PoE gives you power over the Ethernet

Learn about power over Ethernet and its advantages.

"Power to the Ethernet." It's a rallying cry for network managers and technicians. Well, at least it's an enhanced technical standard designed to save money and simplify installations for network connected devices. That makes it well worth knowing about.

Power over Ethernet, abbreviated PoE, is a way to provide electrical power as well as digital signals on a single Ethernet cable. You know that PCs, servers, routers and switches all have AC power plugs as well as RJ45 Ethernet jacks. They still will. There's not THAT much power you can send on a network cable. But for devices needing only a few watts to operate, it's a great solution.

Power over networks is not really a new idea. It has been used by the telephone companies since the days of "number, please." Before the advent of multi-function wireless digital spread spectrum speaker phone answering machines, there was the generic black desk set. It weighed a ton but it always worked, power or no power. That's because the phone company maintains a room full of lead acid batteries that powers all the phones that are off-hook. The same pair of copper wires that carries the two-way voice signal also provides 48 volt power to the set.

You know how they say "everything old is new again?" That hundred year old idea of providing power and signal on one cable is looking pretty good in the digital age. The impetus is a move to VoIP, where telephones are being plugged into data networks. But now there's an extra piece. The sophisticated electronics in the phone sets need power and with standard Ethernet connections there is none available. You have to add one of those power bricks to every phone.

PoE takes us back to the days when you could just plug a phone cord into a wall jack and not worry about making sure there is AC power nearby. Curiously, the standard is 48 volts that mimics what the phone company supplies. You get about 13 watts to use as you wish, although there are devices called high power midspans that can provide up to 39.5 watts for more power hungry devices.

VoIP phones are not the only uses for Power Over Ethernet. Any remote device, such as a security camera, badge reader, wireless hotspot or access point, remotely located networking equipment, or other device inconveniently located can benefit. PoE saves you the trouble of running extra AC or DC power lines and makes it easy to turn the device on and off or reset it remotely. Battery backup is conveniently provided from a single central location just like the telco central office.

You'll find a nice tutorial on Power Over Ethernet at PowerOverEthernet.com. The official IEEE Standard 802.3af is available to download at the IEEE Standards Organization.


T1 Rex's Business Telecom Explainer offers easy to understand information about complex telecommunications and networking technology. T1 Rex explains how T1 lines work, VoIP telephone, PBX, virtual private networks, digital audio transport, WiFi & WiMax, fiber optic carriers and other business telecom services. Written by John Shepler.

For an excellent price on your next T1, T3, Optical Carrier or Ethernet WAN connection, get free quotes from several competitive providers courtesy of T1 Rex.

This was first published in February 2005

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