4 ms·

Like the 6 independent 24-satellite (plus spare) constellations that constantly orbit Earth and output synchronized beacons accurate to nanoseconds?

toomuchtodo 2y ago
How effective is receiving precision time from a GNSS constellation within structures, urban areas, and other challenging SNR envs? Another comment mentions cell towers broadcast this unencrypted and without the need for service, so perhaps the solution is to instead require strong SLAs around that service, with the gov potentially paying for that service level? https://news.ycombinator.com/item?id=40388421 https://news.ycombinator.com/item?id=40388421
- smallmancontrov 2y ago
  Yep, reception is a real problem with straight GNSS. WWVB suffered from it too, and cellular (which is locked to GPS) is a big upgrade. I suppose that now the thing to do is wait for the $0.10 cellular clock chip that makes it easy.
  - toomuchtodo 2y ago
    My interest is as a bit of a precision time enthusiast and an advocate of public goods. We’re awash in “good time”, GNSS, RF, NTP over IP, cellular, but it still feels like there is a gap to fill to make precision time super cheap and ubiquitous. Getting time over mains power or other previously convenient but potentially low precision sources should be over, but getting precision time should be as easy and reliable as mains power. Thanks for riffing with me!
- lxgr 2y ago
  I feel like once you're concerned about SLAs for precision timekeeping, you need to start worrying about spoofing as well, which is tricky to combat in an inherently unidirectional protocol. Galileo has an interesting signal authentication service [1], but even that is subject to replay attacks by definition (although you can't skip ahead a receiver's time). In comparison, networked bidirectional protocols like NTP are almost trivially secure-able, by including a challenge in the request and a cryptographic signature over the response. [1] https://berthub.eu/articles/posts/galileos-authentication-algorithm-part-1/ https://berthub.eu/articles/posts/galileos-authentication-al...

toomuchtodo 2y ago

How effective is receiving precision time from a GNSS constellation within structures, urban areas, and other challenging SNR envs? Another comment mentions cell towers broadcast this unencrypted and without the need for service, so perhaps the solution is to instead require strong SLAs around that service, with the gov potentially paying for that service level? https://news.ycombinator.com/item?id=40388421 https://news.ycombinator.com/item?id=40388421

smallmancontrov 2y ago
Yep, reception is a real problem with straight GNSS. WWVB suffered from it too, and cellular (which is locked to GPS) is a big upgrade. I suppose that now the thing to do is wait for the $0.10 cellular clock chip that makes it easy.
- toomuchtodo 2y ago
  My interest is as a bit of a precision time enthusiast and an advocate of public goods. We’re awash in “good time”, GNSS, RF, NTP over IP, cellular, but it still feels like there is a gap to fill to make precision time super cheap and ubiquitous. Getting time over mains power or other previously convenient but potentially low precision sources should be over, but getting precision time should be as easy and reliable as mains power. Thanks for riffing with me!
lxgr 2y ago
I feel like once you're concerned about SLAs for precision timekeeping, you need to start worrying about spoofing as well, which is tricky to combat in an inherently unidirectional protocol. Galileo has an interesting signal authentication service [1], but even that is subject to replay attacks by definition (although you can't skip ahead a receiver's time). In comparison, networked bidirectional protocols like NTP are almost trivially secure-able, by including a challenge in the request and a cryptographic signature over the response. [1] https://berthub.eu/articles/posts/galileos-authentication-algorithm-part-1/ https://berthub.eu/articles/posts/galileos-authentication-al...