Simplex (SX) is a transmission mode where communication is possible in one direction only. In this mode, one data station can only transmit while the other can only receive.
This operation mode is also called directional operation and allows only one-way message flow. In simplex mode, no feedback or error correction is possible.
In contrast to simplex operation are half- duplex and duplex. In these transmission modes, the transmitting and receiving stations can transmit and receive simultaneously.