Abstract: A digital communication trunk employing digital discrete multitone communication over twisted pair copper network segments to increase the effective bandwidth therethrough. Each central office includes an end unit to connect to the network segments and digital discrete multitone repeaters are employed throughout the trunk at defined distances to maintain signal quality. A multiplexer can be employed at the central offices to combine multiple baseband signals before transmission and to extract those multiple signals after reception. In one embodiment of the present invention, four T1 rate baseband signals are combined by the multiplexer into a single signal which is transmitted at T2 rates through the trunk.

Abstract: A digital phase-locked loop circuit includes circuitry for generating substantially periodic recovered clock signals each one corresponding to a discrete amount of delay from a local clock signal. Incremental delay is added or subtracted at each clock generation cycle until the data input signal and the last-generated recovered clock signal are substantially phase-aligned. The circuit includes delay measurement circuitry for dynamically measuring the smallest quantity of delay units required to provide at least a 360 degree phase shift of the local clock signal. The circuitry for generating the recovered clock signals is then constrained to generate clock signals having a maximum delay corresponding to the last-measured quantity of delay.

Abstract: A line interface circuit supplies energizing direct current from a power source via tip and ring leads of a two wire communications line connected with a telephone apparatus, and also couples alternating current signals between the telephone line and an associated telephone facility. The line interface circuit is provided with tip and ring terminals for connection to the tip and ring leads, and power terminals for connection to the power source. Coupling circuitry is connected in series with the tip and ring terminals for providing paths for the energizing direct current and for the alternating current signals. An active tip feed circuit is connected in series between the tip terminal and the coupling circuitry for providing a tip feed path having a predetermined resistance while the telephone apparatus is in an OFF HOOK state and having a much higher resistance in response to an excess of voltage at the tip terminal.