Power over Ethernet (PoE):
The Basics
With the introduction of new Ethernet-enabled devices expanding geometrically, the need to power these devices from standard AC power outlets has become a limiting factor. IP telephones, wireless access points, IP cameras and device servers are examples of devices limited by the need to have an AC power outlet nearby to plug in a DC power adapter. At best, power supply installation and wiring adds labor and results in the mess of extra wiring; worst case, the lack of nearby AC power means devices cannot be installed where they are needed.
In response to this need, IEEE developed IEEE802.3af and IEEE802.3at to standardize a system of supplying low voltage power to networked devices via the communications line commonly known as Power over Ethernet (PoE). Devices can be installed wherever structured Ethernet wiring is located, without the need for AC power outlets nearby.
Power over Ethernet or PoE is a standard describing a method of passing power over Ethernet cabling. The power is transmitted using two standards, Alternative A, over spare wires, or Alternative B, along with the data.
Alternative A:
Alternative B:
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