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I'm experiencing a strange behaviour when trying to measure the latency between two computers, running Linux (Ubuntu 16.04 LTS), connected to Wi-Fi (5 GHz 802.11n) through a common access point.
This is happening both when using a custom tool (LaTe, using UDP over IPv4 - available here: https://francescoraves483.github.io/LaMP_LaTe/) and when using ping.
The problem is that, every around 2 minutes, there is something that is slowing down a lot the masurements for a short interval (the latency goes from 2/3 ms to, sometimes, over 200/400 ms), and this is happening periodically.
For instance, when launching a series of tests of 1 minute each, the slow measurements occur, together with an around 5 percent packet loss, in one test every two. Instead, when testing over 2 minutes, they occur during all the tests, with a packet loss of around 2.5 percent, showing how there is probably something periodic that is messing up with the pings.
Do you know why this is happening? Is there some networking service, under Linux, which is periodically activated under certain cirmustances even if the user did not explicitely activated it?
The same behaviour is not occurring if pinging (or testing latency) over Ethernet. There are no cloud services, such as Dropbox, running in the background too (Dropbox was deactivated before performing these measurements) and the same behaviour could be observed when transmitting over 2.4 GHz in a completely different place and with two different computers (in a room over 80 km away from the first one).
As an additional information, one computer mounts an Intel Dual Band Wireless-AC 8265 NIC and the other one a Qualcomm Atheros AR9460 NIC, which is dual band too.
This is part of a LaTe output log showing this strange behaviour (the test was performed sending a packet every 100 ms):
Received a reply from 192.168.1.174 (id=64373, seq=345, rx_bytes=57). Time: 2.833 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=346, rx_bytes=57). Time: 3.717 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=347, rx_bytes=57). Time: 2.168 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=348, rx_bytes=57). Time: 2.174 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=349, rx_bytes=57). Time: 2.119 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=350, rx_bytes=57). Time: 2.118 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=351, rx_bytes=57). Time: 2.075 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=352, rx_bytes=57). Time: 2.032 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=353, rx_bytes=57). Time: 1.889 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=354, rx_bytes=57). Time: 2.010 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=355, rx_bytes=57). Time: 2.024 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=356, rx_bytes=57). Time: 2.113 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=357, rx_bytes=57). Time: 2.203 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=358, rx_bytes=57). Time: 2.014 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=359, rx_bytes=57). Time: 2.152 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=361, rx_bytes=57). Time: 147.029 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=362, rx_bytes=57). Time: 47.065 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=365, rx_bytes=57). Time: 2.150 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=366, rx_bytes=57). Time: 2.095 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=368, rx_bytes=57). Time: 61.026 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=369, rx_bytes=57). Time: 2.097 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=370, rx_bytes=57). Time: 134.886 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=372, rx_bytes=57). Time: 70.658 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=373, rx_bytes=57). Time: 1.798 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=375, rx_bytes=57). Time: 251.165 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=376, rx_bytes=57). Time: 151.179 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=378, rx_bytes=57). Time: 85.217 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=379, rx_bytes=57). Time: 1.853 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=381, rx_bytes=57). Time: 290.875 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=382, rx_bytes=57). Time: 193.427 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=384, rx_bytes=57). Time: 86.089 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=385, rx_bytes=57). Time: 1.805 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=388, rx_bytes=57). Time: 37.579 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=389, rx_bytes=57). Time: 2.214 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=390, rx_bytes=57). Time: 115.016 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=392, rx_bytes=57). Time: 235.182 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=393, rx_bytes=57). Time: 135.198 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=395, rx_bytes=57). Time: 2.143 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=396, rx_bytes=57). Time: 154.826 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=398, rx_bytes=57). Time: 54.547 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=399, rx_bytes=57). Time: 2.241 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=401, rx_bytes=57). Time: 2.111 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=402, rx_bytes=57). Time: 64.163 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=404, rx_bytes=57). Time: 69.373 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=405, rx_bytes=57). Time: 1.838 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=408, rx_bytes=57). Time: 269.563 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=409, rx_bytes=57). Time: 169.589 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=411, rx_bytes=57). Time: 1.842 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=412, rx_bytes=57). Time: 154.918 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=414, rx_bytes=57). Time: 93.432 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=415, rx_bytes=57). Time: 2.122 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=417, rx_bytes=57). Time: 2.579 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=418, rx_bytes=57). Time: 195.314 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=420, rx_bytes=57). Time: 108.841 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=421, rx_bytes=57). Time: 8.815 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=424, rx_bytes=57). Time: 308.488 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=425, rx_bytes=57). Time: 208.501 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=427, rx_bytes=57). Time: 8.505 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=428, rx_bytes=57). Time: 2.451 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=430, rx_bytes=57). Time: 4.135 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=431, rx_bytes=57). Time: 32.459 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=433, rx_bytes=57). Time: 58.180 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=434, rx_bytes=57). Time: 2.145 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=436, rx_bytes=57). Time: 20.896 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=437, rx_bytes=57). Time: 2.144 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=440, rx_bytes=57). Time: 30.552 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=441, rx_bytes=57). Time: 2.237 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=442, rx_bytes=57). Time: 115.026 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=444, rx_bytes=57). Time: 40.270 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=445, rx_bytes=57). Time: 2.037 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=447, rx_bytes=57). Time: 255.116 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=448, rx_bytes=57). Time: 155.147 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=450, rx_bytes=57). Time: 54.869 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=451, rx_bytes=57). Time: 2.349 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=453, rx_bytes=57). Time: 53.936 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=454, rx_bytes=57). Time: 2.153 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=455, rx_bytes=57). Time: 2.159 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=456, rx_bytes=57). Time: 2.106 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=457, rx_bytes=57). Time: 2.019 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=458, rx_bytes=57). Time: 2.107 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=459, rx_bytes=57). Time: 2.159 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=460, rx_bytes=57). Time: 2.170 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=461, rx_bytes=57). Time: 2.156 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=462, rx_bytes=57). Time: 2.155 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=463, rx_bytes=57). Time: 2.165 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=464, rx_bytes=57). Time: 2.192 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=465, rx_bytes=57). Time: 2.031 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=466, rx_bytes=57). Time: 2.094 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=467, rx_bytes=57). Time: 2.098 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=468, rx_bytes=57). Time: 2.076 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=469, rx_bytes=57). Time: 2.110 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=470, rx_bytes=57). Time: 2.109 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=471, rx_bytes=57). Time: 2.168 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=472, rx_bytes=57). Time: 3.457 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=473, rx_bytes=57). Time: 4.354 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=474, rx_bytes=57). Time: 2.142 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=475, rx_bytes=57). Time: 2.140 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=476, rx_bytes=57). Time: 2.156 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=477, rx_bytes=57). Time: 2.150 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=478, rx_bytes=57). Time: 2.157 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=479, rx_bytes=57). Time: 2.097 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=480, rx_bytes=57). Time: 2.173 ms (User-to-user)
Thank you very much in advance.
In my opinion "The same behaviour is not occurring if pinging (or testing latency) over Ethernet." you answer your own question. The wifi part of the router, networking hardware, and/or driver/OS use of is probably at fault and perhaps the only thing you can do is try other ones. If you're getting packet loss you should probably just do a search for that and see if anything improves it. – CmosBattery – 2019-03-06T05:18:09.507
@CmosBattery This seems strange... This behaviour was observed using at least 3 different APs (one 4G to Wi-Fi device at 2.4 GHz, one 5 GHz access point using 802.11n and another 5 GHz using 802.11a) and four different notebooks, with different NICs supported by different drivers (ath9k and iwlwifi for Intel cards). My doubt is actually why this is happening on these different devices and why it is happening when using Linux connected to wireless networks. – es483 – 2019-03-08T11:16:34.850