中文摘要：

分析了几种常见的SIP协议的安全威胁，提出了两种可能性也很大的安全威胁，在此基础上从SIP协议消息交互过程出发．提出了几种新的解决思路和方法。

英文摘要：

This paper firstly analyzes the security threats to SIP protocol and lists another two kinds of threats, then gives a brief introduction of SIP security mechanism, finally improves new solutions based on the course of the exchange of the SIP messages.