SIP, Session Initiation Protocol, was initially proposed by IETF as an IP phone signaling protocol. It has been playing an important role in many fields including VoIP, soft switch, NGN and 3G.

• SIP(Session Initiation Protocol,会话初始协议)是由IETF(Internet工程任务组)提出的IP电话信令协议,发挥着越来越重要的作用,其应用领域从最初的VoIP扩展到软交换、NGN和3G中。