1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 1 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITUSERIES Q: SWITCHING AND SIGNALLINGInternational automatic and semi-automatic working General characteristics for international telephoneconnections and circuits4RANSMISSIONG0CHARACTERISTICSG0OFG0ANG0ANALOGUEI
2、NTERNATIONALG0EXCHANGEITU-T Recommendation Q.45Extract of 2EDG0“OOKG0 600-3400 Hz: 46 dB.Note Some Administrations guided by their knowledge of local conditions may feel a need to specify a figurefor a lower frequency, for instance, 50 Hz.6.4.2 The degree of unbalance to earth is defined as the rati
3、o u/U measured as shown in a) and b) of Figure 4/Q.45and is expressed in decibels as the reciprocal of this ratio in transmission units.The diagrams of Figure 4/Q.45 used for measurement of unbalance differ only in respect of the presence orabsence of an earth at the mid-point of the termination. Un
4、balance measurements according to a) and b) of Figure 4/Q.45can give quite different results according to the nature of the unbalance.6.4.3 The CCITT has recommended in 1968 that the set of limit values of 6.4.1 above should be met for unbalanceto earth measured with both measuring diagrams accordin
5、g to Figure 4/Q.45.7 Use of cables specified by the IECThe cables for telephone exchanges in accordance with the IEC (International Electrotechnical Commission)publication cited in 7 will meet the electrical characteristics required by the CCITT (especially as regards crosstalk) forordinary exchange
6、s, but this may no longer hold good for larger exchanges with considerable lengths of cable.In accordance with Recommendation G.231 8, it will be for the Administrations or the contractors to checkwhether standard cables will be satisfactory in equipping an exchange which requires telephone cables o
7、f exceptionallength.Fascicle VI.1 Rec. Q.45 7Figure 4/Q.45ANNEX A(to Recommendation Q.45, 5.2)Procedure for impulsive noise measurementsA.1 A test circuit should be formed by setting up a connection across the switching unit and terminating theconnection on one side of the exchange by the appropriat
8、e closing impedance and on the other by the impulse measuringdevice in parallel to the closing impedance. Those terminating points should be points A and D in the diagram ofFigure 1/Q.45 (or equivalent points) to include the switching equipment of the exchange. Where it is the desire of anAdministra
9、tion, measurements may be made at points X and Y if precautions are taken to ensure that the results applyonly to the automatic switching equipment, signalling equipment, echo suppressors, relay sets, pads and cabling of theexchange.A.2 The measurements should be made using the device specified in R
10、ecommendation O.71 9. The 600-3000 Hzfilter network described in 10 should be in the circuit.A.3 The measurements should be made at times when the probability of noise occurring is at its highest, that isnormally during the busy-hour.8 Fascicle VI.1 Rec. Q.45A.4 The time of observation for each test
11、 should be five minutes.Note The number of different test circuits set up across the exchange for measuring should take into accountthe size and complexity of the switching unit and should be a number sufficient to represent the various possible types ofcalls and routes through the exchange.See also
12、 the document cited in 11.References1 CCITT Recommendation Definitions for the maintenance organization, Vol. IV, Rec. M.700.2 CCITT Recommendation Four-wire switched connections and four-wire measurements on circuits, Vol. IV,Rec. M.640, 2.3 CCITT Recommendation Linear crosstalk, Vol. III, Rec. G.1
13、34.4 CCITT Definitions: Busy hour, Vol. X, Fascicle X.1 (Terms and Definitions).5 CCITT Recommendation Limits for the maintenance of telephone-type circuits used for data transmission,Vol. VIII, Rec. V.53, 4.6 CCITT Recommendation Characteristics of compandors for telephony, Vol. III, Rec. G.162, 5.
14、2.7 Publication 189 of the I.E.C.8 CCITT Recommendation Arrangement of carrier equipment, Vol. III, Rec. G.231.9 CCITT Recommendation Specification for an impulsive noise measuring instrument for telephone-typecircuits, Vol. IV, Rec. O.71.10 Ibid., 3.5.11 Measurements of impulsive noise in a four-wire telephone exchange, Green Book, Vol. VI-4, Supple-ment No. 7, ITU, Geneva, 1973.
