List of Tutorials in Introduction to Multimedia
SIP It gives a basic understanding of SIP, the components and commands involved and how it works.
RTP This tutorial tells you what RTP is, how it is used and goes into the details of RTP packets upto certain level. RTCP is also discussed.
SDP It contains a short SDP tutorial in the form of a powerpoint presentation. A complete html version of it will be ready soon.
Recently added VoIP section is not really a tutorial but answers a lot of common questions regarding VoIP technology and VoIP phones.