ISO/IEC 7480:1991
(Main)Information technology — Telecommunications and information exchange between systems — Start-stop transmission signal quality at DTE/DCE interfaces
Information technology — Telecommunications and information exchange between systems — Start-stop transmission signal quality at DTE/DCE interfaces
Specifies signal quality requirements for serial data transmission. The interface of concern conforms to CCITT Recommendations V.24 (telephone networks) and X.24 (data networks). Annex A is for information only.
Technologies de l'information — Télécommunications et échange d'information entre systèmes — Qualité des signaux de transmission arythmique aux interfaces ETTD/ETCD
General Information
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Standards Content (Sample)
INTERNATIONAL
7480
STANDARD
Second edition
1991-12-15
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Information technology - Telecommunications
and information exchange between systems -
Start-stop transmission signal quality at
DTE/DCE interfaces
Technologies de l’informa tion -- T&kommunications et &change
d’information entre systemes - Qualit des signaux de transmission
arytl7miqne aux interfaces ETTDIETCD
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Reference nwn ber
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.-.- z.-yz-=I-‘-l- .-- ISCYIEC 7480: 1991 (E)
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DSO/IEC 7480:1991 (E)
Foreword
IS0 (the International Organization for Standardization) and EC (the
International Electrotechnical Commission) form the specialized system
for worldwide standardization. Nationat bodies that are members of IS0
or IEC participate in the development of International Standards through
technical committees established by the respective organization to deal
with particular fields of technical activity. IS0 and IEC technical com-
mittees collaborate in fields of mutual interest. Other international or-
ganizations, governmental and non-governmental, in liaison with IS0
and IEC, also take part in the work.
In the field of information technology, IS0 and IEC have established a
joint technical committee, ISO/IEC JTC I. Draft International Standards
adopted by the joint technical committee at-e circulated to national bod-
ies for voting. Publication as an International Standard requires ap-
proval by at least 75 O/o of the national bodies casting a vote.
International Standard lSO/IEC 7480 was prepared by Joint Technical
Committee lSO/IEC JTC 1, Information technology.
This second edition cancels and replaces the first edition (IS0
7480:1984), of which it constitutes a technical revision.
Annex A of this International Standard is for information only.
0 lSO/IEC 1991
All rights reserved. No part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without
permission in writing from the publisher.
ISO/IEC Copyright Office l Case Postale 56 l CH-1211 Genibe 20 * Switzerland
Printed in Switzerland
ii
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ISOllEC 7480:1991 (E)
Introduction
The intent of this International Standard is to complement the electrical
characteristics specified in CCITT V-series recommendations, and to
provide a measurement for the transmission siqnal quality charac-
\.
teristics not covered in those documents.
The siqnal quality requirement that start-stop transmission equipment
shouldL meet is in part dependent on the application and in part de-
pendent on the mechanism for timing derivation used by the equipment.
For early start-stop transmission equipment, timing was derived or
controlled frorn a mechanical source but nowadays an electronic source
is commonplace.
An additional factor is that, whereas most start-stop transmission car-
ries the timing information inherently within the signalling between the
transmitting equipment and the receiving equipment, start-stop equip-
ment may interface to a converter which encodes the information within
a synchronous transmission system in which case, the required signal
quality at the interface to the converter may need to be more tightly
controlled.
To cover both types of equipment in both types of application, the siqnal
quality specification in this International Standard is given separateI; for
four performance categories, two of which (PI and F2) are intended for
DTEs using mechanical timing l) and two for DTEs using electronic tim-
ing. By having two mechanical categories, early start-stop transmission
equipment with very limited signal quality capability is accommodated
(Category PI). For the two electronic categories, the more stringent
(Category II) is for equipment to be connected to synchronous DCEs
mode in accordance with CCITT Rec-
operating in asynchronous
ommendation V.14. For each of the four categories defined for the
transmitting elements of DTEs (I, II, PI and P’L), four complementary
categories are defined for the receiving elements of DTEs (A, B, PA. PB).
Notwithstanding the obvious pairings implied by the complementary
categories, the intention is that any receiving equipment may ol:)erate
with any transmitting equipment, the actual selection being dependent
on such factors as channel characteristics and economic considerations
of the data communication system. The importance of this Infernational
Standard is particularly evident when the transmitting and receiving
equipments are furnished by different organizations as it provides a
basis for agreement between the parties involved.
-w----e-
1) It is intended to delete the mechanical categories at the next revision (see
footnote 2 to table 1. At that time, consideration will be given to amending the
electronic timing definition by replacing “a signal” in the first line by “an
isochronous signal” and amending the other definitions accordingly.
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Information technology - Telecommunications and
information exchange between systems - Start-stop
transmission signal quality at DTEIDCE interfaces
1.3 This International Standard does not describe
1 Scope
the signal quality of the DCE or the line associated
with it. Neither does it describe any requirement for
an acceptable bit error rate.
1 .l This International Standard specifies signal
quality requirements for serial data transmission at
1.4 This International Standard does not specify
the interface between start-stop transmission Data
the speed characteristics. The nominal value of the
Terminal Equipment (DTE) and Data Circuit-
modulation rate and the character interval are ap-
terminating Equipment (DCE). The interface referred
plication dependent.
to in this International Standard conforms to CCITT
Recommendations V.24 (telephone networks) and
X.24 (data networks) as specified in DCEs of the fol-
2 Normative references
lowinq CCITT Recommendations:
L
-
V.21, V-22, V.22 bis, V.23, V.26 ter, V.32, V.32 bis, The following standards contain provisions \Nhich,
X.20, X.20 bis together with V.28 electrical through reference in this text, constitute provisions
\
characteristics; of this International Standard. At the time of publi-
cation, the editions indicated were valid. All stan-
.-
X.20 together with V.10 and/or V.ll electrical dards are subject to revision, and parties to
characteristics. agreements based on this International Standard
are encouraged to investigate the possibility of ap-
The signal quality requirement is limited to start-
plying the most recent editions of the standards in-
stop transmission at the interface with asynchro-
dicated below. Members of IEC and IS0 maintain
nous DCEs, or with synchronous DCEs operating in
registers of currently valid International Standards.
asynchronous mode in accordance with CCI’TT Rec-
ommendations VI4 or V.42. Signal quality pertaining
CCITT Recommendation 1.411:1988, ISDN clser-
to DTEs working in a synchronous mode of operation
network interfaces --- Reference configurations.
is not part of this International Standard.
CCITT Recommendation V.10 (= X.26):1988. Elec-
This International Standard is also applicable when
trical characteristics for unbalanced double-current
the interface as specified in the above CCITT Rec-
interchange circuits for general me with inkgrated
ommendations is provided at the ISDN Reference
circuit equipmeni in the field of data communi-
point R as defined in CCITT Recommendation 1.411
cations.
and as specified in CCITT Recommendations V.110,
V.120 and X.30.
CCITT Recommendation V.ll (z X.27):1988. Elec-
trical characteristics for balanced double-cwrer7t
interchange circuits for general use with inteqr-ated
circuit e&,,ipment in the field of dafa conbuni-
caiions.
1.2 The signal quality characteristics apply re-
gardless of whether or not multiplexing equipment
CCITT Recommendation V.14:1988, Transmission of
is included. They do not apply where there is inter-
start-stop characters over synchronous hearer c/Ian-
mediate equipment and no signal regeneration is
nels.
provided between interconnected sections.
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ISOllEC 7480:1991 (E)
circuit-terminating equipment (DCE) for start-slop
CCITT Recommendation V-21:1988, 300 bifs pel- sec-
transmission services on public data networks.
ond duplex modem standardized for use jr7 the gen-
eral switcl7ed telephor7e /7etwork.
CCITT Recommendation X.20 bis:1988, Use on public
data networks of data terminal equipment (DTE)
CCITT Recommendation V.22:1988, ? 200 biIs per
which is designed for ir7ferfacing to asynchronous
second duplex modem star7dardized for use in tl7e
duplex V-series moden7s.
general switched telephone network and or7 point-
to-point 2-wire leased telephone-type circuifs.
CCITT Recommendation X.24:1988, List of defkitiom
for inter-change circuits between data terminal
CCITT Recommendation V.22 bis:l988, 2400 hils per
equipn7ent (DTE) and data circuit-terrnir~afjl7g equip-.
second duplex moden using the frequency division
technique standardized for use on the general ment (DCE) on public data networks.
switched telephone network and on point-to-point
Z-wire leased telephone-type circuits. CCITT Recommendation X.30:1988, Support of X.21,
X.21 bis ar7d X.20 his based dais terminal equip-
ments (DTEs) by an integrated services digiial net-
CCITT Recommendation V.23:1988, 600/l 200 baud
modem staf7dardized for use in the general switcl7ed work (ISDN).
telepl7one network.
3 Definitions
CCITT Recommendation V.24:1988, List of defit7itions
for ir7terchange circuits between data terminal
For the purposes of this Internafional Standard, the
equipn7ent and data circuit-terminating equipment.
following definitions apply.
CCITT Recommendation V.26 ter:1988, 2400 hifs per
3.1 electronic timing: An implementalion in which
second duplex modem using the echo car7cellafion
a signal serves to determine the duration of signal
technique standardized for use on fl7e qeneral
elements and to achieve synchronization within a
switched telephone network ar7d on point-to-point
2-wire leased telephone-type circuits. transmission system? and is derived from an elec-.
t.ronic circuit.
CCITT Recommendation V.28:1988, Electrical
characteristics for unbalanced double-crlrrenf ir,ter=- 3.2 mechanical timing: An implementation in which
change cir-wits. a signal serves to determine the duration of signal
elements and to achieve synchronization within a
CCITT Recommendation V.32:1988, A family of transmission system, and is generally derived from
Z-wire, duplex modems operating at data sigrlalling the angular velocity of an electric motor (power fre-.
rates of up to 9600 bit/s for use on ti7e general quency used as timing source is also included in this
c
switched telephone r7etwork and 01-7 leased category).
telephone-type circuits.
3.3 start-stop system: Data transmission system in
CCITT Recommendation V.32 bis:l990, A duplex
which each signal representing a character is pre-
modem operating at data signaling rates of up to
ceded by a start signal which serves to prepare the
14400 bit/s for use on the qeneral switched tele-
receiving device for the reception of a character
phone network and on lea& point-to-point 2-wire
signal and registration of a character, and is fol-.
telephone-type circuits.
lowed by a stop signal which serves to prepare i.he
receiving device for the reception of a subsequenl
CCITT Recommendation V.42:1988, Error-correcting
start signal.
procedures for DCEs using asynchr-onous-to-
synchronous conversion.
3.4 start-stop transmission: Asynchronous trans-
mission such that each group of signals represent-
CCITT Recommendation V.110:1988, Support of data
ing a character is preceded by a start signal and is
terminal equipments (DTEs) with V-series type inter-
followed by a stop signal.
faces by ar7 integrated services digital network
\
(ED/V).
3.5 continuous start-stop operation: Method of op-
eration in start-stop transmission in which the
CCITT Recommendation V.120:1988, Support by an
signals representing a series of characters follow
lSDN of data terminal equipment with V-series type
one another contiguously.
interfaces with provision for statistical rnuUiplexing.
3.6 signal element: Each of the parts constituting a
CClTT Recommendation X.203988, Interface be-
telegraph or data signal and distinguished from the
tween data terminal equipment (DTE) and data
others by its nature, magnitude, duration and rela-
tive position (or by one or some of these features
only).
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ISO/IEC 7480:1991(E)
3.7 unit interval: In a system using an equal length 4 Distinction can be made between the degree of late (or
positive) distortion and the degree of early (or negative)
code, or in a system using an isochronous modu-
distortion.
lation, the interval of time such that the theoretical
durations of the significant intervals of a telegraph
5 The theoretical intervals are related to the mean ac-
modulation (or restitution) are whole multiples of
tual incoming modulation rate and not necessarily to the
this interval.
nominal modulation rate.
3.8 modulation rate: Reciprocal of the unit interval 3.14 degree of gross start-stop distortion: Degree
of distortion determined when the unit interval and
measured in seconds. This rate is expressed in
the theoretical intervals assumed are exactly those
baud.
appropriate to the nominal modulation rate.
3.9 character interval: The duration of a character
NOTE 6 The result of the measurement should be com-
expressed as the total number of unit intervals (in-
pleted by an indication of the period, usually limited, of the
cluding information and parity check) plus the start
observation.
and stop signals.
For a prolonged modulation (or restitution) it will be ap-
propriate to consider the probability that an assigned
3.10 start signal: In start-stop transmission, a sig-
value of the degree of distortion will be exceeded.
nal at the beginning of a character that prepares the
receiving device for the reception of the code el- In accordance with the CCITT definition of the theoretical
duration of a significant interval, in practical measure-
ements.
ments the unit interval and the theoretical intervals as-
sumed are those appropriate to the actual mean rate of
NOTE 1 A star t signal i s limi ted to one signal element
modulation (or of restitution).
the dura tion 0 f a uni t interval.
gener ally having
3.15 degree of synchronous start-stop distortion:
3.11 start transition: In a character transmitted in
Degree of distortion determined when the unit in-
a start-stop system, the mark-to-space transition at
terbal and the theoretical intervals assumed are
the beginning of the start signal.
\
those appropriate to the actual mean rate of modu-
lation (or of restitution).
3.12 stop signal: In start-stop transmission, a signal
at the end of a character that prepares the receiving
NOTES
device for the reception of a subsequent character.
7 See note 6.
NOTE 2 A stop signal is usually limited to one signal
8 The degree of distortion is the time displacement of
elernent having any duration equal to or greater than a
the transitions between signal st.ates from their ideal in-
specified minimum value.
stants.
3.13 degree of start-stop distortion
3.16 margin: Maximum degree of distortion com-
patible with a correct translation when the signals .
(1) Ratio to the unit interval of the maximum
are presented to a receiver under t.he most un-
measured difference, irrespective of sign, between
favourable conditions where the composition of the
the actual and theoretical intervals separating any
signals and of the distortion is concerned.
significant instant of modulation (or of restitution)
from the significant instant of the start element im-
The maximum degree of distortion which results in
mediately preceding it.
incorrect translation applies without reference to the
form of distortion affecting the signals. In other
(2) The highest absolute value of individual dis-
words, it is the maximum value of the most un-
tortion affectin
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