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[8023-POEP] AW: [8023-POEP] August interim

Hello Everybody,


I have a question about the PSE Interface, Detection and Safety!


In the actual IEEE 802.3af standard, 33.2.9 Power supply allocation, the behaviour of connecting a PSE PI with another PSE PI is not explained.




33.2.9 Power supply allocation

A PSE shall not initiate power provision to a link if the PSE is unable to provide the maximum power level

requested by the PD based on the PD’s class. Where a PSE does not provide the optional classification function

specified in 33.2.7, all PDs are treated as Class 0.

The PSE may manage the allocation of power based on additional information beyond the classification of

the attached PD. Allocating power based on additional information about the attached PD, and the mechanism

for obtaining that additional information, is beyond the scope of this standard with the exception that

the allocation of power shall not be based solely on the historical data of the power consumption of the

attached PD.

If the system implements a power allocation algorithm, no additional behavioral requirement is placed on

the system as it approaches or reaches its maximum power subscription. Specifically, the interaction

between one PSE PI and another PSE PI in the same system is beyond the scope of this standard.



In the industrial field, line and ring topologies are very common, so my question is:


Does the new IEEE 802.3at standard explain this issue?

What happens if I connect two PSE PI’s together?



Can anybody help me with this question?


Manny thanks!


With best regards, mit freundlichen Grüssen

Pascal Unterdorfer
Product Manager Industrial Networking


Hirschmann Automation and Control GmbH
Stuttgarter Str. 45-51
D-72654 Neckartenzlingen
( +49 7127 14-1120
v    +49 172 9446954

Ê  +49 7127 14-1561
* Pascal.Unterdorfer@xxxxxxxxxxxxx



Von: owner-stds-802-3-poep@xxxxxxxx [mailto:owner-stds-802-3-poep@xxxxxxxx] Im Auftrag von McCormack, Michael
Gesendet: Freitag, 5. Juni 2009 00:59
An: STDS-802-3-POEP@xxxxxxxxxxxxxxxxx
Betreff: [8023-POEP] August interim




I would like to update everyone on the schedule for our work.


  • We should begin balloting draft 4.2 next week.  
  • During the July plenary we will review the comment we receive on 4.2.  If there are any changes to the draft and/or any new unsatisfied negative ballots, we will need to recirculate.
  • In the event that a recirculation is required, we will need to have an August meeting.
  • After August, I see no realistic reason we will need to meet again :(  I am presently attempting to negotiate a date at the UNH OIL offices for the second or third week of August.


We are down to the end, please remain focused so we can complete.







Michael McCormack

Business Development Manager, Power over Ethernet Products
Texas Instruments, Power Interface Products
50 Phillippe Cote St.
Manchester, NH 03101 USA


Mobile: +1 603 264 0146
Email: mike_mccormack@xxxxxx
Web Site:



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