RE: [802.3af] Your TR Comment
Goeff and all.
scenario presented here is exactly what we have discussed over the reflector on
the least two weeks and I have already commented on that.
suggested the remedy of mandating full diode bridge on data pairs and
spare pairs (i.e. polarity insensitive in mode A and mode B) which is option 4
choices offered below.
5 may work too however the bets is option 4 which gives polarity insensitive
feature and solves other problems.
difference in cost between option 4 and 5 is negligible even for low cost
Dissipation is the same so option 4 is my favorite.
addition, we also have a requirement for the PD that it will not source
power to the MDI (or back power to the MDI) however we didn't put numbers behind
this requirement and the best time to do this is now.
suggesting the following:
In page 60 line 19 paragraph 33.3.1 the draft requires "The PD shall not
source power on its PI"
suggest to change it to say:
shall not source power on its PI.
Compliance for this requirement shall be tested by applying a
voltage of 57.0V across the PI at a polarity specified to mode A
according to table 33-7 for MDI or MDI-x configuration and measuring a voltage
less or equal to 2.8Vdc across the PI for Mode
same requirement shall apply when a voltage of 57.0V across
the PI at a polarity specified for mode B according to table
33-7 and measuring a voltage less or equal to 2.8Vdc across the PI for
Please post your diagram to the reflector
exists a scenario whereby two or more PDs with different power mixing
when PSE-Midspan powered, may cause damage to a legacy 802.3 data
switch to which
the PDs are attached which may be sharing unused pair
Chad to provide a drawing if
There are several ways to prevent
this damage to legacy 802.3 equipment (listed in order
of least desireable):
- 1. Disallow the Midspan PSE
- 2. Force environment B for Midspans
- 3. Define an environment B- that can address this mixed scenario
- 4. Mandate a full diode bridge on each power pair in the PD
- 5. Mandate a half diode bridge on each power pair in the PD
Comment Status X
Jones, Chad Cisco Systems
| Geoffrey O.
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