Re: NTP Sync Issue Across Tata (Europe)

[John Gilmore <gnu () toad com>]

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