Technical Telecommunications Alternatives

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Telecommunications is a highly technical, rapidly changing field of information systems technology.

Most end users do not need a detailed knowledge of its technical characteristics. However, it is important that you understand some of the important characteristics of the basic components of telecommunications networks.

This understanding will help you participate effectively in decision making regarding telecommunications alternatives. Telecommunications Media Telecommunications channels (also called communications lines or links) are the means by which data and other forms of communications are transmitted between the sending and receiving devices in a telecommunications network.

A telecommunications channel makes use of a variety of telecommunications media. These include twisted-pair wire, coaxial cables, and fiber optic cables, all of which physically link the devices in a network. Also included are terrestrial microwave, communications satellites, cellular and LAN radio, all of which use microwave and other radio waves, and infrared systems, which use infrared light to transmit and receive ...
... data.

Fiber Optics. Fiber optics uses cables consisting of one or more hair-thin filaments of glass fiber wrapped in a protective jacket. They can conduct light pulses generated by lasers at transmission rates as high as 30 billion bits per second.

This is about 60 times greater than coaxial cable and 3, 000 times better than twisted pair wire lines. Fiber optic cables provide substantial size and weight reductions as well as increased speed and greater carrying capacity.

A half-inch-diameter fiber optic cable can carry up to 50, 000 channels, compared to about 5, 500 channels for a standard coaxial cable.

Fiber optic cables are not affected by and do not generate electromagnetic radiation; therefore, multiple fibers can be placed in the same cable. Fiber optic cables have a minimal need for repeaters for signal retransmissions, unlike electrical wire media.

Fiber optics also has a much lower data error rate than other media and is harder to tap than electrical wire and cable. The biggest disadvantage of fiber optics has been the difficulty of splicing the cable to make connections, though this is also a security advantage that limits line tapping. However, new splicing techniques have made it easier to splice fiber cables.

Fiber optic cables have already been installed in many pans of the United States, and they are expected to replace other communications media in many applications in the near future.

Terrestrial Microwave. Terrestrial microwave involves earthbound microwave systems which transmit high-speed radio signals in a line-of-sight path between relay stations spaced approximately 30 miles apart.

Microwave antennas are usually placed on top of buildings, towers, hills, and mountain peaks, and they are a familiar sight in many sections of the country. They are still a popular medium for both long-distance and metropolitan area networks.

Communications Satellites. An important telecommunications medium is the use of communications satellites for microwave transmission. There are several dozen communications satellites from several nations placed into stationary geosynchronous orbits approximately 22,000 miles above the equator.

Satellites are powered by solar panels and can transmit microwave signals at a rate of several hundred million bits per second. They serve as relay stations for communication signals transmitted from earth stations.

Earth stations use dish antennas to beam microwave signals to the satellites, which amplify and retransmit the signals to other earth stations thousands of miles away.

While communications satellites were used initially for voice and video transmission, they are now also used for high-speed transmission of large volumes of data.

Because of time delays caused by the great distances involved, they are not suitable for interactive, real-time processing. Many large corporations and other users have developed networks of small satellite dish antennas known as VSAT (very small aperture terminal) to connect their distant work areas.

These satellite networks are also called bypass networks because firms are bypassing the regular communications networks provided by communications carriers.

Cellular Radio. Cellular radio is a radio communications technology that divides a metropolitan area into a honeycomb of cells. This greatly increases the number of frequencies and users that can take advantage of mobile phone service.

Each cell has its own low power transmitter, rather than having one high-powered radio transmitter to serve an entire city. This significantly increases the number of radio frequencies available for mobile phone service.

However, this technology requires a central computer and other communications equipment to coordinate and control the transmissions of thousands of mobile phone users as they drive from one cell to another. Cellular radio has become an important communications medium for mobile voice and data communications.

Wireless LANs. LAN radio uses radio transmissions to interconnect LAN components. LAN radio may involve a high-frequency radio technology similar to cellular radio, or a low-frequency radio technology called spread spectrum. The other wireless LAN technology is called infrared, because it uses beams of infrared light to establish network links between LAN components.

Obviously, a wireless LAN eliminates or greatly reduces the need for wires and cables, thus making a LAN easier to set up, relocate, and maintain. However, current wireless technologies have higher initial costs and other limitations.

For example, an infrared LAN transmits faster than radio LANs but is limited to line-of-sight arrangements to a maximum of about 80 feet between components.

High-frequency radio LANs do not need line-of-sight links, but are limited to 40 to 70 feet between components in enclosed areas. Spread spectrum radio LANs can penetrate masonry walls and link components from 100 to 200 feet away in enclosed areas, but are more subject to receiving or generating radio interference. However, even with these limitations, the use of wireless LAN technologies is expected to increase significantly.

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