Data Transmission Mode of Communication Mode
The communication method is the way that the two people talking to each other work together or send messages.
1. Simplex, half-duplex and full-duplex communication
For point-to-point communication, according to the direction and time relationship of message transmission, the communication mode can be divided into simplex, half-duplex, and full-duplex communication.
(1) Simplex communication refers to the working mode in which messages can only be transmitted in one direction, as shown in Figure 1-6(a).
So one of the two communication parties can only send and the other can only receive, such as broadcasting, telemetry, remote control, wireless paging, and so on. (2) Half-duplex communication refers to the mode of operation in which both parties in the communication can send and receive messages, but not at the same time, as illustrated in Figure 1-6(b). For example, common walkie-talkies use the same carrier frequency, inquiry and retrieval, etc.
(3) Full-duplex (Duplex) communication refers to a mode of operation in which both parties can send and receive messages at the same time. Generally speaking, the channel of full-duplex communication must be a bidirectional channel, as shown in Figure 1-6(c). A telephone is a common example of full-duplex communication, where both parties to the call can speak and listen at the same time. The same is true for high-speed data communication between computers.
2.Parallel transmission and serial transmission
Data communication (mainly communication between computers or other digital terminal equipment), according to the different transmission methods of data symbols. They can be divided into parallel transmission and serial transmission.
(1) Parallel transmission is the grouping of two or more parallel channels that transmit digital symbol sequences representing information at the same time. For example, a binary symbol sequence consisting 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 transferred from one device to another within one clock tick. For example, 8-bit characters can be transmitted in parallel using 8 channels, as shown in Figure 1-7.
The advantage of parallel transmission is that it saves transmission time and is fast. 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 data transmission between a computer and a printer.
(2) Serial transmission is to transmit a sequence of digital symbols on a channel in a serial manner, symbol by symbol, as shown in Figure 1-8. This method is often used for long-distance digital transmission.
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