Is the connection between the OpenWrt router and the dumb AP wired or wireless and what sort of WiFi connection do you have to your dumb AP? And what sort of transfer rates are we dealing with?
I have even just a wireless connection between my OpenWrt router and dumb AP and at my sub-100Mbit/s rates cannot see any noticeable WiFi-induced delay (less than 5ms on top of my circa 45ms LTE connection).
it's definitely not most likely, this haven't come to mind even a bit. the DUMP ap is tplink AX1800 which theoretically can handle 1.2Gbps on the 5ghz network with no issue even though my internet speed is only 300Mbps, when set the SQM for 100 there is no ping spikes 0-5ms , when raise it to 200 the ping increased a little 5-10ms, with 300 it become +40ms.
I would appreciate any suggestion for the replacement to fix the ping spikes.
The theoretical speeds are marketing bloated numbers for optimal conditions which don't apply in real life.
Other than that, make sure no other devices use the access point, the channel is not congested from neighbornets, and that the client is using the 5G band without obstacles.
Is this however an issue or just an experiment that didn't go as planned? I mean, do you often download at maximum speed and worry about the latency?
It's even less than on my WDS-setup in which I have dumb AP's connected wirelessly to my main OpenWrt router - 3x RT3200's. I see circa 750Mbit/s between OpenWrt and dumb AP and circa 350Mbit/s between client and OpenWrt router indirectly via dumb AP.
Then again, this is in the middle of the woods in the Scottish Highlands. So no interference whatsoever.
I would first try and work out if you can improve the WiFi bandwidth. Are you dealing with lots of interference and if so have you optimised as much as possible channel, bandwidth and AP placement?
Let's start with the fake 1.2 Gbps number, and to be very clear it does not matter what the vendor says. Your connected device is likely the one limiting you. Let's say it's a common device 2x2 MIMO (MCS 9, doubt you can get MCS 11), you will be talking about 960 Mbps which 60% (if you are lucky and your air is not congested in the channel) will be your real bandwidth (one way, as WiFi is not full-duplex). So, there you go 576 Mbps.
Now, if your bandwidth with the ISP is 300 Mbps, you should configure your SQM to be between 85-95% of it, let say 90%. To see the real benefit of SQM you must use 270 Mbps as the bandwidth configured in SQM.
QQ, is your AX1800 running OpenWrt? If not, expect spikes of +20 ms at least under heavy load. For a real world example see the following:
ISP -> RBPi4 (SQM) -> Dumb AP WiFi 5 (Nano HD running OpenWrt with AQL/AQM support)
ISP bandwidth 1000/50 Mbps
SQM bandwidth 800/42 Mbps
Test ran while downloading a file in another computer (computer connection 2x2 MIMO MCS 9 867 Mbps), FYI.