Evaluating SIP proxy servers based on real performance data

VoIP services have become a major competitor to the PSTN networks and will replace them in the near future. Based on this fact the SIP protocol became very popular. But handling tens of thousand of clients, despite the network and application delays is a challenging task. The SIP proxy servers need to be implemented very efficiently to reduce the application delays. This work evaluates and compares the performance and authentication costs of four popular open source SIP proxy servers based on real performance data. The results show that there is a lot of space for improvement in the SIP proxy server implementations.