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From: Steve Robbins
[mailto:steve@xxxxxxxxxxxxx] Yair, I have to disagree with some of your
assertions.
3.2 This makes no sense to me. The AT-midspan can issue an
unlimited number of detection cycles, but there is NO GUARANTEE that it will
EVER detect the PD because the AF-endspan has no backoff period. And we
can’t add a back-off period to AF-endspans retroactively. So I
don’t think there is any way to “play” with the detection
timing that will fix this problem. Regarding your last comment; it’s
true that we don’t have to fix every problem. But we definitley
must fix this particular problem. This setup will be very common, so if
the solution isn’t plug-and-play it will undoubtedly cause a lot of
customer confusion. Steve From: Hi Steve, I believe I understand the problem you are
showing and I still think that the solution is a bit complex to the problem
presented and I would like to explain more on this issue:
3.1 IT manager when connected at-Midspan to at Endspan disable endspan
power. This is simple and straightforward and within IT manager
responsibilities to connect the system segments to function properly. If we
want that it will be done automatically then we can use 3.2. 3.2 In this alternative an at –Midspan will issue n detection and
classification tests right after first detection of invalid signature until
valid signature is obtained. This is a change to the 802.3af concept that
allowed the Endspan to win the detection race. We can
play with the numbers of detection trials and timing etc and it is not
important now. What I am trying to emphasis is to use current tools that we
have in the 802.3af without loading the hardware with extra functions which
will complicate the PSE chip and increase its cost. We have
to remember that not every problem we have to solve. We need to decide first if
this is a problem that is within our scope or not. If we
can solve it as in 3.1 without adding more functions to the PSE, I would prefer
such solution. Yair From:
owner-stds-802-3-poep@xxxxxxxx [mailto:owner-stds-802-3-poep@xxxxxxxx] On Behalf Of Yair, I think you missed the point. The solution is NOT to
“…mandate separate signatures for each 2P…” because we
also want “medium power” on 2P. The Task Force already
agreed to this. So there will be some PDs in the 15W to
30W(?) range that have an input structure like an Af-PD (SS with diode
bridges). The obvious upgrade path for a user would
be to add a medium-power At-midspan in-line with his existing Af-endspan.
These two PSEs can’t share the load since the PD is SS. So the
At-midspan has to supplant (take the place of) the Af-endspan. I showed a method to assure the midspan
will power the MP PD every time. I think this will be essential to the
802.3at standard. Steve From: Steve and all, The problem shown in this presentation can
be easily solved by mandating detection and classification signature for every
2P in the PD. Specifically separate signatures for each
2P and not a common one as measured at the RJ45. See attached presentation in page 13 for
the proposed scope of work. This is the idea of how standard can be
simplified. Doing the above is not requiring any
special specifications from the PSE. The Endspan PSE will detect and classify
pair A. The Midspan PSE will detect and classify
pair B. Both channels will turned on within the
current 802.3af timings or similar to it. Since each channel A and B are not tied
together at the diode bridge output, the PD can be operated easily by using the
PD circuitry which is TBD (implementation independent). Yair From:
owner-stds-802-3-poep@xxxxxxxx [mailto:owner-stds-802-3-poep@xxxxxxxx] On Behalf Of 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 |