@article {35, title = {Adding long-term availability, obfuscation, and encryption to multi-cloud storage systems}, journal = {Journal of Network and Computer Applications}, volume = {59}, year = {2016}, month = {01/2016}, pages = {208-218}, abstract = {

Abstract Nowadays, storage services offer a new way for Cloud providers to do business. This new trend is proved by the number of Cloud storage providers that are continuously appearing on the market. By now, using Cloud storage services is becoming a common practice for end-users. However, the current Cloud storage providers do not offer any guarantees regarding long-term availability and privacy. In fact, data stored in the Cloud could be locked-in, lost, or violated in terms of privacy. In this work, we present an innovative system that on one hand allows end-users to simultaneously rely on different Cloud storage providers in a transparent way and on the other hand to enforce long-term availability, obfuscation, and encryption. Our system is highly reliable, in fact, if a provider is not temporarily or permanently available, end-users continue accessing their data in a secure way. In addition, only the end-users have the full control of the overall security of their data and no sensitive information are disclosed to Cloud storage providers. Several experiments allow us to discuss the performance of our system compared against existing solutions.

}, keywords = {cloud computing, Long-term availability, Privacy, Reliability, Storage Clouds}, issn = {1084-8045}, doi = {10.1016/j.jnca.2014.09.021}, url = {http://www.sciencedirect.com/science/article/pii/S1084804514002288}, author = {A. Celesti and M. Fazio and M. Villari and A. Puliafito} } @article {Longo2015280, title = {Dependability modeling of Software Defined Networking}, journal = {Computer Networks}, volume = {83}, year = {2015}, note = {cited By 6}, pages = {280-296}, publisher = {Elsevier}, abstract = {

Software Defined Networking (SDN) is a new network design paradigm that aims at simplifying the implementation of complex networking infrastructures by separating the forwarding functionalities (data plane) from the network logical control (control plane). Network devices are used only for forwarding, while decisions about where data is sent are taken by a logically centralized yet physically distributed component, i.e., the SDN controller. From a quality of service (QoS) point of view, an SDN controller is a complex system whose operation can be highly dependent on a variety of parameters, e.g., its degree of distribution, the corresponding topology, the number of network devices to control, and so on. Dependability aspects are particularly critical in this context. In this work, we present a new analytical modeling technique that allows us to represent an SDN controller whose components are organized in a hierarchical topology, focusing on reliability and availability aspects and overcoming issues and limitations of Markovian models. In particular, our approach allows to capture changes in the operating conditions (e.g., in the number of managed devices) still allowing to represent the underlying phenomena through generally distributed events. The dependability of a use case on a two-layer hierarchical SDN control plane is investigated through the proposed technique providing numerical results to demonstrate the feasibility of the approach. {\textcopyright} 2015 Elsevier B.V.

}, keywords = {Availability, Complex networks, Controllers, Degree of distributions, Distributed components, Electric network topology, Information dissemination, Markov processes, Networking infrastructure, Non-Markovian, Quality control, Quality of service, Random processes, Reliability, Reliability and availability, Software defined networking (SDN), Software reliability, Software-defined networkings, Stochastic models, Stochastic systems, Topology, Type expansions}, issn = {13891286}, doi = {10.1016/j.comnet.2015.03.018}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84946489290\&doi=10.1016\%2fj.comnet.2015.03.018\&partnerID=40\&md5=b4f32c89d2b7b79fefcaf97082764960}, author = {Francesco Longo and Salvatore Distefano and Dario Bruneo and Marco Scarpa} } @booklet {47, title = {Data Reliability In Multi-provider Cloud Storage Service With RRNS}, journal = {Advances in Service-Oriented and Cloud Computing}, volume = {393}, year = {2013}, month = {13}, pages = {83{\textendash}93}, publisher = {Springer - Verlag Berlin Heidelberg}, address = {Berlin}, abstract = {Nowadays, more and more Cloud storage providers are appearing on the market. Nevertheless, data availability and confidentiality represent critical issues considering Cloud computing. This paper discusses an approach that on one hand enables customers to use at the same time different Cloud storage providers, and that on the other hand guarantees both data redundancy and obfuscation. According to our approach, files are fragmented and stored in different Cloud storage providers by means of the Redundant Residue Number System (RRNS). Besides providing us data redundancy, RRNS allows us to preserve the data confidentiality by means of an obfuscation-base strategy spreading metadata over different cloud providers. In addition, our approach allows a customer to retrieve his/her files even if a cloud storage provider is not available anymore. Experiments highlight the factors that have to be considered to configure the system according to the customer{\textquoteright}s requirements.}, keywords = {Big Data, cloud computing, Confidentiality, Reliability, Storage}, url = {http://link.springer.com/chapter/10.1007/978-3-642-45364-9_8}, author = {M. Villari and A. Celesti and F. Tusa and A. Puliafito} } @article {43, title = {Evaluating A File Fragmentation System For Multi-provider Cloud Storage}, journal = {SCALABLE COMPUTING. PRACTICE AND EXPERIENCE}, volume = {14}, year = {2013}, pages = {265{\textendash}277}, abstract = {

Currently, storage services represent a new way to do business in Cloud computing. This new trend is proved by the number of Cloud storage providers that are appearing on the market. In this work, we present an innovative approach useful for using different Cloud storage providers in a transparent way, avoiding both data lock-in and possible data privacy violation that can be caused by providers themselves. More specifically, we propose an approach enabling Cloud customers to rely on many Cloud storage providers. Differently from other solutions, with our approach only the customers have the full control of their data, and in addition, if a provider suddenly disappears and/or it is not available anymore, the customers will be able to continue accessing their data, reconstructing them from data fragments replicated in other Cloud storage providers. The paper shows how such an approach works. In particular, experiments, besides proving the goodness of our approach, also provide several guidelines regarding how to properly configure software systems in order to meet the customer{\textquoteright}s requirements (in terms of both QoS and costs).

}, keywords = {Big Data, cloud computing, Confidentiality., Reliability, Storage}, doi = {10.12694/scpe.v14i4.932}, url = {http://www.scpe.org/index.php/scpe/article/view/932/0}, author = {Massimo Villari and Antonio Celesti and Maria Fazio and Antonio Puliafito} } @article {Bruneo20132090, title = {Stochastic evaluation of QoS in service-based systems}, journal = {IEEE Transactions on Parallel and Distributed Systems - IEEE Computer Society}, volume = {24}, number = {10}, year = {2013}, note = {cited By 7}, pages = {2090-2099}, abstract = {

WS-BPEL language has become the industrial standard to design and orchestrate modular applications, formalizing service compositions and business relationships among providers and consumers. Once service level agreements (SLAs) among the parties are established, effective tools for evaluating appropriate measurements have to be developed to meet the requirements. However, the design of quality of service (QoS)-guaranteed composed Web services (WSes) still requires several efforts. This work aims at proposing a complete method to study the QoS of a composed WS at design time, i.e., when the process is specified by using WS-BPEL. Starting from the nonfunctional properties of the WS to compose, we propose a technique to derive non-Markovian stochastic Petri net (NMSPN) models from WS-BPEL processes, with the final goal of evaluating parameters such as the service time distribution and the service reliability. To demonstrate the effectiveness of the proposed method and to validate the obtained model, a nontrivial example implementing a travel agency flight reservation process, exposed as a synchronous composed WS, is investigated. {\textcopyright} 1990-2012 IEEE.

}, keywords = {Business Process, Business relationships, Design, Information services, Non functional properties, Performance, Quality of service, Random access storage, Reliability, Service level agreement (SLAs), Service oriented architecture (SOA), Service time distribution, Stochastic Petri Nets, Web services, WS-BPEL}, issn = {10459219}, doi = {10.1109/TPDS.2012.313}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-84883410035\&partnerID=40\&md5=cdebb3fe5a36e131fd3a9485d01fe3c6}, author = {Dario Bruneo and Salvatore Distefano and Francesco Longo and Marco Scarpa} } @article {Bruneo2012521, title = {Evaluating wireless sensor node longevity through Markovian techniques}, journal = {Computer Networks - Elsevier }, volume = {56}, number = {2}, year = {2012}, note = {cited By 13}, pages = {521-532}, 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. {\textcopyright} 2011 Published by Elsevier B.V.

}, keywords = {Algebra, Battery discharge, Continuous phase, Discharge process, Electric network synthesis, Energy utilization, Kronecker algebra, Markov reward, Markov reward model, Markov reward models, Markovian, Randomly distributed, Reliability, Reliability theory, Sensor nodes, Sensors, Wireless sensor node}, issn = {13891286}, doi = {10.1016/j.comnet.2011.10.003}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-84856063119\&partnerID=40\&md5=ecbae538bceec8598d787ee3b936a8e1}, author = {Dario Bruneo and Salvatore Distefano and Francesco Longo and Antonio Puliafito and Marco Scarpa} } @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.} } @article {Distefano20123701, title = {Investigating dynamic reliability and availability through state-space models}, journal = {Computers and Mathematics with Applications - Elsevier Ltd}, volume = {64}, number = {12}, year = {2012}, note = {cited By 7}, pages = {3701-3716}, abstract = {

Quality standards impose increasingly stringent requirements and constraints on quality of service attributes and measures. As a consequence, aspects, phenomena, and behaviors, hitherto approximated or neglected, have to be taken into account in quantitative assessment in order to provide adequate measures satisfying smaller and smaller confidence intervals and tolerances. With specific regards to reliability and availability, this means that interferences and dependencies involving the components of a system can no longer be neglected. Therefore, in order to support such a trend, specific techniques and tools are required to adequately deal with dynamic aspects in reliability and availability assessment. The main goal of this paper is to demonstrate how state-space based techniques can satisfy such a demand. For this purpose some examples of specific dynamic reliability behaviors, such as common cause failure and load sharing, are considered applying state-space based techniques to study the corresponding reliability models. Different repair policies in availability contexts are also explored. Both Markovian and non-Markovian models are studied via phase type expansion and renewal theory in order to adequately represent and evaluate the considered dynamic reliability aspects in case of generally distributed lifetimes and times to repair. {\textcopyright} 2012 Elsevier Ltd. All rights reserved.

}, keywords = {Availability, Common cause failure, Confidence interval, Dynamic aspects, Dynamic reliability, Load sharing, Markov processes, Markov regenerative process, Markovian, Non-Markovian, Quality of service, Quality standard, Quantitative assessments, Reliability, Reliability and availability, Reliability model, Renewal theory, Repair policy, Semi Markov model, State-space, State-space models, Stringent requirement}, issn = {08981221}, doi = {10.1016/j.camwa.2012.02.038}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-84870249108\&partnerID=40\&md5=9ecb143c24c7493a16292faa4f50d175}, author = {Salvatore Distefano and Francesco Longo and Kishor S. Trivedi} } @proceedings {Bruneo20128, title = {Software rejuvenation in the cloud}, journal = {Proceedings of the 5th International Conference on Simulation Tools and Techniques (SIMUTools)}, year = {2012}, note = {cited By 0; Conference of 5th International Conference on Simulation Tools and Techniques, SIMUTools 2012 ; Conference Date: 19 March 2012 Through 23 March 2012; Conference Code:110134}, pages = {8-16}, publisher = {ICST}, address = {Desenzano del Garda, Italy, 19-23 March 2012}, 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. Copyright {\textcopyright} 2012 ICST.

}, keywords = {Availability, cloud computing, Continuous phase type distributions, Continuous time Markov chain, Continuous time systems, Endocrinology, Java programming language, Markov processes, phase type distributions, Rejuvenation, Reliability, Reliability principles, Software rejuvenation, Virtual machine monitors, Virtual reality, Virtualized environment}, isbn = {9781450315104}, doi = {10.4108/icst.simutools.2012.247772}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-84922767370\&partnerID=40\&md5=a03b06eec703c94d55c0f4875f181902}, author = {Dario Bruneo and Francesco Longo and Antonio Puliafito and Marco Scarpa and Salvatore Distefano} } @article {275, title = {Energy control in dependable Wireless Sensor Networks: a modeling perspective}, journal = {PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS. PART O, JOURNAL OF RISK AND RELIABILITY}, volume = {225}, year = {2011}, pages = {424{\textendash}434}, abstract = {

Wireless sensor networks (WSN) are composed of a large number of tiny sensor nodes randomly distributed over a geographical region. In order to reduce power consumption, battery-operated sensors undergo cycles of sleeping-active periods that reduce their ability to send/receive data. Starting from the Markov reward model theory, this paper presents a dependability model to analyse the reliability of a sensor node. Also, a new dependability parameter is introduced, referred to as producibility, which is able to capture the capability of a sensor to accomplish its mission. Two different model solution techniques are proposed, one based on the evaluation of the accumulated reward distribution and the other based on an equivalent model based on non-Markovian stochastic Petri nets. The obtained results are used to investigate the dependability of a whole WSN taking into account the presence of redundant nodes. Topological aspects are taken into account, providing a quantitative comparison among three typical network topologies: star, tree, and mesh. Numerical results are provided in order to highlight the advantages of the proposed technique and to demonstrate the equivalence of the proposed approaches.

}, keywords = {Energy consumption, Markov reward models, network topology, non-Markovian stochastic Petri nets, producibility, Reliability, Wireless sensor networks}, doi = {10.1177/1748006X10397845}, author = {D. Bruneo and A. Puliafito and Marco Scarpa} } @proceedings {Distefano201045, title = {Symbolic representation techniques in dynamic reliability evaluation}, journal = {Proceedings of the 12th IEEE International Symposium on High Assurance Systems Engineering (HASE)}, year = {2010}, note = {cited By 9; Conference of 2010 IEEE 12th International Symposium on High Assurance Systems Engineering, HASE 2010 ; Conference Date: 3 November 2010 Through 4 November 2010; Conference Code:83929}, pages = {45-53}, publisher = {IEEE Computer Society}, address = {San Jose, CA, United States, 3-4 November 2010}, abstract = {

The increasing demand of quality presses towards more specific requirements, tighter constraints, and higher standards. It is thus necessary to provide new paradigms, techniques, and tools to adequately model and evaluate complex systems. This paper mainly focuses on reliability aspects, also taking into account dynamic-dependent interactions among components. Starting from the conservation of reliability principle, we characterize the time to failure of the system components through continuous phase type distributions. The system reliability is thus modeled by an expanded Markov chain expressed in terms of Kronecker algebra in order to face the state space explosion and to represent the memory policies related to the aging process. A two-component system is taken as example to demonstrate the effectiveness of the technique and to validate it. {\textcopyright} 2010 IEEE.

}, keywords = {Aging process, Algebra, Complex systems, Continuous phase, Dynamic reliability, Kronecker algebra, Markov Chain, Markov processes, phase type distributions, Quality assurance, Reliability, State-space explosion, symbolic representation, System components, System reliability, Systems engineering, Time to failure, Two component systems}, isbn = {9780769542928}, issn = {15302059}, doi = {10.1109/HASE.2010.28}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-79951924261\&partnerID=40\&md5=8ed2be2a9f6a7e9d891ed3fb58789d6f}, author = {Salvatore Distefano and Francesco Longo and Marco Scarpa} }