Some CityFibre UK Broadband Lines with Nokia ONTs Suffer Upload Speed Bug
A small portion of consumers connected via ISPs on CityFibre’s national UK full fibre (FTTP) broadband network, specifically some of those with a cream white coloured Nokia Optical Network Terminal (ONT) on their interior walls, are currently known to be suffering from a bug that causes a significant drop in upload speeds.
Just to recap. CityFibre’s full fibre network currently covers over 4.7 million UK premises (4.5m Ready for Service) and they aspire to reach 8 million premises in the future. Customers who have had this installed will typically receive a small ONT (or optical modem) device from either Calix (older GPON lines) or Nokia.
The ONT is usually installed inside your home or office, near to where the fibre optic broadband cable physically enters your property, and its primary job is simply to take the optical signal and convert it into an electrical one that can be connected to your broadband router via a Local Area Network (Ethernet) port.
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Most of the time ONTs just work and you don’t need to think about them, but not always. Recently some broadband customers on CityFibre’s network – across multiple ISPs – appear to have been observing a significant drop in upload speeds (e.g. customers on faster than 1Gbps seeing uploads of c.100-300Mbps). Granted that’s not the end of the world and many may not even notice, but it’s still a huge fall (credits to WKDRED for first bringing it to our attention).
According to our industry sources, the issue was initially traced to the Nokia ONTs that CityFibre use, although some ISPs did still struggle to get related issues escalated and, in a few cases, it has caused multiple engineer visits before any action was taken.
So far, the network operator has been dealing with this and trying to mitigate the problem on a case-by-case basis, rather than deploying a network-wide fix, which is understood to have caused some frustrations among a few of their partners. Such an approach also means that consumers who aren’t yet aware of the issue may unwittingly continue to suffer from it.
What’s the cause?
CityFibre has confirmed that the issue, which appears to be primarily impacting multi-gigabit customers, exists, although they didn’t clarify what the cause was or when the final fix will be ready. In addition, there still appears to be some uncertainty around whether the Nokia ONTs are actually the cause or merely a closely associated symptom (CityFibre primarily use Nokia kit for multi-gig lines).
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However, multiple sources have informed us that CityFibre’s own engineers allegedly said the issue stems from a configuration issue, which has been preventing Nokia’s ONT devices from fully being able to utilise their upload bandwidth (swapping those for a Calix ONT or applying a generic profile to Nokia-based connections seemed to resolve it).
A CityFibre spokesperson said:
“We’re aware of an issue affecting multi-gig upload speeds for a very small number of customers on CityFibre’s network. Our team has identified the cause, agreed a mitigation and we’ll keep our partners up-to-date as we work with our supplier and implement a permanent fix.”
The issue itself is understood to have been occurring for roughly the past couple of months. Clearly something was deployed to start this all off in the first place, although at present it’s unclear whether the blame sits more with Nokia’s kit, the way CityFibre deployed an update (incorrect configuration) or at some other point in the network.
Either way, we spoke to multiple sources and most were less than pleased with CityFibre’s handling of the ongoing issue. So, if you have a multi-Gigabit line on CityFibre then it might be worth doing a few speedtests, just to check (report to your ISP if uploads are dramatically lower than expected). But remember that problems with broadband speed can also be caused by other things (slow WiFi, network congestion etc.), so make sure to rule your home environment out as much as possible.
Mark is a professional technology writer, IT consultant and computer engineer from Dorset (England), he also founded ISPreview in 1999 and enjoys analysing the latest telecoms and broadband developments. Find me on X (Twitter), Mastodon, Facebook, BlueSky, Threads.net and Linkedin.
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I had a similar issue with my BRSK (now YouFibre) ONT. I upgraded from the 1Gbps plan to the 2Gbps plan recently – all my kit was capable already and got a brand new Cat6 cable from ONT to router and also to my computer with a 2.5Gb adapter – although my download speed was affected. Uploads shot up to between 1800 – 2100 Mbps but download was still stuck at 900 ish Mbps. Took 3 weeks of emails and tests but finally got it sorted once it was escalated. Could just be residual issues from the BRSK/YouFibre merge, but odd to see a similar issue happening to me with a similar ONT.
It was a provisioning issue 🙂
I had 3 weeks of speed problems too – in the end 1 message to a guy on reddit and it was sorted within 20 mins.
Wish I had just done that in the first place
I wish YouFibre customer service replied as quickly to support requests as Jeremy does to ISPreview comments! People wait weeks to get a generic “reboot your router” response, if they bother to reply at all and don’t just black hole the ticket.
On the Brsk network, the speed profile is applied in two places, on the BNG for traffic from the internet towards the customer, and on the ONT for traffic from the customer towards the internet. It is possible for a different speed to be applied on each end which is what it’s likely to have caused the issue for you.
If it is a provisioning issue then maybe get your engineers to fix it? @Jeremy
Typical case of the automation not being done just because management and directors have not bothered to assign resources to fix the root cause.
Misstuned: We have YouFibre at my other half’s place. Service been great – get speeds promised all the time, a couple of outages when we joined, but solid since.
I agree on the customer service though, it’s gone to pot. Family recommendation turned into a farce for the recommendation cashback, and as you say “black-holed” on other things EVEN when asking questions to join as a new customer about the phone service. They won’t care now in my opinion, as all in the departure lounge waiting for VMO2 to receive the letter from CMA saying how wonderful it is for consumers and to proceed takeover. I expect Jeremy and the top team are waiting for their gold plated leaving gift.
The other bad thing is sending a letter by post and having online checkers saying your property is going to get it, only for them to ignore it and not bother, and do all the roads within a handful of metres. The houses down my road have more disposable income too compared to the houses they did and were more likely to do take-up.
My ONT was fixed on May 12th after complaining to Zen about it for about 3 weeks, since then I’ve had no issues. Shocking they’re not just rolling the fix out to everyone! Are we beta testing it?
Power cycling the ONT did give random upload speeds between about 250 and 800.
I had this exact problem in March. My normally totally stable 2.35Gbps upload speed dropped to around 250Mbps at some point in early March. Due to other things going on at the time I never got around to speaking to Zen about it but it fixed itself on March 30th and I have have had no further issues.
So it turned out people *weren’t* getting symmetrical speeds and the world didn’t end? Who could’ve guessed?
The world didn’t end, not sure why it would, but it generated a lot of complaints to ISPs (and also wasted a lot of time).
The world didn’t end but I had a lot of unhappy family member asking why things got really slow all of a sudden.
Asymmetrical speeds are a technological dead-end, anyone who argues for them is living in the past
“connected to your broadband router via a Local Area Network (Ethernet) port.”
Wrong, the ONT connects to your broadband router using its WAN port. ONTs do not connect via your Local Area Network (LAN Ethernet port).
Fritzbox ADSL routers will connect to the ONT using the LAN 1 port (when set to external modem mode) as they do not possess a WAN port.
Working for an ISP I have to say that City fibre have been awful at telling us what was going on. Several engineers visits, sending customers replacement routers, etc and then one day last week they started saying they “fixed it” but would not detail what they did.
They probably didn’t even know themselves. Problems like this are why well established companies like Openreach are so slow moving. But surely there has to be a middle ground that balances agility and cautiousness.
I had this exact issue with Zen Internet, reported it when I had some concrete historical data to show them and to their credit they were as upfront and honest with me as they could be. Eventually a fix was rolled out and they rebooted my ONT remotely. My Unifi Gateway reported a brief interruption to my ISP connection then when it came back it was guns blazing, full fat 2.3Gbps
I’ll agree though, CityFibre need to be more transparent about these things. In an ever growing connected world upload speeds are becoming more and more important by the day.