It tests your bandwidth while fully saturating your upload AND your download. If maxing out your upload has a huge impact on your download (like, a 70% drop), then that’s probably a sign you could tweak your network for better flow control.
That’s sort of the idea of `networkQuality`. It’s a new idea for how to measure that’s different from the standard speed test.
Through if you run it with the `-s` flag it’ll test them sequentially.
In my case, it appears that maximizing my download has a huge impact on my upload as well, which makes sense from a TCP/IP point of view. In this case, do you mean the ISP's flow control?
I'm sure others know waaay more about this, but I think it's a thing you can improve locally. Though usually I think of it as the other way around, where maxing out upload severely impacts download. My understanding is that this causes bufferbloat[0], making packets queue up for a long time on your gateway, ultimately limiting you to way less bandwidth then you should be able to get.
My one experience with this is on Ubiquiti hardware where there's a feature called "Smart Queues" you can enable. Really it's FQ_CODEL[1] under the hood. If you tell it your real maximum up/down bandwidth, minus ~5%, it'll enforce those limits in a way that prevents buffer bloat and lets you use nearly your full download bandwidth even when your upload bandwidth is maxed out. On Ubiquiti gear this has a CPU impact since it has move some traffic handling from dedicated hardware to the CPU. But it was a huge night and day difference for me. After enabling this, having a couple people on Zoom calls (highish upload) no longer tanked everyone else's download speed.
Also I think this stuff matters more when you have a large multi-user network. For normal home life, definitely not worth it. (In my case it was wifi for ~20 people).
