1、 ITU-T RECMN*S-20 73 = 4862573 0586370 433 INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU TELEGRAPHY ALPHABETICAL TELEGRAPH TERMINAL EQUIPMENT s.20 (03/93) AUTOMATIC CLEARING PROCEDURE FOR A TELEX TERMINAL ITU-T Recommendation S.20 (Previously “CCIlT Reco
2、mmendation”) FOREWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom- munication Union. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecom
3、munications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. ITU-T Recommendation S.20 was revised by the ITU-T
4、Study Group IX (1988-1993) and was approved by the WTSC (Helsinki, March 1-12, 1993). NOTES 1 As a consequence of a reform process within the International Telecommunication Union (ITU), the CCITT ceased to exist as of 28 February 1993. In its place, the ITU Telecommunication Standardization Sector
5、(ITU-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector. In order not to delay publication of this Recommendation, no change has been made in the text to references containing the acronyms “CCITT, CCIR or IF
6、RB” or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminology related to the new ITU structure. 2 telecommunication administration and a recognized operating agency. In this Recommendation, the expression “Admi
7、nistration” is used for conciseness to indicate both a O ITU 1994 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 ITU. Recommendation S.2
8、0 AUTOMATIC CLEARING PROCEDURE FOR A TELEX TERMINAL (Geneva, 1980; amended at Melbourne, 1988 and at Helsinki, 1993) The CCITT considering (a) op er at or ; that new equipment should be capable of automatic performance of functions that would normally require an (b) considered most immediately for a
9、utomation of a terminal; that those operator functions that involve repetitive work or idle waiting on the part of an operator should be (c clearing of call; that one of the most straightforward operator functions that could benefit from automatic assistance is the (4 Recommendation assumes that an
10、operator is present to initiate the calling condition. that conditions for automatic establishments of calls are laid down in Recommendation U.40 13 whereas this unanimously recommends that the following procedure should be adopted for new equipment to assist operators by automatically providing a c
11、learing down procedure following automatic transmission of a message. 1 control, or automatic control, can be selected according to the requirements of a particular call. the activation of this automatic procedure should be under the control of the operator, so that either manual 2 this connection h
12、as been confirmed by examination of the answer-back sequence received from the called subscriber. It is assumed that connection to the desired subscriber has already been established, and that the correctness of 3 It is also assumed that the message to be transmitted is ready for release to line via
13、 the automatic transmitter. 4 The subsequent procedure may be described as a series of steps as follows: a) b) Operate the special control that initiates the following automatic transmission and clearing procedure. (Optional, according to national requirements.) The equipment transmits a WRU signal
14、in order to obtain a sample of the answer-back sequence of the called subscriber. This sequence is stored for subsequent checking. NOTE - If step b) is not implemented it may be desirable to modify the subsequent procedure. For example, step h) may also be eliminated, with corresponding changes to s
15、tepg) and stepk). Also if this check procedure is not considered to be necessary, it may be desirable to reduce the period of alarm in step m) to less than 30 seconds before the terminai automatically clears the call. c) Automatic transmission is started. d) At any time, automatic transmission may b
16、e stopped by either the detection of incoming teleprinter signals or the forced clearing of the call. In the latter case an alarm should be given and then the call should be re-established by the operator. However, if the connection is still established but the automatic transmission has stopped, an
17、 alarm should be given to the operator. If the alarm is cleared by the operator within 30 seconds, proceed to step n) else step m). Automatic transmission may be resumed after a delay of 1 second. If the transmission includes a TDM system with loop back facilities refer to 3.6.2 b)/R.101, this condi
18、tion may continue for aperiod of 5 to 7 seconds. Recommendation S.20 (03/93) 1 ITU-T RECMN*S.20 93 W 48b259L 0586173 1YO The end of automatic transmission is detected locally by the tape-out contacts of the tape reader, or by the recognition of the transmission of an end of message pattern or by oth
19、er means arranged within the terminal. The terminal then automatically transmits the WRU signal (combinations Nos. 30 and 4) and awaits reception of the called subscribers answer-back. If the called subscribers answer-back is received in less than six seconds the terminal immediately follows it by s
20、tep h), otherwise it proceeds to step k). If the received answer-back code is the same as the stored answer-back step b) the terminal makes step i), otherwise it proceeds to step 1). The terminal transmits its own answer-back signal. A clearing signal is initiated, and maintained until a clear confi
21、rm signal is recognized. This is followed by assumption of the free line condition. If the called subscribers answer-back is not received within six seconds, or if, it differs in more than one character from that stored in step b), then step f), the transmission of the WRU signal is repeated once mo
22、re. If this results in the reception of a called subscribers answer-back that is identical with that stored in step b), then the terminal proceeds to step i), otherwise to step 1). An alarm is operated to attract an operators attention. This alarm may be the same as that used for combination No. 10
23、(Beil) or it may be a separate alarm provided for the purpose. If the operator does not cancel the alarm and restore manual control of the terminal functions within 30 seconds, the terminal moves to step i), sending its own answer-back and automatically clearing the Call. Having waited for a period
24、of at least 7 seconds from the commencement of the alarm, the operator should send carriage return, line feed then a WRU signal. This delay is necessary to allow TDM systems with loop back to restore or normal or choose an alternative bearer refer 3.6.2 b)/R.101. If the called partys answer-back is
25、correctly received, the tape should be reset after giving a further carriage return and line feed. Automatic transmission can again be started. 5 Clearing of a broadcast call shall be in accordance with Recommendation U.44. References il CCI” Recommendation Reactions by automatic tenninals connected to the telex network in the event of ineffective call attempts or signalling incidents, Rec. U.40. 2 Recommendation S.20 (03/93)
