SIST EN 300 931 V7.0.1:2003

Digital cellular telecommunications system (Phase 2+) (GSM); Technical realization of facsimile group 3 transparent (GSM 03.45 version 7.0.1 Release 1998)

Upgrade from Phase 2+ to Release 1998

Digitalni celični telekomunikacijski sistem (faza 2+) – Tehnična realizacija faksimilne skupine 3 transparent (GSM 03.45, različica 7.0.1, izdaja 1998)

General Information

• Status: Published
• Publication Date: 30-Nov-2003
• ICS: 33.070.50 - Global System for Mobile Communication (GSM)
• Technical Committee: SS EIT - Technical Board for the electrotechnical, information technology and telecommunications fields
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 01-Dec-2003
• Due Date: 01-Dec-2003
• Completion Date: 01-Dec-2003
• Ref Project: ETSI EN 300 931 V7.0.1 (2000-01) - Digital cellular telecommunications system (Phase 2+) (GSM); Technical realization of facsimile group 3 transparent (GSM 03.45 version 7.0.1 Release 1998)

Standards Content (Sample)

SLOVENSKI STANDARD
01-december-2003
'LJLWDOQLFHOLþQLWHOHNRPXQLNDFLMVNLVLVWHPID]D±7HKQLþQDUHDOL]DFLMD
IDNVLPLOQHVNXSLQHWUDQVSDUHQW*60UD]OLþLFDL]GDMD
Digital cellular telecommunications system (Phase 2+) (GSM); Technical realization of
facsimile group 3 transparent (GSM 03.45 version 7.0.1 Release 1998)
Ta slovenski standard je istoveten z: EN 300 931 Version 7.0.1
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 Standard (Telecommunications series)
Digital cellular telecommunications system (Phase 2+);
Technical realization of facsimile group 3 transparent
(GSM 03.45 version 7.0.1 Release 1998)
R
GLOBAL SYSTEM FOR
MOBILE COMMUNICATIONS
(GSM 03.45 version 7.0.1 Release 1998) 2 ETSI EN 300 931 V7.0.1 (2000-01)
Reference
REN/SMG-040345Q7
Keywords
Digital cellular telecommunications system,
Global System for Mobile communications (GSM)
ETSI
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© European Telecommunications Standards Institute 2000.
All rights reserved.
ETSI
(GSM 03.45 version 7.0.1 Release 1998) 3 ETSI EN 300 931 V7.0.1 (2000-01)
Contents
Intellectual Property Rights.5
Foreword.5
0 Scope .6
0.1 References .6
0.2 Definitions and abbreviations.7
1 Service definition .8
2 Network architecture.8
3 Reference configuration at the mobile station .9
3.1 Fax Adaptor functionality.10
3.2 GSM Facsimile Machine functionality.10
4 Connection types.11
4.1 Information transfer protocol model.12
4.2 Interactions with T.30.13
4.2.1 Link control strategy.13
4.2.1.1 Message detection .14
4.2.2 Speed conversion for BCS phases .14
4.2.3 Compatibility checking .15
4.2.3.1 Group 1 and Group 2 support.15
4.2.3.2 2 400 bit/s handshaking.15
4.2.3.3 Non-standard facilities .15
4.2.3.4 12 000 and 7200 bit/s Facsimile Document Transfer.15
4.2.3.5 Procedure interrupts .15
4.2.4 Speed checking .15
4.3 Radio Channel Modification Procedures.16
4.3.1 In Call Modification (ICM) .16
4.3.2 Channel Mode Modify (CMM).17
5 Use of terminal adaptation functions .18
5.1 Standard TAFs for synchronous services .18
5.2 Specific TAFs for facsimile service.18
5.2.1 Working principle.18
5.2.2 Basic protocol structure .19
5.2.2.1 Frame formats .19
5.2.3 Protocol description.20
5.2.3.1 IDLE state .20
5.2.3.2 BCS-REC state.20
5.2.3.3 BCS-TRA state.20
5.2.3.4 MSG-REC state.21
5.2.3.5 MSG-TRA state .21
5.2.4 DCS and TCF processing.22
5.2.5 DCN (disconnect) frame .22
5.2.6 Clocking.22
5.2.7 Timeouts .23
5.3 Specific TAFs for facsimile service (T.30/A).23
5.3.1 Frame detection.23
5.3.2 Message phase .23
5.3.3 Additional CMM request .23
6 Signalling aspects.24
6.1 Handling of Tonal Signals.24
6.2 Call establishment.24
6.2.1 Mobile Terminated Call - Speech then Fax .24
6.2.2 Mobile Terminated Call - Auto answer.25
6.2.3 Mobile Originated Call - Speech then Fax.25
ETSI
(GSM 03.45 version 7.0.1 Release 1998) 4 ETSI EN 300 931 V7.0.1 (2000-01)
6.2.4 Mobile Originated Call - Auto calling .25
6.2.5 Mobile Originated Call - Manual calling .26
6.3 Call release .26
7 Interworking to fixed networks.26
7.1 Interworking to PSTN .26
7.2 Interworking to ISDN.27
Annex I (informative): Protocol entities from CCITT T.30 and T.4.28
Annex II (informative): Procedure examples.29
Annex III (informative): Change Request History .42
History .43
ETSI
(GSM 03.45 version 7.0.1 Release 1998) 5 ETSI EN 300 931 V7.0.1 (2000-01)
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 Standard (Telecommunications series) has been produced by the Special Mobile Group (SMG).
The present document defines the technical realization of facsimile group 3 using transparent network support within the
digital cellular telecommunications system.
The contents of the present document is subject to continuing work within SMG and may change following formal SMG
approval. Should SMG modify the contents of the present document it will be re-released with an identifying change of
release date and an increase in version number as follows:
Version 7.x.y
where:
7 indicates Release 1998 of GSM Phase 2+;
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.
The specification from which the present document has been derived was originally based on CEPT documentation,
hence the presentation of the present document may not be entirely in accordance with the ETSI/PNE Rules.
National transposition dates
Date of adoption of this EN: 31 December 1999
Date of latest announcement of this EN (doa): 31 March 2000
Date of latest publication of new National Standard
or endorsement of this EN (dop/e): 30 September 2000
Date of withdrawal of any conflicting National Standard (dow): 30 September 2000
ETSI
(GSM 03.45 version 7.0.1 Release 1998) 6 ETSI EN 300 931 V7.0.1 (2000-01)
0 Scope
The present document deals with the procedures allowing the technical realization of the Group 3 facsimile Service
within the GSM PLMN using transparent Network support, according to the definition of Teleservice 61 and 62
specified in the GSM 02.03 [2].
0.1 References
The following documents contain provisions which, through reference in this text, constitute provisions of the present
document.
• References are either specific (identified by date of publication, edition number, version number, etc.) or
non-specific.
• For a specific reference, subsequent revisions do not apply.
• For a non-specific reference, the latest version applies.
• A non-specific reference to an ETS shall also be taken to refer to later versions published as an EN with the same
number.
• For this Release 1998 document, references to GSM documents are for Release 1998 versions (version 7.x.y).
[1] GSM 01.04: "Digital cellular telecommunication system (Phase 2+): "Abbreviations and
acronyms".
[2] GSM 02.03: "Digital cellular telecommunication system (Phase 2+); Teleservices supported by a
GSM Public Land Mobile Network (PLMN)".
[3] GSM 02.34: “Digital cellular telecommunications system (Phase2+): High Speed Circuit Switched
Data (HSCSD) - Stage1”.
[4] GSM 03.10: "Digital cellular telecommunication system (Phase 2+); GSM Public Land Mobile
Network (PLMN) connection types".
[5] GSM 03.34: "Digital cellular telecommunications system (Phase2+): High Speed Circuit Switched
Data (HSCSD) - Stage2.
[6] GSM 04.02: "Digital cellular telecommunication system (Phase 2+); GSM Public Land Mobile
Network (PLMN) access reference configuration".
[7] GSM 04.08: "Digital cellular telecommunication system (Phase 2+); Mobile radio interface layer 3
specification".
[8] GSM 04.21: "Digital cellular telecommunication system (Phase 2+); Rate adaption on the Mobile
Station - Base Station System (MS - BSS) interface".
[9] GSM 07.01: "Digital cellular telecommunication system (Phase 2+); General on Terminal
Adaptation Functions (TAF) for Mobile Stations (MS)".
[10] GSM 07.03: "Digital cellular telecommunication system (Phase 2+); Terminal Adaptation
Functions (TAF) for services using synchronous bearer capabilities".
[11] GSM 09.07: "Digital cellular telecommunication system (Phase 2+); General requirements on
interworking between the Public Land Mobile Network (PLMN) and the Integrated Services
Digital Network (ISDN) or Public Switched Telephone Network (PSTN)".
[12] CCITT Recommendation T.35: "Procedure for the allocation of CCITT members' codes".
[13] CCITT Recommendation F.160 Fascicle II.5: "General operational provision for the international
public facsimile".
ETSI
(GSM 03.45 version 7.0.1 Release 1998) 7 ETSI EN 300 931 V7.0.1 (2000-01)
[14] CCITT Recommendation T.4 Fascicle VII.3: "Standardization of group 3 facsimile apparatus for
document transmission".
[15] CCITT Recommendation T.30 Fascicle VII.3: "Procedures for document facsimile transmission in
the general switched telephone network".
[16] CCITT Recommendation V.21 Fascicle VIII.l: "300 bits per second duplex modem standardized
for use in the general switched telephone network".
[17] CCITT Recommendation V.24 Fascicle VIII.l: "List of definitions for interchange circuits between
data terminal equipment (DTE) and data circuit-terminating equipment (DCE)".
[18] CCITT Recommendation V.25bis Fascicle VIII.l: "Automatic calling and/or answering equipment
on the general switched telephone network (GSTN) using the 100-series interchange circuits".
[19] CCITT Recommendation V.27ter Fascicle VIII.l: "4 800/2 400 bits per second modem
standardized for use in the general switched telephone network".
[20] CCITT Recommendation V.29 Fascicle VIII.l: "9 600 bits per second modem standardized for use
on point-to-point 4-wire leased telephone-type circuits".
[21] CCITT Recommendation V.33 Fascicle VIII.l: "14 400 bits per second modem standardized for
use on point-to-point 4-wire leased telephone-type circuits".
[22] CCITT Recommendation X.300 Fascicle VIII.6: "General principles for interworking between
public networks, and between public networks and other networks for the provision of data
transmission services".
[23] CCITT Recommendation V.17: "A 2-wire modem for facsimile applications with rates up to 14
400 bit/s".
0.2 Definitions and abbreviations
In addition to those below, abbreviations used in the present document are listed in GSM 01.04 [1].
BCS Binary Coded Signalling phase of Facsimile transmission as per CCITT T.30
CT105 Interchange Circuit 105 as per CCITT V.24
CT106 Interchange Circuit 106 as per CCITT V.24
CT107 Interchange Circuit 107 as per CCITT V.24
CT108.2 Interchange Circuit 108/2 as per CCITT V.24
CT109 Interchange Circuit 109 as per CCITT V.24
CT114 Interchange Circuit 114 as per CCITT V.24
CT115 Interchange Circuit 115 as per CCITT V.24
FA/MT The Fax Adaptor specifically located at MT side
FA/IWF The Fax Adaptor specifically located at IWF side
MSG Message phase of Facsimile transmission as per CCITT T.30
All protocol entities from CCITT Facsimile Recommendations (T.4 and T.30) apply; in the present document they are
referenced to in the same way as in the above CCITT Recommendations (see also annex I to the present document).
ETSI
(GSM 03.45 version 7.0.1 Release 1998) 8 ETSI EN 300 931 V7.0.1 (2000-01)
1 Service definition
The fixed network Group 3 Facsimile service, as basically defined in CCITT Recommendation F.160, is an international
telematic service for ISO A4 document transmission between two facsimile stations.
The service specification is comprised of two parts: the control protocol described in CCITT Recommendation T.30,
and the document transmission coding described in CCITT Recommendation T.4.
The GSM facsimile Teleservice is intended to allow facsimile connections between group 3 apparatus using:
- a GSM PLMN as a stand alone facility, for mobile to mobile communication;
- a GSM PLMN to gain access to fixed networks PSTN and ISDN, for mobile to/from land communication.
For this Teleservice, the document coding is as CCITT Recommendation T.4 with no modifications. The protocol used
is CCITT Recommendation T.30 modified within the PLMN as detailed in the present document.
The interworking between different networks is based on CCITT Recommendation X.300.
The particular features of this Teleservice are:
- it uses point-point communication;
- the information transfer capability is dual "Speech"/"Group 3 Facsimile" for Teleservice 61 and "Group 3
Facsimile" only for Teleservice 62;
- both mobile originated and terminated calls are supported;
- the information transfer mode is circuit, duplex, synchronous and symmetric;
- different end-to-end transfer rates are used within the same call to take advantage of the better radio path error
rate;
- use of a standard synchronous terminal adaptation function (as per GSM 07.03) within the MS.
2 Network architecture
The network architecture applicable to this Teleservice is shown in figure 1/03.45, below.
PLMN
v v
PSTN FAX
FAX BSS MSC/IWF
MT
ISDN
Figure 1/03.45: Network architecture
This shows the case of mobile to fixed network interworking. For mobile to mobile calls, there would effectively be a
loop back within the PLMN, using two IWFs.
ETSI
(GSM 03.45 version 7.0.1 Release 1998) 9 ETSI EN 300 931 V7.0.1 (2000-01)
3 Reference configuration at the mobile station
The mobile reference configurations described in this clause are defined as per GSM 04.02.
Mobile Station
R U
2w
m
FAX
a)
FAX /
MT2
Adapt.
S
2w
FAX
b)
FAX /
MT1
TA
Adapt.
2w
FAX
/
c) FAX TA MT1
Adapt.
R
d) FAX
FAX
MT2
Adapt.
FAX
e)
FAX TA
MT1
Adapt.
f)
MT0
Figure 2/03.45: Reference configurations
The Teleservice definition in GSM 02.03 regards the group 3 facsimile terminal as a 2-wire analogue terminated
equipment. In order to connect this to the MT2 a separate "Fax Adaptor" device is necessary.
This configuration, shown in figure 2a/03.45, has to be considered as the standard configuration, so that all the existing
Group 3 facsimile apparatus can be connected to the PLMN.
An alternative realization would be to combine a standard group 3 facsimile machine and the Fax Adaptor into a
specially developed "GSM facsimile machine", directly providing a digital output. Although such a device must appear
to the MT2 as identical to the Fax Adaptor (i.e. with an identical interface and protocol), it would allow for a
significantly smaller and simpler facsimile machine. This configuration is shown in figure 2d/03.45 and is regarded as a
desirable alternative.
In addition of course, it is always possible to realize an MT0, as per figure 2f/03.45, where both the facsimile and
mobile termination functions are considered to be part of one integrated unit.
The remaining configurations concern the use of an S interface and are considered as optional configurations. Their use
is for further study.
The particular terminal adaptation functions used are those detailed in GSM 07.03 and the interface to the MT2 used is
synchronous V.24 with an option for support of V.25bis procedures for autocalling and autoanswering.
ETSI
(GSM 03.45 version 7.0.1 Release 1998) 10 ETSI EN 300 931 V7.0.1 (2000-01)
3.1 Fax Adaptor functionality
The Fax Adaptor block, figure 3/03.45, is intended to specifically complement the Group 3 facsimile apparatus in order
to be able to communicate over a GSM PLMN.
COMPOSITE
MODEM
R
2W
PROTOCOL
MONITORING
&
CONTROL
TONE
HANDLING
Figure 3/03.45: Fax Adaptor scheme
Whether it has to be a function internal to the GSM PLMN, or an external accessory associated with the Group 3
apparatus, is beyond the scope of the present document, and in any case, does not affect at all the working of the
procedure as here described.
It can be functionally partitioned in two sections:
- an analogue section, dealing with:
- the modulation and demodulation processes according to CCITT Recommendation V.21, V.27ter, V.29 and
V.17 as explained in T.4 and T.30;
- handling of the signalling on the 2-wire path to the facsimile machine, including autocalling and autoanswer
functions where necessary (see clause 6).
- a digital section, dealing with:
- monitoring and where necessary, manipulation of the T.30 protocol as detailed in the rest of the present
document;
- overall control of the adaptor;
- connection over the synchronous V.24 interface to the MT as described in GSM 07.03;
- where necessary, autocalling and autoanswering functions according to V.25bis.
In the following this specification will reference the Fax Adaptor functionality, considering the most general case where
it operates as a full-featured (see figure 3/03.45) separate block (see figure 2a/03.45), as this reference configuration is
implicitly or explicitly exhaustive of all service related technical aspects.
3.2 GSM Facsimile Machine functionality
The special GSM facsimile machine shown in the MS configuration of figure 2d/03.45 has a similar functionality to the
digital part of the Fax Adaptor, but without any of the analogue portions.
It appears over the V.24 interface as identical to the Fax Adaptor, i.e. the MT2 needs to have no knowledge of the
particular configuration used.
When necessary this reference configuration, will be explicitly referenced to in the following; otherwise all technical
aspects relevant to the configuration implicitly apply.
ETSI
(GSM 03.45 version 7.0.1 Release 1998) 11 ETSI EN 300 931 V7.0.1 (2000-01)
4 Connection types
Table 1/03.45 shows the connection elements attributes applicable to this Teleservice (note), adapted from GSM 03.10.
NOTE: Teleservice 61 includes both speech and data connection types, but Teleservice 62 only the data
connection type.
Table 1/03.45: Elements of connection types
Protocol type Access to TAF Radio interface Intermediate BS-MSC/IWF
of Figure 6 of TS of the Mobile connection element rate connection
GSM 03.10 Station RA1 to RA2 element
Model 6: Speech - Speech/GSM - CCITT
A-law
Model 5: C/D/S UDI C/D/S UDI C/D/S UDI C/D/S UDI
Facsimile - 14.4 kbit/s - 14.5 kbit/s - 16 kbit/s - 64 kbit/s
Group 3 - 9.6 kbit/s - 12.0 kbit/s - 16 kbit/s - 64 kbit/s
- 4.8 kbit/s - 6.0 kbit/s - 8 kbit/s - 64 kbit/s
- 2.4 kbit/s - 3.6 kbit/s - 8 kbit/s - 64 kbit/s
(note)
Model 5b C/D/S UDI C/D/S UDI C/D/S UDI C/D/S UDI
Facsimile - 14.4 kbit/s 14,5 or 2X12 kbit/s 16 or 2X16 kbit/s - 64 kbit/s
Group 3 - 9.6 kbit/s 12 or 2X6 kbit/s 16 or 2X8 kbits - 64 kbit/s
- 4.8 kbit/s 6 kbit/s 8 kbit/s - 64 kbit/s
- 2.4 kbit/s 6kbits 8 kbit/s - 64 kbit/s
NOTE: The highest Access Rate actually supported in this teleservice will be consistent with the highest Access Rate
of the Transparent Bearer Service provided by the Network Operator.
C = Circuit switched S = Synchronous
D = Full-duplex UDI = Unrestricted Digital Information
Table 1a/03.45
Fax modem rates No. of substreams Radio i/f rate Intermediate Rate Padding Scheme
14.4 kbit/s 1 14,5 kbit/s 16 kbit/s
2 12 kbit/s 16 kbit/s
12.0 kbit/s 1 14,5 kbit/s 16 kbit/s FA(5D + S)
2 12 kbit/s 16 kbit/s FA(5D + S)
9.6 kbit/s 1 12 kbit/s 16 kbit/s
2 6 kbit/s 8 kbit/s
7.2 kbit/s 1 12 kbit/s 16 kbit/s FA(3D + S)
2 6 kbit/s 8 kbit/s FA(3D + S)
4.8 kbit/s 1 6 kbit/s 8 kbit/s
2.4 kbit/s 1 6 kbit/s 8 kbit/s
FA = Padding is performed in the FA
(nD + mS) means that m SYNC frames will be added every n’th DATA frame
The MS must support the combinations in table 1a/03.45, restricted to what has been negotiated between the MS and the
network.
All transitions from one combination in table 1a/03.45 to another combination in the same table, must be supported by
the MS, as long as the fax modem rate is kept constant or the transition of fax modem rate is performed in steps of 2,4
kbit/s.
The figure 4/03.45 shows the scheme of a typical GSM PLMN connection for this Teleservice, considering respectively
R and S access at Network Termination.
ETSI
(GSM 03.45 version 7.0.1 Release 1998) 12 ETSI EN 300 931 V7.0.1 (2000-01)
To grant full support to the CCITT Recommendation T.30, requiring different transmission speeds, the following
strategy shall be implemented:
- PLMN provides for four Access Rates only, that is 14 400 bits/s, 9600 bit/s, 4800 bit/s, 2400 bit/s;
- radio channel modification procedures are used for switching between Speech phase and facsimile phase, as well
as to select the suitable Access Rate (14 400,9600/4800/2400 bit/s) within the facsimile phase, as resulting from
the preliminary end-to-end negotiation between the terminals;
- to transport Binary Coded Signalling (BCS) requiring a synchronous 300 bit/s bit-rate, speed conversion will be
used at both the PLMN ends.
DTE DCE
MT2
MSC/IWF
3.1 kHz audio
P
2w
FAX
FAX 2w
L
Adaptor
R I/F M Adaptor
(V.24)
N
MT1
MSC/IWF
3.1 kHz audio
FAX
P
2w
2w
L
Adaptor
M
S I/F
N
Figure 4b/03.45: Optional Teleservice connection (F.F.S)
4.1 Information transfer protocol model
The Figure 5/03.45 depicts the conceptual protocol model for this Teleservice, deduced from model 5 and 5b of Figure
6/03.10.
The main point to be underlined is that all the protocol modules specific for this Teleservice are confined in the Fax
Adaptation functions at both the MT and IWF ends. Note that model 5b of figure 6/03.10 details the placing of the
splitting and combiner function for multislot configurations.
ETSI
GR 3 Apparatus
GR 3 Apparatus
FAX
Adaptor
TA
GR 3 Apparatus
GR 3 Apparatus
(GSM 03.45 version 7.0.1 Release 1998) 13 ETSI EN 300 931 V7.0.1 (2000-01)
Mobile Station Base Station MSC/IWF
Radio I/F
R I/F
BSS-MSC I/F
Fax
Adapt.
Fax
Fax
T.30
T.30
Adaptation
Adaptation
function
function
RA1
RA1'
RA1'
RA1
FEC RA2
FEC RA2
I/F Cct I/F Cct
Figure 5/03.45: Information transfer protocol model
4.2 Interactions with T.30
The philosophy of this specification is to allow the T.30 protocol to pass transparently wherever possible, through the
Fax Adaptors at both ends of the PLMN channel. Manipulations are only made to the protocol where necessary to
overcome problems resulting from the differences between the PSTN and the GSM system. Basically, these problems
fall into four categories:
- supporting facsimile on a digital connection type;
- bit errors during transfer of BCS frames;
- the need to change speed to reduce the impact of bit errors during transfer of Fax encoded Messages;
- inability to support some features of T.30.
4.2.1 Link control strategy
Though the T.30 procedure is plain half-duplex, between the FAs at both the GSM PLMN ends a full-duplex mode
connection will be established. Information transfer is structured in fixed length blocks, carrying either data received
from the local modem, or idle synchronization patterns.
Establishment, maintenance and release of the data circuit is performed autonomously by each FA, by properly handling
the physical interface to its local modem.
Due to the rigid timeout constrains in T.30 protocol procedure, which will be actually concatenated to the procedure
defined here for the GSM connection part, a strictly forwardonly approach is adopted for data link control; that is no
retransmission means are explicitly introduced to recover corrupted information blocks.
Although in the majority of cases the T.30 protocol can take care of lost frames and easily recover, there are some
particularly critical points where two consecutive segments in the procedure, without any interposed acknowledgement,
require different transmission speeds (BCS speed/Message speed).
In these cases, to grant that a correct change-over from one modem type to another takes place at both the PLMN ends,
some additional protection is necessary in the GSM environment. This protection, actually at the beginning and at the
end of the Fax page transmission, is given by means of a confirmation mechanism, whereby the originating FA waits
while transmitting a fixed pattern until an explicit acknowledgement is received from the terminating FA. In these cases
an interruption of the normal T.30 information flow may eventually result.
ETSI
(GSM 03.45 version 7.0.1 Release 1998) 14 ETSI EN 300 931 V7.0.1 (2000-01)
Aiming at minimizing any possible delay in the end-to-end transmission between the two facsimile apparatuses, the FAs
will pass on information without error control of the message integrity (note). To this regard, however, it is worth
underlining that an essential requirement in this procedure is the detection of some key messages exchanged between the
terminals, carrying basic control information. Hence, in parallel to the primary information passing process, a
continuous monitoring of the information flowing across the FA is necessary, to detect these messages, fully checked in
their logical integrity.
NOTE: All V.21 modems in the FAs shall use the faster response time provided by CCITT Rec. V.21 (see table
2/V.21) for OFF to ON transition of CT109 and CT106.
In addition, as detailed below, some fields in some frames may need to be changed.
4.2.1.1 Message detection
While in BCS, the following frames have to be detected:
- DIS/DTC, to monitor all operational parameters proposed to the sender terminal by the receiver terminal;
- DCS, to realize (see table 2/T.30) the actual message transmission speed accepted by the sender terminal and the
relevant message transfer direction;
- NSF, to inhibit Non-Standard Facilities, if explicitly required by the user Fax Adaptor configuration;
- DCN, to initiate the Call release procedure.
During the Message phase (C phase of T.30) a single bit pattern has to be detected, the EOL character, a unique
codeword that can never be found within a valid line of Fax coded Data (see CCITT Recommendation T.4, subclause
4.1.2), and therefore used to control the buffer level in each FA, as detailed in the following subclause 5.2.6.
4.2.2 Speed conversion for BCS phases
Given the signalling load caused by the Channel Mode Modify procedure, rather than changing the radio channel speed
to 300 bit/s to carry the BCS frames, a speed conversion mechanism is exploited at both the PLMN ends, allowing to
maintain the Channel rate of the Message phase (14 400/9600/4800/2400 bit/s) during BCS phases.
A speed conversion factor can be defined as:
Fax Message speed (14 400 or 9600 or 4800 or 2400 bit/s)
---------------------------------------------------------------------
Standard BCS speed (300 bit/s)
which will assume the value 8 or 16 or 32 or 48, depending on the actual Message speed negotiated between the
terminals.
On the basis of the above speed conversion factor, in the originating FA up-conversion to Message speed will be
performed according to the repetition algorithm specified in subclause 5.2.3.2.
In the terminating FA, down-conversion to the BCS speed will require a decimation algorithm (see subclause 5.2.3.3);
this algorithm is assumed implementation dependent, and hence its actual definition is beyond the scope of the present
document.
As the actual Access Rate over the GSM-TCH may change throughout the Call, speed conversion factor needs to be
updated in both FAs.
The FA/IWF will update this value upon successful completion of a CMM procedure (see subclause 4.3.2).
The FA/MT which does not have direct access to the GSM signalling channel (except for MT0 configuration), shall
estimate the actual Access Rate established over the GSM-TCH from the effective Access Rate of the MT data interface
(or any other means in case of MT0); this check shall be performed whenever a BCS frame is sent towards the Radio
path after which a change for GSM-TCH Access Rate may be expected (e.g., DIS and DCS frames for Normal Fax
mode, PPR and CTC frames for Error Correction Mode).
ETSI
(GSM 03.45 version 7.0.1 Release 1998) 15 ETSI EN 300 931 V7.0.1 (2000-01)
4.2.3 Compatibility checking
Some features of T.30 cannot be supported in the GSM PLMN environment. Fax Adaptation function is in charge of
dealing with such compatibility checking.
4.2.3.1 Group 1 and Group 2 support
Group 1 and Group 2 equipments are not supported by the Teleservice as described in the present document.
To this purpose, any tonal signalling specific to the above kind of Fax apparatus will be ignored by the Fax adaptation
function at MS and IWF.
4.2.3.2 2 400 bit/s handshaking
Only standard 300 bit/s Binary Coded Signalling is supported. To this purpose the FA will ignore this capability within
the B segment of T.30 procedure, looking for DIS frame, by default, from V.21 modem only.
4.2.3.3 Non-standard facilities
Non-standard facilities are supported in so far they are not in conflict with the standard procedure described in the
present document. All the relevant BCS frames are passed end-to-end, unless an explicit deletion is required by the user
(e.g. by a specific input at the Fax Adaptor associated with the MS). In this case, upon detection (see subclause 4.2.1.1)
of the NSF frame identifier (the Facsimile Control Field octet according to T.30 terminology), the whole HDLC frame
shall be stripped and replaced by a GSM specific NSF frame, containing a Country Code and a unique identification of
the FA manufacturer, encoded as per CCITT T.35 and according to national regulations; the Information field of this
NSF frame shall have a maximum length of 6 octets, and shall not require any specific functionality in the PLMN.
4.2.3.4 12 000 and 7200 bit/s Facsimile Document Transfer
End-to-end transfer of T.4 information at 12 000 and 7 200 bit/s can be supported, even if this Bearer Service is not
provided by a GSM PLMN.
To this purpose a 14 400 bit/s or 9 600 bit/s Access Rate shall be used in the PLMN, by exploiting only part of the
available bandwidth. The originating FA will add padding information to data received from the MSG modem, before
transmission over the GSM-TCH; the terminating FA will remove the same information to restore the net 12 000 or 7
200 bit/s continuous data stream to be transmitted over its local MSG modem.
The relevant procedures are fully described in sections 5.2.3.4 and 5.2.3.5.
4.2.3.5 Procedure interrupts
Procedure interrupts are only possible in Teleservice 61; in case of Teleservice 62 any attempt to invoke procedure
interrupts by MMI on the MT (see subclause 4.3.1 below) will be ineffective.
4.2.4 Speed checking
Upon receiving DIS/DTC frame, the FA/IWF shall perform a basic speed checking procedure, aiming at verifying
compatibility between the bit-rate possibilities offered by the called Fax apparatus (bit fields 11, 12, 13, 14 in the IF)
and the actual Access Rates allowed on the GSM PLMN (2 400/4 800/9 600/14400 bit/s); in addition, some of these bit
rates may result inhibited during the call, if a speed lower than 9 600 bit/s has been chosen by the user in the call set up
message (for example if a better error rate is required).
The following cases may occur:
- some of the bit-rates indicated in DIS/DTC are not allowed on GSM-TCH (e.g. the max speed indicated in setup
is 9 600 bit/s, while DIS/DTC requests V.33); a possible strategy to cater for this case is altering the indication in
DIS/DTC to a compatible value (e.g. V.29) by forcing appropriately the relevant bits (note); other strategies are
possible and allowed, as long as the same goal of supporting the progress of the call is pursued, by constraining
the Fax apparatuses to use as message speeds the access rates actually available in the PLMN.
ETSI
(GSM 03.45 version 7.0.1 Release 1998) 16 ETSI EN 300 931 V7.0.1 (2000-01)
NOTE: Is beyond the scope of this specification to specify the implementation strategy adopted to recalculate the
frame CRC after the manipulation; additional delays, if any, shall not have a significant impact on T.30
operability.
- the full set of bit-rates indicated in DIS/DTC are not compatible with the allowed Access Rates on GSM-TCH
(e.g. the max speed indicated in setup is 2 400 bit/s while DIS/DTC requests V.29 only); in this case the call shall
be failed;
- the full set of bit-rates indicated in DIS/DTC are compatible with the allowed Access Rates on GSM-TCH; in this
case no action shall be taken, independently of the access rate actually established.
It should be noted that the "14400 bit/s" as max speed indication in the SETUP message, does not preclude the
establishment of a Call towards a Fax GR 3 equipment supporting only 9600, 4 800 and 2 400 bit/s as Message speed.
As a matter of fact, due to the multiplexing mechanism for BCS phases the initial Access Rate (14 400 bit/s) will affect
only the connection part between the called MS and the associated IWF, whilst the appropriate Message speed will be
actually negotiated during the initial BCS phase, and settled upon reading the appropriate field in DCS frame (see
subclause 4.2.1.1). Therefore, if a request for MSG transmission is received, without a valid DCS frame being detected
in advance (hence the message speed is undefined), the FA/IWF shall release the call immediately.
4.3 Radio Channel Modification Procedures
There are two reasons why the characteristics of the radio channel may need to be changed during a call.
Firstly, for the swap from speech to data and vice versa. In this case the In Call Modification procedure as detailed in
GSM 04.08 is carried out.
Secondly, if a T.30 speed drop back is requested, a channel mode modify procedure as detailed in GSM 04.08 is
initiated to match the radio channel rate to the facsimile transmission speed to optimize the error rate.
4.3.1 In Call Modification (ICM)
Applies only for Teleservice 61.
The speech to facsimile change is initiated by MMI at the MS as in other data services starting the ICM procedure via
MODIFY signalling. CT108.2 ON condition towards MT is a basic requirement to allow speech/data transition take
place.
Additionally, the data call direction (DCD) must be known to both the FA's because of a correct tone handling. The
DCD identifies the call direction from the calling to the called station according to CCITT T.30 phase "A" tonal signals.
The DCD is derived from the evaluation of the behaviour of the mobile Fax machine. No later than 3 sec after
connecting the Fax apparatus to the line the FA/MT is able to determine the DCD. If a CNG tone or nothing is detected
by the FA/MT the mobile Fax station is the calling station, if a CED tone or a BCS signal is detected by the FA/MT the
mobile Fax station is the called station. The FA/MT indicates this towards the MT by means of CT105: CT105 OFF
condition indicates "mobile terminated", CT105 ON condition indicates "mobile originated". The detection of CT105
condition and subsequent triggering of the MODIFY message has to be done 3 sec after reception of the ON condition
of CT108.2.
A reverse DCD compared with the initial call setup direction is indicated to the FA/IWF by means of the "Reverse Call
Setup Direction" (RCSD) information element within the MODIFY message. If the MODIFY message had contained
this information element, the same information element shall be included in the MODIFY COMPLETE message (ACK).
On the basis of RCSD and additional information about the initial call setup direction (e.g. Transaction Identifier flag as
per GSM 04.07),
...