Power over Ethernet (PoE) is any technology that transmits power over an Ethernet cable. Guidelines for standardization are set forth as the IEEE 802.3af protocol. This protocol and PoE are not necessarily the same thing but, in practice, devices that conform to the standard will probably end up dominating the market.
Whenever there is an Ethernet cable available but plugging into a wall outlet is a hassle, Power over Ethernet can be useful. The technology is threatened by the fact that Ethernet cords are almost universally being phased out in favor of wireless networks. In the 802.3af standard, 48 volts of DC power are sent through the cable at a current of 350 mA to provide around 13 watts of power. Discussions in 2005 led to a new standard, 802.3at, that doubles the available power.
Desktop computers in offices of the future may be powered by nothing but an Internet cable, eliminating the need for additional electrical wiring. Power over Ethernet is also ideal for older buildings with limitations on preexisting electrical wiring. The technology is facilitated by a simple adapter, which "probes" a target first, to see if it can accept electrical power. After this is verified, power is sent through the cable concurrently with data.
Power over ethernet technology is popular for use with voice over IP (VOIP) phones, which may eventually replace conventional phones. Dedicated minicomputers have been built that only draw 13 watts, making them highly compatible with this form of power distribution. Because the technology only supplies 13 or 26 watts, use with traditional power-hungry PCs in the near future is not likely.
The goal behind Power over Ethernet is to supplant traditional power supplies for computing worldwide. Plugs and sockets vary by country, but Ethernet technology and cords are universal. For this reason, the technology is especially popular in countries where computing is still being rolled out. There are hundreds of companies pioneering the technology and trying to push it into the mainstream.