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

Maarten Wiltink maarten at kittensandcats.net
Wed Jun 16 21:32:39 UTC 2010

"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.

> I need accurancy at least of 1ms in 100% of time.

That's a *very* tall order.

Maarten Wiltink

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