from
The Free On-line Dictionary of Computing (8 July 2008)
Plesiochronous Digital Hierarchy
PDH
<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 channels to be bit interleaved. The
receiver discards these bits once the signals have been
demultiplexed.
PDH combines multiple 2 Mb/s ({E1}) channels in Europe and
1.544 Mb/s ({DS1}) channels in the US and Japan.
PDH is being replaced by {SONET} and other SDH ({Synchronous
Digital Hierarchy}) schemes.
(2003-09-30)