Transmission systems.

The past 15 years have seen very rapid progress in the technology of telecommunications and the development of services which have totally eclipsed the evolution of the previous 100 years. Transmission-system development has played a key role in this progress, with the migration from analogue carrier systems operating over twisted-pair, coaxial and radio bearers to digital systems which are now concentrated on optical fibre. These changes have themselves been fuelled by the dramatic progress made in semiconductor technology, which opened the door to an unprecedented revolution in electronic equipment and information technology. The direct result has been a very rapid fall in the cost of transmitting information over long distances.