Giovanni Cordeiro Barroso

Multiobjective Optimization Algorithm for Switch Placement in Radial Power Distribution Networks

Customer satisfaction counts very much to the electric power distribution companies. The improvement of reliability indices is an effective way to achieve this goal. The optimal placement of power switches is a desirable procedure because while it reduces investment in network assets, it also reduces the number of customers not supplied by outages and, accordingly, improves system reliability. This paper proposes a multiobjective optimization approach for switch placement based on the particle swarm optimization method applied to radial distribution networks of power utilities. The proposed algorithm gives a set of solutions instead of a single one. It intends to be a valuable and flexible tool for planning modern and reliable power distribution networks. Simulation results when using the IEEE 123-node test system and the Roy Billinton Test System are presented as testbeds.

Assuring QoS differentiation and load balancing on web servers clusters

The number of users of services deployed on the Internet has been increasing continually. This has been causing overload in a great amount of Web servers reducing QoS (quality of service) offered by service providers. Furthermore, users with different QoS aspirations have been forced to share available processing resources in a same way even they can pay more. To deal with these problems, a possible solution is the balancing of imposed load among a certain number of computers to improve performance and the use of admission control mechanisms to allow differentiated allocation of resources for specific service classes. This paper presents WS-DSAC (Web servers ifferentiated services admission control), a diffserv-based admission control and load balancing mechanism conceived to improve QoS on Web servers clusters. WS-DSAC has three main aims: to balance the imposed load, to guarantee different QoS levels and to use available resources in an effective way. We also present evaluation experiments showing the mechanism is able to achieve these objectives

A Petri net-based decision-making framework for assessing cloud services adoption

Cloud services are widely used nowadays, especially in Infrastructure as a service (IaaS), with vendors offering several purchasing options and expanding the range of services offered on almost a daily basis. Cost reduction is a major factor promoting the adoption of cloud services among enterprises. However, qualitative factors need to be evaluated as well, thus rendering the decision regarding the adoption of cloud services among enterprises a non-trivial task for Information Technology (IT) managers. In this paper, we propose a place/transition or Petri net-based multi-criteria decision-making (MCDM) framework to assess a cloud service in comparison with a similar on-premises service. The framework helps IT managers choose between two such options, and can be used for any type of cloud service: Infrastructure as a Service (IaaS), Platform as a service (PaaS), Software as a service (SaaS), etc. Because its low cost is among the most important reasons for adopting cloud services, we also propose a Petri net to model cost savings using the spot instances purchasing option in public clouds. Through simulation of several scenarios, we conclude that spot instances present a very interesting cost-saving option in the auto-scaling process, even for simple business applications using few servers. A Petri net-based multi-criteria decision making framework to assess a cloud service against a similar on-premises service.Our framework helps IT managers choose between two such options, and can be used for any type of cloud service.We also propose a Petri net to model cost savings using the spot instances purchasing option in public clouds.Simulations showed that spot instances present a promising cost-saving option in the auto-scaling process, even for simple business applications using few servers.

Switch placement algorithm for reducing customers outage impacts on radial distribution networks

Electricity has become a highly valuable resource for human beings. Its shortage is handled the same way as water, food and other essential environmental resources by governments. Outages of electricity are not acceptable by customers and are fully controlled by regulatory agencies through power system reliability indexes. The violation of such indexes normally imply in penalties to power utility companies. The application of methods and techniques to improve the power systems reliability, efficiency and customer satisfaction are desirable and constantly pursued by electric power utilities. The suitable placement of sectionalizer switches along radial distribution feeders to reduce the impact of outages is a useful approach to improve the system reliability performance. Heuristic methods are suitable and successfully employed for this task. This paper proposes a switch placement optimization algorithm aimed to reduce the number of affected customers by power outages. The algorithm is based on Particle Swarm Optimization method and its feasibility is demonstrated by applying it on a typical 3-bus distribution system. Failure rates are commonly applied in switch placement issues. A new objective function based on the number of customers not supplied is proposed to substitute the failure rates which are not always given to know by the utility companies.

SPEWS: A Framework for the Performance Analysis of Web Services Orchestrated with BPEL4WS

This paper addresses quality of service aspects of Web Services (WS) orchestrations created using the Business Process Execution Language for Web Services (BPEL4WS). BPEL4WS is a promising language describing the WS orchestrations in form of Business Processes, but it lacks of a sound formal semantic, which hinders the formal analysis and verification of business processes specified in it. Formal methods, like Petri Nets (PN), may provide a means to analyse BPEL4WS processes, evaluating its performance, detecting weaknesses and errors in the process model already at design-time. A framework for transformation of BPEL4WS into Generalized Stochastic Petri Nets (GSPN) is proposed to analyse the performance and throughput of WS, based on the execution of orchestrated processes.

DARC: A Dynamic Architecture for Reconfiguration of Web Servers Clusters Using Multiagent Systems

Allocating resources in a web server cluster is usually performed nowadays by a cluster administrator. However, due to the dynamics of the Internet as far as the use of resources is concerned, such task may be considered critical and inefficient if accomplished manually. This paper presents an architecture that performs an automatic dynamic reconfiguration using a multi agent system. The conception, specification and implementation of the architecture are presented. Moreover, several experimental results prove the efficiency and the interest of the proposal.

A load-balancing distributed platform based on differentiated services for a telecare application

Telecare applications are composed by different kinds of services. Some of these services require high level availability and performance because they involve human lives. One possible solution to improve availability and performance in these applications is to make an efficient distribution of service avoiding concentration of several tasks on only one server. This work presents a load-balancing platform based on differentiation of services that increases application-level QoS (quality of service) in a telecare application. The platform allows the coexistence of Internet services and distributed objects. We also present experimental results showing that the platform balances the imposed load and differentiates the QoS offered to different services.

Modelagem de um sistema de gestão na Educação a Distância no Brasil utilizando redes de Petri Coloridas

A gestao e uma pratica que envolve planejamento, organizacao, direcao, controle e acompanhamento de atividades. Este trabalho apresenta a modelagem em redes de Petri coloridas (RPC) de um sistema de gestao em Programas de Educacao a Distância (EaD), em instituicao publica de ensino no Brasil. E importante ressaltar que a gestao envolve alto grau de complexidade, pois para implantar e manter os cursos ha necessidade de integrar um conjunto de processos que se influenciam mutuamente, visando o alcance de metas pre-definidas. Para isso ha divisao de tarefas, atribuicoes de responsabilidades, definicao de niveis de autoridade e estabelecimento de mecanismos de comunicacao. O sistema de gestao sistemica atualmente aplicado nos cursos ofertados na modalidade a distância no IFCE (Instituto Federal de Educacao, Ciencia e Tecnologia do Ceara), compreende cinco grandes pilares, que sao: institucional, pedagogico, tecnologico, administrativo-financeiro e recursos humanos. O escopo deste trabalho trata da modelagem do processo de gestao administrativo-financeira em redes de Petri coloridas. A analise do modelo ajudou a identificar e melhorar as acoes/atividades desenvolvidas nesse processo e permitiu uma visualizacao grafica do fluxo do processo administrativo-financeiro auxiliando a equipe da IES (Instituicao de Ensino Superior) nas acoes de planejamento e execucao dos recursos captados para oferta dos cursos na modalidade a distância. Outro aspecto importante do resultado da modelagem refere-se a transformacao de conhecimento tacito em conhecimento explicito. Sendo assim, a execucao do processo administrativo-financeiro torna-se menos dependente das pessoas envolvidas na elaboracao do proprio processo.

Scenario preprocessing approach for the reconfiguration of fault-tolerant NoC-based MPSoCs

The latest technologies of integrated circuit manufacturing allow billions of transistors to be arranged on a single chip, enabling the chip to implement a complex parallel system, which requires a communications architecture that has high scalability and a high degree of parallelism, such as a Network-on-Chip (NoC). These technologies are very close to the physical limitations, which increases the faults in manufacturing and at runtime. Therefore, it is essential to provide a method for fault recovery that would enable the NoC to operate in the presence of faults and still ensure deadlock-free routing. The preprocessing of the most probable fault scenarios enables us to anticipate the calculation of deadlock-free routings, reducing the time that is necessary to interrupt the system during a fault occurrence. This work proposes a technique that employs the preprocessing of fault scenarios based on forecasting fault tendencies, which is performed with a fault threshold circuit operating in accordance with high-level software. We propose methods for dissimilarity analysis of scenarios based on cross-correlation measurements of link fault matrices. Experimental results employing RTL simulation with synthetic traffic prove the quality of the analytic metrics that are used to select the preprocessed scenarios. Furthermore, the experiments show the efficacy and efficiency of the proposed dissimilarity methods, quantifying the latency penalization when using the coverage scenarios approach.

Modeling the use of spot instances for cost reduction in cloud computing adoption using a Petri net framework

An effective decision-making about using Infrastructure as a Service (IaaS) resources in cloud computing projects is still a challenge to managers. We need to optimize resources use in cloud services, to obtain financial success in cloud projects. In this work, we propose a Petri net framework to model possible cost savings using public clouds spot instances pricing scheme. The results from initial simulations indicate that spot instances can be a very interesting option for savings in autoscaling process.