, each of which is a non-hierarchical CPN. We don't care about the formal definition of a whole HCPN, as hierarchical method here only contributes to the modeling process. For SIP modeling, as we mention above, denote SIP messages and system states which are stored in P mapping through C. IN defines the initialized state of SIP such as UA owns a SIP message token INVITE. A, G and E master the whole control flows of SIP. G is similar to R of FSM. By formally defining CPN, we can apply the properties and related analysis tools of CPN for analysis of the SIP model, which will be presented in 16.3.4. The timed factor in the HCPN model can be represented to two ways. The first is to add time to that each token could take time which indicates the time it runs. The other is to add time to T that each transition consumes time to deal with the input tokens and to finish defined actions. And then, the whole system is labeled with time. Here, we introduce the tool we use to model and simulate SIP through timed HCPN, which gives powerful functions for our purpose-CPN tools [29]. CPN tools support hierarchical modeling of SIP with a set of tools called hierarchical tools, such as the "Move to Subpage" tool to relate a transition with a subpage and "Set Subpage" tool to assign subpages to the substitution transitions on a superpage. CPN tools also support timed modeling, which provides temporal inscription. It introduces a new color set called timed color set, which appends the keyword "timed" to the color set declaration, then tokens representing the color set would take time and change the value as model runs. Also, each transition owns a function to add time by attaching an INT time to keyword "@+." With the definition of timed color set, there are also time simulator functions for query and analysis [29]. One of the main advantages of CPN tools is the powerful simulation, perfor- mance, and state space analysis tools. Simulation tools can run a simulation of an existing model, manually choose bindings, change marking durin