-------------- Original message --------------
From: Mark Hahn <[EMAIL PROTECTED]>
> I've got an situation where a 20-25M IB cable would be very handy,
> and as far as I can tell, such cables exist. What's not clear to me
> is how they work - I think they all have some form of active components.
> some appear to be copper; others fiber, but all seem to draw a few Watts.
I can say a few words about optical active cable (OAC) choices. The current in
production choice is from Intel, their Connects Cable. This is a VCSEL laser
multi mode fiber design with a CX4 connector that runs at DDR speeds out
to100m. A 25m cable is going to run you about $300 (US). Power consumption at
each end is 1.1w. It is plug compatible with CX4 NICs that have power. Has the
small bend radius advantages that you can expect from fiber and other fiber
attributes. There is an excellent study published by ORNL covering their
plug-and-play abiliity in the field, performance, and 1000x lower BER
(important for full bandwidth utilization).
Another choice, although they are have not fully ramped up production (Q1
08??) is the Blazar OAC from Luxtera. This cable is based on a DFB laser and
single mode fiber. It has only three discrete components limited by their very
interesting on-chip splitters and wave guides which are used to bend the
normally edge-emitted DFB laser light vertically and into the smaller single
mode fiber. The connector is QSFP, not really that common yet. Power draw
is about the same as Intel Connects VCSEL. Range is 300m. Bandwidth is QDR.
No real in-the-field test data that I know of, but the technology has gotten a
lot of notice and I think has been selected for special attention at SC07.
Rumor has it that is is already in at least one HPC vendors interconnect
technology. The transceiver-on-a-chip technology is supposed to be a cost
reducer, but that has not been proven. SMF fiber is much harder to align ....
I don't know as much about 10GBASE-T, but it requires cat 6a or 7 cable, is
supposed to have a 100m meter range, but the power consumption at both ends is
like 5w until they get the transceiver chips down to 65nm. The signal
correction technology is elaborate and may neutralize the "cheap-transceiver"
advantage that copper has had over fiber historically, especially as the above
fiber alternatives ramp up production and begin to compete with each other. Of
course, per media foot copper has always (?) been more expensive that fiber.
Hope that helps ...
rbw
PS There some very good white papers and studies on both the Intel and Luxtera
web sites.
--
"Making predictions is hard, especially about the future."
Niels Bohr
--
Richard Walsh
Thrashing River Consulting--
5605 Alameda St.
Shoreview, MN 55126
Phone #: 612-382-4620
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