Pdh vs sdh describes difference between pdh and sdh

PDH vs SDH | Difference between PDH and SDH

This page PDH vs SDH describes difference between PDH and SDH. It explains basics of PDH and SDH and mentions useful difference between terms. 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. These hierarchies will comprised of many such bit streams/channels (either 24,30 or multiples) often called as tributaries.

PDH

In PDH, digital multiplexer's inputs(bit streams) are of same bit rate and are derived from different clocks from different oscillators. Each will differ within tolerance of few clock periods. Hence it is called plesiochronous.

Bit Interleaving is used in PDH to combine digital signals.

In PDH there are two main standards i.e. 30 channel one used in Europe and 24 channel one used in North America/Japan. Basic rate is 64 Kbps in North America(designated as DS0) and in Europe (designated as E0). Rates derived from 2.048 Mbps basic rate including bit stuffing in 30 channel case are mentioned below.

2.048 x 4 gives 8.448 Mbps (120 channels)
8.448 x 4 gives 34.368 Mbps (480 channels)
34.368 x 4 gives 139.264 Mbps (1920 channels)
139.264 x 4 gives 564.992 Mbps (7680 channels)

The figure-1 depicts PDH level hierarchy used in North America while figure-2 depicts PDH levels used in Europe. Rates derived from 1.544 Mbps basic rate including bit stuffing in 24 channel case are mentioned below.

1.544 x 4 gives 6.312 Mbps (96 channels)
6.312 x 7 gives 44.736 Mbps (672 channels)
44.736 x 6 gives 274.16 Mbps (4032 channels)
44.736 x 3 gives 139.264 Mbps
44.736 x 12 gives 564.992 Mbps

The table below mentions PDH rates used in Japan.