Abstract: An auxiliary baseband telephone instrument interface is provided in an answering machine to which any auxiliary telephone instrument, whether corded or cordless, can be connected and can control the answering machine functionality by use of in-band control signals. More specifically, a controllable switch arrangement is employed to connect outputs of an auxiliary instrument jack to outputs of a telephone line jack to which the answering machine is connected, or to the answering machine functionality itself and to disconnect the outputs of the auxiliary jack from the outputs of the telephone line jack or the answering machine functionality.

Abstract: A multiplexed data channel telephone system comprising a master station (221) and one or more remote stations (222) is disclosed. Each station (221, 222) is bridged, in a parallel electrical connection, onto a wire-pair (201) that extends from the stations to a telephone switching system. Each station (221, 222) includes a voiceband line interface (110, 310) for connecting to the wire-pair (201) at voiceband frequencies, and a radio frequency line interface (700, 800) for connecting to the wire-pair (201) at radio frequencies. Each station further includes multiplexer and demultiplexer equipment (500, 600) for frequency shifting a data channel between baseband and rf. Amplitude modulation and half-duplex transmission are used in the data channel. Telephone status and control information, including ringing and answer control, are exchanged between controllers (160, 360) via the data channel.

Abstract: In order to prevent excessive voltages originating in customer owned terminal equipment from creating a hazardous condition in an associated telephone line, a protective circuit is connected between the equipment and the line. This circuit responds to an unbalanced current flow by disconnecting the equipment from the line and providing a local path to ground for the current. The circuit remains activated as long as the unbalanced current flow continues and reconnects the equipment to the line only when the current flow ceases.