Modeling of IMS Call Flows: Load Estimation for Core Network

The support of mobile multimedia applications will require powerful control capabilities, such as those envisaged in the IP Multimedia Subsystem (IMS), which enables operators and service providers to control bearers, sessions and charging of multimedia services using Internet protocols. IMS enables operators and service providers to control bearers, sessions and charging of multimedia services using Internet protocols. IMS is seen as the main "enabler" to fixed-mobile convergence, as IMS provides services independently of the access technology and enables a smooth interoperation between different network types. Estimating the load and stress on core network components for IMS services is a requirement for the successful implementation of the IMS architecture. In this paper, we describe a formal procedure for characterizing a network service or application by means of annotated sequence diagrams, and deriving analytical models that allow us to investigate the load on different network elements imposed by the application. Our approach brings together software models that capture the semantics of the application and analytical models that describe the application in terms of states and state transitions. Our procedure is embodied in a software component and here, as a prototypical example of its utility, we apply it to the estimation of the load on the Serving Call Session Control Function (S-CSCF) for a Voice Call Continuity (VCC) Service between a GSM network and a WLAN - to demonstrate generality, we also apply it to an IMS compliant content distribution scenario. Such semi-automated results are critical in the planning and provisioning of IMS-compliant architectures, particularly those that support resource intensive mobile multimedia applications.