What is Power Over Ethernet or POE

I had been wondering over this buzz word POE lately, all newer network devices are coming with this option built in. I did some reasearch to look this up and  thought it would be worthwhile to share this with you all.

Power Over Ethernet is a newer technology which allows network devices like Wireless Access Points, Routers or evn switches to run without being plugged into an electrical outlet.  The power for the device is actually drawn from the Ethernet cable (often a CAT5, CAT5E or CAT6 cable).

However, it is not entirely to think that the power drawn is simply provided from another network device that is attached to the POE enabled device (such as a wireless access point). The power is provided at some point by a device often called the "injector" which inserts the required power on to a Ethernet Cable. Hence in order for a POE device to work, it is necessary to have an injector device in the loop.

Basically, the injector device is connected three ways, one to the power outlet in the wall, one side to the ethernet hub or switch via an ethernet cable and the third side is connected to a POE enabled device. See if the diagram below makes any sense.

Non POE devices can also be used with POE, but you have to add another device in between, which provides a DC voltage to the DC input pin on the NON POE device and provides the Ethernet signal to the Ethernet port.

The advantage of POE devices is savings on infrastructure costs as you don't have to run power lines every where to achieve this.