The traditional sources of information provide electronic information signals in analogue form. This explains why voice and video signals were originally transported and routed in telecommunications networks in analogue formats. Theoretical studies later demonstrated the advantages of representing these analogue signals in digital form by using sampling, analogue-to-digital (A/D) conversion and coding. The rapid progress of microelectronics made this conversion from analogue to digital feasible, leading to a low cost and almost error-free technology. The advantages of the new digital technology have become so obvious that it will eventually replace all analogue systems in the telecommunications network.