Basic process of network transmission using tcp/ip four layer model

OSI The seven layer model logically divides the network into 7 layer , The main function is to realize two Communication between different hosts . actually OSI The seven layer model is not practical , We usually use the four or five layer protocol , The statement of the fourth floor is Just talk about software , We need to know the fourth floor , But software is based on hardware , So there are five layers .

The lower left half is a seven layer model , The right half is a four layer model , We call these four floors “TCP/IP Five floors ( four layers ) Model ”. These four layers also have a certain corresponding relationship with the computer architecture

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Catalog

One 、 What is an agreement

Two 、TCP/IP Five floors ( four layers ) Model

3、 ... and 、 The basic flow of network transmission

1、 The seller ( host A)

(1) application layer  

(2) Transport layer

(3) The network layer

(4) Data link layer

 2、 buyers ( host B)

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One 、 What is an agreement

The so-called agreement is a kind of agreement , There are people from different places in a dormitory , If everyone just speaks their own dialect , It's impossible to communicate , At this time, someone made a suggestion , Everyone speaks Mandarin , After reaching this agreement , Everyone can communicate normally .

From the perspective of network , On the transport layer TCP and UDP agreement , This agreement is to choose whether there is connected transmission or connectionless transmission .

Two 、TCP/IP Five floors ( four layers ) Model

TCP/IP Is a synonym for a group of agreements , You can understand that almost every layer has its own agreement .

- application layer ： Responsible for communication between applications , Such as simple email Transfer Protocol (SMTP)、 File transfer protocol (FTP)、 Network remote access protocol (Telnet).

- Transport layer ： Decide how to transmit data between two hosts , Such as transmission control protocol (TCP).

- The network layer ： Responsible for address management and routing . It can be understood as the way to transfer data to the other host . For example, in IP Agreement , adopt IP Address to identify a host , And through the way of routing table Draw the data transmission line between the two hosts . The router works on this layer .

- Data link layer ： Responsible for the transmission and identification of data frames between devices . For example, conflict detection ( If a conflict is detected , It will automatically resend )、 Data error checking, etc . The switch works at the data link layer .

- The physical layer ： Responsible for light / How electrical signals are transmitted . We often say coaxial cable 、 Optical fiber 、wifi All belong to the content of this layer . It can be simply understood that most of the contents of the physical layer have entities . The physical layer determines the maximum transmission rate 、 Anti interference, etc . The hub works on the physical layer ( Enlarge data , Reduce data loss ).

3、 ... and 、 The basic flow of network transmission

You may think , Still a little obscure , Here is a simple example to get familiar with the functions of the above layers , At the same time, I have a preliminary understanding of network transmission .

Network transmission can be seen as the relationship between sellers and buyers , Suppose you buy a bottle of shampoo from Taobao , So the mainframe A The application layer of is equivalent to the seller , host B The application layer of is equivalent to the buyer .

1、 The seller ( host A)

(1) application layer  

The seller puts shampoo in a box , This process is equivalent to the application layer adding a data header to the data , This header contains the length of the header 、 Length of load 、 What is the upper layer protocol . In fact, it is equivalent to putting it in the product box , The product box has the quality of the product 、 Production date and other information .

The application layer is equivalent to OS Users in , No matter how the data is sent 、 And how the data is delivered . Only deal with the details of the application .

(2) Transport layer

After the goods arrive at the express station , The express station should affix the express bill to the goods , The delivery address is on the express bill . This process is actually equivalent to adding a data header to the data at the transport layer .

After that it ？ That is to decide which express to send . The transport layer is equivalent to OS The kernel part of , The details of communication are here , There is also the network layer of the next layer . The transport layer determines the transmission mode of data , yes TCP still UDP.

(3) The network layer

Now that you have decided which express to send , Now it's time to decide the route . This floor also needs to add a header .

The network layer determines the transmission route of data .

(4) Data link layer

The express is on the way , Suppose we arrive in Nanjing now , The express station in Nanjing will send you to the next stop, Zhejiang . The data link layer determines the process of transferring data from the transfer station .

 

 2、 buyers ( host B)

The buyer received the goods , What we need may be wrapped in many layers , Now we need to dismantle it layer by layer . This process is unpacking .

  For the process of encapsulation and unpacking, please refer to the following blog .

Network foundation —— Headlines 、 Package and unpack _abs(ln(1+NaN)) The blog of -CSDN Blog https://blog.csdn.net/challenglistic/article/details/125643881?spm=1001.2014.3001.5501