A Hierarchical Approach for Dynamic Fault Trees Solution Through Semi-Markov Process

Dynamic fault tree (DFT) is a top-down deductive technique extended to model systems with complex failure behaviors and interactions. In two last decades, different methods have been applied to improve its capabilities, such as computational complexity reduction, modularization, intricate failure distribution, and reconfiguration. This paper uses semi-Markov process (SMP) theorem for DFT solution with the motivation of obviating the model state-explosion, considering nonexponential failure distribution through a hierarchical solution. In addition, in the proposed method, a universal SMP for static and dynamic gates is introduced, which can generalize dynamic behaviors like functional dependencies, sequences, priorities, and spares in a single model. The efficiency of the method regarding precision and competitiveness with commercial tools, repeated events consideration, computational complexity reduction, nonexponential failure distribution consideration, and repairable events in DFT is studied by a number of examples, and the results are then compared to those of the selected existing methods

Leveraging Engaged Parties in SIP Domains of eTOM Framework by using ITSM Reference Model

the telecommunications industry plays an important role in providing ICT services to a wide range of customers. In addition to individual customers, corporate customers also are user of these services and have an important role to make return on investment for telecom companies (Telcos). Therefore, this group of customers should not be ignored by any reason. This is where the Telecom Companies provide special services that named B2B to these customers. The Business Process Framework eTOM is proposed as a telecom. Framework to standardize and mature B2B processes by a separate section called Engaged Parties. In this paper, by using the ITSM Reference Model, we aim to improve the B2B processes in the business process framework already named item. Hereby, considering the ever-increasing Demands and needs of customers (in this paper customers mostly are Enterprises and Companies), and declaring the power inherent while using Customer Relationship Processes of ITSM Reference Model, we aim to complete B2B processes of the eTOM framework while focusing on Telcos

Definition and Empirical Evaluation of Voters for Redundant Smart Sensor Systems Definición y Evaluación Empírica de Algoritmos de Voteo para Sistemas Redundantes de Sensado Inteligente

Abstract This study is the first attempt for integration voting algorithms with fault diagnosis devices. Voting algorithms are used to arbitrate between the results of redundant modules in fault-tolerant systems. Smart sensors are used for FDI (Fault Detection and Isolation) purposes by means of their built in intelligence. Integration of fault masking and FDI strategies is necessary in the construction of ultra-available/safe systems with on-line fault detection capability. This article introduces a range of novel software voting algorithms which adjudicate among the results of redundant smart sensors in a Triple Modular Redundant (TMR) system. Techniques to integrate replicated smart sensors and fault masking approach are discussed, and a classification of hybrid voters is provided based on result and confidence values, which affect the metrics of availability and safety.Thus, voters are classified into four groups: Independent-diagnostic safety-optimised voters, Integrated-diagnostic safety-optimised voters, Independent-diagnostic availability-optimised voters and Integrated-diagnostic availability-optimised voters. The properties of each category are explained and sample versions of each class as well as their possible application areas are discussed. Keywords: Ultra-Available System, Smart Sensor, Fault Masking, Triple Modular Redundancy. Resumen Este estudio es una primer aproximación para la integración de algoritmos de voteo con dispositivos de diagnóstico de fallas. Los algoritmos de voteo son usados para arbitrar entre los resultados de elementos redundantes en sistemas tolerantes a fallas. Los sensores inteligentes son usados para propositos de detección y separación de fallas (FDI) dada la capacidad su capacidad de inteligencia construida. La integración de enmascaramiento de fallas y las estrategias de FDI is necesaria en la construcción de sistemas altamente disponibles y seguros con la capacidad de detección de fallas en línea. Este artículo introduce un rango de algoritmos de voteo los cuales adjudican un resultado entre los resultados generados por los sensores inteligentes en un módulo de redundancia triple. Las técnicas para integrar los sensores inteligentes replicados y la aproximación de enmascaramiento de fallas son revisadas en este artículo. Una clasificación de algoritmos de voteo híbrido es provista con base en el resultado y los valores de confianza los cuales afectan las métricas de disponibilidad y seguridad de estos algoritmos. De hecho los algoritmos de voteo son clasificados en cuatro grupos: Diagnóstico-Independiente con seguridad-optimizada, Diagnóstico-Integrado con seguridad-optimizada, Diagnóstico-Independiente con disponibilidad-opitimizada y Diagnóstico-Integrado con disponibilidad-optimizada. Las propiedades de cada categoria son revisadas asi como muestras de sus implementaciones son discutidas

Towards a Metric for the Assessment of Safety Critical Control Systems

There is a need for better integration of the fault tolerant and the control designs for safety critical systems such as aircraft. The dependability of current designs is assessed primarily with measures of the interconnection of fault tolerant components: the reliability function and the mean time to failure. These measures do not directly take into account the interaction of the fault tolerant components with the dynamics of the aircraft. In this paper, a first step to better integrate these designs is made. It is based on the observation that unstable systems are intrinsically unreliable and that a necessary condition for reliability is the existence of a stabilizing control law that depends on the interconnection of the working fault tolerant components. Since operation of a fault tolerant interconnection of digital computers in a harsh environment can result in transient errors, a methodology to analyze the mean square stability of the fault tolerant closed-loop system is presented. A definition for mean square stabilizability is then used to introduce the new dynamical system reliability concept. An example illustrates the effect on mean square stability of several fault tolerant design choices and illustrates possible dynamical system reliability plot