What Is An ONT & How Is It Used In Fiber Networks?

What Is An ONT

If you are looking to install fiber technology in your office or home, then you should understand the different components involved including an ONT.

So, what is an ONT?

An ONT or Optical Network Terminal is a device commonly known as a ‘fiber box’ that enables you to get a fiber-optic internet connection to your office or home by directly communicating with an ISP (internet service provider).

Simply put, an ONT is an outlet for fiber technology to the internet just like how a cable modem acts as an outlet to the internet for a coaxial cable connection.

Knowing where you want the ONT to be installed is important as this can affect your internet experience.

Therefore, to ensure that you have an optimal connection, place the ONT in the center of your home, nearer to power sockets, and in a location close to where you will be using the internet.

In this article, we will explore what an ONT is, how it works, and more!

What Is An ONT (Optical Network Terminal)?

ONT Terminal

An ONT, also known as an Optical network terminal, is a type of customer-premises equipment (CPE) used to connect your external network box.

Typically, it is a small white plastic box that links your internet service provider’s optical network with your local area network (LAN).

The ONT performs the crucial function of converting fiber optic broadband signals into phone, Ethernet, and Wi-Fi connections.

Without an ONT, it is not possible to utilize the high-speed capabilities of fiber optic internet.

Hence, when you are subscribed to a fiber optic service, the ISP will provide you with an ONT and send a technician to install it at your home.

Certain ISPs (Verizon and CenturyLink) offer combined WiFi routers and ONT, creating a gateway-like device that acts as both an entry and exit point for your network.

In most cases, you can still use your own router by placing the ONT into bridge mode. This ensures that you avoid the risk of Double NAT (network address translation) when two routers are present on the same network.

Double NAT can result in IP address conflicts and potential performance issues.

Bridge mode essentially disables the routing functionality of your router, allowing it to work seamlessly with the combined ONT and Wi-Fi router devices given by the ISP.

ONTs, like modems and routers, have indicator lights that display the status of your network. The specific lights and their meanings may vary depending on the model.

Common lights include

  • LOS (Loss of Signal),
  • PON (Passive Optical Network),
  • WAN (Wide Area Network),
  • AUTH
  • LINK

These lights need to be solid to indicate normal functionality. If they are flashing, it could indicate a network issue.

Modem vs ONT

A modem, short for Modulator Demodulator, is a term used for devices such as DSL, telephone, and cable modems.

It converts analog radio frequencies to digital internet signals and vice versa, using 1’s and 0’s as the signal translation.

Optical Network Terminals (ONTs) function as modems, but specifically for fiber optic internet. Both devices establish direct communication with your internet service provider.

Unlike traditional coaxial cables, an ONT uses a fiber optic cable that enables communication with the ISP through infrared light pulses.

When utilizing an ONT, a separate modem is unnecessary. Instead, devices can be connected directly to the Optical Network Terminal.

Difference Between an ONU and an ONT

While the ONT is located inside your home, you would typically find an optical network unit (ONU) outside. The ONU converts optical signals to electrical signals using fiber cables.

It then enhances and organizes different types of data, sending them upstream to the optical line terminal (OLT), which serves as the ISP’s endpoint in a PON (Passive Optical Network).

In essence, both ONTs and ONUs receive signals from the OLT, albeit with different physical locations and signal conversion functions.

How Does an ONT Work?

Data from your ISP’s optical line terminal is transmitted through a passive optical splitter. Fiber optic cables then carry the data downstream and upstream to your ONT or ONU.

If you connect devices directly to your ONT using Ethernet, you will receive internet access.

Alternatively, you can connect your ONT to a router, which will then distribute wireless signals throughout your home.

What Is the Use of ONT?

ONTs are utilized in Fiber to the Business (FTTB) or Fiber to the Home (FTTH) scenarios and serve several functions:

  • Telephone power: Certain ONT plans may offer a battery backup, enabling you to make or receive calls during power outages.
  • De-multiplexes fiber optic signals: This means that the fiber optic signals are transmitted as a single signal. The ONT separates this signal into individual components, such as internet, phone, and television signals.
  • Terminates fiber optic lines: The ONT receives fiber optic signals from the ISP’s central office and delivers them to your business or home.

How to Connect an Optical Network Terminal (ONT)?

When it comes to installing the ONT in your home, a technician will handle most of the work for you, ensuring a smooth setup process. Connecting the ONT to other devices is straightforward.

Similar to a modem, you can take an Ethernet cable, connect one end to a LAN port on the ONT, and plug the other end into your router or device.

In situations where relocating the Optical Network Terminal is not possible but you require an Ethernet connection, Powerline adapters offer a solution and they come in pairs.

You can plug one adapter into an outlet near the ONT and another near the device where you want an Ethernet connection, enabling connectivity over your home’s electrical wiring.

To set up Powerline adapters, use two Ethernet cables. Connect one cable between the ONT and the first Powerline adapter, and the second cable between your device and the second Powerline adapter.

These adapters utilize your home’s electrical wiring to transmit internet signals, provided that the wiring is on the same circuit.

However, it’s important to note some weaknesses of Powerline adapters, including:

  • Limited support up to 200 Mbps.
  • Inefficiency in homes with poor electrical wiring.
  • Incompatibility between Powerline adapters from different brands.

Powerline adapters are particularly useful in homes where running wires or dealing with thick walls is not desirable, making them a viable solution in such situations.

What Is the Best Place to Put an ONT?

It is essential to plan the placement of your ONT before the ISP technician arrives for installation. Moving the ONT later would require an additional technician visit, incurring additional costs.

Consider the following factors when deciding on the placement of your Optical Network Terminal:

  • Avoid placing it in a busy area to prevent accidental bumps or damage.
  • Ensure proximity to an electrical outlet, unless you are willing to use an extended power cable.
  • Opt for a location close to where you will primarily use the internet for an optimal and reliable connection.

During the installation, technicians will run the fiber cable from the External Termination Point (ETP) through floor, wall, or roof cavities.

When deciding on the indoor placement of the ONT, consider the ideal location for your router as well. Incorrect router placement can result in significantly reduced internet speeds.

To optimize your WiFi signal, position your router in the center of your home on a shelf. Routers emit signals in a spherical pattern, so this central placement minimizes signal obstruction by objects and prevents coverage in unused areas of your home.

What To Do When an ONT Stops Working?

If you encounter issues with your internet connection, checking the lights on your ONT can help identify the problem.

In rare cases, your ONT’s short-term memory may store errors, leading to stability and speed issues. Manually rebooting the fiber network terminal can clear these errors. To do so, simply unplug the ONT.

It’s important to note that some ONTs have a ‘Reset’ button. Avoid pressing it unless it is a last resort, as doing so will reset the device to its default settings.

The duration of the unplugged period varies, but AT&T’s Community Support suggests leaving your ONT disconnected for at least a few minutes to get it working again.

Over time, battery backup units (BBUs) can experience issues due to factors like loose wiring, overheating, or idle operation.

These problems can also affect your ONT. To troubleshoot, start by unplugging the BBU and allowing it to cool for 30 seconds.

While the ONT is unplugged, inspect the air filters of the fan. If they are clogged, clean them to prevent future overheating.

Afterwards, plug the BBU back into the outlet and check for a green light. If the light is absent, it means the BBU is not receiving power.

To confirm, test the outlet with a lamp to check its functionality. If the outlet is working, it indicates the need for a replacement BBU.

Do I Need an ONT?

For a fiber-to-the-premises (FTTP) plan, an Optical Network Terminal (ONT) is necessary. However, the installation of an ONT cannot be done by the subscriber.

Fiber optic termination, the process of enabling fiber cable connection to your wall, requires specialized tools and equipment to test the reception of fiber optic signals.

Therefore, professional installation by trained technicians is required for the proper setup and functioning of the ONT.

Final Words

Optical Network Terminals (ONTs) play an important role in delivering fiber optic internet services to your home.

Hopefully, you now understand how an ONT works, where to place it in your home as well as what you need to do if it does not work.

Daniele Besana

Daniele Besana

Daniele is a freelancer consultant with 15 years of experience in network security, customer support, Linux and Salsa. He worked for Juniper Networks in Netherlands, providing support and consultancy on security projects across Europe and Middle-East.

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