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Re: [802.3_4PPOE] Are diode bridges really needed (2).pptx

Hugh, and John – Yes, and Yes.  Crossovers are a part of life, and are valid.  Wiring errors are also part of life, even if they are invalid according to standards.

Immunity to pair swap is generally listed in the objectives of modern BASE-T PHYs.  As a result, data transmission in Ethernet systems is immune to, if not blind, to these defects, whether they are legal or not.


If we are going to consider removing the robustness against pair swaps from powering, what we will need is some kind of data-gathering exercise that spans multiple installations and installation classes.  It’s a big job, and has to include not just the professional installation and cabling community but also the end-user IT manager community – because these things change over time, and we will be running on cabling installed years ago, with additions and changes made over time.



George Zimmerman

Principal, CME Consulting

Experts in Advanced PHYsical Communications Technology






From: Hugh Barrass (hbarrass) [mailto:hbarrass@xxxxxxxxx]
Sent: Wednesday, February 12, 2014 10:13 AM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_4PPOE] Are diode bridges really needed (2).pptx




We need to be clear – crossover cables are not, in any way, faulty. Crossover and straight-through are part of standard connectivity.




From: John Camagna [mailto:John.Camagna@xxxxxxxxxxxxxxxx]
Sent: Wednesday, February 12, 2014 9:59 AM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_4PPOE] Are diode bridges really needed (2).pptx



Has anyone spent time with cable installers?  Bad installations or crossed cables will always be blamed on the vendor


Sent via the Samsung Galaxy Note® II, an AT&T 4G LTE smartphone

-------- Original message --------
From: Dan Dove <dan.dove@xxxxxxxxxxxxxxxxxx>
Date: 02/12/2014 9:46 AM (GMT-08:00)
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_4PPOE] Are diode bridges really needed (2).pptx

Hi Yair,

Do you have any idea what the percentage of installations with inherent wiring defects may be? If its 20%, your point makes sense. If its .01%, it would seem that those customers may be willing to fix their wiring rather than pay additional cost and efficiency (OPEX) and have the entire industry taking a hit on OPEX.

Such wiring defects should be identifiable with a cable tester. Most professional installers certify wiring upon installation, and so this seems like a really small exposure. But if you have data otherwise, it would be useful.

Dan Dove
Chief Consultant
Dove Networking Solutions
530-906-3683 - Mobile

On 2/12/14 9:15 AM, Darshan, Yair wrote:

Dave and all,
The "ALT C" looks a nice idea however I don't s how it would solve the concern that Hugh raised regarding PD working in some locations and in some it will not.
Please consider the following  situation:
You have a multiport Switch that through that patch panel, goes to several locations in the building. The cabling installation is already there. So some PDs that have the diode bridge will work and some PDs that doesn't will not. This is problem #1.
Now your suggestion may be good for new cabling installations. What will be the "interoperability index"  now with mixed installation. This is problem #2.
In cases that you have large switches with spare ports, the IT manager probably will use the same switch, will not install new cables (so no guarantee now of straight cables with fixed polarity) 
so we back in square 1.
I believe that PD vendors that doesn't care about polarity insensitive (just care to prevent damage) may decide to do so regardless of the standard and we may not need to preclude it just leave it "out of scope" etc. If you add solution options by the spec, it increases the concerns for interoperability.
-----Original Message-----
From: Dave Dwelley [mailto:ddwelley1@xxxxxxxxx] 
Sent: Wednesday, February 12, 2014 6:31 PM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_4PPOE] Are diode bridges really needed (2).pptx
It would seem to me that we need to define a new "Alt-C", which has all four pairs powered with a defined polarity (like Alt-B). This is similar to Christian's and Ken's suggestions, with a new name attached. Then we can either:
- make full autopolarity optional in a .bt PD, but mandate some sort of notification (like an LED indicator) when it's plugged in backwards. One can argue that this implements some amount of functionality with either polarity.
- make autopolarity mandatory in all PDs (as it is now), but the defined Alt-C polarity makes it pretty obvious what the PD should do if it doesn't care about full compliance.