Wikipedia
Power over Ethernet, or PoE, describes any of several standard or ad hoc systems that pass electric power along with data on twisted pair Ethernet cabling This allows a single cable to provide both data connection and electric power to devices such as wireless access points, IP cameras, and VoIP phones There are several common techniques for transmitting power over Ethernet cabling Three of them have been standardized by IEEE 8023 since 2003 These standards are known as Alternative A, Alternative B, and 4PPoE For 10BASE-T and 100BASE-TX, only two of the four signal pairs in typical Cat 5 cable are used
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