Data communications can be carried from one location to another through a variety of communications channels. These communications media include telephone lines (twisted pairs), coaxial cable, fiber-optic cable, microwave, and satellite. In general, there can be two ways of connecting microcomputers with each other and with other equipment: guided and radiated media.

• Guided Media: Refer to channels that allow the transmission of data and information through a physical media such as a twisted pair wire, coaxial cable, or fiber optic cable.

• Radiated media: Refer to those that transmit data and information through the air such as microwave, or satellite.

Twisted Pair

The telephone lines used to carry most of the voice and data communications consist of a pair of thin-diameter insulated copper wires (called twisted pairs). The wires are twisted around each other to minimize interference from other twisted pairs in the cable. Twisted pairs have fewer bandwidth than coaxial cable or optical fiber. They have been the standard communication channels for voice, data and information, but are now diminishing because of more reliable media such as coaxial cable, optical fibers, microwave, or satellite.

Coaxial cable can be used for telephone lines for transmission at a high frequency. Coaxial cable consists of a single core of solid copper. A coaxial cable can handle 80 times as many telephone transmissions as twisted pair media. Many computers in local area networks are linked by coaxial cables. Because of its sturdiness, coaxial cable is often used for telephone lines that must be carried under bodies of water. Because coaxial cables have very little distortion and are less prone to interference, they have low error rates.

A fiber-optic cable consists of tubes of glass through which data are transmitted as pulses of light. Although a fiber- optic cable is diametrically smaller than a human hair, it has 26,000 times the transmission capacity of twisted pair media. A major advantage of fiber-optic media is its high level of security. These communications channels are not susceptible to electronic interference. Therefore, they are a more reliable form of data transmission. Fiber-optic cables are also significantly less expensive than coaxial cable. A disadvantage of fiber-optic channels is that they cannot carry information over great distances.

Microwave data transmission differs from the previously mentioned communications channels in that data is transmitted through the air instead of through cables or wires. Microwaves are high-frequency radio waves that can only be directed in straight lines. Consequently, microwave transmission is usually limited to communications occurring within the limits of a particular city or community. For microwave transmissions to be able to occur over larger distances, data messages must be relayed from one location to another using antennas placed at high altitudes usually twenty to thirty miles apart.

Instead of antennas, satellites can also be used to transfer microwave messages from one location to another. Satellites rotate approximately 23,300 miles above the earth in precise locations. Satellite transmission stations that can both send and receive messages are known as earth stations. A major advantage of satellite transmission is that large volumes of data can be communicated at once. A particular drawback of several disadvantages is bad weather can severely affect the quality of satellite transmissions. Another one is that it has a serious security problem, because it is easy to intercept the transmission as it travels through the air.

Bandwidth

Refers to transmission capacity of a communications channel. It is the difference between the lowest and highest frequencies transmitted. It is expressed in cycles per second (Hertz).

Data Transmission/Bandwidth

Satellite

Many of these are offered by Intelsat, the International Telecommunications Satellite Consortium, which is owned by 114 governments and forms a worldwide communications system.

Tips

In late 1994, RCA introduced a direct broadcast satellite (DBS) system that enables homeowners or businesses to install 18-inch KU-band VSATs to receive satellite broadcasts for about $700. DBS lets owners receive more than 150 TV channels of higher quality video and audio than traditional cable TV. The real potential for DBS lies not only in the replacement of cable TV, but with the coming integration of video, voice, and data, as another high speed circuit into the home and office.

Ku-band

Ku-band satellites use very short waves that can be caught and concentrated in much smaller dish antennas, called VSAT (Very Small Aperture Terminal), which can be installed on virtually any buildings (or vehicles).