In 1988, only 2% of the World's transoceanic flow of messages and data was carried by undersea cables. Satellites were the dominant carrier. Today, cables carry 80% of a much bigger, ever-growing total. The reason: bandwidth, or more accurately, channel capacity, which is a function not only of bandwidth but of noise level as well. The latest optical-fiber cables have at least 3000 times the capacity of their coaxial forebears, whereas today's satellites have improved only modestly over theirs. What's more, optical cables themselves are improving at an impressive rate. Current cables from Alcatel SA, Paris, for example, carry 10 Gb/s on each of 42 wavelengths for a total capacity of 420 Gb/s over a single fiber. That is likely to grow to 68 wavelengths by 2001. Besides the enormous and continuing increases in capacity, cables enjoy other advantages over satellites: better longevity, security, and adherence to installation schedules (there are no booster rocket failures in the cable business), to name three. Undersea cables-all 580000 km (120000 leagues) of them-live a comparatively sheltered life compared with satellites, which are threatened by meteor showers, space debris, and sun spots. In the hazardous region from the shore line out to the depths, the cables are usually heavily armored and buried beneath the sea floor. Out in the deep ocean, where the hazards are few and far between, they simply lie on the bottom, suspended occasionally over sharp depressions, in a calm, isothermal environment of about 2/spl deg/C, surrounded by the worlds largest heat sink.
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