Copyright Goodheart-Willcox Co., Inc. 67 Chapter 2 Network Media—Copper-Core Cable In Figure 2-20B, the last character is a letter and represents the media type—in this case, twisted pair. Sometimes a classifi cation will have two characters at the end, such as VG in 100BaseVG or TX in 100BaseTX. In the case of 100BaseVG, the VG rep- resents voice grade. However, in 100BaseTX, the T represents twisted pair and the X represents Fast Ethernet, as demonstrated in Figure 2-20C. Th e name of a given classifi cation details quite a bit of information. Th e fi rst number (in this case 10) is the bandwidth in Mbps. Th e base refers to baseband (as opposed to broadband). Th e T tells you it is twisted-pair cable. For example, Category 5 cable would be 100BaseT. Th is is not only used for twisted-pair cable, but for other types of cable, such as coax. Th ree specifi c types are discussed in this section. 10Base2 Th e 10Base2 classifi cation specifi es the use of RG-58 (thinnet) cable and a data rate of 10 Mbps. Figure 2-21 illustrates the physical characteristics of a 10Base2 network. Note that a 10Base2 network is confi gured in a bus topology and that the maximum segment length is 185 meters. Th is means that the segment length cannot exceed 185 meters. If it does, the signal strength will deteriorate due to attenuation and im- pedance. Also, note that the minimum segment length between nodes is 0.5 meters. Terminating resistors are installed to absorb the electrical signals when they reach the end of the segment. If a terminating resistor is not installed, the signal will refl ect, causing the other signals transmitted across the cable to distort. Also, one end of the segment must be electrically grounded. Remember, a fl uctuating digital signal traveling along a cable’s core produces an electromagnetic wave, which can be absorbed by a neighboring conductor. In the case of a copper-core cable, the cable’s shielding absorbs the electromagnetic wave. Grounding one end of the cable helps to drain this interference so that the original signal is not aff ected. Remember, if there is a break in the cabling or a problem with a BNC connector or a terminating resistor, no communication will take place. Th is is a major reason why coaxial cable is no longer used in networking. 10Base2 10BaseT 100BaseTX Data rate A Transmission method Approximate maximum segment length Data rate B Transmission method Media type Data rate C Transmission method Media type IEEE 802.3 category Figure 2-20 Each IEEE 802.3 classification has an identifying name that reveals the classification’s data rate, transmission method, and either the approximate maximum segment length or media type. A—10Base2 means 10 Mbps, Baseband, with a maximum segment length of 200 meters. B—10BaseT means 10 Mbps, Baseband, using twisted-pair cable. C—100BaseTX means 10 Mbps, Baseband, using twisted-pair cable and the Fast Ethernet specification. Goodheart-Willcox Publisher