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

Marcelo Pimenta marcelopimentacs at gmail.com
Thu Jun 17 13:46:27 UTC 2010

2010/6/16 Maarten Wiltink <maarten at kittensandcats.net>

> "Marcelo Pimenta" <marcelopimentacs at gmail.com> wrote in message
> news:AANLkTilAoduNIQjGpigOHpZvJcV_zMsw_tR7Naj6BpBT at mail.gmail.com...
> > [...] accuracy of 1ms. On a local network 100usec?? Even if we use
> > only switches(no routers), how is that possible if I have 4 types of
> > Latency increasing about 80us?
> The latency is corrected for. A query-response cycle is a back-and-forth
> exchange. The assumption is that the latency for the response (going
> forth) is equal to the latency for the response (going back), and both
> are half of the total latency, which you do know. So you estimate that
> the response was sent half the total latency time before the moment you
> received it.
> This often works well, and sometimes not so well. Domestic ADSL with a
> saturated upstream and downstream capacity left is one common case where
> it works not so well.

Yeh, I agree with you.

> [...]
> > I need accurancy at least of 1ms in 100% of time.
> That's a *very* tall order.

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??

> Groetjes,
> Maarten Wiltink
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