We are increasingly powering network devices with power provided over the Ethernet connection. In this video, you’ll learn about Power over Ethernet (PoE) and how it can be used in conjunction with your network switch and devices.
<< Previous: Switch Interface ConfigurationNext: Switch Management >>
Power over Ethernet is a way to power the devices connected to our Ethernet cables without requiring any additional power sources. We’re putting the power on the Ethernet cable itself, and we’re able to power things like cameras, wireless access points, voice over IP telephones, and many other devices. This can be very useful if you just want to run a single wire to an access point, and that way you don’t need power in the ceiling or any additional power sources, you only need that one Ethernet connection.
So where’s this power going to come from? Well, if you have a switch that supports power over Ethernet, it’s coming directly from the switch itself. That’s called an Endspan. Sometimes, you’ll need to provide power for that in-device, but your switch doesn’t support power over Ethernet. And for those scenarios, you would need an in-line power injector. This is a PoE injector that I have in my network that is supporting a large camera. And I’ve taken the data coming directly from my switch, it goes into this power over Ethernet injector, which is also a power device, and it outputs the same data and provides power on the line from the injector. This is called a Midspan connection.
You’ll generally see two different kinds of modes for power over ethernet devices. One is Mode A, where the power is being placed on exactly the same wires that the data is traveling on. This uses a functionality called phantom power, and it means that you can run your data and your power over exactly the same copper. Mode B is one where data is on one set of pairs and the power is running on a completely different set of pairs. This is separating the power and the data inside the same cable.
The original Power over Ethernet standard was called IEEE 802.3af. This was created in 2003. This was also wrapped into the updated Power over Ethernet standard, which was 802.3at. We’ll talk about that in just a moment. Now, Power over Ethernet is part of the Ethernet standard. So if you look at the 2012 version 802.3, this has now been all wrapped into that single standard.
This original Power over Ethernet provided 15.4 watts of DC power and a maximum current over that connection up 350 milliamps. We soon realized that we wanted to have more power and more capabilities over these Ethernet connections, so we updated the standard to what we call POE+. This is IEEE’s 802.3at, and this was created in 2009. This is also a standard that is now been wrapped into the 802.3 standard.
This provided for 25.5 watts of DC power and a maximum current of 600 milliamps. These will certainly not be the last Power over Ethernet standards. We’re working on ways that we could effectively power everything over our Ethernet connections, so you want to keep watching to see what we do with these Power over Ethernet specifications.