Skip to Main Content
Authentication, authorization, and accounting (AAA) systems are one of the most significant architectural components of the current cellular networks and within the emerging IP multimedia subsystem (IMS) standard. Despite the operators' experience in AAA operations, very little is fundamentally known about the expected signaling rate towards the AAA system. In this paper, using stochastic and renewal theoretic techniques, we develop the first analytical model for the AAA signaling rate as a function of protocol parameters, users' access rates, session durations, and mobility. We provide model approximations and evaluate their accuracy under various operational conditions. Our results show that the AAA signaling rate is a monotonic non-linear function of the mobility rate and asymptotically converges to the AAA signaling rate in fixed networks. We also show that by adjusting the accounting interim and the authorization-lifetime intervals from half to full mean session duration, it is possible to define an AAA operational range for accounting messages that minimizes the signaling rate fluctuations due to likely perturbations in session and mobility statistics. The results also include the effect of the session dropping during handoffs and shows that is marginal in operational networks.