Simplex, Half Duplex,Full Duplex

Simplex
It is the mode of transmission in which data is transmitted in one way only.The transmitter will always transmit signal and receiver will always work as receiver and can’t be used as transmitter.This method is not often used because it is not possible to send back error or control signals to the transmit end.
Best example of Simplex mode of transmission is,data transmission from keyboard to mouse.

Half Duplex 
in Half Duplex Mode transmission can be in both ways ,but one at a time.Means if reciever is recieving data then it can not transmit data and if it is sending data than it can’t recieve data.
The best example for half duplex mode is walkie talkie. Below given image illustrates how it works.


Full Duplex
 It is the transmission mode in which data can travel in both directions simultaneously.There is no need to switch from transmit to receive mode or vice versa ,like in half duplex.
Communication between two computers that are connected peer to peer is the best example of Full Duplex or Simply Duplex Mode.