Zhang SAN, a programmer, falls in love with xiao Fang, a girl from the next village, but he is too shy to talk to her face to face. He added a small fang WeChat and use computer to send a message to her, “hello, can you make a friend with you”, he wants to know the news have successfully sent out, so he decided to track this information (don’t ask me how I track), first of all, he in WeChat (application layer) to send a piece of content (message) zhang SAN home using the HTTP protocol, This message will be added to Zhang SAN’s 32 bit network address and some other content, and then the message goes to the transport layer. The transport layer knows that it wants to communicate with Xiao Fang based on the content added by the application layer. The first thing it does is not send a message to Zhang SAN. John is a careful man, so his network follows TCP protocol (TCP protocol goes through three handshakes to establish a solid and reliable connection). Let’s move on to this message. Actually, at the transport layer, this message is no longer what it used to be. Into multiple short message segment “hello”, “can make a friend with you?” “” and attached more information to make the network layer would be able to send, and the network layer to do the same thing, its purpose is to allow the router to send zhang SAN’s information, the router also through some agreement to encapsulate information, with convenient information transmission at the physical layer, So finally in the physical layer information has become unrecognizable, into one bit after another, sent to xiao Fang home. Just then, the time spent on this process you should also know that in about 0.1 seconds later, zhang ping of the house of the small fang IP (zhang SAN is too like small fang, and secretly recorded her IP address), zhang SAN found they had successful communication, this means that his message has been successfully sent, he can not help some, This is a godsend for me. But xiao Fang has not returned to the news, which makes Zhang SAN a little antsy. To find out what happens next, please listen to the next episode.