Full-Duplex Ethernet

Full-Duplex Ethernet

In the party line scenario, congestion occurs when more than two people attempt to talk at the same time. When only two people are talking, or only two devices, virtually all the bandwidth is available. In cases where only two devices need to communicate, Ethernet can be configured to operate in full-duplex mode as opposed to the normal half-duplex operation. Full-duplex operation allows a network device to "talk" or transmit and "listen" or receive at the same time. (See Figure 1-5.)

Because Ethernet is based on CSMA/CD, full-duplex devices either need to be directly connected to each other or be connected to a device that allows full-duplex operation (such as a LAN switch). Ethernet hubs do not allow full-duplex operation, as they are only physical layer (Layer 1) signal repeaters for the logical bus (Layer 2). Ethernet still operates as a logical bus under full duplex.