I also assumed that despite what you wrote you were using your (too few) S1 devices. I would agree that you probably should not poll NIST at small intervals for various reasons. However I suspect that there's a deeper misunderstanding. Per NIST the US Federal GNSS system (known as the Global Positioning System or GPS) can be part of system* that is considered to produce measurements traceable to the NIST national standards. Using NIST servers via the public Internet likely *cannot* produce measurements that are traceable to NIST (in a meaningful way).
*"GPS disciplined oscillators can be used to establish traceability to the national time and frequency standards maintained by NIST" [ https://www.nist.gov/pml/time-and-frequency-division/services/gps-data-archive]. Note that NTP fed by a GPS PPS produces a GPS disciplined oscillator. On Fri, May 26, 2017 at 10:31 AM, Matthew Huff <mh...@ox.com> wrote: > We do sync our systems to our stratum 1 servers. The issue is that the > regulations require us to verify that we aren't 50 msec away from NIST > time, not GPS time. By running our stratum 2 servers with a preference to > nist servers and also other ntp servers, our client machines can connect to > our stratum 1 and 2 servers and we can monitor the diff between the local > client time and NIST > > > On May 26, 2017, at 9:49 AM, Miroslav Lichvar <mlich...@redhat.com> > wrote: > > > >> On Fri, May 26, 2017 at 12:11:30PM +0000, Matthew Huff wrote: > >> Thanks. I agree that the appliance doesn’t appear to exist. It’s a > shame that it doesn’t, I think it would be a good idea. > >> > >> The 50 msec isn’t that hard to reach on an average basis, but we > routinely see drifts away from that on occasions. The minpoll idea would > probably fix this, but was hesitant to poll that frequently. I just found > NIST’s NTP page and they specify to not poll more frequently that every 4 > seconds (minpoll 2). I wouldn’t have thought that they would want polling > with minpoll 3, but it appears I was wrong. This may fix the issue by > itself. > > > > Using such a short polling interval over Internet would be a horrible > > idea. NIST servers are overloaded and located in a network that has > > problems with asymmetric routing. It's better to avoid them if > > accuracy is a requirement. I thought you were using those stratum-1 > > servers you have and the requirement for accuracy was 10 or 100 > > microseconds, not milliseconds. > > > > Anything should do better than 50 milliseconds as long as it's on > > local network. > > > > -- > > Miroslav Lichvar > _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions