[ntp:questions] Can NTP sync within 1ms

William Unruh unruh at invalid.ca
Sun Apr 27 02:20:48 UTC 2014


On 2014-04-27, Paul <tik-tok at bodosom.net> wrote:
> On Sat, Apr 26, 2014 at 8:30 PM, William Unruh <unruh at invalid.ca> wrote:
>
>> use the offset scatter as an estimate of the
>> time performace (It is at least some sort of upper bound, but as I have
>> said, not terribly accurate)
>>
>
> I suspect you shouting CANNOT is probably overstating the issue.  After all
> if offset was of no value how would NTP (or any other offset based time
> transfer system) work?
To get a good idea of the actual offset from UTC, you need another time
source (or two) to compare with each other. The straight offsets do not
give it to you. However, I will admit that they are probably an upper
bound (although even that is not true-- the link could have assymetric
offsets.)

> To the previous point -- if someone says "my offsets are always 10s of
> microseconds" that is likely to be a refutation of the 'NTP can't do
> better
> than 10s of milliseconds" position.

agreed.

>
> I don't know what "terribly accurate" might be to you but in the real
> world
> sufficient accuracy depends on the circumstance.
>
> Someone should conduct an experiment.

I have.



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