During speed tests, what causes network speed to be changing not randomly, but rather in visible "steps" between various almost constant speeds which change every few seconds?

Example from the GIF below: For few seconds, there is 37, then 47, then 40, then 52.

enter image description here

(This time I was measuring on optical connection at home with shaped maximum of 60 Mbps using Network Speed Test app from Microsoft Research. The same speed change behavior can be observed regardless of Wi-Fi or LAN connection to the router. )

  • Would you please consider using a different measuring app to see if the behavior is tied to the app or is global? I would suggest sourceforge.net/speedtest . Then, once you've got more data, please come back here, click on edit above and to the left, and add the results to the original question, for all to see. – K7AAY Nov 12 '18 at 18:56
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    @K7AAY – that one does not work but speed on Speedtest changes more fluently. So probably a tool issue. I will delete the question. – miroxlav Nov 12 '18 at 19:09
  • Naah; answer it in a day or so and someone will find the answer useful. – K7AAY Nov 12 '18 at 19:10
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    window based time averaging. – Mokubai Nov 12 '18 at 19:21
  • @Mokubai – interesting idea. But: if there were few-seconds windows, why they do not take the same time and why inside a time window the speed still changes (within some 1% range) like 10 times per second? – miroxlav Nov 12 '18 at 19:31