Talk about TCP and UDP

Speaking of tcp/ip One of the most complex protocols , I don't think so tcp The agreement belongs to ,tcp The protocol is on the transport layer , It's one of the two transport layer protocols , The other is udp agreement

The transport layer lies between the application layer and the network layer , It's where applications send and receive data , If you know the port number of the transport layer , I must be familiar with how to give data to real application , We don't make too many statements here

Now let's talk about how the two applications transmit data , This involves tcp and udp Different

tcp It's like a couple separating two hills , When they want to give their things to each other , Because you can't see each other , They need to shout to make sure they're ready ：

male ： I'll throw you an apple
Woman ： well , I'll throw you a pear
male ： received , I'll throw you a second apple
…

So they started the process of delivering food to each other . This is a tcp The process of communicating after three handshakes , Every piece of data sent is marked , The other party should confirm and reply after receiving it

If the fruit falls into the valley in the process of throwing , What do I do ？

male ： I'll throw you an apple
Woman ：…
male ：( I didn't reply for such a long time , I didn't get it ？） I'll throw you another apple
Woman ： good , I got the first apple you threw

Even if data is lost in transit , As long as there is a timeout retransmission mechanism , It can realize the timeout retransmission of data

If one side throws too fast , What if the other party can't get it ？

male ： I'll throw you an apple
Woman ： well , I'll throw you a pear
male ： received , I'll throw you three more apples
Woman ： Slow down , It hit me on the head , I can only take two at a time
male ： good , received , I'll throw you two

tcp In the process of communication, they will constantly inform each other of their maximum receiving capacity , stay tcp In the head window size Express , According to window size To adjust the size of the data you send

If their stuff is all gone , You need to tell each other , Or they don't know , Still waiting

male ： I'm done with my stuff
Woman ： understand , Let me see if I have anything else for you ？
Woman ： I don't have either , Then I can withdraw
male ： well , received , I also withdrew

tcp After the data is sent , Need to disconnect , By four waves , Like above

Smart you may ask , After one party completes the transmission , Initiated an active shutdown request , But what if the other party's data is not sent out ？

male ： I'm done with my stuff
Woman ： understand , Let me see if I have anything else for you ？
Woman ： You wait , I still have fruit left to throw , I'll throw you one
Woman ： I'll throw you another one
…
Woman ： Okay , I don't have , I quit
male ： received , Let's go.

When the host A After sending data , Initiate a request to close the connection , At this time, the host B Received a request to close the connection , First reply a confirmation message to A, meanwhile B This side no longer receives data ,A After receiving the confirmation message , And no longer have the ability to send data , It's a half closed state

host A Although it doesn't have the ability to send , But it has the ability to receive , host B Though not capable of receiving , But the ability to send , At this point, if the host B There is still data not sent , Will continue to send , Until it's sent

After sending, the host B Will passively send a disconnect request to A,A After receipt of , Reply a confirmation message to B, This is a complete process of closing the connection

That's it , They each ate sweetly from each other , As both sides have a process of continuous shouting and confirmation , They didn't wait and miss each other's wishes

But one day , They had a fight , Ignore each other , But also concerned about each other , So they still throw their fruit to each other

male ： I throw an apple
male ： I'll throw it again
Woman ： I throw two pears
Woman ： I'll throw it again
male ： I'll throw two more
…
male ： It's over , Back , I don't know if she received it
Woman ： There are a few left , Throw them all over
…
Woman ： It's over , go , hum , Whether you get it or not , Hungry or not

This is it. udp The transmission process of , As long as you have data , Know where they are , You just throw , You don't ask if the other person is there , I don't care if my things fall off , I don't care if the other party will hit the head

udp It's like a setter , Responsible for transferring data from application layer to network layer , As for the others , It doesn't care , It only cares about itself , Bah ！

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