A submarine communications cable is a cable laid on the sea bed between land-based stations to carry telecommunication signals across stretches of ocean.
The first submarine communications cables carried telegraphy traffic. Subsequent generations of cables carried first telephony traffic, then data communications traffic. All modern cables use optical fiber technology to carry digital payloads, which are then used to carry telephone traffic as well as Internet and private data traffic. They are typically 69 millimetres (2.7 in) in diameter and weigh around 10 kilograms per metre (7 lb/ft), although thinner and lighter cables are used for deep-water sections.[1]
As of 2010, submarine cables link all the world's continents except Antarctica.
Contents |
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,[2][3] in the water of New York Harbor, 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 Prussian electrical engineer, as far back as the early 19th century.
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 Palaquium 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 apparatuses. 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 gutta-percha along the coast off Dover.
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. The 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.
The first attempt at laying a transatlantic telegraph cable was promoted by Cyrus West Field, who persuaded British industrialists to fund and lay one in 1858. However, the technology of the day was not capable of supporting the project; it was plagued with problems from the outset, and was in operation for only a month. Subsequent attempts in 1865 and 1866 with the world's largest steamship, the SS Great Eastern, used a more advanced technology and produced the first successful transatlantic cable. The Great Eastern later went on to lay the first cable reaching to India from Aden, Yemen, in 1870.
From the 1850s until 1911, British submarine cable systems dominated the most important market, the North Atlantic Ocean. The British had both supply side and demand side advantages. In terms of supply, Britain had entrepreneurs willing to put forth enormous amounts of capital necessary to build, lay and maintain these cables. In terms of demand, the vast colonial empire Britain held led to business for the cable companies from news agencies, trading and shipping companies, and the British government. Many of Britain’s colonies had significant populations of European settlers, making news about them of interest to the general public in the home country.
The submarine cables were an economic boon to trade companies because owners of ships could communicate with captains when they reached their destination on the other side of the ocean and even give directions as to where to go next to pick up more cargo based on reported pricing and supply information. The British government had obvious uses for the cables in maintaining administrative communications with governors throughout its empire as well as in engaging other nations diplomatically and communicating with its military units in wartime. Location of Britain’s territory was also an advantage as it possessed both Ireland and Newfoundland, making for the shortest route across the Atlantic Ocean (reducing cost significantly).
A few facts put this dominance of the industry in perspective. In 1896, there were thirty cable laying ships in the world and twenty-four of them were owned by British companies. In 1892, British companies owned and operated two-thirds of the world’s cables and by 1923 their share was still 42.7 percent.[4]
An 1863 cable to Mumbai, India (then known as Bombay) provided a crucial link to Saudi Arabia.[5] In 1870 Bombay was linked to London via submarine cable in a combined operation by four cable companies, at the behest of the British Government. In 1872 these four companies were combined to form the mammoth globespanning Eastern Telegraph Company, owned by John Pender. A spin-off from Eastern Telegraph Company was a second sister company, the Eastern Extension, China and Australasia Telegraph Company, commonly known simply as "the Extension". In 1872, Australia was linked by cable to Bombay via Singapore and China and in 1876 the cable linked the British Empire from London to New Zealand.[6]
This was completed in 1902–03, linking the US mainland to Hawaii in 1902 and Guam to the Philippines in 1903.[7] Canada, Australia, New Zealand and Fiji were also linked in 1902.[8]
Decades later, the North Pacific Cable system was the first regenerative (repeatered) system to completely cross the Pacific from the US mainland to Japan. The US portion of NPC was manufactured in Portland, Oregon, from 1989–1991 at STC Submarine Systems, and later Alcatel Submarine Networks. The system was laid by Cable & Wireless Marine on the CS Cable Venture in 1991.
Transatlantic cables of the 19th century consisted of an outer layer of iron and later steel wire, wrapping India rubber, wrapping gutta-percha, which surrounded a multi-stranded copper wire at the core. The portions closest to each shore landing had additional protective armor wires. Gutta-percha, a natural polymer similar to rubber, had nearly ideal properties for insulating submarine cables, with the exception of 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. In the 1920s, the American military experimented with rubber-insulated cables as an alternative to gutta-percha, since American interests controlled significant supplies of rubber but no gutta-percha manufacturers.
Early long-distance submarine telegraph cables exhibited formidable electrical problems. Unlike modern cables, the technology of the 19th century did not allow for in-line repeater amplifiers in the cable. Large voltages were used to attempt to overcome the electrical resistance of their tremendous length but the cables' distributed capacitance and inductance combined to distort the telegraph pulses in the line, reducing the cable's bandwidth, severely limiting the data rate for telegraph operation to 10-12 words per minute.
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 noticed by Latimer Clark (1853) 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. In 1831, Faraday described this effect in what is now referred to as Faraday's law of induction. As the two charges attract each other, the exciting charge is retarded. The core acts as a capacitor distributed along the length of the cable which, coupled with the resistance and inductance of the cable limits the speed at which a signal travels through the conductor of the cable.
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 West 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.
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. A first attempt to lay a pupinized telephone cable failed in the early 1930s due to the Great Depression.
In 1942, Siemens Brothers of New Charlton, London 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.
In the 1960s, transoceanic cables were coaxial cables that transmitted frequency-multiplexed voiceband signals. A high voltage direct current on the inner conductor powered the repeaters. The first-generation repeaters are among the most reliable vacuum tube amplifiers ever designed.[9] Later ones were transistorized. Many of these cables are still usable, but abandoned because their capacity is too small to be commercially viable. Some have been used as scientific instruments to measure earthquake waves and other geomagnetic events.[10]
In the 1980s, fiber optic cables were developed. The first transatlantic telephone cable to use optical fiber was TAT-8, which went into operation in 1988. A fiber-optic cable comprises multiple pairs of fibers. Each pair has one fiber in each direction. TAT-8 had two operational pairs and one backup pair.
Modern optical fiber repeaters use a solid-state optical amplifier, usually an Erbium-doped fiber amplifier. Each repeater contains separate equipment for each fiber. These comprise signal reforming, error measurement and controls. A solid-state laser dispatches the signal into the next length of fiber. The solid-state laser excites a short length of doped fiber that itself acts as a laser amplifier. As the light passes through the fiber, it is amplified. This system also permits wavelength-division multiplexing, which dramatically increases the capacity of the fiber.
Repeaters are powered by a constant direct current passed down the conductor near the center of the cable, so all repeaters in a cable are in series. Power feed equipment is installed at the terminal stations. Typically both ends share the current generation with one end providing a positive voltage and the other a negative voltage. A virtual earth point exists roughly half way along the cable under normal operation. The amplifiers or repeaters derive their power from the potential difference drop across them.
The optic fiber used in undersea cables is chosen for its exceptional clarity, permitting runs of more than 100 kilometers between repeaters to minimize the number of amplifiers and the distortion they cause.
The rising demand for these fiber-optic cables outpaced the capacity of providers such as AT&T. Having to shift traffic to satellites resulted in poorer quality signals. To address this issue, AT&T had to improve its cable laying abilities. It invested $100 million in producing two specialized fiber-optic cable laying vessels. These included laboratories in the ships for splicing cable together and testing its electrical properties. Such field monitoring is important because the glass of fiber-optic cable is less malleable than the previous copper cable that had been used. The ships are further equipped with special additional propellers that increase maneuverability. This capability is important because fiber-optic cable must be laid out straight from the stern (another factor copper cable laying ships did not have to contend with).[11]
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 fibers 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 organizations 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.
A further redundant-path development over and above the self-healing rings approach is the "Mesh Network" whereby fast switching equipment is used to transfer services between network paths with little to no effect on higher-level protocols if a path becomes inoperable. As more paths become available to use between two points, the less likely it is that one or two simultaneous failures will prevent end-to-end service.
As of 2006, overseas satellite links accounted for only 1 percent of international traffic, while the remainder was carried by undersea cable. The reliability of submarine cables is high, especially when (as noted above), multiple paths are available in the event of a cable break. Also, the total carrying capacity of submarine cables is in the terabits per second while satellites typically offer only megabits per second and display higher latency. However, a typical multi-terabit, transoceanic submarine cable system costs several hundred million dollars to construct.[12]
As a result of these cables' cost and usefulness they are highly valued not only by the corporations building and operating them for profit, but also by national governments. For instance, the Australian government considers its submarine cable systems to be “vital to the national economy.” Accordingly, the Australian Communications and Media Authority (ACMA) has created protection zones that restrict activities that could potentially damage cables linking Australia to the rest of the world. The ACMA also regulates all projects to install new submarine cables.[13]
Almost all fiber optic cables from TAT-8 in 1988 until approximately 1997 were constructed by "consortia" of operators. For example, TAT-8 counted 35 participants including most major international carriers at the time such as AT&T.[14] Two privately-financed, non-consortium cables were constructed in the late-1990s, which preceded a massive, speculative rush to construct privately-financed cables that peaked in more than $22 billion worth of investment between 1999 and 2001. This was followed by the bankruptcy and reorganization of cable operators such as Global Crossing, 360networks, FLAG, Worldcom, and Asia Global Crossing.
There has been an increasing tendency in recent years to expand submarine cable in the Pacific Ocean (the previous bias always having been to lay communications cable across the Atlantic Ocean which separates the United States and Europe). For example, between 1998 and 2003, approximately 70% of undersea fiber-optic cable was laid in the Pacific. This is in part a response to the emerging significance of Asian markets in the global economy.[15]
Although much of the investment in submarine cables has been directed toward developed markets such as the transatlantic and transpacific routes, in recent years there has been an increased effort to expand the submarine cable network to serve the developing world. For instance, in July 2009 an underwater fiber optic cable line plugged East Africa into the broader Internet. The company that provided this new cable was SEACOM, which is 75% owned by Africans.[16] The project is based on the hope that new information technology will reduce the cost of doing business in Africa and between Africa and other international parties. Still, the project was delayed by a month due to increased piracy along the coast, a reminder that the developing world faces other struggles that new technologies such as this may not necessarily solve.[17]
Antarctica is the only continent yet to be reached by a submarine telecommunications cable. All phone, video, and e-mail traffic must be relayed to the rest of the world via satellite, which is still quite unreliable. Bases on the continent itself are able to communicate with one another via radio, but this is only a local network. To be a viable alternative, the fiber-optic cable must be able to withstand temperatures of −80˚ C as well as massive strain from ice flowing up to 10 meters per year. Thus, plugging into the larger Internet backbone with the high bandwidth afforded by fiber-optic cable is still an as yet infeasible economic and technical challenge in the Antarctic.[18]
Cables can be broken by fishing trawlers, anchors, earthquakes, turbidity currents and even shark bites.[19] 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 per year from 1959 to 1979. That rate was reduced to 0.44 faults per 1,000 km per year after 1985, due to widespread burial of cable starting in 1980.[20] Still, cable breaks are by no means a thing of the past, with more than 50 repairs a year in the Atlantic alone,[21] and significant breaks in 2006, 2008 and 2009.
The propensity for fishing trawler nets to cause cable faults may well have been exploited during the Cold War. For example, in February 1959 a series of 12 breaks occurred in five American trans-Atlantic communications cables. In response, a United States naval vessel, the U.S.S. Roy O. Hale detained and investigated the Soviet trawler Novorosiysk. A review of the ship’s log indicated it had been in the region of each of the cables when they broke. Broken sections of cable were also found on the deck of the Novorosiysk. It appeared that the cables had been dragged along by the ship’s nets, and then cut once they were pulled up onto the deck in order to release the nets. The Soviet Union’s stance on the investigation was that it was unjustified, but the United States cited the Convention for the Protection of Submarine Telegraph Cables of 1884 to which Russia had been committed (prior to the formation of the Soviet Union) as evidence of violation of international protocol.[22]
Shore stations can locate a break in a cable by electrical measurements, such as through spread-spectrum time-domain reflectometry (SSTDR). SSTDR is a type of time-domain reflectometry that can be used in live environments very quickly. Presently SSTDR can collect a complete data set in 20ms.[23] Spread spectrum signals are sent down the wire and then the reflected signal is observed. It is then correlated with the copy of the sent signal and mathematical algorithms are applied to the shape and timing of the signals to locate the break.
A cable repair ship will be sent to the location to drop a marker buoy near the break. Several types of grapples are used depending on the situation. If the sea bed in question is sandy, a grapple with rigid prongs is used to plough under the surface and catch the cable. If the cable is on a rocky sea surface, the grapple is more flexible, with hooks along its length so that it can adjust to the changing surface.[24] In especially deep water, the cable may not be strong enough to lift as a single unit, so a special grapple that cuts the cable soon after it has been hooked is used and only one length of cable is brought to the surface at a time, whereupon a new section is spliced in.[25] The repaired cable is longer than the original, so the excess is deliberately laid in a 'U' shape on the seabed. A submersible can be used to repair cables that lie in shallower waters.
A number of ports near important cable routes became homes to specialised cable repair ships. Halifax, Nova Scotia was home to a half dozen such vessels for most of the 20th century including long-lived vessels such as the CS Cyrus West Field, CS Minia and CS Mackay-Bennett. The latter two were contracted to recover victims from the sinking of the RMS Titanic. The crews of these vessels developed many new techniques and devices to repair and improve cable laying, such as the "plough".
Underwater cables, which cannot be kept under constant surveillance, have tempted intelligence-gathering organizations since the late 19th century. Frequently at the beginning of wars nations have cut the cables of the other sides in order to shape the information flows into cables that were being monitored. The most ambitious efforts occurred in World War I, when British and German forces systematically attempted to destroy the others' worldwide communications systems by cutting their cables with surface ships or submarines.[26] During the Cold War the United States Navy and National Security Agency (NSA) succeeded in placing wire taps on Soviet underwater communication lines in Operation Ivy Bells.
The main point of interaction of cables with marine life is in the benthic zone of the oceans where the majority of cable lies. Recent studies (in 2003 and 2006) have indicated that cables pose minimal impacts on life in these environments. In sampling sediment cores around cables and in areas removed from cables, there were few statistically significant differences in organism diversity or abundance. The main difference was that the cables provided an attachment point for anemones that typically could not grow in soft sediment areas. Data from 1877 to 1955 showed a total of 16 cable faults caused by the entanglement of various whales, but such deadly entanglements have entirely ceased after the transition from telegraph cables to coaxial cables and then fiber-optic cables (the new cables are better designed in terms of torsional balance so that they have less of a tendency to coil).[27]
The Newfoundland earthquake of 1929 broke a series of trans-Atlantic cables by triggering a massive undersea mudslide. The sequence of breaks helped scientists chart the progress of the mudslide.
In July 2005, a portion of the SEA-ME-WE 3 submarine cable located 35 kilometres (22 mi) south of Karachi that provided Pakistan's major outer communications became defective, disrupting almost all of Pakistan's communications with the rest of the world, and affecting approximately 10 million Internet users.[28][29][30]
The 2006 Hengchun earthquake on December 26, 2006 rendered numerous cables between Taiwan and Philippines inoperable.
In March, 2007, pirates stole an 11-kilometre (6.8 mi) section of the T-V-H submarine cable that connected Thailand, Vietnam, and Hong Kong, affecting Vietnam's Internet users with far slower speeds. The thieves attempted to sell the 100 tons of cable as scrap.[31]
The 2008 submarine cable disruption was a series of cable outages, two of the three Suez Canal cables, two disruptions in the Persian Gulf, and one in Malaysia. It caused massive communications disruptions to India and the Middle East.[32][33]
In April 2010 the undersea cable SEA-ME-WE 4 was under an outage the South East Asia–Middle East–Western Europe 4 (SEA-ME-WE 4) submarine communications cable system, which connects South East Asia and Europe, was reportedly cut in three places, off Palermo, Italy.
The 2011 Tōhoku earthquake and tsunami damaged a number of undersea cables that make landings in Japan, including[34]:
|
||||||||||||||
