The session initiation protocol (SIP) will provide the signaling network in the next generation networks, such as UMTS and cdma2000. Here we study the traffic load generated by the use of this protocol from a methodological point of view. We propose an analytical technique to simulate SIP finite state machine (FSM) in an IP network by means of the theory of queuing networks. Based on this approach, we derive a simple model which can be applied to different network scenarios for performance evaluation and engineering purposes. We conclude this study by showing some results about call dropping rate in a wireless access network.