ETSI ETS 300 948 ed.5 (2000-05)

SLOVENSKI STANDARD
SIST ETS 300 948 E5:2003
01-december-2003
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Digital cellular telecommunications system (Phase 2+) (GSM); Group Call Control (GCC)
protocol (GSM 04.68 version 5.4.1 Release 1996)
Ta slovenski standard je istoveten z: ETS 300 948 Edition 5
ICS:
33.070.50 Globalni sistem za mobilno Global System for Mobile
telekomunikacijo (GSM) Communication (GSM)
SIST ETS 300 948 E5:2003 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST ETS 300 948 E5:2003

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SIST ETS 300 948 E5:2003
EUROPEAN ETS 300 948
TELECOMMUNICATION April 2000
STANDARD Fifth Edition
Source: SMG Reference: RE/SMG-030468QR4
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+);
Group Call Control (GCC) protocol
(GSM 04.68 version 5.4.1 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.:+33492944200- Fax:+33493654716
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 2000. 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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Contents
Intellectual Property Rights.5
Foreword.5
1 Scope .7
2 Normative references.7
3 Definitions and abbreviations .7
3.1 Definitions .7
3.2 Abbreviations .8
4 Applicability.8
5 Main concepts .8
6 Elementary procedures for Group Call Control .9
6.1 Overview .9
6.1.1 General.9
6.1.2 Group call control states.11
6.1.2.1 Group call control states at the MS side of the interface .11
6.1.2.1.1 Attributes and parameters of GCC in
the MS.11
6.1.2.1.2 NULL (U0).11
6.1.2.1.3 MM CONNECTION PENDING (U0.p) .11
6.1.2.1.4 GROUP CALL INITIATED (U1) .11
6.1.2.1.5 GROUP CALL ACTIVE (U2).12
6.1.2.1.6 GROUP CALL PRESENT (U3).12
6.1.2.1.7 GROUP CALL CONNECTION
REQUESTED (U4).12
6.1.2.1.8 TERMINATION REQUESTED (U5).12
6.1.2.1.9 Sub-states of the Group call active
state .12
6.1.2.1.10 GCC Timers in the MS.13
6.1.2.1.11 Consistency of parameters and states .13
6.1.2.2 Group call control states at the network side of the
interface.14
6.1.2.2.1 NULL (State N0) .14
6.1.2.2.2 GROUP CALL INITIATED (N1) .14
6.1.2.2.3 GROUP CALL ACTIVE (N2).14
6.1.2.2.4 GROUP CALL ESTABLISHMENT
PROCEEDING (N3).14
6.1.2.2.5 TERMINATION REQUESTED (N4).14
6.2 Procedures for establishment of a group call .14
6.2.1 Activation of a group call by the network .14
6.2.2 Mobile originated establishment.14
6.2.2.1 Termination during mobile originated establishment.15
6.2.2.2 Abnormal cases.15
6.2.3 Mobile terminating group call establishment in the MS .16
6.3 Procedures during the active state of a group call.16
6.3.1 Mobile station procedures in the active state .16
6.3.1.1 Sub-state transitions in the MS.16
6.3.2 Network procedures in the active state .17
6.4 Procedures for release, abortion, and termination of a group call.17
6.4.1 Termination procedure .17
6.4.2 Abort and release procedures .17
6.5 Miscellaneous procedures .18

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6.5.1 Status procedures. 18
6.5.1.1 Get status procedure. 18
6.5.1.2 Set parameter procedure . 18
7 Handling of unknown, unforeseen, and erroneous protocol data . 18
7.1 General. 18
7.2 Message too short. 19
7.3 Unknown or unforeseen transaction identifier. 19
7.4 Unknown or unforeseen message type. 19
7.5 Non-semantical mandatory information element errors . 19
7.6 Unknown and unforeseen information elements in the non-imperative message part . 20
7.6.1 Information elements unknown in the message . 20
7.6.2 Out of sequence information elements. 20
7.6.3 Repeated Information elements. 20
7.7 Non-imperative message part errors. 20
7.7.1 Syntactically incorrect optional Information elements. 20
7.8 Messages with semantically incorrect contents . 20
8 Message functional definitions and contents. 21
8.1 CONNECT. 22
8.2 GET STATUS.22
8.2.1 mobile identity. 22
8.3 IMMEDIATE SETUP . 23
8.3.1 Mobile identity . 23
8.4 SET PARAMETER. 23
8.5 SETUP . 24
8.6 STATUS . 24
8.6.1 Call state. 24
8.6.2 State attributes. 24
8.7 TERMINATION.25
8.8 TERMINATION REJECT . 25
8.9 TERMINATION REQUEST . 25
9 Contents of information elements value parts . 26
9.1 Protocol Discriminator . 26
9.2 Transaction identifier. 26
9.3 Message Type. 26
9.4 Other information elements. 27
9.4.1 Call Reference . 27
9.4.2 Call state. 28
9.4.3 Cause. 29
9.4.4 Originator indication. 30
9.4.5 Not used. 31
9.4.6 Spare Half Octet . 31
9.4.7 State attributes. 31
Annex A (Informative): Change Request History. 32
History. 33

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Intellectual Property Rights
IPRs essential or potentially essential to the present document may have been declared to ETSI. The
information pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-
members, and can be found in SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially
Essential, IPRs notified to ETSI in respect of ETSI standards", which is available from the ETSI
Secretariat. Latest updates are available on the ETSI Web server (http://www.etsi.org/ipr).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI.
No guarantee can be given as to the existence of other IPRs not referenced in SR 000 314 (or the
updates on the ETSI Web server) which are, or may be, or may become, essential to the present
document.
Foreword
This European Telecommunication Standard (ETS) has been produced by the Special Mobile Group
(SMG) Technical Committee of the European Telecommunications Standards Institute (ETSI).
The contents of this ETS is subject to continuing work within TC-SMG and may change following formal
TC-SMG approval. Should TC-SMG modify the contents of this ETS, 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
5 Indicates GSM Phase 2+ Release 1996;
x the second digit is incremented for all changes of substance, i.e. technical enhancements,
corrections, updates, etc.;
y the third digit is incremented when editorial only changes have been incorporated in the
specification.
Proposed transposition dates
Date of adoption of this EN: 31 March 2000
Date of latest announcement of this ETS (doa): 30 June 2000
Date of latest publication of new National Standard
or endorsement of this ETS (dop/e): 31 December 2000
Date of withdrawal of any conflicting National Standard (dow): 31 December 2000

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1 Scope
This European Telecommunications Standard (ETS) specifies the Group Call Control (GCC) protocol
used by the Voice Group Call Service (VGCS) on the radio interface.
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 telecommunication system (Phase 2+);
Abbreviations and acronyms".
[2] GSM 02.68 (ETS 300 925): "Digital cellular telecommunication system
(Phase 2+); "Voice Group Call Service (VGCS) - Stage 1".
[3] GSM 03.03 (ETS 300 927): "Digital cellular telecommunication system
(Phase 2+); Numbering, addressing and identification".
[4] GSM 03.67 (ETS 300 932): "Digital cellular telecommunication system
(Phase 2+);"enhanced Multi-Level Precedence and Pre-emption service
(eMLPP) - Stage 2".
[5] GSM 03.68 (ETS 300 933): "Digital cellular telecommunication system
(Phase 2+);Voice Group Call Service (VGCS) - Stage 2".
[6] GSM 04.06 (ETS 300 938): "Digital cellular telecommunication system; Mobile
Station - Base Station System (MS - BSS) interface Data Link (DL) layer
specification".
[7] GSM 04.07 (ETS 300 939): "Digital cellular telecommunication system
(Phase 2+); Mobile radio interface signalling layer 3 General aspects".
[8] GSM 04.08 (ETS 300 940): "Digital cellular telecommunication system
(Phase 2+); Mobile radio interface layer 3 specification".
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:
attachment of the user connection: See GSM 04.08, subclause 5.2.
calling user: GCC entity in the Mobile Station (MS) initiating or having initiated a group call.
clearing the context related to the group call establishment: All running GCC timers in the relevant
GCC entity are stopped, all attributes in the relevant GCC entity are deleted.
downlink: Network to mobile station direction.
group call: Is used in the same sense as "voice group call".
group call channel: Combined uplink/downlink to be allocated in each cell of the group call area for a
particular group call. The uplink can be used by the presently talking service subscriber only. All MSs of
the listening service subscribers in one cell shall listen to the common downlink.

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group receive mode: See GSM 04.08.
originating mobile station: Mobile station initiating or having initiated the group call. (Note that, in certain
situations, a MS assumes to be the originating MS of a group call without actually being the originating MS
of that group call. Note that there may be one or none originating MS for a given group call.)
uplink: Mobile station to network direction.
3.2 Abbreviations
Abbreviations used in this ETS are also listed in GSM 01.04.
For the purposes of this ETS, the following abbreviations apply:
GCC Group Call Control
4 Applicability
Support of the group call protocol is optional in the MS and in the network.
5 Main concepts
This ETS describes the group call control (GCC) protocol, which is one of the protocols of the Connection
Management (CM) sublayer (see GSM 04.07).
There is in general more than one MS engaged in a group call. Consequently, there is in general more
than one MS with a GCC entity engaged in the same group call, and there is one GCC entity in the
network engaged in that group call.
Under which conditions a GCC message is passed from lower (sub-)layers to the GCC entity is defined in
the specifications of the sub-layers.
The MS shall ignore GCC messages that it receives which were sent in unacknowledged mode and which
explicitly specify as destination a mobile identity which is not a mobile identity of the MS.
Higher layers and the MM sub-layer decide when to accept parallel GCC transactions and when/whether
to accept GCC transactions in parallel to other CM transactions.
The group call may be initiated by a mobile user or by a dispatcher. Specification of a protocol for
dispatchers is out of the scope of this ETS. Hence, in the scope of this ETS, there are:
- one GCC entity in the network; and
- one or more than one GCC entities in different MSs
engaged in a group call, and one ore none of the MSs is the originator of the group call (called the
originating MS in this ETS). Note that, in certain situations, a MS assumes to be the originator of a group
call without being the originator.
The originator of the GCC transaction chooses the Transaction Identifier (TI). A MS not assuming to be
the originator of the transaction will chose the transaction identifier received from the network, setting the
TI flag to 1+x mod 2 where x is the received TI flag.
This ETS describes the group call control protocol only with regard to two peer entities, one in a MS, the
other one in the network. The call control entities are described as communicating finite state machines
which exchange messages across the radio interface and communicate internally with other protocol
(sub)layers. In particular, the GCC protocol uses the MM and RR sublayer specified in GSM 04.08. This
description in only normative as far as the consequential externally observable behaviour is concerned.
For simplicity, instead of using the terms "GCC entity in the MS" and "GCC entity in the network", this ETS
often uses the terms "MS" and "network" if no confusion may arise.

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Certain sequences of actions of the two peer entities compose "elementary procedures" which are used
as a basis for the description in this ETS. These elementary procedures are defined in clause 6.
The network should apply supervisory functions to verify that the GCC procedures are progressing and if
not, take appropriate means to resolve the problems. This, however, is out of the scope of this ETS.
6 Elementary procedures for Group Call Control
6.1 Overview
6.1.1 General
The elementary procedures may be grouped into the following classes:
- group call establishment procedures;
- group call termination procedures;
- call information phase procedures;
- miscellaneous procedures.
Figure 6.1 gives an overview of the main states and transitions on the MS side.

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6.1.2 Group call control states
6.1.2.1 Group call control states at the MS side of the interface
The GCC entity of the MS is described as an extended finite state machine. It performs transitions
between (main) states, and in main state GROUP CALL ACTIVE (U3) it performs transitions between
sub-states. It has certain parameters and attributes, e.g. configuration parameters and behaviour
parameters, which it sets and changes based on interaction with higher and lower (sub-)layers and on
message exchange with its peer entity. If a configuration parameter is set to a certain value, the MS shall
also adapt the configuration accordingly. Behaviour parameters decide on (part of) the behaviour of the
GCC entity. When the GCC entity in the MS receives a message, it shall first analyse whether it shall
ignore the message, see clauses 5 and 7.
6.1.2.1.1 Attributes and parameters of GCC in the MS
For the following behaviour parameters, the description is informative.
Parameter Description
ORIG Depending on the context, the MS assumes to be the originator of the call (ORIG = T) or
not to be the originator of the call (ORIG = F).
COMM Depending on the context, the MS assumes that communication with its peer entity is
enabled in both directions (COMM = T) or not (COMM = F).
For the following configuration parameters the MS shall adapt its configuration according to the parameter
value and parameter definition.
Parameter Definition
D-ATT D-ATT = T means that the MS attaches the user connection for the group call in the
downlink.
D-ATT = F means that the MS does not attach the user connection for the group call in
the downlink.
U-ATT U-ATT = T means that the MS attaches the user connection for the group call in the
uplink.
U-ATT = F means that the MS does not attach the user connection for the group call in
the uplink.
6.1.2.1.2 NULL (U0)
No group call exists for the GCC entity. When entering the state, parameters shall be set to the following
values, and configuration shall be adapted to the new values of configuration parameters: ORIG = F,
COMM=F,D-ATT =F,U-ATT =F.
6.1.2.1.3 MM CONNECTION PENDING (U0.p)
The GCC entity has requested the explicit establishment of an MM connection. When entering the state,
parameters shall be set to the following values, and configuration shall be adapted to the new values of
configuration parameters: ORIG = T, COMM = F, D-ATT = F, U-ATT = F.
6.1.2.1.4 GROUP CALL INITIATED (U1)
The GCC entity has requested the peer entity in the network to establish a group call. When entering the
state, parameters shall be set to the following values, and configuration shall be adapted to the new
values of configuration parameters: ORIG = T, COMM = T, D-ATT = F, U-ATT = F.

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6.1.2.1.5 GROUP CALL ACTIVE (U2)
The group call is established at least in one cell; depending on the sub-state, the MS has attached the
user connection in the uplink and/or downlink. The following sub-states exist:
- separate link (U2sl);
- wait for receive mode (U2wr);
- receive mode (U2r);
- wait for send and receive mode (U2ws);
- send and receive mode (U2sr);
- no channel (U2nc).
6.1.2.1.6 GROUP CALL PRESENT (U3)
The MS has received a notification about an ongoing group call. Higher layers are requested to accept or
reject the call. When entering the state, parameters shall be set to the following values, and configuration
shall be adapted to the new values of configuration parameters: ORIG = F, COMM = F, D-ATT = F,
U-ATT = F.
6.1.2.1.7 GROUP CALL CONNECTION REQUESTED (U4)
The MS has received a notification about an ongoing group call. Higher layers have decided to accept the
call. When entering the state, parameters shall be set to the following values, and configuration shall be
adapted to the new values of configuration parameters: ORIG = F, COMM = F, D-ATT = F, U-ATT = F.
6.1.2.1.8 TERMINATION REQUESTED (U5)
The MS (which assumes to be the originator of the group call) has been in state U1 or U2 and has sent a
TERMINATION REQUEST message to the network. When entering the state, parameters shall be set to
the following values, and configuration shall be adapted to the new values of configuration parameters:
ORIG = T, COMM = T, D-ATT = T, U-ATT = T.
6.1.2.1.9 Sub-states of the Group call active state
NOTE: Control of the user connection attachment is seen as a group call control function. This
is a reason why the sub-states are distinguished.
6.1.2.1.9.1 separate link (U2sl)
A dedicated one to one RR connection exists between MS and network. When entering the sub-state,
parameters shall be set to the following values, and configuration shall be adapted to the new values of
configuration parameters: COMM = T, D-ATT = T, U-ATT = T.
6.1.2.1.9.2 wait for receive mode (U2wr)
The MS has asked the network to enter receive mode but a dedicated one-to-one channel is still
assigned. When entering the sub-state, parameters shall be set to the following values, and configuration
shall be adapted to the new values of configuration parameters: COMM = T, D-ATT = T, U-ATT = F.
6.1.2.1.9.3 receive mode (U2r)
The MS uses a group call channel. When entering the sub-state, parameters shall be set to the following
values, and configuration shall be adapted to the new values of configuration parameters: COMM = F,
D-ATT = T, U-ATT = F.
6.1.2.1.9.4 wait for send and receive mode (U2ws)
The MS (which was in U2r or U2wr) has asked for the uplink. When entering the sub-state, parameters
shall be set to the following values, and configuration shall be adapted to the new values of configuration
parameters: COMM = F, D-ATT = T, U-ATT = T.

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6.1.2.1.9.5 send and receive mode (U2sr)
The MS has been informed by its peer entity that the uplink is granted. When entering the sub-state,
parameters shall be set to the following values, and configuration shall be adapted to the new values of
configuration parameters: D-ATT = T, U-ATT = T.
6.1.2.1.9.6 no channel (U2nc)
The GCC entity has been informed that no channel is currently available. Timer T is running.
no channell
When entering the sub-state, parameters shall be set to the following values, and configuration shall be
adapted to the new values of configuration parameters: COMM = F, D-ATT = T, U-ATT = T.
6.1.2.1.10 GCC Timers in the MS
Table 6.1 specifies the timers used in GCC. The denotation of columns is defined as follows:
timer ::= name of the timer;
set ::= under which conditions the timer is set (i.e., started);
stopped ::= under which conditions the timer is stopped;
running in state(s) ::= in whi
...