A Digital Telephone with Extensions

A digital telephone concept is described where each subscriber set sends and receives digital signals (8-bit PCM). Duplex, simultaneous operation of extensions on a single pair of wires is made possible by time division multiplex (TDM) techniques. A successful feasibility demonstrator of the concept that operates at 512 kbits/s is also described. It has a digital switch at one end and digital telephones at the other, with up to three extensions talking at one time. The telephones feature a separate digital signaling channel, automatic loop-back testing, and low-power transducers.