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PSE Denying power is definitely not a fault. It is permitted operational behavior.

PD may reduce its power requirements through different means and then next power up it will work.



From: Chad Jones (cmjones) [mailto:cmjones@xxxxxxxxx]
Sent: Wednesday, February 11, 2015 11:39 PM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_4PPOE] POWER_DENIED



I would also agree with Bruce that a PSE denying power to a port is not necessarily a fault condition. If there was a PD fault then the PSE would not be granting power. The PSE choosing to not provide power is a system decision that is likely not a fault at all. 


I would suggest that you assume that POWER_DENIED is NOT a fault in the interest of expedience. I’d rather have you do it once than twice. 


I would like to hear more opinions as this is a group decision. Please respond to this thread with a simple “IS A FAULT” or “IS NOT A FAULT” and we can do an informal (and certainly not binding) ‘opinion of the reflector' poll.


Chad Jones

MGR, HW ENG, Cisco Systems

Chair, IEEE P802.3bt 4PPoE Task Force



From: Dan Dove <dan.dove@xxxxxxxxxxxxxxxxxx>
Organization: Dove Networking Solutions
Reply-To: Dan Dove <dan.dove@xxxxxxxxxxxxxxxxxx>
Date: Wednesday, February 11, 2015 at 3:26 PM
To: 4PPOE Reflector <STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx>
Subject: Re: [802.3_4PPOE] POWER_DENIED


Hi Bruce,

Agreed. I think your point below is exactly the logic and reasoning most people will have.

The question I pose, is that if you go to a candy machine with due number of coins, and it doesn't have the choice you want, do you consider that a fault?

If you are a candy machine mechanic, just order a restock for it. If you are a customer, you go back to the conference room and tell everyone "that *#(! candy machine doesn't have my candy!" and while it may be the candy-stocker's fault, its clearly a fault in their eyes.

All humor aside, the language in the text is ambiguous and we probably want to straighten it out. Fixing the state diagram will be relatively easy once we hash through the text. Its only a question of which hierarchical block the state resides within the diagram.

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

On 2/11/15 11:16 AM, Bruce Nordman wrote:

I am not literate in the uses/implications/etc. of the state
diagrams, and recognize that.

That said, I don't see a PSE denying or removing power
from a PD as necessarily a "Fault" in the sense of failure,

particularly as a PD may be dealing with more potential
power demand from devices than the PSE has the capacity for.

As an imperfect analogy, this seems to me like a vending
machine that could be broken (so a fault) and not able to
deliver candy bars -- or one that is simply out of the kind
you want (so also unable to deliver, but not a fault in the
sense of equipment failure).

Whether this should change how the state diagrams are
constructed or labeled, I can't say.  Thanks,



On Wed, Feb 11, 2015 at 10:39 AM, Dan Dove <dan.dove@xxxxxxxxxxxxxxxxxx> wrote:

Hi All,

In my work related to cleaning up the PSE state diagram as initiated at our last meeting, a drawing was put together by Dave Dwelley as a first stab of how one might break down the PSE diagram.

In this, (attached), the state "POWER_DENIED" was included in the "Delivering Power" group. As I proceeded on my task, I noted that POWER_DENIED could be considered a "Fault" condition depending on how you read the text.

I looked at the text and found the following; Power Denied or Removed (12.12)
When read as a one, bit 12.12 indicates that power has been denied or has been removed due to a fault
condition. This bit shall be set to one when the PSE state diagram (Figure 33–9) enters the states
‘POWER_DENIED’ or ‘ERROR_DELAY.’ The Power Denied bit shall be implemented with latching high
behavior as defined in 33.5.1.

So it occurs to me that the text is somewhat ambiguous. If you read it "{has been denied or has been removed} due to a fault condition"... you read the condition as a fault for either. If you read it "has been denied or {has been removed due to a fault condition}, then denial is not considered a fault, but removal due to a fault condition is a fault.

So, in order to move forward, I am going to consider the former for the basis of my effort. I will presume that denial of power is a "self-imposed fault" to advance this effort. If, due to consideration of the Task Force, its decided that this state should not be within the Fault group, it will be relatively easy to redraw things.

Feedback appreciated. In the last meeting, we discussed using the reflector for this purpose, hence, I'm reflecting on this issue.


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


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