Analysis of the impact of IPSec on performance characteristics of VoIP networks and voice quality

Providing secure communication has become an essential requirement for VoIP networks. To meet this requirement in a VoIP environment is more complex than in conventional data networks due to the implementation of realtime applications. Network traffic can be encrypted by many solutions. One of them is a widely used and standardized IPSec. During the experiments we have consequently tested the impact of the IPSec encryption on the router CPU utilization, bandwidth required and voice quality. All of these parameters are functions of the number of performed calls. Setting the appropriate Voice Payload Period (VPP) can change the number of simultaneously transmitted and processed packets. The tests were carried out on Integrated Services Cisco 2811 routers that are suitable for small companies. Measurements were carried out for two types of codecs. The outcomes proved a significant effect of VPP on the CPU utilization and also on bandwidth. If the VPP is chosen properly, up to 40 to 60 % of bandwidth can be saved. The call quality, expressed by MOS scales, remains almost constant up to the moment when the utilization is close to 80 %.