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Re: [art] summary of updates - draft-time-touch

John Hawkinson <jhawk@MIT.EDU> Wed, 19 April 2017 03:02 UTC

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Date: Tue, 18 Apr 2017 23:02:04 -0400
From: John Hawkinson <jhawk@MIT.EDU>
To: Joe Touch <touch@isi.edu>
Cc: art@ietf.org
Message-ID: <20170419030204.GB87484@mit.edu>
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Subject: Re: [art] summary of updates - draft-time-touch
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Joe Touch <touch@isi.edu> wrote on Tue, 18 Apr 2017
at 08:03:38 -0700 in <0751aeaa-56ae-e953-3b76-308a6a3478b4@isi.edu>:

> > The '25ns' sillyness of GPS with respect to TAI is still there. I now have
> > an idea where the 100ms for NTP is coming from. That's really sad.
> can you clarify?

A problem here is that your ID conflates a known offset with
with a typical uncertainty with a theoretical maximum uncertainty.
You label the field "d-TAI" and name it a delta, but it isn't one.
And the name is evocative of DUT1, which is different kind of thing.

It might be better to adopt a standard name for this field
(uncertainty? imprecision? +/-?; I am not sure) rather than coining
your own.

> The 25ns of GPS is the result of a claim in the GPS spec.

You should probably cite it explicitly.

> The 100ms is from a claim in NTP documentation.

You should *definitely* cite this one explicitly. While I have no doubt
it is there, that's not what people with untuned run-of-the-mill
ntp systems encounter in the public Internet. (And I'm not sure
it is really an upper bound either -- I don't think a 101ms error
is appreciably less likely than a 99ms error?) And of course,
people with finely tuned ntp systems easily achieve far better than 1ms.

--jhawk@mit.edu
  John Hawkinson

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