BT Full Fibre 900 - Single TCP connection upload capped at 4-5mbps?

AaronL98 — Fri, 07 Aug 2026 14:41:50 GMT

Hi all, hoping someone from BT can help as I've been going in circles with support for a while now.

I'm on BT Full Fibre 900 (900 down / 110 up) and have a consistent upload issue that I've now been able to narrow down quite specifically.

The problem:
Single TCP connection upload is capped at around 4-5mbps regardless of destination. Multi connection speed tests (Ookla default) show 30-40mbps upload which looks normal on the surface, which is why support keeps dismissing the issue.

My primary use case is streaming to platforms like Twitch. For a stable 1080p60 stream I need at least 6000kbps reliably. I am consistently unable to achieve this despite being on a 110mbps upload plan.

How I've confirmed this:

Ookla in single connection mode: 4-5mbps upload
Cloudflare speed test (single connection by design): 4-5mbps upload
Twitchtest (a dedicated tool for testing upload speed directly to Twitch's ingest servers, eliminating streaming software from the equation) to Ireland and Paris: 1000-4000kbps, fluctuating
YouTube upload: similarly poor
All tests done wired, late at night when no other devices are active, ruling out local congestion

What I've already ruled out:

WiFi: all testing wired
Local network congestion: same results late at night as peak time
Home networking equipment: switch and cabling all gigabit rated
Streaming software: same results in OBS, Meld Studio, and confirmed independently via Twitchtest which bypasses streaming software entirely
VPN routing: tested NordVPN and Surfshark across multiple server locations including London, Amsterdam and Paris, no improvement
Bufferbloat: Waveform bufferbloat test returns an A grade with only +4ms upload latency increase under load

WinMTR trace findings:

YouTube trace exits BT's network cleanly, reaches Google destination with 0% loss at 14ms latency
Twitch ingest trace never visibly exits BT's network, runs out of hops without confirming delivery
Both traces show identical behaviour through BT's own hops

What BT support has done so far:

Multiple calls to support
ONT replacement
BT can see 90-97mbps at the hub on their end
BT are not raising a fault as they consider everything perfectly healthy, pointing to the 10mbps minimum guarantee being met

Each time I call I am dismissed over the phone with no escalation to a technical team. When I try to relay my findings I am told it is going over the customer support agent's head. I have a 110mbps upload plan, being told it's 97 on the hub's end which is fine, and being told the minimum guarantee is 10mbps which I'm still not hitting.

My conclusion:
The gap between multi connection (30-40mbps) and single connection (4-5mbps) upload, consistent across every destination and unaffected by VPN, points to a fault in how my line is handling individual TCP connections rather than a routing or peering issue. This isn't something I can fix on my end.

Can anyone from BT advise how to get this properly escalated to a technical team who can look at the line configuration rather than just the headline speed figures?

Re: BT Full Fibre 900 - Single TCP connection upload capped at 4-5mbps?

licquorice — Fri, 07 Aug 2026 15:00:43 GMT

As BT don't guarantee upload speed, I suspect you will have difficulty in getting a resolution.

You would probably be better served by a more professional connection rather than a BT residential connection.

This topic

BT Full Fibre 900 - Single TCP connection upload capped at 4-5mbps?

Re: BT Full Fibre 900 - Single TCP connection upload capped at 4-5mbps?