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

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Maybe you all know this, but ANSI/TIA-568-C.2 superseded ‘B.2, ‘B.2-1, and ‘B.2-10.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