International Journal of Computer Applications
VOIP (Voice Over Internet Protocol) has many advantages but at the same time it has security threats not encountered in PSTNs (Public Switched Telephone Networks). The paper deals with the security of the widely used protocol for signaling. The Session Initiation protocol (SIP) is considered the most used signaling protocol for calls over the internet. Securing SIP is becoming more and more important. This paper focusing on the SIP security mechanisms of authentication and proposing an authentication model based on the Kerberos protocol to provide single sign-on, achieving two way authentications, to reduce the computation against authentication checks for each client and prevent against session teardown attack and registration hijacking attack.