Digital cellular telecommunications system
(Phase 2+); Radio subsystem link control".
[7] GSM 08.08: "Digital cellular telecommunications system (Phase 2+); Mobile
Switching Centre - Base Station System (MSC - BSS) interface Layer 3
specification".
[8] CCITT Recommendation E.164: "Numbering plan for the ISDN era".
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3 Definitions and abbreviations
3.1 Definitions
Definitions used in this ETS are also defined in GSM 02.68.
For the purposes of this ETS, the following definitions apply:
voice group call channel: Combined uplink/downlink to be allocated in a cell of the group call area for a
particular voice group call. The uplink can be used by the presently talking service subscriber only. All
mobile stations of the listening service subscribers in one cell shall listen to the common downlink.
group members: Service subscribers entitled to belong to a particular group classified by a certain group
identification (group ID).
voice group call member: Any group member or dispatcher participating in an on going voice group call.
group call attributes: Group call area, dispatcher identities, and the non-activity time which results in the
release of the voice group call by the network.
Group Call Register (GCR): A functionality in the network containing the group call attributes.
group call anchor MSC: The MSC responsible for managing and maintaining a particular voice group
call. The group call anchor MSC is determined as the one controlling the cells of the group call area (see
also group call relay MSC). For voice group call services where the group call area exceeds one MSC
area, the group call anchor MSC is predefined in the network.
group call relay MSC: MSC controlling cells of a group call area which are not under control of the group
call anchor MSC for those voice group call services where the group call area exceeds one MSC area.
notification: Notifications are given on common control channels or dedicated channels in order to inform
group members which are either in idle mode or in dedicated mode or participating in a voice group call or
voice broadcast call on the existence of voice group calls.
Notification Channel (NCH): Common control channel on which the notifications are sent by the network
(equivalent to a paging channel).
3.2 Abbreviations
Abbreviations used in this ETS are also listed in GSM 01.04.
For the purpose of this specification the following abbreviations apply:
eMLPP enhanced Multi-Level Precedence and Pre-emption
GCR: Group Call Register
NCH: Notification Channel
VBS: Voice Broadcast Service
VGCS: Voice Group Call Service
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4 Main concepts
4.1 Group definition
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.
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. 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. 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.
4.2 Group conversations
4.2.1 Group call initiation
4.2.1.1 Normal operation with successful outcome
A group call area can be restricted to a single MSC area or can exceed one MSC area (implementation
option).
A voice group call shall be initiated by a calling subscriber by a related MMI action for the service selection
and the group ID dialled.
The MSC in which a voice group call is initiated obtains (by requesting the Group Call Register (GCR, see
clause 5) the group call attributes.
This GCR interrogation after call initiation also determines whether the MSC shall act as anchor or as
relay MSC. If the MSC is not the MSC then the call will be "forwarded" from the relay to the respective
MSC (information also delivered by GCR) and further "call-establishment" is done by the anchor MSC as
described in the following.
When a calling subscriber initiates a voice group call, one voice group call channel shall be established in
each cell of the group call area and notifications for that call shall be sent in each of these cells. As an
alternative, voice group call channels may only be established in cells in reaction to responses received
from mobile stations on the notifications. At the same time standard connections to dispatchers in the
mobile network or in an external network shall be established.
A voice group call channel shall consist of a combined uplink/downlink. The uplink will be used exclusively
by the presently talking service subscriber. All mobile stations of the listening service subscribers in one
cell shall only listen to the same common downlink.
The calling subscriber shall have its dedicated standard uplink/downlink during call establishment and for
the first period when he will be the talking service subscriber up to the time when the network decides that
he shall join the voice group call channel. The mobile station of the calling subscriber shall then go to the
voice group call channel and the dedicated standard uplink/downlink shall be released. From that moment
on the calling subscriber shall be treated as all the other services subscribers.
Only one voice group call channel shall be established in each cell for any given voice group call, although
there may be a number of simultaneous voice group calls within the same cell.
Service subscribers shall be notified on the voice group call in each cell. These voice group call
notification messages shall be broadcast on the notification channel (NCH).
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ETS 300 933 (GSM 03.68 version 5.4.1): July 1998
The notification messages use the group ID rather than individual TMSIs/IMSIs. Additionally, a group call
area identification shall be included in order to enable a resolution in the case of overlapping group call
areas. A service subscriber's mobile station needs to be able to recognise notification messages for those
group IDs subscribed to and presently activated.
The network may also send messages on appropriate voice group call channel FACCHs, in order to notify
group call members who may participate in other voice group calls. In addition, also paging information
messages for standard calls may be sent in order to inform group call members on actually paged point-
to-point calls.
Further the network may provide notification on the voice group call to service subscribers who have
subscribed to the paged group ID and which are in dedicated mode. The process of broadcasting
messages on NCHs is to be carried out throughout the call in order to provide the "late entry" facility
whereby group members entering the area can join the call.
On receiving notification of a voice group call a group call member's mobile station shall adjust to the
nominated channel to receive the voice group call if this channel was described in the notification
message and receive the information on the downlink. Whilst receiving, the mobile station shall not
transmit on the uplink SACCH. This group receive mode is different to the normal idle mode or dedicated
mode. If no channel description was provided in the notification message, the mobile station shall
establish a dedicated connection in order to respond to the notification. The network may then provide the
mobile station with a channel description for the voice group call.
As a further mobile station option, the mobile station may read its paging subchannel in the current cell
while in group receive mode or in group transmit mode in order to receive paging messages for mobile
terminated calls.
4.2.1.2 Exceptional procedures
Completion of links into congested cells where pre-emption did not occur is required.
On receiving details of a voice group call the user may choose to move to the notified call or the mobile
station may automatically move to the notified call if the new call is of higher priority than the existing call
and automatic acceptance applies for this priority level.
4.2.2 On-going group calls
4.2.2.1 Normal operation with successful outcome
Within each voice group call starting from the instant where the calling subscriber first becomes a listening
service subscriber, one service subscriber has the access at any one time to the uplink of the voice group
call channel and his speech is then broadcast on all voice group call channel downlinks accordingly. The
mobile station of the talking service subscriber shall mute the downlink speech to avoid non intelligible
echos.
If more than one service subscriber apply to the uplink, contention resolution shall be performed in the
network. Contention resolution shall be performed in the group call anchor MSC.
Additionally, in order to speed up the uplink access procedure, the BSS may grant the uplink prior to
contention resolution being performed by the group call anchor MSC. This would mean that more than
one service subscriber may access to the uplink and the respective speech may be combined in the group
call bridge and broadcast onto all voice group call downlink channels during a transitional period. The
anchor MSC shall then select one of the talking subscribers and pre-empt the uplink use of the other
talking subscribers.
Dispatchers voice involved shall be broadcast on the voice group call channel downlink at any time.
Mobile dispatchers are provided with a standard link and thus with an dedicated permanent uplink different
from the voice group call channel.
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All non-dispatcher group call members are provided with an indication on the voice group call channel of
whether the uplink is in use. When the uplink is not in use, any non-dispatcher group call member can
request access to the uplink. Any speech from dispatchers is combined with any speech from a talking
service subscriber.
In case of one talking service subscriber plus a parallel talking dispatcher, the talking service subscriber's
mobile station shall receive an indication by means of signalling from the network so that it can unmute
the downlink.
The release of the uplink is triggered by the user and indicated by the mobile station to the network. The
network shall then indicate to the listening mobile stations that the uplink is free.
Mobile stations in group receive mode use the group receive mode procedure (see GSM 03.22) to "camp-
on" in a new cell to be able to listen to the group call channel. The mobile station may find the voice group
call channel details of a new cell on the related NCH.
A network may decide not to establish voice group call channels in all cells. Instead, notifications
containing no channel description may be provided. If a mobile station moves to such a cell, it must
respond to the notification in order to receive the voice group call. The network may then establish a voice
group call channel and inform the mobile station on the channel position.
A network may obtain knowledge on whether mobile stations are listening in a cell by sending an uplink
access request on the voice group call channel downlink when no talking service subscriber is present.
Mobile stations receiving such a request shall send uplink access bursts on the voice group call channel
uplink with the establishment cause "reply on uplink access request". If no uplink access bursts are
received by the network, the network may decide to release the voice group call channel in that cell and
then provide notifications containing no channel description.
NOTE: Concerning security aspects, whilst authentication and membership checking of mobile
call originators and of mobile uplink users can be carried out, it is not possible to
authenticate service subscribers in group receive mode if they have not before
established a dedicated connection to responded to a notification. No equivalent of a
group "TMSI" is provided to protect the "identity" of established voice group calls.
4.2.2.2 Exceptional procedures
When a talking subscriber's mobile station loses contact with the network, the network must detect this
loss and set the uplink free so that other mobile stations may access the uplink. The talking subscriber's
mobile station which has lost the contact with the network shall return immediately to the group receive
mode.
If a mobile station in group receive mode indicates a failure due to radio link time-out, the mobile station
shall behave as specified in GSM 05.08 and go back to idle mode, possibly in another cell, as determined
by the cell re-selection algorithm. If a notification is received for the same call, the mobile station shall try
to reconnect.
4.2.3 Leaving of a group call without termination
A service subscriber can leave the voice group call at any point by "deselecting" it via an MMI function.
Having deselected the voice group call the mobile station returns to idle mode and "ignores" any further
notification messages related to that voice group call.
NOTE: If a service subscriber does not wish to participate in calls to a particular group ID for
long periods of time, the group ID shall be switched to deactive state by the subscriber.
The service subscriber shall have the capability to reselect the voice group call. The mobile station shall
not ignore notification messages to that call any more.
The dispatcher shall be able to leave a voice group call without terminating it.
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4.2.4 Group call termination
A voice group call can only be terminated by the calling subscriber or by an entitled dispatcher or due to
no activity timer expiry (see subclause 8.1.2.3).
The calling subscriber can terminate the call only if the calling subscriber has access to the uplink. He
shall remain the calling subscriber during the length of the particular voice group call even if he leaves the
call and then returns to it later.
The dispatcher can terminate the call by a network defined user operation (e.g. via DTMF).
4.2.5 Acknowledgements
The acknowledgement is an application option.
For voice group calls which are identified by an acknowledgement flag mobile stations which have
acknowledgement facilities have to return an acknowledgement message with a predefined content in a
predefined manner.
The acknowledgement shall be sent using an appropriate data service, to a predefined address or with a
predefined short code stored on the SIM card. The network may apply geographical routing to a
predefined acknowledgement service centre.
4.2.6 Transactions between the mobile station and the network
Mobile stations which are in group receive mode shall not perform any transactions with the network while
adjusted to the voice group call channel. They shall leave the group receive mode and act in a standard
way to perform any transaction if necessary and return to the voice group call afterwards.
Mobile stations which have access to the voice group call channel uplink shall not perform any
transactions for supplementary services and SMS.
5 General architecture
5.1 Group Call Register (GCR)
The general architecture of GSM is maintained. In addition, a network function is required which is used
for registration of the group call attributes, the Group Call Register (GCR).
The GCR function is mainly a database function, holding information about voice group calls.
NOTE 1: The GCR implementation is not specified. It may be realized e.g. as a new network
node, in a PABX directly attached to an MSC, inside an MSC or as an HLR. The
interface between the GCR function and other functions is not specified in the GSM
technical specifications. As a consequence, the functional split between MSC and
GCR as developed in this document is only indicative, and other functional splits can
be implemented.
The GCR data for a specific voice group call is set at the creation of the group call attributes, and can be
subsequently modified. No support for these functions is specified in the GSM technical specifications.
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External network
HLR GMSC
Anchor
VLR GCR
MSC
VLR Relay GCR
MSC
VLR Relay GCR
MSC
Figure 1: Functional architecture with a Group Call Register
The signalling between the entities shown in figure 1, for the two cases of service subscriber and
dispatcher originated calls, shall be as defined in the following.
Service subscriber originated: The MSC containing the cell within which this voice group call is initiated
shall perform subscription checking against VLR records. It shall then consult its GCR to determine the
group call attributes related to its MSC area and whether it is the group call anchor MSC for that voice
group call. If it is not, the GCR shall provide with the group call attributes the routing information identifying
the group call anchor MSC to the originating MSC. The originating MSC shall then route the voice group
call to the anchor MSC. If the originating MSC is the group call anchor MSC, along with the group call
attributes, the GCR shall provide information on all group call relay MSCs to be involved.
The group call anchor MSC shall set up links to all group call relay MSCs. Each MSC involved in a voice
group call obtains its proper group call attributes from the GCR related to the MSC.
The IMSI of the calling service subscriber must be provided to and stored in the anchor MSC and each
relay MSC in order to allow the originator to clear the group call later on.
Dispatcher originated: In the case of dispatchers calling from an external network, the call request, in
the form of an ISDN number, shall be received at a GMSC. The number shall be analysed and the call
shall be directly routed to the group call anchor MSC by the GMSC based on the called identity without
requesting an HLR. The group call anchor MSC shall interrogate the GCR and obtain the group call
attributes. If an identical voice group call is currently in progress, the dispatcher shall be connected to this
call and no new call shall be initiated. When interrogating the GCR, the identity of the dispatcher is
compared with the list of dispatchers which are allowed to initiate the call. If the dispatcher is not in the list,
or an identity is not provided, the network shall reject the call.
NOTE 2: Optionally dispatchers may also be user of the GSM network in which the VGCS
service is provided or may directly be connected to a PABX containing the GCR.
Dispatcher which are registered 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.
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5.2 Voice group call responsibility
The MSC responsible for the voice group call is the one nominated within the GCR or the one to which the
call is routed from the GMSC in the case of a dispatcher originated call. This MSC is termed the group call
anchor MSC.
If the group call area extends beyond one MSC area then any MSCs controlling cells in the area outside of
the group call anchor MSC are referred to as group call relay MSCs.
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6 Compatibility issues
VGCS can not be used with standard Phase 1 or Phase 2 mobile stations. A dedicated mobile station with
VGCS capability is required.
A mobile station with VGCS capability shall also provide the complete functionality in order to allow the
use of Phase 2 services.
Standard Phase 1 and Phase 2 mobile stations in a network shall not be impacted by the presence of
VGCS services in that network due to VGCS signalling, also if the mobile station is operated with a SIM of
a VGCS service subscriber.
7 Transmission
7.1 Transmission architecture
A conference bridge is required to connect the transmission paths of the nominated cells. The bridge is to
be located within the group call anchor MSC. The group call anchor MSC is responsible for setting up all
connections, both to the nominated cells (voice group call channels) in the group call anchor MSC and in
any related group call relay MSC, and to the dispatchers. There shall be one link towards every relay MSC
and a distribution function in the relay MSCs and from there one link per cell within the group call relay
MSC which is involved in the voice group call, i.e. there shall be no secondary bridges in BSCs or group
call relay MSCs (the distribution function is not a secondary bridge).
NOTE 1: The conference bridge shall not mute the uplink speech.
NOTE 2: As GSM Phase2+ evolves, distribution functions may be realised in the BSC.
A mechanism is required to indicate the downlink muting and uplink busy when the dispatcher is talking.
This mechanism is for further study.
7.2 Radio channels
In each cell of the group call area one voice group call channel may be established consisting of a
downlink received by all service subscriber's mobile stations and an uplink which shall be used by the
talking subscriber's mobile station only.
The calling subscriber's mobile station shall use a dedicated standard uplink/downlink which is connected
to the conference bridge up to the instant where the network decides that the mobile station shall join the
voice group call channel and the dedicated connection is released.
The network may decide to switch a talking subscriber's mobile station from the voice group call channel
to a dedicated standard uplink/downlink at any time. This dedicated connection shall then be maintained
up to the instance where the network decides that the mobile station shall join the voice group call channel
again and the dedicated connection is released.
A listening subscriber's mobile station which responds to a notification because no description of the voice
group call channel was provided in the notification may be assigned a dedicated standard uplink/downlink
which is connected to the conference bridge up to the instant where the network decides that the mobile
station shall join the voice group call channel and the dedicated connection is released.
Voice group call channels shall be standard full rate or half rate speech channels. A specific voice group
call can have cells in the group call area where the voice group call channels are either only half rate
speech or only full rate speech or there are cells with half rate speech and cells with full rate speech.
Those implementations are optional for the network operator.
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Mobile station using the uplink are in group transmit mode. Signalling for this RR mode is specified in
GSM 04.08. Mobile stations not using the uplink and not in dedicated mode shall ignore any signalling
concerned only with uplink usage.
Full standard duplex channels shall be provided to all dispatchers listed in the GCR. These may be
provided either via GSM, or via an external network. The links to the dispatchers are connected to the
conference bridge.
The mobile station of the talking service subscriber will transmit on the uplink related to the downlink of the
voice group call channel. The downlink of this channel which is also received by the mobile station using
the uplink will typically echo the uplink unless one or more dispatchers are talking simultaneously. The
mobile station of the talking service subscriber shall mute the downlink speech unless more than one
speaker is talking. In this case, an indication shall be provided to the mobile station, and the mobile station
shall no longer mute the downlink. When the downlink is not muted it is acceptable for the talking
subscriber to hear an echo, and possibly other distortions which may occur, as the intention is to alert the
talking subscriber to the fact that someone else is talking, rather than allow them to hear the message
from the dispatcher. If no dispatcher is talking anymore and the talking service subscriber still has access
to the uplink, an indication shall be provided to the mobile station, and the mobile station shall mute the
downlink again.
7.3 Data confidentiality
Data confidentiality on the radio can be provided as a network option.
If data confidentiality is provided, both the uplink and the downlink of the voice group call channels in each
cell of the group call area shall be ciphered using the same group key.
The group key is related to the group ID. For each group ID, there is a number of group keys stored on the
SIM which are identified by a group key number. The group key number identifying the group key to be
used for a particular voice group call is provided with the notification to the mobile stations. Mobile stations
which have a dedicated connection shall be informed of the group key number before they join the voice
group call channel.
The distribution of the group keys to the related SIMs shall be done off-line.
NOTE: The distribution of group keys shall be done by the service provider when editing the
SIM. Distribution of group keys via the radio interface may be possible with future
features as the SIM-toolkit. Those distribution schemes are for further study.
Details on data confidentiality for voice group calls are provided in GSM 02.09 and GSM 03.20.
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ETS 300 933 (GSM 03.68 version 5.4.1): July 1998
8 Information storage
8.1 Information stored in the GCR
8.1.1 Information used for routing of service subscriber originated voice group calls
The GCR shall hold for a related MSC area for each group ID and cell from which voice group calls can be
established by service subscribers the group call reference to be used for a voice group call to be
established and an indication whether the originating MSC is the group call anchor MSC.
If the originating MSC is the group call anchor MSC, the GCR shall provide the group call attributes
related to that group call reference as defined in subclause 8.1.2 to the originating MSC and the
originating MSC shall establish the voice group call.
If the originating MSC is not the anchor MSC, the GCR shall provide the group call reference plus the
routing information identifying the anchor MSC to the originating MSC and the originating MSC shall route
the voice group call to the anchor MSC.
NOTE: In case the GCR function is distributed over different physical entities, each may hold
only the information needed to treat requests coming from the MSCs connected to the
physical GCR entity.
8.1.2 Group call attributes
Each MSC involved in a voice group call requests its proper group call attributes from its related GCR. For
any group call reference the GCR shall provide the corresponding group call attributes to the requesting
MSC. These lists shall be programmed by the service pr
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