kamailio

Very fast and configurable open source SIP proxy

Kamailio is an open source SIP proxy server that is capable of handling thousands of up calls in a second. Among the features it provides, are support for TCP, UDP and SCTP, secure communication via TLS for VoIP (voice, video), accounting, the most popular open source databases and much more. Originally starting out as the SIP Express Router (SER) project by the Fraunhofer Society in 2001, the design team got together in 2008, merged old and new source code and rebranded SER to Kamailio.