In recent times, the usage of Voice and Video over Internet Protocol (VoIP) services has increased tremendously. There are many signaling protocols such as Bearer Independent Call Control (BICC), H.323, Media Gateway Control Protocol (MGCP), Session Initiation protocol (SIP) etc., that are used for establishment of sessions and to carry out voice and video data services. SIP has become popular because of its easy implementation, flexibility and good scalability. Choice of Open Source SIP server software (OS-SIP Server Software) is important when deploying in a VoIP based network. So we need to evaluate the performance of OS-SIP Server Softwares in an ideal condition before it is deployed to real environment. This document evaluates and compares the performance of three OS-SIP Server Softwares which are quite popular. A SIPp traffic generator tool is used to generate scenarios namely Registration with authentication, Registration without authentication, Session establishment, and Session establishment with response delay at User Agent Server (UAS) side. Using these scenarios, the performance of OS-SIP Server Softwares is evaluated with respect to parameters such as Registrations per second, Calls per second, Response delay, and Percentage of successful calls and registrations. From the experimental results, we observed that there is a significant performance difference among the SIP server softwares. OpenSIPS is the best OS-SIP Server Software for the scenarios Registration with authentication, Registration without authentication and Session establishment with response delay. Asterisk server is the best OS-SIP Server Software when compared with the other two (OpenIMSCore and OpenSIPS) servers for the scenario Session establishment.