Re: [802.3_4PPOE] MPS issue due to the allowance for reflected voltage i

Thread Links	Date Links
Thread Prev	Thread Next	Thread Index	Date Prev	Date Next	Date Index

Yair, please succinctly state your minimum requirement to make this go away. It looks like you would be happy with this:

add text to the PD MPS section: "IPort_MPS may be affected by Irev. See 145.2.10.4, 145.3.8.8.”

Please confirm: If the group adds this, we cover your concern.

Chad Jones

Tech Lead, Cisco Systems

Chair, IEEE P802.3bt 4PPoE Task Force

Principal, NFPA 70 CMP3

From: George Zimmerman <george@xxxxxxxxxxxxxxxxxxxx>
Reply-To: George Zimmerman <george@xxxxxxxxxxxxxxxxxxxx>
Date: Wednesday, June 13, 2018 at 8:52 AM
To: 4PPOE Reflector <STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx>
Subject: Re: [802.3_4PPOE] MPS issue due to the allowance for reflected voltage in 3-pair mode

Chris/ Yair, and all.-

The notion that a pd designer should only know the pd part of the spec is just plain wrong. Someone who does not read the whole clause to know what the behavior of his link partner with does so at his own risk.

If I am designing a phy and am looking at the receiver, I’d better damn well know the limits of behavior I can count on from the transmitter. I do that by reading the transmitter spec. This is no different.
On Jun 13, 2018, at 8:21 AM, Chris Bullock (bullock) <00000b693072df40-dmarc-request@xxxxxxxx> wrote:

Hi Yair,

In clause 33, we did not tell the PD designer about Ihold. Why is this different?

Thanks,

Chris

From: Yair Darshan <YDarshan@xxxxxxxxxxxxx>
Sent: Wednesday, June 13, 2018 8:39 AM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_4PPOE] MPS issue due to the allowance for reflected voltage in 3-pair mode

Hi George,

I am not necessarily suggesting new values or more informative information etc. This is not my intention. You are welcome to offer simpler text.

I can’t agree to leave this as is. Again, the problem is:

If PD vendors don’t read PSE section, how they can be aware of Irev in 3-pair mode which is in the PSE section and affect the MPS on the PD section?

Before we wavered on backffed requirements in 3-pair mode i.e. backfeed was required to be met and all PSE voltage range, we had never this situation before that meeting the PD spec depends on PSE spec. This situation will be a source of interoperability issues and I am trying to resolve it at ZERO cost/issues for the ideal diode bridges in the field (instead of asking again to disallow new Type 3 and 4 PDs from having backfeed issues in power on state).

Without adding some hint/link/text to the PSE Irev in PD MPS clause, we will mislead the PD designer.

Please note that my proposed approach was the normal approach we took in similar cases. This is no different than the other cases.

Yair

From: George Zimmerman [mailto:george@xxxxxxxxxxxxxxxxxxxx]
Sent: Tuesday, June 12, 2018 9:56 PM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_4PPOE] MPS issue due to the allowance for reflected voltage in 3-pair mode

EXTERNAL EMAIL

Yair – all of these values are tutorial in nature. There are no requirements in your proposed text, therefore they are completely advisory.

We write standards – the important thing to capture is what is required. The information may be valuable to implementers, I don’t argue that. However, publish that elsewhere (for example, in an EA whitepaper) if you so desire.

George A. Zimmerman, Ph.D.

President & Principal Consultant

CME Consulting, Inc.

Experts in PHYsical Layer Communications

1-310-920-3860

george@xxxxxxxxxxxxxxxxxxxx

From: Yair Darshan [mailto:YDarshan@xxxxxxxxxxxxx]
Sent: Tuesday, June 12, 2018 11:23 AM
To: George Zimmerman <george@xxxxxxxxxxxxxxxxxxxx>
Cc: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: RE: [802.3_4PPOE] MPS issue due to the allowance for reflected voltage in 3-pair mode

Hi George,

The value of the proposed text is much higher that you have described see why:

The issue is:

-PD operates in 3-pair mode with ideal diode bridge that has the backfeed issue. This means that whatever load is in the unpowered PSE alternative, it is reflected to the PD load and added up.

-PD wants to be powered off. As a result it sets its MPS to 3.9mA which means must be OFF. PD vendor may not be aware of the Irev spec since it is in the PSE spec.

-Now in this condition Irev=1.3mA will be added from the PSE to the PD MPS i.e. 3.9mA+1.3mA=5.2mA and PD will not be disconnected.

This is the problem.

The solution is that the PD vendor will take the 1.3mA in account of the MPS setting.

The problem is that the PD vendor is not aware of Irev since this is the PSE spec and many times as a response to comment we agree to add text to PD section to tell PD about parameters that affects the PD but appear in the PSE i.e. we said that the PD vendor get a PD spec and start to design without looking on PSE spec or aware of it which I believe it is a correct scenario.

By the way, during last meeting we change the PSE and PD spec to address similar issues concerning to the effect of Irev on other spec items and this is one of them.

I can never agree to a situation that you have a clear requirement in a PD for what to do regarding MPS (or other spec items) without telling the PD vendor that there is something waiting for him in the corner… in the PSE spec that is not mentioned in the PD spec that can make his PD uncompliant. I don’t see a reason to hide such critical information.

Yair

From: George Zimmerman [mailto:george@xxxxxxxxxxxxxxxxxxxx]
Sent: Tuesday, June 12, 2018 8:36 PM
To: Yair Darshan <YDarshan@xxxxxxxxxxxxx>
Cc: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_4PPOE] MPS issue due to the allowance for reflected voltage in 3-pair mode

EXTERNAL EMAIL

Yair - the proposed text is purely advisory and informative. At this stage we should only be concerned with missing or incorrect requirements or correcting (preferably deleting) incorrect information. I just don’t see the point of adding more informative advice to the standard.

George A. Zimmerman, Ph.D.

CME Consulting, Inc.

Experts in PHYsical Layer Communications

george@xxxxxxxxxxxxxxxxxxxx

310-920-3860

On Jun 12, 2018, at 10:27 AM, Yair Darshan <YDarshan@xxxxxxxxxxxxx> wrote:

Hi Lennart,

I agree that it doesn’t affect the case when the PD is disconnected from the cable.

I was referring to the case that the PD is connected and wants power removal. The question if it is rare or not, is irrelevant since it is already in the spec and we need to address it somehow and meet it.

I agree that the solution can be that PDs that do want to have power removed can set their Iport_mps value for power removal to be lower than (4mA-1.3mA)=2.7mA. However, in order to make this clear to the PD vendor (since Irev is in the PSE section) I believe that we need to add text to the PD MPS section as follows (or equivalent):

Proposed remedy:

Add the following text in clause 145.3.9, page 222 text after line 49:

"When a PD is operating under 3-pair mode conditions, the value of IPort_MPS as seen by the PSE over the powered pair may increase by Irev (See 145.2.10.4, 145.3.8.8 ). As a result, the PD may need to set IPort_MPS to alower value than IPort_MPS min to ensure power removal."

Yair

From: Lennart Yseboodt [mailto:00000b30a2081bcd-dmarc-request@xxxxxxxx]
Sent: Tuesday, June 12, 2018 12:04 AM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_4PPOE] MPS issue due to the allowance for reflected voltage in 3-pair mode

EXTERNAL EMAIL

Hi Yair,

Your analysis is correct, the reverse current is added to the PDs own current.

I don't consider this an issue we need to do anything about however:

- it does not impair the primary function of MPS in any way (to remove power when the PD is disconnected)

- it only affects PDs that use the method of removing MPS in order to have the PSE remove power, I would say this is pretty rare;

- PDs that do want to have power removed can accommodate for the maximum 1.3mA of reverse current (draw less than 2.7mA of their own)

Note that reverse current only happens under 3-pair conditions, and then the 'must disconnect' current level is 4mA for PSEs.

Kind regards,

Lennart

On Mon, 2018-06-11 at 12:03 +0000, Yair Darshan wrote:

Hi all,

I found new problem that we need to discuss how to handle it.

In 3-pair mode during power on state, when a PD don’t want to be powered, it generates e.g. MPS=1.9mA which means PSE must disconnect, but due to the PD that doesn’t meet the backfeed on the unpowered pair, the unpowered pair consumes additional 1.3mA and this is added to the MPS. Under these conditions, the PD will not be disconnected.

Moreover, in general, a constant error of additional MPS current is added by the PSE…..instead of PD only should control the MPS current.

Let’s start to discuss this.

Yair

Darshan Yair

Chief R&D Engineer

Analog Mixed Signal Group

Microsemi Corporation

1 Hanagar St., P.O. Box 7220
Neve Ne'eman Industrial Zone
Hod Hasharon 45421, Israel
Tel: +972-9-775-5100, EXT 210.

Cell: +972-54-4893019
Fax: +972-9-775-5111

E-mail: <mailto:ydarshan@xxxxxxxxxxxxx>.

To unsubscribe from the STDS-802-3-4PPOE list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=STDS-802-3-4PPOE&A=1

To unsubscribe from the STDS-802-3-4PPOE list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=STDS-802-3-4PPOE&A=1