ETSI ETS 300 933 ed.5 (1998-12)

SLOVENSKI STANDARD
SIST ETS 300 933 E5:2003
01-december-2003
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Digital cellular telecommunications system (Phase 2+) (GSM); Voice Group Call Service
(VGCS); Stage 2 (GSM 03.68 version 5.5.1)
Ta slovenski standard je istoveten z: ETS 300 933 Edition 5
ICS:
33.070.50 Globalni sistem za mobilno Global System for Mobile
telekomunikacijo (GSM) Communication (GSM)
SIST ETS 300 933 E5:2003 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST ETS 300 933 E5:2003

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SIST ETS 300 933 E5:2003
EUROPEAN ETS 300 933
TELECOMMUNICATION December 1998
STANDARD Fifth Edition
Source: SMG Reference: RE/SMG-030368QR4
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 5.5.1 Release 1996)
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.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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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 Standards Making Support Dept." at the address shown on the title page.

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ETS 300 933 (GSM 03.68 version 5.5.1 Release 1996): December 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.13
6 Compatibility issues.14
7 Transmission.14
7.1 Transmission architecture.14
7.2 Radio channels .14
7.3 Data confidentiality.15
8 Information storage .16
8.1 Information stored in the GCR.16
8.1.1 Information used for routing of service subscriber originated voice group
calls .16
8.1.2 Group call attributes .16
8.1.2.1 Group call area .17
8.1.2.2 Dispatcher identities .17
8.1.2.3 No activity time .17
8.1.2.4 Priorities.17
8.2 Information managed per subscriber.18
8.2.1 Stored in the HLR.18
8.2.2 Stored in the VLR .18
8.2.3 Stored in the SIM.18
8.3 Information used for routing of dispatcher originated voice group calls .18
9 Identities .19
9.1 Elementary identities for group calls.19
9.2 Use of identities in the network.19
10 Operation and maintenance aspects .20

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ETS 300 933 (GSM 03.68 version 5.5.1 Release 1996): December 1998
11 Function and information flows. 20
11.1 Group management . 20
11.2 Group membership management . 20
11.3 Call management . 21
11.3.1 Call establishment . 21
11.3.1.1 Service subscriber call establishment. 21
11.3.1.1.1 Initial stage . 21
11.3.1.1.2 Establishment of the transmission
means . 22
11.3.1.1.3 Release of the dedicated transmission
means of the calling service
subscriber. 22
11.3.1.1.4 Release of the dedicated transmission
means of mobile stations responding
to a notification . 22
11.3.1.1.5 Transfer of a talking service
subscriber to a dedicated connection. 22
11.3.1.2 Dispatcher call establishment . 23
11.3.1.3 Notification procedures . 23
11.3.1.4 Destination subscribers. 25
11.3.1.5 Called dispatchers. 25
11.3.2 Call release. 25
11.3.3 Leaving of a dispatcher. 26
11.3.4 Leaving and returning to a voice group call . 26
11.3.5 Cell change. 26
11.3.5.1 Listening subscriber . 26
11.3.5.2 Talking subscriber. 26
11.3.5.3 Dispatcher. 26
11.3.6 New calls . 27
11.3.7 Uplink transmission management . 27
11.3.8 Overview of signalling. 27
11.4 Functional requirement of Anchor MSC. 42
11.5 Functional requirement of Relay MSC . 49
11.6 Functional requirement of GCR . 57
11.7 Functional requirement of VLR . 60
12 Content of messages. 62
12.1 Messages on the B-interface (MSC-VLR). 62
12.1.1 Allocate Group Call Number. 62
12.1.2 Allocate Group Call Number ack . 62
12.1.3 Allocate Group Call Number negative response. 62
12.1.4 Release Group Call Number. 63
12.2 Messages on the E-interface (MSC-MSC). 63
12.2.1 Prepare Group Call. 63
12.2.2 Prepare Group Call ack . 63
12.2.3 Prepare Group Call negative response . 63
12.2.4 Send Group Call End Signal. 63
12.2.5 Forward Group Call Signalling. 64
12.2.6 Process Group Call Signalling . 64
12.3 Messages on the I-interface (MSC-GCR) . 65
12.3.1 GCR Interrogation. 65
12.3.2 GCR Interrogation ack. 66
12.3.3 GCR interrogation negative response . 66
12.3.4 Call released. 66
Annex A (informative): Status of GSM 03.68. 67
History. 68

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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 (ASCI Phase 1)) within
the digital cellular telecommunications system.
The contents of this specification is subject to continuing work within SMG and may change following
formal SMG approval. Should SMG modify the contents of this specification, it will be resubmitted for OAP
by ETSI with an identifying change of release date and an increase in version number as follows:
Version 5.x.y
where:
5 indicates GSM Phase 2+ Release 1996;
x the second digit is incremented for all other types of changes, i.e. technical enhancements,
corrections, updates, etc.
y the third digit is incremented when editorial only changes have been incorporated in the
specification.
Transposition dates
Date of adoption of this ETS: 4 December 1998
Date of latest announcement of this ETS (doa): 31 March 1999
Date of latest publication of new National Standard
or endorsement of this ETS (dop/e): 30 September 1999
Date of withdrawal of any conflicting National Standard (dow): 30 September 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
(Phase 2+); 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).
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

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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
echo's.
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 de
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