Telephone Circuit Paths

Voices and sounds are converted into electrical signals that are carried by many different kinds of cables and wireless transmissions. These routes are called transmission paths, and they play a role in carrying those electrical signals accurately to faraway places. Transmission paths may be wires in cables or telephone lines, or they may be wireless paths that carry transmissions through the air.

Shockwave

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Wire Transmission Paths (Cables) Balanced-Pair Cable The most basic type of copper cable, used for phone lines connecting normal households and offices to NTT.

Coaxial Cable A type of copper cable capable of carrying as many as 10,000 conversations, and used for relay connections between large and medium-sized cities. However, the signals it carries are too weak for long distances, so that amplifiers must be placed along the way to boost the signal.

Optical Fiber Cable A thin cable approximately 0.125mm in diameter (about the size of a human hair), made from silicon glass fiber. One strand can carry more than 100,000 conversations. Because the glass material acts as an insulator, this type of cable will not lose its signal by coming into contact with other cables.

The Principle of the Optical Fiber Cable The optical fiber cable conducts signals of light which are reflected repeatedly within the fiber as they travel, due to differences in the index of refraction of its materials. Each optical fiber cable is divided into two layers of glass with different indices of refraction, the outer layer referred to as the cladding and the inner layer as the core. And because the core has a higher index of refraction than the cladding, light passing through the core is reflected back from the interface with the cladding and is thereby prevented from escaping.

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Wireless Transmission Paths Microwave Communication Microwaves, low-power signals with very short wavelengths, are relayed while strengthened between dish-shaped parabolic antennas in places like the tops of NTT buildings and mountains.

Satellite Communication Signals are also relayed by satellites launched into positions 36,000 km above the Earth's equator. This system can reach receivers placed anywhere on Earth, so it is particularly useful for reaching remote islands and during disasters when cables have been broken.

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