用通俗的大白话来理解 TCP 协议的三次握手和四次分手

The concept of a socket is the cornerstone of network communication and is the basic unit of operation for network communication that supports the TCP/IP protocol. It is an abstract representation of the endpoints in network communication and contains the five pieces of information necessary for network communication: the protocol used for the connection, the IP address of the local host, the protocol port of the local process, the IP address of the remote host, and the protocol port of the remote process. When the application layer communicates data through the transport layer, TCP encounters the problem of providing concurrent services to multiple application program processes. Multiple TCP connections or multiple application program processes may need to use the same socket to communicate.