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Re: [8023-POEP] Problems with remedy regarding PSE type 2 behaviour when it reads bad classification



Statement #1: "802.3af PD that takes 50mA during classification is still a compliant device."
Yair, you are mixing up the ends here.  You are correct that it is perfectly legal for an AF PSE to power a PD that draws <50mA during classification.  I think you are overlooking the fact that it is illegal for the PD to actually draw more than 44mA (see 33.3.4 of 802.3af: In addition to a valid detection signature, PDs shall provide the characteristics of a classification signature as specified in Table 33-11).  
 
A PD that draws more than 44mA during classification is non-compliant.
 
 Statement #2 "It is allowed by the 802.3af and is treated by the 802.3af PSE."
 
I think I proved above that it is not allowed for the PD.
 
Statement #3 "If it was a mistake to allow it or not in the 802.3af is not relevant now due to the fact that it was allowed."
 
It is only relevant for Type 1 PSEs -- and only if anyone else cares to continue to allow power to non-compliant devices.  I have no problem closing a loophole in the first standard to disallow bad behavior.
 
Statement #4 "In addition, it was not a mistake to allow 802.3af PSE to power 802.3af PD with bad classification due to the fact that in 802.3af the whole classification issue was optional and especially in 802.3af PSE it was optional so in order to give the PD the same treatment when it is connecting to a PSE that do classification to a PSE that is not doing classification you had to power the PD in case of classification error of any kink."
 
Classification was only optional in the PSE, the PD is strictly required to conform to some sort of classification.  It was considered optional because you can get Class 0 for free with the detection resistor.  I don't really care if I don't get equal treatment between PSEs that perform classification and PSEs that don't when we are talking about a non-compliant PD.  Maybe classification should have been mandatory for the PSE.  That is certainly a better solution than allowing power to a non-compliant device.
 
 
To clarify my statement that you didn't understand, let me place some sentences here:
 
from 33.2.8.1: "A Type 2 PSE that has failed to complete mutual identification may provide Class 0 power."
from July 2007 Plenary: "Move that Type 2 PSEs may optionally power Type 1 PDs with Type 2 current limits."
Figure 33-14 PI operating current templates, this applies to both Type 1 and Type 2 PSEs and makes no distinction between T1 and T2 PDs.
 
It is not explicitly stated but via the statements above I can rationally make a PD that fails to complete mutual ID and gets Class 0 power.  But according to the agreement in SF in July 2007 (moved by Schindler, Seconded by Darshan), the Type 2 PSE is free to power the Type 1 PD with Type 2 limits.  So now I can be a non-compliant PD and I can reasonably expect that I will get 30W from a Type 2 PSE.  And the PSE is not required to police and only has to conform to the operating current template which will allow 600mA for a Type 2 PSE.  That was the point of my statement.
 
Statement #5 "The fact is Chad, that any one that want to do dumb PD can do it without investing in a circuit in a PD that draws 60mA. How? Very easy. He design a PD with resistor signature and without classification at all. So when voltage is applied it will take full power without any issue. It is not compliant behavior but you can not prevent it…"
 
The PD you mention is impossible to design.  If it draws no current during classification (disables the detection resistor), it is still Class 0.  Any other current falls into some category, Class 1, 2, 3, 4 or fail.  I know we can't prevent all non-compliant behavior but, in my opinion, it is bad form to make it SO EASY to misbehave and still get powered.
 
Statement #6 "Now what will cause PSE vendors or PD vendors more problems and noise from the field? Type 1 PD that always working with Type 1 PSE but not working with Type 2 PSE OR fooling our selves that we have the ultimate solution how to prevent using dumb PDs? You can see to you don’t have to be smart to create dumb PDs."
 
My assumption here is that people have been making compliant PDs and there will be no noise from the field.  As I said above, I am not fooling myself into thinking this can be made bulletproof, but this is a glaring hole in the spec.  And I disagree, you have to be very smart to make the dumb PDs and you have to do it on purpose because you thoroughly read the standard and understand all the intertwined rules that allow misbehavior.
 
-Chad
 


From: Darshan, Yair [mailto:YDarshan@microsemi.com]
Sent: Thursday, May 22, 2008 3:14 AM
To: Chad Jones (cmjones); Clay Stanford; Matthew Landry; Fred Schindler (frs); Patoka, Martin; Bill Delveaux (bdelveau); Anoop Vetteth (avetteth); McCormack, Michael; gthompso@nortelnetworks.com; Jetzt, John J (John); Reshef, Tamir; Feldman, Daniel; Rimboim, Pavlick
Cc: STDS-802-3-POEP@listserv.ieee.org
Subject: RE: Problems with remedy regarding PSE type 2 behaviour when it reads bad classification

Hi Chad,

 

802.3af PD that takes 50mA during classification is still a compliant device.

It is allowed by the 802.3af and is treated by the 802.3af PSE.

If it was a mistake to allow it or not in the 802.3af is not relevant now due to the fact that it was allowed.

 

In addition, it was not a mistake to allow 802.3af PSE to power 802.3af PD with bad classification due to the fact that in 802.3af the whole classification issue was optional and especially in 802.3af PSE it was optional so in order to give the PD the same treatment when it is connecting to a PSE that do classification to a PSE that is not doing classification you had to power the PD in case of classification error of any kink. This was exactly an interoperability issue only because PSE classification function was optional.

 

Regarding the argument " The other problem with your remedy is that there is a two layer slight of hand going on here.  If you allow a Type 2 PSE to assign this noncompliant PD class 0 there is another statement that says the Type 2 PSE can treat the class 0 PD as Class 4 and now we are back to the start.  You are allowing a noncompliant device to draw up to 30W, therefore enabling dumb PDs.  My opinion is this is completely unacceptable.  If I were a devious designer, I would just draw 60mA during class and then move on to drawing 30W."

 

I dot understand the point you are trying to make since I am not sure that the facts are correct or I didn’t understand you:

You said: " there is another statement that says the Type 2 PSE can treat the class 0 PD as Class 4 and now we are back to the start.  "

The specification says that in 802.3af Class 4 PD is treated as class 0 and not as you mentioned above. So I don’t understand the argument?

 

You said: .  "You are allowing a noncompliant device to draw up to 30W, therefore enabling dumb PDs.  My opinion is this is completely unacceptable.  If I were a devious designer, I would just draw 60mA during class and then move on to drawing 30W."

 

How I allow non compliant PD to get 30w?

Case 1: PD is drawing 60mA during classification.

What could be the options?

  1. It is Type 1 PD which according to 802.3af it will get power from the PSE.
  2. It is Type 2 PD with bad classification circuit or a non compliant PD or dumb PD.

The fact is Chad, that any one that want to do dumb PD can do it without investing in a circuit in a PD that draws 60mA. How? Very easy.

He design a PD with resistor signature and without classification at all. So when voltage is applied it will take full power without any issue. It is not compliant behavior but you can not prevent it…

 

Now what will cause PSE vendors or PD vendors more problems and noise from the field?

Type 1 PD that always working with Type 1 PSE but not working with Type 2 PSE OR fooling our selves that we have the ultimate solution how to prevent using dumb PDs? You can see to you don’t have to be smart to create dumb PDs.

 

Yair

 


From: Chad Jones (cmjones) [mailto:cmjones@cisco.com]
Sent: Wednesday, May 21, 2008 9:05 PM
To: Darshan, Yair; Clay Stanford; Matthew Landry; Fred Schindler (frs); Patoka, Martin; Bill Delveaux (bdelveau); Anoop Vetteth (avetteth); McCormack, Michael; gthompso@nortelnetworks.com; Jetzt, John J (John); Reshef, Tamir; Feldman, Daniel; Rimboim, Pavlick
Cc: STDS-802-3-POEP@listserv.ieee.org
Subject: RE: Problems with remedy regarding PSE type 2 behaviour when it reads bad classification

 

We only have to guarantee interoperability for compliant devices.  A device that draw more than 51mA during classification is noncompliant. 

 

As I pointed out in my comment it was a mistake in AF to allow a PSE to power a device that has failed classification and that we should fix that in AT.  I'm not concerned that a device that is noncompliant will not get power from a Type 2 PSE. 

 

The other problem with your remedy is that there is a two layer slight of hand going on here.  If you allow a Type 2 PSE to assign this noncompliant PD class 0 there is another statement that says the Type 2 PSE can treat the class 0 PD as Class 4 and now we are back to the start.  You are allowing a noncompliant device to draw up to 30W, therefore enabling dumb PDs.  My opinion is this is completely unacceptable.  If I were a devious designer, I would just draw 60mA during class and then move on to drawing 30W. 

 

the only thing we have to be careful of is that we are not making all legacy PSEs noncompliant by removing their ability to power devices that fail classification as Class 0.  I would support your statement if it said:

 

If a PSE detects Iclass_lim, it may power the PD strictly at Class 0 levels or it may choose to enter the IDLE mode.  A Type 2 PSE that decides to power a PD that violates Iclass_lim shall limit Pport to 15.4W.  In this case, there is no allowance for the Type 2 PSE to power at Type 2 levels.

 

or some other equivalent but better wording.  I would want a shall statement that generates a PICS that would check that a PSE will police at 15.4W if it powers a noncompliant device.  Of course we would also have to figure out how to work this into the state diagram.

 

To me the easier solution is to make the decision to not power these devices.

 

-Chad

 

 


From: Darshan, Yair [mailto:YDarshan@microsemi.com]
Sent: Wednesday, May 21, 2008 10:05 AM
To: Chad Jones (cmjones); Clay Stanford; Matthew Landry; Fred Schindler (frs); Patoka, Martin; Bill Delveaux (bdelveau); Anoop Vetteth (avetteth); McCormack, Michael; gthompso@nortelnetworks.com; Jetzt, John J (John); Reshef, Tamir; Feldman, Daniel; Rimboim, Pavlick
Cc: STDS-802-3-POEP@listserv.ieee.org
Subject: Problems with remedy regarding PSE type 2 behaviour when it reads bad classification

Hi guys,

 

I have found a problem with the remedy on the above subject.

 

We have 3 cases in which we agree last meeting to return to IDLE state.

 

Case 1:

If PSE type 2 reads class 4 in 1st finger and other reading in 2nd finger, it will return to IDLE state.

The rational was that we don’t want to encourage someone using different coding so we can reserve it for future use.

So far it makes sense.

 

Case 2:

If PSE Type 2 pass detection successfully and fails to complete classification, it will return to IDLE state.

Rational:

Classification in Type 2 PSE and PD is mandatory. If it is not working then probably one of the two parts PSE or PD is non compliant or defective.

 

Case 3:

If PSE detects Iclass_lim, it will return to IDLE.

 

The problem is in Case 3.

Rational:

a) If PSE type 2 connected to PD type 1, and PSE reads Iclass_lim then according to last week change, PSE will return to IDLE state.

b) But If PSE type 1 connected to PD type 1, and PSE reads Iclass_lim, PSE is assign Class 0 which mean the PD will be operated.

 

Which means that in (a), PD type 1 will not work ever never with PSE type 2 under Iclass_lim and may work with PSE type 1.

This is violates backwards compatibility and creates interoperability problems between PSE type 1 and PSE type 2 connected to PD type 1 exhibiting Iclass_lim.

 

The solution for this problem is:

In Case 3 (and maybe also in case 2) , The PSE type 2 shall assign Class 0 as well as Type 1 PSE, if it detects Iclass_lim.

 

What is your opinion on these guys?

 

Yair

 

Darshan Yair
Chief R&D Engineer

Analog Mixed Signal Group

Microsemi Corporation

 

1 Hanagar St., P.O. Box 7220
Neve Ne'eman Industrial Zone
Hod Hasharon 45421, Israel
Tel:  +972-9-775-5100,

Cell: +972-54-4893019
Fax: +972-9-775-5111

 

E-mail: <mailto:ydarshan@microsemi.com>.