1. What is full duplex and half duplex
1. Full-duplex transmission (English Full-Duplex)
It means that the switch can also receive data while sending data, and the two are synchronized. This is like when we usually make a phone call, and we can also hear the other party's voice while talking. Current switches support full duplex.
The advantage of full duplex is that the delay is small and the speed is fast.
2. Half Duplex (English Half Duplex)
Corresponding to the concept of full-duplex, it means that only one action occurs in a period of time. For example, on a narrow road in one day, only one car can pass at the same time. When there are two cars facing each other, this In this case, only one car can pass first, and the other car can be driven after the first one. This example vividly illustrates the principle of half-duplex. Early walkie-talkies and early hubs were all half-duplex products. With the continuous advancement of technology, the half-duplex union has gradually withdrawn from the stage of history.
Two, full-duplex and half-duplex transmission mode
In serial communication, data is usually transmitted between two stations (such as a terminal and a microcomputer). According to the direction of the data flow, it can be divided into three basic transmission modes: full-duplex, half-duplex, and simplex. However, simplex is rarely used at present, and only the first two methods are introduced below.
Full Duplex and Half Duplex
1. Full duplex mode (full duplex)
When the transmission and reception of data are split and transmitted by two different transmission lines, both parties in the communication can perform transmission and reception operations at the same time. This transmission method is full-duplex. In the full-duplex mode, a transmitter and a receiver are set at each end of the communication system, so the control data can be transmitted in two directions at the same time. The full-duplex mode does not need to switch directions, so there is no switching operation. The resulting time delay is very beneficial for those interactive applications (such as remote monitoring and control systems) that cannot have time delays. This method requires both senders and receivers on both sides of the communication. At the same time, 2 data lines are required to transmit data. Signals, (may also require control and status lines, and ground).
For example, the computer host uses a serial interface to connect a display terminal, and the display terminal has a keyboard. In this way, on the one hand, the characters entered on the keyboard are sent to the host memory, and on the other hand, the information in the host memory can be sent to the screen for display. Usually, to After entering a character on the keyboard, it will not be displayed first. After the computer host receives the character, it will immediately return it to the terminal, and then the terminal will display the character. In this way, the return process of the previous character and the input process of the next character are: Simultaneous, that is, working in full duplex mode.
2. Half duplex
If the same transmission line is used for both reception and transmission, although data can be transmitted in both directions, both parties cannot send and receive data at the same time. This transmission method is half-duplex. When half-duplex is used, the communication system will The transmitter and receiver at one end are transferred to the communication line through the send/receive switch to switch directions. Therefore, a time delay will occur. The send/receive switch is actually an electronic switch controlled by software.
When the computer host uses a serial interface to connect the display terminal, in the half-duplex mode, the input process and the output process use the same channel, and some computers and the display terminal work in half-duplex mode. At this time, the input from the keyboard Characters are sent to the terminal for display at the same time as they are sent to the host, instead of loopback, so the simultaneous receiving process and sending process are avoided.
At present, most terminals and serial interfaces provide commutation capability for half-duplex mode and two independent pins for full-duplex mode. In actual use, it is generally not necessary for both parties to transmit and receive at the same time. , One-way transmission equipment such as printers, half-duplex or even simplex can be competent, and there is no need to reverse.
3. The difference between full-duplex mode and half-duplex mode in network cards
1. In full-duplex mode, the 8 mesh wires must be connected to the corresponding line sequence positions of the crystal head respectively;
2. In half-duplex mode, only need to connect 4 wires, refer to T568B standard, generally use 4 wires on the 1, 2, 3, 6 line sequence position, namely: white orange, orange, white green, green four root line;
White-orange and orange are used to send data, and white-green and green are used to receive data.
3. In full-duplex mode, the maximum speed of the network cable can reach more than 100 megabits;
In half-duplex mode, the speed that the network cable can reach is usually around 10 megabits.
4. The network cable in full-duplex mode can work in both full-duplex mode and half-duplex mode; but the network cable in half-duplex mode cannot work in full-duplex mode.
5. In half-duplex mode, the extra two sets of lines can be used to connect telephone lines, for example, separate the "white-blue, blue" sets of lines for use as telephone lines. In the LAN network wiring, this method can save the wiring cost, and a twisted pair can be used as a network cable and a telephone line at the same time.
How to use the half-duplex mode of the network card to solve the network connection failure
If one or several wires in a full-duplex mode network cable are short-circuited or have poor contact, such as a problem with the blue wire group or the brown wire group, then change the network card to half-duplex mode to avoid problems with the use of the blue line group or the brown line group, so as to solve the problem of unstable network connection, dropped line and so on.
4. Summary
Finally, use a metaphor to summarize full-duplex and half-duplex, so that everyone can understand more vividly.
Duplex is relative to simplex. Simplex is one-way transmission. For example, if there is a road from A to B, then single-way is a one-way road, which can only go from A to B but not from B to A. And half-duplex means that this road can go from A to B, and from B to A, but not at the same time. Duplex is a two-way street that can go from A to B, or B to A, and at the same time. Therefore, simplex is equivalent to a BB machine. Others can send it to you, but you can't reply directly; half-duplex is a walkie-talkie, one speaks and the other speaks; it can't be done at the same time; full-duplex is a mobile phone, and both parties may do it at the same time. This is the difference between simplex, half duplex and full duplex.
And 10M/100M is the transmission speed of the network card. When you use a 10M bandwidth, there is no difference between using a 10M network card and a 100M network card, but when you use a 100M bandwidth, then you can use a 10M network card. less than optimal performance. Now the general network card is 10M/100M adaptive.
