1. Plesiochronous Digital Hierarchy PDH

2. PDH - 1 PDH employs PCM multiplexing techniques PDH is one of the most widely used transmission techniques today The basic rate of data transfer in Europe consists of 32 multiplexed base PCM channels offering 2 Mbps (E-1) PDH is standardised by the ITU (not fully)

3. PDH - 2 The shape of the line signal may vary between different vendors The multiplexing level was intended to utilize the existing copper wire networks Coaxial cable, optical fibre and radio links are applied for PDH at rates over 2Mbps Higher data rates are achieved by multiplexing lower rates connections using hierarchical equipment

4. A typical Plesiochronous Drop and Insert

5. PDH - 3 The main limitations of PDH are: Inability to identify individual channels in a higher-order bit stream; Insufficient capacity for network management; Most PDH network management is proprietary; There is no standardised definition of PDH bit rates greater than 140 Mbit/s; and,

6. PDH - 4 There are different hierarchies in use around the world. Specialized interface equipment is required to interwork between two hierarchies.