Without a doubt my favorite issue of any magazine ever. I still have my copy somewhere.
One small nit ... dark fiber represents unused capacity. There are several places where the article says something like "dark fibre signals" which is incorrect. Dark fiber has no signal, while lit fiber does.
The last thing I'll mention is that these systems are obviously single-mode fiber. The laser powers feeding each channel are probably around 12dBm in the 1550nm spectrum (per channel). If you look into the end of one of these fibers that's lit from the other end, you'll end up with burned spots on your retina. Wiggle it around a bit and you'll have squiggle shaped burns. So if you're ever around fiber equipment, don't look directly at the ends (or into the connectors). You can get laser safety glasses cheaply ... save your sight!
"Do not look directly into fiber with remaining eyeball".
Amazing. I think if people back in 2000 would have realized the capacity coming along in fiber, then a site like youtube would have been obvious to many more people. Back then, I think a lot of people thought it would be cool to have a video distribution site... but how the heck would you pay for it. I remained amazed and confused by how Google could somehow afford to embed video on every random website -- becoming the video provider of the entire Internet. But I guess for them it was a simple formula of using their excess capacity for something.
However, I can also imagine that quite a non-neglectible proportion of Youtube/Netflix traffic cannot be retrieved from such a cache.
One blurb from the book that stuck with me was the notion that in theory, accessing an external hard drive half-way across the world via a pure fiber connection could be quicker than accessing an external hard drive on your desk via copper. True? I don't know, but he thought so at the time.
"Talking of which, John looked up the latency of the two Atlantic cables; the shorter journey clocks up a round trip delay (RTD) of 66.5ms, while the longer route takes 66.9ms. So your data is travelling at around 437,295,816 mph. Fast enough for you?"
Too fast. Like breaking the law fast.
Edit: oops my bad. That's mph and c is 186k miles per second. So this is like 0.66c - nothing to see here, move along!
From the article:
6,500km cable length
148 (& 149) amplifiers
66.5 (& 66.9) ms of round trip latency
Wikipedia says the refractive index of typical optical fibres is 1.44
So the light travel time down 6500km of fibre would be 6,500x10^3/(3^10^8*1.44) = 0.0312ms, and twice that for the round trip = 62.4ms
From that we get that the total latency of 66.5ms is 62.4ms of light travel time plus 4.1ms of (presumably) inline amplifier and terminating equipment latency.
That means each of the 148 amplifiers are doing their thing in something less than 28 microseconds, possibly way less since it'd be easy to assume the terminating equipment at each end is doing a way more time consuming task that just amplifying the signal, so could easily be taking up the bulk of that 4.1ms non-travel-time latency.
Anyone know how those amps work?
Basically, the repeater is another laser, but the emmission of new photons is stimulated by low-energy photons exciting the partially-excited atoms in the amplifier.
Or, telling it the other way, a laser is like a sound amplifier that has mic feedback. (high gain and return causes feedback)