What are submarine communications cables?

Submarine (tele)communication cables are metal or fibre optic cables that convey information underwater, between islands and continents. They are now typically fibre-optic, but were all metallic wires before the 1980's. They carry trans-continental internet traffic as well as telephony. While they connect land masses together, end-users do not directly connect to them - instead major network operators (such as some ISP's and tier-1 carriers) are leased ports or wavelengths, although some organisations wholly own some cable systems. Each cable has at least two landing stations where links branch off to other networks (often by the same network operator) and where electricity is supplied to power any repeaters. Because of the cost and difficulty in installing and maintaining these cables, they would be designed for heavy traffic (often accessed by many customers); nowadays each cable would normally have multiple fibre pairs, each with multiple wavelengths/frequencies, each already high-bandwidth.

Almost all trans-continental telecommunications travel through such cables, making them highly depended on. Some islands have only one cable, mainly due to a low population, which leaves them vulnerable to being cut-off from the rest of the world if the cable breaks or a major issue occurs at their landing stations. Nonetheless, new cables have been made increasingly resilient and a diverse fleet of ships that can repair them remain on standby around the world. Modern cables can split part way, diversifying their paths, while landing stations can connect to two or more undersea cables, including redundant ones for further resiliency and capacity.