1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU TELEGRAPH SWITCHING INTERNATIONAL TELEX SERVICE u.202 (03/93) TECHNICAL REQUIREMENTS TO BE MET IN PROVIDING THE INTERNATIONAL TELEX SERVICE WITHIN AN INTEGRATED SERVICES DIGITAL NETWORK ITU-T Recommendation U
2、.202 (Previously “CCIlT Recommendation“) ITU-T RECMN*U.ZOZ 93 M 4862573 0594222 783 M FOREWORD The IT 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
3、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, established the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendati
4、ons on these topics. IW-T Recommendation U.202 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 Februa
5、ry 1993. In its place, the IT 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 Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector.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 ma
6、de 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 proper terminology related to the new ITU structure. 2 telecommunication administration and a re
7、cognized 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 utilized in any form or by any means, electronic or mechanical, including photocopying and mi
8、crofilm, without permission in writing from the ITU. ITU-T RECMN*U-202 93 4862571 0594223 blT D CONTENTS Scope . PART I - GENERAL CONSIDERATIONS APPLICABLE TO ALL CONFIGURATIONS 1 General principles 2 Quality of Service objectives . 3.1 Minimum integration 3.2 Maximum integration . 4 Terminal adapto
9、rs . INTERNATIONAL TELEX SERVICE 1 Minimum integration model . 2 Maximum integration model 3 Call establishment sequences . 3.1 Minimum integration model . 3.2 Maximum integration model 4 Terminal adaptor functions 5 Access unit . 6 Tasks of the interworking function 7 Other telex service features P
10、ART III - USE OF THE D-CHANNEL FOR THE PROVISION OF THE INTERNATIONAL TELEX SERVICE . 3 Configuration models . PART II - USE OF THE B-CHANNEL OF THE ISDN IN CIRCUIT MODE FOR THE PROVISION OF THE 1 Quality of Service 2 Switching signalling . 3 Text and data transmission . 4 Telex access points . 5 Te
11、lex-to-ISDN connections and vice versa 6 Special procedures for different configuration models, incorporating switching 7 Switching signalling conversion 8 Conversion of telex message characters . 9 Recapitulation Recommendation U.202 (03/93) Page 1 1 1 2 2 2 3 4 4 4 4 4 4 8 10 10 10 10 10 10 10 11
12、11 11 11 16 16 17 ITU-T RECMN*U=202 93 W 4862591 0594224 556 D INTRODUCTION Recognizing that some Administrations have implemented, or plan to implement, integrated services digital networks (ISDN) in accordance with I-Series Recommendations, there may be economic and operational benefits to be gain
13、ed if the international telex service was also supported within the ISDN environment. Accordingly, the provisions of this Recommendation should be followed whenever the ISDN is used to support the international telex service. 11 Recommendation U.202 (03/93) TECHNICAL REQUIREMENTS TO BE MET IN PROVID
14、ING THE INTERNATIONAL TELEX SERVICE WITHIN AN INTEGRATED SERVICES DIGITAL NETWORK (Melbourne, 1988; revised at Helsinki, 1993) Scope This Recommendation is structured in three parts, as follows: Part I: Part II: General considerations applicable to all configurations Use of the B-channel of the ISDN
15、 in circuit mode for the provision of the international telex service Part III: Use of the D-channel for the provision of the international telex service This Recommendation lays down general principles to be followed and outlines configuration models for the provision of the intemational telex serv
16、ice in the ISDN environment. It is assumed throughout this Recommendation that the service and operational provisions in respect of the international telex service, as detailed in Recommendations F.59 and F.60, are maintained in ali identified configurations. The specification of the interface betwe
17、en the telex terminal and terminal adaptor within the ISDN is outside the scope of this Recommendation. PART I - GENERAL CONSIDERATIONS APPLICABLE TO ALL CONFIGURATIONS 1 General principles i) ii) iii) i v) v vi) The service principles and basic characteristics of the international telex service, de
18、tailed in Recommendations F.59 and F.60, must be applied and maintained end-to-end. No burden shall be placed on existing telex networks in setting up telex connections to telex terminals connected to the ISDN and accordingly single-stage call Set-up shall be employed in either direction. The plan f
19、or telex destination codes contained in Recommendation F.69 shall be applied in sending telex calls towards an ISDN which supports the international telex service from an existing telex network in another country which has not implemented an ISDN environment. Accordingly, ISDN-based telex terminals
20、should be assigned a telex number which is part of the national telex numbering plan. However, an integrated numbering plan may be employed in national implementations provided the maximum number of digits required to address an ISDN-based subscriber across the international telex network does not e
21、xceed i2 in accordance with the U-Series signalling Recommendations. The technical requirements in relation to subscriber-to-subscriber performance, permissible distortion levels, and signal transfer delay, as specified in Recommendations R.58, R.58 bis, and U.8 shall be met in all cases. A telex te
22、rminal connected to an ISDN should respond to a received WRU signal by transmitting its answerback sequence formatted in accordance with Recommendation F.60 with a maximum delay of 6ms from receipt of the second start element within the WRU signal, in accordance with Recommendation S.6. Recommendati
23、on U.202 (03/93) 1 2 Quality of Service objectives In accordance with the provisions of the F-Series Recommendations, and in particular Recommendations F.59 and F.60, the Quality of Service objectives, as defined in the referenced Recommendations and as perceived by subscribers of the international
24、telex service, shall be met in all configurations where the international telex service is provided in the ISDN environment. Accordingly, telex subscribers connected to an ISDN and participating in the international telex service shall see no degradation in the Quality of Service which they would ex
25、perience if connected to a dedicated telex network. Conversely, telex subscribers connected to a dedicated telex network shall see no degradation in their Quality of Service when sending telex messages to ISDN-based telex subscribers across international boundaries. 3 Configuration models Several co
26、nfiguration models may be developed by each Administration (or ROA), depending on the extent to which the telex service is integrated into the ISDN. These models range from minimum integration to maximum integration as described below. 3.1 Minimum integration The minimum degree of integration is whe
27、re the ISDN is used only as a means of connecting terminals to a serving exchange, with all switching occurring within the telex network. In this configuration, the link between the terminal and the telex network is therefore equivalent to a subscriber line built across the ISDN. This method require
28、s the availability both of a telex network and an ISDN. An ISDN subscriber should normally be able to use it to connect his telex, although there may also be telex subscribers, who do not subscribe to the ISDN and who are connected by the usual means. If either of the two countries X or Y use minimu
29、m integration of telex into ISDN, the link between those countries for international telex calls can only be established over the international network (see Figure 1). Country X Country Y R TE R TA SiT AU TU SUBS INTLTRUNK PC TU SUBS INTLTRUNK TU( SUBS I TE 1 A TU( SUBS _ TU i i i TA “Y i SK i AU SU
30、BS AU International ISDN X TO90143094/d01 Telex termlnal Telex interface Terminal adaptoc SiT reference point Access unit Telex subscriber line International telex trunk Permanentisemi-permanent connection on ISDN FIGURE 1hJ.202 Minimumintegration dei 2 Recommendation U.202 (03/93) ITU-T RECMN*Um202
31、 93 4862593 0594227 265 m TELEX -+ 3.2 Maximum integration .- TEW TRUNK i More complex configuration models might be considered where the switching is also integrated within the ISDN, to a greater or lesser extent. In these types of configuration, the link-up between the ISDN and the telex network w
32、ill be at circuit level. In the extreme case, an Administration might consider replacing its telex network with an ISDN, to which all telex subscribers would be connected. In this case, the technical means should be provided for applying the telex services own call establishment and connection proce
33、dures not normally available in the ISDN. If the two countries X and Y use both maximum integration (see Figure 2), the link between them for a telex call can be established either over the international telex network or by interconnection of their ISDNs. This last possibility must be agreed bilater
34、ally. A, B C, D IWF Interworking facility TA Terminal adaptor TLX SUBS Telex subscriber line TELEX TRUNK Telex national trunk INTLTRUNK Telex international trunk Tdex terminals on a telex network Tdex terminals within an ISDN network NOTES 1 For calls originated from the telex network (e.g. A to C o
35、r B to C), the destination telex network should be able to route calls intended for telex subscribers within the ISDN to the IWF. The IWF will perform the address validation and translation if necessary. The actual number assignment is a national matter. 2 For calls originated by telex terminals wit
36、hin the ISDN (e.g. C to A or C to B), the ISDN should route these calls to the national IWF. This may imply the use of escape code sequences before time “I“, or other means as appropriate. (Concept of time “T is defined in Study Group IIs Recommendation E. 165.) 3 Interconnection of ISDNs to support
37、 the telex service should be agreed bilaterally. FIGURE YU.202 Maximum integration model Recommendation U.202 (03/93) 3 ITU-T RECMN*U.202 93 4862571 O574228 LTL = 4 Terminal adaptors The usual type of telex terminal model, connected on the ISDN, should be equipped with a terminal adaptor (TA), or an
38、 equivalent internal mechanism, which can provide the extra functions and conditions required as a result of connection to the ISDN. The interface between terminals and adaptors should be a national matter. The supply of telex terminals specially designed for connection to the ISDN should remain opt
39、ional, for decision at national level. PART II - USE OF THE B-CHANNEL OF THE ISDN IN CIRCUIT MODE FOR THE PROVISION OF THE INTERNATIONAL TELEX SERVICE 1 Minimum integration model The connection across the ISDN may be provided on a permanent, or semi-permanent basis, however, access to the telex netw
40、ork must be provided on a dedicated basis per subscriber. The B-Channel in circuit mode of the ISDN is used for the text transmission 2 Maximum integration model Where the Administration provides both a telex network and an ISDN, then the signalling system to be used between the interworking functio
41、n and the telex network is a national matter. However, it is recommended that signalling systems in accordance with CCIT Recommendation U. 1 1 or U. 12 be used. It is recommended that where an ISDN only is provided, then connection to telex networks of other Administrations should be in accordance w
42、ith CCITT U-Series Recommendations, preferably U. 1 1 or U. 12. Interconnection of ISDNs to support the telex service should be agreed bilaterally. The B-Channel circuit mode of the ISDN is used for the text transmission. The routing of the call through the ISDN is a national matter. 3 Call establis
43、hment sequences 3.1 Minimum integration model Where connection across the ISDN is provided on a permanent basis, the telex call establish sequences will take place on the B-Channel. Typical telex subscriber outgoing and incoming signal sequences should be in accordance with the examples given in Fig
44、ure 3 and Figure 4 respectively. The method of establishing the permanent connection across the ISDN is a national matter. Where connection across the ISDN is on a semi-permanent basis, typical telex subscriber outgoing and incoming signal sequences should be in accordance with Figures 3, and Figure
45、 4 respectively. The method of establishing the semi-permanent connection is a national matter, but the outgoing and incomig call establishment sequences may be in accordance with Figures 5 and 6 respectively. 4 Recommendation U.202 (03/93) ITU-T RECMN*U.202 93 W Y862591 0594229 038 F B AZ AZ ab: 10
46、0 ms CU CU-CFM PTS FIGURE 3N.202 Typicai telex subscribers outgoing signai sequence F B AZ AZ ab:2c- L - CU-CFM /PTS CCWRU I FIGURE 4N.202 Typicai telex subscribers incoming signal sequence Recommendation U.202 (03/93) 5 TO901 470-9Ud 05 Bchannel Path Establishmerit +- S$ids on Dchmnd Signals an B-c
47、harnel NOTE - in case of a permanent connection no ISDN signalling in the D-channel occurs. FIGURE 5N.202 Call establishment sequence in the direction d an JSDN to a telex network (minimum integratiai model) 6 Recommendation U.202 (03/93) ITU-T RECMN*UI202 93 = 4662591 0594233 796 CONNECT ACK CCWRU
48、CONNECT ACK -, _-.- CCSNJRU .I_ CCYWRU . -+ . 11 I AAB AAB AAB Data Data Transfer -.-. - Transfer - - .I Data Transfer I 7- i- CCWRU I . AAB Data Transfer . I ,111111. - - Telex EX B-channel Path Establishment +- Signals On D-ChanWl 4- Signals on Bchannel NOTE - In case of a permanent connection to
49、ISDN signalling in the D-channel occurs. FIGURE 6AJ.202 Cai1 establishment sequence in the direction of a telex network to an JSDN (minimum integration model) Recommendation U.202 (03/93) 7 ITU-T RECMN*U.202 93 H 4862593 0594232 622 3.2 Maximum integration model Where Administrations implement the maximum integration model, telex subscribers connected to the ISDN may communicate with other telex subscribers connected to the same ISDN and to telex subscribers connected to existing telex networks. Typical telex subscriber outgoing and incoming signai
