The Experts below are selected from a list of 2403 Experts worldwide ranked by ideXlab platform

Kishor S. Trivedi - One of the best experts on this subject based on the ideXlab platform.

  • Performability Modeling for RAID Storage Systems by Markov Regenerative Process
    IEEE Transactions on Dependable and Secure Computing, 2018
    Co-Authors: Fumio Machida, Ruofan Xia, Kishor S. Trivedi
    Abstract:

    This paper presents a Performability model for RAID storage systems using Markov regenerative process to compare different RAID architectures. While homogeneous Markov models are extensively used for reliability analysis of RAID storage systems, the memory-less property of the sojourn time assumed in such models is not satisfied in reality, especially in disk rebuild process whose progress is not interrupted even at an event of another disk failure. In this paper, we use Markov regenerative process which allows us to model the generally distributed rebuild times providing a needed extension of the traditional Markov models. The Markov regenerative process is then used to assess the Performability of the storage system by assigning reward rates to each state based on the real storage benchmark results. Our numerical study characterizes the Performability advantage of RAID6 architecture over RAID10 architecture in terms of sequential read access. Our findings include that the effect of exponential assumption for the rebuild times has practically negligible effect when we focus on data availability. However, the effect this approximation on Performability prediction may not be negligible especially when the performance level drastically changes in degraded states. Our MRGP model provides more accurate prediction of Performability in such cases.

  • Dependability Modeling Using Petri-Nets Manish Malhotra SPN Stochastic Petri Net
    2016
    Co-Authors: M. Malhotra, Kishor S. Trivedi, Srn Stochastic, Reward Net
    Abstract:

    Petri-net based models have been extensively used for per-formance & Performability modeling to analyze computer & com-munication systems [ 1- 71. However, in the dependability model-ing co-unity, Petri-net based models have received co~i&rably less attention [8- 101. This paper describes a methodology to con

  • A Performability Modeling Framework Considering Service Components Deployment
    2015
    Co-Authors: Razib Hayat, Khan Fumio, Machida Poul, E. Heegaard, Kishor S. Trivedi
    Abstract:

    Abstract- The analysis of the system behavior from the pure performance viewpoint tends to be optimistic since it ignores failure and repair behavior of the system components. On the other hand, pure dependability analysis tends to be too conservative since performance considerations are not taken into account. The ideal way is to conduct the modeling of performance and dependability behavior of the distributed system jointly for assessing the anticipated system performance in the presence of system components failure and recovery. However, design and evaluation of the combined model of a distributed system for performance and dependability analysis is burdensome and challenging. Focusing on the above contemplation, we introduce a framework to provide tool based support for Performability modeling of a distributed software system that proposes an automated transformatio

  • Dharamraja S., “Performance Modeling of Wireless Communication Systems
    2015
    Co-Authors: Kishor S. Trivedi, S. Dharmaraja
    Abstract:

    The high expectations of performance and availability for wireless mobile systems has presented great challenges in the modelling and design of fault tolerant wireless systems. The proper modelling methodology to study the degradation of such systems is so-called Performability modelling. In this paper, we give overview of approaches for the construction and the solution of Performability models for wireless cellular networks. First, we start with the Erlang loss model, in which hierarchical and composite Markov chains are constructed to obtain loss formulas for a system with channel failures. Consequently, we develop two level hierarchical models for the wireless cellular system with handoff and channel failures. Then, for a TDMA system consisting of base repeaters and a control channel, we build a hierarchical Markov chain model for automatic protection switching (APS). Finally, we discuss stochastic reward net (SRN) models for Performability analysis of wireless systems. Copyright # 2003 John Wiley & Sons, Ltd. KEY WORDS: channel allocation; handoff; Markov chain; Markov reward model; Performability; stochastic reward net; wireless communication system

  • survivability analysis of power distribution in smart grids with active and reactive power modeling
    Measurement and Modeling of Computer Systems, 2012
    Co-Authors: Daniel Sadoc Menasche, Kishor S. Trivedi, Rosa M M Leao, Edmundo De Souza E Silva, Alberto Avritzer, Sindhu Suresh, Raymond A Marie, Lucia Happe, Anne Koziolek
    Abstract:

    A paradigm shift is taking place in the realm of power distribution networks. Power distribution networks that have been traditionally built to meet peak demand are now being automated to offer reliability on demand, i.e., smart distribution power grids can be automatically reconfigured after events such as power failures. In future distribution automation networks an important design decision will consist of which approach to use to avoid voltage drops. A standard approach is to add static capacitors to the distribution circuit. Novel techniques include the automatic reduction of active or reactive load through demand response, or the addition of distributed generators that can tradeoff active load for reactive load. In this paper, we introduce a new modeling approach to assist in such design decisions. The survivability of a system is its ability to function during and after a failure. In survivability analysis, the initial state of the system is set to a failure state, so survivability is “conditional Performability” [9, 11]. The main contribution of this paper is the development of a model to study the power distribution in smart grids during the (transient) period that starts after a failure till the system fully recovers. The proposed model bridges power flow modeling of reactive power compensation [8, 14] with Performability/survivability modeling of automation distribution networks [1]. We use a Markov chain to characterize the phased recovery of the system after a failure [5]. Then, we associate to each state of the Markov chain a set of corresponding rewards to characterize the active and reactive power supplied and demanded in that state.

Zhihe Zhou - One of the best experts on this subject based on the ideXlab platform.

  • 1 A Case Study: Validation of Guidance Control Software Requirements for Completeness, Consistency and Fault Tolerance
    2015
    Co-Authors: Frederick T Sheldon, Hye Yeon Kim, Zhihe Zhou
    Abstract:

    In this paper, we discuss a case study performed for validating a Natural Language (NL) based software requirements specification (SRS) in terms of completeness, consistency, and fault-tolerance. A partial verification of the Guidance and Control Software (GCS) Specification is provided as a result of analysis using three modeling formalisms. Zed was applied first to detect and remove ambiguity from the GCS partial SRS. Next, Statecharts and Activity-charts were constructed to visualize the Zed description and make it executable. The executable model was used for the specification testing and faults injection to probe how the system would perform under normal and abnormal conditions. Finally, a Stochastic Activity Networks (SANs) model was built to analyze how fault coverage impacts the overall Performability of the system. In this way, the integrity of the SRS was assessed. We discuss the significance of this approach and propose approaches for improving Performability/fault tolerance. 1

  • a case study validation of guidance control software requirements for completeness consistency and fault tolerance
    Pacific Rim International Symposium on Dependable Computing, 2001
    Co-Authors: Frederick T Sheldon, Hye Yeon Kim, Zhihe Zhou
    Abstract:

    We discuss a case study performed for validating a natural language (NL) based software requirements specification (SRS) in terms of completeness, consistency, and fault-tolerance. A partial verification of the Guidance and Control Software (GCS) Specification is provided as a result of analysis using three modeling formalisms. Zed was applied first to detect and remove ambiguity from the GCS partial SRS. Next, Statecharts and Activity-charts were constructed to visualize the Zed description and make it executable. The executable model was used for the specification testing and fault injection to probe how the system would perform under normal and abnormal conditions. Finally, a Stochastic Activity Networks (SANs) model was built to analyze how fault coverage impacts the overall Performability of the system. In this way, the integrity of the SRS was assessed. We discuss the significance of this approach and propose approaches for improving Performability/fault tolerance.

Armin Zimmermann - One of the best experts on this subject based on the ideXlab platform.

  • Performability analysis of services in a software defined networking adopting time based moving target defense mechanisms
    ACM Symposium on Applied Computing, 2020
    Co-Authors: Julio Mendonca, Jinhee Cho, Terrence J Moore, Frederica F Nelson, Hyuk Lim, Armin Zimmermann, Dong Seong Kim
    Abstract:

    Moving target defense (MTD) has been developed as an emerging technology to enhance system/network security by randomly and continuously changing attack surface. Despite the significant progress of recent efforts in analyzing the security effectiveness of MTD mechanisms, critical gaps still exist in terms of the impact of running MTD mechanisms on system performance and dependability, exposing a critical design tradeoff between security and performance. To investigate the tradeoff, we propose Performability models for evaluating services hosted in software-defined networks with a time-based MTD mechanism being deployed. We developed analytical models for evaluating key Performability metrics, in terms of response time, throughput, availability, host utilization, a number of requests lost, and cost (i.e., energy consumption plus profits lost due to dropped jobs). Our results showed that using the time-based MTD mechanism can (1) improve service response time and host utilization; (2) introduce a higher number of requests lost and higher overall cost; and (3) reduce service availability while still handling most of the jobs without much performance degradation.

  • GeoClouds Modcs: A Perfomability Evaluation Tool for Disaster Tolerant IaaS Clouds
    2016
    Co-Authors: Bruno Silva, Paulo Maciel, Jonathan Brilhante, Armin Zimmermann
    Abstract:

    Abstract—Performance and availability are key aspects to evaluate the quality of cloud computing systems. The assess-ment of these systems should consider the effects of queuing and failure/recovery behavior of data center subsystems and disaster occurrences. Additionally, penalties may be applied if the defined quality level of SLA contracts is not satisfied. Thus, IaaS providers need to evaluate the Performability level of its environment, considering, also, the possibility of disasters. A possible approach to protect cloud systems from natural disasters corresponds to the utilization of redundant data centers located far enough apart. However, the time to back up the VM data increases with the distance. To accomplish these issues, we propose a user-friendly tool, namely GeoClouds Modcs, for evaluating distributed cloud computing systems deployed into multiple data centers considering disaster occurrence. The proposed environment adopts a hybrid heterogeneous modeling approach, which includes Reliability Block Diagrams (RBD), Stochastic Petri Nets (SPN) and Cloud System High-Level models to perform the system evaluation. For specialized users, the tool also provides specific features that enable edit and evaluate the result SPN and RBD models on external evaluation tools (i.e., Mercury and TimeNET). To illustrate the proposed tool’s usability, we present a case study that evaluates a cloud computing distributed in different cities considering diverse user loads. Keywords—Performability evaluation tool, IaaS systems, stochas-tic petri nets I

  • petri net modelling and Performability evaluation with timenet 3 0
    Lecture Notes in Computer Science, 2000
    Co-Authors: Armin Zimmermann, Jorn Freiheit, Reinhard German, Gunter Hommel
    Abstract:

    This paper presents TimeNET, a software tool for the modelling and Performability evaluation using stochastic Petri nets. The tool has been designed especially for models with non-exponentially distributed firing delays. A general overview of the software package and its new features is given. The graphical user interface is completely rewritten. It integrates different model classes in a user-friendly and consistent way. One of the recent enhancements is an environment for the modelling and performance evaluation of manufacturing systems based on coloured stochastic Petri nets. A manufacturing system is modelled and analysed as an application example.

Frederick T Sheldon - One of the best experts on this subject based on the ideXlab platform.

  • 1 A Case Study: Validation of Guidance Control Software Requirements for Completeness, Consistency and Fault Tolerance
    2015
    Co-Authors: Frederick T Sheldon, Hye Yeon Kim, Zhihe Zhou
    Abstract:

    In this paper, we discuss a case study performed for validating a Natural Language (NL) based software requirements specification (SRS) in terms of completeness, consistency, and fault-tolerance. A partial verification of the Guidance and Control Software (GCS) Specification is provided as a result of analysis using three modeling formalisms. Zed was applied first to detect and remove ambiguity from the GCS partial SRS. Next, Statecharts and Activity-charts were constructed to visualize the Zed description and make it executable. The executable model was used for the specification testing and faults injection to probe how the system would perform under normal and abnormal conditions. Finally, a Stochastic Activity Networks (SANs) model was built to analyze how fault coverage impacts the overall Performability of the system. In this way, the integrity of the SRS was assessed. We discuss the significance of this approach and propose approaches for improving Performability/fault tolerance. 1

  • Journals> Annals of Software Engineering> Abstract Annals of Software Engineering Discontinued Export Citation: Text RIS
    2014
    Co-Authors: Frederick T Sheldon, Stefan Greiner
    Abstract:

    Composing, analyzing and validating software models to assess the Performability of competing design candidate

  • a case study validation of guidance control software requirements for completeness consistency and fault tolerance
    Pacific Rim International Symposium on Dependable Computing, 2001
    Co-Authors: Frederick T Sheldon, Hye Yeon Kim, Zhihe Zhou
    Abstract:

    We discuss a case study performed for validating a natural language (NL) based software requirements specification (SRS) in terms of completeness, consistency, and fault-tolerance. A partial verification of the Guidance and Control Software (GCS) Specification is provided as a result of analysis using three modeling formalisms. Zed was applied first to detect and remove ambiguity from the GCS partial SRS. Next, Statecharts and Activity-charts were constructed to visualize the Zed description and make it executable. The executable model was used for the specification testing and fault injection to probe how the system would perform under normal and abnormal conditions. Finally, a Stochastic Activity Networks (SANs) model was built to analyze how fault coverage impacts the overall Performability of the system. In this way, the integrity of the SRS was assessed. We discuss the significance of this approach and propose approaches for improving Performability/fault tolerance.

Ever Enver - One of the best experts on this subject based on the ideXlab platform.

  • Performability Analysis Methods for Clustered WSNs as Enabling Technology for IoT
    Performability in Internet of Things, 2019
    Co-Authors: Ever Enver
    Abstract:

    The Internet of Things (IoT) where sensors are used to couple the physical infrastructure with information and communication technologies is the main concept enabling applications such as smart homes, smart cities and intelligent transportation. The distributed sensor networks are used for interconnecting devices to transmit measured information, and control instructions. Therefore, energy efficiency and Performability of wireless sensor networks (WSNs) are critical for IoT applications. It is possible to combine WSN nodes into smaller groups and set one of the nodes as cluster head (CH) in order to increase the energy efficiency and decrease transmission delay. This approach of combining sensor nodes is known as clustering. Clustering is a technique that has been widely applied for achieving goals such as prolonging the network lifetime, improving scalability and balancing the residual energy of all nodes. Development of algorithms using equal and unequal clustering techniques has been a popular topic in recent studies. Most of these techniques use residual energy of nodes and distance to base station as parameters for selecting cluster heads.This chapter considers analytical modelling approaches of homogeneous clustered WSNs with a centrally located CH responsible for coordinating cluster communication. Unlike most of the existing studies, the performance and energy efficiency of the cluster head are considered together. Furthermore, potential failure of WSN nodes is considered and performance and availability models are integrated as well as the potential repair or replacement of sensor nodes. Existing techniques used in performance evaluation of multiserver systems in general are investigated and analysed in detail. Similarly, pure availability modelling approaches are also analysed. Pure performance modelling techniques, pure availability models and Performability models are considered critically for WSN configurations. Since the pure performance models tend to be too optimistic and pure availability models are too conservative, Performability models are used in turn for the evaluation.The two-dimensional continuous-time Markov chains (CTMC) which are popularly used in Performability analysis are considered together with queuing theory, in order to merge the performance and reliability processes which are relatively mutually independent. The possible use of open queuing networks to model the behaviour of the CH which is expecting intra-cluster as well as inter-cluster traffic while in various operative states is discussed. Among the possible operative conditions, we have states where the servers are broken, fully operational states, states with degraded service facilities and states where sleep scheduling mechanisms are also incorporated to extend the proposed energy models.

  • Approaches to Modelling and Analysis of Performability Evaluation in Wireless Environments
    2015
    Co-Authors: Ever, Yoney Kirsal, Kirsal Yonal, Ever Enver
    Abstract:

    Most wireless communication and mobile computing systems are expected to be operational 24 hours a day, 7 days a week. However, wireless communication systems encounter failures. Performability modelling and evaluation of wireless and mobile systems have been of interest for recent research work. Especially, because of the complexity of the next generation wireless and mobile systems, modelling and performance evaluation is essential to improve the architecture according to the quality of service (QoS) requirements and performance characteristics. This paper presents a Performability evaluation framework for wireless cellular networks in wireless environments using analytical modelling approaches. The availability and mobility issues are also considered in the proposed models. Well-known approximate Markov reward model solution and the exact Spectral expansion solution approaches are considered. Performability measures of proposed models, such as blocking probability and mean queue length are presented

  • Performability modelling of homogenous and heterogeneous multiserver systems with breakdowns and repairs
    2015
    Co-Authors: Ever Enver
    Abstract:

    This thesis presents analytical modelling of homogeneous multi-server systems with reconfiguration and rebooting delays, heterogeneous multi-server systems with one main and several identical servers, and farm paradigm multi-server systems. This thesis also includes a number of other research works such as, fast Performability evaluation models of open networks of nodes with repairs and finite queuing capacities, multi-server systems with deferred repairs, and two stage tandem networks with failures, repairs and multiple servers at the second stage. Applications of these for the popular Beowulf cluster systems and memory servers are also accomplished. Existing techniques used in performance evaluation of multi-server systems are investigated and analysed in detail. Pure performance modelling techniques, pure availability models, and Performability models are also considered. First, the existing approaches for pure performance modelling are critically analysed with the discussions on merits and demerits. Then relevant terminology is defined and explained. Since the pure performance models tend to be too optimistic and pure availability models are too conservative, Performability models are used for the evaluation of multi-server systems. Fault-tolerant multi-server systems can continue service in case of certain failures. If failure does not occur at a critical point (such as breakdown of the head processor of a farm paradigm system) the system continues serving in a degraded mode of operation. In such systems, reconfiguration and/or rebooting delays are expected while a processor is being mapped out from the system. These delay stages are also taken into account in addition to failures and repairs, in the exact Performability models that are developed. Two dimensional Markov state space representations of the systems are used for Performability modelling. Following the critical analysis of the existing solution techniques, the Spectral Expansion method is chosen for the solution of the models developed. In this work, open queuing networks are also considered. To evaluate their Performability, existing modelling approaches are expanded and validated by simulations, for Performability analysis of multistage open networks with finite queuing capacities. The performances of two extended modelling approaches are compared in terms of accuracy for open networks with various queuing capacities. Deferred repair strategies are becoming popular because of the cost reductions they can provide. Effects of using deferred repairs are analysed and Performability models are provided for homogeneous multi-server systems and highly available farm paradigm multi-server systems. Since one of the random variables is used to represent the number of jobs in one of the queues, analytical models for performance evaluation of two stage tandem networks suffer because of numerical cumbersomeness. Existing approaches for modelling these systems are actually pure performance models since breakdowns and repairs cannot be considered. One way of modelling these systems can be to divide one of the random variables to present both the operative and non-operative states of the server in one dimension. However, this will give rise to state explosion problem severely limiting the maximum queue capacity that can be handled. In order to overcome this problem a new approach is presented for modelling two stage tandem networks in three dimensions. An approximate solution is presented to solve such a system. This approach manifests itself as a novel contribution for alleviating the state space explosion problem for large and/or complex systems. When two state tandem networks with feedback are modelled using this approach, the operative states can be handled independently and this makes it possible to consider multiple operative states at the second stage. The analytical models presented can be used with various parameters and they are extendible to consider systems with similar architectures. The developed three dimensional approach is capable to handle two stage tandem networks with various characteristics for Performability measures. All the approaches presented give accurate results. Numerical solutions are presented for all models developed. In case the solution presented is not exact, simulations are performed to validate the accuracy of the results obtained

  • Analytical Modelling and Performability Evaluation of Multi-Channel WLANs with Global Failures
    'Agora University of Oradea', 2015
    Co-Authors: Ever Enver, Kirsal Yonal, Kirsal-ever Yoney, Gemikonakli Orhan
    Abstract:

    Wireless local area networks (WLANs) which are based on IEEE 802.11 standard are used widely in existing local area network configurations. IEEE 802.11 offers multiple non-overlapping channels to increase the capacity of the network. There are strong evidences that WLANs are prone to impairments. In order to improve the quality of service (QoS) and to evaluate the performance of WLANs realistically, the availability of the systems should be considered. This paper studies Performability evaluation of a multi-channel WLAN using analytical modelling approach. Unlike the existing studies, the failures of the overall system, where a critical function unit fails making all the channels unavailable are considered. A new term is introduced as global failures. It is possible to solve the models considered using matrix geometric method where system parameters and minimal non negative solution R is computed by an iterative method. However spectral expansion method is a well-known alternative where the iterative calculations for solving R is avoided using eigenvalues and eigenvectors. The exact spectral expansion method is employed to obtain Performability measures such as mean queue length and blocking probability. Iterative refinements are employed in solution of simultaneous equations.Publisher's Versio

  • Analytical Modelling and Performability Evaluation of Multi-Channel WLANs with Global Failures
    Agora University Press, 2015
    Co-Authors: Kirsal-ever Yoney, Kirsal Yonal, Ever Enver, Gemikonakli Orhan
    Abstract:

    Wireless local area networks (WLANs) which are based on IEEE 802.11 standard are used widely in existing local area network configurations. IEEE 802.11 offers multiple non-overlapping channels to increase the capacity of the network. There are strong evidences that WLANs are prone to impairments. In order to improve the quality of service (QoS) and to evaluate the performance of WLANs realistically, the availability of the systems should be considered. This paper studies Performability evaluation of a multi-channel WLAN using analytical modelling approach. Unlike the existing studies, the failures of the overall system, where a critical function unit fails making all the channels unavailable are considered. A new term is introduced as global failures. It is possible to solve the models considered using matrix geometric method where system parameters and minimal non negative solution R is computed by an iterative method. However spectral expansion method is a well-known alternative where the iterative calculations for solving R is avoided using eigenvalues and eigenvectors. The exact spectral expansion method is employed to obtain Performability measures such as mean queue length and blocking probability. Iterative refinements are employed in solution of simultaneous equations