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Re: [802.3_4PPOE] PSE current limiting (ILIM / TLIM)



Lennart:
 
I believe this does need some clarification.
 
I'm confused by the phrase "for a duration of at least TLIM".
 
Historically going back to 802.3at, Tlim is a variable.   Given this, the phrase should be
"for a duration of at least TLIM_min".
 
Looking at table 145-16, Tlim is shown as a minimum with no maximum.  Does that make it a fixed value ??   Looking at Figures 145-23,24,  there is a Tlim_min on the time axis.  So that supports that it is still a variable.
 
In my way of thinking, Tlim is the amount of time that a PSE tolerates a state of current limiting and/or foldback prior to removing power.   It varies by PSE and by other factors.   Tlim_min is the hard requirement.
 
I'm also concerned about the phrase "...and is required to shutdown before TLIM".   In 802.3at, Tlim_max was not defined in the power supply table but was definitely conveyed by the current template as 75 msec, or Tcut_max.   So in 802.3at, you could say "...and is required to shutdown before Tcut_max".
 
In 802.3bt, the current templates allow that currents higher than Ilim-2P_min could run forever.  Does that mean a PSE could hypothetically go into current limiting  (> Ilim_min) and stay that  way indefinitely?  No doubt a weird case, but this would not have been possible in 802.3at.
 
Regards,
Pete J

Sifos
 
 
 
-------- Original Message --------
Subject: [802.3_4PPOE] PSE current limiting (ILIM / TLIM)
From: Lennart Yseboodt <lennart.yseboodt@xxxxxxxxxxx>
Date: Tue, April 17, 2018 7:44 am
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx

Hello,

Please see proposed baseline for PSE current limiting.

Kind regards,

Lennart

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