Project for a Digital Telephone Network

A digital communication network is proposed that would integrate present telephone services and switched mediumspeed data or facsimile channels into a single general-purpose system. Efficient use of the cable plant is made through decentralization of switching and centralized control. Subscribers are connected to voice or data concentrators, and switching between different digital trunks is done in standardized asynchronous switching units. A novel synchronization method prevents any information losses. In view of the optimization of such a system, a reappraisal of basic system characteristics has been undertaken. For example, a ternarybased code system is used together with dc-balanced binary transmission. This facilitates the construction of simple noncritical terminals and repeaters. To allow all sorts of digital speech processing, such as conferencing or digital filtering, a companding law is chosen such that a linear addition of compressed samples is easily realizable. A higher than usual sampling rate of 12 kHz was chosen for several reasons: 1) simple low-pass filters in the PAM voice-concentrator are possible; 2) it allows a potential voice bandwidth of 6 kHz with a corresponding increase in telephone quality; and 3) data or picture transmission speed is considerably increased.