Islamic Azad University
Today, optimal performance and cost advantages of using Internet telephony are obvious. Despite current standardized techniques, voice transferring through protocol has lower security than traditional telephony. One of the most important security issues which should be noticed in using VoIP is end -to-end user identity, i.e. when there is a connection between user A and B, user A should be assured of the identity of user B, and vice versa. The authentication of identity is one of so important information that could guarantee the security and integrity of information.