1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU u .75 (03193) TELEGRAPH SWITCHING INTERWORKING BETWEEN NEW INFORMATION SERVICES AND TELEX AUTOMATIC CALLED TELEX ANSWERBACK CHECK ITU-T Recommendation U.75 (Previously “CCIlT Recommendation“) ITU-T RECMN*U.75
2、 93 = 4862593 0590070 TO5 = 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 standa
3、rdizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by the IT-T Study Groups which, in their turn, produce Recommendations on these topics. IT-T Recommendation U.75 was revised
4、by the ITU-T 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 Telecommunication Standardizatio
5、n Sector (IT-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 Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector.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 “CC, CCIR
6、or IFRB” or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminology related to the new IT structure. 2 telecommunication administration and a recognized operating agency. In this Recommendation, the expression “
7、Administration” 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 IT. ITU-T RECMNrU.7
8、5 93 4862591 0590071 941 = Recommendation U.75 AUTOMATIC CALLED TELEX ANSWERBACK CHECK (Malaga-Torremolinos, 1984; amended at Melbourne, 1988 and at Helsinki, 1993) The CCITT, considering (a conversion facility (CF)/ or store and forward unit (SF); that there is a need to check the answerback of the
9、 called telex number e.g. delivery from a telex-Teletex (b) (c) that Recommendation F.60 defines a preferred structure for the telex answerback; that different forms of answerback exist; (4 device, that Recommendation F.74 defines a structure for an answerback associated with an intermediate storage
10、 unanimously declares that the following requirements are recommended for automatic answerback check of a called telex terminal by an administrations equipment: 1 Case 1: reference information for the check is provided by the calling subscriber This information can be in total or part of the called
11、subscriber answerback (contiguous printable characters and space). There is no restriction on the number of characters supplied. In this case, the called party answerback check consists of verifying the presence of the provided character string. Considering the information provided in the directorie
12、s and terminal identifications, allowance is to be made for the following differences: - - one character mismatch in the letter part; one hyphen or one space is ignored in the national call number. 2 Case 2: no information on the answerback of the called terminal is provided by the calling subscribe
13、r The reference information for the answerback check is the selection information provided by the calling subscriber. In this case, the called party answerback check consists of - - extracting the national call number and F.69 code from the answerback; comparing the obtained national call number and
14、 F.69 code with the supplied selection information code. Allowance is made for the following cases of mismatch: a) a positive national call number match without a valid telex network identification code (TNIC) match; a match between the least significant part of the supplied selection information an
15、d the national call number obtained from the called party answerback, considered to be positive if the difference in field length is limited to two characters. b) 3 In some circumstances, it may be necessary to compare the answerback of the called subscriber with the answerback received and recogniz
16、ed at the beginning of the call. An algorithm which meets the preceding criteria for cases 1 and 2 is shown in Figure 1 Recommendation U.75 (03/93) 1 ITU-T RECMN*U.75 93 W 4B6259L 0590072 888 W In such cases, if the received string consists of more characters than the previously recognized answerbac
17、k, then a check should be made as to whether the recognized answerback is part of the received string. WRU sig-id (Nde 8) I IF G * 1 (See Figue 1N.74, sheet 1 of2) No TTNIC corres- I i NCN = fwdd Selection? (Nde 6) received at auto speed? (Note 1) I !n YeS Isthe mbinatbns in the AIB218and 5221 nunbe
18、r d No foiwarded F.69 YB Y8S Isitaretry? (Note 2) -.- CASE 1 CASE 2 TWO1 1-WdO1 AB Answerback NCN Nalonalcallnumber lTNIC Tempariryteiex network identifcatiai code TNIC Telex netwwk Micam cade FIGURE 1AJ.75 Evaluntionofded telex answmkk 2 Recommendation U.75 (03193) ITU-T RECMN*U.75 93 4862593 05900
19、73 734 Notes to Figure 1: 1 detection of a 300 ms period of idle. 2 3 4 Check the automatic emitting speed and wait for the end of the answerback. The answerback is considered to have ended after ?Retry? refers to another attempt to trigger the answerback. If unsuccessful, perform one retry if allow
20、ed in the protocol. The answerback provided could be a contiguous part of the expected answerback or all of it. In case of a return call to the calling subscriber e.g. PDN (positive delivery notification) or NDN (negative delivery notification) delivery the stored calling telex answerback is conside
21、red as a ?provided? one. 5 mismatch in the letter part. 6 A zero in the selection, but not in the answerback in front of the national number is to be ignored. If the received figure group is shorter than the selected one, consider it as match, but make a note in the call record ?received figure grou
22、p is not complete?. It is possible that the received figure group includes the F.9 code. 7 8 9 This comparison is to verify the presence of the provided character string in the received answerback, allowing one character Forward message, but make a note ?area code-check was not possible? into the call record. If called AB is not available from previous procedures. If a digit ?0? appears at this stage between the F.69 code and the ?NCN? it should be ignored. Recommendation U.75 (03/93) 3
