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Hi 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?
The fact is 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: 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. - From: 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 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
Analog Mixed Signal Group Microsemi Corporation
Cell: +972-54-4893019 E-mail: <mailto:ydarshan@microsemi.com>. |