[ntp:questions] Isolated Network Drift Problem
cwebster at ec.rr.com
Wed Nov 26 13:31:21 UTC 2008
On Tue, 2008-11-25 at 20:06 -0500, Richard B. Gilbert wrote:
> The most important thing to do or attempt is to get a primary source of
> time. This can be an atomic clock (extremely expensive, extremely
> stable, extremely accurate), or something directly connected to an
> atomic clock. A GPS timing receiver will capture signals from four
> satellites and solve a system of four equations in four unknowns: time,
> latitude, longitude, and elevation. Each of the satellites carries an
> atomic clock! The GPS timing receivers sell for ~$100 and up. If you
> can site such a receiver so that it has an unobstructed view of the sky,
> this is a very good source of time.
> If it is not possible for you to have your own stratum 1 time server,
> there are a fair number of them on the internet. Stratum 2 servers are
> even more plentiful. Stratum one servers have direct access to an
> atomic clock or equivalent; e.g. GPS receiver. Stratum two servers get
> their time from stratum 1 servers. Stratum 3 gets time from stratum 2.
> . . . If you can't use internet servers and you can't set up your own
> stratum one server, you are SOL.
> It is possible to "fake it" using a server that has a good clock but
> performance will not be as good as having an atomic clock at the root of
> the tree. That rock solid beat of one second per second is easy to get
> in step with and easy to keep step with.
> An unsynchronized clock WILL drift and will be more difficult to get in
> step with and keep step with.
> I can tell you from experience that a GPS receiver will give you rock
> solid time and that clients will synchronize easily with it. So will an
> atomic clock but that costs $50,000 or $100,000 more than the GPS receiver!
Thank you for the detailed explanation. I appreciate that. :-)
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