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

[Miroslav L. <mli...@re...>]

On Mon, Jan 08, 2018 at 09:02:52PM -0800, Richard Cochran wrote:
> On Mon, Jan 08, 2018 at 03:56:29PM +0100, Miroslav Lichvar wrote:
> > You mean asymmetry added by boundary clocks on the path to the
> > grandmaster?
> 
> Yes, or from any other source at all.

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?

My feeling is that the protocol was not intended for accurate
measurements, but rather for detecting faults and bugs, where the
clocks drift off too much, etc.

>     13.4 Suffix
> 
>     An application layer message is suffixed by a contiguous sequence
>     of zero or more entities of data type TLV ... Nodes should append
>     no TLV entity to event messages.
> 
>     NOTE -- Appending TLV entities to an event message is likely to
>     change the transmission delay suffered by the messages in passing
>     through non-PTP bridges.
> 
> Notice it only says "should" and not "must not".  So I would say that
> TCs must allow TLVs in any message.

Ok. If anyone tests this with a TC, I'd be interested to hear if it
worked.

Thanks,

-- 
Miroslav Lichvar