Chapter three discusses mainly the two categories of communications media. The categories are physical or conducted media and radiated or wireless media. Later in the chapter, the section will explain the seven basic group of wireless media used for data transfer, which includes terrestrial microwave, satellite transmission, cell phone systems, broadband wireless distribution services, Bluetooth, wireless LAN, and various more.
Conducted Media:
There are three types of conducted media: twisted pair, coaxial cable, and fiber optic. Twisted pair "comes as two or more pairs of single-conductor copper wires that are twisted together." The twisting of the pairs of wires helps reduce the chances of crosstalk. Crosstalk is when a current or signal in one wire produces unwanted currents or signals in the second wire. This twisted pair comes in many different forms. To help categorize each form, the Category 1-7 (CAT 1-7) was created. Category 1 is used for standard telephone wires and has few to no twists. Category 2 twisted pairs are also used for telephone wires and some low-speed LANs. This category has some twist, which will help reduce noise. Category 3 pairs are designed to conduct 10Mbps of data over a LAN for distances up to 100 meters. A repeater can be used to extend this distance further than 100 meters. Category 4 was designed to transmit 20Mbps of data for the same distance as category 3. Category 5 was designed to transmit 100 Mbps for 100 meters as well. Category 6 was created to support signals at 250 MHz for 100 meters. Category 7 supports data transmissions up to 600 MHz. The second type of cable is the coaxial cable. Coaxial cable is a single wire wrapped in a foam insulation, surrounded by a braided metal shield and then covered in a plastic jacket. This cable is excellent for carrying analog signals with a wide range of frequencies. Therefore, it is good for video channels and cable tv. There are two major coaxial cable technologies which are baseband coaxial and broadband coaxial. Baseband coaxial transmits data using digital signals. Broadband coaxial transmits data using analog signals. Fiber-optic cable helps avoid electromagnetic interference completely. Fiber-optic cable is in a thin glass cable, surrounded by a plastic coating. The downfall for fiber-optic cable is that it can only transmit light pulses one way. Therefore, if you want to transmit pulses two, you need to cables. Fiber-optic cables are also expensive, so if you need two cables to transmit data back and forth, expect high expenses.
Wireless Media:
There are several different types of wireless media. However, all types of wireless media transmit data using radio waves. The types of wireless media include terrestrial microwave, satellite transmission, cell phone systems, broadband wireless distribution services, Bluetooth, wireless LAN, and various more. Terrestrial microwave transmits focused beams of radio signals from one antenna to another. Satellite microwave transmits beams of radio signals from an antenna to a satellite and then back down to a ground station. Broadband wireless systems transmit voice, data, and video over high radio frequencies. Bluetooth uses low-power and short-range radio frequencies to communicate between two or more devices. Wireless local area networks (WIFI) transmits data in the 2.4 GHz frequency range.
Media Selection Criteria:
This next section discusses the different criteria anyone should follow to select the best type of media. The criteria that will be discussed are costs, speeds, expandability and distance, environment, and security.
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