[ntp:questions] NIST vs. pool.ntp.org ?

Robert Scott no-one at notreal.invalid
Thu Mar 28 16:29:07 UTC 2013

On 28 Mar 2013 13:37:50 GMT, Rob <nomail at example.com> wrote:

>Maybe for your application it would be wise to check the roundtriptime
>only to see if it has already fallen from some initial high value,
>but not to use it in the calculation of real time (i.e. don't take
>a midpoint between request and reply).
>That is because excessive and variable delays are more likely to
>occur on the uplink than on the downlink.

I think what I may do is make the most conservative assumption about
the assymetry, i.e. that it is as bad as possible.  Then calculate the
precision based on the round-trip time.  If the round-trip time is
small enough then I don't care about the asymmetry.  Since the overall
calibration period is under my control, and is only limited by the
time the user leaves his phone on charge overnight, I could
potentially wait for 7 or 8 hours before taking my final time-stamp
reading.  That will relax the time-stamp precision to something more
like 280 msec.

Robert Scott
Hopkins, MN

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