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Very simplified, but assuming a 5000 km cable and 300 000 km/s speed of light (is slightly slower in fiber), light needs 0.01666... seconds for that. At 10 Gbit/s (fairly slow), that'd mean ~ 166 Mbit or ~ 20 Megabyte in flight. (I hope I didn't forget a factor 1000 somewhere)

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Your calculation makes sense. However, for those 20 MB in flight, how much data is stored in buffers? I think that could be approximated by comparing ping time with speed of light.

e.g. if a 5000 km long link at 10 Gbit/s has latency of 0.0166 s, then you have zero buffering. If you have latency of 0.2 s, then around 2 Gbit of data must be stored in buffers somewhere, making 20 MB in flight only 1% of all data stored in such a ping filesystem.

How about the earth-moon-earth path for 768,000km?

EDIT: For the EME path that's around 3 gigs in flight

We've found a viable way to a space elevator: Sell it as a delay-line storage device.

In a small toroidally shaped universe, your radio is also your memory. All emissions eventually return to their origin, but you can reorder memory transmissions by moving while the data is in flight.

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