[ntp:questions] IEEE 1588 (PTP) at the nanosecond level?
unruh at invalid.ca
Mon Mar 17 05:40:20 UTC 2014
On 2014-03-16, Joe Gwinn <joegwinn at comcast.net> wrote:
> I keep seeing claims that Precision Time Protocol (IEEE 1588-2008) can
> achieve sub-microsecond to nanosecond-level synchronization over
> ethernet (with the right hardware to be sure).
> I've been reading IEEE 1588-2008, and they do talk of one nanosecond,
> but that's the standard, and aspirational paper is not practical
> hardware running in a realistic system.
1ns is silly. However 10s of ns are possible. It is achieved by Radio
Astronomy networks with special hardware (but usually post facto)
> I've seen some papers reporting tens to hundreds of nanoseconds average
> sync error, but for datasets that might have 100 points, and even then
> there are many outliers.
> I'm getting PTP questions on this from hopeful system designers. These
> systems already run NTP, and achieve millisecond level sync errors.
Uh, perhaps show them to achievement of microsecond level sync errors?
That is already a factor of 1000 better than they achieve.
One of the key problems is getting the packets onto the network (delays
withing the ethernet card) special hardware on teh cards which
timestamps the sending and receiveing of packets on both ends could do
better.a But it also depends on the routers and switches between the two
> Anyway, how much truth is there to all this? Are there any papers I
> should read?
> Joe Gwinn
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