What Are the Different Methods of Data Transmission?

Data transmission mode (data transmission mode) is the method used for data transmission on the channel. According to the order of data transmission, it can be divided into parallel transmission and serial transmission; if the data transmission is synchronized, it can be divided into synchronous transmission and asynchronous transmission; if the data transmission flow direction and time relationship can be divided into simplex and half-duplex And full-duplex data transmission. ^[1]

In serial transmission, the measures taken by the receiver on how to correctly divide the characters sent from the serial data stream are called character synchronization. According to different ways to achieve character synchronization, there are two ways of data transmission: asynchronous transmission and synchronous transmission.

Asynchronous transmission transmits one character code (5 to 8 bits) at a time. A "start" signal is added before the transmission of each character code. The length is specified as 1 symbol, and the polarity is "0". One stop signal, when using the International Telegraph II number, the stop signal length is 1.5 symbols, and when using the international five number (see data communication code) or other codes, the stop signal length is 1 or 2 symbols, polarity Is "1". Characters can be sent continuously or individually; when no characters are sent, the stop signal is sent continuously. The start time of each character can be arbitrary (this is also the meaning of asynchronous transmission), but the length of each symbol in the same character is equal. The receiving end detects the "start" signal that recognizes a new character according to the transition from the stop signal to the start signal between characters ("1" "0"), so as to correctly distinguish each character. Therefore, such a character synchronization method is also called start-stop synchronization. The advantage of this method is that it is relatively simple to implement synchronization, and the clock signals of the sending and receiving sides do not need to be accurately synchronized. The disadvantage is that each character is increased by 2 to 3 bits, which reduces the transmission efficiency. It is often used for low-speed data transmission at 1200bit / s and below.

Synchronous transmission sends data signals at fixed clock ticks. In a serial data stream, the relative positions of each signal symbol are fixed. To correctly distinguish the characters sent from the received data stream, the receiver must establish bit timing synchronization and frame synchronization. Bit timing synchronization is also called bit synchronization. Its function is to synchronize the bit timing clock signal at the receiving end of the data circuit termination device (DCE) with the input signal received by the DCE, so that the DCE correctly determines each signal code from the received information stream Element to generate the received data sequence. There are two methods for generating timing at the DCE sending end: one is to generate bit timing in the data terminal equipment (DTE), and send the DTE data to the DCE at this timing. This method is called external synchronization. The other is to use the internal bit timing of DCE to extract DTE end data. This method is called internal synchronization. For the receiving end of the DCE, the received data is sent to the DTE at a bit timing beat within the DCE. Frame synchronization is the correct grouping or framing from the received data sequence in order to correctly distinguish individual characters or other information. The advantage of synchronous transmission is that it does not need to add and stop symbols for each character separately, so the transmission efficiency is high. The disadvantage is that the implementation technology is more complicated. Usually used for data transmission at a rate of 2400bit / s and above. ^[2]

According to the direction and time relationship of data transmission, data transmission methods can be divided into simplex, half-duplex, and full-duplex data transmission.

Simplex data transmission is data transmission between two data stations only in a specified direction. That is, the DTE at one end is fixed as the data source, and the DTE at the other end is fixed as the data sink.

Half-duplex data transmission is that two data stations can transmit data in two directions, but not at the same time. That is, the DTE at each end can be used as a data source and a data sink, but cannot be used as a data source and a data sink at the same time.

Full-duplex data transmission is between two data stations and can be transmitted simultaneously in both directions. That is, the DTE at each end can be used as a data source and a data sink at the same time. Four-wire lines usually implement full-duplex data transmission. The two-wire line realizes simplex or half-duplex data transmission. When frequency multiplexing, time division multiplexing, or echo cancellation is used, the two-wire line can also realize full-duplex data transmission. ^[3]

(1) Open a synchronous transmission channel between the sender and receiver;

(2) The transmission end sends multiple transmission start indicator packets through the synchronization channel until the receiving end receives an acceptance response on the component (

(3) After the sender receives the acceptance response, the sender sends at least one payload packet through the synchronization channel;

(4) After detecting bad reception of the packet, the receiver sends an error message to the sender;

(5) When the error message sent by the receiver is received by the sender, the payload data is transmitted from the error location and then restarted.

A more standardized solution must also be established. In terms of transmission efficiency, since it is a simulation test, more problems may be encountered in practical applications, so the data transmission algorithm needs to be further optimized.