FTTP - What can go wrong with speeds?

My FTTP connection has gone abysmally slow (between 1Mbps and 100 Mbps) and I have a 900mbs connection. Openreach have come out to do tests, shining a light down the fibre etc.. and have decided that they need to dig up the road somewhere it seems.

I'm really curious as to what can 'go wrong' with a fibre connection that requires physical remediation? I thought it more or less worked or not unlike copper that could slow down due to inference or degrading wires.

A bad splice, or a microbend on the fibre, leading to a high light loss reading.

Whether this would cause wildly varying throughput speeds … well I’m not so sure.

I had an ONT fault in 2019 a few months after the service was live. Long story short, we had a very bad lightning strike that back fed via the network switches and structured cabling to the copper port - effectively crippling the copper port of the ONT and not allowing it to handshake or connect at speeds beyond 100 Mbps. It actually got off lightly compared to some other gear, but that's another story...

This speed capping issue was only able to be resolved by replacing the ONT, which Openreach did promptly the day after it was reported to my CP. Although it took a bit of convincing them, that was where the problem lay.

It doesn't sound like this is your issue, but I mention it on the off chance that its not a fault with the network/PON, as ONT's are by and large very, very reliable kit.

I've heard of other faults in the CSP with insects infiltrating and nesting and then affecting the service/conection, but ultimately you really just need to leave it to Openreach to resolve. Good luck.

In reply to a post by Pheasant:

I had an ONT fault in 2019 a few months after the service was live. Long story short, we had a very bad lightning strike that back fed via the network switches and structured cabling to the copper port - effectively crippling the copper port of the ONT and not allowing it to handshake or connect at speeds beyond 100 Mbps. It actually got off lightly compared to some other gear, but that's another story...

This speed capping issue was only able to be resolved by replacing the ONT, which Openreach did promptly the day after it was reported to my CP. Although it took a bit of convincing them, that was where the problem lay.

It doesn't sound like this is your issue, but I mention it on the off chance that its not a fault with the network/PON, as ONT's are by and large very, very reliable kit.

I've heard of other faults in the CSP with insects infiltrating and nesting and then affecting the service/conection, but ultimately you really just need to leave it to Openreach to resolve. Good luck.

Thank you for the reply. I will of course leave it to OpenReach although as they need to involve the council they have no idea how long it'll take.

I was wondering what could go wrong as I realised for the last couple of years I lost interest in how things work and just wanted to expand my knowledge.

Your low speedtest results are likely due to high bit error rate, resulting in high packet loss - which you can confirm, at least roughly, by sending say 500 pings to a remote endpoint and seeing how many come back.

TCP will perform retransmits to compensate for the lost packets. However, lost packets also cause TCP's congestion control algorithm to reduce sending speed drastically, as it assumes that packet loss is caused by congestion in the network, rather than by transmission errors.

Are the lights on the ONT otherwise normal: no red LOS light and the PON light is solid green?

If you directly connect your computer to the ONT does it connect at the full gigabit link speed (rather than 100 or even 10 Mbps)?

In reply to a post by boxst:

My FTTP connection has gone abysmally slow (between 1Mbps and 100 Mbps) and I have a 900mbs connection. Openreach have come out to do tests, shining a light down the fibre etc.. and have decided that they need to dig up the road somewhere it seems.

I'm really curious as to what can 'go wrong' with a fibre connection that requires physical remediation? I thought it more or less worked or not unlike copper that could slow down due to inference or degrading wires.

Check your laptop or pc maybe your network card only support 10/100Mbps link speed.

If the OP was previously getting full >900 Mbps DL speed, then presumably the NIC on the computer would have to support more than 10/100.

Saying that it doesn't completely rule out a faulty NIC, network cable, or router or a lot of other stuff.

However sounds like Openreach believe the fault is on their side.....

I tried different computers, cables, wifi (which I get >500mbps with normally), different operating systems and router. I try to be thorough before calling Zen.

I assume they can do a light test to the splitter if need be etc