10 Gigabit EMI
In the world of EMI, my personal experience is that the problems are a
combination of religion, black magic, and some practical experience (with a
little knowledge of Maxwell's equations thrown in). Historically, it has
been very difficult to get "experts" to step up to the plate because
invariably there are problems in the actual implementations that the
"experts" simply can't explain. This is not a dig on the experts, just a
point on the extreme difficulty of the problem.
It is my opinion that the coding will be an important, but second order
effect. My opinion is that the rise times are a second order effect. My
opinion is that the actual bit rate is a second order effect. I know, I
know. You can bring me Maxwell's equations and show me the math that
demonstrate the direct relationship between these parameters and the
emissions.
But, in the end, it is the holes is the system that matter!!! It is the
little antennas built into the boxes. It is the phase array of optical
transceivers.
Most transceiver companies will claim that the majority of the noise that
radiates from the nose of the optical transceiver is generated inside the
system, not inside the transceiver. The new "small form factor"
transceivers, with ~1/2 the aperture size of the SC, are not inherently
going to solve the EMI problem at 10 Gig.
In short, from an implementation perspective, we have a very fundamental
problem: the way we design systems today as racks of modules with arrays of
optical transceivers poking out through the EMI enclosure may simply not
hack it.
Up to Gig E, we have had the luxury (admittedly, with a fair amount of pain)
of having a "convenience based, user friendly" box design. With 10 Gig, have
we finally hit the wall?
jonathan
Jonathan Thatcher
Chair, IEEE 802.3ae (10 Gigabit Ethernet)
Director of Engineering, World Wide Packets
PO BOX 141719, Suite B; 12720 E. Nora, Spokane, WA 99214
509-242-9000 X228; Fax 509-242-9001; jonathan@xxxxxxxxxxxxxxxxxxxx
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