1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 / TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU30%#) amended Malaga-Torremolinos, 1984)1 GeneralThis specification describes an in-service code violation monitor for the first and second level in the digitaltransmission hierarchy.The pseudoternary codes t
2、o be monitored are alternate mark inversion (AMI), high density bipolar with amaximum of 3 consecutive zeros (HDB3), B6ZS and B8ZS.2 Definition of code violation1)2.1 AMITwo consecutive marks of the same polarity. This may not be the absolute number of errors.2.2 HDB3Two consecutive bipolar violatio
3、ns of the same polarity. This may not be the absolute number of errors.2.3 B6ZSTwo consecutive marks of the same polarity excluding violations caused by the zero substitution code. Thismay not be the absolute number of errors.2.4 B8ZSTwo consecutive marks of the same polarity excluding violations ca
4、used by the zero substitution code. Thismay not be the absolute number or errors.3 Input signal3.1 InterfaceThe code violation monitor shall be capable of operating at the following bit rates and corresponding interfacecharacteristics as described in the appropriate paragraphs of Recommendation G.70
5、3 1:a) 1544 kbit/s;b) 6312 kbit/s;c) 2048 kbit/s;d) 8448 kbit/s.3.2 Instrument operation3.2.1 The instrument may be equipped to monitor only one or two of the listed codes and operate at the appropriatebit rates for those codes.3.3 Input sensitivity3.3.1 The instrument is required to operate satisfa
6、ctorily under the following input conditions.3.3.1.1 Input impedances and levels in accordance with Recommendation G.703 1.3.3.1.2 The instrument shall also be capable of monitoring at protected test points on digital equipment. Therefore, ahigh impedance input and/or additional gain of 30 dB (40 dB
7、 see Note) shall be provided to compensate for the loss atthe monitoring points already provided on some equipment._1)According to the definitions of code violations in this Recommendation it should be taken into account that the code violationmonitor will not detect zero sequences which violate the
8、 relevant coding rules.2 Fascicle IV.4 - Rec. O.161Note As an option for instruments operating at an interface of 1544 kbit/s corresponding to theRecommendation cited in 1, the additional gain, where provided, shall be 40 dB.3.3.1.3 Additionally, the instrument is required to operate satisfactorily,
9、 in both the terminated and monitor mode,when connected to an interface output in accordance with Recommendation G.703 1 via a length of cable which canhave an insertion loss of 0 dB to 6 dB at the half bit rate of the signal. The insertion loss of the cable at other frequencieswill be proportional
10、to f.3.4 Input impedance3.4.1 The instrument shall have a return loss better than 20 dB under the conditions listed in Table 1/O.161.TABLE 1/O.1613.5 Signal input gating3.5.1 The instrument shall incorporate a sampling circuit, operated from the incoming digital signal, such that theinstrument sense
11、s only the voltages which are present during a short gating period at the midpoint of each digit time slot.3.6 Input jitter tolerance3.6.1 The instrument shall be able to tolerate the lower limit of maximum tolerable input jitter specified in theappropriate paragraph of Recommendation G.703 1.4 Disp
12、lay4.1 The instrument shall incorporate an indicator to show the presence of a digital signal of correct amplitude andbit rate.4.2 The code violation rate shall be indicated in the range 1 in 103to at least 1 in 106. Indication of code violations,occurring in the input signal and detected as defined
13、 in 2 above, shall be determined by counting the number of codeviolations that occur during the period of at least 106digit time slots.4.3 It shall be possible to indicate the sum of the code violations. This facility will not be required at the same timeas the code violation rate is being counted a
14、nd displayed.4.4 The count capacity shall be 99 999 and a separate indicator shall be given if the count exceeds this figure.4.5 The counting sequence shall be started by operating a “start” control and shall be stopped by a “stop” control.4.6 The counter, and its display, shall be capable of being
15、reset.5 Instrument check5.1 A check facility shall be provided. This facility is to enable a check to be made of the display, counter andrecorder output and optionally of the instrument input circuits.5.2 Where the optional check of the input circuits is provided, the method of introducing code viol
16、ations into theinput digital signal shall be agreed. The violations shall be as defined in 2 above.Instrumentoperating at(kbit/s)Test conditions1544 100 ohms, nonreactive 20 kHz to 1.6 MHz2048 75/120/130 ohms, nonreactive 40 kHz to 2.5 MHz6312 75/110 ohms, nonreactive 100 kHz to 6.5 MHz8448 75 ohms,
17、 nonreactive 100 kHz to 10.0 MHzFascicle IV.4 - Rec. O.161 36 Recorder output6.1 An output signal may optionally be provided by the instrument to enable the status of the digital signal to berecorded externally in analogue and/or digital form.6.2 For the analogue output, the signal shall vary corres
18、ponding to the measured result.6.3 If the instrument has an analogue output, appropriate means for calibrating the external recorder shall beprovided.6.4 A possible arrangement relating the status of the digital input signal to the d.c. output signal is given inTable 2/O.161. The actual arrangement
19、will depend upon the count period specified for the instrument (see 4.2 above).6.5 For the digital output of the measurement result, where provided, a parallel signal in binary coded decimal(BCD) form with transistor-transistor logic (TTL) levels shall be used.7 Operating environmentThe electrical p
20、erformance requirements shall be met when operating at the climatic conditions as specified inRecommendation O.3, 2.1.TABLE 2/O.161Reference1 CCITT Recommendation Physical/electrical characteristics of hierarchical digital interfaces, Vol. III,Rec. G.703.StatusDeflection(mA or volts)Tolerance(mA or volts)No signal 0 Valid signal 5 0.2Violation rate 1 1032 0.2Violation rate 1 1042.5 0.2Violation rate 1 1053 0.2Violation rate 1 1063.5 0.2Single code violation 4 0.2
