Re: [Linuxptp-devel] [PATCH RFC V1 00/18] NetSync Monitor support

[Richard C. <ric...@gm...>]

On Tue, Jan 09, 2018 at 05:21:39PM +0100, Miroslav Lichvar wrote:
> > I think I said that this works when N==GM.
> 
> Hm, does that change anything? If the delay of event messages going
> from GM/N to S is larger than the delay of messages going from S to
> GM/N, the clock of S will be running behind GM. The measurements of S
> done by the GM/N will have the opposite error.

Yes, you are right, of course.  I wasn't thinking.

The Meinberg doc has this statement:

   One big advantage of this mechanism is, that the communicated
   offset and delay from the monitored device can be compared to the
   measured offset and delay values and - assumed that the monitoring
   system is perfectly synchronized - asymmetries can be detected.

So assuming the asymmetry on the monitor's path is known, then you can
measure a constant offset on the normal GM path.

Thanks,
Richard