Skip to content

CONCEPT Cited by 1 source

Submarine cable

Definition

A submarine (subsea) cable is a fiber-optic cable laid on the ocean floor to carry data between continents. It is "the least visible, yet one of the most critical layers of the internet" — roughly 99% of intercontinental data traffic (nearly every cross-continent message, call, or video) travels through glass strands under the sea, not via satellite. (Source: sources/2026-09-21-meta-inside-petal-building-the-worlds-first-petabit-class-transoceanic-subsea-cable)

A transoceanic cable is a long, repeatered system: a ~7,000 km transatlantic link needs "about a hundred repeaters" to re-amplify the optical signal along its length, and terminates at cable landing stations where it interconnects with terrestrial networks.

Anatomy and constraints

  • Fiber pairs / cores — capacity scales with the number of parallel optical paths in the cable (see concepts/spatial-division-multiplexing).
  • Repeaters — periodic optical amplifiers (historically EDFA, erbium-doped fiber amplifier) that boost the signal; they are power-fed from shore over the cable, so the whole system is power-limited. Petal stays within existing ≤18 kV power-feeding-equipment limits; exceeding that voltage would trigger a costly "requalification of the subsea ecosystem."
  • Landing stations — shore endpoints and the terrestrial-network handoff; the landing party (e.g. Orange for Petal on France's Atlantic coast) owns the "security and resilience of the terrestrial segment."
  • Multi-year horizon — cables are announced years before service (Petal: announced 2026, in service 2029), and reliability at the country level is a function of cable diversification decisions taken over a multi-year horizon, not real-time failover.

Resilience: a country-scale single point of failure

For countries with few alternative routes, a single submarine cable can be a near-sole international capacity path, turning a cable incident into a national-scale connectivity event. The West Africa Cable System is the canonical wiki example: a 2026 WACS incident drove Republic of Congo traffic 82% below expected for ~63 hours. Well-connected regions with many competing cables (e.g. South Africa) absorb the same incident with minimal impact. This makes cable diversification — not per-ISP failover primitives — the load-bearing resilience lever.

Capacity is a foundational backbone investment

Because subsea cables carry ~99% of intercontinental traffic, adding capacity is a strategic Internet-backbone investment. The capacity frontier has advanced through distinct regime shifts — EDFA amplification (1980s), coherent optical transmission + dispersion-uncompensated designs (2010s), and now spatial division multiplexing including multi-core fiber. Meta's Petal is the first petabit-class transoceanic cable and the first to deploy multi-core fiber at scale.

Seen in

Last updated · 766 distilled / 2,225 read