PDH Over SONET/SDH: A Comprehensive Guide

This section of the SDH/SONET tutorial explains PDH concepts and the various PDH rates, including 2Mbps, 8Mbps, 34Mbps, and 140 Mbps.

PDH (Plesiochronous Digital Hierarchy) traffic, such as DS-1, E1, DS-1C, DS-2, and DS-3, is encapsulated with extra framing bytes/octets. This encapsulation allows the PDH traffic to be carried over an SDH/SONET channel.

This encapsulation is achieved using Virtual Tributaries (VT) in SONET and Virtual Containers (VC) in SDH. This means we can carry multiple DS-1 signals over a single SDH channel. For instance, 28 DS-1 signals can be carried on a single STS-1.

The term “Plesiochronous” is used because each multiplexer in the system uses its own clock for operation. ITU-T has finalized different series of recommendations for PDH. The G-series focuses on transmission systems and multiplexing equipment. The O-Series details measuring equipment specifications, and the M-Series covers transmission system maintenance.

The following rates are derived from the PDH base rate of 2.048Mbps, as described in the table below. These standards are finalized by ITU-T.