Forrest Christian (List Account) wrote:
The NIST time servers do NOT get their time from GPS.
No, of course. I know it very well.
However, as I wrote:
> But, additionally relying on remote servers (including those
> provided by NIST) is subject to DOS attacks.
the (mostly wired) Internet is just as secure/insecure as
wireless GPS, over which NIST servers can not be reliably
accessed.
Just as many people who only know wired Internet blindly
think wireless channels are secure, you can not recognize
various attack modes for the mostly wired internet.
These are physical realizations of UTC... that is, a phase-aligned 1PPS
pulse and a high precision clock signal. These realizations are used to
directly drive the NIST NTP servers at each location. GPS is not
involved.
UTC??? You are totally wrong.
Just as many other people, you are purposelessly seeking
meaningless accuracy assuming inertial frame of UTC,
which is *NOT* required for correct transactions
Because of relativity, we can assume *ANY* inertial frame
for simultaneity, which means simultaneity requirement is
not so strong.
Moreover, information cone allows even less simultaneity
for correct transactions.
These two timescales are within a few ns
of each other, also verified with GNSS common view technology, so one can
consider them the same for most purposes.
You don't understand simultaneity of theory of relativity at all.
10ns of time difference can not be physically or logically meaningful
between locations with 3m distance.
Note that a similar process is used to derive UTC(NICT) in Japan.
Depending on inertial system, time in US and JP can be different
a lot more than 1ms, which means timing error between mainland
US and Japan can be a lot more than 1ms.
As far as a rubidium clock goes, I'd much rather see it disciplined
regularly to a GPS time source, but that comes from the fact that I like my
1PPS to be within a microsecond or so of UTC due to the precision I need in
the lab.
As I already wrote:
: For millisecond accuracy, Rb clocks do not need any synchronization
: for centuries.
: Rb clocks on GPS are a lot more frequently synchronized, because
: a lot more accuracy is required for positioning (10ns of timing
: error means 3m of positioning error).
you didn't understand the required accuracy for the Internet operators,
which is your problem.
Note that some of the high end appliances I'm referring to just use GPS
over days and weeks to discipline a precision oscillator (sometimes
rubidium) which is essentially an automatic calibrating version of what
you're proposing.
That has nothing to do with the a lot more broad required accuracy
required by the theory of special relativity for proper causality.
Masataka Ohta
