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Optical technologies of submarine cables consist in sending information in the form of light pulses along a fibre, which gives access to higher data rates than analogue technologies.
The first transatlantic optical cable (TAT 8) will be put into service in 1988 between the United States, France and Great Britain. Between 1988 (TAT 8) and 2002 (APPOLO), the capacity of similar submarine cables will be multiplied by a factor of 5,000 (and by a factor of 40,000 over a wider reference period, from 1988 to 2009).
During the 20th century, the capabilities of optical cables, coupled with their rapid evolution, will lead to the premature abandonment of all analogue cables. Transmission satellites, until now used in addition to analogue cables, will also be outdated, before being reserved for certain sectors (television, telephone services in sparsely populated areas, etc.).
Intercontinental wireless networks will also gradually be marginalized. Thanks to the use of optical technologies, submarine cables quickly accounted for 99% of intercontinental data exchanges.
An underwater optical cable consists of a protective sheath (1 and 2 in the diagram below), a metal reinforcement (3, 4, 5 and 6), an insulating sheath (7) and pairs of optical fibres (8).
By 2014, most long-distance networks use 1,550 nm wide windows, which limits loss while ensuring significant transmission capacity.
The capacity of a cable is used to estimate the amount of data it can transmit. It is traditionally measured in flow rates:
The efficiency of the transmissions depends on the number of colours passing through each optical fibre. This number varies according to the type of multiplexer used: SDH (Synchronous Digital Hierarchy) multiplexers allow time multiplexing of waves; WDM (Wavelenght Division Multiplexing) multiplexers allow wave frequencies to be multiplexed. In practice, the complementary use of these technologies significantly improves the capabilities of optical fibres:
It is theoretically possible to transport large capacities, measured in Tbit/s, on a pair of optical fibres. However, large intercontinental submarine cables have available capacities ranging from a few tens to a few thousand Gbit/s. This difference between practice and theory finds several technical and/or economic explanations:
An underwater optical cable alone rarely ensures the routing of traffic from an overseas territory to the exchange nodes of the global Internet.
It is therefore necessary for operators to interconnect their traffic with other submarine cables; these interconnections form lightpaths to delivery and exchange nodes (GIXs).
These interconnections and the creation of these lightpaths are obtained either through direct purchase or by exchanging capacity from one submarine cable to another, and make it possible to define redundant and secure traffic routing routes. If only one submarine cable lands on a territory (as in the case of Mayotte or French Guiana in 2014), this redundancy cannot be implemented on the entire lightpath.
The installation, maintenance and operation of submarine optical cables require a significant mobilization of technical, human and financial resources.
The installation of an underwater optical cable involves two complex operations:
The financing, establishment and operation of submarine optical cables are complex and risky operations:
The marketing of a submarine cable can be carried out according to different alternative sharing methods:
Tactis has more than 20 years of recognised expertise in this field, both with telecommunications operators, submarine cable consortia, government authorities, regulators, investors and major financial backers. Tactis first worked on projects in Europe, the Indian Ocean, then in the Mediterranean, in the Caribbean, North and South America and in recent years on projects specific to the African continent. In total, our teams have been involved in more than twenty projects in recent years.
For submarine cable projects, Tactis conducts market studies, studies the technical and economic feasibility, assists in defining the technical specifications of a project, seeking financing, setting up the project, drafting technical specifications and negotiating with manufacturers, monitoring deployment and commissioning, audit/expertise following operational incidents (particularly interruptions) and monitoring return to service.
A question about underwater cables? Need to remove doubts in view of a future project? Send an email to Benjamin Fradelle, Tactis Associate Director.