[ntp:questions] Looking for a NTP stratum 2 appliance

Paul tik-tok at bodosom.net
Sat May 27 05:32:20 UTC 2017


On Fri, May 26, 2017 at 10:33 PM, Harlan Stenn <stenn at ntp.org> wrote:

> NIST doesn't control GPS.  That's done by USNO and the USAF.
>

This is true(ish)* but irrelevant.  NIST defines traceability to NIST and
GPS can be a component of UTC(NIST) traceability.

More importantly the premise of this issue is incorrect (if it has been
properly presented).  If I have an S2 clock peering both with a GPS
disciplined S1 clock and a NIST clock via NTP then "apparent" errors
("drift") are measurements of network instability not variance from
UTC(NIST).  E.g. this line:

 time-d.nist.gov .NIST.           1 u   35  512    7   48.037    1.714
2.137

does not mean this clock has a 1.7ms offset and 2.1ms of jitter with
respect to UTC(NIST).

Since NIST specs the NTP error O(50ms) due to network issues it's
insufficient for the stated need in any case.

*NIST publishes the delta and the two groups work to maintain constrained
offset between UTC(NIST) and UTC(USNO) so they can be considered equivalent
instances of UTC in the US.


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