Abstract: Traditional Ethernet is merely used in data transmission previously, so that the Ethernet device must work with own battery or external supply adapter, which increases the difficulty of wiring work. The standard which Ethernet can also deliver DC power supply in data transmission line is defined in IEEE 802.3af, promulgated in June, 2003, it can not only reduce network construction costs and simplify wiring works, but also resolve the compatibility problem of various vendors equipments. Based on the research on key technologies of IEEE 802.3af, this paper implements the function of supplying power to powered devices.

Key words: power over Ethernet (POE), IEEE 802.3af, power sourcing equipment (PSE), powered device (PD)