1、ITU-T RECNN*N*302O 73 m 4862573 0572372 IT3 INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU MAINTENANCE: INTERNATIONAL LEASED CIRCUITS M.1020 (03/93) CHARACTERISTICS OF SPECIAL QUALITY INTERNATIONAL LEASED CIRCUITS WITH SPECIAL BANDWIDTH CONDITIONING ITU-T
2、 Recommendation M.1020 (Previously “CCITT Recommendation”) ITU-T RECMN*MLOZO 73 = 486257L 0572373 03T = FOREWORD The 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 ta
3、riff 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 -T Study Groups which, in their turn, produce
4、Recommendations on these topics. ITU-T Recommendation M.1020 was revised by the ITU-T Study Group IV (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 a
5、s 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 Similarly, in this reform process, the CCJR and the IFRB have been replaced by the Radiocommunication Sector. In order not to delay publication of this Recommendation, no cha
6、nge has been made in the text to references containing the acronyms “CC, CCJR 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 administrat
7、ion 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 photoco
8、pying and microfilm, without permission in writing from the ITU. ITU-T RECMN*M*1020 73 4862593 0592374 T76 CONTENTS 1 Scope 2 Characteristics 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 2.1 1 2.12 2.13 Nominal overall loss . Loss/frequency distortion . Group-delay distortion Variation of overall loss w
9、ith time . Random circuit noise Phase jitter Impulsive noise . Total distortion (including quantizing distortion) . Single tone interference Frequency eTTor . Harmonic and intermodulation distortion . Crosstalk . Power source interferences . Annex A . Noise and distortion A.l Random circuit noise A.
10、2 Total distortion References . Recommendation M.1020 (03/93) Page 1 1 1 1 1 3 3 3 3 3 3 3 4 4 4 4 4 5 5 1 ABSTRACT This Recommendation provides the characteristic of a circuit, especially applicable for use by modems without equalizer, for data transmission rates higher than those normally achievab
11、le on telephone-type circuits. KEYWORDS Characteristics, leased circuits, special bandwidth conditioning. Il Recommendation M.1020 (03/93) Recommendation M.1020 CHARACTERISTICS OF SPECIAL QUALITY INTERNATIONAL LEASED CIRCUITS WITH SPECIAL BANDWIDTH CONDITIONING (Published in 1980; revised in 1984, 1
12、988 and 1993) 1 Scope This Recommendation deals with leased circuits for uses other than telephony - for example, data transmission. The requirements of this Recommendation are intended to ensure the provision of a circuit which will meet the requirements of digital transmission rates higher than th
13、ose possible on a normal telephone-type circuit. In particular. circuits meeting the requirements of this Recommendation are intended for use with modems that do not contain equalizers. 2 Characteristics?) 2.1 Nominal overall loss Because of the differing nominal level at renters premises due to the
14、 various national practices, it is not normally possible to predict the nominal overall loss of the circuit at the reference frequency. Only exceptionally can a predetermined specified nominal overall loss at the reference frequency between renters installations be offered to renters and then only a
15、fter prior consultation among the Administrations concerned. For 4-wire circuits the value of the receiving relative level at the renters premises should not be lower than -13 dBr. For circuits intended to be used for data transmission using modems to V-Series Recommendations, higher receiving relat
16、ive levels may be required in some circumstances. Reference should be made to Supplement No. 2.16, Blue Book, Volume IV (Fascicle IV.3). It should be noted that the overall loss in each direction of transmission may not have the same value. 2.2 Losdfrequency distortion The limits for the overall los
17、s relative to that at 1020 Hz for the circuit between renters installations are given in Figure 1. 2.3 Group-delay distortion The limits that apply to group-delay distortion are given in Figure 2 in which the limiting values over the frequency band are expressed as values relative to the minimum mea
18、sured group delay. _._ . I) Thc applic.:iticwi O! this Recommendation to multiterminal leased circuits is intended only for radial networks in which these spccilc;itroii arc to he met between a designated central station and each of the outlying stations. It does not apply to multitri-miriai cwii cr
19、cncc networks between any two stations. Additioii;ill. thc characteristics and limits for short intemptions in transmission and phase hits are under study for inclusion in this Rcc.ctiiiiiriilatinn It may be noted that clause 6/M, 1060 1 1 J gives provisional limits for short intemptions in transmis
20、sion and phase as guidance for fault finding purposes. Recommendation M.1020 (03/93) 1 ITU-T RECMN*M-1020 93 I 4Bb2591 0592397 785 = O 300500 1020 2800 3ooo Hz T040498WdOl NOTES 1 2 Below 300 Hz and above 3000 Hz the loss shall not be less than 0.0 dB but is otherwise unspecified. 1020 Hz is the ref
21、erence test frequency as explained in Recommendation 0.6 9. FIGURE 1iM.1020 Limits for overall lm of the arcuit relative to that at 1020 Hz “O 500 600 1000 2000, 2600 2800 M Frequency TWO4890-Wdo2 FIGURE uM.1020 Lids for grmp delay relative to the minimum meanrd group delay in tbe 500-2800 Hz band 2
22、 Recommendation M.1OU) (0-3) ITU-T RECMN*M-1020 93 4862571 0592398 611 2.4 Variation of overall loss with time 2.4.1 Amplitude hits Where the circuit is to be used for data transmission using modems employing amplitude modulation techniques, for example, modems to Recommendation V.29 l, amplitude hi
23、ts may result in data errors. Using an instrument complying with Recommendation 0.95 2, the number of amplitude hits greater than f 2 dl3 should not exceed 10 in any 15 minute measuring period. The value of f 2 dB and the number of amplitude hits are provisional and subject to further study. 2.4.2 O
24、ther variations For all circuits, variations with time of the overall loss at 1020 Hz (including daily and seasonal variations but excluding amplitude hits) should be as small as possible but should not exceed f 4 dB. 2.5 Random circuit noise The level of the psophometric noise power at a renters pr
25、emises depends upon the actual constitution of the circuit, in particular upon the length of circuit of frequency division multiplex carrier systems in the circuit. The provisional limit for leased circuits of distances greater than loo00 kilometres is -38 dBmOp. However, circuits of shorter length
26、will have substantially less random noise (see also Annex A and 3.5/M.1050 lo). 2.6 Impulsive noise Impulsive noise should be measured with an instrument complying with Recommendation 0.71 3. As a provisional limit, the number of impulsive noise peaks exceeding -21 dBmO should not be more than 18 in
27、 15 minutes. 2.7 Phase jitter The value of phase jitter measured at a renters premises depends upon the actual constitution of the circuit (for example, upon the number of modulation equipments involved). It is expected that any measurement of phase jitter using an instrument complying with Recommen
28、dation 0.91 4 will not normally exceed 10“ peak-to-peak. However, for circuits of necessarily complex constitution and where 10“ peak-to-peak cannot be met, a limit of up to 15“ peak-to-peak is permitted. The limits for low frequency phase jitter are under study. 2.8 Total distortion (including quan
29、tizing distortion) On a mixed analoguddigital circuit, the signal will be accompanied by quantizing distortion. An end-to-end distortion measurement made using an instrument conforming to Recommendation O. 132 5 will include contributions from random circuit noise, single tone interference and harmo
30、nic distortion. The level of random noise power at the renters premises depends upon the length of circuit of frequency division multiplex carrier systems. The level of quantizing distortion power depends on the number of unintegrated digital processes in the circuit. The signal-to-total-distortion
31、ratio should be better than 28 dB using a sine wave signal at -10 dBmO (see also Annex A). 2.9 Single tone interference The level of single tone interference in the band 300-3400 Hz shall not exceed a value which is 3 dB below the circuit noise objective indicated in Figure A. 1. 2.10 Frequency erro
32、r The frequency error introduced by the circuit must not exceed f 5 Hz. It is expected that in practice the error will be within closer limits than these. Recommendation M.1020 (03/93) 3 4862593 0592339 211 = 2.11 Harmonic and intermodulation distortion When a 700 Hz test frequency of -13 dBmO is in
33、jected at the transmit end of a point-to-point circuit, the level of any individual harmonic frequency at the receiving end shall provisionally be at least 25 dB below the received level of the fundamental frequency. When intermodulation products are measured using an instrument complying with Recom
34、mendation 0.42 at a four-frequency signai of the total level -13 dBmO the second and third order products at the receiving end shall be at least 25 and 26 dB below the received four-frequency signal respectively 8. These values are provisional and are for further study. 2.12 Crosstalk Crosstalk atte
35、nuation at the near end (between forward and reverse transmission direction of a leased circuit) should not be less than 43 dB. Crosstalk attentuation between different circuits (between leased circuits and between a leased and any other telephone-type circuit) should not be less than 58 dB. 2.13 Po
36、wer source interferences When a sine wave signal is transmitted over the circuit at a OdBmO, each side component level should not exceed 45 dBmO. Annex A Noise and distortion (This annex forms an integral part of this Recommendation) A.l Random circuit noise Figure A.l displays random noise versus l
37、ength of circuit of FDM carrier systems and is presented as a guide to the random noise performance which may be found on an international leased circuit. dBm0p km Length of circuit of FDM carrier systems TO405000-94/dO3 FIGURE A. 1 /M. 1020 Random circuit-noise performance 4 Recommendation M.1020 (
38、03193) NOTE - At the present time the section of the circuit provided by a satellite (between earth stations) employing FDM techniques contributes approximately 1OooO pWOp (-50 dBmOp) of noise. Therefore, for the purpose of determining maintenance limits for noise measurement on leased circuits, the
39、 length of this section may be considered to be equivalent to lo00 km in Figure A. 1. Type of circuit Analogue Composite circuit The contribution to noise of a circuit section provided by a satellite employing TDM technique remains as a subject for further study. Distance in analogue transmission (k
40、m) 641 1601 2501 5001 10001 to to to to to to 640 1600 2500 5000 IOOOO 20000 NumberofQDUs Unit 320 321 (Note) O dB 43 41 38 36 33 30 28 1 dB 34 34 33 32 31 29 28 2 dB 32 31 31 31 29 28 28 3 dB 30 30 30 29 28 28 28 4 dB 29 29 28 28 28 28 28 5 dB 28 28 28 28 28 28 28 A.2 Total distortion Table A.l is
41、a guide to the signal-to-total distortion ratio which may be found on circuits with different analogue section lengths and numbers of quantizing distortion units (QDU). When interpreting this table, particularly for circuits with long analogue sections, it should be noted that it may be possible to
42、increase the number of QDUs in a circuit provided the analogue sections contribute less noise than might be expected from Figure A.l. TABLE A.lM.1020 Signal-to-total distortion ratio using a sinusoidal signal at -10 dBmO References CCITT Recommendation 9600 bir/s modem standardized for use on point-
43、to-point 4-wire leased telephone-type circuits, Rec. V.29. CCITT Recommendation Phase and amplitude hit counters for telephone-type circuits, Rec. 0.95. CCITT Recommendation Impulsive noise measuring equipment for telephone-type circuits, Rec. 0.7 1. CCITT Recommendation Phase jitter measuring equip
44、ment for telephone circuits, Rec. 0.9 1. CCITT Recommendation Quantizing distoflion measuring equipment using a sinusoidal test signal, Rec. O. 132. Recommendation M.1020 (03/93) 5 4862591 0592141 9T W 6 J CC Recommendation Equipment to measure non-linear distortion using the 4-tone intermodulation
45、method, Rec. 0.42. CC Recommendation Transmission impairments. Rec. G. 1 13. Transmission Systems for communications (revised third edition) by members of the technical stafs, Bell Telephone Laboratories - Chapter 8: Modulation distortion in AM systems; Formulae: (8-1 8) and (8-20). CCIT Recommendat
46、ion 1020 Hz reference test frequency, Rec. 0.6. CCIT Recommendation Lining up an international point-to-paint leased circuit, M. 1050. CCITT Recommendation Maintenance of international leased circuits, M. 1060. 7 8 9 101 1 1 6 Recommendation M.1020 (03193) LiBb25L 0592142 806 Printed in Switzerland Geneva, 1994
