1、ITU-T RECMN*U-LL 93 48b2591 0588747 329 M INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STAN DARD I ZATI ON SECTOR OF ITU TELEGRAPH SWITCHING SPECIFIC SIGNALLING SCHEMES AND INTERWORKING BETWEEN SIGNALLING SYSTEMS u.ll (03/93) TELEX AND GENTEX SIGNALLING ON INTERCONTINENTAL CIRCUITS
2、USED FOR INTERCONTINENTAL AUTOMATIC TRANSIT TRAFFIC (TYPE C SIGNALLING) ITU-T Recommendation U.ll (Previously “CCIlT Recommendation”) ITU-T RECMNUU-11 93 = 4862591 0588748 265 FOREWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom- municat
3、ion Union. The 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 Conference (WTSC), which meets every four years, establishe
4、d the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. ITU-T Recommendation U.11 was revised 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
5、 the International Telecommunication Union (ITU), the CCIT ceased to exist as of 28 February 1993. In its place, the ITU Telecommunication Standardization Sector (ITU-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunicat
6、ion 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 IFRB” or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the prope
7、r terminology related to the new ITU structure. 2 telecommunication administration and a recognized operating agency. In this Recommendation, the expression “Administration” is used for conciseness to indicate both a O ITU 1994 All rights reserved. No part of this publication may be reproduced or ut
8、ilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. ITU-T RECMN*U=LL 73 W 4862573 0588747 IT3 W Recommendation U.ll TELEX AND GENTEX SIGNALLING ON INTERCONTINENTAL CIRCUITS USED FOR INTERCONTINENTAL AUTOMATIC
9、 TRANSIT TRAFFIC (TYPE C SIGNALLING) (Geneva, 1964; amended at Mar del Plata, 1968; Geneva, 1972, 1976; Malaga-Torremolinos, 1984; Melbourne, 1988 and Helsinki, 1993) The CCIT, considering (a) that it is necessary to standardize an intercontinental signailing system to be used between intercontinent
10、al transit centres as the present standard systems A and B, in the limits of CCIT Recommendations, do not comply with all the requirements of an intercontinental signalling system; (b) that the intercontinental links that are used and could be used in the future for telex and gentex operation use va
11、rious transmission systems, including not only the standard voice-frequency telegraph channels - normally used in the continental field - but also 7-unit error-proof multiplex systems over radio circuits and 6-unit or 5-unit multiplex systems over VF channels. Other transmission systems will perhaps
12、 be used in the future. Therefore, it seems necessary that the intercontinental signailing system should be suitable for as wide a variety of transmission systems as possible; (cl that this signalling system must enable the channels to be operated on a both-way basis. This type of operation can prod
13、uce collisions; therefore it was noted that the intercontinental signailing system must provide for limiting collisions, or at least for simple facilities to detect head-on collisions and for taking appropriate action after their detection; (4 that another important feature of the intercontinental s
14、ignalling system should concern the automatic testing of the ability of the multiplex equipment to transmit teleprinter characters, before establishing a call to the distant subscriber, through an intercontinental transit centre. The class-of-traffic signal, the class-of-traffic-check signal, and th
15、e transmissionxonfirmation signal in the form proposed can provide an efficient and simple method of meeting this requirement. The signals provided also check the functioning of the FRXD when used. It is important that the correct class-of-traffic and class-of-traffic-check signals be transmitted fo
16、r the required category; (e) that the use of teleprinter characters, for selection information and other signalling functions, appears to be most advantageous, as they can be transmitted over the error-proof radio circuits, which undoubtedly wiil be part of the intercontinental transit network; (0 t
17、ransit network to the terminal networks in the outgoing and in the incoming countries; that it is emphasized that the signals, in the form proposed, simplify interconnection of the intercontinental (g) that as regards the method of transmission of selection information, it has been decided that the
18、selection by complete block will be adopted on intercontinental routes. Under this arrangement, the telex destination code and the national number of the called subscriber will be signalled as a single group of characters without awaiting backward path signals. There may be some advantage with regar
19、d to reducing the occupancy of intercontinental trunks and equipment and in preventing the mutilation of signals if the complete group of selection signals is assembled, preferably by the originating country, before commencing to route the call. However, the retransmission of selection signals from
20、one switching centre to the next may start even before the block has been completely received; (h) that exemption from selection by complete block is permissible for manual testing of intercontinental links. The receiving centre should take account of this and also of the fact that calls via an erro
21、r-proof multiplex radio channel may prevent selection signals being received as a complete block; (i) and U. 12 (type D) have been defined in Recommendation U. 15 (interworking rules), that interworking requirements between signalling standards according to U. 1 (types A and B), U. 1 I (type C) Reco
22、mmendation U.ll (03/93) 1 ITU-T RECMN*U.LL 93 4862573 0588750 933 = unanimously declares the view 1 The signalling system between two intercontinental transit centres will be as described in Table 1. NOTE 1 - In this Recommendation: X denotes the intercontinental transit centre that originates the c
23、all under consideration on the intercontinental circuit; Y denotes the intercontinental transit centre that receives the call considered on the intercontinental circuit. Both the forward and backward path signals are described at the moment of their emission on the intercontinental circuit. It shoul
24、d be noted that the signals in Tables 1,2 and 3 are those transmitted by the switching equipment, irrespective of the type of transmission used for the intercontinental trunk circuit. It is possible that the teleprinter signals, although transmitted at automatic speed, may be delayed or separated by
25、 periods of stop polarity after transmission via multiplex systems and that the original periods of start and stop polarity may be either lengthened or shortened by the incidence of error-correction on radio circuits. The circuits between X and Y may transmit calls in both directions. Recommendation
26、 cited in 2. NOTE 2 - For the description of the combinations of International Telegraph Alphabet No. 2, see Table US.13 i or the 2 incidence of head-on-collision is recommended. For bothway working circuits used in the intercontinental transit network, the following action to minimize the At opposi
27、te ends of a group of bothway trunk circuits, either inverse order testing should be adopted or a close approximation to it by testing the route in smaller groups of circuits in a fixed order starting the search from the same initial position. That calls should be offered in such a way that each cir
28、cuit is tested once only for the minimum period of time necessary to ascertain whether it is free or busy, and the switching equipment should not have facilities for delayed searching. A head-on collision is provisionally assumed if centre X receives combination No. 20 (100 ms pulse of polarity A) i
29、nstead of combination No. 22 (40 ms pulse of polarity A). When this combination No. 20 has been detected, centre X checks receipt of the second combination No. 20 to establish whether a head-on collision or a signal mutilation due to faulty transmission has occurred. During this time, centre X conti
30、nues signalling towards centre Y, until both combinations No. 20 of the calling signal have been transmitted. The clearing signal is then sent and the trunk is released. When a head-on collision has been assumed upon receipt of a single combination No. 20, the switching equipment may make another at
31、tempt to select a free circuit either on the same group of circuits or on a group of overflow circuits, if they exist. In the event of a further head-on collision on the recall, or on the call attempt via the overflow route, no further recall will be made and the call will be cleared down after retu
32、rnhg the transit failure signal. Should the second combination No. 20 not have arrived in the five seconds following the commencement of receipt of the fust combination No. 20, centre X will put into operation the automatic retest procedure on the circuit concerned. 3 There is no need to distinguish
33、 on a circuit XY whether a call is to terminate in centre Y or if it is to pass in transit via Y to a country other than the country (or network) of Y. The advantage of not having to transmit on circuit XY the digits of the destination code in the case of a call termination in Y is offset by the com
34、plication of the registers and the necessity for an additional discrimination in the class-of-traffic signal. 4 uniform format is: The transit centre will be provided with an identification code consisting of seven characters, of which the - combination No. 29: - either one letter combination and co
35、mbination No. 29 or two letter combinations designating the transit Administration; - combination No. 30; - a one-, two- or three-digit number identifying the centre andlor equipment in the transit Administrations network. 2 Recommendation U.ll (03/93) ITU-T RECMN*U*LL 93 m 486259L 0588751 85T m If
36、the numerical portion of the transit centre identification code comprises one or two digits, two or one combinations No. 30 should be added to maintain the seven-character format. The letter (or two letters) designating the transit Administration shall be the letter (or two letters) of the telex net
37、work identification code as far as possible. In interworking cases the numeric portion may be replaced by combinations No. 30 to maintain the seven character format. The transit centre identification code will be returned automatically in all cases and will continue as far as the calling country. If
38、 several transit centres are involved in setting up a call, the calling network will receive the codes of these transit centres one after the other. This information is useful for retracing the route followed by a call (for traffic statistics, international accounts and the clearing of faults). 5 ma
39、y return back to the original exchange) overflow for each call will be allowed at only one centre. This question will be discussed when the routing plans are established. To simplify the solution of problems raised by overflow (increased congestion of systems, risk that the call NOTE - The rigour of
40、 this rule could be eased by admitting alternative (2nd choice) routings in certain traffic relations. 6 A transit centre will have to be advised: 1) that an incoming call is: a) b) c) a telex call (between telex subscribers), a gentex call (between gentex stations), a call, generally originating fr
41、om a switchboard operator or from maintenance staff, to a manual switchboard or service point. This class-of-traffic signal is to be used if signalling conditions for calls to manual switchboards or other service points in the destination network are different from those returned on calls to subscri
42、bers, d) that the call concerned has already been subjected to overflow. a special category call (see 7.1 and 7.2 below); 2) Other possibilities must be reserved, such as routing via telegraph circuits for 100 or 200 bauds, and a reserve supply of class-of-traffic signals has been envisaged to this
43、end. 7 Class-of-traffk signal 7.1 The class-of-traffk signals are divided into two categories: - Category A - Signals for transmission at 50 bauds, the utilization of which is allocated as shown in Tables 4 and 5. Category B - Signals reserved to meet future uses, not yet defined, such as use of cir
44、cuits for more than 50 bauds. - 7.1.1 characterized by A polarity of the first element. 7.1.2 categories: telex, gentex, service traffic and a special category (see Note under 7.2). The signals of category A are characterized by Z polarity of the first element; the signals under category B are For c
45、ategory A signals the second and third elements are associated to discriminate the four following 7.1.3 whether or not the call has already been overflowed. For the signals of category A as well as for those of category B, the polarity of the fourth element indicates 7.1.4 For the signals of categor
46、y A as well as for those of category B, the fifth element must always have an A polarity in order to avoid the use as a class-of-traffic (COT) signal of the special signals, combination No. 20 (calling signal) and combination No. 30 (special pre-signal). 7.2 through time-division multiplex channels
47、see the Recommendation cited S. 15 3. Table 5 indicates the combinations used for class-of-traffic and class-of-traffic-check signals. NOTE - For 50-baud transmissions during which an alphabet with a non-5-unit code could be used, to avoid routing 7.3 equipment in the centre at which overflow occurs
48、. The class-of-traffic combination for a previously alternatively routed call shall be inserted by the switching Recommendation U.ll (03/93) 3 ITU-T RECMN*U.LL 93 = 48b259L 0588752 79b m 8 The ability of the forward signalling path of the trunk to transmit 5-unit signals is checked by using compleme
49、ntary class-of-traffic and class-of-trafc-check (COTC) signals. The two combinations of the transmission-confirmation signal are also complementary and provide a similar check of the backward signalling path. Failure to receive the reception-confirmation and transmission-confirmation signals correctly within 5 seconds from the start of the calling signai, or receipt of the transmission-failure signal, should initiate the automatic retest signai on the circuit concerned. 9 The equipment of centre Y should preferably begin the forward selection as soon as the first digit of the call
