SWITCHING.

Abstract

As demands on switching systems have grown, the systems have become less mechanical and more electronic, as exemplified by the evolution of switching from electromechanical devices (such as panel and crossbar switches) to semiconductor devices. The step-by-step system brought automatic switching to towns, the panel system brought automatic switching to large cities, and No. 4 ESS is bringing electronic switching to long-distance calls. The evolution in switching has been accompanied by advances in related areas, for example, in Automatic Message Accounting (AMA) and signaling by tones.