First SIP Call - Call Flow Analysis 

Shows how to download & install a SIP User Agent (SIP soft phone), and use it to set up a peer-to-peer SIP call. You'll then be guided to analyse the User Agent's SIP log and learn the 7 message SIP exchange needed to set up a call, and how to differentiate between SIP Requests and SIP Responses.
'First SIP Call - Call Flow Analysis' is the fourth lesson from sipsense.com 's free SIP Basics.
Check out • sipsense.com - old for an overview.