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With satellites, why still use submarine communication cables?

Satellites are great for certain applications. Satellites do a wonderful job of reaching areas that aren’t yet wired with fiber. They are also useful for distributing content from one source to multiple locations.

However, on a bit-for-bit basis, there’s just no beating fiber-optic cables. Cables can carry far more data at far less cost than satellites.

It’s hard to know exactly how much of all international traffic is still carried via satellite, but it’s very small. Statistics released by U.S. Federal Communications Commission indicate that satellites account for just 0.37 percent of all U.S. international capacity.

How many submarine cables are there?

As of early 2017, there are approximately 428 submarine cables in service around the world; over 1.1 million kilometers of submarine cables in service globally. The total number of cables is constantly changing as new cables enter service and older cable are decommissioned.

 


Submarine cable map

Where are the cables actually lay?

Submarine communication cables go all the way down on the bottom of the ocean floor. Nearer to the shore cables are buried under the seabed for protection, which explains why you don’t see cables when you go the beach, but in the deep sea they are laid directly on the the ocean floor.


Example Trans-Atlantic cable route seabed profile

Of course, considerable care is taken to ensure cables follow the safest path to avoid fault zones, fishing zones, anchoring areas, and other dangers. To reduce inadvertent damage, the undersea cable industry also spends a lot of time educating other marine industries on the location of cables.

Modern submarine cables use fiber-optic technology. Lasers on one end fire at extremely rapid rates down thin glass fibers to receptors at the other end of the cable. These glass fibers are wrapped in layers of plastic (and sometimes steel wire) for protection.


A cross section of the shore-end of a modern submarine communications cable.
1 – Polyethylene
2 – Mylar tape
3 – Stranded steel wires
4 – Aluminium water barrier
5 – Polycarbonate
6 – Copper or aluminium tube
7 – Petroleum jelly
8 – Optical fibers
The core is fiber for transmitting data, the other seven layers are applied for protection.

How much information can a cable carry?

Cable capacities vary a lot. Typically, newer cables are capable of carrying more data than cables laid 15 years ago. The planned MAREA cable will be capable of carrying 160 Tbps (terabits per second, equal to 1 million megabits per second).

There are two principal ways of measuring a cable’s capacity.

Potential capacity is the total amount of capacity that would be possible if the cable’s owner installed all available equipment at the ends of the cable. This is the metric most cited in the press.

Lit capacity is the amount of capacity that is actually running over a cable. This figure simply provides another capacity metric. Cable owners rarely purchase and install the transmission equipment to fully realize a cable’s potential from day one. Because this equipment is expensive, owners instead prefer to upgrade their cable gradually, as customer demand dictates.

Sharks are known for biting cables?

Cables can be broken by fishing trawlers, anchors, earthquakes, turbidity currents, and even shark bites. Based on surveying breaks in the Atlantic Ocean and the Caribbean Sea, it was found that between 1959 and 1996, fewer than 9% were due to natural events. In response to this threat to the communications network, the practice of cable burial has developed. The average incidence of cable faults was 3.7 per 1,000 km (620 mi) per year from 1959 to 1979. That rate was reduced to 0.44 faults per 1000 km per year after 1985, due to widespread burial of cable starting in 1980. Still, cable breaks are by no means a thing of the past, with more than 50 repairs a year in the Atlantic alone, and significant breaks in 2006, 2008, and 2009.

How to repair the submarine cable?

The first step of repairing is to find the cable break. The cable engineer can find the find the approximate location of the break by phone and internet interruption situation. The shore terminal can emit light pulses, and normal fibers can always transmit these pulses in the sea, but if the fiber is broken, the pulse will bounce back from that point, that’s how the shore terminal find a break. Afterwards, the ship will need to transport a new cable to repair, but the first step is to bring up the broken fiber. If the cable in the water under the depth of 2000 meters, you can use robots to salvage the cable.

Once it located in the water depth of about 3000 meters to 4000 meters, only grapple is workable. The grapple takes over ten hours to fetch a cable.

 

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