Hi Richard,
I understand that you might find this requirement to be pointless. However in
protocols it is not uncommon that certain bits are reserved for future use. In
order to provide forward compatible implementations it is a common practice to
require reserved bits to be ignored on reception.
In any case, the point of standards is not to cherrypick what one finds good on
them (and indeed there are bad standards too), but to fully comply to them to
get the maximum compatibility between devices.
Due to the non-compliant implementation Linuxptp does not work in a mixed AES67
network where Dante devices are present. Other AES67 implementations work well
because they correctly ignore bits 1-3.
RegardsPetr
-------- Původní zpráva --------Od: Richard Cochran <richardcoch...@gmail.com>
Datum: 12.02.18 1:41 (GMT+01:00) Komu: Petr Kulhavy <br...@jikos.cz> Cc:
linuxptp-devel@lists.sourceforge.net Předmět: Re: [Linuxptp-devel] Transport
specific in UDP
On Sun, Feb 11, 2018 at 05:55:25PM +0100, Petr Kulhavy wrote:
> It seems linuxptp does not comply to the IEEE1588-2008 standard when it
> comes to processing of the transport specific field in UDP transport.
>
> The Annex D.4 of the standard says "bit 1-3, reserved, The bit shall be
> transmitted as zero and ignored by the receiver".
> Linuxptp does not ignore bits 1-3, it requires them to be identical to the
> configured value.
>
> Why this incompatibility?
This is one of a few requirements that is illogical, pointless, and
just plain wrong. Probably some vendor with a legacy, non-fixable HW
got this text in, but only because the vendor sat on the committee. I
can't think of any valid technical reason to ignore these bits.
Having said that, do you actually have some equipment that depends on
this behavior?
Thanks,
Richard
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