# Re: [802.3_4PPOE] End to End Channel Pair to Pair Unbalance Ad Hoc Presentation

Yair,

Your chart is an excellent example of why the mathematical model you have chosen is not a good representation of the channel.  It greatly over or under estimates the imbalance of all but two of the 16 use cases you have chosen here.

Further, there is only one or two cases of these 16 that will ultimately determine the maximum pair current which is necessary for the design of PSEs, magnetics, PDs etc..  The simulation method solves all of the problems much more accurately.

Regards,

 Jeff HeathDesign Center Manager paper: 402 East Carrillo Street, Suite D Santa Barbara, California 93101 voice: 805.965.6400 fax: 805.965.1701 computer:

From: Darshan, Yair [mailto:YDarshan@xxxxxxxxxxxxx]
Sent: Thursday, July 03, 2014 11:02 AM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_4PPOE] End to End Channel Pair to Pair Unbalance Ad Hoc Presentation

Hi Wayne and all,

You can see ,as expected, the peaks of the "nonrealistic use cases" and one realistic use case B are happens when channel Resistance difference is below 0.2 ohm.

Also consider the fact that the connectors that I have use in the simulations are with Rmin=30 miliOhm  and Rmax=50miliOm which means Rdiff=80miliom max for 4 connectors or 40miliokms for 2 connectors etc. which you can see from the plot that the peaks of the "nonrealistic use cases" is below 40 miliOhm or so for <=2 connectors.

Now what I thought to do with it is to have a text saying that:

I am proposing the following text to fix all issues:

The Channel P2PRUNB shall not acceded 7% or maximum pair to pair resistance difference of 0.1 ohm whichever is greater.

Channel P2PRUNB of a channel with maximum pair to pair resistance difference of 0.2 ohm may be ignored.

(Or instead of "may be ignored", shall be limited to 25% max. (25% max is the mathematically upper bound of P2PRUNB of any number of connectors with zero cables with the parameters we used)

I'll appreciate, any comments on this.

Yair

From: Larsen, Wayne [mailto:WLARSEN@xxxxxxxxxxxxx]
Sent: Thursday, July 03, 2014 4:13 PM
To: Darshan, Yair; STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: RE: [802.3_4PPOE] End to End Channel Pair to Pair Unbalance Ad Hoc Presentation

Hi Yair,

Would the existence of a spec, such as, not more than the max of .2 Ohms (or .1 Ohms) or 7% (or 6%) achieve this closure?

Wayne

7/3/14

From: Darshan, Yair [mailto:YDarshan@xxxxxxxxxxxxx]
Sent: Thursday, July 03, 2014 8:01 AM
To: Larsen, Wayne; STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: RE: [802.3_4PPOE] End to End Channel Pair to Pair Unbalance Ad Hoc Presentation

Hi Wayne,

Wayne I agree that we shouldn't be worried about.

The question is how to convert "don’t worry it is unrealistic in real installations" to "don’t worry, the spec says A, B, C"  therefore don’t worry.

I am looking for some text/other means to close this hole in the future spec so if someone during tests will have "unrealistic channel" that is used in the lab and not in real life installation I can point him to the spec and say "this is wrong setup ..and this is why, see the spec." .

I am working on such closure.

Yair

From: Larsen, Wayne [mailto:WLARSEN@xxxxxxxxxxxxx]
Sent: Thursday, July 03, 2014 3:31 PM
To: Darshan, Yair; STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: RE: [802.3_4PPOE] End to End Channel Pair to Pair Unbalance Ad Hoc Presentation

My opinion would be that the unrealistic use cases do not need to be worried about.

From: Darshan, Yair [mailto:YDarshan@xxxxxxxxxxxxx]
Sent: Thursday, July 03, 2014 2:12 AM
To: Larsen, Wayne; STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: RE: [802.3_4PPOE] End to End Channel Pair to Pair Unbalance Ad Hoc Presentation

Hi Wayne,

This solution, filters the "unrealistic use cases" that were resulted from short cables.

How it helps?

If we set a limit for the channel for 7%, and a user did use cabling and connectors combinations that is considered "not typical use case" or even "not realistic use case" and he got 12% it will be an issue for him. The spec says A and he got B.

This filters all the results of B which are not relevant to him when the channel is tested as standalone part.

The justification for this approach is, when the channel is connected to a system, and the channel uses short cables, the End to End current/resistance unbalance will be dominant since their unbalance is higher than the channel.

This is one of the solutions from the table.

There is 5th solution that in after our adhoc meeting Sterling and I were discussing and I am working on its details.

Regards

Yair

From: Larsen, Wayne [mailto:WLARSEN@xxxxxxxxxxxxx]
Sent: Thursday, July 03, 2014 6:09 AM
To: Darshan, Yair; STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: RE: [802.3_4PPOE] End to End Channel Pair to Pair Unbalance Ad Hoc Presentation

Hi Yair,

You showed a spreadsheet of four possible solutions, and one of them was to measure the DC resistance unbalance of the cabling channel with resistors in series with it.

What is the problem these solutions are solving?

Wayne

7/2/14

From: Darshan, Yair [mailto:YDarshan@xxxxxxxxxxxxx]
Sent: Wednesday, July 02, 2014 7:15 PM
To: Larsen, Wayne; STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: RE: [802.3_4PPOE] End to End Channel Pair to Pair Unbalance Ad Hoc Presentation

H Wayne,

Your question Is not clear to me can you elaborate?

Yair

From: Larsen, Wayne [mailto:WLARSEN@xxxxxxxxxxxxx]
Sent: Wednesday, July 02, 2014 11:38 PM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_4PPOE] End to End Channel Pair to Pair Unbalance Ad Hoc Presentation

Hi Yair,

I was trying to ask, what problem is being solved by this?

Wayne

7/2/14

From: Jeff Heath [mailto:jheath@xxxxxxxxxx]
Sent: Wednesday, July 02, 2014 11:25 AM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_4PPOE] End to End Channel Pair to Pair Unbalance Ad Hoc Presentation

Please announce when and why the ‘formal meeting’ has ended in the future.

Regards,

 Jeff HeathDesign Center Manager paper: 402 East Carrillo Street, Suite D Santa Barbara, California 93101 voice: 805.965.6400 fax: 805.965.1701 computer:

From: Darshan, Yair [mailto:YDarshan@xxxxxxxxxxxxx]
Sent: Wednesday, July 02, 2014 9:00 AM
To: Jeff Heath; STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: RE: [802.3_4PPOE] End to End Channel Pair to Pair Unbalance Ad Hoc Presentation

I meant that we continue to discuss after the time of the forma meeting. The formal meeting ends when there is not sufficient attendees or someone ask to finish on time, or most of the group agrees to continue, so after that time we can continue discussion whit out having decisions.

Yair

From: Jeff Heath [mailto:jheath@xxxxxxxxxx]
Sent: Wednesday, July 02, 2014 6:16 PM
To: Darshan, Yair; STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: RE: [802.3_4PPOE] End to End Channel Pair to Pair Unbalance Ad Hoc Presentation

What do you mean by formal ad hoc meeting?

Regards,

 Jeff HeathDesign Center Manager paper: 402 East Carrillo Street, Suite D Santa Barbara, California 93101 voice: 805.965.6400 fax: 805.965.1701 computer:

From: Darshan, Yair [mailto:YDarshan@xxxxxxxxxxxxx]
Sent: Wednesday, July 02, 2014 3:53 AM
To: Jeff Heath; STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: RE: [802.3_4PPOE] End to End Channel Pair to Pair Unbalance Ad Hoc Presentation

Thanks Jeff.

I am working on this direction too and few others that we discuss after the formal 1 hour time of the adhoc meeting.

Yair

From: Jeff Heath [mailto:jheath@xxxxxxxxxx]
Sent: Tuesday, July 01, 2014 7:53 PM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_4PPOE] End to End Channel Pair to Pair Unbalance Ad Hoc Presentation

Yair,

The entire principle of adding balanced resistance to test imbalanced channel resistance does not represent any real system.  PSE PI and PD PI will add imbalance in worst case analysis.  At the end of the day only full worst case analysis using all three components will give us the correct worst case maximum current

Regards,

 Jeff HeathDesign Center Manager paper: 402 East Carrillo Street, Suite D Santa Barbara, California 93101 voice: 805.965.6400 fax: 805.965.1701 computer:

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