OpenSIPStack是一个SIP协议栈，符合RFC3261标准，C++编写。-The OpenSIPStack Library is an implementation of the Session Initiation Protocol as described in RFC 3261.

opensips是一个成熟的开源SIP服务器，除了基本的SIP代理和SIP路由外，还能实验一些功能级的应用-OpenSIPS is a GPL licensed SIP server implementation. It started as a fork of Fokus Fraunhofer SIP Express Router (SER) project. OpenSIPS wants to be a more open project, not only from license

opensip 的源码，主要方便开发Parley SIP,目前使用的人不多。-opensip protocol stack, use the Parley SIP,can develop the SIP callcenter