OpenSIPS - Configuration and Integration with Asterisk (NAT Traversing)
OpenSIPS is open-source software that suits well for medium and large businesses to handle all the above-mentioned scenarios. It supports common database access like MySQL and Postgres but still very well supports the carrier-grade deployments. OpenSIPS is a multi-purpose signaling SIP server. It can act as SIP Router, SIP Switch, SIP Registrar, Application Server, Redirect Server, Load Balancer, Dispatcher, Back-to-Back User Agent, Session Border Controller, SIP Front-End, NAT traversal Server, IP Gateway (SMS, XMPP) among others.