Through "confession", let us quickly understand the seven-layer network protocol

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This chapter mainly introduces the network protocol, which is called the OSI protocol (a series of protocols). It is divided into seven layers according to different functions and divisions of labor. In fact, these seven layers do not exist. There is no concept of these seven layers, it is just an artificial division. When we talk about any network protocol, we will talk about OSI (network seven-layer protocol model). We must follow this protocol model so that our mobile phones and computers can communicate on the Internet. Next, let's take a look at the seven-layer protocol of OSI (network seven-layer protocol model).

The above are seven-layer protocols, and the industry has also produced some other protocol models, such as TCP/IP four-layer protocol and five-layer protocol.

TCP/IP four-layer protocol model:

Mainly include:

• Application Layer
• Transport Layer
• Network Layer
• Physical Link Layer

Five-layer protocol model

Mainly include:

• Application Layer
• Transport Layer
• Network Layer
• Data Link Layer
• Physical Layer

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By looking at the rigid concepts above, it may be difficult for us to understand what the seven-layer network protocol is all about. Next, I will use a short story to help everyone understand and remember the seven-layer network protocol.

Short story

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Our story is based on the five-layer agreement, with Xiao Wang's confession to Xiao Hong as the main line.

Xiao Wang has been secretly in love with Xiao Hong for a long time, but he is too shy to express his love to her face. So he decided to write an email to Xiao Hong to express his love.

Xiao Wang bought a bunch of physical cables, network cable interfaces, optical fibers, etc. from the store. One end was connected to his home, and the other end was connected to Xiao Hong's home. Xiao Wang's question was: how can these two pieces of physical hardware communicate with each other?

So Xiao Wang invented the bit stream, which is used to convert 1 and 0 into the strength of the electric current to transmit the signal, which is commonly known as digital-to-analog conversion and analog-to-digital conversion. At this time, the communication between two physical hardware has been completed. This is what we usually call the physical layer

Step 2:

Xiao Wang thought: I have completed the communication between these two physical hardware, but how can I ensure that the transmitted data is reliable and safe? Because Xiao Wang wants this letter to be reliable and safe. He doesn't want others to know that he likes Xiao Hong.

Because in our real life, physical lines are often unreliable and unsafe. They may be eavesdropped on by others, or the network cable may be dug up by others, etc.

So Xiao Wang invented the data link layer. The data link layer is used to ensure the correct transmission of data. There is a thing called a data packet, which transmits data through data packets. The data packet verifies whether the data is correct through parity check or other forms. At this time, we have completed the transmission of data packets from one node to another.

Step 3:

Xiao Wang thought, I can send the letter to Xiao Hong's home now, but what if Xiao Hong is not at home? Is she at school or traveling somewhere else? Then she won't be able to see my letter?

At this time, Xiao Wang invented the network layer, that is, the router. At this time, Xiao Wang will first send his data packet to the router, and then the router will send it to the router, and then it will be sent all the way to Xiao Hong's computer. This is the network layer. At the same time, in order to identify each node in the network layer, Xiao Wang defined the IP protocol. Therefore, each node will have an IP.

Step 4:

Xiao Wang thought, at this time, at our data link layer, we can ensure that the data is correct, but we cannot guarantee that our data is reliable. At this time, we need a mechanism that can automatically retransmit our data after an error occurs. Automatically check whether the data is sent correctly.

At this time, Xiao Wang invented the transport layer. In the transport layer, Xiao Wang formulated the TCP/UDP protocol. The TCP protocol is connection-based and will establish a connection between Xiao Wang and Xiao Hong's computer to transmit data on this connection.

Step 5:

At this time, Xiao Wang has done what he should do. But which application does our data serve? Is it an HTTP? Or an FTP? Or an Email protocol? This is a protocol invented by Xiao Wang - the application layer protocol.

In this way, Xiao Wang completed the five-layer protocol from the unreliable and insecure first layer to the application layer, which is reliable and secure. Xiao Wang confessed his love to Xiao Hong as he wished. As for whether Xiao Wang and Xiao Hong are still together, I don't know. This is what we later knew as OSI (network seven-layer protocol model). In the seven-layer protocol, two layers will be downplayed, so we only discuss the five-layer protocol here.

Unreliable

• Packet loss, packet duplication
• Error (can only be solved by retransmission)
• Out of order

Unsafe

• Easy to be stolen information (at the network layer, calls made through routing can be monitored by hackers at any time)
• steal
• tamper

Reference articles:

https://www.cnblogs.com/carlos-mm/p/6297197.html https://blog.csdn.net/taotongning/article/details/81352985