Need advice - large throughput drops when downloading large files (single threaded only) - via ethernet

[g67575]

I'm getting large throughput drops when downloading a 1GB file from the following server (and other similar websites):

Download Test Files

Download speed test files to help diagnose problems.

xcal1.vodafone.co.uk

Here are some screenshots of the issue on an ethernet 1gbps LAN connection:

The same problem occurs via WI-FI also:

I've tried the same ethernet port in my room with a laptop, and the 1GB file downloads at a steady 400mbps.

The issue only occurs with single threaded / single connection downloads (multi connection downloads are approx. 400mbps), it's very strange.

My ISP is Virgin Media, technology type= FTTP (via Nexfibre).

The testing I've done so far indicates an issue with my PC, I think it's probably a Windows 11 issue. Changing the ethernet adapter makes no difference. I've tried a full reset of the network connection, followed by a full repair of Windows 11, but no luck yet.

EDIT - tested safe mode with networking as well, with the same result.

 

[Quartz]

Do you have jumbo packets enabled in the Advanced tab of the NIC's properties?

 

[g67575]

Do you have jumbo packets enabled in the Advanced tab of the NIC's properties?

It's disabled.

A couple of days ago, I found out about different TCP profile configurations in Windows, which can be changed with this command via command prompt:

netsh interface tcp set global autotuninglevel=

The options are:

• disabled
• highlyrestricted
• restricted
• normal
• experimental

Setting it to disabled seems to stabilise the download rate, but reduces the bandwidth significantly.

I'm going to try a Linux Live CD install, to see if Linux behaves in a similar way.