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Re: [802.3_4PPOE] Unbalance margin (yseboodt3)

Yair, Lennart:


I would question the 2mA margin.   For an Icon_unb_2P at 935mA, 2mA margin is 0.2%.


Effectively, if a PSE is configured to allow 937mA when the worst case valid possible pairset current is 935mA, that puts a lot of burden on the measurement of PSE performance to be super accurate and consistent between different testing setups.   So I would hope to see a bit more margin for that reason alone, if no other reasons.   Maybe 5 mA ?



Pete J







From: Lennart Yseboodt [mailto:lennartyseboodt@xxxxxxxxx]
Sent: Sunday, August 27, 2017 3:59 AM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_4PPOE] Unbalance margin (yseboodt3)


Hi Yair,

I see three issues raised in your review:

1) Incorrect description text. ==> Has been updated, see v103.

2) "How to calculate ICon-2P" ==> I will have a presentation to explain how this works, there seems to be confusion around this.

3) The amount of margin needed between ICon-2P-unb and IUnbalance-2P.

If, and only if, we are all 100% sure that the model used to calculate the values of ICon-2P-unb reflects what can be achieved by real implementations then no additional margin is needed.

We're in the process of checking if that is true.

If we decide no additional margin is needed, we can replace item 5a by an equation as you suggest.


Kind regards,



On Sat, Aug 26, 2017 at 4:38 PM, Yair Darshan <YDarshan@xxxxxxxxxxxxx> wrote:

Hi Lennart and all,


You want to define Icon-2P_unb as a maximum value which is the correct approach and

To define Iunbalance-2P as the minimum current that the PSE should support which is also correct.

I still see issues in the language here are some:

  1. Table 145-16 item 5a; To make the distinction between Iunbalance-2P and Icon-2P_unb you need just to specify Iunbalance-2P>Icon-2p_unb as Iunbalance-2P=Icon-2p_unb+0.002. This will give you what you want without forcing additional margins and cost to the power. If you want more margin in Icon-2P_unb, this should be addressed by the 4P model limits.

This is a simple approach that don’t create mass in our work so far for unbalance requirements.

  1. Equation 145-8: Before you change Icon-2P_unb to Iunbalance-2P, we couldn’t solve the equation due to the absence of Iport-2-other equation/data. Now you replace it with Inubalance-2P which doesn’t correlate to Icon-2P_unb at all and as a result, now I this more impossible to calculate.

Please show how you can calculate Icon-2P now. You will see that it is impossible. Using my proposal in (1) will bring the issue back to one problem only that can be solve by defining how to calculate Icon-2P-other.


  1. Comparing the language, you use and its correlation with the objectives:

Icon-2P_unb item 5: “Pairset current for PSE and PD due to unbalance per the assigned Class (for single-signature PDs)”

Table 145-16 item 5a: “Supported pairset current including unbalance effect per the assigned Class (for single-signature PDs)”

IUnbalance-2Pat Equation 145-8: is the current a PSE is able to source on a pairset due to unbalance as defined in Table 145–16


Not clear distinctions for the difference between all 3.




From: George Zimmerman [mailto:george@xxxxxxxxxxxxxxxxxxxx]
Sent: Saturday, August 26, 2017 3:14 AM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_4PPOE] Unbalance margin (yseboodt3)



Lennart –

I’m afraid I may not be understanding what you are trying to say (or else you changed wording without actually meaning to) –


You make a distinction in your wording, which is either unintentional, or the meaning is obscure:

Icon-2P-unb max for the PSE and PD, item 5 in the table is: “Pairset current for PSE and PD due to unbalance”, and

Iunbalance-2P min that the PSE must support, in item 5a is:  “pairset current including unbalance effect”.


Then, in, you specify the other language for Iunbalance: “is the current a PSE is able to source on a pairset due to unbalance as defined in Table 145–16”


You changed the Icon-2P-unb max language FROM “pairset current including unbalance effect” TO “due to unbalance”, which would ordinarily mean “the component of the current due to unbalance (excluding the nominal current)” to me (and I expect most readers). If you are trying to communicate something with this change of language, I don’t know what it is, and I suggest we need another try at it.  Otherwise I think that:

“Pairset current for PSE and PD due to unbalance including the unbalance effect per the assigned Class (for single-signature PDs)” is the right thing to say for item 5.


I would also suggest the same language in


On a different note, you’ve gone to this trouble of defining a new, separate parameter Iunbalance to be the current supported, only so you can compute Icon2P.  why not just put Icon2P in the table appropriately?

It might look a little messier in the table, because it will have a min (Icon - IPort-2P-other; (whatever the value of Iunbalance-2P is for that class )) in it, but for the reader, it would all be in one place then, and be simpler to follow.

And, you wouldn’t have to define new values…




From: Lennart Yseboodt [mailto:lennartyseboodt@xxxxxxxxx]
Sent: Friday, August 25, 2017 8:56 AM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_4PPOE] Unbalance margin (yseboodt3)


Hi all,

I copy-pasted the table and forgot to update the name in the second table. Sorry about the confusion.

Attached a new version with correct naming.

Yair - the intention is twofold

a) make appropriate parameters for the 3 requirements

b) create margin between maximum allowed unbalance and what the PSE needs to support

This goes beyond adding a few mA. I've rounded off to the nearest 100mA multiple, but we can also pick something else.

Kind regards,



On Fri, Aug 25, 2017 at 5:46 PM, Yair Darshan <YDarshan@xxxxxxxxxxxxx> wrote:

Hi Lennart


Thanks for this work.

I saw some issues please see detailed review inside the file attached. The main issues are:

  1. In Table 145-16 you have duplicate names. It is not clear which is IUnbalance-2P.
  2. It will be better to propose numbers for the additional item 5a based on technical consideration. It looks that the end result of this work is to get effective higher Icon-2P_unb margins which, I guess is not the objective of this presentation/baseline. The purpose of this base line is to decouple between the maximum current unbalance current on a pair in PSE and PD that meets current unbalance requirements and the current that the PSE has to be capable to supply over 2-pairs which need to be a minimum value. For this purpose, you need just to specify that:

Icon_pse_capable_2P (or whatever the name is) = Icon-2P_unb+0.002 (I used this concept for ILIM-2P). This will create the gray area required between the two-definition of “max current” and “current capability “ and will resolve the confusion you have raised.

    1. As for the need (or not ) for margins in Icon-2P_unb value, please see darshan_03_0917.pdf that will update these numbers due to other reasons based on analysis and you will get a bit more margins (You saw this during our discussions and we can talk more about it if needed.







From: Lennart Yseboodt [mailto:lennartyseboodt@xxxxxxxxx]
Sent: Friday, August 25, 2017 3:57 PM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: [802.3_4PPOE] Unbalance margin (yseboodt3)



Hi all,

Please see the attached baseline for review.

Kind regards,