Your summary is correct however it is not clear to me why you say “I would
agree that any PSE that computes Icon,
Ipeak based on any value
below maximum Rchan would necessarily fail a conformance test.” ?
As we know currently in the spec Icon and Ipeak are function of Vpse and Rchan so a PSE that use Icon and Ipeak based on Vpse and Rchan is compliant.
ILIM-2P is a fixed number and is designed to be ILIM_2P=2mA+ Ipeak-2P_unb_max.
From: Peter Johnson [mailto:peter_johnson@xxxxxxxxx]
Sent: Saturday, January 07, 2017 10:45 PM
Subject: Re: [802.3_4PPOE] Rewrite of 220.127.116.11
Ipeak is both a function of
Vpse (PSE output voltage).
PSE's with higher output voltage get an "advantage" in supporting lower values for Icon
and Ipeak - and that would also extend to
Ilim_min, however, is not dependent on
Vpse. So tuning Ipeak or
Ilim_min gives away that advantage.
Testing PSE's for their sourcing capacity as a function of output voltage is not such a big deal. I would agree that any PSE that computes
Icon, Ipeak based on any value
below maximum Rchan would necessarily fail a conformance test.
-------- Original Message --------
Subject: Re: [802.3_4PPOE] Rewrite of 18.104.22.168
From: George Zimmerman <george@xxxxxxxxxxxxxxxxxxxx>
Date: Fri, January 06, 2017 6:59 pm
David – everyone may have figured it out, but if they did, as you say, here’s the rub -
If, in fact, everyone has figured out to avoid the red box, then, that is defacto the template – might as well make it the template.
However, if someone decides to use the extra room, and invade the red box based on the channel, then, the individual evaluating compliance needs to test at multiple
Rchan values to check compliance. Not so good.
If that use of Rchan is only something we might WANT to allow in the future, we can spec it for the appropriate devices. Don’t burden every device fail with
a full set of second tests.
I’m not trying to preclude the capability – just don’t want an untestable spec, or to create (any more) questions of compliance or not.
Hi George, Heath, and Lennart,
I have to agree with Lennart here. If you look at the existing standard (I will use 2012 because that what I have lying around), Ipeak is defined as:
Which not only depends on the channel but VPSE as well. While I understand your concern about it being related to the channel (really hard for the PSE to figure
out), I would point out that most PSEs just assume a worst case value (lowest value allowed) for VPSE as well. And just for reference, here is the lower bound template for 2012:
And while yes, the lower bound template relies on this parameter, you don’t actually need to do anything with it. Using the same picture I used in my last
I would point out that the PSEs just needs to include the red box as part of the lower bound template (use the top of the red box). This removes any relation
to the channel from the lower bound template. I don’t see why we would need to change this as I believe everyone has figured this out already.
Lennart – just because the template depended on Rchan in the past doesn’t make it good practice – we’ve uncovered more than a few ambiguities that we’ve dealt
with in the new spec.
If dependency on the template is essential and adds a substantial benefit (and is actually used in legacy products or necessary for broad market potential of
new products), that’s another story. It comes with a not-insignificant testing cost if one really wants to be compliant.
Testing compliance of the template when the template lower bound varies with Rchan requires testing over various values of Rchan. This is why I was saying that
the template should not depend on Rchan. (unless it provides a substantial benefit actually used in legacy products or necessary for BMP of new products)
IPeak-2P indeed depends on Rchan, in 2 ways.
First in Eq 33-10, IPeak depends on Rchan.
Second, KIPeak in Eq 33-12 also depends on Rchan.
Because this is so complex (and useless to optimize for), a 'simple' worst-case calculation is provided in the form of IPeak-2P-unb_max. This number is higher
than IPeak-2P-unb and using this would automatically mean meeting peak unbalance requirements.
With regard to George's comment that the lowerbound template should not depend on Rchan... that has always been the case, since at least AT.
ICon also depends on Rchan for instance. Here it does make sense as it allows a PSE to optimize the power output to match with the channel losses.
We are noticing a few incongruities after looking at this longer.
"Alternatively, an over-margined value of IPeak-2P-unb, IPeak-2P-unb_max which is defined by Equation (33–14), may be used."
is incorrect. It creates an alternate definition of IPeak-2P-unb.
It used to create a new variable, IPeak-2P-unb_max, which happens to have a relationship to IPeak-2P-unb. We need to preserve the original wording. This term
is only used to form Iunb.
"The worst case value of IPeak-2P-unb is IPeak-2P-unb_max which is defined by Equation (33–14)."
2) The lower-bound template as defined by IPeak-2P (by way of IPeak-2P_unb) now has a third dimension, Rchan-2P. This is not only strange but is at odds with the
definition of Icon-2P_unb, which is a scalar.
I just wanted to give everyone a chance to review my rewrite of 22.214.171.124. I have attached a final version and a marked up version to this email. I have tried to include everyone
else’s comments on this section.