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

Magnus Danielson magnus at rubidium.dyndns.org
Tue Mar 18 21:24:32 UTC 2014

On 18/03/14 10:26, Martin Burnicki wrote:
> Joe Gwinn wrote:
>> I've used IRIG-B004 DCLS before, for cables two meters long within a
>> cabinet.  Worked well.  How well do they handle 100 meter cables, in
>> areas where the concept of "ground" can be elusive?
> You could use fiber optics to transfer an IRIG DCLS signal.
> However, if you want highest accuracy you need to take care how much
> delay is inserted by the transceivers, and the length of the connection.
> PTP has the advantage that constant delays can be measured and
> compensated automatically.
> In any case it's a good thing if you can measure the accuracy, e.g.
> compare a 1 PPS slope generated by a time client to a 1 PPS slope
> generated by the device providing the time.
> This helps to find out if the time transfer suffers from uncompensated
> delays (IRIG) or asymmetries (PTP).

You need to check and have means to check an installation. Possibly 
allow for adjustments (at calibration) to achieve the goal.

Depending on your system, different approaches may give best bang for 
the buck, and work more or less well. I prefer systems where key 
parameters can be monitored routinely so that warning bells can ring 
when something goes astray.


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