Building complex Voice over IP (VoIP) applications based on open-source

The paper summarizes and proofs that existing VoIP programs are powerful and flexible enough to build complex applications. The applications are independent and can be used either stand-alone or within carrier-grade Telco environments. The described example of building a call center application (outbound calling) shows the power that lies not only in existing open-source Session Initiation Protocol (SIP) servers, but also in simple SIP tools. The costs for implementing those systems are at a very low level, as the functions each project performs are rather kept simple, but the combination possibilities are tremendously flexibility. The presented application has been deployed successfully within NGNlab as a Proof of Concept (PoC).