@proceedings {250,
	title = {Workload-Based Software Rejuvenation in Cloud Systems},
	journal = {IEEE TRANSACTIONS ON COMPUTERS},
	volume = {62},
	year = {2013},
	pages = {1072{\textendash}1085},
	abstract = {<p>Cloud Computing is a promising paradigm able to rationalize the use of hardware resources by means of virtualization. Virtualization allows to instantiate one or more virtual machines (VMs) on top of a single physical machine managed by a virtual machine monitor (VMM). Similarly to any other software, a VMM experiences aging and failures. Software rejuvenation is a proactive fault management technique that involves terminating an application, cleaning up the system internal state, and restarting it in order to prevent the occurrence of future failures. In this work, we propose a technique to model and evaluate the VMM aging process and to investigate the optimal rejuvenation policy that maximizes the VMM availability under variable workload conditions. Starting from dynamic reliability theory and adopting symbolic algebraic techniques, we investigate and compare existing time-based VMM rejuvenation policies. We also propose a time-based policy that adapts the rejuvenation timer to the VMM workload condition improving the system availability. The effectiveness of the proposed modeling technique is demonstrated through a numerical example based on a case study taken from the literature.</p>
},
	keywords = {cloud computing, Dynamic Availability, Kronecker algebra, phase type distributions, Time-based Rejuvenation},
	doi = {10.1109/TC.2013.30},
	author = {Bruneo D. and Distefano S. and Longo F. and Puliafito A and Scarpa M}
}
@proceedings {256,
	title = {Evaluating wireless sensor node longevity through Markovian techniques},
	journal = {COMPUTER NETWORKS},
	volume = {56},
	year = {2012},
	pages = {521{\textendash}532},
	abstract = {<p>Wireless sensor networks are constituted of a large number of tiny sensor nodes randomly distributed over a geographical region. In order to reduce power consumption, nodes undergo active-sleep periods that, on the other hand, limit their ability to send/receive data. The aim of this paper is to analyze the longevity of a battery-powered sensor node. A battery discharge model able to capture both linear and non linear discharge processes is presented. Then, two different models are proposed to investigate the longevity, in terms of reliability, of sensor nodes with active-sleep cycles. The first model, well known in the literature, is based on the Markov reward theory and on the evaluation of the accumulated reward distribution. The second model, based on continuous phase type distributions and Kronecker algebra, represents the main contribution of the present work, since it allows to relax some assumptions of the Markov reward model, thus increasing its applicability to more concrete use cases. In the final part of the paper, the results obtained by applying the two techniques to a case study are compared in order to validate and highlight the benefits of our approach and demonstrate the utility of the proposed model in a quite complex and real scenario.</p>
},
	keywords = {Battery discharge process, Continuous phase type distributions, Energy consumption, Kronecker algebra, Markov reward models, Reliability},
	doi = {10.1016/j.comnet.2011.10.003},
	author = {Bruneo D. and Distefano S. and Longo F. and Puliafito A. and Scarpa M.}
}
