Re: Low capped TCP network speeds over the Internet

[Michael van Elst <mlelstv%serpens.de@localhost>]

On Sat, Mar 07, 2026 at 12:19:11AM -0300, z411 wrote:
> 
> In any case, I tried different buffer sizes, and the stability of the
> connection seems to change with it. For example, with a 6303600 byte
> buffer it can reach surprising speeds in the best case:
> 
> https://u.omaera.org/nbsd_good_6303600.png

Yes, that window size caps speed at about 30MByte/s.


> That said, increasing the buffer this much makes the packet loss more
> common and whenever it happens it seems to have a really hard time
> recovering from it, to the point it often stalls completely. It's as if
> it's choking:
> 
> https://u.omaera.org/nbsd_bad_5042880.png

When you use a tool like xplot or wireshark you can see that the
send window collapsed. It should still transmit at least at 7kbyte/s
and slowly recover. Without further "congestion events" it would
take about 15 minutes, but with such events, it stalls again.

https://cdn.netbsd.org/pub/NetBSD/misc/mlelstv/tcp.diff

is a patch with my local changes to the TCP code.

It would be interesting to see how that affects your setup.


Greetings,
-- 
                                Michael van Elst
Internet: mlelstv%serpens.de@localhost
                                "A potential Snark may lurk in every tree."