[ntp:questions] Re: Improving ACTS performance

Richard B. Gilbert rgilbert88 at comcast.net
Thu Apr 6 19:26:48 UTC 2006


Joshua Coombs wrote:

> I finally have my stratum 2 servers working as good as I think they can 
> given their environments.  Now I'm working on my stratum 1 clock which 
> pulls it's time via ACTS.
> 
> I'm currently dialing NIST so I can take advantage of the automatic 
> latency compensation.  Problem is, the time I get back seems to vary by 
> up to 20ms.  I may get 3 or 4 calls where the reported time stays within 
> a couple ms of what I believe true time to be, and then a call will come 
> back close to 20ms off.  When ntpd has decided to stretch out to it's 
> max call interval, that glitch induces drift in the clock, resulting in 
> an eventual 40ms offset before it corrects.
> 
> I've tried the following:
> - switched to manual latency adjustment using time1
> - only configured 1 number to avoid different latencies for different paths
> - dialing USNO instead of NIST
> 
> I can't seem to shake the random wild offsets.
> 
> I'm running the 4.2.1RC on FreeBSD 4.11, soekris 4501, and a Microcom 
> 28.8 external modem.
> 
> I'm open to any suggestions on how to improve things.
> 
> Joshua Coombs

I've seen ACTS referred to as "Automated Containerized Trash Service". 
What you see may be the best that ACTS can do.

Have you considered using another technology?  A GPS receiver is not 
terribly expensive (as low as $85 US) and such a receiver designed for 
timing applications can deliver accuracy in the neighborhood of 1 
microsecond.  The PPS signal is accurate to better than 100 nanoseconds 
but few computers are capable of that degree of accuracy.  1 microsecond 
  is easily obtainable.  I use a Sun Ultra 10 (440MHz processor), 
Solaris 8 and ntpd 4.0 and get that accuracy.  That's eight year old 
technology; more modern hardware and software might do better.






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