Forrest Christian (List Account) <lists@packetflux.com> wrote:
At some point, using publicly available NTP sources is redundant unless one wants to mitigate away the risks behind failure of the GPS system itself.
On Fri, Aug 11, 2023, 3:33 AM Masataka Ohta wrote:
Your assumption that public NTP servers were not GPS-derived NTP servers is just wrong.
Subsequent conversation has shown that you are both right here. Yes, many public NTP servers ARE using GPS-derived time. Yes, some public NTP servers ARE NOT using GPS-derived time. Up to this point, popular public NTP pools have not made these distinctions readily configurable, though. For sites that need to run even during a war, or a similar situation that is likely to disrupt or distort GPS, they might like to have access to NTP servers that are completely independent from GPS. At one point I proposed that some big NTP server pools be segregated by names, to distinguish between GPS-derived time and national-standard derived time. For example, two domain names could be e.g.: fromnist.pool.tick.tock fromgps.pool.tick.tock If you wanted particular redundancy, say because you have a local GPS clock and you want a non-GPS check on that, you'd use fromnist.pool.tick.tock (or fromnict.pool.tick.tock for the Japanese timebase, etc). (If you were agnostic about where your times comes from, you would just use a generic domain name like vendorname.pool.tick.tock.) An automated tool could periodically trace that the stratum 0 source currently being used by each node in each of the pools is actually the same as advertised in its domain name. Alerting any difference to the relevant system administrators would allow those clocks to continue running with a backup timebase, while making it more likely that some human would work to restore their access to the correct stratum 0 source. So far this is just an idea. John PS: When we say "GPS", do we really mean any GNSS (global navigation satellite system)? There are now four such systems that have global coverage, plus regionals. While they attempt to coordinate their time-bases and reference-frames, they are using different hardware and systems, and are under different administration, so there are some differences in the clock values returned by each GNSS. These differences and discontinuties have ranged up to 100ns in normal operation, and higher amounts in the past. See: Nicolini, Luca; Caporali, Alessandro (9 January 2018). "Investigation on Reference Frames and Time Systems in Multi-GNSS". Remote Sensing. 10 (2): 80. doi:10.3390/rs10010080. https://www.mdpi.com/2072-4292/10/1/80