[802.3af] Re:Some comments from an outside engineer trying to use 802.3af
First and upfront, while I am the editor, I am also a regular member of the task
force and am replying solely as a member, the editor does not stoop to the level
of expressing opinions, if the editor did he would become hopelessly depressed
on the basis of all the comments he receives. Also, the 802.3af task force has
just completed its twelfth meeting, it is impossible to recap everything that
has gone into the decisions made during those meeting in one e-mail to the
reflector, but to your specific points....
1) As Alternative A and Alternative B are required at the PD, it really doesn
?t
matter which is the most widely deployed PSE, all PDs will work with either
selection - that was the intent. Not all cabling is four pair, and not all
customers will want to replace their closet equipment, which alternative is more
widely deployed remains to be seen.
2) PDs are meant to operate with any PSE, a dual power PD would violate this
objective.
3) As stated in the front page, numerous informative sections and all PICs are
missing, and the IEEE does not provide reference designs similar to IC vendors.
Some participants have suggested that something like a Zener in series with a
resistor could provide a mechanism to include class identifications beyond Class
0.
4) First - you are wrong in you premise, the power limit is actually less than
the 13 watts you mention, 12.95 is the ABSOLUTE maximum and may be going
somewhat lower. The cabling is not the limiting factor in a installation;
connectors, patch panels and other parts of the whole cable plant are
limitations too. The Task Force is well aware that each reduction in power
disenfranchises some parties, but the installed base is rather large and
certainly pre-existing.
5) Isolation is a matter for the 10BASE-T, 100BASE-TX and 1000BASE-T media that
are being supported for powering. The isolation requirements are repeated in
the current draft but may be removed and are in the current version just for
completeness. Nothing says we may not leave them in Clause 33, but they are cut
and pasted from the appropriate other clauses of 802.3
If you need further clarification on the reasons for the task force?s decisions,
I?d suggest reading the minutes and presentations that are posted in the public
area of the DTE power web site. And again, the above are my personal
recollections of the task force decisions, somewhat tainted by my personal views
- the editor has no opinion of the content of the draft.
We will shortly be announcing the site of our next interim meeting and, as
always, anyone is welcome to attend. A few of us have been attending from the
first call for interest, but the majority have joined in at some mid point, and
we have always added new members at each meeting, we could use all the help we
can get. Also, comments are always welcome, though the editor will not get into
issues of intent or purpose, task force members may provide a response.
Mike