Transmission Modes -Simplex, Half-Duplex and Full-Duplex

Transmission Modes refers to the direction of data transmission between two devices. For example, your cell phone is a full-duplex because both parties can talk at once but, a walkie-talkie is a half-duplex device because only one party can transmit at a time. Radio is the example of simplex communication, where radio only can receive the signal and never transmit. Half-duplex communications limit the exchange of data to one direction at a time while full-duplex allows the sending and receiving of data at the same time.

Simplex Communication

In simplex transmission, the communication between sender and receiver only occurs in one direction.  Simplex in one way communication in which the signals can travel only in one direction. The sender only can send and receiver only can receive nor send. Radio Broadcasting, television broadcasting computer to printer communication, and keyboard to computer connections are the examples of simplex communication.

Half-duplex communication

In half-duplex communication, one side can talk at a time another side should be on listening. When one side has complete transmitting its data, the other side can reply. Only one node can talk at a time. If both try to talk at the same time, a collision will take place on the network. So both devices can transmit and receive on the media but cannot do so at the same time.

The half-duplex mode is used in legacy bus topologies and with Ethernet hubs. WLANs also operate in half-duplex. Half-Duplex is used with contention-based access methods. This method of communication is not very efficient and requires more time to send/receive larger amounts of data. Older networks mostly based in half-duplex mode, due to the constraints of the network medium (coax cable) and hardware equipment (hubs) as shown in the figure below.

half-duplex

Full-duplex communication

Full-duplex is the type of communication where Both devices can transmit and receive on the media at the same time. The data link layer assumes that the media is available for transmission for both nodes at any time without any danger of a collision. So, the transfer of data occurs much faster. Ethernet switches operate in full-duplex mode by default but can operate in half-duplex if connecting to a device such as an Ethernet hub. Below figure illustrates the full-duplex communication.

Full-Duplex

Today, all networks make use of switches instead of hubs and UTP Ethernet cabling instead of co-axial cabling, which allow full-duplex communication between all connected hosts. It is important that both interconnected interfaces operate using the