Date Added: Jan 2010
The Session Initiation Protocol (SIP) has become the most predominant protocol for Voice over Internet Protocol (VoIP) signaling. Security of SIP is an important consideration for VoIP communication as the traffic is transmitted over the insecure IP network. And the authentication process in SIP ranges from pre-shared secret based solutions to Public Key Infrastructure (PKI) based solution. However, due to the limitations in PKI based solutions, some PKI less authentications mechanisms are proposed. This paper aims to present an overview of different authentication methods used in or together with SIP.