[time-nuts] Basic Stratum 1 question
Richard H McCorkle
mccorkle at ptialaska.net
Thu Aug 2 13:13:31 EDT 2007
Symmetricom has a Stratum definition page at:
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.
So when you are comparing time servers and they say that they
are Stratum 1 and Stratum 2 time servers, what does that mean?
Lets take Symmetricoms NTS-200 for an example. The NTS-200
is a Stratum 1 level time server because it derives accurate
time directly from the atomic clocks aboard the Stratum 0 GPS
satellite system. It is also a Stratum 2 level time server
because, if the GPS signal is lost, the NTS-200 can automatically
revert to a Stratum 2 mode and retrieve time from other user-
designated internal or external network time servers. The
obvious advantage of this is that it prevents disruption of
time service to the network.
So what are Stratum 3-15 level servers? They are usually
workstations, servers, or Controlled Time Devices (CTDs).
Hope this explanation of what we mean by the word "stratum"
This Symmetricom page can be used as an "official" guideline
describing what stratum your local server really falls under.
If it isn't referenced to an external clock in some fashion
it isn't a stratum clock at all.
> ); SAEximRunCond expanded to false
> Errors-To: time-nuts-bounces+mccorkle=ptialaska.net at febo.com RETRY
> I am having a debate with our CIO. He wrote in a memo about timing:
> *Local hardware is to be considered Stratum 1, since it get time from its
> own CMOS.*
> I told him that absurd and that it can't be considered stratum 1.
> Please clarify.
> Thanx much,
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