Patent ID: 6754339
Filing Date: 2004-06-22
Classification: H04M

Abstract:
A message transmission system having at least one subscriber's terminal unit, which is connected by way of a subscriber's line that is comprised of a first and second lead, with a subscriber's interface circuit (SLIC), preferably integrated, which comprises a loop detector circuit and subscriber's feeder circuit, such that in the area of, or on the subscriber's terminal device, a subscriber signaling display is provided, which may be controlled by way of a signaling control circuit, comprising:a controllable switch connected between the subscriber's interface circuit and the first lead of the subscriber's line which switch, in a first position, connects the first lead of the subscriber's line and an input of the subscriber's interface circuit with each other, and in a second position, connects the first lead of the subscriber's line with a pole of an additional power source, such that another pole of the additional power source is connected to a voltage supply input of the subscriber's interface circuit, and the controllable switch may be controlled by way of the signaling control circuit, wherein the additional power source is comprised of a first power source and a second power source, which is connected to the latter in series, such that one of the poles of the first power source, exhibits negative polarity and one of the poles of the second power source exhibits positive polarity, relative to ground potential, and that the negative pole of the first power source is connected to the feeder voltage input of the subscriber's interface circuit and in the second position of the controllable switch, the positive pole of the second power source is connected to the first lead of the subscriber's line, such that the extent of the terminal voltage of the first power source does not exceed the maximum allowable operating voltage of a subscriber's interface circuit.