Re: TransAtlantic Cable Break

[Steve Gibbard <scg () gibbard org>]

On Fri, 22 Jun 2007 Valdis.Kletnieks () vt edu wrote:

> > On Fri, 2007-06-22 at 10:27 -0400, Roderick S. Beck wrote:
> > > So none of the customers on that well known system have any ring
> > > protection at this point nor will they during the next two weeks.
>
> [...]
>
> Oh, there *is* no "*other* other side"?  That must be what Roderick 
> meant.. ;)

This strikes me as much ado about nothing.

Mr. Beck (apparently a cable sales person, probably for the cable he says 
doesn't share the vulnerabilities) started this out by dismissing a cut 
that caused actual outages in an apparently less important part of the 
world, telling us that the "real news" is that one side of a redundant 
transatlantic ring was broken, leaving customers relying on the other 
side.  He has then continued to post and post and post on the subject.

Redundancy is a statistical game, a bet that some number of pieces won't 
all break at the same time.  With a single point of failure, it's pretty 
likely that at some point you'll have an outage.  As long as those outages 
are relatively rare and short, adding a second path makes it significantly 
less likely that both will break at once, but there's still some chance. 
Adding additional paths reduces the probability of simultaneous failure 
further, but never to zero.  As you add more paths, you reach a point of 
diminishing returns pretty quickly.  You also add complexity, which can 
cause its own problems.

If it takes two weeks to repair a broken cable, carriers need to do a 
cost-benefit analysis.  With a single cable, what are the chances of that 
cable breaking, and how much will it cost them to be down for two weeks, 
as compared the cost (including complexity) of a second path?  With two 
paths, what are the chances that the second one will break during the same 
period that the first one is broken, how much will the resulting outage 
cost, and how does that risk compare to the cost of a third path?

Presumably, most of the carriers are doing this analysis already.  If 
their customers are sufficiently concerned, they're presumably doing such 
an analysis of their own.  If any aren't, perhaps they should think about 
it, but whether doing that analysis will have them running out to buy an 
additional path across the Atlantic is far from clear.

-Steve