[ntp:questions] SNTP with 1ms of precision?

Danny Mayer mayer at ntp.org
Thu Jul 8 04:12:33 UTC 2010

On 6/17/2010 9:46 AM, Marcelo Pimenta wrote:

> Yep but I have an equipment for specific use with RFC2030 implemented
> because of a standard that I have follow that say it is mandatory SNTP -
> RFC2030. My equipment ask for time every minute and frequence tolerance of
> the crystal is less then 1ms/min. They are in a intranet with 2 switches
> isolated so... my question was about the SNTP because some people said to me
> that SNTP cannot garantee 1ms accuracy. Is it possible, in that described
> cenario to no have 1ms of accuracy? I expect that a implementation
> of RFC2030 made by a person at equipment X and the implementation of the
> same RFC at the same equipment X BUT by another person could give me
> different results??

Someone has been feeding you a bunch of nonsense. If you have a Meinberg
GPS directly attached to your server then an SNTP server is all you
need. See RFC 5905. For the precision of the unit you should consult the
specs of the unit. There are delays getting the data from the GPS to
your server and the usual delays for NTP and the O/S in disciplining the
clock but that's the only areas you need to worry about (apart from CPU
load from other processes). SNTP has nothing to do with guaranteeing
accuracy. The error budget comes from the various components involved
and the Internet is not involved here. If you use an SNTP server
provided by anyone it will obviously not give you the same exact results
as a different implementation just because the code is different and it
is not easy to account for variations in the code. Even a different
version of the same code will give you different results but with a
refclock hanging off the box you will get very good results.


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