What Does Plesiochronous Digital Hierarchy (PDH) Mean?
The plesiochronous digital hierarchy (PDH) is a telecommunications network transmission technology designed for the transport of large data volumes across large scale digital networks.
The PDH design allows the streaming of data without having isochronous (clocks running at identical times, perfectly synchronized) to synchronize the signal exchanges. PDH clocks are running very close, but not exactly in time with one another so that when multiplexing, signal arrival times may differ as the transmission rates are directly linked to the clock rate.
PDH allows each stream of a multiplexed signal to be bit stuffed to compensate for the timing differences so that the original data stream could be reconstituted exactly as it was sent.
PDH is now obsolete and has been replaced by synchronous optical networking and synchronous digital hierarchy schemes, which support much higher transmission rates.