work structure. Later in this section, we review the structure and operation of the twisted-pair and higher-data-rate variations of Ethernet. 6.5.3 CSMA/CD Network Structure For collision detection it is essential to define the maximum delay of the net- work SO that a station can be sure that transmission has been successful or collision has occurred (during transmission). In the case of a coaxial network, each cable segment is terminated by a 50-S resistor at both ends to avoid reflections. The maximum length of the cable segments and number of workstations (or transceivers) connected to each segment are specified. Thick coaxial cable (10Base5) specifications allow for a maximum section length of Data Communications 500m and the maximum number of workstations in one segment is 100. A thin coaxial cable (10Base2) network allows a maximum section length of 185m and the maximum number of workstations in one segment is 30. Thick coaxial cable was typically used in a backbone network that interconnects thin coaxial cable segments into which workstations are connected. If the network is longer than one cable segment, repeaters may be used to regenerate attenuated signals. Repeaters are physical layer devices that retransmit signals in both directions. Logically the network remains a single physical network in which all frames are transmitted to every cable segment (see Figure 6.26). Collision detection requires that the maximum delay not exceed a cer- tain value and this restricts how many cable segments can be connected with repeaters. The definition states that the maximum number of repeaters in a 10-Mbps network between workstations is four and two of the segments between have to be link segments, which have no workstations. If further extension to the network is needed, bridges or switches can be used. The physical size is then no longer a limitation because physical net- works are now isolated from each other by a MAC layer device. It stores and forwards frames according their MAC layer addresses and acts as a se