Simplex, Half Duplex, and Full Duplex Communications

Telecommunications and computer/device network communications can be broadly divided into three types: simplex, half duplex, and full duplex. The simplex communication means one-way communication. It’s like a one-way road. The communication can only be performed in one direction all the time. For example, communication between mouse and keyboard to computer (the mouse and keyboard always giving input to the computer) and communication between computer and traditional monitor (the computer always giving output to the monitor, in contrast to touch-screen monitor).

The half duplex (HDX), also called the semi-duplex, communication allows two-way communication but not at the same time. In other words, at a given time, only transmission in one direction is allowed. A well known example is walkie-talkie communication. That is why one needs to say “over” or “roger” or “another sign” to indicate that he/she is over and lets another party to speak.

The main advantage of the simplex and half duplex communications, despite their limitations, is that they can take the entire capacity of the communication channels.

The full duplex (FDX) communication allows two-way communication at all times. This is like a two-way road. Such communication is required when both transmitting and receiving are required at all times. For example, telephone and computer-to-computer communications. Of course, such communication needs to share/divide the capacity of the channels for transmitting and receiving at the same time.