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Powering an AT&T ONT with Power over Ethernet

Recently my neighborhood suffered from a power outage that lasted for a little less than an hour. Normally I wouldn’t think much of it, but with everyone in the house needing internet for work and school the one hour long outage was much more of an issue than it would have been in pre-COVID days. I decided that I should go ahead and invest in a Uninterruptable Power Supply (UPS) to prevent future network outages as the UPS can keep the internet up and laptop batteries will last at least as long as a UPS. I recently moved into a neighborhood with AT&T Fiber which presented a unique challenge to this power redundancy strategy. The fiber network requires an Optical Network Terminal (ONT) to convert the fiber optic medium to a copper one for simpler transmission through a home. Since my ONT is mounted in my garage far away from my router, I would have to either move my router into the garage or purchase two separate Uninterruptible Power Supplies (UPS). My solution to this is to instead power the ONT using a Power Over Ethernet (PoE) splitter and PoE injector powered by the same UPS that my router will use. These two devices allow the transmission of data and power over the same network cable, potentially saving a substantial amount of money and trouble.

When I began considering doing this there wasn’t anything I could find that explained that this would or would not work. I knew I could at least custom make a power cord for between the splitter and ONT, but I really didn’t want to have to do that. All I found was this DSLReports forum post that insinuated that the TP-Link splitter came with the right cable. I went for it and thought I would share my experiences so that others can benefit from them.

What do I need?

In order to power your ONT that is located away from where your UPS will be, you’ll need two things:

  • A Power over Ethernet Injector
  • A Power over Ethernet Splitter (includes DC power cable that fits the ONT)

I recommend the TP-Link TL-PoE150S Injector and the TP-Link TL-PoE10R Splitter. The splitter includes the correct power cable for the ONT, they both work at gigabit speeds (important for gigabit internet), TP-Link has always been reliable for me, and they are inexpensive at about $16 each.

Diagram for understanding the PoE setup

How do I do this?

Setting this up should be easy for nearly anyone who has any sort of experience setting up a TV or a desktop computer. If you can set up your PS4 or Xbox One, you can do this.

Splitting Power and Data for the ONT

First, you need to purchase a PoE Splitter like the one here. This device will split power and data from a network cable according to the 802.3af power delivery standard. The POWER + DATA IN port will connect to your PoE Injector (more on that in a moment), so go ahead and connect that to the network cable that previously plugged directly in to your ONT. The LAN Out port will connect to your ONT’s RJ-45 port, and the DC Out port will connect using the included power cable to the power port of the ONT. After you have all of this connected be sure to cable manage it so that next time you move something around in the garage your ONT doesn’t end up on the floor.

There are two things here that are very important to note. The first is that the PoE splitter voltage MUST be set to the 12v setting, as this is the voltage level that the ONT is expecting. Supplying any other voltage may result in damage to your ONT. This can be adjusted by using the switch next to the POWER+DATA IN port.

The second note is that the ONT (as far as my research has shown) does NOT support PoE natively. This means that if you connect your PoE power source (e.g. injector) to the ONT without using the splitter, you may damage your ONT.

Injecting Power and Data into the ONT Line

Before starting this step, make sure that you have either completed the above steps, or do not have your ONT connected to its network cable.

With that out of the way, we can begin installing the PoE injector you can find here that will supply power through the network cable to the PoE splitter wherever your ONT is located. First, you need to locate your AT&T supplied router and trace the cable that goes out of the (likely red) port labeled ONT. This cable is the one that connects to, you guessed it, your ONT. Go ahead and and power off your router and disconnect the cable from the ONT port on it. Now, connect the port on your PoE injector labeled POWER+DATA OUT to the cable that was connected to your router’s ONT port. After double-checking that the cable is connected to the correct port on the injector, you can go ahead and connect a network cable from the LAN IN port to the ONT port on your router. Go ahead and connect the power adapter for the PoE injector into the DC 48V port and plug your router back in using the same power adapter you have always used for it.

Checking Your Work

Now that all of the connections are made and everything is powered up, you should go and check the ONT. It should be powering up and connecting to the fiber optic network. After waiting a bit your network should be all set and will be able access the internet.

All that is left now is to get everything connected to your UPS for power redundancy. Next time you have a power outage, you will stay connected.

How does this work?

This setup uses the IEEE 802.3af standard for transmitting power and data over the same cable. This is a very common way of powering devices in the prosumer/enterprise networking world. Many devices like wireless access points, VoIP phones, and access control terminals use this to greatly simplify wiring. If this is your first time using it, I hope that it has opened up your eyes to all of its uses in your home.

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