Slow network performance - Speedtest is fast?

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boland

310 posts

Ultimate Geek

#272928 25-Jul-2020 14:17

I'm investigating slow speeds to my QNAP NAS. I suspect because the NAS is old (10+ years) and the load (via putty > top) is always 6+ I'm planning to replace it, but I want to make sure it's not my network that's causing the issues.

All clients are connected to a Unifi AP Lite at 5GHz. All very close to the access point.

But then I started to investigate further. When I run an internet Speedtest on any device, I get my maximum internet speed of 100Mbps. When I run an iperf3 server though and test between WiFi devices, or from a WiFi device to a Raspberry Pi4, I only get about 30-40 Mbit/sec? I'm running iperf3 from either Windows or Android client devices, and have tested as server on a Raspberry Pi4 and a Windows machine. All similar speeds, 40Mbit/sec.

Network topology is a 8-port Gbit switch with Raspberry Pi4 & QNAP TS-412 connected, and the Unifi AP Lite.

Why do I get such low speeds when running iperf3? Why seems my LAN speed slower than my internet speed?

chevrolux

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#2528601 25-Jul-2020 14:52

Silly question probably, but are you running multiple threads on your iperf client? i.e. the "-P" flag has a number set?

boland

310 posts

Ultimate Geek

#2528727 25-Jul-2020 17:42

chevrolux:

Silly question probably, but are you running multiple threads on your iperf client? i.e. the "-P" flag has a number set?

Thanks for your reply! No, I wasn't, and then I get way better performance, about 160-190 Mbit/ sec when using 5 threads.

Still not even close the advertised speed of 800Mbps though. My Intel AC 9260 is supposed to support up to gigabit speeds, but not getting that.

chevrolux

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#2528740 25-Jul-2020 18:53

Yep, so iperf is single threaded, unless you say otherwise.

What kind of Unifi AP have you got? I would suggest 200Mbps is really dam good over wifi in a "normal" situation.

boland

310 posts

Ultimate Geek

#2528741 25-Jul-2020 18:55

chevrolux: Yep, so iperf is single threaded, unless you say otherwise.

What kind of Unifi AP have you got? I would suggest 200Mbps is really dam good over wifi in a "normal" situation.

Got the latest AC Lite. 5Ghz up to 866 MBPS. Link speed in Windows is 300-600 MBPS as there's a wall.

sbiddle

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#2528799 25-Jul-2020 20:38

boland:
chevrolux: Yep, so iperf is single threaded, unless you say otherwise.

What kind of Unifi AP have you got? I would suggest 200Mbps is really dam good over wifi in a "normal" situation.

Got the latest AC Lite. 5Ghz up to 866 MBPS. Link speed in Windows is 300-600 MBPS as there's a wall.

Your expectations of what is possible are not how WiFi works.

Your AP is only 2x2 so it doesn't matter what sort of client device you have, you're limited to 2 spatial streams because that's all the AP supports.

To get a PHY rate of 866 you need to be running a 80MHz channel to maintain MCS9. Running 80MHz channels in a home environment is not recommended because your coverage will be very limited - you're basically looking at half the power of 40Mhz channels and 1/4 of the power of a 20Mhz channels. Unless you only ever want to use 5GHz in the very same room as the AP you should really only ever use 20MHz or 40MHz channels. In a normal home environment I'd only ever recommend running 20MHz channels if you're wanting to cover a whole house with a single AP.

And then we get to PHY vs real world. WiFi delivers real world speeds of around of around 60% of PHY, so the maximum possible real world throughout of a MCS9 80MHz channel at 866 PHY is around 500Mbps. Drop to 40MHz channels and the maximum speed at MCS9 400 PHY is just over 200Mbps in the real world.

Your network is working perfectly for how you've configured it. It is simply not possible to get anywhere close to 800Mbps real world throughput over WiFi with the hardware you have.

If you're going to test speeds *between* WiFi devices you also need to understand that WiFi is half duplex, and not full duplex like Ethernet. A speedtest from one WiFi connected device to another is going to be lower than a speedtest between a WiFi and the same device connected via Ethernet as a result simply because of how WiFi works.

boland

310 posts

Ultimate Geek

#2528810 25-Jul-2020 22:36

Thank you for the thorough explanation! Makes perfect sense. Guess I'll have to get a cable to my PC to get better performance.

Thanks again, much appreciated.