This article described the “Phase analysis technique” used in evaluatingpattern depended jitter in high speed SDH system and this method would be adopted by nextversion ITU-T O.172 specification. It also gave a candid way to evaluate SDH instruments bycomparing the SDH instrument’s test result with the standard result evaluated by “Phaseanalysis technique” For more easily understanding

the paper also gave some backgroundknowledge of pattern depended jitter in high speed SDH system at the very beginning.