Submarine communications cable

From Free net encyclopedia

A submarine communications cable is a cable laid beneath the sea to carry telecommunications between countries.

The first submarine communications cables carried telegraphy traffic. Subsequent generations of cables carried first telephony traffic, then data communications traffic. All modern cables use fiber optic technology to carry digital payloads, which are then used to carry telephone traffic as well as Internet and private data traffic.

As of 2005, submarine cables link all the world's continents except Antarctica.

Contents

[edit]

History

[edit]

Trials

After William Cooke and Charles Wheatstone had introduced their working telegraph in 1839, the idea of a submarine line across the Atlantic Ocean began to be thought of as a possible triumph of the future. Samuel Morse proclaimed his faith in it as early as the year 1840, and in 1842 he submerged a wire, insulated with tarred hemp and india rubber, in the water of New York harbour, and telegraphed through it. The following autumn Wheatstone performed a similar experiment in Swansea bay. A good insulator to cover the wire and prevent the electric current from leaking into the water was necessary for the success of a long submarine line. India rubber had been tried by Moritz von Jacobi, the Russian electrician, as far back as 1811.

Another insulating gum which could be melted by heat and readily applied to wire made its appearance in 1842. Gutta-percha, the adhesive juice of the Isonandra Gutta tree, was introduced to Europe by William Montgomerie, a Scottish surgeon in the service of the British East India Company. Twenty years earlier he had seen whips made of it in Singapore, and he believed that it would be useful in the fabrication of surgical apparatus. Michael Faraday and Wheatstone soon discovered the merits of gutta-percha as an insulator, and in 1845 the latter suggested that it should be employed to cover the wire which was proposed to be laid from Dover to Calais. It was tried on a wire laid across the Rhine between Deutz and Cologne. In 1849 C.V. Walker, electrician to the South Eastern Railway, submerged a wire coated with it, or, as it is technically called, a gutta-percha core, along the coast off Dover.

[edit]

The first commercial cables

In August 1850, John Watkins Brett's Anglo-French Telegraph Company laid the first line across the English Channel. It was simply a copper wire coated with gutta-percha, without any other protection. The experiment served to keep alive the concession, and the next year, on November 13, 1851, a protected core, or true cable, was laid from a government hulk, the Blazer, which was towed across the Channel. Next year Great Britain and Ireland were linked together. In 1852, a cable laid by the Submarine Telegraph Company linked London to Paris for the first time. In May, 1853, England was joined to the Netherlands by a cable across the North Sea, from Orford Ness to The Hague. It was laid by the Monarch, a paddle steamer which had been fitted for the work.

[edit]

Transatlantic telegraph cable

Template:Main

The first transatlantic telegraph cable was promoted by Cyrus Field and laid in 1858. However, the project was plagued with problems from the outset, and was in operation for only a month. Subsequent attempts in 1865 and 1866 were more successful.

[edit]

Construction

Transatlantic cables of the 19th century consisted of steel wire, wrapping india rubber, wrapping gutta-percha, which actually surrounded the multi-strand copper wire. The portions for a distance from each shore had additional protective armor wires. Gutta-percha, a natural polymer similar to rubber, had nearly ideal properties for insulating submarine cables, aside from a rather high dielectric constant which made cable capacitance high. Gutta-percha was not replaced as a cable insulation until polyethylene was introduced in the 1930s. Gutta-percha was so critical to communications that in the 1920s the American military experimented with rubber-insulated cables, since American interests controlled significant supplies of rubber but no gutta-percha manufacturers.

[edit]

Bandwidth problems

Long-distance submarine telegraph cables experienced formidable electrical problems. Unlike modern cables, the technology of the 19th century did not allow for in-line repeater amplifiers in the cable. The cables used large voltages to overcome the electrical resistance of their tremendous length. They also had substantial amounts of capacitance and inductive reactance. The distributed resistance, capacitance and inductive reactance operated in combination to retard and disperse the telegraph pulses in the line, distorting them and limiting the data rate for telegraph operation. In modern terms, the cables had very limited bandwidth.

As early as 1823, Francis Ronalds had observed that electric signals were retarded in passing through an insulated wire or core laid underground, and the same effect was noticeable on cores immersed in water, and particularly on the lengthy cable between England and The Hague.

Michael Faraday showed that the effect was caused by capacitance between the wire and the earth or water surrounding it. Faraday had noted that when a wire is charged from a battery (for example when pressing a telegraph key), the electric charge in the wire induces an opposite charge in the water as it travels along. As the two charges attract each other, the exciting charge is retarded. The speed of a signal through the conductor of a submarine cable is thus reduced. A core, in fact, is an attenuated capacitor.

Early cable designs failed to analyze these effects correctly. Famously, E.O.W. Whitehouse had dismissed the problems and insisted that a transatlantic cable was feasible. When he subsequently became electrician of the Atlantic Telegraph Company he became involved in a public dispute with William Thomson. Whitehouse believed that, with enough voltage, any cable could be driven. Because of the excessive voltages recommended by Whitehouse, Cyrus Field's first transatlantic cable never worked reliably, and eventually short circuited to the ocean when Whitehouse increased the voltage beyond the cable design limit.

Thomson designed a complex electric-field generator that minimized current by resonating the cable, and a sensitive light-beam mirror galvanometer for detecting the faint telegraph signals. Thomson became wealthy on the royalties of these, and several related, inventions. Thomson was elevated to Lord Kelvin for his contributions in this area, chiefly an accurate mathematical model of the cable, which permitted design of the equipment for accurate telegraphy. The effects of atmospheric electricity and the geomagnetic field on submarine cables also motivated many of the early polar expeditions.

Thomson had produced a mathematical analysis of propagation of electrical signals into telegraph cables based on their capacitance and resistance, but since long submarine cables operated at slow rates, he did not include the effects of inductance. By the 1890s, Oliver Heaviside had produced the modern general form of the telegrapher's equations which included the effects of inductance and which were essential to extending the theory of transmission lines to higher frequencies required for high-speed data and voice.

[edit]

Transatlantic telephony

While laying a transatlantic telephone cable was seriously considered from the 1920s, a number of technological advances were required for cost-efficient telecommunications that did not arrive until the 1940s.

In 1942, Siemens Brothers, in conjunction with the United Kingdom National Physical Laboratory, adapted submarine communications cable technology to create the world's first submarine oil pipeline in Operation Pluto during World War II.

TAT-1 (Transatlantic No. 1) was the first transatlantic telephone cable system. Between 1955 and 1956, cable was laid between Gallanach Bay, near Oban, Scotland and Clarenville, Newfoundland and Labrador. It was inaugurated on September 25, 1956, initially carrying 36 telephone channels.

[edit]

Expanding the network

[edit]

Technological developments

In the 1960s, transoceanic cables were waveguides transmitting frequency-multiplexed radio signals. The repeaters were the most reliable vacuum tube amplifiers ever designed. A high voltage direct current wire powered the repeaters. Many of these cables still exist and are usable, but abandoned because their capacity is too small to make money. Some have been used as scientific instruments to measure earthquake waves and other geomagnetic events.

In the 1980s, fibre optic cables were developed. Modern optical fibre repeaters use a solid-state optical amplifier, usually an Erbium-doped fiber amplifier. A solid-state laser is powered by the voltage difference between the ocean and a wire carrying high voltage direct current. The solid-state laser excites a short length of doped fibre that itself acts as a laser amplifier. As the light passes through the fiber, it is amplified. This system also permits wave-division multiplexing, which dramatically increases the capacity of the fibre.

The optic fibre used in undersea cables is chosen for its exceptional clarity, permitting runs of more than 100 kilometres between repeaters to minimize the number of amplifiers and the distortion they cause.

Originally, submarine cables were simple point-to-point connections. With the development of submarine branching units (SBUs), more than one destination could be served by a single cable system. Modern cable systems now usually have their fibres arranged in a self-healing ring to increase their redundancy, with the submarine sections following different paths on the ocean floor. One driver for this development was that the capacity of cable systems had become so large that it was not possible to completely back-up a cable system with satellite capacity, so it became necessary to provide sufficient terrestrial back-up capability. Not all telecommunications organisations wish to take advantage of this capability, so modern cable systems may have dual landing points in some countries (where back-up capability is required) and only single landing points in other countries where back-up capability is either not required, the capacity to the country is small enough to be backed up by other means, or having back-up is regarded as too expensive.

The first transatlantic telephone cable to use optical fibre was TAT-8, which went into operation in 1988.

[edit]

Technology

to be written

A useful and readable overview of one manufacturer's equipment may be found at the following two URLs:

[edit]

Economics

to be written

[edit]

Cultural reaction

[edit]

Owners and operators of submarine communications cables

to be written

[edit]

Owners and operators of cable-laying ships

[edit]

List of international submarine communications cables

This list does not include domestic cable systems, such as those on the coastlines of China, Italy and Brazil. All the cable systems listed below have landing points in two or more countries, and are currently (as of November 2005) in-service. Several older cables, although no longer used for international telecommunications, are used for scientific purposes. Others are simply abandoned.

[edit]

A

[edit]

B

[edit]

C

[edit]

D

[edit]

E

[edit]

F

[edit]

G

[edit]

H

[edit]

I

[edit]

J

[edit]

K

  • KAFOS - (Karadeniz Fiber Optik Sistemi)
  • KJCN - (Korea-Japan Cable Network)
[edit]

L

[edit]

M

[edit]

N

[edit]

O

[edit]

P

  • PAC - (Pan-American Crossing)
  • PacRimEast - (Pacific Rim East)
  • PacRimWest - (Pacific Rim West)
  • PAN AM - (Pan-American Cable System)
  • Pangea
  • PC-1 - (Pacific Crossing)
  • PEC - (Pan-European Crossing)
  • PTAT-1 - (Private Trans-Atlantic Telecommunications System)
[edit]

Q

[edit]

R

[edit]

S

[edit]

T

[edit]

U

[edit]

V

[edit]

W

  • WASC - (West Africa Submarine Cable)
[edit]

X

[edit]

Y

[edit]

Z

[edit]

References

  1. Template:Note Template:Cite web
  2. Template:Note Template:Cite web
  3. Template:Note Template:Cite web
  4. Template:Note Template:Cite web
  5. Template:Note Template:Cite web
  6. Template:Note Template:Cite web

Hunt, Bruce J. Lord Cable. Europhysics News (2004), Vol. 35 No 6.

[edit]

See also

[edit]

External links

cite web |title=Maps of communications cable routes |url=http://www.cybergeography.org/atlas/cables.html |accessdate=February 12 |accessyear=2006 }}

  • {{

cite web |title=Submarine Telecommunications Newsletter |url=http://www.subtelforum.com/ |accessdate=February 12 |accessyear=2006 }}de:Seekabel es:Cable submarino he:כבל תת ימי id:Kabel komunikasi bawah laut zh:海底通訊電纜

Retrieved from "http://www.netipedia.com/index.php/Submarine_communications_cable"