Plesiochronous Digital Hierarchy

(PDH) A transmission system for voice

communication using {plesiochronous} synchronisation.

PDH is the conventional {multiplexing} technology for network

transmission systems. PDH is being replaced by {SONET} and

other SDH ({Synchronous Digital Hierarchy}) schemes. Service

levels are described with terms like {DS1}, as in {ISDN}.

(1995-03-02)