1、ITU-T RECMN*M.1025 93 I 4862591 0592397 558 INTERNATIONAL TELECOMMUN CATION UN ION ITU=T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU MAINTENANCE: INTERNATIONAL LEASED CIRCUITS M.1025 (03/93) CHARACTERISTICS OF SPECIAL QUALITY INTERNATIONAL LEASED CIRCUITS WITH BASIC BANDWIDTH CONDITIONING ITU-T
2、Recommendation M.1025 (Previously “CCITT Recommendation“) FOREWORD The ITU Telecommunication Standardization Sector (-T) is a permanent organ of the International Telecom- munication Union. The -T is responsible for studying technical, operating and tariff questions and issuing Recommendations on th
3、em 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 Recommendations on these topics. ITU-T Recomm
4、endation M.1025 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 as of 28 February 1993. In its place, the IT T
5、elecommunication 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 Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector.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 made in the text to references co
6、ntaining the acronyms “CC, 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 IT structure. 2 telecommunication administration and a recognized operating agency. In this
7、Recommendation, the expression “Administration” is used for conciseness to indicate both a O ITU 1994 All rights reserved. No pari of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writ
8、ing from the ITU. 1 2 ITU-T RECflNtM.3025 93 4862593 0592403 T3b CONTENTS Scope 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 with time . Random circuit noise Impulsive nois
9、e . Phase jitter Total distortion (including quantizing distortion) . Single tone interference Frequency error . Harmonic and intermodulation distortion . Crosstalk . Power source interferences . Annex A . Noise and distortion A . 1 Random circuit noise A.2 Total distortion References Recommendation
10、 M.1025 (03/93) Page 1 1 1 2 2 3 3 3 4 4 4 4 4 4 4 5 5 5 6 1 . ITU-T RECMN*M.1025 93 m 4862571 0592402 972 m ABSTRACT This Recommendation provides the characteristics of a circuit, especially applicable for use by modems with equalizer, for data transmission rates higher than those normally achievab
11、le on telephone-type circuits. KEYWORDS Basic bandwidth conditioning, characteristics, leased circuits. 11 Recommendation M.1025 (03/93) ITU-T RECMN*M.L025 93 4862593 0592403 809 = Recommendation M.1025 CHARACTERISTICS OF SPECIAL QUALITY INTERNATIONAL LEASED CIRCUITS WITH BASIC BANDWIDTH CONDITIONIN
12、G1) (Melbourne, 1988; revised in Helsinki, 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
13、 transmission rates higher than those possible on a normal telephone-type circuit2). In particular, circuits meeting the requirements of this Recommendation are intended for use with modems which contain equalizers. Circuits conforming to this Recommendation may not always support satisfactory opera
14、tion of modems to Recommendation V.29 i. This is dependent upon the equalization capability of the particular modems used. 2 Characteristics3) 2.1 Nominal overall loss Because of the differing nominal level at renters premises due to the various national practices, it is not normally possible to pre
15、dict 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 after prior consultation among the Administrations concerned. Fo
16、r 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 relative levels may be required in some circumstances. Reference sho
17、uld 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. The application of this Recommendation to multiterminal leased circuits is intended only for radial networks in which thes
18、e specifications are to be met between a designated central station and each of the outlying stations. It does not apply to multiterminal conference networks between any two stations. *) in order to ensure the proper operation of certain Series-V modems operating at data signalling rates greater tha
19、n 4800 bitis, it is necessary to specify improved andior modified values for the following transmission system characteristics: random circuit noise, quantizing noise, harmonic distortion (intermodulation distortion). This subject is for further study. 3, Additionally, the characteristics and limits
20、 for short interruptions in transmission and phase hits are under study for inclusion in this Recommendation. It may be noted that clause Wb4.1060 101 gives provisional limits for short interruptions in transmission and phase hits as guidance for fault finding purposes. Recommendation M.1025 (03/93)
21、 1 ITU-T RECMN*M=1025 93 4862591 0592404 745 2.2 Lossfrequency distortion4). 5) The limits for the overall loss relative to that at 1020 Hz for the circuit between renters installations are given in Figure 1. I 1 O 300 500 1020 2000 2500 3000 Hz Frequency TO4051094/601 NOTES 1 These frequencies shou
22、ld be confirmed or amended after further study. 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 reference test frequency as explained in Recommendation 0.6. FIGURE 1M.1025 Limits for overail lass of the circuit relative to that at
23、 1020 Hz 2.3 Group-delay distorti0n4) 5) 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 measured group-delay. 4, It is expected that, in most cases, these “basic bandwidth” cha
24、racteristics may be available without the addition of iosdfrequemy andor group-delay equalization equipment. The values of losdfrequen5y and group-delay distortion are provisional and should be confirmed or amended after further study. 2 Recommendation M.1025 (03/93) ITU-T RECMN*M.L025 93 9 48b259b
25、0592405 b1 NOTE - It should be noted that the value of 3.0 ms between 600 and loo0 Hz should be confirmed or amended after further study, to ensure that equalization would not be necessary in the majority of cases and that proper modem operation is achieved. FIGURE 2M. 1025 Limits for group delay re
26、lative to the minimum measured group delay in the 600-2800 IIZ band 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 i, amplitude hits m
27、ay result in data errors. Using an instrument complying with Recommendation 0.95 2, the number of amplitude hits greater than f 2 dB should not exceed 10 in any 15 minute measuring period. The value of k 2 dB and the number of amplitude hits are provisional and subject to further study. 2.4.2 Other
28、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 k 4 dB. 2.5 Random circuit noise The level of the psophometric noise power at a renters premise
29、s depends upon the actual constitution of the circuit, in particular upon the length of circuit of frequency division multiplex carrier systems. The provisional limit for leased circuits of distances greater than IOOOO kilometres is -38 dBmOp. However, circuits of shorter length will have substantia
30、lly less random noise (see also Annex A and 3.5/M.1050 9). 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 15 minutes. Recornme
31、ndation M.1025 (03/93) 3 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 w
32、ith Recommendation 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 (inc
33、luding quantizing 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 interferenc
34、e and harmonic 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-
35、distortion 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 Fre
36、quency error 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. 2.11 Harmonic and intermodulation distortion When a 700 Hz test frequency of -13 dBmO is injected at the transmit end of a point-to-po
37、int 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 Recommendation 0.42 at a four-frequency signal o
38、f 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 attenuation at the near end (between forward an
39、d 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 Power source interferences When a sine wave s
40、ignal is transmitted over the circuit at a O dBm0, each side component level should not exceed 45 dBmO. 4 Recommendation M.1025 (03/93) ITU-T RECMN*M.L025 93 W 48b2591 0592407 454 m Annex A Noise and distortion (This annex forms an integral part of this Recommendation) A.l Random circuit noise Figur
41、e A.l displays random noise versus length 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 U 1 :I -50 -55 200 500 1000 2000 5Ooo 10000 2omh rnmo3ct-wm Length of circuit of FDM carrier systems FI
42、GURE A. 1/M. 1025 Random circuit-noise performance NOTE - At the present time the section of the circuit provided by a satellite (between earth stations) employing FDM techniques contributes approximately loo00 pWOp (-50 dBmOp) of noise. Therefore, for the pupse of determining maintenance limits for
43、 noise measurement on leased circuits, the length of this section may be considered to be equivalent to IO00 km in Figure A. 1. The contribution to noise of a circuit section provided by a satellite employing TDM technique remains as a subject for further study. A.2 Total distortion Table A.l is a g
44、uide 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 inc
45、rease the number of QDUs in a circuit provided the analogue sections contribute less noise than might be expected from Figure A. 1. Recommendation M.1025 (03/93) 5 TABLE A.lM.1025 Type of circuit Analogue Composite circuit Signal-to-signal distortion ratio using a sinusoidal signal at -10 dBmO Dista
46、nce in analogue transmission (km) NumberofQDUs Unit c320 321 641 1601 2501 5001 10001 to to to to to to 640 1600 2500 5000 10000 20000 (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 I
47、NOTE - The number of QDUs contributed by various digital processes are given in Table 1/G. 113 7. References CCITT Recommendation 9600 bids modem standardized for use on point-to-point 4-wire leased telephone-type circuits, Rec. V.29. CCITT Recommendation Phase and amplitude hit counters for telepho
48、ne-type circuits, Rec. 0.95. CC Recommendation Impulsive noise measuring equipment for telephone-type circuits, Rec. 0.7 1. CCITT Recommendation Phase jitter measuring equipment for telephone circuits, Rec. 0.9 1. CCITT Recommendation Quantizing distortion measuring equipment using a sinusoidal test
49、 signal, Rec. O. 132. CCITT Recommendation Equipment to measure non-linear distortion using the 4-tone intermodulation method, Rec. 0.42. CCITT Recommendation Transmission impainnents, Rec. G. 113. Transmission systems for communications (revised third edition) by members of the technical staff; Bell Telephone Laboratories - Chapter 8: Modulation distortion in AM systems; formulae: (8-18) and (8-20). CCITT Recommendation Lining up an international point-to-point leased circuit, Rec. M. 1050. CCITT Recommendation Maintenance of international le
