@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 = {

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.

}, 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 {250, title = {Workload-Based Software Rejuvenation in Cloud Systems}, journal = {IEEE TRANSACTIONS ON COMPUTERS}, volume = {62}, year = {2013}, pages = {1072{\textendash}1085}, abstract = {

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.

}, 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 = {

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.

}, 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.} } @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 = {

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.

}, 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.} } @proceedings {257, title = {Monitoring Energy Consumption in an Industrial Site}, journal = {Advances in Computer, Communication, Control and Automation}, volume = {121}, year = {2011}, month = {20, 2011}, pages = {53{\textendash}60}, publisher = {Springer}, address = {Heidelberg}, abstract = {

The Smart Grid vision imposes a new approach towards energy supply that is more affordable, reliable and sustainable. The core of this new vision is the use of advanced technology to monitor power system dynamics in real time and identify system in stability. In this pa-per we present a real time analysis tool specifically designed to monitor an industrial site with particular attention to power consumption. This solution, based on Wireless Sensor Networks, is able to produce useful results and to provide statistic analysis useful for the future choices of the industrial company.

}, keywords = {middleware., routing protocols, sensor networks}, author = {Bruneo D. and Cucinotta A. and Longo Minnolo A. and Puliafito A. and Scarpa A.} } @proceedings {304, title = {Mobile Middleware: Definition and Motivations}, journal = {The Handbook of Mobile Middleware}, year = {2006}, pages = {145{\textendash}167}, publisher = {Auerbach (CRC press)}, address = {NEW YORK}, author = {Bruneo D. and Marco Scarpa and A. Puliafito}, editor = {BELLAVISTA P.; CORRADI A. EDS} }