1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 2 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU4%,%2!0(94%,%2!0(G0G042!.3-)33)/.34!.$!2$):%$G0G04%84G0G0amended at Geneva, 1956, 1980, Malaga-Torremolinos, 1984 and Melbourne, 1988)The CCITT,considering(a) that, for a precise definition of the degree of d
2、istortion in service permitting the comparison of results ofmeasurements obtained under similar conditions in different places, it is advisable to standardize the wording of thetext that should be transmitted for the test;(b) that it is best to choose a text that can be received directly by start-st
3、op equipment and that also presentsa sequence of the combinations recognized as those that generally cause the maximum distortion,unanimously declares the view(1) that the text to transmit in the course of measurements of the degree of distortion in service should be asshown in Figure 1/R.51;this te
4、xt corresponds to the following sequence of signals emitted by start-stop equipment:letter-shift S carriage-return line-feed Q figure-shift space 9,and considering, on the other hand,(c) that, in maintenance adjustments and in the various distortion measurements that may arise in the study oflines a
5、nd equipment, it would be necessary to make use of a single apparatus offering the possibility of transmitting thedifferent combinations of signals recognized as the most practical for this purpose;(d) that the unification of the list of these combinations would permit comparison of results obtained
6、 in variousplaces,unanimously declares the view(2) that it is appropriate to recommend the construction of special transmitters for distortion measurements,which could transmit:i) the text specified in Figure 1/R.51 for measuring the degree of distortion,ii) a periodical sequence of significant inte
7、rvals, each of which has a duration of one unit interval,iii) a periodical sequence of significant intervals, each of which has a duration of two unit intervals,iv) a periodical sequence of significant intervals; a period consists of two significant intervals: an interval ofcondition Z whose duratio
8、n is equal to one unit interval and an interval of condition A whose duration isequal to six unit intervals,2 Fascicle VII.1 - Rec. R.51v) a periodical sequence of significant intervals; a period consists of two significant intervals: an interval ofcondition A whose duration is equal to one unit int
9、erval and an interval of condition Z whose duration isequal to six unit intervals;(3) that for all new test equipment, the text specified in Recommendation R.51 bis (QKS) is preferred. In theinterim, either text may be used for testing code-independent systems. For testing routes where code-dependent systemsmay be included, a text having characters with a mean length of at least 7.4 units must be used.
