[time-nuts] NTP stratum 0

Bill Hawkins bill at iaxs.net
Sat Jan 14 13:40:37 EST 2006

Perhaps it needs to be better than a millisecond. I remember an
NTP accuracy of 100 microseconds, after enough round-trip time
statistics were gathered. Perhaps the net is noisier now, and
more uncertain. That certainly characterizes the messages carried
by the 'net.

In any event, the noise from the frequency standards should be at
least a factor of ten smaller than the filtered noise limit of the
Internet, IMHO.

Bill Hawkins

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
Behalf Of M. Warner Losh
Sent: Saturday, January 14, 2006 11:54 AM
To: time-nuts at febo.com; neal at mcburnett.org
Cc: michelangelo.albertazzi at gmail.com
Subject: Re: [time-nuts] NTP stratum 0

In message: <20060114164520.GA25156 at feynman>
            Neal McBurnett <neal at mcburnett.org> writes:
: On Sat, Jan 14, 2006 at 05:25:04PM +0100, TwoSpades wrote:
: > I would like to know where could I find the FORMAL specification of the
: > stratum 0.
: > I often read that it can be a GPS receiver, but I think that there must
be a
: > formal definition
: > of the characteristics of that device.

Well, it depends on what you mean by formal.  The 'rough and ready'
definition for stratum 1 time servers is that they are synchronized to
a time source better than they would get from another ntp server.  If
your system time can be synchronized to within a few tens of
microseconds with the receiver you have, then you are definitely
stratum 1 material.  If you relax the requirement to be only as good
as you need to be to serve time over the internet, then I'd say that
requirement drops to about 1ms.

In general, you want the server to be traceable back to the official
time, as produced by some time authority.  For a simple ntp server,
that tracking doesn't have to be too precise, from a time geeks point
of view.  If you are within about a millisecond, then no one will
notice if the time exchange is over the internet...


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