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

Magnus Danielson magnus at rubidium.dyndns.org
Thu Mar 20 19:46:25 UTC 2014


On 19/03/14 10:43, Martin Burnicki wrote:
> Magnus Danielson wrote:
>> On 18/03/14 10:17, Martin Burnicki wrote:
>>> 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).
>
> As I mentioned in a different posting, even if you use hardware
> timestamping with NTP you are out of luck for highest accuracy since
> there are (AFAIK) no switches which have been designed to timestamp NTP
> packets.
>
> And even if there were, the next question is how to get the measured
> latency compensation parameters to the client without breaking the
> existing protocol?
>
> Maybe this would be an interesting approach for NTP v5.

Indeed. When I look at NTP and PTP, I see two protocols that could learn 
a lot from each other. NTP got some things (more or less) right that PTP 
is bad at, and vice versa.

Cheers,
Magnus



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