Basic knowledge of Embedded Network - introduction of mqtt

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Basic knowledge of network

IP And the role of ports

During network transmission , adopt IP And port to express yourself and the other side .
IP：IP Address , Include host number + network number . Used to represent a device connected to the Internet .
port ： Ports represent transport layer to application layer , Data transmission channels , Each application corresponds to a different port .

Public network IP Not enough use

IP And ports are important , however IP Not enough use ：

• In the home , In the company , Only routers have public networks IP
• Other computers are just local area networks IP, such as 192.168.x.x
• Your home computer , The company's computers ,IP All are 192.168.0.100, But they don't conflict ： Because they are in different LAN （ The connected routers are different ）
• Computers in the LAN access the public network , You need a router to help ！
  

On a foreign visit , Router to help

a key ：
IP And ports are important , however IP Not enough use ： So we need a router to help .
How to help ？
client 1： To his own IP Address and port number （ hypothesis 192.168.200.11）, And the domain name of the server to be accessed （ hypothesis ：qq.com） To the router
Router 1： Router 1 Received the information from the client , Client side IP Replace the address and port number with your own public network IP, And send data to qq.com.qq.com Received a request , It will reply the data to the router
Router 1： Router 1 received qq.com The news will be in your own NAT The transformation mapping table looks up whether there is a device for this request , Send data to the device if there is . If not, lose the data .

So it's not hard to find out , Servers are needed as a bridge between two different LAN devices that send and receive messages from each other .

How to transmit data between the two sides ？

On the hardware

Both sides need to be connected to the Internet , mobile phone , And the development board .

Agreement on

The so-called agreement ： It means that both the sender and the receiver reach an agreement . That is, the rules that both parties must abide by .
In the Internet of things ,MQTT More suitable for . Because its data size is very small , It's perfect for .

MQTT download

Recommended kawail-mqtt, It was written by a big cow in China , very nice.
kawail-mqtt, Consciousness is Kawaii MQTT, Lovely MQTT.

Domestic open source address Open source address

summary

Thank you very much for your teaching and answers , Thank you for your teaching .
It is highly recommended that you learn embedded , Hundreds of questions ！
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