In this article we will discuss PDH, will make brief discussion on PDH, last article we discuss about ISDN.

In telecommunications, a digital multiplex hierarchy is a hierarchy consisting of an ordered repetition of tandem digital multiplexers that produce signals of successively higher data rates at each level of the hierarchy.

The plesiochronous digital hierarchy (PDH) is a technology used in telecommunications networks to transport large quantities of data over digital transport equipment such as fibre optic and microwave radio systems.

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 stands for Plesiochronous Digital Hierarchy and SDH stands for Synchronous Digital Hierarchy. Both PDH and SDH are terminologies associated with digital multiplexers used in exchanges. The different hierarchies having different bit rates are combined.

PDH advantages include:

  • Equipment small enough for use in street cabinets
  • Good for point-to-point connections
  • Cost-effective support for access networks

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