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RE: [802.3ae] XAUI Rj TR comment


Thanks for the redirection. Regarding the activity to define these terms,
please be aware that the jitter test methodology being used in clause 52 is
substantially different than the prior art referenced here from Fibre
Channel and Gigabit Ethernet. Most of the concepts are the same (from a
theoretical perspective), but much of the similarity ends there.

I do not recommend that the XAUI group use this new method (though it should
provide some advantages). But, please be aware and understand it during the
course of refining the definitions.


> -----Original Message-----
> From: Kesling, Dawson W [mailto:dawson.w.kesling@xxxxxxxxx]
> Sent: Wednesday, August 08, 2001 12:03 PM
> To: HSSG_reflector (E-mail)
> Subject: RE: [802.3ae] XAUI Rj TR comment
> All, 
> I've been watching the reflector discussion but have been too 
> busy to reply.
> I'd like to quickly give some background to help clarify the 
> situation.
> Please don't shoot me - I'm only the editor giving some history!
> It has been universally understood in the XAUI group (until 
> recently) that
> DJ is everything bounded and RJ is everything unbounded. 
> Furthermore, RJ has
> been assumed to be Gaussian for the purspose of calculations. 
> Sinusoidal
> jitter (SJ) is a subset of DJ. XAUI does not treat it 
> differently from DJ,
> but only calls out an explicit level for the SJ component of 
> DJ. Jitter that
> is bounded but not correlated to the data is also deterministic by the
> working definition. XAUI does not call this out explicitly, but other
> clauses may.
> Many people came into XAUI from different backgrounds, but 
> agreed to these
> definitions for the sake of normalization and communication. 
> The work done
> in MJS was helpful to XAUI and was the basis for these common 
> definitions.
> Those who have more recently become active in XAUI seem to be making
> different assumptions about the definitions of these jitter 
> terms. Other
> definitions may be valid, but we should not change the underlying
> definitions agreed to by dozens of participants and approved 
> in several
> draft ballots at this late stage. There is nothing wrong with the XAUI
> definitions as long as they are defined. The real problem is, 
> as Pat pointed
> out, that they are not well defined in the document. This has 
> always been
> intended to be done in Annex 48B but has not been finished 
> yet. I belive
> that Anthony Sanders and Tom Lindsay are still working on it. 
> This annex
> needs to be finished and submitted in the upcoming ballot 
> cycle so that
> newcomers and standard readers can understand the meaning of 
> DJ and RJ as
> used in XAUI (and the other clauses).
> In summary, I do not think there is anything inherently wrong with the
> definitions assumed by XAUI and being written into Annex 48B 
> (based on MJS).
> We should all use these definitions and get on with the 
> HOward's real issue
> of limiting the RJ as the term has been defined by the group. 
> Please forgive
> me that I probably won't be able to reply to any further 
> e-mails on this
> topic. I only hoped to refocus us on the important issue 
> while I had a spare
> minute between fires.
> -Dawson
> -----Original Message-----
> From: THALER,PAT (A-Roseville,ex1) [mailto:pat_thaler@xxxxxxxxxxx]
> Sent: Monday, August 06, 2001 4:58 PM
> To: Dennis Petrich; THALER,PAT (A-Roseville,ex1); Lindsay, Tom; Howard
> A. Baumer; HSSG_reflector (E-mail)
> Subject: RE: [802.3ae] XAUI Rj TR comment
> Dennis,
> The MJS document is referenced from an informative part of 
> our draft and it
> is a TR. The terms are used in normative specifications in 
> our draft. The
> definitions should be added to our draft because a 
> specification doesn't
> mean anything if the quantity being specified is left ambiguous.
> Regards,
> Pat
> -----Original Message-----
> From: Dennis Petrich [mailto:dpetrich@xxxxxxxxxxxxx]
> Sent: Wednesday, August 01, 2001 2:11 PM
> To: 'THALER,PAT (A-Roseville,ex1)'; Lindsay, Tom; Howard A. Baumer;
> HSSG_reflector (E-mail)
> Subject: RE: [802.3ae] XAUI Rj TR comment
> Pat,
> The NCITS "TR-25-1999" MJS document provides definitions that can be
> referenced for XAUI use to distinguish between the various 
> jitter types such
> as RJ, DJ, DDJ, SJ and so on.
> Also, FC crosstalk work was done a while back and can be viewed at
> T11/00-064v0 and T11/99-759v0.  In the tests crosstalk showed 
> up as DJ.  But
> I'm sure these results would vary as a function of the 
> crosstalking data
> rate and frequency content.
> Dennis 
> -----Original Message-----
> From: THALER,PAT (A-Roseville,ex1) [mailto:pat_thaler@xxxxxxxxxxx]
> Sent: Wednesday, August 01, 2001 1:43 PM
> To: Lindsay, Tom; Howard A. Baumer; HSSG_reflector (E-mail)
> Subject: RE: [802.3ae] XAUI Rj TR comment
> Tom,
> Jitter always seems to be a difficult subject to sort out and 
> your remark
> below caused me to do some checking on RJ vs. DJ.
> I've looked all through the 802.3 standard and our draft. 
> There doesn't seem
> to be any definition of RJ or DJ. Processes can certainly be 
> random without
> being random or Gaussian. Deterministic means if a set of 
> conditions is set
> up we know what will result. The roll of a die is random 
> though the result
> is bounded.
> If we are using dictionary words with a different or more 
> restricted meaning
> such as random = Gaussian (or truncated Gaussian where the truncation
> happens past 1E-12) then we should define our terms. Since we specify
> deterministic jitter and total jitter, we should at least 
> have a reasonably
> rigorous definition of "deterministic jitter."
> I also notice that in some places jitter is divided into RJ 
> and DJ, but in
> other places in 47 it is RJ, DJ and sinusoidal. (and the
> equivalent subclause of 53) divide jitter into random, 
> deterministic and
> bounded.
> Crosstalk is deterministic in that given a fixed adjacent 
> signal and a fixed
> coupling function one can determine the crosstalk. However, 
> the crosstalk at
> a receiver is often the result of multiple disturbers 
> coupling in each with
> its own function and the signals aren't correlated to the 
> received signal.
> Therefore, the sum of the crosstalk looks like a truncated 
> Gaussian. Even if
> the definition of RJ is Gaussian up to at least 1E-12, it 
> isn't clear to me
> that crosstalk would fall outside that definition. I don't 
> recall seeing any
> studies on the distribution of crosstalk for XAUI or for our optical
> receivers.
> I would expect crosstalk to be part of RJ rather than DJ.
> Regards,
> Pat
> -----Original Message-----
> From: Lindsay, Tom [mailto:tlindsay@xxxxxxxxxxxxxxxxxxxx]
> See below, Tom
> -----Original Message-----
> From: Howard A. Baumer [mailto:hbaumer@xxxxxxxxxxxx]
> Sent: Tuesday, July 31, 2001 11:36 AM
> To: Lindsay, Tom; HSSG_reflector (E-mail)
> Subject: Re: [802.3ae] XAUI Rj TR comment
> >>>>snip<<<<<
> - We're still confused on how you would ever get 0.55UI of RJ. If
> crosstalk adds so much jitter,
> **TL - crosstalk is expected to be bounded, and therefore more
> effectively deterministic (the definition of RJ is 
> unbounded/Gaussian to
> least below 1E-12, and DJ is all other stuff).