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

unruh unruh at wormhole.physics.ubc.ca
Tue Jun 15 17:20:18 UTC 2010

On 2010-06-14, Marcelo Pimenta <marcelopimentacs at gmail.com> wrote:
> Hi everybody!!
> My question is about Time Accuracy of NTP/SNTP protocol. I want to know if
> is possible to have precision of 1ms(could be < 1 ms?) using SNTP in a
> network with 50 hosts(is the same with 100 hosts?) using only swithes, no
> routing. All these hosts are syncronized with a Meinberg GPS. The traffic is
> low(~25%). Is it possible to have the same time accuracy of IRIG-B for
> example?

I think you mean accuracy of 1ms. Yes. it can. On a local network,
100usec is easily possible ( and depending on the routers, it can be
better than that).
> The internal clock in my devices(hosts) starts with the crystal frequence. A
> typical offset or frequence tolerance of the crystal is less then
> 1ms/minute. The resolution is about 0.9ms and the devices acts as unicast
> clients, asking GPS every minute.

Why?  The whole purpose of ntp is to discipline your clock so that it
keeps time much better than that. 
Not sure what you mean by "the resolution is about .9ms" What is your
> Is it enough? The Time Accurancy could be better if I could ask GPS twice a
> minute? A broadcast implementation with GPS sending time every minute could
> help?

It depends on what you want the time for. 

> I know that these kind of issue have many variables but the main question
> is: Is possible to have precision of 1ms(could be <1ms) with SNTP?

Yes, depending on the competence of the writer of the SNTP software.
> Thank you very much

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