Geoff:
There was never any doubt about the viability of 1000BaseT over installed
copper cabling during the development of the 1000BaseT standard. The only
question was precisely how to do it (what line code, error correction, noise
margins, etc). As you can tell from the debate that is going on this
reflector, several individuals including myself have expressed serious doubts
regarding 10GBaseT's theoretical feasibility over 100 meters of CAT5/6
regardless of precise line codes and implementation aspects. These doubts are
well-founded since they were backed up with detailed MATLAB analysis
programs. This is exactly why we are considering the Shannon Capacity
limit now. My point was that regardless of the innovations in DSPs and line
coding schemes that may or may not have happened since 1997, this limit is only
a function of the properties of the cabling, background thermal noise and alien
NEXT assuming that all other self impairments are canceled.
Sreen
-----Original Message-----
From: Geoff Thompson
[mailto:gthompso@nortelnetworks.com]
Sent: Monday, March
03, 2003 3:17 PM
To: Sreen Raghavan
Cc: GEisler@aol.com;
stds-802-3-10GBT-Modeling@ieee.org; stds-802-3-10gbt@ieee.org
Subject: RE: [10GBASE-T]
Reflections
Sreen-
We did not use or even consider the Shannon capacity of twisted
pair cabling in our previous work.
We did do a lot of investigation into twisted pair cabling characteristics when
we developed 1BASE5 and 10BASE-T. After that experience we decided that we
didn't want to do cabling and worked very hard to:
1) See that
useful specs for our applications were developed in TIA and SC 25.
2) Use those specifications.
When those cabling groups were starting on their specification of Cat 6 we did
ask them to characterize the cabling well beyond the zero ACR point (their
traditional cutoff point). They, in fact, did so. What all of this discussion
is about is that they didn't go out far enough so support this project.
Geoff
At 10:17 AM 3/3/2003 -0800, Sreen Raghavan wrote:
While there may have been
innovations in DSP architectures since 1997, Shannon Capacity of CAT5/6 cables
is a theoretical limit, and is unaffected by an individual s time horizon, or
implementation sophistication.
Sreen Raghavan
Vativ Technologies, Inc.
-----Original
Message-----
From:
owner-stds-802-3-10gbt@majordomo.ieee.org [mailto:owner-stds-802-3-10gbt@majordomo.ieee.org]
On Behalf Of GEisler@aol.com
Sent: Friday,
February 28, 2003 8:44 AM
To:
stds-802-3-10GBT-Modeling@ieee.org; stds-802-3-10gbt@ieee.org
Subject: [10GBASE-T] Reflections
Guys,
Nice to hear from a lot of the old crew that created the 1000BASE-T standard. I
think that you can all take a bow, judging from what is happening in the market
and the remarkable improvements in implementations achieved in three short
years. But no good deed goes unpunished, as they say, so you guys earned the
job (and created the need for) taking the next step up. Without a doubt, there
are big jumps in the performance demanded and we don't have the luxury that
1000BASE-T enjoyed, namely the introduction of coding into the design. That has
been done already. This time around, we have to take advantage of the residual
capacity of the cabling, which we barely touched.
On the other hand, you will agree that the levels of sophistication in analysis
and implementation of DSP based systems has also increased dramatically since
1997, when GigT started in earnest.
While I enjoyed fond memories of your recollections of what we knew (or
suspected) then and what we added later when we got smarter, it strikes me that
that history is relatively immaterial today. That was then and our current
circumstances are quite different. We now need to agree in the study group that
it is feasible to do 10Gig on some form of twisted pair cabling at the
desired length and go on to form a Task Force to do the hard work of coming to
agreement on the precise details of the signaling and channel specifications.
It is clear that the channel specifications as written in 11801 will have to be
modified and expanded for our use and installation qualification test
parameters will have to be defined. This is more or less what happened for
1000BASE-T and seems to me to be a normal and reasonable step. After all, why
should the cabling industry be expected to have already characterized cabling
for the use of a standard for which we are still in the Study Group phase? As
for installed cabling, we will see whether or how it may be qualified for 10G
as part of our effort.
I look forward to our meeting in Dallas and hope that we
can get to work on a PAR draft there.
George Eisler