One example embodiment includes a testing device. The testing device comprises a signal reception element, an out-of-band detector and testing logic. The signal reception element is configured to receive a physical layer signal from a communication module via a physical link and to produce an incoming double modulated signal, the incoming double modulated signal including a high-speed data signal and an out-of-band data signal. The out-of-band data signal comprises diagnostic data of the communication module. The out-of-band detector is coupled to the signal reception element and is configured to extract the out-of-band data signal from the incoming double modulated signal. The testing logic is coupled to the out-of-band detector and is configured to extract and analyze the diagnostic data from the out-of-band data signal.