说明：  LwIP是TCP/IP协议栈的一个实现。它的目的是减少内存使用率和代码大小，使LwIP适用于资源受限系统比如嵌入式系统。为了减少处理和内存需求，LwIP使用不需要任何数据复制的经过裁剪的API。
(LwIP is TCP/IP protocol stack of a realization. Its purpose is to reduce memory usage and code size, so that lwIP applicable to resource-constrained systems such as embedded systems. In order to reduce processing and memory requirements, LwIP use data replication does not require any cutting of after the API.)