How are latencies in Up- and Downlink measured? about crusader HOT 4 OPEN

The clocks are synchronized at the beginning of the test. Adjusting for clock drift with a synchronization at the end of the test is on my todo list. You may currently observe some clock drift with longer test durations.

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Okay, so the assumption is then a symmetrical path regarding delays? Could you point me to the code where this is done?

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Yes, it assumes the delays are symmetric on idle. The code is here. This function returns an offset to convert server time into client time.

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On linux it's only a couple calls to sample TCP_INFO:

this one runs out of band, not useful... https://www.measurementlab.net/tests/tcp-info/
https://docs.trafficserver.apache.org/en/9.0.x/admin-guide/plugins/tcpinfo.en.html runs inband, but doesn't do any post-processing

this method could be used to hook some other tool that uses some common rust geturl or equivalent lib - https://linuxgazette.net/136/pfeiffer.html

And these calls can be used on windows:

https://learn.microsoft.com/en-us/windows/win32/winsock/sio-tcp-info
https://learn.microsoft.com/en-us/windows/win32/api/mstcpip/ns-mstcpip-tcp_info_v1

just ULONG RttUs; sampled every 10-50ms
ULONG MinRttUs; vs this baseline

would be a way of measuring inband. Right now crusader just measures the effectiveness of FQ, not the actual behavior of tcp flows.

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