Kamailio, very fast, reliable and flexible SIP Server
Kamailio is a very fast, reliable and flexible SIP (RFC3261)
proxy server. Written entirely in C, Kamailio can handle thousands calls
per second even on low performance hardware. A C Shell like scripting
language provides full control over the server's behaviour. It's modular
architecture allows only required functionality to be loaded.
Among available features: IPv4, IPv6, digest authentication, accounting,
CPL scripts, instant messaging, MySQL, Postgres and UNIXODBC support,
NoSQL backends Redis, Cassandra, Redis, Memcached,
radius authentication, record routing, SMS gateway, ENUM, UDP, TCP,
TLS and SCTP, transaction and dialog module, OSP, statistics support,
registrar and user location, SNMP, SIMPLE Presence, Lua, Perl, Python, Java
and Mono programming interfaces, WebSocket support for WebRTC, IMS extensions,
embedded XCAP server and MSRP relay, DNSSEC, gzip compression.