Simplex: Simply put, one party can only send information, the other party can only receive information, and the communication is one-way.
Half-duplex: It is a little more advanced than simplex, that is, both parties can send messages, but only one party can send messages at the same time.
Full- duplex : It is a little more advanced than half-duplex, that is, both parties can not only send information, but also can send at the same time.
Simplex
Simplex means that A can only send signals, and B can only receive signals, and the communication is one-way, just like a lighthouse to a ship - the lighthouse sends out light signals and the ship can only receive signals to ensure that it is on the correct route. .
half duplex
It means that only one action occurs in a time period. 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, in this case, only one car can pass first. Wait until the leader and then drive the other 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 With the continuous advancement of technology, the half-duplex union has gradually withdrawn from the stage of history.
full duplex
Full－Duplex Transmissions
It means that the switch can also receive data while sending data, and the two are synchronized. It is like we usually make a phone call, and we can also hear the other party's voice while talking. Current switches support full duplex.
In full-duplex mode, the 8 wires must be connected to the corresponding wire sequence positions of the crystal head respectively;
In half-duplex mode, only 4 wires are needed. Referring to the T568B standard, four wires are generally used at positions 1, 2, 3, and 6, namely: white-orange, orange, white-green, and green. ;
White-orange and orange are used to send data, and white-green and green are used to receive data.
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.
The network cable in full-duplex mode can work in either full-duplex mode or half-duplex mode;
However, the network cable in half-duplex mode cannot work in full-duplex mode.
In half-duplex mode, the extra two sets of lines can be used to connect telephone lines, for example, separate the "white, blue, and blue" 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.
Synchronous and asynchronous:
Synchronization refers to the communication method in which the sender sends data and waits for the receiver to send back a response before sending the next data packet.
Asynchronous means: after the sender sends data, it does not wait for the receiver to send back a response, and then sends the next data packet.
Serial communication is serial asynchronous full duplex:
SPI communication is serial synchronous half-duplex:
IIC communication is serial synchronous full duplex:
switch, router, hub
Hub ------ - Hub, also called Hub, works at the physical layer (the bottom layer), without a matching software system, it is a pure hardware device. Hubs are mainly used to connect network terminals such as computers.
The hub is a shared bandwidth. When any device connected to the hub sends data, all other devices must wait. This device enjoys all the bandwidth. After the communication is completed, other devices use the bandwidth. Because of this, the hub is connected to a collision domain network. All devices are used interchangeably, as if we were all crossing a single-plank bridge together.
The hub cannot determine the destination and type of the data packet, so if it is a broadcast packet, it is still forwarded, and all devices send data to each interface by broadcast, so the hub is also connected to a broadcast domain network.
Switch----- Switch Switch, works at the data link layer (layer 2), and a slightly higher-end switch has an operating system to support it. Like a hub, it is mainly used to connect network terminal devices such as computers.
The switch is more advanced than the hub, allowing the devices connected to the switch to communicate in parallel, just like cars on the highway running in parallel, the communication between the devices will no longer conflict, so the switch breaks the collision domain, and each interface of the switch is a collision domain. , there will be no communication conflict with other interfaces.
And the switch with the system can record the MAC address table, the data sent will not be broadcast to each interface, but directly reach the destination interface, saving the interface bandwidth. But the switch, like the hub, cannot judge the broadcast data packet, and will send the broadcast to all interfaces, so the switch is connected to a broadcast domain network like the hub.
High-end switches can not only record the MAC address table, but also divide VLANs (Virtual Local Area Networks) to isolate broadcasts, but communication between VLANs is also impossible. To enable communication between VLANs, a Layer 3 device must be involved.
Router --- --- Router Router, works at the network layer (the third layer), all routers have their own operating system to maintain, and need personnel to debug, otherwise it will not work. Routers do not have so many interfaces and are mainly used for network-to-network connections.
Simply put, a router sends data from one network to another, and this process is called routing. Routers can not only isolate collision domains like switches, but also detect broadcast packets and discard broadcast packets to isolate broadcast domains, effectively expanding the scale of the network.
The routing table is recorded in the router, and the router forwards the data to realize the communication between the networks. The intervention of the router can make the VLANs divided by the switch communicate with each other.
Summarize:
Hub: Pure hardware, used to connect network terminals, cannot break collision domain and broadcast domain.
Switch: A software system that connects network terminals and can break the collision domain, but cannot divide the broadcast domain.
Router: It has a software system, is used to connect the network, can break the collision domain and can also divide the broadcast domain. It is a backup device for connecting large-scale networks.