Network protocol: tcp/ip protocol

One . Network protocol

If you want to understand Socket, Be familiar with TCP/IP Transmission control protocol / Internet Protocol , Defines how the host connects to the Internet , A standard for how data is transferred between them .

TCP/IP Protocol reference model , Put all the TCP/IP The series of protocols are grouped into four abstraction layers ： application layer , Transport layer , The network layer , Data link layer , Each abstraction layer is built on the services provided by the lower layer , And provide services for the higher level .

Why is the Internet layered ？

Set rules between layers （ Is the interface ）, Each layer should do its own thing , Layers can evolve internally .

agreement ： standard , Rules to follow

It is divided into several layers ？5 layer , Let's analyze this in detail 5 layer

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Physical layer

  The physical connection , Optical fiber / Cable, etc . The relay will be 0 and 1

Link layer

  Make a rule 0 and 1 The way of reading .

Ethernet

• It's probably a group of signals as packets , Become a frame -Head-data

• Head: Description information （ sender --- The receiver ）

• Data: Real data

• Data must be from network card to network card （ Each network card has Mac Address ）

• Broadcast , Send it to all network cards of the LAN

The Internet is composed of multiple LANs . LAN is a sub network .

The network layer

• Solve different computers , In different LAN communication problems .

• IPV4 Determine which subnet it belongs to , independent IP More expensive . Every computer has one IP Address ：192.168.1.1 altogether 32 Bit

• Put the frame inside data Divide into 2 block （Head Include IP Address + length ,data Real data ）

• The frame length is limited , If exceeded , Will be broken into different bags , Every bag has it head And package serial number

Transport layer

• problem ： Many programs in the computer use the network , Frame here , To which program ？ There has to be something , Tell me to give that program .（ The port change is shining ....）

• Guarantee ： Information about a program on the computer , Send to a program on a computer .

• port ：0~65535, among 0 To 1023 System use the . Ensure that procedures communicate with procedures

• host + port = Kit word (Socket),socket In fact, it is to ensure the interaction of programs distributed on different computers , Can do network application development

• UDP agreement , hold data Split into head+data（head Only put ports ）. There is no guarantee that the data will be received . characteristic ： Simple , reliable

• TCP agreement , Data accessibility , Make sure the data is not lost , Confirmation process . Complex version UDP. characteristic ： Load inefficiency , Offset more resources , reliable .

application layer

 http Examples of agreements , explain data The meaning of data . Appoint data What format is in it , What's the point .

Two . Network communication

Supersocket There are three main objects ：Session,AppServer,Commands

• Session： Connection of each user , It's just one. Session

• AppServer：Socket Instance of the server

• Commands： The client sends back the command of data

The format of the message sent by the client ：CommandName+ Space -+ Parameters 0+ Space + Parameters 1+ Space + Parameters N+\r\n

Server processing ：CommandName Command class to handle

Heartbeat detection mechanism ：

• Used to detect whether the client is disconnected
  , The client is online , The server sends a heartbeat packet within the interval , The server returned a reply .

• If the heartbeat cycle , received , The server thinks you are offline