Simplex communication

Simplex communication refers to communication that occurs in one direction only. Two definitions have arisen over time: a common definition, which is used in ANSI standard and elsewhere, and an ITU-T definition. The ITU definition of simplex is termed "half duplex" in other contexts.

ANSI definition: One way signaling

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

• Commercial radio and television broadcast (not two-way radio such as walkie-talkies)
• Garage door openers
• Baby monitors
• Wireless microphones
• Radio controlled models
• Public address systems
• Surveillance cameras
• Pagers
• Communication between a mouse or a game controller and a computer
• Internet multicast
• Radio navigation beacons and radiolocation services such as GPS
• Telemetry

ITU-T definition: One way signaling 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. At other times communications can flow in the reverse direction. A more common term for this application is half-duplex. Examples are intercoms, and two way radios such as walkie-talkies, citizens band, and mobile radios used dispatch police, firefighters, and taxicabs.

The old Western Union company used the term simplex when describing the half-duplex and simplex capacity of their new transatlantic telegraph cable completed between Newfoundland and the Azores in 1928. The same definition for a simplex radio channel was used by the National Fire Protection Association in 2002.

See also

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