Digital signal subscriber loop and interface circuit

Abstract

A TDM PCM telephone system and a telephone user terminal are interconnected by a digital subscriber loop circuit which provides at least a single channel communication path for digital signals of data or encoded voice origin. The digital subscriber loop circuit includes transmit and receive paths and a line interface circuit. The line interface circuit converts a selected channel of binary signals appearing at a subscriber line port of the telephone system into a corresponding bipolar return to zero (BPRZ) signals for transmission on the receive signal path. The line interface circuit also converts BPRZ signals from the transmit signal path to corresponding binary signals. These binary signals are accumulated and stored. At a time coincident with the selected channel occurrence, the line interface circuit transmits the stored signals to the subscriber line port for acceptance by the telephone system. In one arrangement, the digital subscriber loop is interfaced at opposite ends by a universal line interface circuit (ULIC) which provides for compatible use with two TDM signal formats and with any one of a plurality of commercially available single channel codecs in the associated telephone user terminal.