EXAMPLE:
Run sipp with embedded server (uas) scenario:
./sipp -sn uas
On the same host, run sipp with embedded client (uac) scenario
./sipp -sn uac 127.0.0.1
You can do the same if you have 2 computers/devices on the same network.
With -ifconfig (assuming you are in linux) you can find out the adress your device running the UAS (Server) scenario
The UAC needs to know IP adress of server it tries to send mesages to.
So lets say you run -ifconfig, and you get the adress 192.168.0.101 for your device that you will run UAS on, then your device that runs UAC will need to be run using
./sipp -sn uac 192.168.0.101
I would advise reading the official documentation. It is a bit confusing at first but it is the best source for learning SIPp
http://sipp.sourceforge.net/doc/reference.html