On Tue, Jan 09, 2018 at 07:52:11AM -0800, Richard Cochran wrote: > On Tue, Jan 09, 2018 at 11:09:43AM +0100, Miroslav Lichvar wrote: > > It's not clear to me how would that work. Let's say I have a > > grandmaster GM, slave S and monitoring node N, and I don't know how > > much asymmetry is there on any of the paths GM-S, GM-N and S-N. How > > will measuring offset of GM and S from N help me? > > 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. If there were no other sources of error (e.g. an error specific to boundary clocks, or an asymmetric delay due to the sync message being shorter than the delay request), the offset of S observed by GM/N should be zero. As I understand it, the only way to determine the asymmetry is to directly compare the clocks with a reference clock, e.g. using a PPS signal. -- Miroslav Lichvar ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Linuxptp-devel mailing list Linuxptp-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linuxptp-devel
