James R Cutler <james.cutler@consultant.com>:
My experience with Dave Mills NTP algorithm is that, giving sufficient diversity in higher stratum sources, GPS versus Internet sources makes no practical difference. This assumes that you are concerned with Time for event logging and scheduling and not concerned with frequency and phase for clocking data on TDM instances.
If you are worrying about backhoe fade — it’s consequences will most likely affect other things more strongly than Time differences.
I'm a subject-matter expert in Internet time service (tech lead of NTPsec) and I concur. Local GPS sources are nice to have and fun to play with but not essential unless you have a mission requitement to run autonomous. Note by the way that you *can* run completely autonomous with NTPsec, but not with the NTF version. https://blog.ntpsec.org/2017/08/30/achieving-autonomy.html -- <a href="http://www.catb.org/~esr/">Eric S. Raymond</a>