1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 2 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU4%,%2!0(94%,%2!0(G0G042!.3-)33)/.-!).4%.!.#%G0G0-%!352%-%.43/.G0G0#/$%G0G13G0).$%0%.$%.4G0G0).4%2.!4)/.!,3%#4)/.3G0G0/amended at New Delhi, 1960, and at Geneva, 1980and Malaga-Torremolinos, 1984)The CCITT,in
2、view ofRecommendations R.50, R.57 and R.90,considering(a) that, for the technical supervision of international telegraph circuits, it is necessary to make periodicmeasurements of distortion on their international sections when they are made up of two or more channels;(b) that certain Administrations
3、 consider it desirable to have available apparatus for making simplemeasurements automatically and periodically, giving an indication of the performance rating and transmitting an alarmwhen this rating exceeds the limits permitted for automatic switched channels,unanimously declares the view(1) that
4、 it is desirable to make distortion measurements every three months on the international sections ofinternational telegraph circuits made up of at least two channels;(2) that these measurements should be made at a modulation rate of 50 bauds;a) with sequences of significant intervals each having a d
5、uration of one or two unit intervals,b) preferably with the standardized text specified in Recommendation R.51 bis;(3) that the values shown in Table 1/R.75 for the inherent distortion in service (extracted fromRecommendation R.57) must not be exceeded on the international section of a telegraph cir
6、cuit;TABLE 1/R.75Number of channels intandem withininternational sectionThe limit of bias distortion on sequences ofsignificant intervals each having a durationof one or two unit intervals at themodulation rate employed for adjustmentshall be equivalent to the following valuesat 50 baudsIsochronous
7、distortion withstandardized textInherent start-stopdistortion withstandardized text23457%10%12%18%24%28%13%17%21%25%Note 1 The above values are valid whether the channels are amplitude-modulated or frequency-modulated.Note 2 The columns giving the limits for degrees of isochronous distortion and sta
8、rt-stop distortion on the text are not intended toestablish a law relating the degree of start-stop distortion to the degree of isochronous distortion; this law of relationship depends onthe constitution of the distortion (relative magnitudes of characteristics and fortuitous distortion).2 Fascicle
9、VII.1 - Rec. R.75(4) that these values do not take into account the possibility of regenerative repeaters or other code-dependentsystems in the international section;(5) that, in future, measurements made with the apparatus mentioned in (b) above will no doubt make itpossible to eliminate the maintenance measurements referred to above.
