What Are Simplex, Half Duplex and Full Duplex?

When talking about fiber optic jumper cables, such as LC LC multimode duplex fiber cable or LC SC single-mode simplex fiber optic patch cable, we came across simplex and duplex, or full duplex. What are simplex and full duplex? They are two kinds of communication channels in telecommunications and computer networking, which provide pathways to convey information. In fact, other than simplex and full duplex, there is another communication channel named half duplex. These three communication channels are commonly used in telecommunication networks.

A communication channel can be either a physical transmission medium or a logical connection over a multiplexed medium. The physical transmission medium refers to the material substance that can propagate energy waves, such as wires in data communication. And the logical connection usually refers to the circuit switched connection or packet-mode virtual circuit connection, such as a radio channel. With communication channels, information can be transmitted without obstruction. In this article, a brief introduction to these three communication channel types will be given.


A simplex communication channel only sends information in one direction. For example, a radio station usually sends signals to the audience but never receives signals from them, thus a radio station uses a simplex channel. And it is also commonly used in fiber optic communication. One strand is used for transmitting signals or for receiving signals. The good part of simplex mode is that its entire bandwidth can be used during the transmission.


Half Duplex

In half duplex mode, data can be transmitted in both directions on a signal carrier but not at the same time. At a certain point, it is actually a simplex channel whose transmission direction can be switched. Walkie-talkie is a typical half duplex device. It has a “push-to-talk” button which can be used to turn on the transmitter but turn off the receiver. Therefore, once you push the button, you cannot hear the person you are talking to but your partner can hear you. An advantage of half-duplex is that the single track is cheaper than the double tracks.


Full Duplex

A full duplex communication channel is able to transmit and receive data in both directions on a signal carrier at the same time. It is constructed by a pair of simplex links that allows bidirectional simultaneous transmission. Take telephone as an example, people at both ends of a call can speak and be heard by each other at the same time because there are two communication paths between them. Thus, using the full duplex mode can greatly increase the efficiency of communication.


Simplex Fiber Optic Cable vs. Duplex Fiber Optic Cable

A simplex fiber optic cable has only one strand of tight-buffered fiber inside the cable jacket for one-way data transmission. The aramid yarn and protective jacket enable the cable to be connected and crimped to a mechanical connector. It can be used for both multimode and single mode patch cable. For instance, single-mode simplex fiber optic cable is suitable for networks that require data to be transmitted in one direction over long distance. Different from simplex fiber optic cable, duplex fiber optic cable has two strands of fibers constructed in a zipcord style. It is often used for duplex communication between devices to transmit and receive signals simultaneously. Duplex fiber optic cable can be applied to all sorts of applications, such as workstations, fiber switches and servers, fiber modems and so on. And single-mode or multimode cable is also available with duplex cables.


To understand the operation of networking, you should at least know the concept of communication channels. Simplex, half duplex and full duplex are three modes of communication channels. Each one can be deployed for different applications. To make a cost-effective decision, you can choose the right fiber optic cable according to the channel mode that you need.