Thread Links Date Links
Thread Prev Thread Next Thread Index Date Prev Date Next Date Index

RE: [802.3ae] XAUI Rj TR comment


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

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

I would expect crosstalk to be part of RJ rather than DJ.


-----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

- 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).