ional infrastructure VARIATIONS Similar to proprietary versions of Ethernet and Fast Ethernet, there are nonstandardized versions of Gigabit Ethernet. Those nonstandardized versions use 850- and 1300-nm lasers; however, the use of high-bandwidth fiber enables support for transmission distances beyond those noted in Table 5.4. Through the use of fiber that has a bandwidth of up to 1000 MHz/km, it becomes possible to transmit at distances as great as 1300 m under 1000BASE-LX and 625 m under 1000BASE-SX. Fig- ure 5.12 provides a more realistic indication of transmission distance ver- sus fiber bandwidth when 62.5/125 multimode fiber is used. Duplex Support Gigabit Ethernet was developed for switched as well as shared media operational environments. Full-duplex operation is considered to repre- sent the preferred mode of operation as it eliminates the possibility of collisions and thus is relatively simple to implement. Full-duplex Gigabit Fiber in the LAN Figure 5.12 Gigabit Ethernet transmission distance. 1000BASE-LX Transmission Distance (Meters) Fiber bandwidth (MHz/km) Ethernet permits simultaneous transmission and reception, permitting a theoretical total of 2 Gbits/s of bandwidth on the same connection. Full-duplex is restricted to a point-to-point networking environment, usually linking hubs together or a hub port to a server. The term "theo- retical" is used as a prefix to full-duplex Gigabit Ethernet providing a total of 2 Gbits/s of bandwidth on a connection because of the manner of operation of different devices. For example, if you connect a server to a hub port, the ability to transmit and receive at the same time depends on the activity of workstations accessing the server and the server's response to the queries. Thus, although a maximum data transfer of 2 Gbits/s is possible, it is highly probable that the actual data transfer rate will be considerably below the theoretical data transfer rate. In a half-duplex operating environment, Gigabit Ethernet uses the CSMA/CD protocol, similar to Ethernet and 