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Re: [802.3ae] XAUI Rj TR comment

	See comments below labeld "HAB>".


Mike Jenkins wrote:
> Howard,
> Your presentation is a very nice summary, particularly of the issues
> regarding jitter tolerance.  Thanks.
> If you don't mind, I would like to make a comment and ask a question:
>  * With regard to your method #2 for RJ testing ("adding noise to
>    clock"), I suspect that very reasonable bandwidth limitations
>    on the Gaussian noise would avoid any unintended zero crossings.
>    The available bit rate clocks seem to have more than adequate
>    amplitude control and spectral purity to make this amplitude-to-
>    phase conversion very reliable and repeatable.

HAB> According to the current draft, extracted from section
lines 53 & 54, the band width limitations are: "The random jitter
spectrum is defined to have a low-frequency corner at 20MHz and to roll
off at 20dB per decade below this."

>  * This is more of a question.  My background is with the Fibre
>    Channel jitter working group which evolved this methodology.
>    The implicit assumption behind allowing RJ =< TJmax - DJ(actual)
>    was that the worst case was DJ=DJmax.  Random jitter was assumed
>    to be more benign than DJ.  Hence, testing is required only for
>    DJ=DJmax.  I would appreciate hearing any argument to rebut that
>    assumption.

HAB> This limitation on the compliance testing would solve the issue,
unfortunately the current draft (3.1 soon to be 3.2) does not have this
limitation.  In fact if we were to limit the testing to be at DJmax then
the required RJ would be 4.11ps rms which is tighter than our
calculations in the presentation material.

> Regards,
> Mike Jenkins
> "Howard A. Baumer" wrote:
> >
> > To all concerned,
> >      I put in a TR Comment against D3.1 stating the desire to put a
> > maximum
> > limit on the TX Rj.  This comment was rejected and left unresolved.
> > There was fairly wide agreement that having a max limit on TX Rj should
> > be done but that we should first get a broader input on what this limit
> > should be.  I took on the action item to start a reflector discussion to
> > determine this limit.
> >      The current draft sets a limit for Tj and a limit for Dj and then
> > defines Rj aa Rj = Tj(max) - Dj(actual).  The TR comment proposes that a
> > limit be set for Tj, Rj and Dj and that Rj(actual) + Dj(actual) <
> > Tj(max). There is a presentation that we are developing that
> > attempts to figure out a limit for Rj.  It can be found at
> >
> > Please review and comment.
> >      This presentation also brings out a problem with the current Jitter
> > Tolerance test technique.
> >
> > Howard Baumer
> --
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