Power over Ethernet, a.k.a. PoE or 802.3af, and its new big sibling Power over Ethernet Plus, a.k.a. PoE+ or 802.3at, are forms of “inline power.” Inline power refers to providing power, either AC or DC, over the same cable that the data signals are travelling. An example of inline power you may be more familiar is USB-powered devices — devices that can be powered through a USB port, like mice, keyboards, small disk drives, reading lights, and that also to do battery recharging on headsets, smartphones, and other devices. (This requires the USB port being supplied with enough power. On some notebooks, not all the USB ports also provide power; similarly, on some desktops, USB ports in the back will also provide power but not the front ones.)
Another example which might not be obvious to people who grew up using mostly cell phones is the non-wireless home table-top telephones and wall phones, which not only didn’t need batteries or AC adapters, but kept working when the neighborhood power went out because they got their power through the phone line.
Power over Ethernet, like the name says, is a way to provide power over Ethernet cabling.
And that’s what PoE does.
According to Daniel Feldman, vice president of Business Development for Microsemi, “We invented PoE in 1998, when we were called PowerDsine.” (Microsemi acquired PowerDsine in 2007.)
When I first encountered PoE, at an Interop around a decade ago, I thought it was (just) another whacky, passing fancy, but the more I write about it, the more useful it sounds — not just for IT types, but also for facilities, security, small/branch offices, and even for residential applications.
Typically, the same cable run being used to carry network traffic, although it doesn’t have to be pushing data as well; for example, if you need to use fiber instead of Ethernet for a cable run because the distance is so great that the data signal would attenuate, you might still be able to use Ethernet to provide power.
Since its inception, PoE has evolved. Specifically, in terms of how much power it can handle.
The 2003 standard for Power over Ethernet allowed delivery of nearly 13 watts, but, notes Microsemi’s Feldman, “In 2009, IEEE ratified 802.3at, also known as Power over Ethernet