1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU$)4!,G0G03%#4)/.3G0G0!.$G0G0$)4!,G0G0,).%G0G03934%-3$)4!,G0G0,).%G0G03934%-3G0G0“!3%$/.G0G04(%G0G0 G0KBIT SG0G0()%2!2#(9/.G0G0#/!8)!,G0G00!)2G0G0#!“,%3)45G134G0G0RecommendationG0G0 (Extract from the “LUEG0“OOK)
2、NOTES1 ITU-T Recommendation G.953 was published in Fascicle III.5 of the Blue Book. This file is an extract from theBlue Book. While the presentation and layout of the text might be slightly different from the Blue Book version, thecontents of the file are identical to the Blue Book version and copy
3、right 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 reserved. No part of this publication may be reproduced or ut
4、ilized in any form or by any means, electronic ormechanical, including photocopying and microfilm, without permission in writing from the ITU.Fascicle III.5 - Rec. G.953 1Recommendation G.953DIGITAL LINE SYSTEMS BASED ON THE1544 kbit/s HIERARCHY ON COAXIAL PAIR CABLES(Malaga-Torremolinos, 1983; amen
5、ded at Melbourne, 1988)1 GeneralThis Recommendation covers digital line systems for the transmission of signals based on the 1544 kbit/shierarchy on coaxial pair cables and includes systems conveying the following bit rates:44 736 kbit/s97 728 kbit/s2 Transmission mediaThe systems can be operated on
6、 coaxial pairs, as defined in the Series G.620 Recommendations, in accordancewith Table 1/G.953.TABLE 1/G.953Transmission mediaSystem (kbit/s) Cable Recommendation44 73697 728G.623G.6233 Overall design features3.1 AvailabilityThe availability objective of the system should be derived taking into acc
7、ount the availability requirement forthe hypothetical reference digital section given in Recommendation G.801.3.2 ReliabilityMTBF values should be specified for the line system as a whole taking into account the requirementsconcerning availability.3.3 Repeater noise marginRepeater Noise Margin is de
8、fined in Annex A together with suggested measurement techniques. The NoiseMargin quantifies the performance of digital regenerators for coaxial pairs. This is a function of BER and repeaterspacing loss A0(at half the line system baud rate).2 Fascicle III.5 - Rec. G.953At a BER = 10-7and over the los
9、s range of the system A1 A0 A2, the Noise Margin should meet thefollowing specification:Noise Margin (M) B + C (A2- A0)It has been possible to recommend specific values for parameters A1, A2, B and C.Note - The degrading effect of timing jitter on Noise Margin should be measured by superimposing app
10、ropriatejitter on the test signal.3.4 Error performanceThe design objective for the error ratio of the individual repeater should take into account the networkperformance objectives given in Recommendation G.821.4 Specific design features4.1 Type of power feedingAlthough CCITT does not recommend the
11、 use of a specific remote power-feeding system for these coaxial linesystems, in practice only the constant current d.c. feeding via the inner conductors of the two coaxial pairs of system isused.These coaxial cable systems may be subject to induced voltages and currents caused by lightning, power l
12、ines,railways, etc.Precautions must be taken to protect the staff from any possible danger arising from the normal operatingvoltages and remote power-feed currents as well as from the induced voltages and currents.Many national Administrations have issued detailed rules and regulations for the prote
13、ction of persons. It isobligatory in most cases to meet these rules and regulations. In addition the CCITT Directives 1 give guidance on theseproblems.Precautions are also needed for the protection of the equipment against induced voltages and currents. Theequipment should therefore be designed in s
14、uch a way that it passes the tests specified in Recommendation K.17 2.4.2 Nominal repeater spacingA specific repeater spacing is not recommended but in practice the nominal values indicated in Table 2/G.953are used by most Administrations:TABLE 2/G.953Nominal repeater spacingsNominal repeater spacin
15、g (km)System (kbit/s) Cable Recommendationa)G.62344 736 97 728 4.5a)Recommendation G.623 refers to 2.6/9.5 mm coaxial pairs.Fascicle III.5 - Rec. G.953 34.3 Maintenance strategy4.3.1 Type of supervision and fault locationIn-service monitoring or out-of-service fault location can be used.4.3.2 Fault
16、conditions and consequent actionsThe fault conditions and consequent actions should be complementary to those recommended for digital linesections.ANNEX A(to Recommendation G.953)Definition and measurement of repeater noise marginA.1 DefinitionThe noise margin mn:mn= SNR / SNRER(A-1)where:SNR = SNRt
17、h F(t, ER) (A-2)The product SNRthF(t, ER) can be considered the actual signal-to-noise ratio SNR, being the measure for theregenerator performance.SNRthis the theoretical signal-to-noise ratio determined by the system parameters such as output pulse,section loss, noise figure of the regenerator inpu
18、t amplifier, etc.F(t, ER) is the reduction factor due to an off-set from the optimum timing instant (including phase jitter) inconjunction with the pulse realized S(t), the intersymbol interference I(t) and any other disturbancewhich causes a corruption in the information signal (Ic).Note - The inte
19、rsymbol interference and other disturbances are fluctuating processes with bounded distributions.The “mean“ reduction factor depends on ER, and, for a ternary signal, is given by:F(t, ER) = S(t)S( )- I(t)S( )- IS( )c0200(A-3)where S(0) is the realized pulse at t = 0 giving the maximum amplitude.SNRE
20、Ris the signal-to-noise ratio required for an error ratio equal to ER. For a ternary signal the relationbetween ER and SNRERis given by the known Gaussian distribution:ER ExSNRER= P = e dx-/4343212pi(A-4)A.2 Derived definitionsThe noise marging can be measured by applying an external disturbing sign
21、al. For that purpose more practicaldefinitions are derived.4 Fascicle III.5 - Rec. G.953A.2.1 SNRER(giving an error ratio ER) can be achieved by injecting sufficient white noise into the input of theregenerator:SNR NNNSNRERTTE=+ (A-5)whereNT= thermal noise that appears at the decision point during n
22、ormal operation.NE= mean power of the external noise that appears at the decision point to induce an error rate ER.Combining (A-1) and (A-5) results in the noise margin M:MmNnET= 20 log = 10 log 1 + A - 6) (N N E(fE=02) df0(A-7)N = kT E(f f dfT) F()20(A-8)N0= power density of the external noise that
23、 is superimposed on the signalE(f) = transfer function of the regenerators equalizerk, T = Boltzmann constant and absolute temperatureF(f) = noise figure of the equalizer amplifier of the regeneratorA.2.2 By injecting a sine wave disturbing signal, a second definition for mncan be derived.This distu
24、rbance causes a decreasing F(t, ER), which can be defined by:Fd (t, ER) = SNRER / SNRthNext in accordance with (A-1) and (A-2),F(t, ER) = mn SNRER / SNRthSubstraction gives:F(t, ER) F (t, ER)s(m )SNR / SNRdIS( )nERth=210where Is / S(0) is the normalized disturbing signal at the decision point.Fascic
25、le III.5 - Rec. G.953 5Substitution of and some rearrangements results in the noise margin:M ISNR . N RsER T=20 log 10(A-9)I S E(f)a s ddc= (A-10)Sd= the magnitude of the disturbing signal at the input of the regeneratorfd= the frequency of the disturbing signalac= a correction factor taking into ac
26、count the effect of the disturbance on the peak detector of theautomatic equalizerR0= the real part of the characteristic impedance of the cable.A.3 MeasurementsMethod A is based on the definition directly related to the noise marging (A-6) and therefore, is the referencetest method. Methods B and C
27、 are alternative test methods.Method A (Figure A-1/G.953)The values of NEand NTare measured directly at the decision point. The value of NTis measured in the absenceof both a signal and externally applied noise. Under these conditions the automatic gain control (AGC) of the equalizermust be external
28、ly controlled to a level appropriate to the corresponding cable attenuation. With the signal restored, thelevel of the externally applied noise is adjusted to give the desired BER. The noise level (NT+ NE) is now measured withthe signal removed and with the AGC set at the same value as in the measur
29、ement of NT.Method B (Figure A-2/G.953)This method realizes a measurement without the need to access the decision point. The applied noise at theinput, to cause a given BER, is measured directly. The corresponding value at the decision point and also the thermalnoise (NT) are evaluated by means of t
30、he transfer function and the noise figure of the amplifier equalizer.Note - Both the transfer and the noise figure of the amplifier equalizer need to be calculated and measured on asample of repeaters before this method can be applied to a particular repeater design.Method C (Figure A-2/G.953)This m
31、ethod is similar to the previous method (B) except that in this case the applied disturbance is a sine wavesignal. This applied signal at the input, to cause a given error ratio, is likewise measured directly.6 Fascicle III.5 - Rec. G.953The corresponding disturbance at the decision point (Is) as we
32、ll as the thermal noise voltage areevaluated by means of the transfer function, the noise figure of the equalizer and the correction factor ac, which have tobe determined.Note - It follows from (A-8) and (A-9):being an unknown factor, which has to be determined on the basis of measurements on a samp
33、le of prototyperegenerators before this method can be applied to a particular regenerator design.For this purpose, the noise margin of the prototype regenerator needs to be measured in accordance with thereference test method (A).Note 2 - This method allows the presence of an LBO-network at the rege
34、nerator input. In contrast to method B itis not necessary to insert a complementary filter in the injection path.Note 3 - To obtain the most accurate measurement the disturbing frequency should be around the Nyquistfrequency.References1 CCITT Manual Directives concerning the protection of telecommunication lines against harmful effects fromelectric power and electrified railway lines, ITU, Geneva, 1988.2 CCITT Recommendation Tests on power-fed repeaters using solid state devices in order to check thearrangements for protection from external interference, Vol. IX, Rec. K.17.
