I agree with you completely.
It also doesn't make sense to try and "extend" Class D/E
channel specs, with all the attendant risks, when 11801 has already specified a
Class F channel that covers the frequency range of relevance to 10GBASE-T.
From: Geoff Thompson
Sent: Wednesday, March 05, 2003
To: Rao, Sailesh
Cc: Geoff Thompson; Sreen
Raghavan; GEisler@aol.com; stds-802-3-10GBT-Modeling@ieee.org;
Subject: RE: [10GBASE-T]
At 04:31 PM 3/4/2003 -0700, Rao, Sailesh wrote:
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.
From: Geoff Thompson [mailto:email@example.com]
Sent: Monday, March 03, 2003 6:17
To: Sreen Raghavan
Subject: RE: [10GBASE-T]
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
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.
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.
Vativ Technologies, Inc.
On Behalf Of GEisler@aol.com
Sent: Friday, February 28, 2003
Subject: [10GBASE-T] Reflections
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