zes Fast Ethernet cabling restrictions based on direct connection and use of different repeaters and media. Other Extenders The IEEE 802.3u Fast Ethernet standard addresses only half-duplex com- munications. Because it is possible to transmit in a full-duplex mode from a workstation to a switch port, several vendors introduced nonstan- dardized 100BASE-FX extenders that use both multimode and single- mode fiber in a full-duplex transmission environment. Table 5.3 summa- rizes the cable distance achievable for 100BASE-TX as well as half- and full-duplex versions of 100BASE-FX, with the latter, as mentioned earlier, not officially contained in the IEEE 802.3 Fast Ethernet standard. Fiber in the LAN Direct connection without using repeaters Figure 5.11 (TX = 100 m, TX & FX = NA, FX = 412 m) Fast Ethernet dis- tance limitations. One Class I repeater (TX=200m, TX & FX = 260.8 m, FX = 272 m) Class I Repeater One Class II repeater (TX=200m, TX & FX = 308.8 m, FX = 320 m) Class II Repeater d. Two Class II repeaters (TX=205 m, TX & FX = 223 m, FX = 228 m) Class II Class II Repeater Repeater TABLE' 5.3 Standard 100BASE-TX 100BASE-FX 100BASE-FX 100BASE-FX 100BASE-FX Permissible Fast Ethernet Media Category 5 Multimode Single-mode Multimode Single-mode full- Cabling Dis- copper half-duplex half-duplex full-duplex duplex tances Distance, m 100 One of the more interesting aspects of the cabling distance achievable with Ethernet and Fast Ethernet extenders is obtained by full-duplex transmission. As indicated in Table 5.3, multimode optical fiber full- duplex transmission permits a cabling distance of up to 300,000 m, while the faster pulse of a laser used with single-mode fiber extends cabling distance to 20,000 m. This makes it possible to connect Ethernet and Fast Ethernet LANs directly to a communication carrier's central office at the LAN operating rate. This also means that it becomes possible to transmit Ethernet and Fast Ethernet at their operating rates, assuming that the applicable fiber is installed to the carrier, e