The complaint was always the same: my calls would go choppy at exactly the moment someone elsewhere in the house started a big download or a 4K stream. The line had plenty of bandwidth on paper. The problem was never bandwidth, it was that a fat download would fill the upstream buffer and everything time-sensitive ended up queued behind it. That's bufferbloat, and it makes a fast connection feel awful under load.
The fix isn't fancy traffic shaping with per-application rules, which I tried years ago and which is a maintenance nightmare. It's just CAKE, the smart queue discipline that's been in OpenWrt for ages now. You set it slightly below your real line rate so the queue lives on your router, where you control it, instead of in the ISP's equipment where you don't:
config queue 'eth1'
option enabled '1'
option interface 'wan'
option download '95000'
option upload '18000'
option qdisc 'cake'
The numbers are kilobits, set to about 95% of the measured rate so CAKE always owns the bottleneck. The result is that a download and a video call now coexist without either party knowing the other exists. Latency under load went from a few hundred milliseconds of jitter to barely moving. Nobody noticed their downloads got fractionally slower, because they didn't, not really; they just stopped starving everything else. It's the rare bit of homelab tuning that you do once and never think about again, which is the highest praise I can give a network change.