[time-nuts] NTP stratum 0

Magnus Danielson cfmd at bredband.net
Sat Jan 14 14:51:50 EST 2006

From: "Bill Hawkins" <bill at iaxs.net>
Subject: Re: [time-nuts] NTP stratum 0
Date: Sat, 14 Jan 2006 12:40:37 -0600
Message-ID: <000a01c6193a$03346200$0500a8c0 at darius.domain.actdsltmp>


> 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.

Yes. The problem about the network noise is that it is

1) Not symmetric

   The delay from one node to another will not be the same as the delay the
   other way. The time-error of the tracking node will be half of the
   difference in delay between the nodes.

2) Non-stable average

   The average delay is not stable around the ideal delay, and the traffic
   usually ensures that the average isn't even symmetric in both directions.

These factors are quite hard to compensate.

> 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.

I agree, it is at least a good rule of thumb.


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