PDH
Plesiochronous Digital Hierarchy (PDH) is the most used
transmission technique nowadays.
PDH is standardized by ITU-T, but not fully, e.g. the physical
shape of the line signal may vary between different vendors.
The basic data transfer rate in Europe consists of capacity of 32
multiplexed base PCM channels offering a 2 Mbps rate (E-1).
This multiplexing level was intended for utilizing the existing
Coaxial cable, optical fiber cable and radio links are applied in
PDH connections over 2 Mbps.
Higher data transfer rates are achieved by multiplexing lower rate
connections using hierarchical branching equipment.