Abstract: In a small PABX with a switching matrix that has electronic crosspoints, integrated selector components comprising multiplexers or demultiplexers in C-MOS technology are used for the switching matrix. By means of individual dialing connection points, which are determined by an appropriate control address supplied by a control computer unit, the individual subscriber lines are to be connected together in internal traffic, and the subscriber lines are to be connected with an exchange line in external traffic. The switching matrix is electrically separated from other operating units by repeating coils in the subscriber lines and in the exchange lines. Central units (tone receiver, tone generator) are connected through free dialing connection points of the multiplexers.

Abstract: Error and condition messages are transmitted from unmanned telecommunication facilities to a central exchange having a maintenance control station. In order to safeguard this interference data alarm system against interferences in the secondary station and in the telephone network, the transmitting test unit is inserted in several lines used for normal telecommunications traffic, said lines leading to the maintenance control station. In order to transmit the messages, any one of these lines can be automatically selected for maintenance purposes by the transmitting test unit, whereupon a connection to the maintenance control station is automatically established and the necessary data sent to such station. A data dialog for error analysis is possible.