1、INTERNATIONAL TELECOMMUNICATION UNIONITU-T V.18TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU(11/2000)SERIES V: DATA COMMUNICATION OVER THETELEPHONE NETWORKInterfaces and voiceband modemsOperational and interworking requirements forDCEs operating in the text telephone modeITU-T Recommendation V.18(Fo
2、rmerly CCITT Recommendation)ITU-T V-SERIES RECOMMENDATIONSDATA COMMUNICATION OVER THE TELEPHONE NETWORKGeneral V.1V.9Interfaces and voiceband modems V.10V.34Wideband modems V.35V.39Error control V.40V.49Transmission quality and maintenance V.50V.59Simultaneous transmission of data and other signals
3、V.60V.99Interworking with other networks V.100V.199Interface layer specifications for data communication V.200V.249Control procedures V.250V.299Modems on digital circuits V.300V.399For further details, please refer to the list of ITU-T Recommendations.ITU-T V.18 (11/2000) iITU-T Recommendation V.18O
4、perational and interworking requirements for DCEsoperating in the text telephone modeSummaryThis Recommendation describes modem procedures to follow for automatic interworking with texttelephones. Text telephones use various modem technologies. This Recommendation specifies thesignal analysis, signa
5、l transmission and logic needed to determine what kind of text telephone thereis on a connection. It also specifies the actions needed to communicate in the mode supported byeach terminal type.This Recommendation is intended for use in text telephones, in interworking units, in text relayservices, i
6、n emergency centres, and in computers to be used for text telephony in the PSTN.This Recommendation specifies transmission of identification signals to determine when theconnection is between two V.18-equipped terminals. For that case, ITU-T V.21 is the defaultmodulation used. For interworking in te
7、xt conversation between humans, not only the modulationmust be specified. Therefore, this Recommendation specifies that when the connection in V.18 modeis established, the presentation protocol specified in ITU-T T.140 should be used, including aninternationally useful character set.The text telepho
8、ne types supported by this Recommendation are: EDT, 5-bit (or Baudot), DTMF,V.21, V.23, Bell 103 and V.18-based devices.In originate mode, V.18 identification signals and V.23 stimulation signals are transmitted until arecognized text telephone signal is received and connection can be established in
9、 that mode.In answer mode, this Recommendation specifies stimulation to connection by transmission ofprobing signals for the different kinds of text telephones while monitoring for text telephone signals.Once determined, the mode of communication is entered.For cases when it is not obvious if the co
10、nnection should be made in originate or answer mode,procedures are provided to resolve that and reach communication.An automode monitor mode is provided for cases when it is desired to have a text telephone deviceprepared on the same line as a voice telephone and indicate when there is an active tex
11、t telephone onthe connection.For DTMF and 5-bit text telephone types using character coding not commonly used with modems,conversion is specified in this Recommendation between these codes and ITU-T T.50.For selection between multimedia protocols and this Recommendation, and also for negotiatingproc
12、edures for simultaneous voice and text, modem connection procedures based on ITU-T V.8 bisare provided.SourceITU-T Recommendation V.18 was revised by ITU-T Study Group 16 (2001-2004) and approvedunder the WTSA Resolution 1 procedure on 17 November 2000.ii ITU-T V.18 (11/2000)FOREWORDThe Internationa
13、l Telecommunication Union (ITU) is the United Nations specialized agency in the field oftelecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ ofITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendationson t
14、hem with a view to standardizing telecommunications on a worldwide basis.The World Telecommunication Standardization Assembly (WTSA), which meets every four years,establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on thesetopics.The approval of ITU-T R
15、ecommendations is covered by the procedure laid down in WTSA Resolution 1.In some areas of information technology which fall within ITU-Ts purview, the necessary standards areprepared on a collaborative basis with ISO and IEC.NOTEIn this Recommendation, the expression “Administration“ is used for co
16、nciseness to indicate both atelecommunication administration and a recognized operating agency.INTELLECTUAL PROPERTY RIGHTSITU draws attention to the possibility that the practice or implementation of this Recommendation mayinvolve the use of a claimed Intellectual Property Right. ITU takes no posit
17、ion concerning the evidence,validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or othersoutside of the Recommendation development process.As of the date of approval of this Recommendation, ITU had received notice of intellectual property,protected by p
18、atents, which may be required to implement this Recommendation. However, implementors arecautioned that this may not represent the latest information and are therefore strongly urged to consult theTSB patent database. ITU 2001All rights reserved. No part of this publication may be reproduced or util
19、ized in any form or by any means,electronic or mechanical, including photocopying and microfilm, without permission in writing from ITU.ITU-T V.18 (11/2000) iiiCONTENTSPage1 Scope 12 References 23 Definitions 24 Operational requirements . 45 Connecting in text telephone mode including procedures for
20、 interworking with theinstalled base of existing text telephones . 45.1 Automoding originating . 45.2 Automoding answering 65.3 Automoding monitor mode 86 Connection in text telephone mode with V.8 and V.8 bis procedures . 116.1 V.8 procedures 116.1.1 Originate mode 116.1.2 Answer mode. 126.1.3 V.8
21、procedure initiated by the answering terminal . 126.1.4 Enter text mode from voice. 126.2 Simultaneous voice and text telephony (SVT). 126.3 Connection procedures based on ITU-T V.8 bis 137 Bibliography. 15Annex A 5-bit operational mode 15A.1 Mode of operation 15A.2 Modulation . 15A.3 Probe. 15A.4 C
22、haracter conversion 15A.5 Informative usage information . 15Annex B DTMF operational mode. 18B.1 Mode of operation 18B.2 Character conversion 18B.3 Timing 19Annex C EDT operational mode 22C.1 Mode of operation 22C.2 Modulation . 22C.3 Characters in the EDT mode 22iv ITU-T V.18 (11/2000)PageAnnex D B
23、ell 103 mode . 22D.1 Mode of operation 22D.2 Modulation . 22D.3 Character code and framing 23D.4 Presentation control 23D.5 Usage conventions 23Annex E V.23 Videotex terminals 23E.1 Minitel terminals 23E.1.1 Mode of operation . 23E.1.2 Minitel “Dialogue“ terminal 24E.1.3 Minitel “Normal“ terminal 24
24、E.2 Prestel terminals . 24Annex F V.21 text telephone mode 24F.1 Mode of operation 24F.2 Modulation . 24F.3 Channel selection 24F.4 Character code and framing 24F.5 Presentation control 25F.6 Usage conventions 25Annex G V.18 text telephone mode . 25G.1 Mode of operation 25G.2 Presentation protocol f
25、or V.18 mode 25G.3 Framing and transmission. 25Appendix I Representative ordering of automoding 25Appendix II Recommended common procedures for terminals using the V.18 DCE . 26II.1 Line status display 26II.2 Connect mode. 26Appendix III Specification of V.18 implementation tests 26III.1 Introductio
26、n 27III.2 Definitions 27III.3 Summary of tests 27III.3.1 Interworking tests 27III.3.2 Implementation tests . 28ITU-T V.18 (11/2000) vPageIII.4 Interworking tests description 30III.4.1 Introduction . 30III.4.2 Test methodology 31III.4.3 Test cases. 31III.5 V.18 implementation tests description . 31II
27、I.5.1 Introduction . 31III.5.2 Test methodology 31III.5.3 Test case identifier numbers 31III.5.4 Test cases. 31vi ITU-T V.18 (11/2000)IntroductionThis Recommendation was revised by ITU-T Study Group 16 (1997-2000) and was approved underthe WTSC Resolution 1 procedure on 6 February 1998.Work with ver
28、sion 3 of this Recommendation was initiated in February 2000 with the followinggoals:1) Include all amendments collected in implementors guides.2) Resolution of the open question from the implementors guide on the contents of the XCIsignal. The contents is decided to be 0x“FF“,0x“FF“.3) Specify full
29、 V.8 connection procedures, in order to allow smooth initiation by a receivingterminal and allow modulation negotiation (still maintaining interoperability with the “TXP“based connection procedures of earlier versions). This obsoletes large parts of Appendix III.4) Remind about the risk for false de
30、tection of DTMF signals as textphone signals whenoperating in automode monitor mode.5) Clarify that the probe list may contain 0-6 elements.6) Move the V.8 bis procedures specified in Appendix III to the main body of theRecommendation.7) The new Appendix III is dedicated to V.18 implementation text.
31、ITU-T V.18 (11/2000) 1ITU-T Recommendation V.18Operational and interworking requirements for DCEsoperating in the text telephone modeBackgroundThe ITU-T,consideringa) that text telephones place special operational needs on the use of DCEs;b) that for historical reasons, many existing text telephones
32、 do not use V-series modulation;c) that there is a desire to have all future GSTN text telephones employ V-series modulation;d) that to provide a migration path from the diverse installed base, it will be necessary toprovide interworking with existing text telephones;e) that to provide for interwork
33、ing, the DCE will need to convert the 5-bit character code orITU-T Q.23 (DTMF) character set used by some existing text telephones into the 7-bit code set asgiven in ITU-T T.50;f) that such character conversion in the DCE will be undertaken solely to enable interworkingwith existing text telephones
34、and to impose no constraints on character sets used in future texttelephones;g) that new technology is being developed that could be used to provide additional texttelephone modes,recommends the procedure below1ScopeThis Recommendation specifies features to be incorporated in DCEs intended for use i
35、n, orcommunicating with, text telephones primarily used by the deaf and hard of hearing. One of thegoals of this Recommendation is to provide a platform on which a universal text telephone can bebuilt. To accommodate this goal, procedures for interworking with identified existing text telephonesare
36、provided in clause 5. In addition, this Recommendation has the goal of identifying ways in whichthe multimedia Recommendations could be used to support new modes of operation or create newmulti-mode text telephone devices. To accommodate this additional goal, clause 6 identifies somepossible uses of
37、 this technology to support text telephony and additionally specifies requirements formulti-mode text telephone devices.To provide for maximum flexibility, it is envisaged that any of the text telephone modes of operationspecified in this Recommendation will be invoked on an as required basis using
38、the commandsspecified in ITU-T V.250 or some equivalent mechanism.It provides for: calling identification signals; no DCE-initiated disconnect; procedures for call establishment; procedures for interoperation with existing text telephones; specification of requirements for the use of text telephones
39、 in a multimedia environment.2 ITU-T V.18 (11/2000)2 ReferencesThe following ITU-T Recommendations and other references contain provisions which, throughreference in this text, constitute provisions of this Recommendation. At the time of publication, theeditions indicated were valid. All Recommendat
40、ions and other references are subject to revision; allusers of this Recommendation are therefore encouraged to investigate the possibility of applying themost recent edition of the Recommendations and other references listed below. A list of the currentlyvalid ITU-T Recommendations is regularly publ
41、ished. ITU-T H.324 (1998), Terminal for low bit-rate multimedia communication. ITU-T Q.23 (1988), Technical features of push-button telephone sets. ITU-T T.50 (1992), International Reference Alphabet (IRA) (formerly InternationalAlphabet No. 5 or IA5) Information technology 7-bit coded character set
42、 for informationinterchange. ITU-T T.140 (1998), Protocol for multimedia application text conversation. ITU-T V.8 (2000), Procedures for starting sessions of data transmission over the publicswitched telephone network. ITU-T V.8 bis (2000), Procedures for the identification and selection of common m
43、odes ofoperation between Data Circuit-terminating Equipments (DCEs) and between DataTerminal Equipments (DTEs) over the public switched telephone network and on leasedpoint-to-point telephone-type circuits. ITU-T V.21 (1988), 300 bits per second duplex modem standardized for use in the generalswitch
44、ed telephone network. ITU-T V.23 (1988), 600/1200-baud modem standardized for use in the general switchedtelephone network. ITU-T V.25 (1996), Automatic answering equipment and general procedures for automaticcalling equipment on the general switched telephone network including procedures fordisabli
45、ng of echo control devices for both manually and automatically established calls. ITU-T V.61 (1996), A simultaneous voice plus data modem, operating at a voice plus datasignalling rate of 4800 bit/s, with optional automatic switching to data-only signalling ratesof up to 14 400 bit/s, for use on the
46、 general switched telephone network and on leasedpoint-to-point 2-wire telephone-type circuits. ITU-T V.70 (1996), Procedures for the simultaneous transmission of data and digitallyencoded voice signals over the GSTN, or over a 2-wire leased point-to-point telephone typecircuits. ITU-T V.250 (1999),
47、 Serial asynchronous automatic dialling and control. ANSI TIA/EIA-825 (2000), A Frequency Shift Keyed Modem for use on the Public SwitchedTelephone Network. ISO/IEC 646:1991, Information technology ISO 7-bit coded character set for informationinterchange.3 DefinitionsThis Recommendation defines the
48、following terms:3.1 carrierless mode: A mode for communication, where signals are only present on theconnection when data is being exchanged (e.g. in response to the pressing of a key on a keyboard).ITU-T V.18 (11/2000) 33.2 carrier mode: A mode for communication, where continuous signals (i.e. carr
49、iers) arepresent on the connection irrespective of whether data is being exchanged or not.3.3 CI: A signal transmitted from the originating DCE to indicate the general communicationsfunction, consisting of a repetitive sequence of bits at 300 bit/s, using modulation in accordancewith the low-band channel defined in ITU-T V.21. The cadence of this shall be bursts of 4 CIsequences separated by 2 s of silence. The CI sequence for textphone is defined in ITU-T V.8.3.4 CM: The Call Menu signal defined in ITU-T V.8.3.5 JM: The Joint menu sig
