Abstract: A built-in test-signal generator (TG) and a built-in error-detection circuit (PE) independent of the test-signal generator are provided in a novel circuit arrangement. In response to an external stimulus, a signal path can be opened at a given point, and the signal from the test-signal generator (TG) can be injected. The signal taken from another, likewise externally selectable point of the signal path is checked in the error-detection circuit (PE); the result is fed out. Such a circuit arrangement is used to advantage where many like circuit arrangements are united in a broadband switching network consisting of a plurality of broadband switching modules. Since the test-signal generators and the error-detection circuits are independent of each other, systems tests can be performed without having to form any additional testing paths.