说明：  本文从VoIP相关知识入手，介绍了IP电话的软硬件结构设计及实现方案，并描述了IP电话基于SIP的呼叫流程，并通过设计杂项的方式详细描述了系统中的几个关键点。内容仅供大家参考，更详细内容可参见源代码，源代码是最好的老师。
(In this paper, starting from the VoIP-related knowledge, introduction of IP telephony hardware and software design and realize the structure of the program, and describes the IP phone based on SIP call flow, and through the design of miscellaneous manner described in detail the system of several key points. Content for your reference, more details can be found in the source code, source code is the best teacher.)