NSA tapping undersea fibers?

[Trei, Peter]

There's an awful lot of uninformed speculation about how
undersea cabling is done in this thread.

I strongly reccomend that folks interested in this topic
read Neal Stephenson's very detailed (and entertaining!)
discussion of the topic in Wired, at
http://www.wired.com/wired/archive/4.12/ffglass.html

Peter Trei
----------------------------
A few quotes:

Shallow water is the most perilous part of a cable's route. Extra
precautions must be taken in the transition from deep water to
the beach, and these precautions get more extreme as the
water gets more shallow. Between 1,000 and 3,000 meters, the
cable has a single layer of armor wires (steel rods about as thick
 as a pencil) around it. In less than 1,000 meters of water, it has
a second layer of armor around the first. In the final approach to
the shoreline, this double-armored cable is contained within a
massive shell of articulated cast-iron pipe, which in turn is
buried under up to a meter of sand. 

[...]
Beyond 300 meters, the cable must still be buried to protect it
from anchors, tickler chains, and otter boards 
[...]

Over long (intercontinental) distances, the difference averages out to about
1 
percent, so you might need a 2,525-kilometer cable to go from Songkhla to
Lan Tao. The extra 1 percent is slack, in the sense that if you grabbed the 
ends and pulled the cable infinitely tight (bar tight, as they say in the
business), it would theoretically straighten out and you would have an extra

25 kilometers. This slack is ideally molded into the contour of the seafloor
as
tightly as a shadow, running straight and true along the surveyed course. As

little slack as possible is employed, partly because cable costs a lot of
money
(for the FLAG cable, $16,000 to $28,000 per kilometer, depending on the
amount 
of armoring) and partly because loose coils are just asking for trouble
from trawlers and other hazards. In fact, there is so little slack (in the
layperson's 
sense of the word) in a well-laid cable that it cannot be grappled and
hauled to the surface without snapping it. 
[...]
> ----------
> From: 	Matt Crawford[SMTP:crawdad at fnal.gov]
> Sent: 	Monday, June 04, 2001 6:03 PM
> To: 	Jim Choate
> Cc: 	Peter Fairbrother; cryptography at wasabisystems.com
> Subject: 	Re: NSA tapping undersea fibers? 
> 
> Trusting that Perry will declare this OT before too much longer ...
> 
> > > To lift the midpoint of a cable 1000 units long by 5 units requires
> > > only 0.067 units of slack, or the ability to stretch by 0.0067%.
> > > (This takes into account the catenary shape of the lifted cable.)
> > 
> > Finish your example please...
> > 
> > You know gravity, calculate the force along the axis of the cable and
> then
> > compare to it's tensile strength. Include the weight of the cable as
> well
> > as the gravitic effects.
> 
> Neither the University of Chicago's graduate program in theoretical
> physics nor Noah Webster's successors introduced to me that that
> science-fictiony word "gravitic", but let's assume it's completely
> redundant with "include the weight of the cable."
> 
> I don't know squat about an undersea cable, except that it's heavily
> armored against damage.  Let's suppose it weighs no more than would a
> 4-cm diameter solid steel cable.  That, in water, would be something
> like 6 kg per meter.
> 
> Assuming there was only the minimum required amount of slack required
> for the hypothetical lifting (or equivalently, that the cable was
> being stretched just enough to reach the surface), and supposing that
> the units of length in the example are kilometers, then the tension
> in the cable turns out to be pretty close to a uniform 1500 kN, which
> also turns out not to be far above the typical tensile strength for
> the assumed cross-section of steel, and well within the strength of
> special-purpose items like conveyor belts in coal mines.
> 
> 
> 
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