The present invention refers to dyestuffs of the general Formula wherein R, X, Y and Z are defined as given in claim 1, dyestuff mixtures and hair dye compositions comprising them, as well as a process for colouring hair. The invention further provides methods for utilizing said compounds in medical practice, for diagnostic and therapeutic purposes. A logic sampling circuit generates a logic driving command of a half-bridge stage, a logic value of which corresponds to a sign of the drive current, by sampling one of the first and second PWM signals based upon active switching edges of the logic XOR signal. Quality of service monitoring devices are coupled to the respective packet-based trunks to monitor quality levels of routes between any two given communities.