From the OSI reference model, TCP is a very important protocol in the transport layer, which is responsible for providing communication between application processes. HTTP belongs to the protocol of application layer. In the request package of the request page you sent. Contains the service type you requested, marked with the destination port number in the header of the TCP message. For example, if the default port number of HTTP is 80, 80 will be used as the destination port number in the TCP header, and the randomly generated data between 0 and 1023 will be used as the original port number used by your local computer application process. After receiving the request, the server will analyze it step by step and finally return the result to you.