RE: [10GBASE-T] Reflections
Sailesh-
At 04:31 PM 3/4/2003 -0700, Rao, Sailesh wrote:
Geoff,
Actually, we discussed the Shannon capacity of Cat-5 cabling for
1000BASE-T in the following presentation:
Sailesh
Rao & George Eisler, "Parameters for Copper Based Transmission
at 1Gb/s",
IEEE
802.3 Higher Speed Study Group,
Jan.
11-12, 1996, Milpitas, CA.
It was not controversial, which is probably why you don't remember
it...
I was afraid that I was wrong on this after I hit the send button.
I sit corrected.
More to the point, it was not controversial because the decision was to
stay within the specified bandwidth rather than the Shannon capacity. The
reason being that we did not own the specs for the cabling. We had no
protection against someone coming up with something clever, that was a
departure from past manufacturing practice, yet would still meet the
established cabling specifications yet wreak havoc with the Shannon
capacity.
We were particularly sensitive to this last situation because we had just
seen such applied cleverness when the teflon shortage hit and we could no
longer depend on the prop delay matching on all 4 pair (another
previously unspecified characteristic) that became a consideration on T4,
T2 and 1000BASE-T.
Thanks for keeping me honest.
Regards,
Cheers,
Sailesh.
Geoff
-----Original Message-----
From: Geoff Thompson
[mailto:gthompso@nortelnetworks.com]
Sent: Monday, March 03, 2003 6:17 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