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Hi George, You said “The notion that a pd designer should only know the pd part of the spec is just plain wrong. Someone who does not read the whole clause to know what the behavior of his link
partner with does so at his own risk.”. is basically correct. Our case is special. This is a case that a PD settings (MPS in this case) is depending on PSE design (Irev) which is a bad thing when
you design a spec. It cannot happen! And if it happens and we want to allow it as we are doing it with backfeed 3-pair problem (we don’t have chice due to backward compatibility argument) , we need at least to give some hint in the PD MPS section to prevent
mistakes. IT IS NOT STRAIGHT FORWARD TO UNDERSTAND that Irev might affect MPS in the PD even if you read the PSE spec (Just to remind you: When people in our group push to allow PSE supporting ideal diode bridge with backfeed issue and also to allow new designs
of PDs with the same ideal diode bridge, they say all is good, no issues to allow it. But some of us for more than a month simulate/analyze/check (we didn’t believe that there are no problem at all),we found problems to adopt it as is, we fix them by adding/deleting/modifying
text/parameters etc. to allow supporting those PDs. So it is not straight forward even if your read both PSE and PD spec to really understand the cross effect. By making the reference for Irev in the PDMPS section, I help to make the awareness of the dependencies.)
We never had such situation. Never. The two specs PSE and PD where designed to be independent. Whenever we had a doubt on this concept, we add text/parameters to prevent it. If you
insist, I will show you many many examples (just look on many of Lennart’s comment that we accept just to keep this concept). I hope that we don’t have a bad communication here i.e. I don’t understand you and you don’t understand me and we both agree in principle
😊 since I don’t understand the resistance to fix the problem that I showed by adding a reference to the PD section for a parameter that is in the PSE section……somebody can supply a reason that make
sense why we should do it after we did it many times? Yair From: George Zimmerman [mailto:george@xxxxxxxxxxxxxxxxxxxx]
EXTERNAL EMAIL Chris/ Yair, and all.- The notion that a pd designer should only know the pd part of the spec is just plain wrong. Someone who does not read the whole clause to know what the behavior of his link partner
with does so at his own risk.
If I am designing a phy and am looking at the receiver, I’d better damn well know the limits of behavior I can count on from the transmitter. I do that by reading the transmitter spec. This is no different. Hi Yair, In clause 33, we did not tell the PD designer about Ihold. Why is this different? Thanks, Chris From: Yair Darshan <YDarshan@xxxxxxxxxxxxx>
Hi George, I am not necessarily suggesting new values or more informative information etc. This is not my intention. You are welcome to offer simpler text. I can’t agree to leave this as is. Again, the problem is: If PD vendors don’t read PSE section, how they can be aware of Irev in 3-pair mode which is in the PSE section and affect
the MPS on the PD section? Before we wavered on backffed requirements in 3-pair mode i.e. backfeed was required to be met and all PSE voltage range, we had never this situation before that meeting the PD spec
depends on PSE spec. This situation will be a source of interoperability issues and I am trying to resolve it at ZERO cost/issues for the ideal diode bridges in the field (instead of asking again to disallow new Type 3 and 4 PDs from having backfeed issues
in power on state). Without adding some hint/link/text to the PSE Irev in PD MPS clause, we will mislead the PD designer.
Please note that my proposed approach was the normal approach we took in similar cases. This is no different than the other cases. Yair From: George Zimmerman [mailto:george@xxxxxxxxxxxxxxxxxxxx]
EXTERNAL EMAIL Yair – all of these values are tutorial in nature. There are no requirements in your proposed text, therefore they are completely advisory. We write standards – the important thing to capture is what is required. The information may be valuable to implementers, I don’t argue that. However, publish that elsewhere (for
example, in an EA whitepaper) if you so desire. George A. Zimmerman, Ph.D. President & Principal Consultant CME Consulting, Inc. Experts in PHYsical Layer Communications 1-310-920-3860 From: Yair Darshan [mailto:YDarshan@xxxxxxxxxxxxx]
Hi George, The value of the proposed text is much higher that you have described see why: The issue is: -PD operates in 3-pair mode with ideal diode bridge that has the backfeed issue. This means that whatever load is in the unpowered PSE alternative, it is reflected to the PD load
and added up. -PD wants to be powered off. As a result it sets its MPS to 3.9mA which means must be OFF. PD vendor may not be aware of the Irev spec since it is in the PSE spec. -Now in this condition Irev=1.3mA will be added from the PSE to the PD MPS i.e. 3.9mA+1.3mA=5.2mA and PD will not be disconnected. This is the problem. The solution is that the PD vendor will take the 1.3mA in account of the MPS setting. The problem is that the PD vendor is not aware of Irev since this is the PSE spec and many times as a response to comment we agree to add text to PD section to tell PD about parameters
that affects the PD but appear in the PSE i.e. we said that the PD vendor get a PD spec and start to design without looking on PSE spec or aware of it which I believe it is a correct scenario. By the way, during last meeting we change the PSE and PD spec to address similar issues concerning to the effect of Irev on other spec items and this is one of them. I can never agree to a situation that you have a clear requirement in a PD for what to do regarding MPS (or other spec items) without telling the PD vendor that there is something
waiting for him in the corner… in the PSE spec that is not mentioned in the PD spec that can make his PD uncompliant. I don’t see a reason to
hide such critical information. Yair From: George Zimmerman [mailto:george@xxxxxxxxxxxxxxxxxxxx]
EXTERNAL EMAIL
Yair - the proposed text is purely advisory and informative. At this stage we should only be concerned with missing or incorrect requirements or correcting (preferably deleting) incorrect information. I just don’t see the point of adding more informative advice
to the standard. George A. Zimmerman, Ph.D. CME Consulting, Inc. Experts in PHYsical Layer Communications 310-920-3860
Hi Lennart, I agree that it doesn’t affect the case when the PD is disconnected from the cable. I was referring to the case that the PD is connected and wants power removal. The question if it is rare or not, is irrelevant since it is already in the spec and we need to address
it somehow and meet it. I agree that the solution can be that PDs that do want to have power removed can set their Iport_mps value for power removal to be lower than (4mA-1.3mA)=2.7mA. However, in order
to make this clear to the PD vendor (since Irev is in the PSE section) I believe that we need to add text to the PD MPS section as follows (or equivalent): Proposed remedy: Add the following text in clause 145.3.9, page 222 text after line 49: "When a PD is operating under 3-pair mode conditions, the value of IPort_MPS as seen by the PSE over the powered pair may increase by Irev (See 145.2.10.4, 145.3.8.8 ). As a result,
the PD may need to set IPort_MPS to alower value than IPort_MPS min to ensure power removal." Yair From: Lennart Yseboodt [mailto:00000b30a2081bcd-dmarc-request@xxxxxxxx]
EXTERNAL EMAIL Hi Yair, Your analysis is correct, the reverse current is added to the PDs own current. I don't consider this an issue we need to do anything about however: - it does not impair the primary function of MPS in any way (to remove power when the PD is disconnected) - it only affects PDs that use the method of removing MPS in order to have the PSE remove power, I would say this is pretty rare; - PDs that do want to have power removed can accommodate for the maximum 1.3mA of reverse current (draw less than 2.7mA of their own) Note that reverse current only happens under 3-pair conditions, and then the 'must disconnect' current level is 4mA for PSEs. Kind regards, Lennart On Mon, 2018-06-11 at 12:03 +0000, Yair Darshan wrote:
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