Submarine Cable Redundancy, Explained

You might have heard about a recent cable cut near Mauritania.

The short version? On March 30, damage to the ACE cable disrupted internet service to connected countries, with reported problems occurring over the next several days. The Dyn blog reported that “of the countries listed as having landing points for the ACE Submarine Cable, 10 had significant disruptions evident in Oracle’s Internet Intelligence data.”

Cable faults have happened before—and they will happen again—but this story highlights why previous faults have been worse. More cables have come online in recent years, resulting in increased redundancy.

Back-Up Submarine Cables

Most cable-using companies follow a “safety in numbers” approach, spreading their networks’ capacity over multiple cables so that if one goes down, their network will run smoothly over other cables while service is restored on the damaged one. This is redundancy.

When multiple submarine cables are available between two nodes, data transmission may take multiple paths. Two cables traveling between nodes provide one level of redundancy. Three provide two levels of redundancy, and so on.

So take David Belson’s story for Dyn, which explains that “with multiple submarine cables landing in Western African countries that provide service between countries…network providers in these countries have an opportunity to take advantage of this redundancy to mitigate the potential impact of problems.”

Outages that occurred following the ACE cable cut were more serious in locations that relied heavily on that cable, indicating a lack of redundancy. On the other hand, Belson uses the example of Benin, which is connected to the ACE cable but saw little impact following the fault due to the redundancy it enjoys via the SAT-3/WASC cable.

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