There are three mode of data transmission that corresponds to the three types of circuit available. These modes are:
a) Simplex
b) Half Duplex
c) Full Duplex
a) Simplex
In simplex communication mode, there is a one way communication transmission. Television transmission is a good example of simplex communication. The main transmitter sends out a signal but it does not expect a reply as the receiving unit cannot issue a reply back to transmitter. Another example of simplex communication is a keyboard attachment to a computer because the keyboard can only send data to the computer.
b) Half Duplex
In a half diplex mode both units communicate over the same medium but only one unit can send mode, the other unit is in the receiver mode. For example two polite people talking to each other one of them could not talk at a same time. The half duplex is most common type of transmission for voice communication. It requires two wires.
c) Full Duplex
A full duplex system is used that allow information to flow simultaneously in both directions on the transmission path. Uses of a full duplex line improve efficiency. It also requires four wires for full duplex system.
