TAILIEUCHUNG - CCNA 1 and 2 Companion Guide, Revised (Cisco Networking Academy Program) part 17

Cisco Networking Academy Program CCNA 1 and 2 Companion Guide, Revised part 17 is the Cisco approved textbook to use alongside version of the Cisco Networking Academy Program CCNA 1 and CCNA 2 web-based courses. The topics covered provide you with the necessary knowledge to begin your preparation for the CCNA certification exam (640-801, or 640-821 and 640-811) and to enter the field of network administration. | Page 129 Tuesday May 20 2003 2 53 PM Copper Media 129 When working with cable consider its size. As the diameter of the cable increases so does the difficulty in working with it because cable must be pulled through existing conduits that are limited in size. Coaxial cable comes in several sizes. The largest diameter 1 cm was once specified for use as Ethernet backbone cable because it had a greater transmission length and better noise rejection characteristics than other types of cable. This type of coaxial cable is frequently referred to as thicknet as shown in Figure 3-11. As its nickname suggests thicknet cable can be too rigid to install easily in some situations because of its thickness. The general rule is that the more difficult the network medium is to install the more expensive it is to install. Coaxial cable is more expensive to install than twisted-pair cable. Thicknet cable is almost never used except for special-purpose installations. Figure 3-11 Coaxial Cable Thicknet Coaxial cable with a diameter of cm sometimes referred to as thinnet was also frequently used in Ethernet networks at one time. Thinnet as shown in Figure 3-12 was especially useful for cable installations that required the cable to make many twists and turns. Because it was easier to install it was also cheaper to install. Thus it was sometimes referred to as Cheapernet. Figure 3-12 Coaxial Cable Thinnet Page 130 Tuesday May 20 2003 2 53 PM 130 Chapter 3 Networking Media However in both types of coaxial cable the outer conductor must be carefully and properly grounded which increases the complexity of the installation. It is for this reason that despite its advantages coaxial cable is no longer commonly used in Ethernet networks. Although many bus topology networks still utilize coaxial cable in use throughout the world the IEEE no longer recommends this cable or topology as a standard for use with Ethernet. Nearly all new LANs use Ethernet extended star .

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