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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).
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
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.
Review & comments attached.
Looks OK but needs couple of fixes.
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).
I’ll appreciate your inputs.
Excellent, that’s not what I got from your original message. But it’s been a long day. My reading comprehension might be lowered… ☺
Tech Lead, Cisco Systems
Chair, IEEE P802.3bt 4PPoE Task Force
We are in violent agreement