Sofia-SIP is an open-source SIP User-Agent library, compliant with the IETF RFC3261 specification. It can be used as a building block for SIP client software for uses such as VoIP, IM, and many other real-time and person-to-person communicat

标准SIP学习文档，rfc3261，绝对权威，内容包括SIP注册，INVITE,等会话管理功能，全面值得学习！-this document is the english standard pdf file,include rfc3261.