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[8023-POEP] IEEE P802.3at PoE+ 350uH adhoc - update

All,

At the IEEE P802.3at PoE+ 350uH adhoc conference call last Tuesday I 
agreed to provide a status update, and a call for contributions, to the 
IEEE P802.3at Task Force reflector.

As I reported at the IEEE P802.3at meeting during the IEEE 802 plenary 
last week, the 350uH adhoc reached consensus that there is a issue with 
the existing 100BASE-T Open Circuit Inductance (OCL) specification in that 
it is only specified up to a maximum DC bias current of 8mA. IEEE P802.3at 
operation will likely result in a DC bias current in excess of this.

Based on this the options proposed were:

[1] Extend 350uH OCL inductance specification to DC bias currents above 
8mA
    - Default option
    - Maximum bias current subject of IEEE P802.3at Transformer and 
Channel adhoc

[2] Relax the OCL inductance requirement above 8mA
    - Specify BLW compensation in PoE+ PHY receivers
    - Specify that Alternative A Midspans limit DC bias to 8mA

[3] Specify a new 100BASE-T transmit template
    - Can be met by existing transmitters and 350uH transformer
    - Can be met by other PHY transmit approaches such as pre-emphasis

Options [2] and [3] are somewhat orthogonal and either one or both could 
be specified. Further information about the above can be found at [ 
http://www.ieee802.org/3/at/public/nov07/law_1_1107.pdf ]. To enable the 
adhoc to best decide what option(s) to recommend to the IEEE P802.3at Task 
Force, there are two areas on which further contributions are invited. 
These are:

[A] Costs supporting a 350uH OCL inductance at DC bias currents above 8mA
[B] Feasibility of transmit template and if this would enable alternative 
implementations

Contributions on [A] will enables the adhoc to better understand if there 
is any need for an approach other than the default approach of extending 
the DC bias range over which the 350uH OCL is required. Contributions on 
[B] will enable us to understand if the transmit template approach would 
be feasible, including ensuring interoperation with the installed base, as 
well as if such an approach will enable implementations other than 350uH 
OCL such as some form of pre-empasis in the PHY based on the transmit 
transition density.

The next meeting of the IEEE P802.3at PoE+ 350uH adhoc will be held 9:00AM 
PST on Tuesday 11th December 2007, duration will be 2 hours. Dial in 
details will be announced on this reflector soon.

Thanks and regards,
  David