我们要讨论的是网络中进程之间如何通信？首要解决的问题是如何唯一标识一个进程，否则通信无从谈起！在本地可以通过进程PID来唯一标识一个进程，但是在网络中这是行不通的。其实TCP/IP协议族已经帮我们解决了这个问题，网络层的“ip地址”可以唯一标识网络中的主机，而传输层的“协议+端口”可以唯一标识主机中的应用程序（进程）。这样利用三元组（ip地址，协议，端口）就可以标识网络的进程了，网络中的进程通信就可以利用这个标志与其它进程进行交互。-We have to discuss how communication between the network processes? The most pressing issue is how to uniquely identify a process, otherwise the communication is out of the question! Locally through the process PID to uniquely identify a process, but it does not work in the network. In fact, the TCP/IP protocol suite has been helping us solve this problem, " ip address"　of the network layer can be uniquely identifies network host transport layer protocol the+ port " can uniquely identify the host application (process). This triples (ip address, protocol, port) can identify the network process, the process of communication in the network can use this flag to interact with other processes.