WPCL 2BJ|x ` H   x|@  @8'@8' Recommendation Q.553 *TRANSMISSION CHARACTERISTICS AT 4WIRE ANALOGUE 1INTERFACES OF A DIGITAL EXCHANGE 9Table of contentsă 1.General 2.Characteristics of interfaces 3.Characteristics of half connections Recommendation Q.553 *TRANSMISSION CHARACTERISTICS AT 4WIRE ANALOGUE 1INTERFACES OF A DIGITAL EXCHANGE1ă 1.HGeneral HThis Recommendation provides characteristics for: H 4wire analogue interfaces (Type C11, C12 and C13),   H input and output connections with 4wire analogue interfaces, and H half connections with 4wire analogue interfaces,  X in digital transit and combined local and transit exchanges in accordance with the definitions given in Recommendation Q.551, particularly in Figures1/Q.551 and 2/Q.551. HThe characteristics of the input and output connections of a given interface are not necessarily the same. The characteristics of half connections are not necessarily identical for different types of interfaces. HThis Recommendation is intended for switch connections that may be part of an international longdistance connection via 4wire line circuits interconnected by 4wire exchanges. Since 4wire analogue interfaces of digital exchanges may connect with circuits which are used for both international and national traffic, the same values recommended for international connections may also be used for connections entirely within the national network. 2.HCharacteristics of interfaces 2.1HCharacteristics common to all 4wire analogue interfaces 2.1.1HExchange impedance 2.1.1.1 Nominal value HThe nominal impedance at the 4wire input and output interfaces should be 600ohms, balanced. 2.1.1.2 Return loss HThe return loss, measured against the nominal impedance, should not be less than 20dB over the frequency range 300Hz to 3400Hz. Note For output measurement, the exchange test point Ti must be driven by a PCM signal corresponding to the decoder output value number 0 for the law or decoder output value number 1 for the Alaw. (See RecommendationQ.551, section1.2.3.1).  1ĠAll references to GSeries Recommendations are to the Red Book and therefore, have still to be verified for the Blue Book. 2.1.2HImpedance unbalance about earth HThe value for the Longitudinal Conversion Loss (LCL) defined in RecommendationG.117, 4.1.3, with the circuit under test in the normal talking state, should exceed the minimum values of Figure1/Q.553, in accordance with RecommendationsQ.45bis and K.10. IFIGURE 1/Q.553 P ,Minimum values of LCL measured in the arrangement shown in Figure 2/Q.553ă Note 1 An administration may adopt other values and in some cases a wider bandwidth, depending upon actual conditions in its telephone network. Note 2 A limit may also be required for the Transverse Conversion Loss (TCL) as defined in RecommendationG.117, 4.1.2, if the exchange termination is not reciprocal with respect to the transverse and longitudinal connections. A suitable limit would be 40dB to ensure an adequate nearend crosstalk attenuation between interfaces. Test method HLCL should be measured in accordance with the principles given in RecommendationO.9, 2.1 and 3. Figure 2/Q.553 shows the basic measuring arrangement. w.Ԍ HMeasurements of the longitudinal and transverse voltages should be performed by means of a frequencyselective level meter. IFIGURE 2/Q.553 P BArrangement for measuring LCLă Note For output measurement the exchange test point Ti must be driven by a PCM signal corresponding to the decoder output value number 0 for the law or decoder output value number 1 for the Alaw. (See Recommendation Q.551, section1.2.3.1). 2.1.3HRelative levels HIn assigning the relative levels to the interfaces, the limiting of "difference in transmission loss between the two directions of transmission" in RecommendationG.121, 6.4 has been taken into account. For the national extension this is the value "loss (tb)loss(at)". (See the text in the cited Recommendation for guidance.) This difference is limited to +4dB. However, to allow for additional asymmetry of loss in the rest of the national network, only part of this difference can be used by the digital exchange. 2.1.3.1 Nominal levels HThe nominal relative levels at the 4wire analogue input and output interfaces of the digital exchange depend on the type of equipment which is connected to the exchange. (See Figure1/Q.551.) HIn practice it may be necessary to compensate for the loss between the output interfaces of the digital exchange and the input ports of the connected equipment to fulfill transmission plan conditions. The definition of adjustable steps for and the location of this compensation (digital exchange or connected equipment) is within national competence. HNominal values of relative levels are given in 2.2.1, 2.3.1 and 2.4.1 for the different types of half connections. 2.1.3.2 Tolerances of relative levels HThe difference between the actual relative level and the nominal relative level should lie within the following ranges: H input relative level: 0.3 to +0.7 dB; H output relative level: 0.7 to +0.3 dB. HThese differences may arise, for example, from design tolerances, cabling (between analogue equipment ports and the DF) and adjustment increments. Note Adjustment of the relative level should be made in accordance with RecommendationG.712, 15. 2.2HCharacteristics of interface C11 HAccording to Figure 1/Q.551, the interface C11 of a digital exchange is intended to interwork with the channel translating equipment of an FDM system. 2.2.1HValues of nominal levels HThe nominal values of relative levels at the channel translating equipment are specified in Table 2/G.232 for the two recommended cases. With the pads in the channel translating equipment set to zero, these values are: H Case 1Case 2 HR +4.0 dBr+7.0 dBr HS 14.0 dBr16.0 dBr HThe nominal values of relative levels at the digital exchange must be adjusted to compensate for the total loss between the interface of the digital exchange and the channel translating equipment. Therefore: HLi = R AR HLo = S + AS where HAR = total loss in the receive path HAS = total loss in the send path 2.3HCharacteristics of interface C12 HAccording to Figure 1/Q.551, the interface C12 of a digital exchange is intended to interwork with the incoming and outgoing relay set of an analogue 4wire exchange. (See Figure 1/Q.45bis.) 2.3.1HValues of nominal levels HThe nominal values of relative levels at the relay set of an analogue exchange are consistent with Table2/G.232 for the two recommended cases. These values are: H Case 1Case 2 HR 14.0 dBr16.0 dBr N%OSP%Q+4.0 dBr+7.0 dBr HThe nominal values of relative levels at the digital exchange must be adjusted to compensate for the total loss between the interface of the digital exchange and the relay sets of the analogue exchange. Therefore: HLi = R AR w.ԌHLo = S + AS where HAR = total loss in the receive path HAS = total loss in the send path 2.4HCharacteristics of interface C13 HAccording to Figure 1/Q.551 the interface C13 of a digital exchange is intended to connect to a 4wire analogue switching stage. (See Figure1/G.142, case5.) 2.4.1HValues of nominal levels HThe nominal values of relative levels are determined by the relative levels of the analogue 4wire switching stages in the national transmission plans. For example, if these relative levels are identical with the virtual analogue switching point of 3.5dBr in both directions of transmission, the nominal input and output levels of a C13 interface are: HLi = Lo = 3.5 dBr. HDifferent levels at the switching stages and transmission loss between interface C13 and the switching stages can require adjusting these levels. 3.HCharacteristics of half connections 3.1HCharacteristics common to all 4wire analogue interfaces 3.1.1HTransmission loss 3.1.1.1 Nominal value HThe nominal transmission loss, according to RecommendationQ.551 1.2.4.1, is defined for input and output connections of a half connection with 4wire analogue interface in 3.2.1, 3.3.1 and 3.4.1. 3.1.1.2 Tolerances of transmission loss HThe difference between the actual transmission loss and the nominal transmission loss of an input or output connection of the same half connection according to 2.1.3.2 should lie within the following values: H0.3 to +0.7 dB. HThese differences may arise for example, from design tolerances, cabling (between analogue equipment ports and the DF) or adjustment increments. 3.1.1.3 Shortterm variation of loss with time HWhen a sinewave test signal at the reference frequency of 1020Hz and at a level of 10dBmO (if preferred, the value 0dBmO may be used) is applied to a 4wire analogue interface of any input connection, or a digitally simulated sinewave signal of the same characteristic is applied to the exchange test point Ti of any output connection, the level at the corresponding exchange test point To and the 4wire analogue interface respectively, should not vary by more than +0.2dB during any 10minute interval of typical operation under the steady state condition permitted variations in the power supply voltage and temperature. 3.1.1.4 Variation of gain with input level HWith a sinewave test signal at the reference frequency of 1020Hz and at a level between 55 dBmO and +3dBmO applied to the 4wire analogue interface of any input connection, or with a digitally simulated sinewave signal of the same characteristic applied to the exchange test point Ti of any output connection, the gain variation of that connection, relative to the gain at the input level of 10dBmO, should lie within the limits given in Figure3/Q.553. HThe measurement should be made with a frequency selective meter to reduce the effect of the exchange noise. This requires a sinusoidal test signal. IFIGURE 3/Q.553 P ?Variation of gain with input levelă 3.1.1.5 Loss distortion with frequency HAccording to RecommendationQ.551, 1.2.5, the loss distortion with frequency of any input or output connection should lie within the limits shown in the mask of Figures 4a and 4b/Q.553 respectively. The preferred input level is 10 dBmO.  w.Ԍ IFIGURE 4a/Q.553 P ALoss distortion with frequencyă HInput connectionă * In the marked frequency ranges relaxed limits are shown which apply if the maximum length of instation cabling (RecommendationQ.551, 2) is used. The more stringent limits shown apply if no such cabling is present. IFIGURE 4b/Q.553 P ALoss distortion with frequencyă HOutput connectionă * In the marked frequency ranges relaxed limits are shown which apply if the maximum length of instation cabling (Recommendation Q.551, 2) is used. The more stringent limits shown apply if no such cabling is present. 3.1.2HGroup delay H"Group delay" is defined in the Yellow Book, Fascicle X.1. 3.1.2.1 Absolute group delay HSee Recommendation Q.551, section 3.3.1. 3.1.2.2 Group delay distortion with frequency HTaking the minimum group delay, in the frequency range between 500Hz and 2500Hz, of the input or output connection as the reference, the group delay distortion of that connection should lie within the limits shown in the template of Figure5/Q.553. Group delay distortion is measured in accordance with Recommendation0.81. IFIGURE 5/Q.553 P :Group delay distortion limits with frequencyă 3.1.3HNoise 3.1.3.1 Weighted noise HTwo components of noise must be considered: noise arising from the coding process and noise from the exchange power supply and other analogue sources transmitted through signalling circuits. The first component is limited by RecommendationG.714, 9 and 10 to 66dBmOp for an input connection; and to 75dBmOp for an output connection. The other component is limited by RecommendationG.123, 3 to (67+3) dBmOp = 70 dBmOp for one 4wire analogue interface. HThis leads to the following maximum values for the overall weighted noise at the output interfaces of a half connection of a digital exchange: H Input connection:64.5 dBmOp for equipment with signalling on L$Mthe speech wires; H 66.0 dBmOp for equipment with signalling on K#LL$MM$Nseparate wires. H Output connection: 68.8 dBmOp for equipment with signalling on L$MM$NN%Othe speech wires; H 75.0 dBmOp for equipment with signalling on K#LL$MM$Nseparate wires. 3.1.3.2 Unweighted noise HThis noise will be more dependent on the noise on the power supply and on the rejection ratio.  w.ԌNote The need for and value of this parameter are both under study. RecommendationsQ.45bis, 2.5.2 and G.123, 3 must also be considered. 3.1.3.3 Impulsive noise HLimits should be placed on impulsive noise arising from sources within the exchange; these limits are under study. Pending the results of this study, Recommendation Q.45bis, 2.5.3 may give some guidance on the subject of controlling impulsive noise with low frequency content. Note 1 The sources of impulsive noise are often associated with signalling functions (or in some cases the power supply) and may produce either transverse or longitudinal voltage at 4wire interfaces. Note 2 The disturbances to be considered are those to speech or modem data at audio frequencies, and also those causing bit errors on parallel digital lines carried in the same cable. This latter case, involving impulsive noise with high frequency content, is not presently covered by the measurement procedure of RecommendationQ.45bis. 3.1.3.4 Single frequency noise HThe level of any single frequency (in particular the sampling frequency and its multiples), measured selectively at the interface of an output connection should not exceed 50dBmO. Note See Recommendation Q.551,  1.2.3.1. 3.1.4HCrosstalk HFor crosstalk measurements auxiliary signals are injected as indicated in Figures 6 to 9/Q.553. These signals are: H the quiet code (see RecommendationQ.551, section1.2.3.1); H a low level activating signal. Suitable activating signals are, for example, a band limited noise signal (see RecommendationO.131), at a level in the range 50 to 60dBmO or a sinewave signal at a level in the range from 33 to 40dBmO. Care must be taken in the choice of frequency and the filtering characteristics of the measuring apparatus in order that the activating signal does not significantly affect the accuracy of the crosstalk measurement. 3.1.4.1 Crosstalk measured with analogue test signal 3.1.4.1.1 Farend and nearend crosstalk HA sinewave test signal at the reference frequency of 1020Hz and at a level of 0dBmO, applied to an analogue 4wire input interface, should not produce a level at either output of any other half connection exceeding 73dBmO for a nearend crosstalk (NEXT) path and 70dBmO for a farend crosstalk (FEXT) path. These paths are shown in Figure6/Q.553. IFIGURE 6/Q.553 P :Measurement with analogue test signal betweenă 9different input connections of half connectionsă 3.1.4.1.2 Gotoreturn crosstalk HA sinewave test signal at any frequency in the range 300 3400Hz and at a level of 0dBmO, applied to the 4wire interface of an input connection, should not produce a level exceeding 66dBmO at the analogue output of the same half connection. See Figure7/Q.553. IFIGURE 7/Q.553 P 8Measurement with analogue test signals between goă 8and return directions of the same half connectionă 3.1.4.2 Crosstalk measured with digital test signal 3.1.4.2.1 Farend and nearend crosstalk HA digitally simulated sinewave test signal at the reference frequency of 1020Hz and at a level of 0dBmO, applied to an exchange test point Ti, should not produce a level exceeding 70dBmO for nearend crosstalk (NEXT) or 73dBmO for farend crosstalk (FEXT), at either output of any other half connection. See Figure 8/Q.553.  w.Ԍ IFIGURE 8/Q.553 P :Measurement with digital test signal betweenă 8different output connections of half connectionsă 3.1.4.2.2 Gotoreturn crosstalk HA digitally simulated sinewave test signal, at any frequency in the range 3003400Hz and at a level of 0dBmO, applied to an exchange test point Ti of an output connection, should not produce a crosstalk level exceeding 66dBmO at the exchange test point To of the corresponding input connection. See Figure9/Q.553. IFIGURE 9/Q.553 P 8Measurement with digital test signals between goă 8and return directions of the same half connectionă 3.1.5HTotal distortion including quantizing distortion HWith a sinewave test signal at the reference frequency of 1020Hz (see RecommendationO.132) applied to the 4wire interface of an input connection, or with a digitally simulated sinewave signal of the same characteristic applied to the exchange test point Ti of an output connection, the signaltototal distortion ratio, measured at the respective outputs of the half connection with a proper noise weighting (see Table4 of RecommendationG.223) should lie above the limits shown in Figure 10/Q.553 for signalling on separate wires and in Figure11/Q.553 for signalling on the speech wires. IFIGURE 10/Q.553 P ,Limits for signaltototal distortion ratio as a function of input levelă 2Input or output connection with signalling on separate wiresă Note The sinusoidal test signal is chosen to obtain results independent of the spectral content of the exchange noise. IFIGURE 11/Q.553 P ,Limits for signaltototal distortion ratio as a function of input levelă 1Input or output connection with signalling on the speech wiresă HThe values of Figure 11/Q.553 include the limits for the coding process given in Figure 5/G.714 and the allowance for the noise contributed via signalling circuits from the exchange power supply and other analogue sources which is limited to (67+3) dBmOp = 70 dBmOp for one 4wire analogue interface by RecommendationG.123, 3. 3.1.6HDiscrimination against outofband signals applied to the input interface  `  H(Applicable only to input connections) 3.1.6.1 Input signals above 4.6 kHz  H HWith any sinewave signal in the range from 4.6 kHz to 72kHz applied to the 4wire interface of a half connection at a level of 25dBmO, the level of any image frequency produced in the time slot corresponding to the input connection should be at least 25dB below the level of the test signal. This value may need to be more stringent to meet the overall requirement. 3.1.6.2 Overall requirement  w.ԌHUnder the most adverse conditions encountered in a national network the half connection should not contribute more than 100pWOp of additional noise in the band 10Hz 4kHz at the output of the input connection, as a result of the presence of outofband signals at the input port of the input connection. 3.1.7HSpurious outofband signals received at the output interface H(Applicable only to an output connection.) 3.1.7.1 Level of individual components HWith a digitally simulated sinewave test signal in the frequency range 3003400Hz and at a level of 0dBmO applied to the exchange test point Ti of a half connection, the level of spurious outofband image signals measured selectively at a 4wire interface of the output connection should be lower than 25dBmO. This value may need to be more stringent to meet the overall requirement. 3.1.7.2 Overall requirement HSpurious outofband signals should not give rise to unacceptable interference in the equipment connected to the digital exchange. In particular, the intelligible and unintelligible crosstalk in a connected FDM channel should not exceed a level of 65dBmO as a consequence of the spurious outofband signals at the half connection. 3.2HCharacteristics for interface C11 3.2.1HNominal value of transmission loss HAccording to the relative levels defined in 2.2.1, the nominal transmission losses of a half connection with a C11 interface are: H Input connection: R AR H Output connection: S AS HSee section 2.2.1 for definitions for R, S, AR and AS. 3.3HCharacteristics for interface C12 3.3.1HNominal value of transmission loss HAccording to the relative levels defined in 2.3.1 the nominal transmission losses of a half connection with a C12 interface are: H Input connection: R AR H Output connection: S AS HSee section 2.2.1 for definitions for R, S, AR and AS. 3.4HCharacteristics for interface C13 3.4.1HNominal value of transmission loss HAccording to the relative levels defined in 2.4.1 the nominal transmission losses of a half connection with a C13 interface are: H Input connection: 3.5 dB, H Output connection: 3.5 dB. HDifferent levels at the switching stages and transmission loss between interface C13 and the switching stages can require adjusting these losses.