I hope by now you have got a basic idea of what SIP is and what it does. You should be able to recognize the major components in a SIP scenario and how different messages are exchanged to establish and terminate sessions. But you must remember that it is just the beginning. You should go through the document of RFC 3261. If you are serious about your learning better get your hands on a book as recommended in the books section.
You should go through the other sections of the site -
- Introduction to RTP : RTP manages the realtime transmission of audio/video data in a session.
- Introduction to SDP : SDP is used for describing a session needed for establishing and sustaining a session.
- VoIP : VoIP is the technology to transmit voice over an IP network. It's an emerging area you would like to know about.
I encourage you to go through the resources listed in internet multimedia resources page.
I intend to include some more pages regarding header fields and proxy servers in near future. So keep coming back. If you have any query or suggestion and more importantly if have found any mistakes in the tutorial, please feel free to email me at koushik.banerjeeATgmail.com.