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12/31/13

The Internet and Physical Communication Media.

The Internet infrastructure consists both of hardware and software.

Hardware part of infrastructure consists also of physical medium. The physical medium can take many shapes & forms and does not have to be the same type for each transmitter-receiver pair along the path. Examples of physical media include twisted-pair copper wire, coaxial cable, multimode fiber-optic cable, terrestrial radio spectrum, and satellite radio spectrum.

Physical media fall into two categories: guided media and unguided media. With guided media, the waves are guided along a solid medium, such as fiber-optic cable, a tristed-pair copper wire, or a coaxial cable. With unguided media, the waves propagate in the atmosphere and in outer space, such as in a wireless LAN or a digital satellite channel.

Twisted-Pair Copper Wire.

The least expensive and most commonly used guided transmission medium is twisted-pair copper wire. Twisted pair consists of two insulated copper wires, each about 1 mm thick, arranged in a regular spiral pattern. When fiber-optic technology emerged in the 1980's, many people disparaged twisted pair because of its relatively low bit rates (speed), but twisted-pair was modernized for speed and did not give up so easily.

Coaxial Cable.

Like twisted pair, coaxial cable consists of two copper conductors, but the two conductors are concentric rather than parallel. With this construction and special insulation and shielding coaxial cable can have high bit rates. Coaxial cable can be used as a guided shared medium. Specifically, a number of internet devices can be connected directly to the cable, with each receiving whatever is sent by the other internet devices.

Fiber Optics.

An optical fiber is a thin, flexible medium that conducts pulses of light, with each pulse representing a bit (unit of information, 0 or 1). A single optical fiber can support tremendous bit rates (speed), up to tens or even hundreds of gigabits per second. They are immune to electromagnetic interference, have very low signal attenuation up to 100 kilometers, and are very hard to tap. These characteristics have made fiber optics the preferred long-haul guided transmission media, particularly for overseas links.

Terrestial Radio Channels.

Radio channels carry signals in the electromagnetic spectrum. They are attractive medium because they require no physical wire to be installed, can penetrate walls, provide connectivity to mobile user, and can potentially carry a signal for long distances. Environmental considerations determine path loss and shadow fading (which decrease the signal strength as the signal travels over a distance and around/through obstructing objects) and interference (due to other transmissions and electromagnetic signals).

Satellite Radio Channels.

A communication satellite links two or more Earth-based microwave transmitter/receivers, known as ground stations. Two types of satellites are used in communications: geostationary satellites and low-earth orbiting (LEO) satellites. Geostationary satellites permanently remain above the same spot on Earth. LEO satellites are placed much closer to Earth and do not remain permanently above one spot on Earth. They rotate around Earth (just as the Moon does) and may communicate with each other, as well as with ground stations.

Quantum Networks.

Quantum networks descend from the study of Quantum cryptography. The idea of a quantum network emerged after successful experiments on quantum teleportation. When two companies (one from Switzerland, 'idQuantique', and another from the USA, 'MagiQTech') released practical communication devices based upon the rules of quantum mechanics, the need for a secure network capable of utilizing quantum principles was realized. These networks are now known as quantum communication networks. In these networks, data are communicated as quantum states through the technique of entanglement via an optical fiber link.

Source: [3], Wikipedia.

Speed.

The speed at which information arrives at destination depends on the route it goes with (length of route, information splitting and joining to send simultaneously via multiple links, speeds of each of partial links [slow links form bottlenecks], transmission errors).

Internet as an idea.

Internet is also idea, in theory even human couriers may carry information (whole or part) from point A to B, and be part of the Internet physical medium links, and so on. If/when sending part of information, for example for security purposes (encrypted information without parts is often much harder to attack), i'd give the 'package' to someone who can do it well: martial artist or soldier, or spy, or appropriate security personnel, depending on the situation.

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