ITU-T U 61-1993 Detailed Requirements to Be Met in Interfacing the International Telex Network with Maritime Satellite Systems - Telegraph Switching Radiotelex Interworking (Study .pdf

1、ITU-T RECUN*U.bL 93 4862593 0590056 635 INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU TELEGRAPH SWITCHING RADIOTELEX INTERWORKING U.61 (03/93) DETAILED REQUIREMENTS TO BE MET IN INTERFACING THE INTERNATIONAL TELEX NETWORK WITH MARITIME SATELLITE SYSTEMS

2、ITU-T Recommendation U.61 (Previously “CCITT Recommendation”) 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 Recommendat

3、ions on them with a view to standardizing telecommunications 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. IT

4、U-T Recommendation U.61 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 the International Telecommunication Union (ITU), the CCITT ceased to exist as of 28 February 1993. In its place,

5、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 Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector. In order not to delay publication of this Recommendation, no change has been made in the text to refe

6、rences 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 proper terminology related to the new ITU structure. 2 telecommunication administration and a recognized operating age

7、ncy. 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 utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permi

8、ssion in writing from the ITU. ITU-T RECMN*U-bL 93 m 4862.593 0590058 408 m CONTENTS Page 3 . Appendix I - Signalling characteristics and timing of the INMARSAT telex service Appendix II - Method employed at the Nordic coast earth station to avoid periods of Z polarity within the answerback signal 1

9、0 Recommendation U.61 (03/93) 1 ITU-T RECMN*U.b1 93 D 4862593 0590059 344 D Recommendation U.61 DETAILED REQUIREMENTS TO BE MET IN INTERFACING THE INTERNATIONAL TELEX NETWORK WITH MARITIME SATELLITE SYSTEMS (Geneva, 1980; amended at Malaga-Torremolinos, 1984 and at Helsinki, 1993) The CCITT. conside

10、ring (a) radiotelex service provided by a maritime satellite system is technically possible; that fully automatic working between subscribers in the international telex service and subscribers to a (b) network with maritime satellite systems, Recommendation U.60, which gives the general requirements

11、 to be met in interfacing the international telex unanimously recommends 1 Maritime satellite systems should be capable of detecting the head-on collision condition at the coast earth station between a ship earth station request for call and a terrestrially originated call for that particular ship e

12、arth station and should: - - permit the ship-originated call to be connected to the international telex network; and terminate the call from the international telex network with an appropriate telex service signal (OCC) and a clear (see Recommendation F.60 i). 2 Should the head-on collision conditio

13、n occur in the connections in the terrestrial network between the coast earth station and the telex exchange, then the normal procedures in accordance with the appropriate Series U Recommendations (see 3.3N.12, clause 2N.11 and 12.2N.1) should prevail. 3 A call-connected signal or a telex service si

14、gnal and clear shall be returned as soon as possible after the receipt of the end-of-selection character at the coast earth station for shore-originated calls. The signal return delay shall not exceed 35 seconds. NOTE - For type C signailing (see Recommendation U. 11) the end-of-selection (EOS) char

15、acter is combination No. 26 in figure-shift mode (+) in International Telegraph Alphabet No. 2. For type D signalling (see Recommendation U.12) the EOS is character No. 11 in the Control Signalling Code (CSC). For signalling to Recommendation U.l, this signal shall be combination No. 26 in figure-sh

16、ift mode (+) in International Telegraph Alphabet No. 2. 4 Recommendation F.60 i), followed by a clearing signal when the maritime satellite system detects: The maritime satellite system returns to the subscriber in the terrestrial network the service signal DER (see - - 5 At the termination of the c

17、all the requirements of the clearing and clear-confirmation signals shall apply to and from the international network (see Recommendations U.l, U. 1 1, U. 12); the maritime satellite system may use different timings in the directions to and from the ship. It is preferred that the total times for suc

18、h signal exchanges should have a minimum time addition to that quoted for the international network. NOTE - Automatic calling equipment and subscribers in the international telex network may attempt, under certain conditions, to place a follow-on call to the same ship. Under conditions of long clear

19、 and clear-confirmation cycle times, such calls will not be successful. that the ships station (teleprinter, control logic, radio equipment) is faulty; failure of the answer-back from the ships teleprinter. 6 In the first generation INMARSAT system, telex characters are transmitted in synchronous ch

20、annels using 6-unit frames. A telex character is thus sent as one start element followed by the five information elements of International Telegraph Alphabet No. 2. Speed differences between the on-board teleprinter and the satellite circuit are compensated for by occasionally inserting six elements

21、 of Z polarity, Le., whenever a frame is to be sent on the synchronous channel and there is no complete telex character available. When the characters are retransmitted into the telex network, a stop element nominally 1.5 units long is added. Therefore, a period of Z polarity equal to the duration o

22、f a telex character may occasionally appear in the data stream. Recommendation U.61 (03/93) 1 ITU-T RECHN*U-bL 93 4862573 0590060 O66 = 6.1 The design of the equipment interfacing the international network should preferably ensure the following: 6.1.1 When type C signalling is employed to connect in

23、to the international network, either: - the class-of-traffic and selection signals should all be transmitted into the international network at cadence speed without any periods of Z polarity between the 7 1/2-unit characters; or the class-of-traffic signal, the class-of-traffic-check signal, the 2 o

24、r 3 digits of the destination code of the called network and the first two digits of the called station should be transmitted as a complete block at cadence speed without any periods of Z polarity between the 7 1/2-unit characters. The remaining selection signals for the called number and the EOS si

25、gnal (+) may be transmitted with periods of Z polarity, providing that the signals are not delayed by more than 4 seconds. - 6.1.2 When type D signalling is employed to connect into the international network, the class-of-traffic signal(s) or network selection signals and selection signals should be

26、 transmitted as a complete block at cadence speed without periods of Z polarity between the Control Signalling Code (CSC) characters. 6.1.3 If these options cannot be exercised, then the provisions of Clause 13N.11, 3.6N.12 or 6.6N. 1 shall apply. 6.2 When operation to automatic terminals, store-and

27、-forward units, etc., is required, it should be noted that periods of Z polarity may occur within an answerback and text during transmission at cadence speed. (See also Recommendation R.59.) A method for avoiding periods of Z polarity within an answerback signal is described in Appendix II. 7 Since,

28、 for automatic calls in the international telex service, there are no arrangements for call priorities such as are envisaged for maritime satellite systems and since it is a principle that a telex call should not be broken down without transmitting a service signal to the affected terminals, maritim

29、e satellite systems should, on exercising the maritime priority: attempt to set up the priority call by cutting down a call that is in the process of being set up, i.e. the call-connected signal was not yet transmitted to the international network before cutting down an established call; when a call

30、 in the process of being set up is cut down, transmit a service signal (NC) followed by a clear to the international network; c) where it is unavoidable that an established call be cut down, clear the call using the standard international clearing procedure. NOTE - Special signals could be used with

31、in the maritime satellite system to reduce the setting-up times of priority calls within that system. Such signals are not required to be related to the time scale of the cut-down of calls from or to the international network. a) b) 8 the purpose of making a group call to ships, then such a service

32、can be provided technically: When the international network is used to permit an authorized telex terminal to access a coast earth station for a) when the originating network cannot apply selective barring to their subscribers, providing that the coast earth station authenticates the calling terrest

33、rial telex station by the transmission of the WRU signal and checks the status of the characters received from the calling terminals answerback; It should be noted that the WRU should be transmitted after the call-connected signal and the coast earth stations answerback has been transmitted to the c

34、alling terminal; when the originating telex network can apply selective barring to its subscribers, providing that the telex selection received by the coast earth station is of the format: b) where DlD2D3 is the appropriate telex destination code assigned to the Maritime Satellite Service in accorda

35、nce with Recommendation F.69 2, and X1X2X3 . . . Xk is the telex number at the coast earth station defining the particular group call request, which, in association with the calling terminal, may be used to identify the appropriate listing of ships to receive the group call. The character X1 in comb

36、ination with the Recommendation F.69 2 code indicates to the international network that a maritime group call is being made. The character XI shall be the character O (zero). (See also Recommendation F.120.) 2 Recommendation U.61 (03/93) ITU-T RECflN*Umbl 93 4862591 05900bl TT2 c) when type D system

37、s exist in the connection to the calling telex terminal. In that case the “calling line identification” procedures of that system may be used during the setting-up phase of the connection to the coast earth station to authenticate the calling terminals identity instead of the use of the WU and answe

38、rback. Where the calling link identification is not available in the terrestrial network the Control Signalling Code (CSC) No. 12 will be received. Under these circumstances the WRU/answerback sequence should be used as detailed in clause 7a). When the request for a maritime group call, from the int

39、ernational network, is rejected due to lack of authorization, the international network should be cleared with a service signal (NA) followed by a clearing signal. NOTE - Group calls may also be set up via a store-and-forward unit associated with the coast earth station. This unit should be accessed

40、 by subscribers or other store-and-forward units in accordance with the relevant Series F and U Recommendations. The authentication of the calling telex subscriber should be done by the store-and-forward unit. 9 The composition of ship terminals answerback codes should conform to Recommendation F. 1

41、30 3. 10 the implementation at the United States coast earth stations. Appendix I gives the characteristics and timings for INMARSAT telex circuits. The example given is based on Appendix I Signalling characteristics and timing of the INMARSAT telex service (This appendix does not form an integral p

42、art of this Recommendation) 1.1 Introduction This appendix describes the characteristics and time sequences of the international telex service operated over the INMARSAT maritime satellite communication system via the USA coast earth station. 1.2 Ship Earth Station (SES) originated telex call Figure

43、 1.1 shows the signalling sequence for a telex call originated from an SES terminal in the INMARSAT system. Figure 1.2 illustrates the telex signalling and timing sequence. The following is a general description of the sequence of events in establishing a telex call from an SES to a gateway switch.

44、1.2.1 To initiate a call, the SES sends a telex request message in the out-of-band request channel. The addressed coast earth station (CES) receiving the valid request message will send back an out-of-band assignment message on its normal TDM channel to the network coordination station (NCS). The NC

45、S will repeat the assignment message on the common TDM channel to which the SES is listening. 1.2.2 Upon receipt of a valid out-of-band assignment message from the CES via the NCS, the SES tunes to the normal TDM and can then access its assigned channel. The SES will normally achieve carrier and bit

46、 timing synchronization within 0.58 s after receipt of the assignment message. This time includes assignment message decoding, carrier recovery and clock recovery. Transmission will normally start upon frame synchronization, which occurs in less than 5.25 s. Therefore, the normal SES response time w

47、ill be less than 5.8 s as seen at the SES or 6.6 s as seen at the coast earth station. The time that the assignment message remains active in the coast earth station is in addition to this 6.6 s, allowing enough time for the SES to start transmitting. Recommendation U.61 (OY93) 3 ITU-T RECMN*U.bL 93

48、 = 4862571 05900b2 939 1.2.3 The coast earth station, which is continually transmitting a polarity, makes the transition A to Z polarity indicating call Confirmation within one character (150 ms, not counting framing delays) after the assignment message is formatted. In cases of heavy traffic, the a

49、ssignment message may be delayed in queue until after the transition has occurred, Le. it is possible for the A to Z transition to be received by the SES before the assignment message. 1.2.4 The initial SES transmission is in the A polarity state. When Z polarity is received from the coast earth station, the SES changes its transmission from A to Z polarity. In the case when the A to Z polarity transition on the coast earth station to SES link reaches the terminal before the assignment message, the SES inserts no more than two characters of A polarity in the initial burst. 1.2.