Your ONT, or Optical Network Terminal, is the small box mounted on a wall in your home, usually near where the fibre cable enters. It's the device that converts the light signals coming down the fibre into electrical signals your router can use. The lights on the front tell you whether your fibre connection is healthy.
ScottishFibre uses a number of different wholesale networks to deliver your service, and the ONT looks slightly different depending on which one you're on. If you're not sure which network you're on, check the paperwork left by the engineer when you were installed, or get in touch and we can tell you.
A note on Virgin Media customers: if your service is delivered over the Virgin Media (Nexfibre) network, you won't have a separate ONT. Your Virgin Media Hub has the ONT built in. Skip to the Virgin Media section below for more.
Common ONT lights, in general terms
Most ONTs have a similar set of lights, though the names and exact behaviour vary. The most common ones are:
Power: confirms the ONT has power. Should be solid green when working.
PON, Optical, or Broadband: shows the connection to the wider fibre network. Should be solid green when working.
LOS or Alarm: stands for "Loss of Signal" or signals a fault. Should be off when working. If lit (usually red), it usually means the ONT isn't receiving a signal down the fibre.
LAN, Ethernet, or Data: shows the connection between the ONT and your router. Should be green or flashing green when your router is plugged in.
TEL or VoIP: only relevant if you have a home phone service. Lights up when your phone service is connected.
Openreach
Openreach uses several different ONT models, all working in the same way but with slight differences in lights and layout. Your ONT will be a small white box. The most common models are:
Huawei 1-port: Power, Tel, Port, LOS, PON
Huawei 4-port: Power, Tel (x2), Port (x4), LOS, PON
ECI and ECI C-Series: Power, Optical, Tel (x2), LAN (x4)
Nokia: Power, PON, TEL (x2), Port
When everything is working normally, you should see:
Power: solid green
PON or Optical: solid green
LOS (where present): off (lit red usually means a problem with the fibre)
Port or LAN: solid or flashing green when your router is connected
CityFibre
CityFibre installs two different ONTs depending on when and where you were connected.
Black or grey ONT (typically Calix)
Power: solid green
Broadband: solid green
Service: solid green
Ethernet: solid or flashing green
White ONT (typically Nokia)
Power: solid green
PON: solid green
Alarm: off (red indicates an external fault)
Data: green or flashing green, indicating the connection to your router
For both models, if any of these lights are off, red, or amber when they shouldn't be, this usually points to a fault.
Virgin Media (Nexfibre)
Virgin Media's setup is different from the other networks. You won't have a separate ONT, because the ONT is built into the Virgin Media Hub itself (typically the Hub 5x for full fibre customers, or older Hubs for cable/coax customers).
For light meanings on your Virgin Media Hub, please refer to Virgin Media's own guidance, as the lights and patterns are specific to their hardware.
Vodafone
Vodafone delivers broadband over the Openreach or CityFibre networks, depending on your area. Your ONT will therefore be either an Openreach or CityFibre model. Please refer to the relevant section above based on what your ONT looks like.
TalkTalk
TalkTalk uses the Openreach and CityFibre networks for full fibre services. As with Vodafone, your ONT will be either an Openreach or CityFibre model. Please refer to the relevant section above.
Freedom Fibre
Freedom Fibre is a North West and Midlands altnet. Their ONT is typically a small white box following the standard layout: Power, PON, LOS, LAN. When working normally, Power and PON should be solid green, LOS should be off, and LAN should be green or flashing when your router is connected.
ITS
ITS Technology Group is a wholesale fibre provider serving mostly business and some residential areas. Their ONTs follow the standard layout: Power, PON, LOS, LAN, with the same patterns described under "Common ONT lights" above.
FullFibre (Zzoomm)
FullFibre and Zzoomm merged in 2025 and now operate as a single network under the Zzoomm brand. The ONT installed is typically a Nokia or Adtran model, following the standard layout: Power, PON or Optical, LOS, LAN. When working, Power and PON should be solid green, LOS should be off, and LAN should be lit when your router is plugged in.
Glide
Glide is a network provider serving mostly business premises and student accommodation. Their ONT follows the standard layout: Power, PON, LOS, LAN, with the same patterns described above.
Gigaclear
Gigaclear is a rural full fibre provider. The internal box, which Gigaclear sometimes calls an NTE (Network Termination Equipment), sits inside your home where the fibre enters, and follows the standard layout: Power, Optical or PON, LAN. When working normally, Power and Optical should be solid green, and LAN should be on when your router is plugged in.
Netomnia
Netomnia is a wholesale network operator (also the network behind YouFibre). Their ONT follows the standard layout: Power, PON, LOS, LAN, with the same patterns described under "Common ONT lights" above.
What to do if a light is off or red
If your ONT is showing a red light, a light that's off when it shouldn't be, or your service isn't working, here's what to try:
Check that the power cable is firmly plugged in at both ends, and the wall socket is switched on.
Check that the fibre cable (usually a thin green or yellow cable) is connected to the ONT and isn't kinked, bent sharply, or damaged. Be gentle with it, as fibre is fragile.
Try restarting the ONT by unplugging the power, waiting 30 seconds, then plugging it back in. Allow a few minutes for it to fully start up.
Check our network status page at [insert URL] for any known issues in your area.
If everything looks fine on your end but the LOS or Alarm light is on, it usually means there's a fault on the line outside your home that we'll need to investigate.
Important: don't press the reset button on the ONT (usually a small recessed button on the front or back) unless we've specifically asked you to. A reset can disconnect your service and isn't a fix for most issues.
Still need help? If your ONT lights are showing a fault and the steps above haven't helped, please report a fault by calling us on 0800 054 8330 or emailing [email protected] and include which lights are showing what colour. Photos of the ONT lights are really helpful, if you're able to take them.