Duplex (telecommunications)
Examples are broadcast radio and television, garage door openers, baby monitors, wireless microphones, and surveillance cameras.
[3] The International Telecommunication Union definition is a communications channel that operates in one direction at a time, but that may be reversible; this is termed half duplex in other contexts.
A pair of walkie-talkie two-way radios provide a simplex circuit in the ITU sense; only one party at a time can talk, while the other listens until it can hear an opportunity to transmit.
[6] [7][8] This terminology is not completely standardized between defining organizations, and in radio communication some sources classify this mode as simplex.
Half-duplex systems are usually used to conserve bandwidth, at the cost of reducing the overall bidirectional throughput, since only a single communication channel is needed and is shared alternately between the two directions.
In half-duplex systems, if more than one party transmits at the same time, a collision occurs, resulting in lost or distorted messages.
From the user perspective, the technical difference does not matter and both variants are commonly referred to as full duplex.
Many Ethernet connections achieve full-duplex operation by making simultaneous use of two physical twisted pairs inside the same jacket, or two optical fibers which are directly connected to each networked device: one pair or fiber is for receiving packets, while the other is for sending packets.
In any case, with full-duplex operation, the cable itself becomes a collision-free environment and doubles the maximum total transmission capacity supported by each Ethernet connection.
[citation needed] Full-duplex audio systems like telephones can create echo, which is distracting to users and impedes the performance of modems.
Time-division duplexing is flexible in the case where there is asymmetry of the uplink and downlink data rates or utilization.
Frequency-division duplex systems can extend their range by using sets of simple repeater stations because the communications transmitted on any single frequency always travel in the same direction.
In this case, time-division duplexing tends to waste bandwidth during the switch-over from transmitting to receiving, has greater inherent latency, and may require more complex circuitry.
Another advantage of frequency-division duplexing is that it makes radio planning easier and more efficient since base stations do not hear each other (as they transmit and receive in different sub-bands) and therefore will normally not interfere with each other.
