1、ITU-T RECMN*U*ZLO 93 qBb259L 0584358 9LL INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU TELEGRAPH SWITCHING INTERNATIONAL TELEX SERVICE u.21 o (03/93) INTEX SERVICE NETWORK REQUIREMENTS TO EFFECT INTERWORKING WITH THE INTERNATIONAL TELEX SERVICE ITU-T Rec
2、ommendation U.21 O (Previously “CCITT Recommendation”) ITU-T RECflN*U.ZLO 93 48b257L 0584357 858 D FOREWORD The ITU Telecommunication Standardization Sector (JTU-T) is a permanent organ of the International Telecom- munication Union. The ITU-T is responsible for studying technical, operating and tar
3、iff 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, established the topics for study by the JTU-T Study Groups which, in their turn, produc
4、e Recommendations on these topics. ITU-T Recommendation U.210 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 reform process within the International Telecommunication Union (ITU), the CCITT ceased to exist
5、 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 Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector. In order not to delay publication of this Recommendation, no c
6、hange has been made in the text to references containing the acronyms “CCITT, CCIR or JFRB” 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 admini
7、stration 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 utilized in any form or by any means, electronic or mechanical, including ph
8、otocopying and microfilm, without permission in writing from the ITU. ITU-T RECMN*U=23O 73 4862593 0584360 57T M CONTENTS Page 1 Recommendation U.210 . Type 1 network requirements to effect interworking with the international telex service 1.1 1.2 Code conversion . 1.3 Recommendation U.210 - Type 2
9、network requirements to effect interworking with the international telex service 2.1 Recommendation U.210 - Interworking between type 1 and type 2 networks Cai1 Routing and establishment Speed conversion and flow control . 2 Call Routing and establishment 3 3 3 4 Recommendation U.210 (03/93) i ITU-T
10、 RECMN*U-ZLO 93 4862571 05843bl 40b Recommendation U.210 INTEX SERVICE NETWORK REQUIREMENTS TO EFFECT INTERWORKING WITH THE INTERNATIONAL TELEX SERVICE (Helsinki, 1993) The CCITT. considering (a) that new networks are being introduced based upon stored program control techniques; (b) that these netw
11、orks as well as being able to carry the intemational telex service, can also carry the Intex service using alphabets other than International Telegraph Alphabet No. 2 and that interworking between these services is essential; (cl that the equipment provided for these networks supports an enhanced ra
12、nge or facilities but that for speed and ease of introduction of the Intex service some Administrations may wish not to offer these enhanced facilities at the outset: (4 that Intex and similar services require the establishment of new types of signalling, and that these signalling types shall permit
13、 interworking between Intex terminals, between Telex terminals and Intex, and between Telex terminals and terminals capable of operating both Telex and Intex dual service: (e) that Recommendation S.33 defines the alphabet and presentation characteristics for Intex; (0 telex service; that Recommendat
14、ion S.34 describes Intex terminal requirements to effect interworking with the international (g) that Recommendation S.35 defines the coding of answerbacks for Intex service; (h) that Recommendation F. 150 defines the operational and service requirements of the Intex service; (i) Intex service and t
15、he international telex service; that Recommendation F.82 defines the operational and service requirements for interworking between the ci) that a prompt response to the WRUENQ request is required when interworking between Intex and Telex, NOTE - The development in the future of services similar to I
16、ntex may occur. It may be possible that some of the provisions of this Recommendation should be applied to such services. unanimously declares the view, (1) services and the intemational telex service; that there are two means (type 1 and type 2) whereby networks can provide interworking between Int
17、ex (2) within the network. type 1 network operation is described in clause 1; in type 1 network operation interworking is effected by the provision of speed and code conversion facilities (3) in type 2 network operation interworking is effected by the dynamic changing of the baud rate and code struc
18、ture of all switching centres and circuits involved in a call after call establishment, or by automatic call reselection. If dynamic changing is involved then the network may have to be speed and code independent. type 2 network operation is described in clause 2; (4) clause 3 describes the establis
19、hment of calls between type 1 and type 2 networks. Recommendation U.210 (03/93) 1 ITU-T RECMN*U.ZLO 93 48b259L 0584362 342 = 1 1.1 1.1. Recommendation U.210 - Type 1 network requirements to effect interworking with the international telex service Call Routing and establishment Calls originating from
20、 Intex or similar terminals shall normally be routed over circuits operating at the same speed as the calling terminal until received at the switching centre from which the called terminal is served. This terminating switching centre will know if the called destination is a customer of the internati
21、onal telex service. Calls from Intex terminals may be routed to intemational telex trunk circuits at an originating or transit switching centre if that switching centre is able to determine that the called destination is a customer of the international telex service from, for example, examination of
22、 the selection received. 1.1.2 On calls incoming from a type E trunk, which are successfully routed to the international telex service (either directly to a telex customer line or via an international telex trunk circuit), the switching centre making the connection to the telex service shall transmi
23、t call progress signal 91 to the calling type E circuit during call establishment as detailed in 1AJ.101. 1.1.3 On calls incoming from a type F trunk, which are successfully routed to the international telex service (either directly to a telex customer line or via an international telex trunk circui
24、t), the switching centre making the connection to the telex service shall transmit to the type F circuit a call connected signal which indicates connection to telex during call establishment as detailed in 2AJ.101. 1.1.4 Indicator sequence (as detailed in Recommendation U.101) if either: On calls in
25、coming from Intex customer lines, the originating switching centre shall not transmit a Speed a) the call is routed directly to a telex customer line or trunk circuit; or b) call progress signal 91 is received over a type E circuit from a subsequent switching centre during call establishment; or c)
26、the call connected signal received over a type F circuit indicates connection to the international telex service. 1.1.5 terminating on Intex customer lines. No Speed Indicator sequence shall be transmitted on calls incoming from the international telex service and 1.2 Code conversion 1.2.1 telex ser
27、vice, or vice-versa, shall provide code conversion facilities for the duration of the call. A switching centre which effects connection from an Intex circuit (customer line or trunk) to the international 1.2.2 Conversion between IA5 and ITA2 and between ITA2 and IA5 shall be as detailed in Recommend
28、ation S.18 with the exception that characters from IA5 Columns O and 1 should be entirely non-printing and that IA5 characters 1/14 and 1/15 convert to ITA2 combinations 29 and 30 in figures mode (L/S and FE) respectively. Similarly, in the reverse direction LIS and F/S convert to IA5 combinations 1
29、/14 and 1/15. 1.2.3 Any characters found to be in error shall be translated as ITA2 character 2 in figures shift (?). When converting from IA5 to ITA2, a switching centre shall check each received character for parity errors. 1.2.4 When converting from IA5 to ITA2, a switching centre shall ensure th
30、at each ITA2 character has been preceded by the appropriate shift character. A shift character shall only be inserted when a change of case is required. The switching centre shall ensure that both the forward and backward signalling paths of the international circuit are maintained in the same shift
31、. 1.2.5 The responsibility for ensuring line length compatibility with the international telex service rests with the Intex terminal (see Recommendation S.34). The network does not therefore need to monitor the number of printing or spacing characters forwarded to the international circuit between l
32、ine feed sequences. The network shall not introduce any line feed sequences. 2 Recommendation U.210 (03/93) 1.3 Speed conversion and flow control Calls from Intex terminals may be routed to international telex trunk circuits at an originating or transit switching centre if that switching centre is a
33、ble to determine that the called destination is a customer of the international telex service I from, for example, examination of the selection received. 1.3.1 telex service, or vice-versa, shall be known for the purposes of this Recommendation as the conversion centre. A switching centre which effe
34、cts connection from an Intex circuit (customer line or trunk) to the international 1.3.2 the call. The conversion centre shall provide speed conversion and character flow control facilities for the duration of 1.3.3 The Intex terminal is required to lower the rate at which it transmits characters to
35、 that of the international telex service (as detailed in Recommendation S.34). However, to allow for the insertion of shift characters the conversion centre shall provide a small buffer store for characters requiring conversion, and shall operate flow control procedures with the Intex terminal. 1.3.
36、4 When the buffer contains more characters than Threshold 1 awaiting transmission to the telex circuit, the conversion centre shall transmit an X-OFF character (IA5 character 1/3) to the Intex circuit. If the buffer continues to fill, additional X-OFF characters shall be transmitted to the Intex cir
37、cuit when other thresholds are exceeded. The conversion centre shall not rely upon a single generation of the X-OFF character (at Threshold 1) to achieve flow control because of the possibility of corruption of this character before reception by the Intex terminal. 1.3.5 The conversion centre shall
38、continue to transmit the contents of the buffer to the international telex circuit. 1.3.6 both the international telex and Intex circuits. If the number of characters in the buffer reaches Threshold 2 the conversion centre shall immediately clear 1.3.7 After transmission of one or more X-OFF charact
39、ers, the conversion centre shall transmit an X-ON character (IA5 character l/i) to the Intex circuit when the number of characters in the buffer awaiting transmission to the international telex circuit has fallen below Threshold 3. 1.3.8 If, after transmission of an X-ON character, no further charac
40、ters are received from the Intex circuit the conversion centre shall transmit further X-ON characters at frequent intervals until a character is received from the Intex circuit, or until a clearing signal is received from either the international telex or tntex circuits. The conversion centre shall
41、not rely upon a single generation of the X-ON character (at Threshold 3) to achieve flow control because of the possibility of corruption of this character before reception by the Intex terminal. 1.3.9 The choice of values for Thresholds 1, 2 and 3 is a matter for individual Administrations to deter
42、mine in conjunction with the designers of switching equipment. However, in order that the delay from transmission of an ENQ signal from an Intex terminal and reception of the consequent answerback is kept within acceptable limits Threshold 2 shall not exceed 50 characters. Furthermore, to allow for
43、propagation and switching delays, plus the response time of an tntex terminai to a received X-OFF character, the interval between Thresholds 1 and 2 shall not be less than 25 characters. 2 Recommendation U.210 - Type 2 network requirements to effect interworking with the international telex service
44、2.1 Cail Routing and establishment 2.1.2 On calls incoming from a type E trunk, which are successfully routed to the international telex service (either directly to a telex customer line or via an international telex trunk circuit), the switching centre making the connection to the telex service sha
45、ll transmit call progress signal 91 to the calling type E circuit during call establishment as detailed in 1AJ.101. Recommendation U.210 (03/93) 3 ITU-T RECMN*U=2LO 93 D 4862591 0584364 115 m 2.1.3 On calls incoming from a type F trunk, which are successfully routed to the international telex servic
46、e (either directly to a telex customer line or via an international telex trunk circuit), the switching centre making the connection to the telex service shall transmit to the type F circuit a call connected signal which indicates connection to the international telex service during call establishme
47、nt as detailed in 2AJ.101. 2.1.4 signal signifying connection to the international telex service (as detailed in Recommendation U. 101) if either: On calls incoming from Intex customer lines the originating switching centre shall transmit a Telex Indictor a) the call is routed directly to the intern
48、ational telex service (via a customer line or trunk circuit); or b) call progress signal 91 is received over a type E circuit from a subsequent switching centre during call establishment; or c) the call connected signal received over a type F circuit indicates connection to the international telex s
49、ervice. The Telex Indicator signal shall be transmitted by the originating switching centre to the calling Intex customer line. This transmission shall be after reception of a call connected signal from the called circuit and before transmission of a WRU signal to the called circuit. 2.1.5 Within 33
50、 milliseconds from the transmission of the Telex Indicator signal the originating switching centre shall ensure that both the calling and called circuits are conditioned to receive and transmit ITA2 characters at a nominal modulation rate of international. 2.1.6 Terminating and transit switching cen
