Abstract: Mitigation of faults in a telephone exchange, the faults being in the form of interruptions in calls in progress caused by brief voltage drops or failure of the AC voltage supply to the exchange. Failure of the AC supply, or a voltage drop in the stabilized Dc voltage is detected, and causes interruption of the program execution in the exchange. Depending on whether the fault has a duration greater or less than a given time, either all connections set up are released, or the connection state for the time before the occurrence of the fault is set up again.

Abstract: In a telephone system for digitalized speech transmission additional digital information is transferred without disturbing a speech communication in progress. At the sending side, time slots for the transmission of the additional digital information are created by momentarily suppressing the digital speech signals transmitted on a digital channel and, at the receiving side, the digital information is extracted from the time slots and replaced by digital signals which constitute a continuous amplitude function starting from the amplitude value which was transmitted immediately before the time slot. To distinguish the additional digital information from speech signals a special identifying code is added at the sending side. The speech transmission may employ either Delta Modulation or Pulse Code Modulation.