ISO/IEC 8481:1996

INTERNATIONAL ISO/IEC
STANDARD 8481
Second edition
1996-06-15
Information technology -
Telecommunications and information
exchange between systems - DTE to DTE
direct connections
Technologies de /‘information - TMcommunica tions et @change
d ‘informa tion en tre sys tkmes - Connexions directes de DTE 2 DTE
Reference number
ISO/lEC 8481 :I 996(E)
ISO/IEC $481:19964E)
Foreword
IS0 (the International Organization for Standardization) and IEC (the Inter-
national Electrotechnical Commission) form the specialized system for
worldwide standardization. National 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 particu-
lar fields of technical activity. IS0 and IEC technical committees collab-
orate in fields of mutual interest. Other international organizations,
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, lSO/IEC JTC 1. Draft International Standards adopted
by the joint technical committee are circulated to national bodies for voting.
Publication as an International Standard requires approval by at least 75 %
of the national bodies casting a vote.
International Standard lSO/IEC 8481 was prepared by Joint Technical
Committee lSO/l EC JTC 1, Information technology, Telecommunications
and information exchange between systems.
This second edition cancels and replaces the first edition (IS0 8481:1986),
which has been technically revised.
Annex A of this International Standard is for information only.
0 ISO/lEC 1996
All rights reserved. no part of this publication may be
Unless otherwise specified,
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/I EC Copyright Office l Case postale 56 l CH-1211 Geneve 20 l Switzerland
Printed in Switzerland
0 ISO/IEC lSO/lEC 8481 :I 996(E)
Introduction
This International Standard provides for the interconnection of Data Terminal Equipment (DTE) without signal conversion, whereby a DTE is not
attached to a Data Circuit-terminating Equipment (DCE), this being part of a telecommunication facility.
be totally located at the user’s premises. The aim is to these interconnections to the elements of
The desired DTE to DTE direct connection may
interfaces, in order to avoid equipment proliferation.
the ITU-T and ISO/IEC standardised DTWDCE
The normative part of this standard provides for interconnection for both asynchronous and synchronous transmission, using CCITT
Recommendation X.24 interchange circuits, including circuit X for synchronous transmission, and using ITU-T Recommendation V.ll electrical
characteristics. An informative annex provides guidance for other cases of interconnection that, though acceptable under limited conditions, cannot be
recommended for general use. These alternatives include timing arrangements for synchronous transmission, not reliant on circuit X being provided in
both DTEs with ITU-T Recommendation V.11 electrical characteristics.
The informative annex does not cover direct connection between ISDN terminal equipments TEl) for which the complexity in the framing of the
(type
transmitted signal is such that no general method of interconnection can be recommended.
. . .
III
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lSO/IEC 8481:1996(E)
INTERNATIONAL STANDARD 0 ISO/IEC
Information technology - Telecommunications and information
exchange between systems.- DTE to DTE direct connections
1 Scope 3 Interconnection configuration
This International Standard describes an arrangement for Only one type of DTE to DTE interconnection configuration is
interconnection of Data Terminal Equipment (DTE), without considered for point-to-point connections with interfaces according to
intermediate Data Circuit-terminating Equipment (DCE), in terms of CCITT Recommendation X.24; this being shown in figure 1.
This
electrical, mechanical, and functional characteristics.
International Standard applies to DTEs with interface circuits There are two lines of demarcation between the two interconnecting
standardised in CCITT Recommendation X.24 for transmission over DTEs, one located at each DTE connector. The adaptor and any
cable linking these two DTE connectors are not part of either DTE.
public data networks. The interconnections are restricted to point-to-
point connections.
Intermediate balanced pair cable may be provided with a maximum
NOTE - The extension to multipoint configurations is at present under study
length mainly dependent on the parameters of the electrical
and would use electrical charqcteristics according to ISO/lEC 8482 -
characteristics of the interchange circuits and the data signalling rate.
Information Technology - Telecommunications and Information Exchange
between Systems - Twisted pair Multipoint interconnection.
Lines of demarcation
I I
I I
This International Standard applies to DTEs which employ the
I I I 1
1 1
t
balanced electrical characteristics of ITU-T V.ll for data signalling X.24
X.24
rates up to IO Mbit/s.
DTE c
DTE
15-pole connectors
The interconnection may be used for start-stop or synchronous
transmission. For synchronous transmission, this International
Figure 1 - DTE interconnection configuration
Standard applies to DTEs which use circuit X - DTE transmit element
timing - and circuit S - Signal element timing - (see clause 5).
An informative annex provides information for the interconnection of
DTEs with interface circuits according to ITU-T Recommendation
V.24 or with electrical characteristics according to ITU-T
Recommendations V.10 or V.28.
2 Normative references
The following standards contain provisions which, through reference
in this text, constitute provisions of this International Standard. At the
time of publication, the editions indicated were valid. All standards are
subject to revision, and parties to agreements based on this
International Standard are encouraged to investigate the possibility of
applying the most recent editions of the standards indicated below.
Members of IEC and IS0 maintain registers of currently valid
International Standards.
IS0 4903:1989, Information technology - Data communication - 15
pole DTEYDCE interface connector and contact number
assignments.
ITU-T Recommendation V.11 (1994)‘), Electrical characteristics for
balanced double-current interchange circuits operating at data
signaling rates up to IO Mbit/s.
CCITT Recommendation X.24 (1989), List of definitions for
interchange circuits between data tenninal equipment (DTE) and
data circuit-terminating equipment (DCE) on public data networks
(PDN).
1) Previously CCIIT Recommendation.

0 ISOAEC
ISOAEC 8481:1996(E)
4.5 Earthing
4 Interchange circuit requirements
Depending on local safety requirements and for electromagnetic
The interchange circuit requirements are specified in terms of
compatibility (EMC) considerations, it may be required to connect
electrical, functional, mechanical and interchange point cross-over
circuit G (Signal ground) to the protective earth in each DTE.
characteristics.
If the DTEs are connected to different primary power supplies with
4.1 Electrical characteristics
different earthing systems, significant potential differences may arise
between the signal ground terminals of interconnected DTEs. If these
The electrical characteristics of ITU-T Recommendation V.11 are
voltages are higher than the common mode acceptance specified in
mandatory.
the electrical characteristics of the interchange circuit, transmission
errors and even damage to the circuitry may result.
Appendix 1 of Recommendation V.ll gives guidance on the
operational constraints imposed by the length, balance, and
If circuit G is completed between the DTEs, it may reduce this
terminating resistance of the interconnecting cable in relation to the
potential difference but excessive circulating currents may result.
data signalling rate. With additional considerations, longer distances
may be possible.
NOTE - In practice, different signal ground arrangements may need to be
considered for a particular situation.
4.2 Functional characteristics
The functional characteristics of interchange circuits conform to
5 Timing provision
CCITT Recommendation X.24 for each interface of an
interconnecting DTE. The interchange circuits required are listed in
For synchronous transmission, signal element timing shall be
the table 1 below.
interconnected by circuit X - DTE transmit signal element timing. It
interconnects to circuit S - Signal element timing, which serves for
Table I - List of X.24 circuits for DTE interconnection.
the receive direction only.
X.24 circuit Interchange IS0 4903 1 Circuit description1 1
Normally DTEs using X.24 interchange circuits obtain signal element
1 remark
designation point V.11 contact
timing information from the DCE. Therefore, these DTEs will require
r I I I
number
I an additional DTE-source element timing circuit X. It is assigned to
1 Cable shield ‘1
share the salme connector contact as circuit B and F in !Sv^ 4303.
Signal ground (see 4.5) ’
G c - C’ 8
Since the direction of transmission of circuit X is opposite to that of
T A-A’ 2 Transmit
circuits B and F, a logical switch or physical option in the DTE may
I
I
B-B ‘9
be necessary if the DTE intends to apply more than one of these
Receive
R A-A’ 4
circuits for alternative applications.
B-B II
6 Signai eiement timing
s A-K
The timing arrangement for connecting two X-series DTEs is
13 (from DCE)
B-B
illustrated in figure 3 and described below.
X A-A’ 7 DTE transmit signal
0-B 14 element timing
I) Contact 1 is for connecting the shieids between tandem sections of The additional DTE signal element timing circuit is provided by each
shielded interface cable.
DTE. The cross-over of these timing circuits (see figure 3j shall be
added to the basic crossover arrangement in figure 2.
4.3 Mechanical characteristics
This arrangement, unlike other arrangements (see Annex A), does
The mechanical characteristics of the interface conform to IS0 4903. not cause skewing between data and timing circuits.
Both DTEs provide the 15pole connector, while the cross-over
arrangement specified in 4.4, including any associated cable, with the Circuit X
mating connector conforming to the DTE connector as described in
IS0 4903, is furnished by the installation authority. s z=====z :
The cross-over arrangement will therefore also be an adaptor Figure 3 - Signal element timing configuration.
between 1 5pole connectors.
4.4 Interchange point cross-over characteristics
6 Use of control procedures
Figure 2 shows the basic cross-over arrangement in accordance with
This International Standard assumes no restrictions on the use of any
the interconnecting configuration shown in figure I. For synchronous
data link control procedure or any higher level data transfer protocol.
transmission, the signal element timing is not included in figure 2, but
is described in clause 5.
Circuit T
R
i:
G 000 G (se 45)
Contact 1 OCO Contact I ‘)
1) Contact 1 is for connecting the shields between tandem sections or shielded
interface cable
Fiaure 2 - Basic circuit cross-over arranqement.
0 ISO/IEC
Annex A
(informative)
Other cases of DTE to DTE direct connection
A.2 References
A.1 Scope
IS0 21 IO:1 989, lnfonnation technology - Data communication - 25-
This annex describes various arrangements for the interconnection of
pole DTEZDCE interface connector and contact number
Data Terminal Equipment (DTE), without intermediate Data Circuit-
assignments.
terminating Equipment (DCE), in terms of electrical, mechanical, and
functional characteristics.
IS0 2110:1989/Amd.l:1991, Information technology - Data
It applies to DTEs with interface circuits standardised in ITU-T communication - 25-pole DTE/DCE interface connector and contact
number assignments - Amendment I : Interface connector and
Recommendation V.24 for data transmission over telephone
contact assignments for a DTEIDCE interface for data signalling
Networks or with interface circuits standardised in CCITT
Recommendation X.24 for transmission over public data Networks. rates above 20 000 bit/s.
The interconnections are restricted to point-to-point connections. IS0 4902:1989, Information technology - Data communication - 37-
Extension to Multipoint configurations requires further study. pole DTEZDCE interface connector and contact number
assignments.
This annex applies:
- To DTEs employing the balanced electrical IS0 4903:1989, Information technology - Data communication - 15-
characteristics of ITU-T Recommendation V.ll for data pole DTWDCE interface connector and contact number
signalling rates up to 10 Mbit/s with V.24 circuits. assignments.
- To DTEs employing the unbalanced electrical
characteristics of ITU-T Recommendation V.10 for data ISO/IEC 11569:1993, Information technology - Telecommunications
signalling rates up to 100 kbit/s and of ITU-T and information exchange between systems - 26-pole interface
Recommendation V.28 for data rates below 20 kbit/s. connector mateability dimensions and contact number assignments.
Interworking between a DTE employing V.10 and a DTE
employing V.ll or with a DTE employing V.28 is permitted.
ITU-T Recommendation V. IO (1994)‘), Electrical characteristics for
unbalanced double-cunen t interchange circuits operating at data
The interconnection may be used for start-stop and synchronous signalling rates nominal/y up to 100 kbit/s.
transmission. For synchronous transmission, the signal element
timing may be provided by either one DTE, both DTEs, or by an
ITU-T Recommendation V. 11 (1994)‘), Electrical characteristics for
external signal element timing source which is inserted as
balanced double-wren t interchange circuits operating at data
intermediate equipment.
signalling rates up to IO Mbit/s.
.
ITU-T Recommendation V.24 (1994)‘), List of definitions for
interchange circuits between data tenninal equipment (DTE) and
data circuit-terminating equipment (DCE).
CCITT Recommendation X.24 (1989), List of definitions for
interchange circuits between data tenninal equipment (DTE) and
data circuit-terminating equipment (DCE) on public data networks
(PDN).
ITU-T Recommendation V.28 (1994) ‘1, Electrical characteristics for
unbalanced double-current interchange circuits.
1) Previously CCllT Recommendation.
0 IS
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