pub fn ntp(
ntp_server: &str,
) -> Result<(Duration, Duration, Duration, Duration), NtpError>Expand description
Retrieve four time from ntp server: t1, t2, t3 and t4.
t1: client transmit time
t2: server received time
t3: server transmit time
t4: client received time
So, system clock offset = ((t2 - t1) + (t3 - t4)) / 2, and round-trip time = ((t4 - t1) - (t3 - t2)) / 2.