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Re: [802.3_4PPOE] PD Load turn on

Hi all--
  I am not someone familiar with most of the details of PoE, but I do have a keen interest in
terminology about power states, particularly of devices.
  I am sure all of you are clear on the meaning here, but an outside reader might well
mis-interpret things.  In particular, when a PD is said to turn On or Off, then it is
easy to think of this as the Device itself turning on or off.  In this case of course, it is
just the power flow on the link, or the PD's part of that, that may change state.
A complete powered device may have an internal battery or access to other external
power sources than the PoE link in question, so may draw no power off the PoE
link but still be very much on.  In addition, a full device might well be in its own
Off state but drawing lots of power on the PoE link.
  In retrospect I think different terminology than PSE and PD might have been
better, but since we have those terms, I think it would be helpful to have a short
description of this issue around to give to people; I would be happy to help craft
such a thing, with others.
  I do think that a subtle shift in language could be done in the 802.3 context and
beyond, to speak more about the state of the link, or the PSE interface and PD interface,
rather than just PSE and PD.  And, when power becomes bidirectional, other terminology
shift may be needed.

On Thu, Mar 19, 2015 at 3:22 PM, Koussalya Balasubramanian (kobalasu) <kobalasu@xxxxxxxxx> wrote:
Here is what I am going to put in the maintenance request and then when it get kicked to us, we can talk it out more in the room.  The summary email I sent can be used as reference to the 3 different branch topics.

Problem Statement:  

Reference - 

- PDs in the field turn on their Load during Inrush.  This leads to PD cap not charging up fully (even if C<180uf and PSE is following inrush rules from  This may lead to operational problems after inrush.  There is a Voff requirement in PD table 33-18 to ensure power supply remains turned off for V<30V, but customers seem to read this as applicable only "after power on" not during "power on" - hence they turn on their DC-DC during inrush causing problems. 

Suggested Solution

Add the following to section

"PDs shall not draw more than the maximum current allowed by a PSE during inrush as outlined in section"

Change 2nd paragraph of section as follows (change shown with underline)

"The PD shall not turn on until a voltage greater than Voff and less than or equal to Von"

From: George Zimmerman <george@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
Reply-To: George Zimmerman <george@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
Date: Thursday, March 19, 2015 10:14 AM

To: "STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx" <STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx>
Subject: Re: [802.3_4PPOE] PD Load turn on

Yes, I agree, and you even pointed out the clarification on “turn on/off”, as “- turn PoE draw off – perhaps just having it say, ‘the PD shall turn PoE draw on’ instead of the ‘PD shall turn on’ might be clearer.


Anyhow, just to be clear, which version of the proposal were you going to suggest?  The original with ‘should’? (which didn’t have half of the issues we discussed) or something else?



George Zimmerman

Principal, CME Consulting

Experts in Advanced PHYsical Communications Technology






From: Dan Dove [mailto:dan.dove@xxxxxxxxxxxxxxxxxx]
Sent: Thursday, March 19, 2015 9:44 AM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_4PPOE] PD Load turn on


Hi Kousi,

I think you have it well stated.

Dan Dove
Chief Consultant
Dove Networking Solutions
530-906-3683 - Mobile

On 3/17/15 5:47 PM, Koussalya Balasubramanian (kobalasu) wrote:



The conversation definitely seems to have taken a bigger scope.  Thank you for all the discussions.  I notice, there are 3 different points in the discussions


1)  Clarifying that Voff applies even during power up and not only after power on has happened

- This was my original intention.  This doesn't change the existing standard behavior at all – this only clarifies that Voff applies during power up as well (as few of us have heard some customers arguing it doesn't).  Hence it will not make any compliant PD non-compliant.

2)  Dead band between Von and Vport_PD 

3)  Does existing IEEE802.3 Std 2012 text indicate PD shall never turn off? 

- Original IEEE802.3Std 2012 language of "The PD shall turn on at a voltage less than or equal to Von" --> does this mean PD shall never turn PoE draw off if it has local source?


The original solution from me suggestion was only for 1).  The suggestion from Dan seems to cover 3) - but it becomes slightly more complicated for 2).  Given there is a language of "less than or equal to" may be the original language of less than or equal to Von suffices ?


Nevertheless, given we have a comment cycle coming up – face to face discussions might help here.  I will go ahead and submit my original suggestion (only as a starter) which we can play with more during comment resolution.




From: Dan Dove <dan.dove@xxxxxxxxxxxxxxxxxx>
Organization: Dove Networking Solutions
Reply-To: Dan Dove <dan.dove@xxxxxxxxxxxxxxxxxx>
Date: Tuesday, March 17, 2015 12:30 PM
To: "STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx" <STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx>
Subject: Re: [802.3_4PPOE] PD Load turn on


Hi Mike,

I think your point is good. A PD should not be mandated to accept power once the PI voltage exceeds Von, but rather it should be restricted from accepting power (beyond a signature/class current) until the PI voltage exceeds Von.

How about this...

"The PD shall not turn on until a voltage greater than Voff and less than or equal to Von or VPort_PD(min) whichever is greater, is present at the PI."

This would allow PDs to draw local power or draw from the LAN based on their own decision making process, but would prevent them from drawing power until the PI voltage meets the appropriate limits.

Nice hearing from you too. :)

Dan Dove

Chief Consultant
Dove Networking Solutions
530-906-3683 - Mobile

On 3/17/15 10:55 AM, Michael McCormack wrote:

How does a PD ever turn off?  In your efforts to be able to affix blame for devices that are non-compliant (trust me - idiots will still do idiotic things you will only now have two things they fail to do properly) you have precluded PDs which allow and prioritize local power supplies.






Michael McCormack



Bruce Nordman
Lawrence Berkeley National Laboratory
m: 510-501-7943