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High ping latency only towards wireless clients

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  • 1.  High ping latency only towards wireless clients

    Posted Mar 29, 2017 04:27 PM

    While trying to analyze a different wifi performance problem I built a really small lab consisting of a Aruba 2530-25G-PoE switch, a single IAP-315 (Central managed).


    Connected to the switch I have Miktotik Firewall that runs the DHCP server, and a Linux Desktop.


    I then connect a Laptop to the wireless 802.1ac PSK network (5GHz) that broadcasts my local network on the IAP-315.


    I've configured:

    Band Steering Mode: Prefer 5 GHz

    Airtime Fairness Mode: Fair Access

    ClientMatch: On

    80 MHz Support: Off

    Background Spectrum Monitoring: On (Both 2,4GHz and 5 GHz)


    Everything works fine I get good throughput with iperf between my laptop and desktop. But what I really can't understand is:


    If I ping from the Laptop to the Desktop, I get stready replies around 2-3 ms (as expected).


    However, if I ping from my Desktop to the Laptop I get much higher and variating rtt:


    64 bytes from icmp_req=1316 ttl=64 time=21.5 ms
    64 bytes from icmp_req=1317 ttl=64 time=52.0 ms
    64 bytes from icmp_req=1318 ttl=64 time=82.1 ms
    64 bytes from icmp_req=1319 ttl=64 time=111 ms
    64 bytes from icmp_req=1320 ttl=64 time=37.6 ms
    64 bytes from icmp_req=1321 ttl=64 time=68.4 ms
    64 bytes from icmp_req=1322 ttl=64 time=97.3 ms
    64 bytes from icmp_req=1323 ttl=64 time=24.4 ms
    64 bytes from icmp_req=1324 ttl=64 time=53.7 ms
    64 bytes from icmp_req=1325 ttl=64 time=82.3 ms
    64 bytes from icmp_req=1326 ttl=64 time=111 ms
    64 bytes from icmp_req=1327 ttl=64 time=38.2 ms
    64 bytes from icmp_req=1328 ttl=64 time=68.3 ms
    64 bytes from icmp_req=1329 ttl=64 time=304 ms
    64 bytes from icmp_req=1330 ttl=64 time=332 ms


    Can anyone explain why I get higher latency pinging in one direction than the other between the exact same two devices?


    I've tested with a few different laptops, and also testing pinging from the switch and still see the same behavior. I also saw the exact same behavior in a customers network with a similar setup.


    IAP-315 is running In my customers network I tried upgrading their IAP to Still the same behavior.



  • 2.  RE: High ping latency only towards wireless clients

    Posted Mar 29, 2017 04:36 PM

    I could also add that this is my laptop 50cm away from the AP, and no one else using the 5GHz band in the neigbourhood:

    a8:bd:27:c0:44:fc# show ap spectrum ap-list
    Spectrum AP Table
    bssid essid spectrum-id chan phy-type signal(dBm) ibss add-time last-seen
    ----- ----- ----------- ---- -------- ----------- ---- -------- ---------
    a8:bd:27:84:4f:d0 MathiasPSK 1 52 80211a-VHT-40 0 no 2017-03-28 18:42:57 2017-03-29 20:31:08
    Current Time:2017-03-29 20:31:08
    a8:bd:27:c0:44:fc# show ap spectrum interference-power
    Interference Power Table
    Channel Noise Floor(dBm) Max AP Signal(dBm) Max AP SSID Max AP BSSID WiFi ACI(dBm) Max Interference(dBm)
    ------- ---------------- ------------------ ----------- ------------ ------------- ---------------------
    52+ -94 - - - N/A -


  • 3.  RE: High ping latency only towards wireless clients

    Posted Mar 29, 2017 07:15 PM

    I would try turning off spectrum.

  • 4.  RE: High ping latency only towards wireless clients

    Posted Mar 30, 2017 12:49 AM

    I've tried turning off "Background Spectrum Monitoring", but it made no difference.

  • 5.  RE: High ping latency only towards wireless clients
    Best Answer

    Posted Mar 30, 2017 03:23 PM

    Found the problem. It was caused by a feature called PSP (Power Save Polling) on the Laptops. This causes the WiFi NIC to not immediately receive all packets sent to it (without a delay).


    On Windows 10 this feature is only enabled when running on battery. To turn it off also on battery, goto Control Panel -> Power Options -> Advanced -> WiFi Adapter and set it "Maximum Performance".


    On Linux this feature is even enabled when running with the power cord connected. To disable it run:


    sudo iwconfig wlan0 power off


    This solved my problem. My ping:


    PSP On:

    64 bytes from icmp_req=20 ttl=64 time=111 ms
    64 bytes from icmp_req=21 ttl=64 time=35.0 ms
    64 bytes from icmp_req=22 ttl=64 time=53.2 ms
    64 bytes from icmp_req=23 ttl=64 time=75.8 ms
    64 bytes from icmp_req=24 ttl=64 time=99.9 ms
    64 bytes from icmp_req=25 ttl=64 time=36.6 ms
    64 bytes from icmp_req=26 ttl=64 time=42.0 ms
    64 bytes from icmp_req=27 ttl=64 time=66.8 ms
    64 bytes from icmp_req=28 ttl=64 time=88.7 ms
    64 bytes from icmp_req=29 ttl=64 time=157 ms
    64 bytes from icmp_req=30 ttl=64 time=31.8 ms
    64 bytes from icmp_req=31 ttl=64 time=53.6 ms
    64 bytes from icmp_req=32 ttl=64 time=94.3 ms


    PSP Off:

    64 bytes from icmp_req=33 ttl=64 time=3.55 ms
    64 bytes from icmp_req=34 ttl=64 time=2.03 ms
    64 bytes from icmp_req=35 ttl=64 time=1.47 ms
    64 bytes from icmp_req=36 ttl=64 time=1.59 ms
    64 bytes from icmp_req=37 ttl=64 time=1.57 ms
    64 bytes from icmp_req=38 ttl=64 time=1.56 ms
    64 bytes from icmp_req=39 ttl=64 time=1.48 ms
    64 bytes from icmp_req=40 ttl=64 time=1.55 ms
    64 bytes from icmp_req=41 ttl=64 time=1.71 ms


    My new MacBook Pro has the same problem, even when running with power cord connected. I've so far been unable to find out how to disable it there.

  • 6.  RE: High ping latency only towards wireless clients

    Posted Sep 20, 2019 08:49 PM

    I'm seeing this on MBP and Linux. Have you figured out how to disable PSP on the Macbook? Does yours have the problem with other vendors? I'm trying to stream Steam games, but the latency is killing the experience.