@proceedings {249,
	title = {Quantitative dependability assessment of distributed systems subject to variable conditions},
	journal = {Internet and Distributed Computing Systems},
	volume = {8223},
	year = {2013},
	pages = {385{\textendash}398},
	publisher = {Springer Berlin Heidelberg},
	address = {Berlin},
	abstract = {<p>Dependability evaluation plays a key role in the design of a broad range of systems, where related properties have to be carefully analyzed in order to meet the requirements. This is particularly challenging in distributed contexts, where several entities may interact influencing each other. In this paper, we present an analytical framework that allows the study of a class of phenomena where different working conditions alternate, changing the stochastic behavior of the system. The proposed solution technique, based on phase type distributions and on ad-hoc fitting algorithms, can be applied in dependability evaluation of a wide class of distributed systems. Examples are provided to show the usefulness and the applicability of the framework, characterizing and investigating different dependability aspects of two distributed computing systems, i.e., connection-oriented networks and Internet of Things.</p>
},
	keywords = {Dependability assessments, Dependability evaluation, Distributed computing systems, Internet of Things (IOT), Phase Type Distributions., Solution techniques, Variable conditions},
	doi = {10.1007/978-3-642-41428-2_31},
	author = {Distefano S. and Bruneo D. and Longo F. and Scarpa M.}
}
@proceedings {255,
	title = {Software Rejuvenation in the Cloud},
	journal = {Proceedings of the 5th International ICST Conference on Simulation Tools and Techniques (SIMUTOOLS 12)},
	year = {2012},
	month = {23 marzo 2012},
	pages = {8{\textendash}16},
	publisher = {ICST},
	abstract = {<p>In this paper, we investigate how software rejuvenation can be used in a Cloud environment to increase the availability of a virtualized system composed of a single virtual machine monitor (VMM) on top of which a certain number of virtual machines (VMs) can be instantiated. We start from the assumption that the aging of a VMM increases with the number of VMs it is managing, thus characterizing the problem in terms of dynamic reliability. Therefore, by identifying the age of the VMM with its reliability and based on the conservation of reliability principle, we characterize the time to failure of the VMM through continuous phase type distributions. The system availability is thus modeled by an expanded continuous time Markov chain expressed in terms of Kronecker algebra in order to face the state space explosion and to keep memory of the age reached by the VMM in case the number of the hosted VMs change. Time-based rejuvenation is taken into consideration and the optimal timer is evaluated in order to maximize the VMM availability.</p>
},
	keywords = {cloud computing, Dynamic Availability, Phase Type Distributions., Rejuvenation, Virtualized Environments},
	author = {Bruneo D. and Longo F. and Puliafito A. and Scarpa M. and Distefano S.}
}
