Quoting "Eric S. Raymond" <e...@thyrsus.com>: :
Hal objected (off list) to me drawing a conclusion from today's offset multiplot that check servers aren't necessary when you have a local GPS - a Stratum 1 really can run autonomously. He said, correctly of course, that the check servers aren't there to improve time accuracy when the GPS has sat lock, but to backstop the GPS when it flakes out.
:
We may already be at a technological place where GPS outages don't bust the tolerable-error budget, even with cheap hardware. If we aren't, we'll probably be there soon. One of my medium-term agenda items is to measure and see.
I had setup a test along these lines a week ago: https://blog.dan.drown.org/gps-pps-drift-when-it-has-no-signal/ The GPS module I'm using still outputs PPS even when it loses lock. That won't be true for every GPS module. My results were a long term average of 250us-500us lost per day (~3-6ppb). This surprised me because of how low it was, I assume I got lucky with the long term average temperature of the GPS module. ntpsec finally rejected the PPS at a 2ms offset. I think I could change that with the "tos mindist" setting (which was at its default of 1ms), but I haven't verified that. Of course, this data doesn't apply to all GPS outage situations. But it does suggest that holdover within 30ms is easy for the "can't hear the satellites for a few hours" case. _______________________________________________ devel mailing list devel@ntpsec.org http://lists.ntpsec.org/mailman/listinfo/devel
