[ntp:questions] IEEE 1588 (PTP) at the nanosecond level?

Magnus Danielson magnus at rubidium.dyndns.org
Tue Mar 18 21:20:08 UTC 2014


On 18/03/14 10:17, Martin Burnicki wrote:
> Paul wrote:
>> On Mon, Mar 17, 2014 at 8:07 PM, Joe Gwinn <joegwinn at comcast.net> wrote:
>>
>>> People are also lusting after sub-microsecond sync.
>>
>>
>> Sure but not optimally in comp.protocols.ntp/questions at lists.ntp.org.
>> With some help NTP can be quite good but the intent really isn't
>> nanosecond
>> accuracy.
>
> We have mades some tests and found that NTP can yield the same accuracy
> as NTP if also hardware timestamping of NTP packets is supported on all
> nodes, similar as for PTP.
>
> In fact this isn't surprising, is it?

No, it's not. NTP is being perceived to be "software timestamping" but 
nothing prohibits you from doing it in hardware. Similarly can you 
implement PTP with software time-stamping (with shitty performance).

Doing HNTP makes NTP match up against PTPv1 to some degree, but PTP then 
pulls out the explicit means to make PTP-aware transparent clocks to 
correct for delays, cancelling some of the asymmetry. You could do NTP 
with PTP 2-step processing, but what we would call such a bastard would 
be an interesting thing, NPTP?

Cheers,
Magnus



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