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Derek, Thanks for your interesting thoughts.
See my comments below, in curly braces. Steve From: owner-stds-802-3-poep@xxxxxxxx
[mailto:owner-stds-802-3-poep@xxxxxxxx] On
Behalf Of Derek Koonce Steve, Can the resistor be higher such that it interferes
with the "signature" detection phase and thus the endspan would never
really win because the signature is out of spec? {See page 6. The circuit presents the
endspan with an invalid signature, which is <Rgood. If we made it Rinhib>Rgood
then we might not reverse-bias D1 and D2, and that might not give the midspan
the window it needs to detect the PD.} {BTW, the switch isn’t intended to
lock out the endspan indefinitely until the midspan detects a PD. Both
endspan and midspan attempt detection concurrently. The switch simply
creates a window for the midspan, to guarantee it has a chance to detect. Under
802.3af, there is no backoff time for an endspan, so a midspan might never even
get a chance without this switch. Therefore the switch by itself isn’t
enough; the PD has to help. (See page 8.) Basically, a MP PD would
force the detection process to repeat until the midspan won. But an Af-PD
would be happy with either endspan or midspan.} The midspan can detect faster and avoid the delay in
order to interfere with the detection for the endspan. Once PD is powered, the
midspan could release the switch and conserve power on the endspan's behalf. {Yes, I forgot to mention this in my
presentation: The switch only closes during the midspan detection cycles.
After the midspan turns on the PD, it opens the switch. So if the PD is
DS, the endspan would be free to detect and turn on the second half of the DS PD.}
Derek Koonce
Guys, I think I’ve solved another problem
that’s inherent with DS. See the attached pdf. (Only about 10
more tough problems to go!) I’d sure appreciate some comments. Steve |