You Are Connected—How?

BY AWAKE! WRITER IN JAPAN

IN Japan, a land with about as many telephones as people, over 300 million phone connections are made each day. Japan also receives some one million international calls daily, and about the same number of overseas phone calls are made.

Likely, you too use the telephone—be it ordinary (fixed line) or cellular—almost every day. As the world becomes more modernized, calling someone on another continent has become a routine matter for many people. But have you ever wondered how your telephone is connected to the telephone of the party you are calling?

Connected Through a Telephone Network

First of all, your telephone needs to be hooked in to a telephone network. If you were to trace the wire attached to an ordinary telephone, it would lead you to a modular jack or a junction box, which is connected to the wiring in your house. * If you were to continue to trace farther, you would find that this line is linked to a cable, on an electric pole or under the ground, that goes to a telephone exchange in a local telephone office. This exchange, in turn, is connected to a bigger exchange, thus forming a telephone network. So when you call a friend in the same town, a voice circuit is formed between your telephone and your friend’s through a network.

What happens in the case of cellular phones? How are they connected? Here, too, the principle remains the same as with the ordinary telephone. An invisible “wire,” namely a radio wave, links your cellular phone to a nearby mobile telephone switching office that is connected to a telephone network. But what about when you talk to someone on another continent?

Cables Across the Oceans

Connecting by cable two continents separated by an ocean is a gigantic project. This requires installing a cable thousands of miles long under the sea and crossing undersea trenches and mountains. Yet, this is how intercontinental telecommunication had its start. The very first transatlantic underwater telephone cable was completed in 1956. * It linked Scotland to Newfoundland and carried 36 telephone circuits. In 1964 the first transpacific cable was laid between Japan and Hawaii. That cable carried 128 telephone circuits. A number of other undersea cables followed, linking continents and islands.

What types of cables are laid across the ocean floor for phone connections? Initially, coaxial cables with copper as conducting wire and copper or aluminum foil as conducting shell were commonly used. One of the last coaxial cables was laid in 1976, and it had the capacity to carry up to 4,200  voice circuits. However, in the 1980’s fiber-optic cable became available. The first intercontinental cable of this type, installed in 1988, was capable of carrying 40,000 telephone conversations concurrently, using digital technology. The capacity of cables has been increased since then. Some cables spanning the Atlantic Ocean can carry 200 million telephone circuits!

How are telecommunication cables placed underwater? They are actually placed on the ocean floor and follow the seabed. Near the shore, the cable is housed in a solid casing placed in a trench that is dug by a remotely operated vehicle. The housing protects the cable from damage by anchors or fishing nets. So when you call up your friend on another continent, one of these cables may carry your voice across the deep sea.

Invisible Cables Tie Distant Places Together

Yet, an underwater cable is not the only means to connect continents and islands. An invisible “wire”—a radio wave—is also commonly used. This type of wave, also called a microwave, ties distant places together for international telecommunications. Since a microwave travels in a straight line like a narrow beam of light, it can only link line-of-sight locations that are in its path. Because of the curvature of the earth’s surface, locations on the opposite side of the globe cannot be linked directly. To link such distant places requires satellite communication.

If a satellite is placed above the equator at an altitude of about 22,000 miles [35,800 km], in what is known as a geostationary orbit, its revolution around the earth is approximately 24 hours—the same as the earth’s rotation. Hence, it remains above virtually the same region of the earth. Since this satellite can see a region that covers one third of the earth, earth stations—locations that transmit and receive microwaves—in this region can communicate with the satellite. How, then, can two distant locations be connected to each other via a satellite?

An earth station under the coverage of a satellite transmits a microwave signal to the satellite. This is called an uplink. Receiving the wave, a radio repeater, or a transponder, mounted on the satellite simply shifts the frequency lower and retransmits it so that it can be picked up by another earth station. This is called a downlink. In this way, two earth stations that cannot directly communicate with each other can be linked by an invisible wire via satellite.

The first commercial communications satellite, INTELSAT 1, also known as Early Bird, was launched in 1965. Now about 200 communications satellites, most of them geostationary, are in operation, connecting places all over the world. These satellites are used not only for  international telecommunication but also for television broadcasting, weather observation, and other purposes. Carrying many transponders, such satellites can provide multichannel circuits. For instance, the Early Bird was capable of relaying either one television circuit or 240 simultaneous telephone circuits. The INTELSAT VIII series, which has been in operation since 1997, can provide three television broadcasts and a maximum of 112,500 telephone circuits simultaneously.

Can You Tell?

All these changes have brought the price of international telephone calls down drastically. Perhaps you are now able to talk more often to your friends or family members on another continent. How can you tell whether you are connected by an underwater cable or a satellite link?

With a satellite link, the length of the invisible wire (which includes the uplink and the downlink) reaches some 44,000 miles [70,000 km]. That is nearly equal to twice the distance around the earth. Even though microwaves travel as fast as a flash of light, the time it takes for them to cover the distance from one earth station to another via a satellite is nearly one fourth of a second. This means that your voice reaches the other person one fourth of a second later, and the same is true of the opposite direction. Thus, there is a time lag of half a second. Not being accustomed to this delay in everyday conversation, you may find yourself talking at the same time as the other person. If you have experienced this, it may be an indication that you are speaking over a satellite link. However, when you call the same number another time, you may not notice any time lag. This may be because you are now linked through an underwater fiber-optic cable. The choice of how to connect you to the other part of the world is made behind the scenes by an intricate telephone network.

The expertise and labors of many are needed to maintain the complex telephone network system of underwater cables, earth stations, and satellites that provides us with the convenience of communication. So the next time you make a phone call to a friend, why not think of all that has been done to connect you?

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RADIO WAVES

Uplink

Downlink

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UNDERSEA CABLES

Cellular phone

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Modern fiber-optic cables can carry 200 million telephone circuits

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INTELSAT VI being worked on by the Space Shuttle crew

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NASA photo

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Ships lay the cables and maintain them

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Courtesy TyCom Ltd.