echoplex
Echoplex is a type of transmission in communications technology in which the receiving station automatically sends back each transmitted character so that the sender can recognize the correctness of the transmission.
It is an asynchronous transmission in which the data is reflected back from the receiving station (usually the central computer) to the transmitting station), which makes it easy to check that the transmission is correct. Thus, an entered character is not displayed on the screen until it has been mirrored by the host. Echoplex is a special form of duplex.