AvaliaÃÃo de dependabilidade de sistemas com mecanismos tolerantes a falha: desenvolvimento de um mÃtodo hÃbrido baseado em EDSPN e diagrama de blocos

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

In current days, we observe a vertiginous advance of technology and a larger dependence of the society on computational systems. A massive use of computerized devices, fixed and mobile, inside a concept of ubiquitous computation, and the increasing pervasiveness of computers and services networks, have been turning systems extremely complex and dynamic. This complexity is increasing every day, as computers become smaller, cheaper and with larger processing capacity. Today they are not only largely present in objects of the daily life, like cellular devices, laptops and desktops, as well as in telecommunication systems, in the means of transportation, in the hospital equipment, and in major part of activities. While economic reasons force the development of new computational systems, with an every time larger number of facilities, quality reasons impose the need for avoiding malfunction of these systems. The consequences of computational systems failure can vary since simple inconveniences, to the loss of human lives or material damage, what motivates the development of methodologies for dependability evaluation of these systems. Due to the stochastic behavior of great part of the faults, techniques of dependability modeling by means of stochastic analytic evaluation or simulation, have been proving be a useful and versatile solution in all phases of life cycle of a system, from the project phase, in the choice of a better solution that satisfies the proposed dependability requirements, until the operational phase, in the detection of bottlenecks that prevent the systems of reaching such requirements. This thesis proposes the development of a methodology that enables modeling, refinement and evaluation of dependable systems with fault tolerance mechanisms utilization, through a hybrid method based on extended deterministic and stochastic Petri nets (EDSPN) and block diagrams, in a flexible and expandable way, that allows automation. The proposed methodology is implemented in 5 different hierarchical levels. The first two levels work with block diagrams and fault tolerant mechanisms to be introduced. The third level, formed by high level Petri nets, defines the interconnection of the Petri nets, which represents the configuration of blocks in the dependable system diagram, in the final configuration. In the forth level, the behavior of each block is modeled by means of EDSPN, which generates numeric or analytic expressions of reliability, availability and safety attributes. Finally, the obtained expressions are used in a dependable and parameterized model (MDP), according to the configuration defined in the third level, for obtaining dependability estimates of the system as a whole. The proposed methodology, not only allows automation, but also aims to hide the mathematical complexity involved and to reduce the state space explosion possibility. To make the models EDSPN and MDP more efficient, a model library is created. A same model, with the aid of different configuration parameters, can assume different fault tolerant mechanisms, which makes the methodology flexible, as well as, a same model, with the aid of structural parameters, can assume different levels of redundancy in a same fault tolerant mechanism, which makes the methodology expandable

ASSUNTO(S)

dependability tolerÃncia a falhas dependabilidade edspn fault tolerance modelos estocÃsticos ciencia da computacao stochastic models edspn

ACESSO AO ARTIGO

Documentos Relacionados