Data communications lines can be connected in two typesof configurations: point to-point and multidrop. A point-to-point line directlyconnects the sending and the receiving devices, and a multidrop line connectsmany devices, not just one sending device and one receiving device.

The two ways of connecting microcomputers with each otherand with other equipments are through the cable and through the air. There arethree basic forms into which data can be converted for communication:electrical pulses or charges, electromagnetic waves, and pulses of light.

Specifically, five kinds of technology are used totransmit data. These are telephone lines (twisted pair),coaxial cable,fiber-optic cable, microwave, and satellite.

Telephone Lines：Inexpensive,multiple-conductor cable comprised of one or more pairs of 18 to 24 gaugecopper strands. The strands are twisted to improve protection against electromagneticand radio frequency interference. The cable, which may be either shielded or unshielded,is used in low-speed communications, as telephone cable. It is used only inbaseband networks because of its narrow bandwidth. Most telephone lines you seestrung on poles consist of cables made up of hundreds of copper wires aretwisted pairs. Twisted pairs are susceptible to a variety of types ofelectrical interference (noise), which limits the practical distance that datacan be transmitted without being garbled. Twisted pairs have been used foryears for voice and data transmission, however they are now being phased out bymore technically advanced and reliable media.

Coaxial Cable：Coaxial cableis a type of thickly insulated copper wire that can carry a larger volume ofdata—about 100 million bits per second, the insulation is composed of a nonconductivematerial covered by a layer of woven wire mesh and heavy-duty rubber orplastic. In terms of number of telephone connections, a coaxial cable has 80times the transmission capacity of twisted pair. Coaxial cables are most oftenused as the primary communications medium for local connected network in whichall computer communication is within a limited geographic area, such as in thesame building.

Coaxial cable is also used for undersea telephone lines.

Fiber-Optic Cable：A transmissionmedium composed of a central glass optical fiber cable surrounded by claddingand an outer protective sheath. It transmits digital signals in the form ofmodulated light from a laser or LED (light-emitting diode). In fiber-opticcable, data is transmitted as pulses of light through tubes of glass. In termsof number of telephone connections, fiber-optic cable has 20,000 times the transmissioncapacity of twisted pair. However, it is significantly smaller. Indeed, afiber-optic tube can be half the diameter of a human hair. Although limited inthe distance they can carry information, fiber-optic cables have several advantages.Such cables are immune to electronic interference, which makes them moresecure. They are also lighter and less expensive than coaxial cable and aremore reliable at transmitting data. They transmit information using beams oflight at light speeds instead of pulses of electricity, making them far fasterthan copper cable. Fiber-optic cable is rapidly replacing twisted-pairtelephone lines.

Microwave：Instead ofusing wire or cables, microwave systems can use the atmosphere as the mediumthrough which to transmit signals. Microwaves are high-frequency radio wavesthat travel in straight lines through the air. Because the waves cannot bendwith the curvature of the earth, they can be transmitted only over shortdistances. Thus, microwave is a good medium for sending data between buildingsin a city or on a large college campus. For longer distances, the waves must berelayed by means of "dishes", or antennas. These can be installed ontowers, high buildings, and mountaintops. Each tower facility receivesincoming traffic, boosts the signal strength, and sends the signal to the nextstation.

Satellites：Satellitecommunications refers to the utilization of geostationary orbiting satellitesto relay the transmission received from one earth station to one or more earthstations. They are the outcome of research in the area of communications whoseobjective is to achieve ever-increasing ranges and capacities with the lowestpossible costs. Orbiting about 22,000 miles above the earth, satellites rotateat a precise point and speed above the earth. This makes them appear stationaryso they can amplify and relay microwave signals from one transmitter on the groundto another. The primary advantage of satellite communication is the amount ofarea that can be covered by a single satellite. It also has other features:long communication distance, and the cost of station building is independent ofthe communication distance, operating in broadcasting mode, easy for multipleaccess, sustaining heavy traffic, able to transport different types of service,independent sending and receiving, and monitoring. Three satellites placed inparticular orbits can cover the entire surface of the earth, with some overlap.Their only drawback is that bad weather can sometimes interrupt the flow ofdata.