Be sure you have installed the SIPp test application, as described in SIPp Test Application.
In a terminal, enter the following command to start the SIPp server on port 5090:
% sipp -sn uas -p 5090
In a new terminal enter the following command to start the SIPp client on port 5080:
% sipp -sn uac -rsa 127.0.0.1:5060 -p 5080 127.0.0.1:5090
You should now see the messages from the client get returned by the server, with the SipProxy application acting as a proxy between them.