说明：  LwIP的RAW API接口及编程指南。本文详细讲述了LwIP在无操作系统支持环境下的API函数介绍及编程应用。首先，介绍了RAW API的特点及优缺点，然后逐个介绍了LwIP提供的所有的RAW API函数，最后通过实例的形式介绍了这些API函数具体编程的方法。
(LwIP the RAW API interface and programming guide. This paper describes LwIP without operating system support environment API function description and application programming. First, the introduction of the RAW API features and advantages and disadvantages, and then introduced one by one LwIP all the RAW API provides a function, and finally through the examples presented in the form of these API functions specific programming methods.)