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Re: [802.3_4PPOE] fallout from the 20 ohm conversation

Hi Pete, Yair,

Updated comments. Yair, your minimum PD voltages are wrong.

About rounding... convention has always been to have "nice" numbers on the PSE side and accept PClass_PD as calculated.

We have made a couple small roundings to PClass_PD (eg. Class 5 was rounded up to 40W).

Having easy to remember numbers is more important than being precise down to 10 mW.

As such I've rounded the numbers to make as much sense as possible (matches with Pete's PClass numbers).

Kind regards,


From: Peter Johnson <peter_johnson@xxxxxxxxx>
Sent: Friday, May 12, 2017 17:12
To: Yseboodt, Lennart; STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: RE: [802.3_4PPOE] fallout from the 20 ohm conversation

Yair, Lennart:


If rounding mathematically, I get same values as Yair except at Class 3, I get 13.9W.


If rounding UP to nearest 10th in order to be conservative at the PSE, it would be:


Class 1 4W

Class 2 6.8W

Class 3 14W


The calculation for Class 5 is 45.1W – rounding this down is of course, NOT conservative.


I don’t like the language “worst case PSE Type parameters”.   Worst case is never very descriptive.   Not sure new text is needed – it should be already covered in footnotes to the table I think.


Also, if we toss out Option B, then the footnotes for the table 145-11 will need be adjusted as they presently say “for minimum Vport_pse-2P” and these values are all for 50V Vport_pse-2P.



Pete J




From: Yseboodt, Lennart [mailto:lennart.yseboodt@xxxxxxxxxxx]
Sent: Friday, May 12, 2017 9:27 AM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_4PPOE] fallout from the 20 ohm conversation


Hi Yair,


Review & comments attached.


Looks OK but needs couple of fixes.




From: Yair Darshan <YDarshan@xxxxxxxxxxxxx>
Sent: Friday, May 12, 2017 2:03
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_4PPOE] fallout from the 20 ohm conversation


Hi all,


1.      Based on the last conclusions, my proposal to exclude the 20 ohms cases form the calculations of Pclass fixed values in Table 145-11

as derived from the worst case of Type 3 and 4 PSEs connected to all PD types, stays as proposed. Agreed?

2.      Please see attached Rev003 in which most of the reviewers choose Option A solution.

3.      In addition, I add proposed changes for Vpd, as result of the consequences of (1) and (2).


Ill appreciate your inputs.




From: Chad Jones (cmjones) [mailto:cmjones@xxxxxxxxx]
Sent: Friday, May 12, 2017 12:46 AM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_4PPOE] fallout from the 20 ohm conversation



Excellent, that’s not what I got from your original message. But it’s been a long day. My reading comprehension might be lowered…



Chad Jones

Tech Lead, Cisco Systems

Chair, IEEE P802.3bt 4PPoE Task Force


From: Geoff Thompson <thompson@xxxxxxxx>
Date: Thursday, May 11, 2017 at 5:18 PM
To: Chad Jones <cmjones@xxxxxxxxx>
Cc: Geoff Thompson <thompson@xxxxxxxx>, "Larsen, Wayne" <WLARSEN@xxxxxxxxxxxxx>, David Law <dlaw@xxxxxxx>, 4PPOE Reflector <STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx>
Subject: Re: [802.3_4PPOE] fallout from the 20 ohm conversation



We are in violent agreement



On May 11, 2017, at 2:10 PMPDT, Chad Jones (cmjones) <cmjones@xxxxxxxxx> wrote:


Geoff, we want to remove support for 20 ohms. I don’t want to include old revisions pick up old specs. Our objective clearly states that we are supporting only Class D from 118011 1995 and 2002, Cat5 and Cat5e, with the added restriction that loop resistance is 25 ohms. I just need to make the draft text match this objective.


We are not taking the most conservative approach. Our system requirements clearly state minimum cabling requirements. We are purposely excluding 40-ohm loop resistance cabling.



Chad Jones

Tech Lead, Cisco Systems

Chair, IEEE P802.3bt 4PPoE Task Force


From: Geoff Thompson <thompson@xxxxxxxx>
Date: Thursday, May 11, 2017 at 4:59 PM
To: "Larsen, Wayne" <WLARSEN@xxxxxxxxxxxxx>, Chad Jones <cmjones@xxxxxxxxx>, David Law <dlaw@xxxxxxx>
Cc: Geoff Thompson <thompson@xxxxxxxx>, 4PPOE Reflector <STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx>
Subject: Re: [802.3_4PPOE] fallout from the 20 ohm conversation




What Wayne says is true

and I believe a similar situation exists wrt the ISO/IEC standard.


The problem is that both of the cabling standards are, in effect, purchase specifications for new builds and installs.


That is somewhat different than the case with 802.3bt where (although we are specifying new attachment equipment) we are specifying operating that equipment on the installed base of cabling, much of which is not new.  The most conservative approach would be to spec everything against the original smaller gauge of TIA Cat 3, DIW and old German quad wiring.  I believe it is our collective opinion that (with exception to the note David mentions) we don't need to do that, rather we believe that the lowest appropriate common denominator at this point in time is legacy Cat 5. It is appropriate to reference old versions of the cabling standards where necessary to pick up those specs.





On May 11, 2017, at 1:42 PMPDT, Larsen, Wayne <WLARSEN@xxxxxxxxxxxxx> wrote:






Maybe you all know this, but ANSI/TIA-568-C.2 superseded ‘B.2, ‘B.2-1, and ‘B.2-10.  ‘2-1 and ‘2-10 were addenda to ‘B.2.









From: Chad Jones (cmjones) [mailto:cmjones@xxxxxxxxx
Sent: Thursday, May 11, 2017 3:39 PM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: [802.3_4PPOE] fallout from the 20 ohm conversation


All, the 20 ohm loop resistance discussion trigger déjà vu for David Law, so he checked through his archives. Sure enough, we had this EXACT conversation during development of 802.3at. as a result of this conversation, we placed some specific text in AT to define the cable while restricting the loop resistance. This also lead to analysis of the objectives and review of D2.4 for compliance. It was found that we are not in compliance with the objectives.


I have put together a doc showing David’s email, the objective, the D2.4 text, the AT text and the late comment I will file to close this hole. The only question I have is for the cabling folks:


For Cat5e, we list 4 ANSI standards: ANSI/TIA-568-C.2, ANSI/TIA/EIA-568-B.2, ANSI/TIA/EIA-568-B.2-1, and ANSI/TIA/EIA-568-B.2-10. In D2.4, we only list ANSI/TIA-568-C.2. Is it sufficient to list this one standard or is there something added by including those other three?



Chad Jones

Tech Lead, Cisco Systems

Chair, IEEE P802.3bt 4PPoE Task Force



Attachment: darshan_03_0517_Pclass_fixed_value_vs_calculated_value_baseline_Rev003_D_LYreview.pdf
Description: darshan_03_0517_Pclass_fixed_value_vs_calculated_value_baseline_Rev003_D_LYreview.pdf