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

Light levels can be checked at various accessible points in the network. Light levels are the very simple first step in testing. OTDR is a more sophisticated next level of diagnosis.

Depending on the type of fault / further diagnostics can be carried out with an OTDR into a live network using a PON-aware OTDR (uses a specific wavelength that doesn’t interfere with GPON or other operational upstream and downstream wavelengths on the network). OTDR’s can pick up “loss events” along the full path of the fibre; splices, connections, PON-aware OTDRs can also detect/map out passive elements like splitters etc. If the fibre has suffered from external damage or an anomaly that isn’t otherwise physically obvious like a macrobend, these will also be detected in an OTDR trace.

As portable OTDRs are usually very expensive, I believe there is a pilot program at Openreach to install permanent OTDRs atthe headend exchange and then a relatively simple, cheap field unit that was connected (typically at a CBT port) that could have engineers run cloud based diagnosis using a smartphone app. It is intended I believe as part of the “build assurance” of new rollouts but wasn’t itself rolled out everywhere.

https://www.exfo.com/en/corporate/news-events/press-...

https://www.exfo.com/en/products/service-assurance-p...

@Zarajaz may have details?

That is actually quite interesting. I didn't know what equipment was used but I knew fibre diagnostic equipement existed but how it worked and in a pon setting i wouldn't have had a clue. Its not something i would know in my daily work or cared for. 😁

The interesting part is that they upping the error correction with the "new" fibre network and that is good long term for the bean counters and us as users of their network

OpenReach turned up this morning and said they had done something to the splitter and to test the speed.

Back up to 800/down and 108/up.

Glad it's resolved. Hopefully it will be fine from here on in.