OpenSIPS is an open source, GPLed, multipurpose SIP server that is able to perform a large set of SIP-related functions, such as SIP Registrar, SIP proxy/router, Instant Messaging server, Presence server, SIP Redirect server, SIP load balancer or SIP Dispatcher, SIP Back-to-Back user agent, Call Queuing System, SIP IP gateway, SIP media controller, SIP application server, and many others.
OpenSIPS defines itself via the following three major capabilities:
Performance: It is translated into a huge throughput actively measured up to 60,000 calls per second, 1.5 million simultaneous calls, 5 million registered users, and 1 million TCP connections, all in a single OpenSIPS instance running on a mid-level server
Feature-rich: It is translated into more than 160 modules providing functionalities or features related to the SIP protocol, SQL or NoSQL DB operations, AAA integrations, routing algorithms (quality, prefix, load-based routing, and dial plans), management and control...