ITU-T U 203-1993 Technical Requirements to be Met When Providing Real-Time Bothway Communications between Terminals of the International Telex Service and Data Terminal Equipments ing .pdf

1、1TU-T RECMN*U*203 73 4862593 0590074 650 U INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU TELEGRAPH SWITCHING INTERNATIONAL TELEX SERVICE U.203 (03/93) TECHNICAL REQUIREMENTS TO BE MET COMMUNICATIONS BETWEEN TERMINALS OF THE INTERNATIONAL TELEX SERVICE AN

2、D DATA TERMINAL EQUIPMENTS ON A PSPDN OR VIA THE PSTN WHEN PROVIDING REAL-TIME BOTHWAY ITU-T Recommendation U.203 (Previously “CCITT Recommendation”) ITU-T RECMN*U-203 93 4862593 0590075 577 m FOREWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International

3、 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 telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four

4、years, established the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. ITU-T Recommendation U.203 was prepared 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 re

5、form 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 (ITU-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRE3 have been replaced b

6、y 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 IFRB” or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation w

7、ill contain the proper terminology related to the new IT structure. 2 telecommunication administration and a recognized operating agency. In this Recommendation, the expression “Administration” is used for conciseness to indicate both a O IT 1994 All rights reserved. No part of this publication may

8、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. CONTENTS Introduction 1.1 Scope 1.2 1.3 Functions of the TPIWF . 1.4 Methods of interworking and addressable terminals 2.1 Considering .

9、Access from the telex network to the PSPDN 3.1 One-stage selection . 3.2 Two-stage selection 3.3 Data transfer phase - Packet forwarding conditions . Access from the PSPDN to the telex network 4.1 Call establishment . 4.2 Text transfer phase 4.3 Reaction of TPIWF to data packets with M-bit set . 4.4

10、 Setting of PSPDN PAD parameters by TPIWF WRU and answerback processing 5.1 Call established from the telex network to the PSPDN 5.2 Call established from PSPDN to the telex network Clearing procedures . 6.1 Clearing initiated within the PSPDN 6.2 Clearing initiated within the telex network . Ineffe

11、ctive call attempts . 7.1 General 7.2 Ineffective calls within the telex network . 7.3 Ineffective calls within the PSPDN TPIWF PAD parameters Abnormal conditions 9.1 Telex-to-PSPDN direction 9.2 PSPDN-to-telex direction . 9.3 Flow control of the teleprinter i . 9.4 Detection of signals on the backw

12、ard path during forward transmission - Counterwriting . Outline of operational principles Special provisions for the use of PAD service signals within the international telex service Appendix I . Handling of clearing procedures by TPIWF . 1.1 General . 1.2 Clearing initiated by PSPDN 1.3 Clearing in

13、itiated from the telex network . Appendix II - Reaction by the TPIWF to ineffective call attempts within the telex network . 11.1 General II.2 Ineffective calls within the telex network . Recommendation U.203 (03/93) Page 2 2 2 3 4 4 4 5 5 7 10 10 10 12 12 12 12 12 13 14 14 14 14 14 15 15 15 15 15 1

14、8 18 18 19 19 19 19 22 22 22 1 Recommendation U.203 TECHNICAL REQUIREMENTS TO BE MET WHEN PROVIDING OF THE INTERNATIONAL TELEX SERVICE AND DATA TERMINAL EQUIPMENTS ON A PSPDN OR VIA THE PSTN REAL-TIME BOTHWAY COMMUNICATIONS BETWEEN TERMINALS (Helsinki, 1993) The CCITT, considering (a) the increasing

15、 number of data terminal equipments (DTEs) connected to public data networks; (b) the world-wide availability of the international telex service; (c) communicate with DTEs and vice-versa; the desirability of providing an appropriate mechanism whereby terminals of the international telex service can

16、(d) Recommendaiton F.69 gives the pian for telex destination codes; that Recommendation F.60 gives the operational provisions for the international telex service and (e) that Recommendation F.59 lists the essential characteristics of the international telex service; (f) international telex service a

17、nd other services; that Recommendation F.80 defines the basic requirements to be met for interworking relations between the (g) DTEs on a packet-switched public data network; that Recommendation F.83 defines the operational principies for communication between telex terminals and (h) that the U-Seri

18、es Recommendations define the technical aspects of the telex service; (i) that the classes of services, facilities and interfaces for data communication networks are defined in the relevant X-Series Recommendations, in particular, X.3, X.28, and X.29, defining the PAD function provided by a PSPDN, a

19、nd X.25 defining the interface between a packet-mode DTE and PSPDN; ti) that Recommedation X. 121 defines the international numbering pian for public data networks, unanimously deciares the view that the mechanisms to be provided to facilitate communication between telex terminals and data terminal

20、equipments (DTEs) connected to a packet-switched public data network should be in accordance with this Recommendation. Definitions The following terms used in this Recommendation have the undermentioned definitions: telex-packet interworking function (TPIWF): The Telex-Packet Interworking Function (

21、TPIWF) is a functional unit which implements the requirement to allow bothway communication between telex terminals and packet-mode and character-mode data terminal equipments directly connected to a packet-switched public data network (PSPDN) or any identified DTE accessing the PSPDN in accordance

22、with Recommendation X.28 or X.32. The method of implementation of any of the TPIW functions in any physical unit is a national matter. The functions of the TPIWF do not apply to interworking between telex and Telematic terminais, being the subject of other Recommendations. Recommendation U.203 (03/9

23、3) 1 ITU-T RECMN*U-203 93 m 4862573 0590078 2Tb W TPIWF answerback In the case of two-stage selection from the telex subscriber, the answerback which is returned in the first stage of selection and which uniquely identifies the destination TPIWF to the telex network. registered DTE: In the case of o

24、ne-stage selection, a DTE which has registered with the TPIWF for the initiation and reception of telex calls and which is assigned a telex number that is part of the telex national numbering plan for this purpose. DTE answerback: In the case of one-stage selection, the answerback that is always ret

25、urned to the telex network in response to a WRU signal and which uniquely identifies the registered DTE to the telex network. DTE identification: In the case of two-stage selection, this is the DTE recall address. real-time communication: The immediate transfer of information from a terminal connect

26、ed to one network to a terminal connected to the other network subject only to the normal transmission delays and those imposed by the packetizing/depacketizing processes. Abbreviations DTE Data Terminal Equipment FAXIWF Facsimile Interworking Function PAD Packet Assembler-Disassembler PSPDN Packet-

27、Switched Public Data Network PSTN Public-Switched Telephone Network SFU Store-and-Forward Unit TAED Telex Automatic Emitting Device 1 Introduction 1.1 Scope The procedures defined in this Recommendation enable telex subscribers to communicate with both packet-mode and character-mode data terminal eq

28、uipments (DTEs) connected to a packet-switched public data network (PSPDN). Conversely, users of packet-mode and character-mode DTEs as well as character-mode DTEs accessing a PSPDN via the Public-Switched Telephone Network (PSTN), may communicate with telex subscribers. 1.2 Outline of operational p

29、rinciples 1.2.1 Recommendation F.83. The operational procedures and full range of facilities available by this mode of interworking are described in 1.2.2 capability shall be possible. 1.2.3 (TPIWF). The method of implementation of the TPIWF in any physical unit is a national matter. 1.2.4 network a

30、nd a packet-mode DTE which supports X.29 procedures to the PSPDN. Interworking shall be in real-time and support interactive communication, i.e. dialogue or conversational Interworking capability shall be established by the provision of a Teleflacket Interworking Function At all stages of call Set-u

31、p and subsequent connection, the TPIWF shall emulate a telex terminal to the telex 1.2.5 In both the telex-to-PSPDN and PSPDN-to-telex directions, the point of interworking between the two networks shall be in the same country as the PSPDN, and therefore the international connection shall be via the

32、 telex network, as shown in Figure 1. 1.2.6 choice is a national matter and shall be at the discretion of the Administration operating the TPIWF. In the telex-to-PSPDN direction, both one-stage and two-stage selection procedures may be employed. The 2 Recommendation U.203 (03/93) ITU-T RECMN*U=203 9

33、3 4862571 0590079 132 1.2.7 This Recommendation does not apply to Telematic services that may be defined within other F-, T- and U-Series Recommendations. For example, interworking between telex terminals and DTEs connected to a PSPDN and which implement either Teletex or MHS protocols are defined i

34、n Recommendations U.201 and U.204 respectively. 1.2.8 This Recommendation does not make provision for a telex subscriber accessing a TPIWF to transit the associated PSPDN in order to access a DTE connected to another PSPDN situated in another country. This is left for further study. 1.2.9 to a telex

35、 subscriber in a third country is left for further study. Similarly, access to the TPIWF from a DTE connected to a foreign PSPDN in order to establish a connection 1.2.10 Access from a telex SFLJ to a two-stage TPIWF is left for further study. International Boundary Country 6 Ccunty A I I Netwxk I T

36、elex Terminal X 25 I DTE I I i I X 28 DTE I PSPDN Telex Network Telex : ! I I I I I 4 I I (/n X 28 netwak or X.32 DTE i i Intermatimal TdexSerUce )i TD9005109(YdOl FIGURE 1KJ.203 Basic model for interworking between telex terminals and DTEs connected to a PSPDN 1.3 Functions of the TPIWF The TPIWF s

37、hall be responsible for the following functions: - translation between telex signalling events and call progress signals within the PSPDN; - receipt of characters from the telex network, and following conversion, packetizing them for forward transmission to the PSPDN; - receipt of data packets from

38、the PSPDN, depacketizing and converting the data for transmission as start- stop characters to the telex network; - code conversion in accordance with Recommendation S. 18, ensuring that the appropriate shift condition is maintained on the telex side: - handling of WRU signals, answerbacks, ENQ and

39、ACK characters; - handling of received data packets with M-bit set; Recommendation U.203 (03/93) 3 - translation of received telex service signals into clearing cause codes and diagnostic codes for forwarding to the PSPDN; - - - - - - translation of received PSPDN clearing cause codes and diagnostic

40、 codes into telex service signals; handling of characters received on the backward path while forward transmission is in progress; processing of clearing signals from either network; packetizing in accordance with the prescribed conditions; relevant X.3, X.28 and X.29 procedures; predefined response

41、 to abnormal conditions. 1.4 Special provisions for the use of PAD service signais within the international telex service To preserve the essential characteristics of the international telex service as detailed in Recommendation F.59, the use of service signals on the telex side of the TPIWF shall b

42、e in accordance with Recommendation F.60 and formatted in accordance with Recommendation U. 1. However, the use of PAD service signais in accordance with Recommendation X.28 is acceptable where they can be accomodated within the additional characters allowed in Recommendation U. 1. Recommendation X.

43、28 PAD service signals suitable for conversion are left for further study. Exceptionally, the call connected PAD service signal and the incoming call PAD service signal is acceptable in the particular cases of a two-stage call from a telex subscriber and a call from the PSPDN to the international te

44、lex network respectively, (see Figure 3 and Figure 5). 2 Methods of interworking and addressable terminais 2.1 Considering a) that Recommendation X.121 allows the use of up to 11 digits in the PSPDN Network Terminai NumberAVational Number; b) c) that Data Network Identification Codes defined in Reco

45、mmendation X.121 consist of four digits; that signalling on telex trunks operating in accordance with Recommendations U.ll or U.12 allow a maximum of 12 digits to be forwarded, then the following methods of accessing the TPIWF from the telex network may be employed, viz: I) interworking with one-sta

46、ge selection; 2) interworking with two-stage selection. 2.2 X-Series Recommendations. The method of accessing the TPIWF across the PSPDN from any DTE shall be in accordance with the relevant 2.3 The following DTE types may initiate calls via the TPIWF into the telex network: - packet-mode DTEs conne

47、cted to a PSPDN by dedicated circuit in accordance with Recommendations X.25 and X.29; - - packet-mode DTEs accessing the PSPDN in accordance with Recommendation X.32; character-mode DTEs connected to a PSPDN by dedicated circuit in accordance with Recommen- dation X.28; - character-mode DTEs access

48、ing a PSPDN across the PSTN in accordance with Recommendation X.28; These possibilities are shown in Figure 1. 4 Recommendation U.23 (03/93) ITU-T RECMN*U*203 93 4862591 0590083 890 2.4 Because of addressing requirements within the PSPDN, only the following DTEs may receive telex calls: - packet-mod

49、e DTEs connected to a PSPDN by dedicated circuit in accordance with Recommendations X.25 and X.29; packet-mode DTEs accessing the PSPDN in accordance with Recommendation X.32; character-mode DTEs Connected to a PSPDN by dedicated circuit in accordance with Recommendation X.28; character-mode DTEs accessing a PSPDN across the PSTN in conformance with Recommendation X.28, this case being for further study. delivery of telex messages to an X.28 dial-up DTE using a store-and-retreive method (Le. an X.28 DTE accessing the PSPDN across the PSTN) is defined in Recommendation U.205. - - - - 2.