Simplex communication is a name for a type of communication circuit. There are two (contradictory) definitions that have been used for the term. When one definition is used for "simplex", then the other definition is actually referred to as half duplex.

One way only – the most common definition

According to the ANSI definition, a simplex circuit is one where all signals can flow in only one direction. These systems are often employed in broadcast networks, where the receivers do not need to send any data back to the transmitter/broadcaster.

Examples according to ANSI definition

• Commercial radio broadcast (not walkie-talkies, etc.)
• Television broadcast
• Internet multicast
• One-way communications from a launcher to a guided missile, where the launcher (airplane, ship, etc.) sends commands to the missile, but does not receive any information sent back.

One way at a time

According to the ITU-T definition, a simplex circuit is one where signals can flow in only one direction at a time. A more common term for this application is half-duplex.
This was also the way the old Western Union company used the term when describing the half-duplex and simplex capacity of their new transatlantic telegraph cable completed between Newfoundland and the Azores in 1928¹. The same definition for a simplex radio channel was used by the National Fire Protection Association in 2002².

References

1. ^ Milnor, J.W. and G.A. Randall. "The Newfoundland-Azores High-Speed Duplex Cable". A.I.E.E. Electrical Engineering. May 1931
2. ^ Report of the Committee on Public Emergency Service Communication. NFPA 1221, May, 2002.

See also

• Communications channel
• Duplex (telecommunications)
• Half-duplex

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