Fast Ethernet. However, to maintain a 200-m collision diameter for half-duplex operations, the min- imum CSMA/CD carrier time and Ethernet slot time were extended from 64 to 512 bytes. The extension occurs through the use of carrier extension symbols as shown in Figure 5.13. In examining this figure, note that the minimum Gigabit Ethernet frame length is still 64 bytes, which maintains interoperability with Ethernet and Fast Ethernet. Because the Ethernet slot time is extended from 64 to 512 bytes, half- duplex Gigabit is ill-suited for transmitting queries, which typically are Chapter Five short in nature. This is because Gigabit Ethernet will first insert pads to form a minimum 46-byte data field in the same manner that Ethernet and Fast Ethernet operate. However, Gigabit Ethernet will then extend the frame via carrier extensions to 512 bytes. Thus, the transmission of a 10-byte query would first result in the addition of 36 pads to a relatively short frame to form a minimum 64-byte frame. Then, 448 carrier exten- sion bytes would be added. When you consider the fact that each ver- sion of Ethernet has 26 bytes of overhead, this means that the transmis- sion of a 10-byte query would require 510 bytes. This also explains why a shared media Gigabit Ethernet network may provide a transmission capacity only marginally above that of Fast Ethernet when most of the transmission carries interactive queries. Now that we are beginning to understand why full-duplex Gigabit Ethernet can provide a significant throughput above the shared media version of this technology, let's con- sider the technology in a network. Network Utilization The primary use of Gigabit Ethernet is in a switched LAN environment, where the switch contains either a mixture of Gigabit Ethernet ports and other types of Ethernet and/or Fast Ethernet ports or Gigabit Eth- ernet ports only. Figure 5.14 illustrates the use of Gigabit Ethernet in a tiered network switch environment. In this networking environment several Ethernet/Fast Ethernet switches are u