Kamailio

Kamailio is a modular SIP server that can act as a registrar, proxy, router, or in other SIP server roles. It is for technical users and organizations that need registration, proxy, and routing functions in a SIP system. Its modular structure allows one program to take on different roles when a deployment calls for a registrar, proxy, router, or another SIP server function. As an open source option, Kamailio can replace paid SIP server software, although no specific commercial product is named. It supports the server side of SIP systems and combines several common server roles in one program. One limitation is that Kamailio is server software, not an end-user SIP client. Its scope is also centered on SIP; support for other protocols, formats, or platforms is not established.