GPON Fibre Internet: How It Works, What the Optical Terminal Does and Why "Gigabit Fibre" Doesn't Always Reach Your Laptop

Fibre internet has become the standard for flats and offices in Tbilisi: providers offer plans of hundreds of megabits and a gigabit, and the line is resistant to interference and doesn't depend on distance from the exchange the way old DSL did. But many customers are puzzled: the plan is 500 Mbit/s, yet a speed test on the laptop shows 80. Or a red light suddenly comes on at the terminal and the internet disappears completely. Let's look at how a GPON fibre connection works, where speed is lost and what to do when problems arise.

How GPON works

GPON is a passive optical network technology. An optical fibre runs from the provider's exchange and is split along the way by passive splitters among many subscribers — for example, a whole stairwell or building. A thin fibre cable enters the flat and connects to an optical network terminal (ONT). The terminal converts the light signal into an ordinary network. From there, either the terminal itself provides Wi-Fi, or a separate router connects to it.

The optical terminal and the router

• A terminal with a built-in router — one device does everything. Convenient, but the built-in Wi-Fi is often weak and the settings are limited by the provider.
• A terminal plus a separate router — the terminal acts only as an "adapter" from fibre, while Wi-Fi and the whole home network run on your router. That gives better coverage and control, but it needs setting up correctly: bridge mode on the terminal, or a proper connection that avoids double address translation.

If IPTV and phone services run over the same fibre, it's important to keep their settings when replacing the router — otherwise the TV channels or the phone will stop working.

Why your plan speed doesn't reach your device

• Wi-Fi. The most common cause. An old router, the 2.4 GHz band, walls and neighbours' networks — and of 500 Mbit/s only 50–100 remains.
• Ports. A gigabit plan won't fit through a 100 Mbit/s port on the router, computer or an old cable.
• The device. An old laptop or phone with a slow Wi-Fi adapter physically can't take a high speed.
• The network cable. An old or damaged patch cable may only run at 100 Mbit/s.
• The test server. A test through a busy or distant server shows less than the line really delivers.

The right way to check is a test on a computer connected to the router or terminal with a good cable, on a gigabit port.

Fibre cable is fragile

Optical fibre mustn't be bent sharply, pinched by a door or furniture, pulled or twisted. A kink attenuates the signal or breaks it completely. The terminal's connectors mustn't be touched with fingers or left uncovered — dust on the fibre end degrades the connection. If the cable needs moving during renovation, it should be done by the provider or a specialist with fibre splicing equipment.

Terminal lights

A terminal usually has lights for power, fibre (PON) and loss of signal (LOS). A red or flashing LOS light means no signal is arriving over the fibre: the cable is damaged in the flat or stairwell, a connector is unplugged or there's a problem on the provider's line. In that case restarting the router won't help — the cable needs checking and the provider contacting. If LOS isn't lit but there's no internet, the problem is more likely in the terminal or router settings, or on the provider's side.

What you can do yourself

• Check that the fibre cable isn't pinched or kinked, and that the connector is firmly in place.
• Restart the terminal and the router — terminal first, then router.
• Connect a computer directly by cable and check whether there's internet.
• Look at the terminal lights and tell the provider what they show.

Don't take the terminal apart, clean the fibre connector with makeshift tools or try to join damaged fibre yourself.

What our technician does

1. Identifies where the problem is: the fibre line, the terminal, the router, Wi-Fi or the device.
2. Measures speed by cable and over Wi-Fi and finds the bottlenecks.
3. Selects and sets up a router for the fibre terminal, including bridge mode, IPTV and phone.
4. Positions the terminal and router neatly and runs network cables around the flat.
5. Helps you word a fault report for the provider if the problem is on the line.

A real example

A small office on Pekini Avenue switched to a 1 Gbit/s fibre plan, but staff noticed no difference: files downloaded from the cloud just as slowly. Our technician found an old router with 100 Mbit/s ports after the terminal, and Wi-Fi running only on 2.4 GHz. We switched the terminal to bridge mode, installed a modern router with gigabit ports and Wi-Fi 6 and ran cables to the desks. Computers on cable now get about 900 Mbit/s and 400–600 over Wi-Fi, and uploading projects to the cloud became several times faster.

The terminal's location is a separate question. It's often placed wherever the provider brought the cable in: in the hallway, in a corner by the front door, sometimes in the fuse box. For Wi-Fi that's the worst spot. If the terminal provides the Wi-Fi itself, it's better to ask at installation for the cable to be brought closer to the middle of the flat. If the terminal stays by the door, a router is connected to it and moved to the centre of the flat on a network cable — inexpensive, and it solves the coverage problem.

Call a technician

If your fibre internet is slower than your plan or keeps dropping, we'll come to any district of Tbilisi around the clock. Learn more on our internet setup, router setup and internet not working pages.