Transmission modes mean the way in which a communication is achieved between two linked device. The device which sends data or information is called the sender and which receives the information is called the receiver. A channel can support either one way communication or two way communication at a time. Based on the way of communication link, transmission modes can be classified as : simplex, half duplex, and full duplex.
A simplex connection is a connection in which the data flows in only one direction, from the transmitter to the receive. This type of connection is useful if the data do not need to flow on both direction.
A half-duplex system provides for communication in both directions, but only one direction at a time. Typically, once a party begins receiving signal, it must wait for the to stop transmitting, before replying. This type of connection makes it possible to have bidirectional communications using the full capacity of the line
The preferred transmission mode for network communication is full-duplex mode. A full-duplex, allows communication tn both directions simultaneously. Each end of the line can thus transmit and receive at the same time, which means that the bandwidth is divided in two for each direction of data transmission if the same transmission medium is used for both direction of transmission. A good analogy for a full-duplex system would be a two lane road with one lane for each direction.