Alternatively referred to as simplex communication or simplex transmission, simplex is a one-way only communication standard. Broadcast information, or data, can only travel in one direction, versus duplex which allows for two-way broadcasting. Examples of simplex include radio broadcasting, television broadcasting, computer to printer communication, and keyboard to computer connections.
The second definition of simplex states that information can only be broadcast in one direction, at one time. Information can be broadcast in both directions in a simplex circuit, but not at the same time, like duplex. Another term for simplex is half-duplex. Back in 1928, Western Union completed the transatlantic telegraph cable, which was a simplex communication method. The National Fire Protection Association used a simplex radio channel for communications in 2002 as well.
Also see: Transmission