The commercial deployment of voice over internet protocol (VoIP) networks (and associated packet switching technologies) has gathered pace in the recent years. However, a major concern with such networks is the issue of the security of networks based on such open standards. Little research has been carried out into examining the options for securing VoIP networks and, more specifically, the impact which implementing such security architectures and protocols will have on the performance of such secure networks. This paper describes the research, which has been carried out into the development of a realistic model for carrying out simulations of the performance of secure session initiation protocol based VoIP networks. The results of the performance analysis obtained using this model are presented with a discussion of the implications of these results for designers considering implementation of real secure VoIP networks. (C) 2002 Elsevier Science B.V. All rights reserved.