Lest I be misunderstood, I am not supporting any
position with regard to including bridge diodes.
My view is that wiring errors DO exist and that
crossover, while rare any more, also does exist.
My position is that either diode bridges should
exist in the PD, or a means of detecting wiring
defects, crossovers, etc.. must exist and
perhaps auto-correction of power application
to address it. An "Auto-MDIX-like"
application of power so to speak.
When these alternatives are weighed,
diode-bridging may be the simplest,
lowest cost, most robust means to
address the problems cited above.
On a side note, plug-n-play
being cited, we should note that
prior to Auto-MDIX, it was not
unusual for someone to burst into
the lab frantically looking
for a crossover cable. Ethernet
was not as plug-n-play as we
like to think.
Dove Networking Solutions
530-906-3683 - Mobile
On 2/12/14 10:44 AM, Rimboim, Pavlick wrote:
to add my 0.02$,
POE LED lighting becomes a commodity anyone could install it
on his desk lighting by using /running RJ45 cable ,
cannot trust everyone to be a professional installer , so
any robustness issue need to be looked at with this
understanding that we are looking at a commodity solution at
the end user might be the one to install it and not only a
(516)342-6586 | Mobile (516)507-4353
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.
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.
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.
in Advanced PHYsical Communications Technology
NOTE NEW EMAIL ADDRESS. THE OTHER WILL STILL WORK, BUT
PLEASE USE THIS FOR CME BUSINESS)
need to be clear – crossover cables are not, in any way,
faulty. Crossover and straight-through are part of standard
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)
Subject: Re: [802.3_4PPOE] Are diode bridges really needed
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
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.
Dove Networking Solutions
530-906-3683 - Mobile
On 2/12/14 9:15 AM, Darshan, Yair
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.
From: Dave Dwelley [mailto:ddwelley1@xxxxxxxxx]
Sent: Wednesday, February 12, 2014 6:31 PM
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.