Radio clocks [1] often don’t use GPS. Many countries have a radio signal they can pick up. In the continental US, it comes from Fort Collins, Colorado. [2]
Technically you can broadcast a new time to your neighborhood and have most people late to work (the ones having that kind of clock alarm), it's far from secure and accurate.
So the pragmatic approach that everyone is utilizing (including AWS’ latest announcement for microsecond accuracy) relies on hardware GPS. Why am I being attacked here. This is how it’s done.
I'm not the one attacking you, but I think I can explain.
Your original statement was quite absolutist "It’s really the only way to do accurate time." A statement which would have had more agreement would be "It’s really the only practical way to do accurate time."
Precision Time Protocol [1] is an alternative. CERN has been using it as part of a project to achieve sub-nanosecond accuracy over a wired network [2].
Comments
It’s really the only way to do accurate time.
Radio clocks [1] often don’t use GPS. Many countries have a radio signal they can pick up. In the continental US, it comes from Fort Collins, Colorado. [2]
[1] https://en.m.wikipedia.org/wiki/Radio_clock
[2] https://en.m.wikipedia.org/wiki/WWVB
To be fair, this isn't really _that_ accurate, it's only good to about 10ms, GPS will get you to 0.001ms accuracy, at least with the right kit.
Technically you can broadcast a new time to your neighborhood and have most people late to work (the ones having that kind of clock alarm), it's far from secure and accurate.
That suffers from the same vulnerabilities.
I have trouble picking up WWVB indoors at home even without jamming.
Well no, it isn't - it's just that every other solution is several orders of magnitude more expensive.
So the pragmatic approach that everyone is utilizing (including AWS’ latest announcement for microsecond accuracy) relies on hardware GPS. Why am I being attacked here. This is how it’s done.
I'm not the one attacking you, but I think I can explain.
Your original statement was quite absolutist "It’s really the only way to do accurate time." A statement which would have had more agreement would be "It’s really the only practical way to do accurate time."
Fair.
Precision Time Protocol [1] is an alternative. CERN has been using it as part of a project to achieve sub-nanosecond accuracy over a wired network [2].
[1] https://en.wikipedia.org/wiki/Precision_Time_Protocol
[2] https://en.wikipedia.org/wiki/White_Rabbit_Project
But PTP needs a grandmaster clock, and that is usually a GPS receiver.
Or atomic clock.