Re: [8023-POEP] Liaison letter from IEC TC65/SC65C/JWG10 - Power over Ethernet performance in industrial environments
To add my "two cents" here - I would side with Hugh and Dan on what needs to
be done.
The episode referenced in the IEC correspondance offers no real insight as
to what went wrong (PD, PSE ???) and therefore does not sort out whether
this is systemic or individual, one-up design / manufacturing / installation
fault. Clearly not a basis to change a standard....
Having tested many thousands of PSE ports, I know well that there is such a
thing as an occasional defective or non-compliant PSE port that is capable
of mis-detection.
One clarification on odd-ball DTE's that might present legal PD signatures -
a 25Kohm resistive load between pairs will not always cause power removal
following a power-up - AC MPS type PSE's will happily maintain power with
this loading. This is perhaps more impetus to add warnings about PD
signatures to 802 PHY clauses.
Regarding "noisy" industrial environments, it is not at all clear to me that
802.3at detection methods present a systemic vulnerability to these
conditions. Also, it must be considered that actual PSE detection methods
vary widely such that if one method were in fact "vulnerable" to some form
of noise ingress, it is quite possible many others would not have that same
vulnerability. The same can be said of other design factors such as
isolation and grounding. Bottom line, the only real way to arrive at the
conclusion that PoE is unsuitable for this environment would be to perform
systematic broad-based testing in representative environments.
That seems more like an application design challenge rather than a
specification challenge.
Regards,
Pete Johnson
Sifos Technologies
1061 East St.
Tewksbury, MA 01876
www.sifos.com
978-640-4900 x113
-----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 5:36 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
>
>
>