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Hi
Ali,
The
location of TP1 and TP4 (refer to slide 8 of http://ieee802.org/3/ap/public/jul04/goergen_03_0704.pdf)
are similar to TP-1 and TP-4 from PICMG 3.1 and the T and R compliance
points for OIF CEI.
They
are located at the "component edge" of the transmitter and receiver
respectively. The definition of "component edge" includes any
external termination components required by the transmitter/receiver and the
AC-coupling capacitors, when used.
This
implies that the backplane connectors (and mezzanine connector, when
used) are part of the "channel" specification. Channel return loss
requirements would need to be satisfied looking into the channel at either TP1
or TP4. Transmitter return loss requirements would be defined looking into
TP1. Receiver return requirements would be defined looking into
TP4.
Channel return loss, based on the conventions that we are using, will
likely be dominated by the first mated connector as you point
out.
To
include the interaction between the transmitter/receiver and the channel, a
cascaded system model is required. This can be accomplished a variety a
ways (cascaded T-parameters for example, refer to OIF). I suspect that
this is something the signaling ad hoc will need to address. The charter
of the channel model ad hoc, like the cabling ad hocs 802.3 has had in the past,
is to define the channel return loss looking into TP1 and TP4. I
use the word "channel" rather than backplane, as it now should be clear the
our definition of TP1 and TP4 is not only the backplane but the trace on
the node/hub (line, daughter, whatever naming convention you
prefer) cards as well.
I
apologize if you already understood this. Of course, you may not agree
with the above methodology, which is fine. Let's discuss it on
the reflector. It sounds like you are advocating that we define the
backplane connector, which is something I think we have been trying to
avoid. Please clarify.
Thank
you,
-Adam
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