A new explanation of tcp/ip five layer protocol model

       After the computer network class, I always feel ,TCP/IP The five layer model of is something that I can't understand , So that I didn't understand this course in the end .

       In the past few days, it was mainly because of the epidemic , It's boring at home , So I decided to start studying this thing again . Then I suddenly realized , I feel that I have understood the truth .

       First of all, let's write what these five layers are .

       application layer , Transport layer , The network layer , Data link layer , The physical layer .

       The explanation here is mainly combined with my understanding of xiexiren's seventh edition 《 computer network 》 The understanding of the textbook tells .

       We know , All software running on the computer , If you want to communicate on the Internet , It must transmit information . There can be no application that does not transmit any information , Network communication simply for network communication . therefore As long as it is the software for network communication , Data must be generated for transmission .

       Now we have the data . You can start preparing to send the data .

       But we know that , Before sending the data, some formatting control should be performed on the data , This is a very simple truth , Just like the anchorman of the news network must be meticulous before he takes the stage , Before delivering a speech, the speaker needs to form his own ideas into a certain format of language .

       After all , You can't hear the news broadcast speak dialect , It is impossible to see the speaker completely unprepared , Just according to their own caprice nonsense .

       All the news , Deliver online , There must be a certain theme and format .

       Then let's think about , The difference between the post office and the escort .

       We won't mention the difference simply because of the level of confidentiality , What we need to see is their communication process .

       The post office may receive a parcel one afternoon , Then transfer to the local branch according to the address , The branch will be transferred to another branch , And so on. , We can see that the delivery mode of the post office is section by section , And the post office is in the process of transportation , You can't say it on your chest “ The package will never be lost ！”, If your package is not lost , Then they can only say sorry . You can only send it again for mailing .

       But escort is different . A bulletproof car , With guns and live ammunition , Most of the time, I will catch up with oneortwo escort vehicles , There are also some military and police officers waiting for them , Escorting a very important cargo over . Although they still can't guarantee , This thing will definitely be delivered to , Because it is also possible that terrorists or armed forces may come out to rob the road , But this is not too much , After all, tens of millions of money can be earned , Life is gone, but everything is gone . So , Escort can ensure that your goods will arrive at the destination in most cases .

       If this shipment is a message , We can come up with another theory .

       All the information , Deliver online , It is necessary to choose a mode of transportation

       Oh, yes , The two modes of transportation are the same ： All the information , Deliver online , It is necessary to choose the destination of transportation

       Then our news has been on the Internet , At this time, no matter what mode of transportation , We all need to put it in the car , Then the driver drove , Start shipping our information , We need such a driver , Because without him , Our news will not go out . But also because of him , We must let the master learn the traffic rules , Traffic jam waiting in line , No traffic lights , Let the master learn which way is closer .

       All the information , Deliver online , It is necessary to transfer link control information

       Then we need a big road . Otherwise, Shifu can't fly over .

       The above five red letters , Corresponding in sequence ：

       Software generates data , Start communicating .

       The software selects the data protocol format .—— application layer

       The software selects the data transportation mode .—— Transport layer

       The software selects the data transportation location .—— The network layer

       Data begins to be transported , Data pay attention to the network , Select route change in time , Always pay attention to data correctness —— Data link layer

       Of course, the last important thing is ： Data begins to be transferred on the physical device —— The physical layer