ETSI ETS 300 492 ed.1 (1996-05)

SLOVENSKI STANDARD
01-december-2003
Javno komutirano telefonsko omrežje (PSTN) – Specifikacija kategorije II za
dupleksne modeme s hitrostmi 14 400, 12 000, 9 600, 7 200 in 4 800 b/s,
standardizirane za uporabo v omrežjih PSTN
Public Switched Telephone Network (PSTN); Category II specification for 14 400, 12
000, 9 600, 7 200 and 4 800 bits per second duplex modems standardized for use on the
PSTN
Ta slovenski standard je istoveten z: ETS 300 492 Edition 1
ICS:
33.040.35 Telefonska omrežja Telephone networks
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN ETS 300 492
TELECOMMUNICATION May 1996
STANDARD
Source:ETSI TC-TE Reference:DE/TE-05033
ICS: 33.020
modem, PSTN
Key words:
Public Switched Telephone Network (PSTN);
Category II specification for 14 400, 12 000, 9 600, 7 200 and
4 800 bits per second duplex modems standardized
for use on the PSTN
ETSI
European Telecommunications Standards Institute
ETSI Secretariat
F-06921 Sophia Antipolis CEDEX - FRANCE
Postal address:
650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCE
Office address:
c=fr, a=atlas, p=etsi, s=secretariat - secretariat@etsi.fr
X.400: Internet:
Tel.: +33 92 94 42 00 - Fax: +33 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 1996. All rights reserved.

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ETS 300 492: May 1996
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 300 492: May 1996
Contents
Foreword .7
1 Scope .9
2 Normative references.9
3 Definitions and abbreviations .10
3.1 Definitions .10
3.2 Abbreviations .10
4 General requirements .10
4.1 References to other ETSs .10
4.2 Information to be provided by the applicant.10
4.2.1 Information required for testing purposes .10
4.2.2 Instructions for use.11
5 Functional requirements specific to Category II modems .11
5.1 General requirements .11
5.2 Modes of operation/use .12
5.3 Line signals.13
5.3.1 Transmitted carrier frequency .13
5.3.2 Receiver carrier tolerance .13
5.3.3 Transmitted spectrum .13
5.4 Line signalling rates .13
5.5 Encoding of data.13
5.6 Scrambler and descrambler.13
5.7 Channel allocation .13
5.7.1 Channel selection.13
5.7.2 Automatic channel selection.14
5.8 Hand-shaking sequences .14
5.8.1 Definitions.14
5.8.2 Calling and answering procedures .16
5.8.2.1 Calling tone.16
5.8.2.2 Answer tone recognition .16
5.8.2.3 Answering tone generation.16
5.8.3 Start-up procedure .16
5.8.3.1 Call Mode Modem (CMM) .16
5.8.3.1.1 Initiation of start-up procedure .16
5.8.3.1.2 Round trip delay determination.16
5.8.3.1.3 Start of rate negotiation.17
5.8.3.1.4 Completion of the rate negotiation.17
5.8.3.1.5 Completion of the hand-shake.17
5.8.3.2 Answer Mode Modem (AMM).18
5.8.3.2.1 Initiation of the start-up procedure .18
5.8.3.2.2 Round trip delay determination.18
5.8.3.2.3 Start of rate negotiation.18
5.8.3.2.4 Completion of rate negotiation.19
5.8.3.2.5 Completion of the hand-shake.19
5.8.4 Retrain sequence .19
5.8.4.1 Initiating signal .19
5.8.4.1.1 Call Mode Modem (CMM).19
5.8.4.1.2 Answer Mode Modem (AMM) .20
5.8.4.2 Response signal .20
5.8.4.2.1 Call Mode Modem (CMM).20
5.8.4.2.2 Answer Mode Modem (AMM) .20
5.8.5 Rate renegotiation procedure.20
5.8.5.1 Initiating procedure .20

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5.8.5.1.1 Call Mode Modem (CMM) . 21
5.8.5.1.2 Answer Mode Modem (AMM) . 21
5.8.5.2 Responding procedure. 22
5.8.5.2.1 Call Mode Modem (CMM) . 22
5.8.5.2.2 Answer Mode Modem (AMM) . 22
5.8.6 Compatibility with V.32 modems. 23
5.8.6.1 Call Mode Modem. 23
5.8.6.2 Answer Mode Modem . 23
5.9 Transmission of start-stop characters. 23
5.10 Threshold of received line signal detector. 23
5.11 Test loop 2. 23
5.11.1 Definitions . 24
5.11.2 Instigation of a remote loop 2 . 24
5.11.3 Termination of a remote loop 2. 24
5.12 Receiver performance. 25
5.12.1 Normal case. 25
5.12.2 Case with satellite delay . 25
Annex A (normative): Testing methods . 27
A.1 General testing conditions . 27
A.1.1 General notes. 27
A.1.1.1 Test set-up. 27
A.1.1.2 Determination of signals . 27
A.1.2 Limitation of number of tests. 28
A.1.2.1 Introduction . 28
A.1.2.2 General rules . 28
A.1.2.3 Specific rules . 28
A.1.3 Proposed order for performing the tests . 29
A.2 Test for subclause 5.3.1 (Transmitted carrier frequency). 30
A.3 Test for subclause 5.3.2 (Receiver carrier tolerance) . 30
A.4 Test for subclause 5.4 (Line signalling rates). 30
A.5 Test for subclause 5.5 (Encoding of data). 31
A.6 Test for subclause 5.6 (Scrambler and descrambler) . 31
A.7 Test for subclause 5.7 (Channel allocation) . 31
A.8 Test for subclause 5.8 (Hand-shaking sequences). 31
A.8.1 Test for subclause 5.8.2 (Calling and answering procedures). 31
A.8.1.1 Test for subclause 5.8.2.1 (Calling tone). 31
A.8.1.2 Test for subclause 5.8.2.2 (Answer tone recognition) . 32
A.8.1.3 Test for subclause 5.8.2.3 (Answering tone generation) . 32
A.8.2 Tests for subclause 5.8.3 (Start-up procedure) . 32
A.8.2.1 Tests for subclause 5.8.3.1 (CMM) . 32
A.8.2.1.1 Test for subclause 5.8.3.1.1 (Initiation of the start-up
procedure). 32
A.8.2.1.2 Test for subclause 5.8.3.1.2 (Round trip delay
determination) . 32
A.8.2.1.3 Test for subclause 5.8.3.1.3 (Start of rate negotiation). 32
A.8.2.1.4 Test for subclause 5.8.3.1.4 (Completion of the rate
negotiation) . 33
A.8.2.1.5 Test for subclause 5.8.3.1.5 (Completion of the hand-
shake) . 34
A.8.2.2 Tests for subclause 5.8.3.2 (AMM). 34
A.8.2.2.1 Test for subclause 5.8.3.2.1 (Initiation of the start-up
procedure). 34
A.8.2.2.2 Test for subclause 5.8.3.2.2 (Round trip delay
determination) . 35

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ETS 300 492: May 1996
A.8.2.2.3 Test for subclause 5.8.3.2.3 (Start of rate negotiation) .35
A.8.2.2.4 Test for subclause 5.8.3.2.4 (Completion of rate
negotiation).35
A.8.2.2.5 Test for subclause 5.8.3.2.5 (Completion of the hand-
shake).36
A.8.3 Tests for subclause 5.8.4 (Retrain sequence).37
A.8.3.1 Tests for subclause 5.8.4.1 (Initiating signal).37
A.8.3.1.1 Tests for subclause 5.8.4.1.1 (CMM) .37
A.8.3.1.2 Tests for subclause 5.8.4.1.2 (AMM).37
A.8.3.2 Tests for subclause 5.8.4.2 (Response signal).37
A.8.3.2.1 Tests for subclause 5.8.4.2.1 (CMM) .37
A.8.3.2.2 Tests for subclause 5.8.4.2.2 (AMM).37
A.8.4 Tests for subclause 5.8.5 (Rate renegotiation procedures).38
A.8.4.1 Tests for subclause 5.8.5.1 (Initiating procedure).38
A.8.4.1.1 Tests for subclause 5.8.5.1.1 (CMM) .38
A.8.4.1.2 Tests for subclause 5.8.5.1.2 (AMM).39
A.8.4.2 Tests for subclause 5.8.5.2 (Responding procedure) .41
A.8.4.2.1 Tests for subclause 5.8.5.2.1 (CMM) .41
A.8.4.2.2 Tests for subclause 5.8.5.2.2 (AMM).42
A.8.5 Tests for subclause 5.8.6 (compatibility with V.32 modems).43
A.8.5.1 Test for subclause 5.8.6.1 (CMM).43
A.8.5.2 Test for subclause 5.8.6.2 (AMM) .43
A.9 Test for subclause 5.9 (Transmission of start-stop characters).44
A.10 Tests for subclause 5.11 (Test loop 2).44
A.10.1 Tests for subclause 5.11.2 (Instigation of a remote loop 2).44
A.10.1.1 Transmission of the test loop initiation signal - Test for subclause
5.11.2(a) (Controlling MUT).44
A.10.1.2 Response to the test loop initiation signal (Test for subclause 5.11.2(b))
(Controlled modem under test) .44
A.10.2 Tests for subclause 5.11.3 (Termination of a remote test loop 2) .45
A.10.2.1 Transmission of the de-activation signal (Test for subclause 5.11.3(a))
(Controlling modem).45
A.10.2.2 Response to the de-activation signal (Test for subclause 5.11.3(b))
(Controlled modem) .45
Annex B (informative): Example proforma for the declaration of modes of operation/use .46
Annex C (informative): Bibliography.51
History.52

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ETS 300 492: May 1996
Foreword
This European Telecommunication Standard (ETS) has been produced by the Terminal Equipment (TE)
Technical Committee of the European Telecommunications Standards Institute (ETSI).
This ETS specifies the technical characteristics required for end-to-end interworking over the Public
Switched Telephone Network (PSTN) for 14 400 bit/s, 12 000 bit/s, 9 600 bit/s, 7 200 bit/s and 4 800 bit/s
modems standardized for use over the PSTN.
These requirements are based upon, and do not conflict with, CCITT Recommendation V.32 bis [1].
Additionally, requirements are included relating to end-to-end interoperability over PSTN connections.
Such requirements are in excess of the CCITT/ITU-T Recommendations.
Except where otherwise indicated, a modem which complies with CCITT Recommendation V.32 bis [1]
should always meet the requirements of this ETS which relate to parameters specified in that CCITT
Recommendation.
Clause 4 of this ETS references the requirements common to both Category I and Category II modems,
which are contained in clause 4 of final draft prETS 300 114 [2]. The definitions for Category I and
Category II modems can be found in the foreword of final draft prETS 300 114 [2].
Clause 5 of this ETS contains Category II requirements specific to CCITT Recommendation V.32 bis [1]
modems. In the case of a certain function common to more than one type of modem (e.g. auto-answering
sequence) reference is made to clause 5 of final draft prETS 300 114 [2], which contains the relevant
requirements.
Transposition dates
Date of adoption of this ETS: 26 April 1996
Date of latest announcement of this ETS (doa): 31 August 1996
Date of latest publication of new National Standard
or endorsement of this ETS (dop/e): 29 February 1997
Date of withdrawal of any conflicting National Standard (dow): 29 February 1997

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ETS 300 492: May 1996
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ETS 300 492: May 1996
1 Scope
This European Telecommunication Standard (ETS) specifies the technical characteristics required for
end-to-end interworking over the Public Switched Telephone Network (PSTN) of 14 400 bit/s, 12 000 bit/s,
9 600 bit/s, 7 200 bit/s and 4 800 bit/s duplex modems standardized for use over the PSTN, in accordance
with CCITT Recommendation V.32 bis [1].
The objective of this specification, the application of which is entirely voluntary, is to provide the users with
an added degree of assurance that modems in compliance with this specification, can interwork, with
each other under most network conditions.
The term "modem" in the context of this ETS includes all physical implementation practices for a voice
band modem, which is conductively connected to the PSTN.
This ETS specifies ten modes of operation, each with up to five modes of use (see subclause 5.2).
This ETS also contains descriptions of the tests to be performed in order to confirm compliance with the
functional requirements contained herein. A general description of the test conditions and test
requirements is given in annex A (normative).
2 Normative references
This ETS incorporates by dated and undated reference, provisions from other publications. These
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 amendments or revision. For undated references the latest edition of the
publication referred to applies.
[1] CCITT Recommendation V.32 bis (1991): "A duplex modem operating at data
signalling rates of up to 14 400 bit/s for use on the general switched telephone
network and on leased point-to-point 2-wire telephone-type circuits".
[2] Final draft prETS 300 114: "Public Switched Telephone Network (PSTN); Basic
Category I and Category II specifications for modems standardized for use on
the PSTN
[3] CCITT Recommendation V.32 (1988): "A family of 2-wire duplex modems
operating at data signalling rates of up to 9 600 bit/s for use on the general
switched telephone network and on leased telephone-type circuits".
[4] ETS 300 001: "Attachments to the Public Switched Telephone Network (PSTN);
General technical requirements for equipment connected to an analogue
subscriber interface in the PSTN".
[5] CCITT Recommendation V.25 (1988): "Automatic answering equipment and/or
parallel automatic calling equipment on the general switched telephone network
including procedures for disabling of echo control devices for both manually and
automatically established calls".
[6] CCITT Recommendation S.33 (1984): "Standardisation of an international text
for the measurement of the margin of start-stop machines using International
Alphabet No 5".
[7] CCITT Recommendation O.153 (1988): "Basic parameters for the measurement
of error performance at bit rates below the primary rate".

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ETS 300 492: May 1996
3 Definitions and abbreviations
3.1 Definitions
For the purposes of this ETS, the definitions in final draft prETS 300 114 [2] apply together with the
following.
NOTE: In addition to the following definitions, some other specific definitions apply (see
subclauses 5.8.1 and 5.11.1 of this ETS).
Modem Conformance Tester (MCT): A simulator designed to meet the requirements of a modem to the
same recommendation as the Modem Under Test (MUT). All individual sub-systems within it are both
accessible (e.g. provide test points and permit functions to be enabled or disabled when required) and
externally controllable (e.g. permit sequences such as the start up procedure to be selectively repeated).
These, within a conformance tester, may be constructed as discrete items of equipment, so as to permit
their assembly into varying configurations required to suit the tests (e.g. the asynchronous to synchronous
converter may be simply applied to a synchronous CCITT Recommendation V.32 bis [1] conformance
tester to achieve an asynchronous CCITT Recommendation V.32 bis [1] conformance tester).
As an interim measure, until the conformance tester is defined and is available, its definition agreed to be
appropriate by ETSI, a modem used for reference may be used in its place. In the case that the modem
used for reference has not been shown to conform to the ETS in the relevant modes of use/operation, the
testing authority ensures that the modem used for reference complies with the relevant ETS to the extent
necessary for the performance of the test.
3.2 Abbreviations
For the purposes of this ETS the following abbreviations apply.
AMM Answer Mode Modem
CcT Circuit
CMM Call Mode Modem
DCE Data Circuit-Terminating Equipment
DTE Data Terminal Equipment
GPA General Polynomial Answer mode modem
GPC General Polynomial Call mode modem
MCT Modem Conformance Tester
MUT Modem Under Test
PSTN Public Switched Telephone Network
TE Terminal Equipment
4 General requirements
4.1 References to other ETSs
The modem shall comply with final draft prETS 300 114 [2], clause 4.
NOTE: Final draft prETS 300 114 [2] in turn refers to ETS 300 001 [4] for the majority, if not
all, of its requirements.
4.2 Information to be provided by the applicant
4.2.1 Information required for testing purposes
The applicant shall declare for which of the modes of operation/use identified in this ETS, the modem is
supposed to undergo tests.
Compliance shall be considered to have been accomplished by provision of the relevant information.
NOTE: This could be accomplished by completion of forms such as those provided in annex B
(informative).
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ETS 300 492: May 1996
4.2.2 Instructions for use
Instructions for use shall be made available with the apparatus. The instructions for use shall include:
a) the apparatus or types of apparatus to which the instructions apply;
b) any information specifically indicated in this ETS for inclusion in the "Instructions for use"; and
c) any national restrictions on the use of the apparatus.
Any additional information that has been included shall be disregarded unless it is the subject of another
ETS.
Compliance shall be checked by inspection.
5 Functional requirements specific to Category II modems
5.1 General requirements
To comply with the requirements of this ETS, it shall be necessary that the modem provide:
- duplex mode of operation by means of the modulation scheme specified in CCITT
Recommendation V.32 bis [1];
- channel separation by echo cancellation techniques;
- quadrature amplitude modulation;
- signalling rates of 14 400 bit/s, 12 000 bit/s, 9 600 bit/s, 7 200 bit/s and 4 800 bit/s;
- compatibility with CCITT Recommendation V.32 [3] modems;
- use of the rate sequence during call establishment to decide the data rate and method of coding;
- means by which the channels may be selected either manually and/or automatically, where a
modem is capable of transmitting in either of the two channels;
- means to respond to a request for a retrain;
- means to respond to a request for an instigation of a digital loop 2;
- means to respond to a request for a rate renegotiation.
NOTE 1: The general requirements described above are a subset of CCITT Recommendation
V.32 bis [1]. In the requirements which follow any deviations from the strict
interpretation of CCITT Recommendation V.32 bis [1] have been identified.
NOTE 2: In the following, references are made to interchange circuits between the modem and
the DTE, as defined in CCITT Recommendation V.24. However, not all modems
provide an interface with such circuits. For these cases the references to CCITT
Recommendation V.24 type interchange circuits indicate equivalent operation of a DTE
and of a modem where this exists.

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ETS 300 492: May 1996
To further comply with this ETS, the interchange circuits (or equivalent) which are required to change state
after an identifiable event or point in time, shall have changed state within a maximum of 3 seconds of that
event, unless otherwise specified.
NOTE 3: This requirement is in addition to CCITT Recommendation V.32 bis [1].
Interworking with 9 600 bit/s uncoded modulation is not mandatory for CCITT Recommendation V.32 bis
[1] modems.
5.2 Modes of operation/use
The following modes of operation are identified:
- 14 400 bit/s trellis coded, call;
- 14 400 bit/s trellis coded, answer;
- 12 000 bit/s trellis coded, call;
- 12 000 bit/s trellis coded, answer;
- 9 600 bit/s trellis coded, call;
- 9 600 bit/s trellis coded, answer;
- 7 200 bit/s trellis coded, call;
- 7 200 bit/s trellis coded, answer;
- 4 800 bit/s non-redundant coding, call;
- 4 800 bit/s non-redundant coding, answer.
It shall be possible to configure the modem to operate at all of the mentioned data signalling rates, in
either call mode or answer mode or both.
For each mode of operation identified for Category II testing, the modem shall provide at least one of the
following modes of use:
a) asynchronous with 8 bits per character;
b) asynchronous with 9 bits per character;
c) asynchronous with 10 bits per character;
d) asynchronous with 11 bits per character;
e) synchronous.
In the asynchronous (start-stop) modes of use, the modem shall accept a data stream from the DTE at
one of the nominal rates as mentioned above. The asynchronous data to be transmitted shall be
converted into a synchronous data stream in accordance with subclause 5.9 suitable for transmission.
Demodulated data shall be decoded in accordance with subclause 5.5, then descrambled in accordance
with subclause 5.6, it shall then be passed for reconversion into an asynchronous data stream in
accordance with subclause 5.9.
In the synchronous modes of use, the modem shall accept synchronous data from the DTE. The data
shall then be scrambled in accordance with subclause 5.6 and passed to the modulator for encoding in
accordance with subclause 5.5.
Demodulated data shall be decoded in accordance with subclause 5.5, then descrambled in accordance
with subclause 5.6.
The modem shall respond to a request to execute a retrain. Optionally, the modem may also provide
facilities to instigate a retrain during data transmission if the modem detects a loss of equalization.
The modem shall respond to a request to execute a rate renegotiation procedure. Optionally, the modem
may also provide facilities to instigate a rate renegotiation procedure during data transmission.
It shall be the applicant's responsibility to specify for which of the above mentioned modes of
operation/use the modem is supposed to undergo tests.

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ETS 300 492: May 1996
5.3 Line signals
5.3.1 Transmitted carrier frequency
The carrier frequency transmitted shall be 1 800 Hz ± 1 Hz.
Compliance shall be checked by the method described in annex A, clause A.2.
5.3.2 Receiver carrier tolerance
The receiver shall be able to operate correctly with a received carrier frequency in the range of 1 800 Hz ±
7 Hz.
Compliance shall be checked by the method described in annex A, clause A.3.
5.3.3 Transmitted spectrum
The national network specific spectral power limits are specified in final draft prETS 300 114 [2], clause 4.
NOTE: Final draft prETS 300 114 [2], clause 4 in turn refers to ETS 300 001 [4].
There are no requirements in this ETS relating to the spectrum of signals presented to the PSTN over and
above those for PSTN access invoked by clause 4 of ETS 300 001 [4].
5.4 Line signalling rates
The signalling rates transmitted to line shall be 2 400 baud ± 0,01 %.
Compliance shall be checked by the method described in annex A, clause A.4.
5.5 Encoding of data
The signal element coding shall be as defined in CCITT Recommendation V.32 bis [1], paragraph 2.3.1
(trellis coding for 14 400 bit/s operation), paragraph 2.3.2 (trellis coding for 12 000 bit/s operation),
paragraph 2.3.3 (trellis coding for 9 600 bit/s operation), paragraph 2.3.4 (trellis coding for 7 200 bit/s
operation) and paragraph 2.3.5 (non-redundant coding for 4 800 bit/s operation).
Compliance shall be checked by the method described in annex A, clause A.5.
5.6 Scrambler and descrambler
A self-synchronizing scrambler and a self-synchronizing descrambler, as specified in CCITT
Recommendation V.32 bis [1], paragraph 4 (introduction) shall be provided in the transmitting part and the
receiving part, respectively, of the modem.
Compliance shall be checked by performing the test for encoding of data, described in annex A,
clause A.6.
5.7 Channel allocation
5.7.1 Channel selection
A modem which is capable of being configured as both a Call Mode Modem (CMM) and an Answer Mode
Modem (AMM) shall provide facilities for at least one of the following techniques of channel selection:
a) manual selection of the channels using facilities provided on the modem;
b) selection of the channels by the DTE (equivalent: CcT 126 control);
c) automatic selection of the channels as described in subclause 5.7.2.

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ETS 300 492: May 1996
NOTE: Other means of channel selection may also be provided but verification of the correct
functioning of such facilities is not a requirement of this ETS.
For techniques a) and b), compliance shall be checked by the method described in annex A, clause A.7.
5.7.2 Automatic channel selection
A modem providing this facility shall, in the absence of manual intervention or a contrary command e.g.
via a digital interface (e.g. an equivalent to control using CcT 126), be automatically configured as:
a) a CMM when exchanging data on-line to another compatible modem, and when the modem has
entered the on-line state other than in response to an incoming PSTN call;
b) an AMM when exchanging data on-line to another compatible modem, and when the modem has
entered the on-line state in response to an incoming PSTN call.
Compliance shall be checked by the method described in annex A, clause A.7.
5.8 Hand-shaking sequences
5.8.1 Definitions
In the following sequences the signals described shall be sent contiguously unless the description
indicates that a period of silence be present.
NOTE: The following definitions refer to the signal states A, B, C and D, which are defined in
CCITT Recommendation V.32 bis [1], figures 2-1/V.32 bis, 2-2/V.32 bis, 2-3/V.32 bis,
2-4/V.32 bis, and 2-5/V.32 bis.
T: T is the reciprocal of the transmitter baud rate. This is also known as the symbol interval.
AA: This signal is generated by transmitting signal state A with the differential encoder inhibited.
CC: This signal is generated by transmitting signal state C with the differential encoder inhibited.
AC: This signal is generated by alternately transmitting signal state A and signal state C with the
differential encoder inhibited.
CA: This signal is generated by alternately transmitting signal state C and signal state A with the
differential encoder inhibited for an even number of symbol intervals (i.e. 2 T, 4 T, etc.).
S: This signal is generated by alternately transmitting signal state A and signal state B with the differential
encoder inhibited.
S(bar): This signal is generated by alternately transmitting signal state C and signal state D with the
differential encoder inhibited for 16 T.
TRN: The scrambler is first set with all registers to "0". The TRN signal is derived by applying binary 1 to
the relevant scrambler with the differential encoder inhibited. The data stream is split into dibits. For the
first 256 T only the first bit of each dibit is considered and where this bit is a "1" signal state "C" is
transmitted and where it is a "0" signal state "A" is transmitted. After 256 T both bits are taken into
account. If both the bits are "0"s", signal state A is transmitted; if both the bits are "1"s", signal state C is
transmitted; if the first bit is a "0" and the second bit a "1", signal state B is transmitted; finally if the first bit
is a "1" and the second bit a "0", signal state D is transmitted. The final symbol of this sequence shall be
used to initialize the differential encoder.
E: This signal is a single 16 bit sequence. It is sent at 4 800 bit/s differentially encoded and scrambled
using the relevant scrambling sequence. The signal is encoded in the same format as a rate sequence but
it indicates a single rate at which the subsequent scrambled binary 1 shall be transmitted.

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B1: The equivalent signal to binary 1 being applied to the transmit data lead. The signal is transmitted at
the data rate indicated by signal E after being scrambled and differentially encoded and, where relevant,
passed through a convolutional encoder.
rate sequence: This is a series of 16 bits which are transmitted by one modem to provide the distant
modem with information about its capabilities. For the purposes of this ETS, in table 1 below the bits
marked "1" or "0" are fixed, whilst the bits marked "*" are able to assume a value of either "0" or "1". A
modem shall not assume that it has detected a valid rate signal until at least two consecutive rate
sequences are found to be identical. In the event that no compatible rate exists, the setting of all of the
bits marked "*" to a "0"(except bit 8 which may take any value) shall signal the intention of clearing down
the call.
Table 1: Coding of rate sequences
B0 B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11 B12 B13 B14 B15
00 00 * * * 1 * * * 1 * 0 0 1
For each bit a "1" indicates the availability of the corresponding rate or option and a "0" that the
corresponding rate or option is not available.
Bit 5 indicates the availability of 4 800 bit/s,
Bit 6 indicates the availability of 9 600 bit/s.
When bit 4 or bit 8 is a "0", then interworking can proceed only in accordance with final draft
prETS 300 002.
For this ETS, bit 4 and bit 8 shall both be set to "1", except where otherwise specified.
When both bit 4 and bit 8 are a "1", then bit 9, 10 and 12 have the following meaning:
Bit 9 indicates the availability of 7 200 bit/s;
Bit 10 indicates the availability of 12 000 bit/s;
Bit 12 indicates the availability of 14 400 bit/s.
Although bits 13 and 14 have not yet been assigned a use by ITU-T, modems seeking Category II testing
shall have set these bits to "0".
R1: This sequence is transmitted by the AMM at 4 800 bit/s scrambled using General Polynomial Answer
mode modem (GPA) and differentially encoded. The relevant bits marked "*" shall be set to a "1"
whenever the modem is currently capable of working at the rate or mode indicated. For this rate
sequence, the bits 4 and 8 shall be set to "1".
R2: This sequence is transmitted by the CMM at 4 800 bit/s scrambled using General Polynomial Call
mode modem (GPC) and differentially encoded. This signal shall indicate which rates of those indicated
by rate signal R1 the call mode modem is able to support.
R3: This sequence is transmitted by the AMM at 4 800 bit/s scrambled using GPA and differentially
encoded. This signal shall indicate which of the rates indicated in rate signal R2 the modem has chosen to
work at.
R4: This sequence is transmitted by the modems which initiates a rate renegotiation procedure, at
4 800 bit/s scrambled using the relevant Generator Polynomial (GPA or GPC) and differentially encoded.
The differential encoder shall be initialized using the final symbol of the transmitted preamble and the
scrambler shall be initialized to all zeros. The relevant bits marked "*" shall be set to a "1" for the desired
rate and all lower data signalling rates at which the initiating modem is enabled to operate.
R5: This sequence is transmitted by the modems which responds to a rate renegotiation request, at
4 800 bit/s scrambled using the relevant Generator Polynomial (GPA or GPC) and differentially encoded.
The differential encoder shall be initialized using the final symbol of the transmitted preamble and the
scrambler shall be initialized using the final symbol of the transmitted preamble and the scrambler shall be
initialized to all zeros. The relevant bits marked "*" shall be set to a "1" for the desired rate and all lower

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ETS 300 492: May 1996
data signalling rates at which the responding modem is enabled to operate irrespective of the rates
indicated in R4.
5.8.2 Calling and answering procedures
5.8.2.1 Calling tone
This ETS does not require the provision of the calling tone defined in CCITT Recommendation V.25 [5].
5.8.2.2 Answer tone recognition
The modem shall comply with the requirements for answer tone detection given in final draft
prETS 300 114 [2], subclause 5.2.1.
In addition, the Modem Under Test (MUT) shall start the start-up procedure (sending AA signal) during the
answer tone or within 1 s after receiving the end of the answer tone.
NOTE: This requirement is in addition to CCITT Recommendation V.32 bis [1]. This
requirement is contained in this specification in order to guard against an AMM ceasing
to send AC, because the AA signal from the CMM was not received in time.
Compliance shall be checked by the method described in annex A, subclause A.8.1.2.
5.8.2.3 Answering tone generation
The modem intended for answer mode operation shall incorporate the procedure for answering calls
based upon CCITT Recommendation V.25 [5] and given in subclause 5.2.2. of final draft prETS 300 114
[2].
Compliance shall be checked by the method described in annex A, subclause A.8.1.3.
5.8.3 Start-up procedure
After the completion of any dialogue between the modem and the DTE for the purpose of establishing the
connection, the modem shall be indicating that:
a) it is not detecting a valid line signal (equivalent: CcT 109 OFF);
b) it is not ready to transmit data (equivalent: CcT 106 OFF).
NOTE: For a modem to indicate that it is ready to transmit data (equivalent: turning ON
CcT 106) it may be necessary for the DTE to indicate that it wishes to transmit data
(equivalent: turning ON CcT 105).
5.8.3.1 Call Mode Modem (CMM)
5.8.3.1.1 Initiation of start-up procedure
After connection to line, the modem shall condition itself to detect answer tone and subsequently to
transmit the AA signal. However, signal AA shall not be transmitted within the first second of the
application of answer tone to the modem line terminals.
Compliance shall be checked by the method described in annex A, subclause A.8.2.1.1.
5.8.3.1.2 Round trip delay determination
The modem shall initiate the start-up sequence by transmitting signal AA. The modem shall monitor the
line for a phase reversal in the incoming signal. Presentation of signal CA to the line terminals of the
modem shall cause the modem to cease transmitting signal AA and commence transmitting signal CC.
The delay between presentation of signal CA to the line terminals of the modem and signal CC appearing
at the line terminals shall be 64 T ± 2 T.

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ETS 300 492: May 1996
The signal CC appearing at the line terminals shall cause a timer to be initiated. The modem shall then
again monitor the line for a phase reversal in the incoming signal. Presentation of signal AC to the line
terminals of the modem shall cause the modem to note the time indicated by the timer and cease
transmitting signals. The time period recorded by the timer is the effective round trip delay for this modem
hereinafter referred to as NT (which includes the turn round delay in the remote modem).
Compliance shall be checked by the method described in annex A, subclause A.8.2.1.2.
5.8.3.1.3 Start of rate negotiation
The modem shall monitor the incoming signals for signal S followed by a phase reversal. The receiver of
the modem shall now be conditioned to receive the TRN sequence, followed by rate signal R1.
When the modem has detected at least two consecutive identical rate sequences R1, the modem shall
transmit either:
a) signal S for a period of NT + 256 T; or,
b) signal S for a period of NT followed by a signal (special echo canceller training sequence) which
maintains the energy transmitted to line in such a way that the sum of the powers in the bands
500 Hz to 700 Hz, 1 700 Hz to 1 900 Hz and 2 900 Hz to 3 100 Hz is at least 1 dB less than the sum
of the power in the bands 700 Hz to 1 700 Hz and 1 900 Hz to 2 900 Hz. The duration of this
optional sequence shall not exceed 8 192 T. This shall be followed by a further period of signal S for
256 T.
After transmission of one of the two sequences (a) or (b) above, the modem shall transmit signal S(bar),
followed by the TRN sequence for a period of not less than 1 280 T and not more than 8 192 T.
After completing the TRN sequence the modem shall immediately start transmitting rate signal R2,
indicating which of the rates included in rate signal R1 it is capable of supporting, and then shall indicate to
the Data Terminal Equipment (DTE) that it is ready to operate (equivalent: turning ON CcT 107).
Compliance shall be checked by the method described in annex A, subclause A.8.2.1.3.
5.8.3.1.4 Completion of the rate negotiation
On detection of at least two consecutive identical rate sequences R3,
...