Application of pulse-code modulation to an integrated telephone network. I. advantages of pulse-code modulation

An integrated telephone network is defined as one in which both speech transmission and switching are done with the same type of modulation. Pulse-code modulation offers great reliability of speech transmission by making noise, crosstalk and attenuation independent of the distance and of the number of repeaters. In switching it offers an on-off operation particularly suitable for transistors; on-off impedance ratio of 10 is satisfactory and no particular speed of operation is required. The integrated network is envisaged as consisting of a local exchange joined by pulse-code highways with a number of concentrators, each having 150-200 subscribers. The highways, operating on two pairs each, provide 24 channels. The local exchange deals only with pulse-code highways. All incoming signals are recorded in a speech memory associated with a time-switching memory. Synchronization, rather difficult in a mesh network, is achieved by introducing varying delays at the writing-in stage. The introduction of the new system into existing networks is discussed and its particular suitability for military requirements is stressed.