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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.
Tech Lead, Cisco Systems
Chair, IEEE P802.3bt 4PPoE Task Force
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.