The simplest signal flow technique is the simplex configuration. In Simplex transmission, one of the communicating devices can only send data, whereas the other can only receive it. Here, communication is only in one direction (unidirectional) where one party is the transmitter and the other is the receiver. Examples of simplex communication are simple radio, and Public broadcast television where you can receive data from stations but can’t transmit data back. The television station sends out electromagnetic signals. The station does not expect and does not monitor for a return signal from the television set. This type of channel design is easy and inexpensive to set up.
Half duplex refers to two-way communication where only one party can transmit data at a time. Unlike, the Simplex mode here, both devices can share data though, not at the same time, that is Half duplex provides Simplex communication in both directions in a single channel. When one device is sending data, the other device must only receive it and vice versa. Thus, both sides take turns sending data. This requires a definite turnaround time during which the device changes from receiving to transmitting mode. Due to this delay, half-duplex communication is slower than simplex communication. However, it is more convenient than simplex communication as both devices can send and receive data. For example, a walkie-talkie is a half-duplex device because only one party can talk at a time.
A full duplex refers to the transmission of data in two directions simultaneously. Here, both devices are capable of sending as well as receiving data at the same time. Sharing the same channel and moving signals in both directions increases the channel throughput without increasing bandwidth. For example, a telephone is a full-duplex device because both parties can talk to each other simultaneously.