Have a look at OpenSIPS

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OpenSIPS is an open-source high performance SIP server. The picture below shows its internal architecture . OpenSIPS has modular architecture. Mainly consists of two parts:

  • The core – This part provides the low-level functionality. It includes so called internal libraries. They collect code shared by several modules.
  • The modules – are the components that provides the most of the functionality that make OpenSIPS powerful in real world deployments.

The architecture for OpenSIPS 1.X is shown in figure below.

opensips-arch