ts Ethernet frames just as they are but at higher data rate. The Gigabit Ethernet may operate in full-duplex mode, that is, two nodes connected via a switch can simultaneously receive and transmit data at 1 Gbps. In half-duplex mode it uses the same CSMA/CD access method principle as the lower rate networks. The Gigabit Ethernet CSMA/CD method has been enhanced in order to maintain a 200-m collision diameter at gigabit speeds. Without this enhancement, minimum-size Ethernet frames could complete transmission before the transmitting station senses the collision, thereby violating the CSMA/CD method. Note that the duration of a frame is now only 1% of that at the 10-Mbps data rate. To resolve this issue, both minimum CDMA/CD carrier time and the Ethernet slot time have been extended from 64 to 512 bytes. The minimum frame length, 64 bytes, is not affected but frames shorter than 512 bytes have an extra carrier extension. This so-called packet bursting affects small-packet performance but it allows servers, switches, and other devices to send bursts of small packets or frames to fully utilize available bandwidth. Devices that operate in full-duplex mode are not subject to the carrier extension, slot time extension, or packet bursting changes because there are no collisions. Many transmission media have been considered for Gigabit Ethernet including multimode and single-mode optical fiber and category 5 twisted pair. 6.5.11 Upgrade Path of the Ethernet Network As we have seen, the Gigabit Ethernet offers a smooth transition for an LAN to higher bit rates where they are needed. Often a greater bandwidth is first needed between routers, switches, hubs, repeaters, and servers. Figure 6.35 shows an example of how different Ethernet technologies could be used in the same network. In the example, we originally had a 10BaseT network in which the workstations were connected to repeaters or hubs. As capacity demand increased, repeaters were upgraded to switches at the same data rate or repeaters or switches at 100 Mbps. If 10