Modelling and Analysis of the INVITE Transaction of the Session Initiation Protocol Using Coloured Petri Nets

The Session Initiation Protocol (SIP) is a control protocol developed by the Internet Engineering Task Force for initiating, modifying and terminating multimedia sessions over the Internet. SIP uses an INVITE transaction to initiate a session. In this paper, we create a Coloured Petri Net (CPN) model for the INVITE transaction. Then we verify the general properties of the INVITE transaction by analysing the state space of the CPN model. The analysis results show that in most cases the INVITE transaction behaves as expected. However, in some circumstances, the transaction may terminate in an undesirable state while one communication party is still waiting for a response from its peer. Hence, we propose a set of changes to the INVITE transaction to correct the above problem. The result has shown that this revised INVITE transaction satisfies the properties that we have specified, and the undesirable terminal state has been eliminated.