Performance Evaluation of IMS-Based Core Networks in Presence of Failures

In order to evaluate performance of mobile networks, it is necessary to consider the occurrence of random failures causing performance degradation and the consequent repair actions. This approach is especially suitable for next generation networks based on the Third Generation Partnership Project (3GPP) IP Multimedia Subsystem (IMS), as a consequence of the very high Quality of Service levels required by telecommunication operators´ subscribers. IMS core network signalling servers can be modeled as multi-state elements, where server states correspond to different performance levels. The number of sessions handled by a single server per time unit is one of the performance figure that can be considered. Given a demand profile, some redundancy techniques must be adopted to meet the typical requirements for a telecommunication network in terms of service availability and, in this paper, a redundancy optimization problem is solved by using a Universal Generating Function approach.