Abstract: Although only more than one year since session initiation protocol (SIP) had been delivered, SIP has already become the research hotspot in telecommunication and network fields. More than 30 RFCs and drafts were delivered by SIP WG, including core protocol, QoS, security, message header and method extension, interconnection with PSTN, firewall and NAT traversal, application, multi-message body, instant messenger, etc. This paper introduces the SIP standard and the newest research trends in its related fields, and points out the future research direction and the promising foreground application.