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.

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).

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.