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Half-duplex
In half-duplex communication, both devices can send and receive messages, but not at the same time (simultaneously). This method of communication works in the way that when device A sends the message, device B waits for the message to arrive. This is because the device that is sending the message absorbs the communication channel, thus leaving no space for the other device to send the message at the same time. An analogy of half-duplex communication is radio communication (walkie-talkie), which is based on the push-to-talk method, as shown in Figure 2.8:
Figure 2.8. Radio communication, which represents a half-duplex communication channel