Abstract: A connection system for varied distance digital communication capable of handling telephone signals utilizes Voice Activity Compression (VAC) to effectively share a given number of digital transmission channels among a greater number of virtual telephone connections. The telephone signals are delta-modulated and demodulated in system connection stations. The VAC processing circuits with a small increment of decision logic provide echo suppression. Echo suppression is thereby rendered as a "value-added" service at a relatively small increment of station cost over the cost of VAC processing. Echo interference with original telephone signal activity in the send channels is reduced by digital control of gain in the demodulation stage. The system also provides connections without VAC handling subject to echo control.

Abstract: A digital communication system employs delta-modulation coders and decoders for voice signal conversion. Signal inequalities at remote ends of a coder-decoder connection, due to unscheduled momentary interruptions of the transmission channel, are adjusted by insertion of a special pseudo-random "noise" signal at the remote demodulator. Voice Activity Compression (VAC) processing circuits, operating upon integrated digital signals which represent the analog (voice) input to the delta-modulation coder, are utilized to develop line activity indications. These indications are processed to produce VAC "channel use" information which is sent over a separate channel for remote demultiplexing control. The same activity indications are used to control remote demodulation handling and line level restoration. The remote control circuits insert the special pseudo-random signal at the remote demodulator during interruptions of the voice transmission (indicated as inactivity).