Huge fluctuations in latency/ping

[Traspler]

Hello

We have an AC87U router at work with about 30-40 Clients connected (over WiFi, mostly MacBook Pros) and noticed that our internal network suffers from huge latency fluctuations. Here is me pining another device on the network, both connected over 5GHz Wifi, both sitting about 2m from the router (no obstructions) in an otherwise empty channel:

PING 10.0.1.122 (10.0.1.122): 56 data bytes
Request timeout for icmp_seq 0
Request timeout for icmp_seq 1
Request timeout for icmp_seq 2
Request timeout for icmp_seq 3
Request timeout for icmp_seq 4
64 bytes from 10.0.1.122: icmp_seq=5 ttl=64 time=85.465 ms
Request timeout for icmp_seq 6
64 bytes from 10.0.1.122: icmp_seq=6 ttl=64 time=1006.359 ms
Request timeout for icmp_seq 8
64 bytes from 10.0.1.122: icmp_seq=7 ttl=64 time=2011.475 ms
64 bytes from 10.0.1.122: icmp_seq=8 ttl=64 time=1007.672 ms
64 bytes from 10.0.1.122: icmp_seq=9 ttl=64 time=2011.558 ms
64 bytes from 10.0.1.122: icmp_seq=10 ttl=64 time=1006.879 ms
64 bytes from 10.0.1.122: icmp_seq=11 ttl=64 time=2011.271 ms
64 bytes from 10.0.1.122: icmp_seq=12 ttl=64 time=1006.211 ms
64 bytes from 10.0.1.122: icmp_seq=13 ttl=64 time=2007.074 ms
64 bytes from 10.0.1.122: icmp_seq=14 ttl=64 time=1005.923 ms
64 bytes from 10.0.1.122: icmp_seq=15 ttl=64 time=5.986 ms
64 bytes from 10.0.1.122: icmp_seq=16 ttl=64 time=511.203 ms
64 bytes from 10.0.1.122: icmp_seq=17 ttl=64 time=2007.580 ms
64 bytes from 10.0.1.122: icmp_seq=18 ttl=64 time=1004.206 ms
64 bytes from 10.0.1.122: icmp_seq=19 ttl=64 time=2005.925 ms
64 bytes from 10.0.1.122: icmp_seq=20 ttl=64 time=1004.862 ms
64 bytes from 10.0.1.122: icmp_seq=21 ttl=64 time=2005.718 ms
64 bytes from 10.0.1.122: icmp_seq=22 ttl=64 time=1003.883 ms
64 bytes from 10.0.1.122: icmp_seq=23 ttl=64 time=1483.749 ms
64 bytes from 10.0.1.122: icmp_seq=24 ttl=64 time=478.711 ms
64 bytes from 10.0.1.122: icmp_seq=25 ttl=64 time=5.811 ms
64 bytes from 10.0.1.122: icmp_seq=26 ttl=64 time=522.801 ms
64 bytes from 10.0.1.122: icmp_seq=27 ttl=64 time=1007.114 ms
^C
--- 10.0.1.122 ping statistics ---
29 packets transmitted, 23 packets received, 20.7% packet loss
round-trip min/avg/max/stddev = 5.811/1139.454/2011.558/674.377 ms

What could cause this? Do you have any ideas what I could try (aside from resetting)?

A reboot temporarily helps but after a while (a couple of minutes) it goes into this oscillating behavior.

 

[reerden]

Try disabling beamforming if it is enabled.

 

[System Error Message]

When there is a lot of wifi traffic latency can increase to a few hundred ms and be inconsistent. If the AP is flooded with wifi traffic that too will increase the latency on each wifi client. It would help if all the clients were MU-MIMO capable.

 

[Traspler]

Thanks for the tip regarding beamforming, that helped, now it at least stopped timing out and the latency went down considerably.
But the latency is still cycling between 200-600ms which is still very problematic.
I don't think it's an issue with congestion.

Pinging a client on LAN from WiFi or even pinging the router yields 3ms pings. The issue is only between different WiFi Clients. Maybe it's a NAT issue?

 

[reerden]

Thanks for the tip regarding beamforming, that helped, now it at least stopped timing out and the latency went down considerably.
But the latency is still cycling between 200-600ms which is still very problematic.
I don't think it's an issue with congestion.

Pinging a client on LAN from WiFi or even pinging the router yields 3ms pings. The issue is only between different WiFi Clients. Maybe it's a NAT issue?

What is regulation mode set to?

 

[System Error Message]

its not a NAT issue. 30 clients all using a single wifi AP at the same time causes the WLAN latency to increase. 200-600ms is what i see in a crowded 2.4Ghz network.

 

[highwire]

I'll support reerden on his advice. To get stable 5GHz performance on my 87U (around 20 clients), I had to set the regulation mode to none/disabled, and disable both kinds of beamforming. Even at the best of times, the Quantenna SoC, which supports the 5GHz radio on the 87U, adds 2ms extra to ping and traffic as compared to the 2.4GHz band and my older AC66U router.

 

[reerden]

I'll support reerden on his advice. To get stable 5GHz performance on my 87U (around 20 clients), I had to set the regulation mode to none/disabled, and disable both kinds of beamforming. Even at the best of times, the Quantenna SoC, which supports the 5GHz radio on the 87U, adds 2ms extra to ping and traffic as compared to the 2.4GHz band and my older AC66U router.

If you're in Europe, like me, you probably can't disable regulation mode. A workaround is to set a manual channel.

 

[Calisro]

Could you have simple interference? I had issues like this stemming from a device in my house with a broken antenna. Changing channels didn't help too much interestingly enough. I started slowly unplugging devices and all of a sudden, things got better as soon as I got to that device.