Communication Mode

The communication mode refers to the working mode or signal transmission mode between the two communication parties.

1. Simplex, half-duplex, and full-duplex communication

For point-to-point communication, according to the direction and time of message transmission, the communication mode can be divided into simplex, half-duplex and full-duplex communication.

(1) Simplex communication means that messages can be transmitted in only one direction, as shown in Figure 1-6(a).
Only one of the two communication parties can send, and the other can only receive, such as broadcasting, telemetry, remote control, wireless paging, etc. (2) In the Half-duplex communication mode, both parties can send and receive messages, but cannot send and receive messages at the same time, as shown in Figure 1-6(b). For example, the use of the same carrier frequency of ordinary walkie-talkies, inquiries and searches.
(3) Full-duplex communication refers to the working mode in which both parties can send and receive messages at the same time. Generally speaking, the full-duplex communication channel must be a bidirectional channel, as shown in Figure 1-6(c). The telephone is a common example of full-duplex communication, where both parties can speak and listen at the same time. High-speed data communication between computers is the same way.

2. Parallel transmission and serial transmission

In data communication (mainly the communication between computers or other digital terminal equipment), according to the different transmission modes of data symbols, it can be divided into parallel transmission and serial transmission.

(1) Parallel transmission is the simultaneous transmission of a sequence of digital code elements representing information in a group manner on two or more parallel channels. For example, a binary sequence of “0″ and “1″ sent by a computer can be transmitted simultaneously on n parallel channels in the form of n symbols per group. In this way, n symbols in a packet can be transmitted from one device to another within a clock beat. For example, 8-bit characters can be transmitted in parallel over 8 channels, as shown in Figure 1-7.
The advantage of parallel transmission is to save transmission time and speed. The disadvantage is that n communication lines are required and the cost is high, so it is generally only used for short-range communication between devices, such as the transmission of data between computers and printers.
(2)Serial transmission refers to the transmission of a sequence of digital symbols on a channel in a serial way, one symbol after another, as shown in Figure 1-8. This is often used for long-distance digital transmission.
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