[time-nuts] Basic Stratum 1 question

[Bill Janssen]

Richard H McCorkle wrote:
> ); SAEximRunCond expanded to false
> Errors-To: time-nuts-bounces+billj=ee.org at febo.com RETRY
>
> Jared,
> Symmetricom has a Stratum definition page at:
> http://www.ntp-systems.com/think_sync_view_article.asp?ID=42&NewsletterID=1&month=4&year=2005
>
> This is what they have to say;
>
> Dr. David Mills from the University of Delaware, when he wrote
> the RFC 1305 that is NTP (Network Time Protocol), developed a
> hierarchical structure in which Stratum 0 is the USNO (United
> States Naval Observatory) clock. Stratum 1 is a radio receiver
> that receives the time from Stratum 0. Stratum 2 is a client
> that receives the time over a network connection from a Stratum
> 1 clock. Stratum 3 is a client that gets the time from Stratum
> 2. This goes on to a theoretical Stratum 15.
>
> In the telecommunications world, stratum refers to the holdover
> performance of an oscillator in the event of loss of
> synchronization. Stratum 1, Stratum 2, Stratum 3, and Stratum 4
> are the most typical. A Stratum 1 clock has an accuracy of
> 1.0 x 10-11, Stratum 2 has an accuracy of 1.6 x 10-8, Stratum 3
> has an accuracy of 4.6 x 10-6, and Stratum 4 has an accuracy of
> 3.2 x 10-5.
>   
Much NTP stuff clipped

In the telecommunications world the goal was to prevent buffer overflows 
(or underflows)
in equipment that may be connected together even though they might both 
be Stratum 5.
In the telecomm. world those buffers are 125 Micro seconds long.

So the assumptions are made that stratum 5 sync.'s to a 4 and a 4 to a 3 
and a 3 to a 2
all the way to a Stratum 1.  In this chain each clock has to follow the 
frequency wander of the connected lower numbered clock. And it has to 
have sufficient frequency adjustment range.
to follow if the lower numbered clock goes into hold-over.

So there are specifications for each stratum level that hopefully  
assures stability of the network.

BTW the stratum 1 specification came from available Cesium standards 
used by AT&T
for many years. They were updated but not by much.

Been 15 years since I looked at this stuff so it may have changed in the 
details.

Bill K7NOM