说明：  TCP/IP协议是一个比较复杂的协议集，有很多专业书籍介绍。在此，我仅介绍其与编程密切相关的部分：以太网上TCP/IP协议的分层结构及其报文格式。
(TCP/IP protocol is a more complex set of agreements, there are many professional books introduced. Here, I just introduced its programming and closely related to the part : Ethernet TCP/IP protocol to the hierarchical structure and its message format.)