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Re: Cascading Failures Could Crash the Global Internet
From: "Stewart, William C (Bill), SALES" <billstewart () att com>
Date: Sat, 8 Feb 2003 22:39:12 -0500


I think the key is that the failures described in the paper
are caused by overload rather than other things -
too much demand for power blows out the generator,
and without it, the grid tries to get the power from the next
nearest generators, which overload and fail, and try to pull an
even large amount from the _next_ nearest, etc.
So the bit about heterogeneity is probably referring to
the fact that some nodes are bigger or better-connected than others,
and are more likely to blow out a bunch of their neighbors when
they fail and shed a big load.

That's not really how Internet systems usually fail.
Overload can cause problems, and we've seen congestion collapse
in the past, but TCP is usually tuned to discourage it;
when a system is overloaded, well-behaved applications
(which is most of them) back off, gradually or rapidly,
but unless the load is weird enough to blow out
router CPUs or crowd out BGP and OSPF packets,
usually the network itself stays up and running.
If what's failing is an overload of BGP routes or something,
that's different - and sometimes the load on the system shrinks
as components fail, but sometimes that just makes everything 
flap all at once, increasing load and delaying convergence.



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