Tcp/ip protocol

TCP/IP—— High concurrent load balancing colony

• OSI
  open system interconnect Open system interconnection model , This model divides the network communication work into seven layers , The physical layer 、 Data link layer 、 The network layer 、 The session layer 、 The presentation layer 、 application layer （ Theoretical reference ）.
  

• OSI 7 Layer reference model （ Reference resources 、 Unrealized ）
  （1） Why layering ？ The interface between layers is stable , Expose interfaces , Direct interface adjustment , Internal methods 、 Logic is replaceable ; Can understand Europe , If there is no stratification, the European quota is higher , It costs a lot to change everything .

• TCP/IP agreement （ Defined Logic 、 Parameters 、 Implementation method ）
  
  （2） Introduce ： There are two types of regional programs in computers ——Linux kernel kernel（ Version maintenance ）+ The system runs in the background demo Programs are user space application Program .
  （3） difference ： Why are some layers placed in the kernel , Such as qq、 WeChat 、 When the game transmits communication data, many codes do not need to be developed repeatedly , The use of common resources is designed by kernel developers , There are rules, resource management and the process of establishing connections in the kernel . Other different procedures , Send a representation of data 、 reliability 、 Whether the security is encrypted Develop in the personalization of the program , The application layer . So there are two levels of classification .
  （4）nc： Establishing a connection ——net connect,nc After sending the agreement in a human way , Both parties can transmit data through connection , You can correctly request the data back , The request function ends .
  （5） There are agreements at every level ： The application layer contains http agreement 、fdp Agreements, etc .
  （6） Transport control layer ：tcp—— oriented Connect Of , Reliable transmission （ Commonly used ）、udp agreement .

• TCP The stage of ：
  Establish a connection with three handshakes , Then data transmission , The last four breakups .
  
  （1） Achieve three handshakes ： Network communication I/O Communication is two-way , When there is an output, there is an input , After three times, the client and server know that their input and output are connected .
  
  ack：acknowledge Indicates that a packet has been received , got it ;
  Connect ： Open up resources in the memory of both sides , Switch state , The process of connection is the process of instantaneous packet interaction ;

IO Model —— file system io、 The Internet io

IO Model essentially ： Kernel exposed to program api Derived from socket packing