Port numbers are a staple of TCP/IP communications.Because several application programs may be running on one machine and using a single network interface,TCP needs to keep track of what data goes to which program.

• 端口号是TCP/IP通信的组成部分，由于几个应用程序可能在一台机器上运行并利用一个网络接口，所以TCP需要跟踪什么数据进到哪个程序中。