Re: [8023-POEP] Liaison letter from IEC TC65/SC65C/JWG10 - Power over Ethernet performance in industrial environments
Dan,
I don't disagree with the idea of adding text to the UTP PHY clauses as
you suggest. However, the way that the PoE behavior is defined makes it
very unlikely that such a design would cause problems (unless the UTP
i/f designer makes a very bizarre design).
If the designer inadvertently makes a design that has a 19k resistance
between the Tx & Rx pairs (as he might) then the PSE will see it as a PD
and will then apply power. However, unless the designer has some exotic
non-linear circuit then a DC resistance >19k will allow less than 1/8W
of power to be delivered to the non-PD. This is unlikely to cause damage
to the front end components and will also cause the PSE to remove power
after a short interval.
In my opinion I think it is unlikely that the failures observed (and
photographed) were caused by a deficiency in the standard. It is
possible that a system with a low impedance between Tx & Rx pairs could
be damaged if the PSE incorrectly applies power, it is also possible
that the failure was related to a number of other conditions that exist
when large inductive loads are switching rapidly.
Hugh.
-----Original Message-----
From: owner-stds-802-3-poep@xxxxxxxx
[mailto:owner-stds-802-3-poep@xxxxxxxx] On Behalf Of Dove, Daniel
Sent: Tuesday, July 07, 2009 2:36 PM
To: STDS-802-3-POEP@xxxxxxxxxxxxxxxxx
Subject: Re: [8023-POEP] Liaison letter from IEC TC65/SC65C/JWG10 -
Power over Ethernet performance in industrial environments
All,
I agree with Hugh's general theme, but I still see a need to add
language into the UTP clauses that directs an implementer to avoid a
valid PD signature at the MDI if they are not building a PD. While Hugh
is correct that an Ethernet designer should be aware of the exposure
created by failing to pay attention to clause 33, such changes would
eliminate the exposure completely.
Its my opinion this is a maintenance issue though, and not an 802.3at
issue.
Dan
-----Original Message-----
From: owner-stds-802-3-poep@xxxxxxxx
[mailto:owner-stds-802-3-poep@xxxxxxxx] On Behalf Of George Zimmerman
Sent: Tuesday, July 07, 2009 1:45 PM
To: STDS-802-3-POEP@xxxxxxxxxxxxxxxxx
Subject: Re: [8023-POEP] Liaison letter from IEC TC65/SC65C/JWG10 -
Power over Ethernet performance in industrial environments
Hugh - I agree with your well-written response.
-george
-----Original Message-----
From: owner-stds-802-3-poep@xxxxxxxx
[mailto:owner-stds-802-3-poep@xxxxxxxx] On Behalf Of Hugh Barrass
Sent: Tuesday, July 07, 2009 10:51 AM
To: STDS-802-3-POEP@xxxxxxxxxxxxxxxxx
Subject: Re: [8023-POEP] Liaison letter from IEC TC65/SC65C/JWG10 -
Power over Ethernet performance in industrial environments
David,
I can see that the liaison from IEC has caused some interesting
discussion amongst PoE experts (and myself), however I think that we are
being asked to comment on what may well be design flaws in specific
products and I do not think that is a healthy discussion within 802.3.
I suggest that we should send a reply along the following lines:
==========================================
The problems described in your liaison spurred some vigorous discussion
amongst our task force members regarding possible causes for the damage
that you describe. However the members are not aware of any similar
reports that might indicate a systemic problem with 802.3 compliant
equipment. It is the opinion of the members of IEEE P802.3at Task Force
that the standard allows product manufacturers to build reliable and
interoperable equipment that will meet the requirements for supplying
power over Ethernet in many environments. However, the standard does not
define how a manufacturer must build the product to ensure reliability
or how an installer should ensure that the media is suitable for correct
operation within the standard. We suggest that you should work with the
equipment manufacturers involved to determine whether the failure is the
result of a systemic problem with the standard and whether a specific
amendment may be required.
With respect to the bit error rate performance of 802.3 links when power
is being supplied over the same link, the members of IEEE P802.3at Task
Force believe that a compliant system supplying power over an 802.3 link
will not perturb the channel sufficiently to degrade the performance of
the underlying link. However, it is the responsibility of the product
manufacturer to ensure that noise introduced by the load does not couple
to the link and violate the power over Ethernet specifications or the
channel specifications required for the link. Similarly it is the
responsibility of the system installer that the channel characteristics
are met in the presence of environmental noise.
===========================================
Hugh.
David Law wrote:
>All,
>
>The IEEE 802.3 Working Group has received a liaison letter from IEC
>TC65/SC65C/JWG10, Industrial process measurement, control and
>automation/Industrial networks with respect to Power over Ethernet
>performance in industrial environments.
>
>I just wanted to inform you that I intend to delegate the generation of
a
>draft response to the IEEE P802.3at DTE Power Enhancements Task Force
>during the plenary week in July. The draft response will be consider
and
>then voted upon at the closing IEEE 802.3 Working Group plenary as part
of
>the IEEE P802.3at closing report. You therefore may wish to review the
>letter prior to the meeting, the letter can be accessed at the URL [
>http://www.ieee802.org/3/minutes/jul09/0709_IEC_SC65C_JWG10_to_802_3.pd
f
>].
>
>Best regards,
> David Law
> IEEE 802.3 Working Group Chair
>
>
>