ITU-T M 1060-1988 MAINTENANCE OF INTERNATIONAL LEASED CIRCUITS《国际租用电路的维护》.pdf
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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
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