[e2e] Accuracy achievable with NTP

[Saad Biaz]

Woojune:

It is not the delay RANGE that hinders precise clock synchronization,
it is the UNCERTAINTY on the delay that matters.

Given a network of hosts, you must MEASURE the UNCERTAINTY on the delay
between all hosts. Then find the diameter D of your network with edges
weighted with the UNCERTAINTY (highest delay - lowest delay).


Your worst case imprecision on the clocks will be  1/2 D (Diameter).
Your average imprecision depends on the distribution of the uncertainty.

For a formal proof, check:

S. Biaz and Jennifer L. Welch, "Closed form Bounds for Clock
Synchronization under Simple Uncertainty Assumptions".




On Thu, 10 Apr 2003, Woojune Kim wrote:

> Hi,
>
> I've been looking for info on how accurate NTP can be. I've looked in various NTP related sites and still not quite sure.
>
> Say I have a LAN like environment with delays in the range of 10s of ms. How accurate a time can I get from NTP, assuming I have the appropriate HW clocks on my host ?
>
> Say I have a corporate network like environment, relatively segregated from the Internet at large, with delays in the range of 100ms. How accurate a time can I get ?
>
> Say the delay range goes upto 500ms, how accurate can the time be ?
>
> Any pointers to specific experiments or data would be appreciated.
>
> thanks
>
> Woojune Kim
>