很好的SIP相关的资料，由浅入深的介绍SIP。包括会议初始化协议：SIP，SIP协议的操作，SIP工具包，用SIP工具包创建应用等。-Good SIP related information, Deep introduction SIP. Including conference initiation protocol: SIP, SIP protocol operation, SIP Toolkit, with the SIP Toolkit to create applications.