This paper presents an analytical modeling of the Session Initiation Protocol(SIP) with the help of Generalised Stochastic Petri Nets(GSPNs) and evaluates the average throughput in a reliable transport medium. SIP is an application layer protocol described by Internet Engineering Task Force (IETF) developed by Working Group of SIP used for generating, reforming and closing the sessions. The session can be carried out through both a reliable or an unreliable transport medium. The sessions which are maintained by SIP include telephone Calls through the internet (eg. VoIP), multimedia distribution and video conferences.
SIP uses INVITE Transaction for initializing the session. Stochastic Petri Nets(SPNs) are derived by connecting stochastic and time information to the Petri Nets. Generalised Stochastic Petri Nets(GSPNs) is an extension of Stochastic Petri Nets(SPNs).