Abstract: The invention is directed to an ATM-System adapted three-step switching unit, including an input circuit including a number of incoming group related conductors connected to a first switching stage, an output circuit including a number of outgoing group related conductors connected to a second switching stage and a third switching stage. A control unit coacts with said switching stages in order to connect one of said incoming conductors with a selected outgoing conductor by way of a connecting path, pointed out through the third switching stage. Each of the outgoing conductors belonging to the first switching stage coacts with an electro-optical converter. The respective connections between the first switching stage and the third switching stage consist of an optical conductor. The third switching stage is adapted to transfer optical information-carrying signals through the connecting path.

Abstract: The invention comprises a three-step switching unit, comprising a number of incoming group related conductors, every group connected to a first switching stage, formed as an input circuit, a number of outgoing group related conductors, every group connected to a second switching stage, formed as an output circuit and a third switching stage. A control unit coacts with the switching stages in order to connect one of the incoming conductors with a selected outgoing conductor by means of a connecting path, pointed out through the between related third switching stage. Each of the outgoing conductors, belonging to the first switching stage, coacts with an electro-optical converter. Respective connection between the first switching stage and the third switching stage consists of an optical conductor. The third switching stage is adapted to transfer optical information-carrying signals through the connecting path.