1、 INTERNATIONAL TELECOMMUNICATION UNION ITU-T V.18TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU Amendment 1(11/2002) SERIES V: DATA COMMUNICATION OVER THE TELEPHONE NETWORK Interfaces and voiceband modems Operational and interworking requirements for DCEs operating in the text telephone mode Amendm
2、ent 1 ITU-T Recommendation V.18 (2000) Amendment 1 ITU-T V-SERIES RECOMMENDATIONS DATA COMMUNICATION OVER THE TELEPHONE NETWORK General V.1V.9 Interfaces and voiceband modems V.10V.34 Wideband modems V.35V.39 Error control V.40V.49 Transmission quality and maintenance V.50V.59 Simultaneous transmiss
3、ion of data and other signals V.60V.99 Interworking with other networks V.100V.199 Interface layer specifications for data communication V.200V.249 Control procedures V.250V.299 Modems on digital circuits V.300V.399 For further details, please refer to the list of ITU-T Recommendations. ITU-T Rec. V
4、.18 (2000)/Amd.1 (11/2002) i ITU-T Recommendation V.18 Operational and interworking requirements for DCEs operating in the text telephone mode Amendment 1 Summary The change is required because of an ambiguity in the original text which caused at least one manufacturer to make products incompatible
5、with existing textphones. The new text removes the ambiguity and refers the reader to ANSI TIA/EIA-825 (2000) for the definition of operation of the existing type of textphone. Source Amendment 1 to ITU-T Recommendation V.18 was prepared by ITU-T Study Group 16 (2001-2004) and approved under the WTS
6、A Resolution 1 procedure on 29 November 2002. ii ITU-T Rec. V.18 (2000)/Amd.1 (11/2002) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ
7、of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the top
8、ics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations 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 are pre
9、pared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the pr
10、actice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation deve
11、lopment process. As of the date of approval of this Recommendation, ITU had received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore
12、 strongly urged to consult the TSB patent database. ITU 2003 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. V.18 (2000)/Amd.1 (11/2002) 1 ITU-T Recommendation V.18 Operational and interworking requi
13、rements for DCEs operating in the text telephone mode Amendment 1 1) Clause A.1 Replace the original text as follows: A.1 Mode of operation The 5-bit mode is defined in ANSI TIA/EIA-825 (2000), A Frequency Shift Keyed Modem for use on the Public Switched Telephone Network. The communication channel
14、is half-duplex with no channel turnaround. Carrier is transmitted 150 ms before the first character is transmitted. The receiver shall be disabled for 300 ms when a character is transmitted to mitigate false detection of echoes (in non-V.18 devices, the carrier may remain for up to 1 s after the las
15、t character to provide this same function). with: A.1 Mode of operation The description of 5-bit mode text telephone operation can be found in ANSI TIA/EIA-825 (2000), A Frequency Shift Keyed Modem for use on the Public Switched Telephone Network. NOTE To improve transmission performance when operat
16、ing in the 5-bit mode, it is recommended that the first character be preceded by a 150 ms burst of 1400 Hz carrier. 2) Clause A.2 Replace the original text as follows: A.2 Modulation The modulation is frequency shift-keyed modulation (i.e. no carrier is present when a character is not being transmit
17、ted) using 1400 Hz (5%) for a binary 1 and 1800 Hz (5%) for a binary 0. A bit duration of either 20 or 22.00 0.40 ms is used providing either a nominal data signalling rate of 50 or 45.45 bits/s respectively. with: A.2 Modulation Please refer to ANSI TIA/EIA-825. Printed in Switzerland Geneva, 2003
18、SERIES OF ITU-T RECOMMENDATIONS Series A Organization of the work of ITU-T Series B Means of expression: definitions, symbols, classification Series C General telecommunication statistics Series D General tariff principles Series E Overall network operation, telephone service, service operation and
19、human factors Series F Non-telephone telecommunication services Series G Transmission systems and media, digital systems and networks Series H Audiovisual and multimedia systems Series I Integrated services digital network Series J Cable networks and transmission of television, sound programme and o
20、ther multimedia signals Series K Protection against interference Series L Construction, installation and protection of cables and other elements of outside plant Series M TMN and network maintenance: international transmission systems, telephone circuits, telegraphy, facsimile and leased circuits Se
21、ries N Maintenance: international sound programme and television transmission circuits Series O Specifications of measuring equipment Series P Telephone transmission quality, telephone installations, local line networks Series Q Switching and signalling Series R Telegraph transmission Series S Teleg
22、raph services terminal equipment Series T Terminals for telematic services Series U Telegraph switching Series V Data communication over the telephone network Series X Data networks and open system communications Series Y Global information infrastructure and Internet protocol aspects Series Z Languages and general software aspects for telecommunication systems
