1、ITU-T RECMN*R=LL 93 W 4862591 0590826 155 INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU R.ll (03/93) TELEGRAPHY TELEGRAPH TRANSMISSION CALCULATION OF THE DEGREE OF DISTORTION OF A TELEGRAPHIE CIRCUIT IN TERMS OF THE DEGREES OF DISTORTION OF THE COMPONENT
2、 LINKS ITU-T Recommendation R.ll (Previously “CCITT Recommendation”) ITU-T RECMN*R.LL 93 = 4862591 0590827 O91 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, operat
3、ing 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, established the topics for study by the ITU-T Study Groups which, in their t
4、urn, produce Recommendations on these topics. ITU-T Recommendation R. 1 1 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 ceas
5、ed 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 Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector. In order not to delay publication of this Recommend
6、ation, 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 proper terminology related to the new ITU structure. 2 telecommunica
7、tion 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 utilized in any form or by any means, electronic or mechanical, i
8、ncluding photocopying and microfilm, without permission in writing from the ITU. Recommendation R.ll CALCULATION OF THE DEGREE OF DISTORTION OF A TELEGRAPH CIRCUIT IN TERMS OF THE DEGREES OF DISTORTION OF THE COMPONENT LINKS (New Delhi, 1960; amended at Geneva, 1964, 1980, at Melbourne, 1988 and at
9、Helsinki, 1993) 1 In general the isochronous standardized test distortion 6 (Definitions 33.07 and 33. i 2, Recommen- dation R. 140) of a telegraph circuit consisting of a number n of links in tandem lies between the arithmetic sum and the square root of the sum of the squares of the degrees of dist
10、ortion of the individual links, n being the number of links in tandem. The few exceptions to this rule that have been observed related to extremely long circuits (for example, four links, each of approximately 3500 km looped at voice-frequency at the distant end to give the equivalent of four links
11、each 7000 km go and return) and a total length of approximately 28 O00 km on cable and open- wire carrier telephone-type channels). 2 For such purposes as the planning of networks, the degree of distortion of a telegraph circuit consisting of n channels or links in tandem in the telex service (wher
12、e a great number of channels will be interconnected at random) is given fairly approximately by: 1 8inherent = c + n Similarly, for the combination of a transmitter and a telegraph circuit consisting of n channels or links in tandem in the telex service, the degree of distortion is given fairly appr
13、oximately by: where ?)inherent is the the probable degree of inherent start-stop distortion on standardized text. be, is the the probable degree of gross start-stop distortion in service. 6, s the the degree of characteristic start-stop distortion of a single channel or link. 6, is the the degree of
14、 synchronous start-stop distortion of the transmitter. 6, is the the degree of start-stop distortion due solely to the difference between the mean transmitter speed and the standardized speed. (The difference to be considered is equal to six times the mean difference for one element.) is the the deg
15、ree of asymmetrical (bias) distortion of one channel measured using 1:l or 2:2 signals (either i: 1 or 2:2 signais should be used according to which is normally employed for adjusting the channels). is the the degree of fortuitous distortion of one channel measured using i : 1 or 2:2 signals. $ias a
16、irreg 3 The values of distortion (except for 6,) inserted in the foregoing formulae must have the same probability of being exceeded ). The degree of characteristic distortion 6, of a channel is fairly constant for each type of voice- frequency channel and can be determined in laboratory tests. Neve
17、rtheless, the maximum degree of characteristic distortion is reached for only about 20% of the signals of International Telegraph Alphabet No. 2. Empirical values for 6, can be obtained with reasonable accuracy by using methods recommended by Recommendation R.4. Recommendation R.ll (03/93) 1 ITU-T A
18、ECMN*R-LL 93 4862593 0590827 964 4 formulae is 0.2 p. The probability of exceeding the degrees of distortion 6inbmnt and hext calculated with the aid of the above 5 The addition of distortion in tandem connected code-independent time-division multiplex systems will differ for non-synchronized and sy
19、nchronized systems. In the case of non-synchronized tandem connected systems the arithmetic addition of the maximum distortion of ail systems can occur. NOTE -The probability of occurrence of distortion and the duration of measurement to be assumed will differ in each case and requires further study
20、 In the case of synchronized systems, the total sampling distortion of all tandem connected systems will by the distortion due to the first system only. 2 Recommendation R.ll (03/93) ITU-T RECMN*R-LL 93 4862591 0590830 b8b = asymmetrical (bias) distortion, 1 CALCULATION OF THE DEGREE OF DISTORTION
21、OF A TELEGRAPH CIRCUIT INTERMS OF THE DEGREES OF DISTORTION OF THE COMPONENT LINKS, 1 characteristic start-stop distortion, 1 degree of distortion of a telegraph circuit, 1 fortuitous distortion, 1 gross start-stop distortion, 1 inherent start-stop distortion, 1 isochronous standardized test distortion, 1 synchronous start-stop distortion, 1 Recommendation R.ll (03/93) 3
