The application layer uses a protocol for generating, reforming and closing the sessions. This protocol is known as Session Initiation Protocol(SIP). Sip is the major protocol of signaling for Internet applications, thus enabling the execution of features making use of SIP, like video conferencing, Internet gaming, instantaneous messaging, and voice mailing. The reason for this protocol modeling is to study how SIP perform in the setup phase of call and which type of features are supported by this protocol. Media connection is also used by Session Initiation Protocol(SIP). The objective of using SIP protocol is to construct it look alike as we make use of a regular phone, i.e. entering the number where we want to call, listen the ringing of the phone or busy signals. The major dissimilarity as per the protocols of a regular phone is that for transporting the call we use the Internet as a transporting device and there is no actual establishment of a circuit in the network. Address resolution, call mapping, and name mapping, used to determine the position of the objective endpoint, are supported by SIP. Session Description Protocol(SDP) is used to determine the media capability of the objective endpoint. Video conferencing are also accepted by media capabilities and supported by all the objective endpoints. To determine the objective end point’s availability- due to the unavailability of the objective endpoint, if the call is incomplete, in this case, SIP find out whether the party we are calling is already on the phone or in the assigning number of rings he/she didn’t answer. SIP then inform the calling party by reverting the message which indicates the unavailability of the objective endpoint. SIP set up a session between the two endpoints, set a session between an originating and an objective endpoint if the call can be done completely.