ired radially from a hub device or switch as illus- trated in Figure 6.31. This is done for two basic reasons: 1. Bus cabled networks are difficult to manage and maintain. Faults in a segment are not easy to locate because a cable break anywhere in the segment prevents all communication. Also, addition of a new workstation or relocation of old ones is difficult. 2. Use of UTP copper cable is preferred because it is low cost, easy to install, and in most buildings spare twisted pairs are already in place. Attenuation of twisted pair is high and it cannot be used in a bus topology network. The twisted pair CDMA/CD networks 10BaseT, 100BaseT, and 1000BaseT use twisted pairs to connect workstations to the wire concentra- tor, a hub. Twisted pair is easier and more flexible to install than coaxial cable and this has made 10BaseT very popular. In the simplest structure the concentrator or hub, which acts as a repeater, transmits frames from one workstation to all others as shown in Figure 6.31. The 10BaseT system operates over two pairs of wires, one pair for receiving signals and one pair for transmitting signals. Each pair is termi- nated at the receiver input by matched impedance SO that signal reflections Wire concentrator or hub that acts as a repeater frames at 10 Mbps 4W connection one pair for reception, one for transmission Max. 100m All computers belong to the same "collision domain." Figure 6.31 Twisted-pair shared media CDMA/CD. Data Communications are avoided. The maximum distance from workstation to hub is 100m for typical voice-grade twisted-pair cable. The hub contains electronics for signal reception, regeneration, and transmission. Note that logically the net- work in Figure 6.31 is still a bus in which all transmitted signals propagate to all other workstations. However, the major disadvantage of a physical bus is avoided because each workstation is separated from the bus by electronics and a break in one workstation's cabling does not disturb the operation of others. In Figure 6.31 the signal from o