Alessandro Testa

AVR-INJECT: A tool for injecting faults in Wireless Sensor Nodes

As the incidence of faults in real Wireless Sensor Networks (WSNs) increases, fault injection is starting to be adopted to verify and validate their design choices. Following this recent trend, this paper presents a tool, named AVR-INJECT, designed to automate the fault injection, and analysis of results, on WSN nodes. The tool emulates the injection of hardware faults, such as bit flips, acting via software at the assembly level. This allows to attain simplicity, while preserving the low level of abstraction needed to inject such faults. The potential of the tool is shown by using it to perform a large number of fault injection experiments, which allow to study the reaction to faults of real WSN software.

Dependable Services for Mobile Health Monitoring Systems

The design and realization of health monitoring systems has attracted the interest of large communities both from industry and academia. Remote and continuous monitoring of patients vital signs is the target of an emerging business market that aims both to improve the quality of life of patients and to reduce costs of national healthcare services. Such applications, however, are particularly critical from the point of view of dependability. This presents the design of a set of services for the assurance of high degrees of dependability to generic mobile health monitoring systems. The design is based on the results of a detailed failure modes and effects analysis FMEA, conducted to identify the typical dependability threats of health monitoring systems. The FMEA allowed the authors to conceive a set of configurable monitoring services, enriching the system with the ability to detect failures at runtime, and enabling the realization of dependable services for future mobile health monitoring systems.

iCAAS: An Interoperable and Configurable Architecture for Accessing Sensor Networks

Wireless sensor networks WSN are spreading as a common mean for mitigating installation and management cost in environment monitoring applications. The increasing complexity ad heterogeneity of such WSN and the differentiated users needs calls for innovative solutions for managing and accessing produced data. This paper presents an architecture, named iCAAS, designed to collect, store, manage and make available to users data received from heterogeneous WSNs. The objective of the architecture is to adaptively deliver data to users depending on their specific interests and transparently to adopted terminals and of networks details. The contribution of the paper is twofold. First the authors detail the requirements that these types of architectures should meet to fill the gap between sensors, details, and users needs. Second, the authors describe the structural organization of the proposed architecture, designed by taking into account the defined requirements. Implementation details and case studies are also provided, showing the effectiveness of the architecture when used in real world application scenarios. Finally, iCAAS architectures scalability is tested against the number of concurrent client querying the same time.

A Failure Modes and Effects Analysis of Mobile Health Monitoring Systems

Many solutions are emerging for the remote and continuous monitoring of unpredictable health problems, such as cardiac diseases. These are designed to be minimally invasive for health monitoring and based on smart and mobile technologies conformable to the human body, helping to improve considerably the autonomy and the quality of life of patients. Clearly, the correct functioning of these systems is very critical for the safety of patients, hence their practical application calls for stringent dependability requirements which need to be assessed against potential failure modes since the inception of the system, in its design phase. Despite the criticality of the problem, there is still little knowledge about the typical failures that may affect the correct functioning of these systems. Without such knowledge, it becomes difficult to devise effective countermeasures to failure events. To fill this gap, this paper proposes a Failure Mode and Effect Analysis (FMEA) for a typical mobile health monitoring system. Based on past results and extensive studies, the analysis allowed to identify the main failures, their consequences, and possible causes, affecting the functional components of modern health monitoring systems.

Heuristic strategies for assessing wireless sensor network resiliency: an event-based formal approach

Wireless sensor networks (WSNs) are increasingly being adopted in critical applications. In these networks undesired events may undermine the reliability level; thus their effects need to be properly assessed from the early stages of the development process onwards to minimize the chances of unexpected problems during use. In this paper we propose two heuristic strategies: what-if analysis and robustness checking. They allow to drive designers towards optimal WSN deployment solutions, from the point of view of the connection and data delivery resiliency, exploiting a formal approach based on the event calculus formal language. The heuristics are backed up by a support tool aimed to simplify their adoption by system designers. The tool allows to specify the target WSN in a user-friendly way and it is able to elaborate the two heuristic strategies by means of the event calculus specifications automatically generated. The WSN reliability is assessed computing a set of specific metrics. The effectiveness of the strategies is shown in the context of three case studies.

Static Verification of Wireless Sensor Networks with Formal Methods

Wireless Sensor Networks (WSNs) are widely recognized as a solution to build monitoring systems, even in critical environments. WSNs, however, are subjected to faults due to several causes (i.e. rain, EMF radiations, vibrations, etc..) and tools and methodologies for the design of dependable WSN-based systems are needed. Formal methods partially meet such needs by assessing the degree of correctness of design models and identifying potential system bottlenecks. The aim of this paper is to define a methodology for the static verification of WSN based systems using a formal language (Event Calculus). In particular we show how the formal specification can be used to verify the design of a WSN in terms of its dependability properties. To this aim, we define a set of correctness specifications that apply to a generic WSN, coupled with specific structural specifications describing the target network topology to evaluate. Finally, after having presented an automatic tool, designed to support the designer, we adopt this methodology to a case study.

An effective approach for injecting faults in wireless sensor network operating systems

This paper presents an effective approach for injecting faults/errors in WSN nodes operating systems. The approach is based on the injection of faults at the assembly level. Results show that depending on the concurrency model and on the memory management, the operating systems react to injected errors differently, indicating that fault containment strategies and hang-checking assertions should be implemented to avoid spreading and activations of errors.

A survey on resiliency assessment techniques for wireless sensor networks

Resiliency is becoming one of the most important non functional properties of Wireless Sensor Networks (WSNs), as their adoption is more and more hypothesized in critical application scenarios. Hence, assessing the resiliency of WSN applications, protocols, and platforms is starting to be an import concern for WSN designers and developers. This paper presents the techniques that are currently used in the field of WSN resiliency assessment, categorized as experimental, simulative, analytical and formal techniques. After reporting the state-of-art according to the four categories, the paper discusses research trends, strengths and weaknesses of existing approaches, and concludes with open issues and ongoing challenges.

Analyzing and modeling the failure behavior of Wireless Sensor Networks software under errors

As Wireless Sensor Networks (WSNs) are starting to be adopted in critical scenarios, it becomes important to study the behavior of WSN software in response to errors induced by hardware faults. To this aim, in this paper we present the results of an extensive fault-injection campaign, conducted on three different WSN operating systems (OSs). Results show that, depending on the concurrency model and on the memory management, the OS reacts to injected faults differently, indicating that fault containment strategies and hang-checking assertions should be implemented to avoid spreading and activations of errors. Analysis also allowed us to define a detailed dependability model of the WSN software, to be used to simulate the expected failure behavior of a given OS when solicited by given low-level hardware faults.

A logging framework for the on-line failure analysis of Android smart phones

This paper introduces the design of a logging framework for the on-line failure analysis of Android Smart Phones. The framework enables the collection of failure data at runtime, useful to assess the dependability of smart phones, to deeply investigate the causes of failures, and to reduce maintenance efforts. Existing tools mainly focus on the collection of failure data about application crashes. The aim of the proposed framework is to extend the collection to other types of failures, such as, application hang, phone freeze and phone self-reboot. The paper describes the main design choices behind the components of the framework, and investigates advantages and disadvantages of different solutions.