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. 52.9.10.4 (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).