ITU-T G.230-1989 Measuring Methods for Noise Produced by Modulating Equipment and Through-Connection Filters - International Analogue Carrier Systems Study Group 15
The above requirement is derived from a consideration of data signals on a telephone-type
circuit over a 2500-km hypothetical reference circuit. Conforming to this requirement will ensure a high probability that the overall phase jitter from this source
ITU-T G.230-1989 history
1989ITU-T G.230-1989 Measuring Methods for Noise Produced by Modulating Equipment and Through-Connection Filters - International Analogue Carrier Systems Study Group 15