Duplex is a point-to-point communication system. It is composed of two connected devices that can communicate with one another. Duplex communication system can be divided into either half duplex or full duplex. Half duplex allows communication in both direction but only one direction at a time. An example of half-duplex communication is a walkies-talkie, where one must use predestination command to indicate the end of transmission. In half-duplex communication, only one party can speak at a time because both the parties cannot speak and listen on the same frequency. On the other hand, in full duplex communication, both parties can speak and listen at the same time.