1、INTERNATIONAL TELECOMMUNICATION UN ION ITU=T TELECOMMUNICATION STAN DARD IZATI ON SECTOR OF ITU V.25 Corrigendum 1 (07/2001) SERIES V: DATA COMMUNICATION OVER THE TELEPHONE NETWORK Interaces and voiceband modems Automatic answering equipment and general procedures for automatic calling equipment on
2、the general switched telephone network including procedures for disabling of echo control devices for both manually and automatically established calls Corrigendum I ITU-T Recommendation V.25 - Corrigendum 1 (Formerly CCIT Recommendation) ITU-T V-SERIES RECOMMENDATIONS DATA COMMUNICATION OVER THE TE
3、LEPHONE NETWORK I +q General Interfaces and voiceband moderns - Y - Wideband mode& - Error control Transmission quality and maintenance Simultaneous transmission of data and other signals Interworking with other networks Interface layer specifications for data communication Control procedures Modems
4、 on digital circuits v.1-v.9 V.lGV.34- v.40-v.49 v.50-v.59 V.60-V.99 v. 100-v. 199 V.200-V.249 V.250-V.299 V.300-V.399 *- - I - 1x _ “,“A v.35-v.39- I! Forfirrther details, please refer to the list of ITU-T Recommendations. ITU-T Recommendation V.25 Automatic answering equipment and general procedur
5、es for automatic calling equipment on the general switched telephone network including procedures for disabling of echo control devices for both manually and automatically established calls CORRIGENDUM 1 Summary Corrigendum 1 to V.25 adds a Note after paragraph 5 of clause 5. Source Corrigendum 1 to
6、 ITU-T Recommendation V.25 was prepared by ITU-T Study Group 16 (2001-2004) and approved under the WTSA Resolution 1 procedure on 29 July 2001. ITU-T V.25/Cor.l(07/2001) i FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunicat
7、ions. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of . lTU-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 S
8、tandardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of -T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of informatio
9、n technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with IS0 and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. I
10、NTELLECTUAL PROPERTY RIGHTS IT draws attention to the possibility that the practice 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,
11、 whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors a
12、re cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. o ITU 2002 All rights reserved. No part of this publication may be reproduced or utiiized in any form or by any means, electronic or mechanical, including photocopying
13、 and microfilm, without permission in writing fiom . ii ITU-T V.25/Cor.l (07/2001) ITU-T Recommendation V.25 Automatic answering equipment and general procedures for automatic calling equipment on the general switched telephone network including procedures for disabling of echo control devices for b
14、oth manually and automatically established calls CORRIGENDUM 1 1) Clause 5 Add the following Note after paragraph 5 of clause 5 (Proposed line procedures) : 1.8 to 2.5 s after the answering modem is connected to the line (i.e. circuits 125 and 108 are ON), it sends a continuous answering tone for a
15、duration of not more than 4.0 s. If it is intended to disable network echo cancellers as well as echo suppressors, the answering modem shall transmit phase reversals (see Figure 3). NOTE - Experience in the field has indicated that, when connecting on circuits fitted with some network echo cancellers, there is a potential for failure to connect if the phase reversal option of answer tone is not used. ITU-T V.29Cor.l (07/2001) 1
