This paper proposes the use of SIMPLE / SIP for future Instant Messaging ( IM ) and presence services, analyzes the advantages of using SIP for presence and explains the SIMPLE architecture. The author also designs a more functional, robust, and flexible presence services model. 本文提出了如何利用SIMPLE/SIP协议实现未来的在席和即时消息服务,通过分析SIP技术的优势和SIMPLE实现的机理,提出了较为健壮、安全、灵活的在席服务程序模型。