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How do submarine cables work?
Submarine optical cables are actually optical fibers, which use the propagation characteristics of light in optical fibers to transmit data. However, the submarine optical cable is not a simple optical fiber, it is actually a complex transmission system.
The submarine optical cable system consists of two parts: underwater equipment and shore equipment.
Underwater equipment
It mainly includes optical cable, optical amplifier/repeater and underwater branch unit.
What is the repeater used for?
As we all know, despite the high speed and sufficient bandwidth of optical fiber, the signal transmission distance is limited. Due to the attenuation of light, it cannot be transmitted indefinitely.
Therefore, in order to achieve long-distance transmission, it is necessary to add a repeater (signal amplifier) in the middle.
Obviously, the repeater diameter is much larger than the submarine cable.
It's the size of this guy that limits the number of cores in a submarine cable. Because the more fiber cores of the optical cable, the repeater will be expanded proportionally, and at the same time, the requirements for power supply will also increase.
By the way, submarine cables contain multiple pairs of fibers. For example, Google laid the fastest submarine optical cable in history in June 2016 (connecting Oregon, USA in the east, Chiba and Mie prefectures in Japan in the west, with a total length of 9,000 kilometers), and its fiber core consists of 6 pairs. Its capacity is 60Tb/s (100Gb/s x 100 wavelengths x 6 pairs of cores).
Shore equipment
It mainly includes optical cable terminal equipment, remote power supply equipment, line monitoring equipment, network management equipment and marine grounding devices.
Optical cable terminal equipment is responsible for signal processing, transmission and reception at both ends.
Detection equipment is the alarm monitoring and fault location and so on.
Let's take a look at the shore equipment section. The first is the remote power supply.
What is the remote power supply equipment used for?
Just mentioned, in order to achieve long-distance transmission, it is necessary to add a repeater (signal amplifier) in the middle. The repeater needs electricity. Therefore, it is necessary to use "remote power supply equipment".
The submarine optical cable system is equipped with remote power supply equipment on the land at both ends. It feeds the submarine repeater through the remote supply conductor on the submarine optical cable, thereby solving the problem of power supply.
This power supply uses a high-voltage, low-current DC power supply, the supply current is about 1 amp, and the supply voltage can be as high as several thousand volts.
So, if you see a submarine cable, it's best to stay away.
What does a power supply room with a voltage of several thousand volts look like?
This blue cabinet is actually composed of DC converters. Each converter provides several thousand volts of DC power and is backed up by N+1.
Of course, as with all power rooms, there must be battery backup to switch to battery power in the event of a power outage.
There are also huge diesel generators.
Then go to the line terminal equipment room.
After the submarine optical cable goes ashore, it emerges from the ground and is connected to the land terminal equipment (as shown in the figure below).
These yellow fiber optic cables are connected to various distribution frames. These distribution frames realize the connection, distribution and dispatch of submarine optical cable lines, and are connected to the operator's transmission terminal equipment through the distribution frame.
Through transmission equipment, it is connected to major data centers.
In other words, this is the egress/egress of the Internet.
