说明：  Microchip的TCPIP协议栈的说明文档，Microchip将协议栈分为多层，每层实现代码驻留在一个独立的源文件中。
(Microchip's tcpip protocol stack description document. Microchip divides the protocol stack into multiple layers, and each layer of implementation code resides in an independent source file.)