Authentication is a process by which the sender and the receiver identify the legal communicating partners prior to commencement of message transactions. Authentication is a part of security which is ascertained at the time of initiation of the communication between the two communicating entities like client and server. Network communications are found to be vulnerable due to the increase in number of threats from unknown intruders. Session Initiation Protocol (SIP) is used for initializing the session between two communicating devices or entities. This protocol is widely used in multimedia communications.