1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU42!.3-)33)/.G0G0-%$)!G0G0#(!2!#4%2)34)#3?#(!2!#4%2)34)#3G0G0/&G0G039-%42)#G0G0#!“,%0!)23G0G053!“,%G0G07(/,9G0G0&/2G0G04(%42!.3-)33)/.G0G0/&G0G0$)4!,G0G03934%-3G0G07)4(!G0G0“)4G0G02!4%G0G0/&G0G050G0G04/G0G0 G0-B
2、ITS)45G134G0G0RecommendationG0G0 (Extract from the “LUEG0“OOK)NOTES1 ITU-T Recommendation G.613 was published in Fascicle III.3 of the Blue Book. This file is an extract fromthe Blue Book. While the presentation and layout of the text might be slightly different from the Blue Book version, theconten
3、ts of the file are identical to the Blue Book version and copyright conditions remain unchanged (see below).2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both atelecommunication administration and a recognized operating agency. ITU 1988, 1993All rights
4、 reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic ormechanical, including photocopying and microfilm, without permission in writing from the ITU.Fascicle III.3 - Rec. G.613 1Recommendation G.613Fascicle III.3 - Rec. G.613CHARACTERISTICS OF S
5、YMMETRIC CABLE PAIRSUSABLE WHOLLY FOR THE TRANSMISSION OF DIGITAL SYSTEMSWITH A BIT RATE OF UP TO 2 Mbits(Malaga-Torremolinos, 1984)1 PreambleThis Recommendation deals with cables designed for the transmission of standard digital systems(Recommendations of the G.900 series), although these cables ca
6、n also be used to transmit digital signals with a lowerbit rate and voice frequency signals. The cables described carry signals in both transmission directions simultaneously.The provisions of this Recommendation apply to cables designed to allow for digital operation of all the cable circuits.Howev
7、er, some of the provisions may be used to assess the possibility of (partial or full) digital operation of existingcables.2 Parameters to be measured2.1 Direct current resistanceThe following formula is used to correct the value Rtof direct current resistance measured at tC for 20 C:R20= Rt /(l + 0.
8、004 (t - 20)2.2 Capacitance per unit lengthThis is measured at 800 Hz or 1000Hz.2.3 Attenuation coefficientThe value of the attenuation coefficient is obtained either by direct measurement of the attenuation or bycalculation on the basis of the mutual capacitance and direct current resistance of the
9、 pair. The attenuation coefficient ismeasured at one frequency only, f0, near the timing half-frequency.System Recommendation f01544 kbit/s G.951 772 kHz2048 kbit/s G.952 1 MHzFor cables with polyolefin insulation, the value of the attenuation coefficient at frequency f (for values of fabove with a
10、few hundred kHz) can be related to0by the equation The value of the attenuation coefficient measured at tC is corrected for 20 C by the equation:20= t /(1 + 0.002 (t - 20)2 Fascicle III.3 - Rec. G.6132.4 Characteristic impedance2.4.1 Echometric measurementWhen a pulse echometer is used, the impedanc
11、e of the pair measured must be compensated by a calibratedbalancing network which can be set in steps of about 0.5 . Pulse duration will be equal to or less than 500 ns. With thismethod, which is both fast and simple, the value of the end impedance of the pair measured is read off directly on thesca
12、le of the balancing network.2.4.2 Sinusoidal measurementIn this case, the pair tested will be terminated across an impedance, which is constantly equal to that measuredby the bridge, unless it is long enough for the result of the measurement to be independent of end impedance (as forelementary cable
13、 sections).2.5 CrosstalkCrosstalk can be measured sinusoidally or digitally. The assignment of pairs to the direction of transmissiondepends on the structure and type of manufacture of the cable.2.5.1 Sinusoidal measurement2.5.1.1 Far-end crosstalkThe measurements are made between pairs assigned to
14、the same direction of transmission, at frequency f0. If thefrequency at which measurement is carried out is not the timing half-frequency, the value is corrected using the 20 logl0flaw. When the measurement is carried out on a pair of length, L, which is different from the specified reference length
15、L0, the measured value is corrected using LL/0when the value is expressed in mV or 10 log10LL0when the value isexpressed in dB.2.5.1.2 Near-end crosstalkThe measurements are made between pairs assigned to transmission in opposite directions at a frequency nearthe systems timing half-frequency.2.5.2
16、Digital measurementBy means of digital measurement, it is possible to estimate the total noise on an elementary section, takingaccount of both near-end and far-end crosstalk. This estimate can be made on the basis of separate near-end and far-endcrosstalk measurements on either factory lengths or el
17、ementary sections.1)These measurements can be made either infactory conditions or on installed cables.2.5.2.1 Far-end crosstalkThe measurements are carried out between pairs assigned to the same direction of transmission. When the measurementis carried out on a pair of length, L, which is different
18、from the specified reference length L0, the measured value iscorrected using LL/0when the value is expressed in mV or 10 log10(L / L0) when the value is expressed in dB.2.5.2.2 Near-end crosstalkThe measurements are made between pairs assigned to transmission in opposite directions.3 Circuit charact
19、eristicsThese are given in Table 1/G.613._1)One advantage of digital measurements is that it is possible to make a direct overall measurement of the totalnoise on an elementary section if enough generators are available.Fascicle III.3 - Rec. G.613 34 Characteristics of connected cable sectionsThese
20、are given in Table 2/G.613.TABLE 1/G.613Circuit characteristics *CharacteristicsType of cableType I Type II Type IIbisType III*f)Operational bit rate (kbit/s) 2048 2048 2048 2048Repeaters gain * 34 dBElements constituting the cable star quad pairs pairs pairsNominal conductor diameter (mm) 0.8 0.7 1
21、 0.6Nominal impedance * at f0MHz () 1 MHz 100 130 130772 kHzNominal attenuation coefficient at f0and at 1 MHz 16 11.5 b) 8.5 b) 15.520 C * (dB/km)772 kHzCrosstalk in digital operation a) c) - - -Total noise voltage (maximum value) a)Minimum near-end crosstalk (mV) a) - 60 d, g) 60 d, g)a)Minimum far
22、-end crosstalk (mV) a) - 45 e, g) 45 e, g)a)Near-end (dB) 1 MHz 78 3h)Sinusoidal crosstalk 772 kHzFar-end (dB) 1 MHz 64 3h)772 kHzNominal direct current resistance at 20C(/km)68.6 94.1 b) 46.1 b) 63Nominal mutual capacitance (nF/km) 50 39 39 444 Fascicle III.3 - Rec. G.613Notes of Table 1/G.613* At
23、the present stage the values are given for information.* Reference value for the numerical data of the cable in question.* A standard deviation or margins will be given at a later stage.* Cable with diametral screen separating the pairs assigned to the two directions of transmission.a) To be specifi
24、ed.b) Maximum value.c) The specification value for factory controls is calculated to ensure compliance with the characteristics of connected cable.d) Between pairs of different groups.e) Between pairs belonging to one and the same group.f) Other columns will contain the data supplied by administrati
25、ons.g) Values given in dB.h) The value given here depends on the content of the cable. It is the rounded-down mean of a standard deviation of the totalproduction and is therefore not a specification for individual cable lengths.TABLE 2/G.613Characteristics of connected cable sections *Characteristic
26、s Type of cableType I Type II Type IIbisType III a)Operational bit rate (kbit/s) 2048 2048 2048Nominal impedance at f0MHz () 1 MHz 100 130 130772 kHzNominal attenuation coefficient at f0and at 1 MHz 16 11.5 8.520C (dB/km) 772 KHzCrosstalk in digital operation b) 40 mVTotal noise voltage (maximum value) b)Minimum near-end crostalk (mV) b)b)Minimum far-end crosstalk (mV) b)b)Near-end (dB) 1 MHzSinusoidal crosstalk 772 MHzFar-end (dB) 1 MHz772 MHz* At the present stage the values are given for information.a) Other columns will contain the data supplied by Administrations.b) To be specified.
