Abstract
Wireless Sensor Networks (WSN) currently represent the best candidate to be adopted as the communication solution for the last mile connection in process control and monitoring applications in industrial environments. Most of these applications have stringent dependability (reliability and availability) requirements, as a system failure may result in economic losses, put people in danger or lead to environmental damages. Among the different type of faults that can lead to a system failure, permanent faults on network devices have a major impact. They can hamper communications over long periods of time and consequently disturb, or even disable, control algorithms. The lack of a structured approach enabling the evaluation of permanent faults, prevents system designers to optimize decisions that minimize these occurrences. In this work we propose a methodology based on an automatic generation of a fault tree to evaluate the reliability and availability of Wireless Sensor Networks, when permanent faults occur on network devices. The proposal supports any topology, different levels of redundancy, network reconfigurations, criticality of devices and arbitrary failure conditions. The proposed methodology is particularly suitable for the design and validation of Wireless Sensor Networks when trying to optimize its reliability and availability requirements.

Abstract

Abstract
This chapter reviews a dependability model for evaluation of the behavior of a CAN network in situations of transient faults, which affect the data communications. The fault occurrence can be modeled by a Markov Modulated Poisson Process (MMPP), which is capable of describing the typical behavior of the electromagnetic interferences (EMI) that occur in the industrial environments. An accurate and efficient representation of the network behavior is achieved by adopting a set of assumptions that reduces the pessimism level and are closer to the real operating conditions. The model used for analysing the dependability evaluation is based on the Stochastic Petri Nets, which are a high-level modeling formalism able to produce very compact and efficient models, supporting both the analytical and simulation solutions. Dependability measures are established from the achievement of the real-time constraints (deadlines) defined on the messages exchanged among the network nodes. The chapter concludes by reviewing a case study that is proposed to assess both the model performance and the network dependability.

Abstract
We present a reliability evaluation of a group membership protocol (GMP), by computing the probability of violating the fault assumptions made in its proof. The evaluation of the reliability of a GMP is of paramount importance because group membership services are often used as building blocks in the design of fault-tolerant applications. The GMP that we consider here has been proposed for dual scheduled TDMA networks such as FlexRay, a protocol that is likely to become the de-facto standard for next generation automotive networks. Our study is carried out by modeling the GMP with discrete-time Markov chains. The models consider different fault scenarios, including permanent, transient and common-mode faults, affecting both channels and nodes. Furthermore we perform a sensitivity analysis to assess the influence of different parameters on the protocol's reliability. The results show that the GMP can achieve reliability levels in the range required for safety critical applications.

Abstract
The timing behavior of the EDCA mechanism defined in the IEEE 802.11e standard is analyzed. More specifically, the target of this paper is to evaluate the limitations of the highest priority level of the EDCA mechanism (voice category) when supporting real-time (RT) communication. By RT communication, we mean small-sized packets generated in periodic intervals that must be delivered before the end of the message stream period. Otherwise, the message is considered to be delayed and a deadline loss occurs. We have assessed the EDCA mechanism considering an open communication environment, where both RT and non-RT stations share the same frequency band. Furthermore, a realistic error-prone model channel was used to measure the impact of interferences against an error-free channel. We show that, for most part of the evaluated scenarios, when using the default parameters of the EDCA mechanism both the number of packet losses and the average packet delays forecast an unacceptable number of deadline losses. However, if adequate Contention Windows (CW) parameters are configured in the set of RT stations, it becomes possible to adequately handle RT traffic. As a conclusion of this paper, we present some potential future directions toward improved QoS in wireless networks.

Abstract
Camera-enabled sensor nodes deployed for visual monitoring can considerably enlarge the applicability of wireless sensor networks. Due to the stringent requirements of visual data transmission and processing, when compared with scalar wireless sensor networks, quality assessment becomes a relevant issue. Although academic investigation has been focused on QoS parameters such as end-to-end delay, throughput and packet error rate, what is being seen by source nodes may be more important for the application than the quality of received data. In such way, we propose the novel concept of Quality of Viewing (QoV) to be employed as an important QoS parameter when assessing the monitoring quality in visual sensor networks. Some issues for the establishment of the QoV of monitoring applications will be presented, as well as practical exploitation of this parameter for dynamic verification, control and management of wireless sensor networks composed of camera-enabled source nodes. © 2012 IEEE.