SIP 是一种在IP 网络中建立、修改和终止多媒体会话的应用层控制协议，是下一代网络的一个重要信令协议。当前的因特网主要是基于IPv4 的，IPv6 被设计来代替IPv4，但是在相当长一段时间内，两者将共存。IPv4 与IPv6 终端间的互通显得尤为重要。本文介绍了IPv4 与IPv6 终端间的SIP 会话，同时对其会话的安全性做了讨论，并针对其安全性提出了一种解决方案。关键词： SIP，NAT-PT，IPv4，IPv6，安全Abstract: Session Initiation Protocol (SIP) is an application level control protocol that caninitiate, modify and terminate multimedia sessions. SIP is an important Signaling Protocol in the Next Generation Network. While current networks are still mostly based on IPv4, IPv6 is designed to replace the IPv4. However, that will be long time. So it’s important for the transition from IPv4 to IPv6. This paper describes the SIP sessions between IPv4 domain and IPv6 domain and presents a solution about SIP end-to-end security with NAT-PT traversal.Keywords: SIP, NAT-PT, IPv4, IPv6, Security