Very Senior Member
I noticed that in a situation where airtime fairness should help it actually makes things worse. With airtime fairness on, when I copy a large file from the USB drive attached to RT-AX56U to my laptop that has Wi-Fi 4 and 2 streams (we can consider this laptop a slow client) and, at the same time, play a video (via DLNA) from that drive on my TV (Wi-Fi 5, 2 streams), the video stutters every two seconds. At this time, the copy speed remains stable. When I run a speed test on my TV during the copy operation, I get about 20Mbits. My understanding is that with airtime fairness the file copy speed should be reduced to give more airtime to the TV, but it does not happen.
Turning airtime fairness off solves the problem: the video plays normally, and, during the playback, the file copy speed is reduced a bit. Moreover, the same speed test on the TV shows speeds that are on average 15 Mbits higher. I don't know whether it applies to other router models, but looks like Broadcom's driver copes with multiple clients better without the airtime fairness setting enabled.
I'm old school. Is WiFi 4 ac or n? I think where airtime fairness helps the most is with really old/slow clients still on g.