Regenerators are responsible for maintaining the physical charactertistics of the signal throughout the network, supervising the quality of the signal received.

Inevitably, every signal sent through any medium will suffer from the following:

• Attenuation or loss of power of the original signal, as a result of dispersion and resistance of the transmission media
• Distortion or deformation of the pulses transmitted
• Noise, to a greater or lesser extent depending on the transmission medium, although it tends to be the prime cause of error.

The regenerators reconstruct the signal by amplifying it and equalizing it so that the pulses take on their original shape (amplitude and period) once more.

The physical transmission media used by the SDH network are optical fibre (terrestrial or submarine cable), metallic cable and digital radio links (terrestrial or via satellite).