[Beowulf] using two separate networks for different data streams

Keith D. Underwood kdunder at sandia.gov
Mon Jan 30 06:32:37 PST 2006

> The Cray XT3 is an example, I think, of a system which sends
> non-IB-like packets over an IB physical layer. But I don't think the
> details are public and I don't know much about the XT3.

The only heritage that the XT3 shares with IB is that IB was a strong
(but by no means exclusive) driver of the development of high-speed-
signaling technology.  The physical layer on a link by link basis
doesn't even have the same signaling rate as IB (3.2 Gb/s/wire pair for
XT3 vs. 2.5 Gb/s/wire pair for IB).  XT3 is 12 bits wide and I'm not
sure if anybody has done a 12X IB yet.  Most importantly, XT3 has a
physical layer reliability protocol with retransmit on the links between
the routers so that end-to-end messaging is extremely reliable.  The
requirement was for them to have no more than a 10^-21 BER host-to-host
and so the physical links between routers are much better than that.


Keith D. Underwood                            Scalable Computing Systems
Senior Member of Technical Staff            Sandia National Laboratories
kdunder at sandia.gov

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