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What is an ONT?

Headshot of Dave Schafer
Researched by
Dave SchaferContributing Writer
Headshot of Bri Field
Reviewed by
Bri FieldAssigning Editor
Updated 3/21/23

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An optical network terminal (ONT) is a device that converts fiber signals into a format your devices can understand. It then turns the signals from your devices back to light to send them out along the fiber cables to the internet. Essentially, it's a modem for fiber optic internet.

Your internet service provider runs their fiber line to the ONT at your home, which then converts the signal and sends it either directly to your device (if you’re plugged in via Ethernet) or to your wireless router, which can then broadcast the signal as a Wi-Fi network to your home.

In this article, we’ll explore what an ONT does, how it works, and more.

ONT vs. OLT, ONU, and PON

The world of fiber internet is filled with acronyms. This can make things a bit confusing for people who aren’t familiar with them, particularly if you’re trying to google troubleshooting steps. Let’s break down some of the acronyms you’re likely to see alongside ONT and look at how they’re different.


An Optical Line Terminal (OLT) is the device that essentially acts as the gateway between the fiber provider and the wider network of customers. It takes the internet service provider’s (or ISP’s) signal (Verizon Fios, for example) and converts it into the correct frequency for the network so that the ONTs can understand it and bring those gigabit speeds to your devices.


Optical Network Unit (ONU) is simply another name for an ONT. The two terms exist because there are multiple bodies that set and govern telecommunication standards:

The two terms can be used more or less interchangeably, although ONT is used in nearly all consumer-facing applications (like fiber internet).


Passive Optical Network (PON) is the technical term for the fiber network that brings you your internet. The entire network, from the internet service provider to your home, constitutes the PON. This means that the OLT and ONT/ONU are components of the PON.

How are ONTs different from modems?

Why does fiber require special equipment? Why won’t a “regular” modem work? Well, fiber internet uses a different type of signal from other internet technologies. Fiber optic cables transmit information via pulses of light, so something designed to decode the signals in a copper cable won’t be able to understand the fiber signal.

In other words, an ONT is a modem, just one that works with fiber connections rather than DSL or cable. Requiring a different type of modem isn’t unique to fiber. DSL and cable modems are also different—again, because DSL and cable signals are different.

Aside from the type of signal they’re designed to work with, ONTs are different from modems in another key way: their form factor. Most cable and DSL modems are small boxes designed to sit neatly on a desk. They’re relatively easy to hide and can be moved to wherever your cable or phone jack is located.

ONTs, on the other hand, are a bit larger. They are most often installed outdoors on the side of a building, or in an out-of-the way area like a closet. It’s possible that we’ll reach a point where the two are the same size and this is no longer an issue, but for the most part, we aren’t there yet.

This does mean that some additional installation work is usually required to get fiber hooked up. You may need holes drilled in your walls so that the fiber cables can be run inside your home to the ONT, for example. Usually this isn’t terribly invasive, though—we wouldn’t let it deter us from getting fiber installed.

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Fiber is faster and more reliable than cable, but cable is much more available and usually cheaper than fiber. Fiber is the clear winner when it comes to speed and performance, but its limited availability makes it off limits for most folks. That said, fiber and cable are the two best internet types out there, so really you’ll be happy with either—as long as you get
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Deciding between fiber internet and DSL is mainly a question of speed—fiber packages tend to start at DSL’s

Where is an ONT installed?

Since the ONT is usually a fixed device (in other words, you can’t move it), the location you choose to install it is important. As mentioned before,  ONTs are typically installed in out-of-sight areas like a closet or garage. This helps ensure that it doesn’t ruin your home decor (they’re not particularly attractive devices) and also keeps things out of the way if you ever need a technician to do additional work.

ONTs are also sometimes mounted externally, on the side of a house or building. There’s no particular advantage to having your ONT in one location over another—it’s more about aesthetics and maintenance considerations.

How to troubleshoot ONT problems

Unfortunately, if you suspect your ONT is having issues, there isn’t a whole lot you can do. They aren’t designed to be user-serviceable, so typical troubleshooting steps are limited:

  • Reboot the device: You can unplug the ONT and plug it back in to restart it. This can sometimes fix issues by giving the software a fresh start.
  • Reset the fiber line: You can unplug the fiber line from your ISP and plug it back in.

If these don’t resolve your internet issues, you’ll need to contact your ISP for additional help.

Get your fiber on with an ONT

The optical network terminal (ONT) serves a crucial role in your home fiber network. It is the device that makes sure your internet signal is understandable to all other devices in your home! While it’s not the easiest device to self-install or troubleshoot, it sure does help make lightning-fast internet a possibility.

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Even if you’re paying for speeds of 1 Gbps or faster for home internet, you probably won’t see those speeds on your devices. Just like that old TV game show from 20 years ago, it’s all about the weakest link.

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We believe the best information comes from first-hand customer experience and methodical research by subject-matter experts. We never source information from "content farms," and we don’t generate content using artificial intelligence (AI). You can trust that our recommendations are fact-checked meticulously and sourced appropriately by authentic, industry-recognized people.
Contributing researcher
Headshot of Dave Schafer
Researched by
Dave SchaferContributing Writer

Dave Schafer is a freelance writer with a passion for making technical concepts easy for anyone to understand. He’s been covering the world of gadgets, tech, and the internet for over 8 years, with a particular focus on TV and internet service providers. When he’s not writing, Dave can be found playing guitar or camping with his family and golden retriever, Rosie.

Contributing reviewer
Headshot of Bri Field
Reviewed by
Bri FieldAssigning Editor

Bri Field has a background in academia, research writing, and brand marketing. She has edited scientific publications, conference papers, digital content, and technical communications. As Assigning Editor, she enjoys ensuring all content is accurate, clear, and helpful. In her free time, you can find her in the kitchen trying a new recipe, out on a hike, or working through her massive TBR list.