"A telecommunications network, at its simplest, may be regarded as comprising a transmission network, an arrangement of transmission paths and switching centres through which signals are conveyed by a physical transmission medium. Information coming from a source, or to a receiver, is converted via a terminal into signals appropriate to the characteristics of the particular network". (Bawden and Blakeman). For example, in the standard voice telephone network system, the changes in air pressure at the microphone are represented by a corresponding variation in electrical voltage. This is an example of an analogue signal. In contrast, computer systems generate digital signals, which are represented as one of two discrete states, namely on or off (1 or 0). Other sections of this Unit will be devoted for a brief description and discussion of the process of data transmission, communication channels, transmission media, switching mechanisms, terminals and networks - all of which form the basic components of telecommunications.