AX73, AX20, etc... - Broadcom chipset OFDMA issue?
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I did one test with a WiFi 6 router TP-Link AX73 (1.0.3 Build 20210717 rel.64680(4555)) and it was very frustrating for me.
I have also received independent validation of my tests using professional equipment: https://www.snbforums.com/threads/sta-to-sta-ofdma-issue.74943
I wrote about its results to the local support (months ago), and after a long period the support answered me, that the problem was not on their side, but global - in the OFDMA technology itself (in reality - a chipset).
If this is the case, and it is impossible to fix it due to the design error of the chipset, then this is an epic fail!
OFDMA not only does not fulfill its widely advertised function, it is harmful!
So, the test is like this. It is very simple. Each user can check for himself.
- We take a Wifi 6 router. I had a TP-Link AX73 (I also tested this on AX20 router - the result is the same)
- We connect only two wireless clients to the router. Both are in AX mode. In my case, these are laptops with Intel AX200 and AX210 adapters.
- The OFDMA function must be disabled in the router settings
- With the iPerf 3, we check the speed of the wireless connection between these two clients (WLAN->WLAN test, or STA-to-STA). One of them is running a server, the other is in the role of a client. (The command I use is the simplest one: iperf-3.1.3-win64 \ iperf-3.1.3-win64 \ iperf3.exe -c 192.168.1.70 -R -P 8 -t 30)
- We get a speed about 600 Mbps
- Now turn on OFDMA and repeat the test
- We get the speed three times worse! About 200 Mbps! The result does not depend on the direction server-client or client-server.
If you do a similar test, but LAN->WLAN, if there is only one wireless client, then enabling OFDMA does not affect the WiFi speed in any way.
Degradation occurs only when two wireless clients work at the same time (and more, as I suppose).
By the way, I use the following router settings:
Power high, channel 36, width 160, WPA2 / WPA3-Personal, 802.11a / n / ac / ax mixed
TWT, Smart Connect - OFF
MU-MIMO, WMM, Airtime Fairness, Zero Wait DFS - ON
I tried different combinations of these settings, but I did not find anything critical when turning them on and off. Only OFDMA behaves inadequately.
If we take two wireless clients + two wired servers and simultaneously conduct two parallel sessions of iperf3 (LAN->WLAN + LAN->WLAN), then again - with OFFDMA turned off, the speed in each of the two client-server pairs turns out to be two to three times higher than with OFDMA turned on.
And further. If one of the wireless clients operates in the AС mode, and the second one - in AX mode, then turning ON / OFF OFDMA does not affect the speed of the wireless network.
I suspect a bundle of Broadсom's router chipset and two Intel wireless cards is to blame.
Unfortunately, I have no way to test this issue with other clients and other routers.
I am sure this is incorrect behavior. OFDMA should not degrade the bandwidth of a network in which there are only two clients and both support OFDMA. However, I cannot conduct additional tests to understand who is to blame for this issue: the firmware of the router, the Broadcom chipset and its drivers, Intel adapters or the OFDMA technology itself.
Is it possible to fix this problem?
Does the TP-link work in this direction?
Is Broadcom trying to fix her?
If the problem cannot be fixed, is the TP-link going to honestly declare this and recall the routers affected by this failure?
PS. With router AX20, the situation improved slightly after the release of firmware 1.3.1 Build 20210524 rel. 40909 (4555). So, earlier the speed was equal to 140 Mbit with OFDMA on, and 350-400 with OFDMA off. On the latest firmware, it became 300-360 with ON and 400-420 with OFDMA OFF. But there is still a loss of speed (minus 50-100 Mbps), and it is clearly and objectively noticeable - every time I switch OFDMA ON/OFF, the speed changes.
