RT-AX56U slow iperf3 in one direction

[petr23]

Hi everyone, I recently purchased RT-AX56U and when testing LAN speeds with iperf3 (TCP, 5 streams) somehow I get expected throughput only in one direction. My first device is desktop connected via ethernet cable to the router and the other device is WiFi 6 Android phone, but only when the phone is server I get 850 Mbps in AX mode (or 600 in AC mode) as expected. When my desktop acts as a server, the speed is really unstable and fluctuates between 150-350 Mbps (both AX and AC). If I create mobile hotspot using my desktop's WiFi 5 card and connect with the same phone I get 600 Mbps no matter who's client/host.

I tried to fix this by updating and resetting the router to default settings, flashing Merlin, changing cable/different ports, even tried to boot Live Ubuntu on desktop but nothing seems to help with Phone -> Desktop speeds via the router. Sadly I don't have any other pc or phone to test as well, but everything indicates it's the router.

Any tips what might be causing this? Is it possible that the router is faulty?

 

[Tech9]

Any tips what might be causing this?

Phone’s power management may cause this behaviour.

 

[petr23]

Only in one direction and only when connected to the router though (and not the PC WiFi)? Also I made sure the phone (Galaxy S10) is not in power saving mode and WiFi power savings are disabled.

 

[Tech9]

I wouldn’t even bother testing the throughput to/from mobile phone or tablet. Any speed 100Mbps or above is plenty for such devices. It just doesn’t matter.

 

[petr23]

Yea the speed is not an issue, it's just that in that one case there's clearly something wrong with the connection since the speeds iperf3 numbers wildly fluctuate and the speeds are way lower than expected unlike all other cases. I'll try to get another device for more testing in case it's my phone (even though it performs fine with the WiFi card).

 

[petr23]

So today I got my hand on WiFi 6 laptop and the behavior is still similar - when my desktop connected via eth to the router is server and the laptop sends data to it (iperf3 -c -P 10) the speed is slightly above 400 Mbps (although more stable than the phone), but when the direction is reversed and the client (laptop) is receiving data I get 800+ Mbps.

I mean the speeds are totally fine ofc, but it's still bugging me what could be causing the always lower throughput only in one direction, any ideas?

 

[Tech9]

No ideas, but another forum member was fighting recently with similar issue and found weird settings relation:

AX86U and AT&T 1 gig upload speed problem

What do you mean by "put it in access point mode". If you're doing that then you're not touching any of the AX86U's routing functions or things like hardware acceleration, AiProtection, QoS, etc. So assuming you're using Ethernet connections and not WiFi you are effectively just using the LAN...

www.snbforums.com

 

[ColinTaylor]

Check the number of spacial streams your router has enabled. Go to System Log > Wireless Log. If you're using Merlin's firmware then click on Display low level details.

Now look at the number of "NSSn" entries for Tx and Rx.

 

[Tech9]

I don't see separate NSS information for Tx and Rx:

I can only guess the number of streams by looking at link rates.

Asuswrt 49599 on AX86U.

 

[petr23]

Oh well, I just flashed older FW and the speeds are better (890/670 with my phone) so it seems to be a FW issue affecting both latest ASUSWRT and Merlin. I'll check which fw is the last good one and report back.

Btw my USB 3.0 was disabled and the Wireless log was like this for both 2.4 and 5 Ghz:

Supported VHT MCS:
NSS1 Tx: 0-11 Rx: 0-11
NSS2 Tx: 0-11 Rx: 0-11
Supported HE MCS:
80 Mhz:
NSS1 Tx: 0-11 Rx: 0-11
NSS2 Tx: 0-11 Rx: 0-11

EDIT:

Yea so it's definitely the latest FW 3.0.0.4.386.49380, with the previous one (3.0.0.4.386.45934) my client to server speeds are ~750 Mbits instead of unstable 200-350, also after applying each fw I made sure to reset the router and used only default configuration.

Any idea what would be the best way to report this to Asus so they can potentially fix it?

EDIT 2:

Same with Merlin, 386.7_0 is slow, 386.5_2 is fine.