Semi-Markov models for performance evaluation of failure-prone IP multimedia subsystem core networks

Next generation telecommunication core networks are typically based on the Third Generation Partnership Project Internet protocol (IP) multimedia subsystem (IMS). Their planning and deployment must take into account the occurrence of random failures causing performance degradations, in order to assess and maintain a high level of quality of service. In particular, IMS signalling servers can be modelled as repairable multi-state elements where states correspond to different performance levels. This article provides an evaluation of IMS signalling network performance in long runs in terms of two metrics adopted in the practice, such as the number of call set-up sessions that the network can manage at the same time and the call set-up delay. A semi-Markov model has been adopted for the IMS servers, which allows as well for non-exponential probability distributions of sojourn times, as often observed in real networks. Furthermore, a redundancy optimization problem is solved in an IMS-based realistic scenario, to the aim of minimizing the deployment cost of a telecommunication network with a given availability requirement.