1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 - TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU-!).4%.!.#% ).4%2.!4)/.!,G0G0,%!3%$G0G0#)2#5)43-!).4%.!.#%G0G0/2 Fascicle IV.2 - Rec. M.1060 the section between the terminal national centre and the interface at the customers premises. In the caseof 4-wire
2、circuits it may be possible to check the continuity of both directions of transmission by utilizingthe loop facility available at the interface point. To this end the customer may be requested to cooperate inthe utilization of this facility; the national system, i.e. between the terminal internation
3、al centre and the interface at the customerspremises. For 4-wire circuits a check of the continuity of the national system, in both directions oftransmission, may be achieved by utilizing the loop facility which may be available at the interface for thecustomer as previously mentioned; the internati
4、onal section, i.e., from terminal international centre to distant terminal international centre.Care must be taken to avoid simultaneous operation of loop facilities should they exist at both terminals.3.4 For special quality circuits to M.1020 and M.1025 certain limits may be apportioned while othe
5、rs are not(see M.1050, 4). When a fault investigation indicates that the fault can be possibly attributed to one or moreunallocated parameters, sectional measurements should be made of these parameters. The section not meeting statedstandards (for example, according to national practice), or that is
6、 significantly changed from readings recorded at thetime of initial line-up, shall be carefully investigated in an effort to isolate a fault condition.End-to-end measurements on a coordinated basis may still be required in order to fully isolate the fault, and inthis case the section making the grea
7、test contribution to the total readings should be first investigated and improvementsought.4 Overall circuit checkDepending on the nature of the fault and/or any adjustments that are made, there may be need to check theperformance of the overall circuit.5 Special care with multiterminal circuitsIn t
8、he case of multiterminal leased circuits care should be taken that fault localization and clearance procedureson one branch should not affect the availability or performance of other branches or the main body of the circuitinvolved.In the case of circuits conforming to Recommendation M.1030, such a
9、check may take the form of test calls.6 Maintenance parametersMaintenance measurements should normally be evaluated by comparison with those made during the line-upof the circuit and with the specified limits.In the case of random noise, any substantial deterioration in performance from the original
10、 line-up value mayserve to indicate a fault but with the overriding requirement that a noise level of 38 dBm0p should not be exceeded.In addition to those specified in Recommendations M.1020 and M.1025, the following characteristics andlimits may be employed for fault finding purposes on special qua
11、lity leased circuits: go-to-return crosstalk ratio of 43 dB; short interruptions in transmission. Short interruptions in transmission should be measured with aninstrument complying with Recommendation O.61 1 or O.62 2, with the threshold level set at 10 dBand the instrument dead time set at 125 ms.
12、The objective is that there should be no short interruptions intransmission, of durations 3 ms-1 min, in any 15 minute measurement period. However, where a shortinterruption is detected, the measuring period should be extended to 30 min for which the total number ofshort interruptions should not exc
13、eed one (see Notes 1-4 below); number of phase hits greater than 15 should not exceed 10 in 15 minutes. Phase hits should be countedusing an instrument complying with Recommendation O.95 3 (see Notes 2-4 below).Fascicle IV.2 - Rec. M.1060 3Note 1 Where a particular circuit is used primarily for data
14、 transmission, a more precise threshold level maybe used. Such a threshold level should be established with reference to the actual overall loss of the circuit involved andthe “line signal detector” levels of the modems being employed. For example, refer to the Recommendation cited in 4.Note 2 The l
15、imits for short interruptions in transmission, and phase hits are provisional and subject to furtherstudy.Note 3 Administrations should note that short interruptions in transmission, phase hits and amplitude hits areinterrelated such that, for example, a short interruption in transmission may result
16、 in a count on phase hit and amplitudehit measuring instruments. This must be taken into account in the application of the respective limits for shortinterruptions, phase hits and amplitude hits.Note 4 To determine if the long-term performance of a leased circuit is satisfactory, it is highly desira
17、ble tocheck for transient impairments over a protracted period, for example, 24 hours.7 Preventive maintenance measurementsIn principle, the Recommendations concerning routine tests for international telephone circuits andvoice-frequency telegraph links apply, as far as they can, to international le
18、ased circuits.It will be necessary for Administrations to agree with the renters concerned upon the times at which the circuitmay be released for test purposes.The periodicities shown in Table 1/M.1060 for measurements should be used as a guide as far as is practicableand as is appropriate to the ty
19、pe of circuit.TABLE 1/M.1060All the measurements above would normally be made only between the installations of Administrations closestto the renters installations, that is, between terminal national centres, and normally equipped with the necessary testequipment.If measurements are required to be m
20、ade at renters installations then special arrangements must be madebetween the parties concerned.Type of test PeridoicityOverall loss at 1020 Hz As given in Recommendation M.610 5Overall loss/frequency distorsion AnnuallyNoise power level (see note) As 1020 Hz testImpulsive noise 6-monthlyGroup-dela
21、y distorsion AnnuallyTotal distorsion AnnuallyNote See Recommendation M.1050 3.5.4 Fascicle IV.2 - Rec. M.10608 Signal transmission levelThe signal transmitted by the renters apparatus should not exceed the limits (Note 3) shown below at the inputto the international section: Data transmission (Reco
22、mmendation V.2 6 13 dBm0 Voice-frequency telegraphyamplitude-modulatedfrequency-modulatedSee Recommendation M.810, 4.1 Phototelegraph or facsimileamplitude modulation (white level) 3 dBm0frequency modulation 13 dBm0 Simultaneous transmission of various signalstotal power 13 dBm0Note 1 The above reco
23、mmendations apply when the whole of the bandwidth is devoted to one particulartransmission at any one time. When the band is divided among two or more types of transmission, the power levelspermitted by the various Recommendations mentioned above should be reduced by the quantity 10 log (3100/x) dB,
24、where x is the nominal bandwidth in hertz occupied by the transmission concerned.Note 2 In addition to the above specification, discrete frequency signals must comply with the requirementsof Recommendation G.224 7.Note 3 These are considered too high by some Administrations and additional study of t
25、hese limits isanticipated in the future.9 Level limiterWhere level limiting devices are fitted on the circuit, they should not introduce distortion when the levelstransmitted are within the permitted limits.10 Short-time rerouting of special quality leased circuitsThe make good of a special quality
26、circuit in case of a breakdown or planned outage needs special attention inorder to keep the circuit characteristics within the required limits.If there is a breakdown or planned interruption of a transmission system, rerouting should be carried out as faras possible at group, supergroup, etc., or d
27、igital path level. This would normally not seriously affect the attenuation andgroup-delay distortion. When such a rerouting of transmission links cannot be effected or when only the circuitconcerned is faulty, a reroute circuit or circuit section of similar constitution as that in service should be
28、 chosen, inparticular with regard to the number of FDM carrier sections and the relative number of analogue and digital circuitsections. The procedure of short-time rerouting at audio level can be facilitated if nominated reroute circuit sectionshaving the same characteristics as the circuit section
29、s of the regular route are available. This consideration also applies tothe local line sections.The circuit control station, if not directly involved, should be apprised of short-time rerouting which mightaffect the operation of the circuit. If a complete line-up is not practical, e.g., due to the e
30、xpected short duration of therearrangement, it is a minimum requirement that at least a check of the circuit overall loss at the reference frequency anda measurement of the random circuit noise should be made.Fascicle IV.2 - Rec. M.1060 5References1 CCITT Recommendation Simple equipment to measure i
31、nterruptions on telephone-type circuits, Vol. IV, Rec.O.61.2 CCITT Recommendation Sophisticated equipment to measure interruptions on telephone-type circuits,Vol. IV, Rec. O.62.3 CCITT Recommendation Phase and amplitude hit counters for telephone-type circuits, Vol. IV, Rec. O.95.4 CCITT Recommendat
32、ion 9600 bits per second modem standardized for use on point-to-point 4-wire leasedtelephone-type circuits, Vol. VIII, Rec. V.29, 6.1.5 CCITT Recommendation Periodicity of maintenance measurements on circuits, Vol. IV, Rec. M.610.6 CCITT Recommendation Power levels for data transmission over telephone lines, Vol. VIII, Rec. V.2.7 CCITT Recommendation Maximum permissible value for the absolute power level (power referred to onemilliwatt) of a signalling pulse, Vol. III, Rec. G.224.
