TABLE OF CONTENTS Telecommunications is today widely understood to mean the electrical means of communicating over a distance. The first form of telecommunications was that of the Telegraph, which was invented quite independently in 1837 by two scientists, Wheatstone and Morse. Telegraphy was on a point-to-point unidirectional basis and relied on trained operators to interpret between the spoken or written word and the special signals sent over the telegraph wire. However, the use of telegraphy did greatly enhance the operations of railways and, of course, the dissemination of news and personal messages between towns. This usefulness of telecommunications on the one hand and the limitation of needing trained operators on the other led to the aspiration for a simple means of bi-directional voice telecommunications that anyone could use. Alexander Graham Bell met this need when he invented the telephone in 1876. Remarkably soon afterwards, the World's first telephone exchange was opened in 1878 in New Haven, Connecticut, USA. Since then, telephony has become the ubiquitous means of communicating for humankind, and telephone networks using the principles of Alexander Graham Bell have been implemented throughout the World.
This chapter introduces the basic principles of telephony, covering the operation of a telephone and the way that telephones are connected via a network.
Fig. 1.1(a) illustrates a basic simple one-way telephone circuit between two people. The set-up comprises a microphone associated with the speaker, which is connected via an electrical circuit with a receiver at the remote end associated with the...
