摘要： IETF组织提出的SIP是建立、修改和终止多媒体会话的端到端应用层协议，能够满足移动性的要求。但是在会话切换的过程中会丢失数据包，产生不能忍受的延迟。该文分析了延迟产生的原因，并在此基础上提出了充分利用网络资源、由用户终端发起的BS服务器来完成软切换的解决方法。并证明这种方法能够解决切换延迟问题，有效地提高了通话质量。

关键词: 会话初始协议, 软切换, 切换延迟

Abstract: Session initiation protocol is an application-layer protocol standardized by IETF for establishing, modifying, and terminating peer-to peer multimedia communication, and it provides mobility in such network. However, the handoff procedure with SIP suffers from undesirable delay and packet loss. In this paper, the cause of handoff delay is analyzed and it is proposed that the soft handoff processing is initiated by MA and carried out by BS. It is proved that this is an effective solution for avoiding the hand off delay and improving the session QoS.

Key words: Session initiation protocol (SIP), Soft handoff, Handoff delay