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Hi,
I would like to discuss the
benefits in mandating diode bridge at the input of both data pairs and spare
pairs.
Background
The PD is required to be ready
to accept power from the spare pairs or from the data pairs.
Typical implementation of Oring
the power from data pairs or spare pairs could be one of the following
options:
1. Data pairs has diode bridge
and spare pairs using single diode.
2. Data pairs has diode bridge
and spare pairs has diode bridge.
3. Data pairs and spare pairs
has has single series diode each, data pair should have diode bridge if the PD
is auto-mdi-x.
Now lets consider the following
case:
A multiport system activate
port number x and send power to the PD.
The PD is configured per option
1 or 3.
Now, there is voltage present
at the output of the oring diode, but, due to the fact that one of the leads of
the spare pair is directly connected to one pair data pairs
There is a leakage current path
from the data pairs to the spare pairs back to the PSE.
This leakage current will find
its way to other ports in the PSE and may affect the detection
function.
In some bob-smith
termination configurations that was good for a switch without pse and
are not suitable for switch with pse some ports may see voltages above
30V even if they are at OFF state.
In order to prevent such
scenarios, option 2 is suggested that keep DC isolation from the spare pare to
the data pairs and vice versa.
In addition, using diode bridge
at the data pairs will fix the issue raised by Moti Goldish regarding the
MDI-X/AUTO MDI-X issue.
Mandating diode bridge on both
pairs will ensure powering of the PD in any PSE configuration and in any cable
type straight or crossed cable
so we can
eliminate the potential of interoperability problems regarding
the ability to successfully powering the PD.
The data issue is solved by the
definitions for the PSE and PD, by the pin assignment and polarity for the
MDI/MDI-X/AUTO MDI-X configurations as described in tables 33-1and table
33-7.
Actually referring to Auto
MDI-X in tables 33-1 and table 33-7 will not be required
anymore.
Summary:
The suggested remedy to support
the above is:
Draft 4.2 page
60:
1. Delete the text at
lines 50-51:
"If the interface
is implemented as an MDI-X or Auto-MDI-X per Clause 14,the PD shall be polarity
insensitive "
Replace it with the following
text: "The
interface in Mode A and in Mode B shall be polarity
insensitive.
2. Consider to delete the
reference for Auto-MDI-X from tables 33-1 and 33-7 as it is not required due to
(1).
I believe that to mandate the
above is required.
Please comment over the above
issue as soon as possible.
Thanks
Yair.
Darshan Yair
Chief Engineer PowerDsine Ltd. - Powering Converged Networks 1 Hanagar St., P.O. Box 7220 Neve Ne'eman Industrial Zone Hod Hasharon 45421, Israel Tel: +972-9-775-5100, Cell: +972-54-893019 Fax: +972-9-775-5111 E-mail: <mailto:yaird@xxxxxxxxxxxxxx>.
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