QUESTION: There are discrepancies between standards bodies regarding tolerable jitter and wander parameters - why?
ANSWER:
You are correct in observing that there are sometimes apparent discrepancies between different standards. Sometimes these discrepancies are because of historic occurences. The G.824 standard, for example, tries to provide a uniform superset that is applicable to ALL equipment handling the 1.544 hierarchy. This would include not just asynchronous multiplexers such as an M12 or M13, but other equipment as well, including cross-connects, switches, SDH/SONET equipment and so on. The G.743 standard is somewhat more specific and relates to asynchronous (i.e. PDH) multiplexers that accommodate frequency offsets between tributary and line clocks via bit stuffing (positive justification). Usually the specific standard is tighter than the generic one. The standards often vary based on the year of introduction since they reflect the "state of the art". For instance, clock recovery used to be done using analog means with resonant L-C circuits (many years ago!) but are now based on digital circuits (DPLLs) and can thus tolerate wider ranges. .
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