The data that is transmitted over the network can flow using one of three modes: simplex, half-duplex, or full-duplex.
Simplex, also called unidirectional, is a single, one-way transmission. An example of simplex transmission is the signal that is sent from a TV station to your home TV.
When data flows in one direction at a time it is known as half-duplex, as shown in the figure. With half-duplex, the channel of communications allows alternating transmission in two directions, but not in both directions simultaneously. Two-way radios, such as police or emergency communications mobile radios, work with half-duplex transmissions. When you press the button on the microphone to transmit, you cannot hear the person on the other end. If people at both ends try to talk at the same time, neither transmission gets through.
When data flows in both directions at the same time it is known as full-duplex, as shown in the figure. Although the data flows in both directions, the bandwidth is measured in only one direction. A network cable with 100 Mb/s in full-duplex mode has a bandwidth of 100 Mb/s.
A telephone conversation is an example of full-duplex communication. Both people can talk and be heard at the same time.
Full-duplex networking technology increases network performance because data can be sent and received at the same time. Broadband technologies, such as digital subscriber line (DSL) and cable, operate in full-duplex mode. Broadband technology allows multiple signals to travel on the same wire simultaneously. With a DSL connection, for example, users can download data to the computer and talk on the telephone at the same time.