Plesiochronous Digital Hierarchy

communications (PDH) A transmission system for voice

communication using plesiochronous synchronisation.

PDH is the conventional multiplexing technology for network

transmission systems. The transmitter adds dummy information

bits to allow multiple 2-Mbit/s channels to be bit

interleaved. The receiver discards these bits once the

signals have been demultiplexed. [Is this correct?]

PDH is being replaced by SONET and other SDH (SynchronousDigital Hierarchy) schemes. Service levels are described

with terms like DS1, as in ISDN.

(2001-04-27)