I.

Introduction

Telephone, communication instrument designed to transmit speech and other sounds to a distant point by means of electricity, and to reproduce them. The telephone contains a diaphragm, which vibrates when struck by sound waves. The vibrations (wave motion) are converted into electrical impulses and transmitted to a receiver, which converts the impulses back into sound.

In common usage, the term “telephone” is also applied in a much broader sense to the entire system to which an individual telephone set is connected; a system which allows the sending of not only a user’s voice but also data, pictures, or any other information which can somehow be encoded and converted into electrical energy. This information is exchanged between points connected to the network. The telephone network consists of all of the transmission paths between subscriber’s sets and of the switching machinery used to select a particular path or group of paths between subscribers.