Load testing asterisk servers

I have been informed that SipP is a wonderful tool for load testing an asterisk server. I have installed the program and attempted to run it as per the instructions, with the server and client running on the same box. However, I only get one set of results. Under the “messages” heading it registers the number of calls made, and under the “unexpected-msg” heading, it displays the same number. According to the manual it should have a bit of something in the successive rows under “messages”. Has anyone tried this tool that can point me in the right direction? With those kind of results, does that mean that my asterisk configuration is incorrect? Or do I need to halt asterisk to achieve my goal? Thank you in advance to anybody that can offer advice here.