Nic Full Duplex, Half-duplex, simplex, automatic detection

The network card transmits the data, according to the direction of the data flow can divide into four kinds of basic transmission way: full duplex, Half-duplex, simplex and automatic detection four kinds of way.

But simplex is now rarely used, and the following are just two common ways

If at any point in the communication process, the information can only be transmitted by one Party A to the other party B, it is called Simplex.

If at any time, the information can be transmitted from a to B, but also by B to pass a, but any time can only be in one direction of the transmission, called Half-duplex transmission.

If, at any time, a two-way signal transmission of A to B and B to a is present on the line, it is called Full-duplex.

A telephone line is a second-tier Full-duplex channel. Because of the use of ECHO cancellation technology, two-way transmission signals are not confused. The duplex channel also sometimes separates the receiving and transmitting channels, and uses separate lines or bands to transmit signals in the opposite direction, such as back line transmission.

Below we use the popular saying to explain to everybody:

Half Duplex (Half Duplex), so-called half-duplex means that only one action occurs in a time period, as a simple example, a narrow road, and only one car to pass, when there are currently two vehicles off, in this case can only be one before the first, wait until the boss after the other one to open, This example illustrates the principle of half-duplex in the image. Early walkie-talkie, as well as early hubs and other devices are based on Half-duplex products. With the continuous progress of technology, the half-double trade union gradually withdrew from the historical stage; single-work communication means that the data on the communication line is transmitted in a single direction.

The following is a detailed description of Full-duplex and Half-duplex.

① Full-duplex mode (full duplex)

When data is sent and received streaming, when transmitted by two different transmission lines, both sides of the communication can send and receive at the same time, so the transmission mode is Full-duplex. In Full-duplex mode, the transmitter and receiver are set at each end of the communication system. Can control data transmission in two directions at the same time. The Full-duplex approach eliminates the need for directional switching, so there is no time delay for switching operations, which can be beneficial for interactive applications that cannot have time delays, such as remote monitoring and control systems. This requires that both sides of the communication have a transmitter and a receiver, and require 2 The root data line transmits data signals. (You may also need control and status lines, as well as ground).

For example, the computer host uses the serial interface to connect the display terminal, the display terminal has a keyboard. In this way, the characters entered on the keyboard are sent to the host memory, on the other hand, the host memory information can be sent to the screen display. Usually, after 1 characters to the keyboard, the computer host receives the characters, Immediately loopback to the terminal, and then the terminal to display this character. In this way, the back process of the previous character and the input process of the latter character are simultaneous, that is, working in Full-duplex mode.

② Half Duplex mode (half duplex)

If the same transmission line is used for both receiving and sending, although the data can be transmitted in two directions, but the communication can not send and receive data at the same time, such transmission mode is half duplex system, using Half-duplex mode, the communication system at each end of the transmitter and receiver, through the receiving/sending switch to the communication line, the direction of the switch, Therefore, a time delay is generated. The receiving/sending switch is actually an electronic switch controlled by the software.

When the computer host uses a serial interface to connect the display terminal, in Half-duplex mode, the input process and the output process use the same path. Some computers and display terminals in a Half-duplex mode of work, at this time, the characters from the keyboard to send to the host at the same time is sent to the terminal display, rather than using the loopback method, Therefore, the reception process and the sending process are avoided at the same time.

At present, most terminals and serial interfaces provide commutation capability for Half-duplex mode, also provides two separate pins for Full-duplex. In actual use, generally do not need to communicate both sending and receiving, such as printers such as one-way transmission equipment, half-duplex or even simplex can be competent, do not have to reverse.

③ single working mode (SIMPLEX) and automatic detection

Simplex is basically out of use now. and automatic detection, the computer will be based on the current transmission of data, using the above three kinds of one, called automatic detection.