As the amount of traffic generated by next generation mobile services keeps increasing, the operators face the scalability challenges of VoIP protocols. This paper presents an analysis tool to evaluate the effect of SIP retransmission mechanism on the SIP server overloading. Our tool is capable of creating various arrival and departure processes using Markov Modulated Poisson Process (MMPP). In order to evaluate effects of the SIP retransmission mechanism on server overloading, test results obtained by using various MMPP parameters and buffer sizes are reported. The performance analysis of priority based SIP server scheduling mechanism in which the original incoming SIP requests have strict priority over the retransmitted requests has been performed and published in our previous papers. Researchers can access to the developed open source software that allows modifications.