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Re: [10GBT] Symbol rate

At the March 2004 meeting there was a presentation that proposed 4PAM for distances up to 55m and suggested 8PAM for distances greater than 55m and up to 100m.  The 4PAM proposal was a low complexity, low power proposal suitable and probably very appropriate for short cable lengths. The proposers themselves were not trying to claim it was appropriate for 100m.
With 4PAM, with the additional constraint that you limit the signaling rate to 1300Msym/sec to stay within the maximum specified frequency for the channel model, the maximum bit rate possible is 1300M*4pairs*2bits/pair which comes out to 10.4Gb/s. This leaves insufficient signaling for any significant FEC hence it will be hard to make this work for 100m cable lengths . For more details on why, you will have to look at the prior presentations on minimum capacity required - there was one on the subject by Scott Powell and another jointly by Jose Tellado and Ofir Shalvi and probably several others.
You can make different assumptions and draw a different conclusion so feel free to make a case for 4PAM if you like, but clearly lay out the performance you expect and state the assumptions and we will have an opportunity to review it at the upcoming meeting at Long Beach. I think we will see multiple proposals that claim to meet the objectives and the discussion at Long Beach is likely to focus on which one appeals to a majority of the task force participants.
Given that there are likely to be multiple proposals that meet the distance objectives, I am not greatly inclined to expend time on proving that certain schemes will not work if the proposers are not claiming that they will meet the distance objectives.
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From: stds-802-3-10gbt@IEEE.ORG [mailto:stds-802-3-10gbt@IEEE.ORG] On Behalf Of SAMIR THOSANI
Sent: Saturday, May 15, 2004 9:36 PM
Subject: Re: [10GBT] Symbol rate

Dear Mr. Kasturia,
Can u please clarify based on what u r making the following statement:
" As I understand it, the PAM 4 type schemes that would use the much higher symbol rate would NOT meet our distance objectives "
This might be just YOUR understanding. so far, i dont think we have seen a single SOLID evidence to the above in past 2 yrs.
i think we r all still under the clouds, as they say. And as far as ur comment regarding the 802.3 voters,  i wud say that apart from
Mr. Sailesh Rao, i dont think any of the major PHY vendors associated with development of 10GBASE-T ever designed a PHY before,
like 1GBASE-T. This is a small world, btw, and we all know one another's track record. so, lets just leave at that.
----- Original Message -----
Sent: Tuesday, May 11, 2004 10:12 AM
Subject: [10GBT] Symbol rate

At the March meeting, there was a motion to bound the range of symbol rates. The motion, moved by George Zimmerman, suggested  a symbol rate that would range from 714Msym/sec per pair to 1000Msym/sec per pair.

This motion failed to get the requisite 75% yes vote. Some of the people who voted against this proposal were in favor of schemes that would require higher symbol rates - e.g. 1250Msym/sec per pair but were probably not very familiar with 802.3 operation. With 802.3 voters in the room, the motion would have passed. See the vote tally appended below from the meeting minutes.

As I understand it, the PAM 4 type schemes that would use the much higher symbol rate would NOT meet our distance objectives but offered some value in that they could enable much lower power transceivers for shorter distances than called for in our objectives.

Should these schemes, which do not meet our distance objective, but could still be valuable for customers who want shorter reach and lower power be considered in separate class - possibly in a different forum than 802.3an?

Can our chair, Brad Booth, give us his opinion on this?

Vote count from minutes of March meeting

TF Voters Y: 24 N: 15 A: 19

802.3 Voters Y: 21 N: 5 A: 9

Sanjay Kasturia
cell (650) 704-7686
office (408) 653-2235
Teranetics Inc.
2953 Bunker Hill Lane, Suite 204
Santa Clara, CA 95054