The case history started in the 1940s of the last century when the European and American PA/GA and intercom paradigms originated. At the time, industrial intercom and control communication became duplex and simplex. Military application and high requirements to speech illegibility led to the creation of standards for communication in high ambient noise environment. At half-duplex (variation of duplex connection) connection, the built-in echo suppression system automatically controls the direction of the voice transmitting; in this case, communication delays happen as well as loss of speech and parts of important information. These peculiarities caused the development of simplex communication systems and technologies of simplex calls management correspondingly.
