Abstract: An energy efficient sleep signature in power over Ethernet. In one embodiment, a signature of a powered device is first detected. It is then determined whether the detected signature is indicative of an unknown powered device. In one example, a detected signature of an approximately 25 k? impedance is indicative of an unknown powered device. Where the detected signature is indicative of an unknown powered device a normal PoE startup powering process can be used that includes a conventional detection, classification and powering process. Where the detected signature is indicative of a powered device that was previously known to the PSE, then powering of the PD can proceed with a fast-restart powering method that retains previous powering parameters.