SIP称为会话发起协议（Session Initiation Protocol)。SIP是Internet工程任务组（IETF）提出的建议中的一项协议，其目的是为了替代H.323的部分协议，主要是考虑到在下一代网络（NGN）中，由于IP产品和IP网关将在网络中得到大规模使用和集成，使得端到端都可以采用IP以实现纯IP的业务应用；而基于纯IP的SIP借鉴了HTTP和SMTP，结构简单并具有可扩充性和可扩展性。此外，SIP还提供良好的QoS支持。对于NGN在IP网络上实现VOIP和多媒体通信来讲，SIP在全面满足NGN特性要求的应用上具有独特的优势，必将成为下一代网络VOIP的重要解决方案。

-called SIP Session Initiation Protocol (Session Initiation Protocol l). SIP is the Internet Engineering Task Force (IETF), the recommendations of an agreement, its purpose is to replace the H.323 part of the agreement is mainly on account of the next generation network (NGN), As IP and IP gateways in the network will be large-scale use and integration, making end-to-end IP can be applied to achieve a pure IP business applications; For pure IP SIP from the HTTP and SMTP, simple structure and is designed to be scalable and scalability. In addition, the SIP also provides good QoS support. IP NGN for the realization of the VoIP network and multimedia communications speaking, SIP to meet the full requirements of the characteristics of NGN application has unique advantages, the next generation w