Working with Larry!
Thank you for asking- I am encouraged.
Cisco's proposal has the following A, B sections.
A- Use the Signal pair 1,2 and 3,6 to deliver power on a new switch.
B- Use unused pair (4,5 and 7,8 ) to deliver power for mid-span.
Powering from the center tap is a classic approach, All right, we are all worried
about the phys doing bad things to us, how many phys can we test and under
what conditions, please note that I can have a phy on my board now that has
300ps of transmit jitter and can receive up to 130m over cat-5 with the far
end transmitter doing 1.2ns peak-peak jitter on the far end. quite a few
phy vendors have gotten good at this.
Crosstalk and noise are another issue, well, we filter the power supply
(we sleep better doing so for EMI reasons...)
And some phys have good crosstalk performance- No Spec was present/ details.....
This does not guarantee you that
every phy will be happy, then again did you ever think that this would be the case
To this, I did present the MLT3 waveform with and without power via the center
tap, and overlaid the results on the scope. We did not see any difference.
it would be nice to measure rise time, and every other spec. but I don't
think at this point it is worth my time when my slides showed no change
in the signal for up to 250ma or so. Magnetic vendors claim 300ma....
I did spice the Nortel bandpass approach and the series resistance of the CAT-X cable
seems to lower the Q of the DTE BP filter no data was presented on your scheme
either- at least none that I have seen. Could you please fill me in on how this is done?
2- Powering over center taps, is a classic approach (exclude the 100BT) signals
that are worrying a lot of people- and where we trust our magnetic vendors to
do a good job and a good characterization on these components, along with
the one we have done...
3- a general statement here,
I am not sure that I owe the group every detail and my schematics at this point
when we are going in with the attitude that only midspan or unused pairs is the way
to go, leaving the burden of the proof on me alone....
please see a reply to your questions below,
>I have a few questions to start with:
>1. In the slideware, we always see a 4-pole relay at the DTE equipment end
>used to switch out the discovery filter when power is applied.
>a) Are you actually using a relay?
Yes, we are currently using a DECENT relay, but the relay and the filter
have a 90% chance that they will disappear in the future (will be inside the phy)
Please note here, that we are not out to discuss the millivolts, the number of
components, to start do we as a group beleive that this loopback appoach
where differential signaling is employed with magnetics- something we
know how to do, handle, and deal with will be robust over a current pulse
from the center tap approach. Also please note that this detection
scheme may have good alternatives, and they may be your's or Mr X...
so Let's keep in mind that. On the other hand my argument is that
differential signals, magnetics, and phy integration are realistic, familiar
and with some improvements!!! lower risk? what am I missing?
even if this was your approach that would still be my engineering opinion...
>b) Do you have to use a relay for some reason, or could there be some
>solid-state analog switching equivalent. If so, what are the isolation
Again, Improvements to this scheme will place relays next to the phy
or inside the phy delivering esd protection and 1500v-2000v isolation
via the magnetic. Something we have done for years...
A lot of this can be looked at once we open our mind to the possibilities
and think that things may not be as risky....
>2. What kind of margins are you asking for/getting in terms of S/N on your
Larry, the detection pulse is supposed to be a low frequency pulse in schemes
A, and B above you are looking at wider pulses that the FLP = 100ns up 10 1us, that
could easily leave 400-500mv (again to be improved when we all get involved)
Please note we are talking DIFFERENTIAL SIGNALS.
when I designed the 10BT phys, I remember that
the spec was at least 900mv for the 5mhz signal (preamble) to turn the slicer
on, but a lot of aggressive vendors designed down to 500mv to claim longer
cat-3 cable length performance ..... Details....
>a) Do you have to cope with a certain amount of bit errors here?
Once finished with the detection, Detection Pulses disappear,
and then we are back at doing 10/100 til link fails....
this is honest 10/100 after all, and we have done it for years,
and per my MLT3 - power/no power -no difference slides, I can say that the pulses
are crude and unused doing 10/100 operation, we have not seen any BER
degradation- again I did not test to every phy that ever existed- and every
>b) How about some scope pix of what the detection pulses look like after
>they go through the filter and a round-trip run (200m) of CAT-5 cable and
>c) What are the tolerances (maybe a template) on what the returned pulse(s)
>must look like?
>Our SPICE models show what we have seen in the slides to be rather
>marginal, but we don't claim to have the whole picture.
>These are the kind of questions that will have to be answered for the
>standard even if your proposal were the only one, so you might as well get
All right Larry, I could do more work here, and present the slides for
B, C, and D. above. what I would like to know though is that does anyone believe
that this differential scheme is worth looking into- it seems like I am the only
one who always show up with real measurements, are you going to show the
details of your scheme?, is Dan doing the Same. and everyone else.
it would be encouraging to get out of this mode where this is CISCO's scheme
think like engineers see the pluses and minuses of everything and get to
a decent solution. So far all we seem to care about is mid-span power
unless of course I really prove that every other detail in the signal - pair
approach is solid and has no holes, leaving me little time to understand
your solution that may be superior.
After years and million of Ethernet ports, do we doubt our ability to loopback a
differential pulse and have a differential stage detect it ????
it may be a challenge to integrate this on a phy, but it is not impossible.