I was quite puzzled recently when, after unpacking a TP-LINK TL-WR740N router, plugging it in and configuring a wireless network on it, ICMP ping delays between the router and a laptop connected to it via Wi-Fi were reaching 100 milliseconds, despite a mere distance of a couple of meters between the two devices (without any obstacles). Changing channels and supported speeds didn’t help. It turned out that the reason was WMM (Wi-Fi MultiMedia) which is enabled by default.
WMM is a standard which is supposed to provide proper QoS level to various services like VoIP or video running via Wi-Fi. Apparently ICMP pings are qualified as low priority traffic (whether that makes sense or not is questionable), which results in getting the following when pinging the router from a laptop placed 3 meters away:
Reply from 192.168.67.1: bytes=32 time=3ms TTL=64
Reply from 192.168.67.1: bytes=32 time=1ms TTL=64
Reply from 192.168.67.1: bytes=32 time=1ms TTL=64
Reply from 192.168.67.1: bytes=32 time=1ms TTL=64
Reply from 192.168.67.1: bytes=32 time=3ms TTL=64
Reply from 192.168.67.1: bytes=32 time=1ms TTL=64
Reply from 192.168.67.1: bytes=32 time=1ms TTL=64
Reply from 192.168.67.1: bytes=32 time=49ms TTL=64
Reply from 192.168.67.1: bytes=32 time=73ms TTL=64
Reply from 192.168.67.1: bytes=32 time=92ms TTL=64
Reply from 192.168.67.1: bytes=32 time=115ms TTL=64
Reply from 192.168.67.1: bytes=32 time=33ms TTL=64
Reply from 192.168.67.1: bytes=32 time=55ms TTL=64
Reply from 192.168.67.1: bytes=32 time=77ms TTL=64
Reply from 192.168.67.1: bytes=32 time=98ms TTL=64
Reply from 192.168.67.1: bytes=32 time=17ms TTL=64
Reply from 192.168.67.1: bytes=32 time=39ms TTL=64
Reply from 192.168.67.1: bytes=32 time=60ms TTL=64
Reply from 192.168.67.1: bytes=32 time=82ms TTL=64
Reply from 192.168.67.1: bytes=32 time=103ms TTL=64
After disabling WMM (for the TL-WR740N router: Wireless → Wireless Advanced → uncheck Enable WMM):
Reply from 192.168.67.1: bytes=32 time=1ms TTL=64
Reply from 192.168.67.1: bytes=32 time=1ms TTL=64
Reply from 192.168.67.1: bytes=32 time=1ms TTL=64
Reply from 192.168.67.1: bytes=32 time=1ms TTL=64
Reply from 192.168.67.1: bytes=32 time=1ms TTL=64
Reply from 192.168.67.1: bytes=32 time=1ms TTL=64
Reply from 192.168.67.1: bytes=32 time=1ms TTL=64
Reply from 192.168.67.1: bytes=32 time=1ms TTL=64
Reply from 192.168.67.1: bytes=32 time=1ms TTL=64
Reply from 192.168.67.1: bytes=32 time=1ms TTL=64
Reply from 192.168.67.1: bytes=32 time=3ms TTL=64
Reply from 192.168.67.1: bytes=32 time=1ms TTL=64
Reply from 192.168.67.1: bytes=32 time=1ms TTL=64
Reply from 192.168.67.1: bytes=32 time=1ms TTL=64
Reply from 192.168.67.1: bytes=32 time=1ms TTL=64
Reply from 192.168.67.1: bytes=32 time=1ms TTL=64
Reply from 192.168.67.1: bytes=32 time=1ms TTL=64
Reply from 192.168.67.1: bytes=32 time=1ms TTL=64
Reply from 192.168.67.1: bytes=32 time=1ms TTL=64
Reply from 192.168.67.1: bytes=32 time=1ms TTL=64
I don’t know if WMM causes similar effects on other vendors’ hardware, but that possibility is worth considering if your pings are suspiciously high while “everyday” services work flawlessly.
Do you use 802.11 bgn, when i disabled a WMM the 802.11n is not working correct, I have only 54mbit that speed is 802.11g
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The person using the router mentioned in this post just sent me a screenshot from a laptop connected to it at 65 Mbit/s with WMM disabled.
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Michal, thank you very much !! I tried to solve a case a long time. After disabling the WMM setting the router and extenders based on worked as expected. Previous to that we have always dropouts and lost pings.
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