Braking device for a railway vehicle

The brake system for a rail vehicle has at least one switch unit (2) connected to brakes (4), with the switch unit and brakes in communication via a safe communication bus (1). The communication bus for its functional testing is connected to at least one safe slave sensor (7) for the sending of a known telegram and connected to at least one safety monitor (8) for identification of the telegram and for the activating of the brake in the event of an erroneous or false telegram. The telegram is in the form of a bit rate.