en development, which helps narrow the gap between a model and the corresponding system it represents to make it accu- rate. The diagrams of recent UML edition are of two categories [25]: structure diagrams (e.g., class, component diagrams) to show the static structure of the system being modeled and behavior diagrams (e.g., activity, use case, sequence diagrams), which show the dynamic behavior between the objects in the system. We model those UML SIP models through UML software design tools such as Rational Rose Platform, Microsoft Visio and the SIP Modeling Toolkit. Specifically, the SIP Modeling Tookit is a plugin for IBM Rational Software Architect that adds SIP-specific extensions to the UML modeling and devel- opment platform and supports the analysis and design of applications using the Session and Initiation Protocol [25]. The toolkit provides call flow mod- eling, servlet design, and transformation before application development. By using the model templates and a train of modeling elements of the toolkit, it is easy to create a SIP design and a SIP servlet model. The powerful function of the toolkit is transformation, which translates servlet models and sequence diagrams into standard JAVA code that would be deployed in applications. While defining the activities and collaboration of a SIP application, the sequence diagram [25], which describes the object that has completed a certain course and the information of time sequence between objects, is fit for call flow modeling. SIP designs are often expressed as sequence diagrams. In fact, SIP in RFCs is always described as a simple form of sequence diagram. Based on the SIP modeling toolkit and the platform, Figure 16.4 is the sequence diagram model of the general SIP dialogue in RFC 3261 and Figure 16.5 is the message content of the INVITE message in Figure 16.4. While designing and before coding, the class diagram helps to design the class structure of SIP application. Important classes like SIP type, call flow messages, etc., are bases of SIP programmi