Mon, 22 Aug 1994

From Marseilles to Singapore in 1/10th of a Second

By Jean Chabrier

Telecommunications technology, which accompanies the incredible increase in communications needs (40 percent a year on the whole and 150 percent in certain areas such as the facsimile), has made a terrific leap forward in the last ten years, and it does not stop there.

PARIS: Not long ago, the only known means of transmission was the electromagnetic signal, carried by the airwaves, the co-axial cable, and then the satellite.

Although it was perfectly suited to carrying the voice, it soon proved inadequate for pictures and computer-data. It was then that, in the early 80s, digitalization appeared. This technique consists in transforming the signal emitted, whether in the form of data or pictures, into a series of binary numbers. This method, which stems directly from computers, makes it possible to transport "packages of figures" which, decoded, transmit their message with excellent quality.

Even more recent progress and the object of considerable stakes and extremely advanced research is the compression of data. The principle is simple. In any conversation, there are spaces between words, silences and pauses. This can be grouped together into a single "package", without any gaps. When it comes to transmitting pictures, the signals for the stationary parts are only transmitted once until the next modification in the scene, while the moving part is transmitted continuously.

At present, this compression makes it possible to increase the efficiency from one to five. The market for compressors is fully developing and has applications in the most varied areas, in particular scientific ones. IFREMER (the French Institute for Sea Research and Exploitation) has presented a model for the automatic observation of abysses and, for the first time in the world, it was able to transmit pictures in real time from a depth of 4,000 meters. Discussion now focuses on the means of transmission: whether a satellite or an underwater cable should be used.


The wonder of satellites has been familiar to us for the last 30 years. They are indispensable for many applications but now appear inadequate for the boom in telecommunications. They are expensive and their lifespan does not exceed ten years. Another drawback is that, in geostationary orbit, they can only serve a well-defined area and their transmission flow appears rather limited compared to needs. So the number of satellites has to be increased. With their orbits being 36,000 kilometers away, it takes 300 milliseconds for the signal to make the return journey, which is quite adequate for transmitting the voice or pictures, but becomes almost incompatible between computers, which usually transmit their data at a rate of five to 30 million operations a second.

So, there is once more talk of the underwater cable. Already, in 1878, Jules Verne spoke of such a cable in "A Floating City". But, since then, some progress has been made. The technique of optical fiber cables is highly developed and is the prerogative of a few large firms: ATT (American) with 32 percent of the market, Alcatel (French) and STC (British) with 23 percent each, and NEC (Japan) with 17 percent. Moreover, the first three of these firms have grouped together under the "Sea We Me" banner.

This famous cable consists of three pairs of fibers, buried in a gel and in polythene film with the whole of this protected by a steel sheath which is, itself, covered with a layer of copper serving as a conductor for the electronic repeaters and all of that is then covered in a massive sheath of polythene, bringing the diameter up to 21 centimeters.

As early as 1972, France had proceeded with tests, even creating a link between Marseilles and Ajaccio, a distance of 390 kilometers, in 1987, which was the world record until 1988 when nearly 6,400 kilometers were covered between the United States, Great Britain and France. From the point of view of performance, there was an increase from 28 megabits per second in 1978 to 560 megabits per second in 1982, and cables carrying five Gigabits per second are being tested.

From a practical point of view, the cable is less expensive. It has a lifespan of 25 years and, above all, it makes it possible to transmit a very high density of data while allowing numerous derivations. The cable compares to the satellite as an oil pipeline compares to a watering-can.

So "Sea Me We" decided to lay a cable between Marseilles and Singapore (18,751 kilometers) with nine derivations. The project, which was signed by 51 countries in October 1991, has been operational since June 1994. A total of 38,000 tons of cable with a capacity of 560 megabits per second (that is to say 16,000 simultaneous circuits with 150 repeaters) allow a photon to travel in 1/10th of a second. The 700 three-dimensional maps of the seabed were produced by a French company, ISM, in 150 days, thanks to a multibeam sounder which it invented. These maps indicate everything which could present a risk for the cable and the best route for laying it. The cable was laid by a special boat and an underwater robot which digs a trench as soon as the seabed is less than 1,000 meters deep and buries the cable as soon as it is laid in the trench.

According to Emmanuel Blanc, the vice-president of Alcatel- Submarcom, there is extraordinary technological competition in a market which he describes as explosive. Indeed, the cable network, which is already extensive, will supply all homes. So the 200 television channels, the portable computer and the pocket telephone are on the doorstep, as well as the possibility of working a at a high level and in real time with all the places on earth.

-- AFI