Post processing of NTP data...

Hello,

I've run a few ntp servers, but I consider myself a complete novice at many of the details so I apologize up front if this question is ill-conceived.

However, I'm interested to know if one could reliably increase the accuracy of the use of a system clock by periodically measuring the offset between a lower statum sever and the local clock and correcting time-stamps issued by the local clock in post-processing (or I suppose even near real time).

Here's the scenario:
I want to log several things with time stamps on the order of ~ .1ms - maybe less. Although I've read posts in this list archive of others achieving these results more or less reliably, in my own experience I have not seen ntp regulate time of a stratum 2 server without occasional excursions in the 100's of ms range (this is for lots of reasons, I don't want to argue with anyone about it here).

It appears to me that an unloaded server on a network with little traffic and reasonably good hardware might be able to meet these timing requirements. But these conditions would prevent the very purpose of the server - to log many data streams with a highly accurate time stamp, and to provide network access to that data to users.

So I thought, well if one can measure the offset between the local clock and that of a stratum 1 server, why not log this information separately from the other data streams and then after the fact, adjust the logging time-stamps by this offset such that regardless of the drift of the local clock with temperature, network jitter, server load, etc., the logging time stamps will very nearly equal that of the stratum 1 server. One might make these corrections after the fact, but one could conceivably make these corrections in near-real- time too.

Is this possible? Anyone have any back-of-the-envelop type calculations that might give an idea of how accurate one might be able to get?

-Val



------------------------------------------------------
Val Schmidt
CCOM/JHC
University of New Hampshire
Chase Ocean Engineering Lab
24 Colovos Road
Durham, NH 03824
e: vschmidt [AT] ccom.unh.edu
m: 614.286.3726


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