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Thanks for reviewing.
Please see my response to your comments below.
Hi Pete, Yair,
Updated comments. Yair, your minimum PD voltages are wrong.
Yair: I agree in principle. We need that Type 3 and 4 PDs class 1-3 will be supported by Type 1 and 2 PSEs with Vpse=44V for class 1-3 with 12.5 ohms. So these are the numbers I got.
Class 1: 42.88V è 42.8 (rounding down for worst case) instead of 42.9
Class 2: 42.07V è 42 (rounding down for worst case) instead of 42.1
Class 3: 39.94V è 39.9
See calculations attached.
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).
Yair: Since this is a spec, and spec need to be accurate and sync, accurate and make sense with text and related Tables, we must make sure that the calculated values will not be higher than the fixed worst case numbers in Table 145-11.
So, to round up PClass is OK. Rounding done is not.
As a result, we can round the following up:
3.92W è 4W
6.72W è 6.8W
451.W stays 45.1W since the calculated value is higher than 45W. We can adjust PD number, I don’t like it, but we can do it. Are you preferring this option? In This case Ppd for Class 5 will be 39.94W instead of 40W.
See other solution to this issue in the document to add a text to clarify the source of potential differences between the calculated values and fixed values in Table 145-11.
Having easy to remember numbers is more important than being precise down to 10 mW.
Yair: It was never an objective to remember numbers….
As such I've rounded the numbers to make as much sense as possible (matches with Pete's PClass numbers).
Yair: Please see above for what is the definition in my opinion for “making sense” underlined above.
Yair: Regarding your comment in page 4: “Does not match D2.4 text, nor does it produce a valid sentence. Please check.”
The text without the changes is D2.4 text.
The modified proposed changes is to split the sentence to two parts.
The first part says the when you plug the Vpse_min and Rch you will get the over-margined values in Table 145-11.
The 2nd part is explaining that the over-margined values where taken per the lowest PSE Type which is Type 3.
From: Peter Johnson <peter_johnson@xxxxxxxxx>
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