Dependability evaluation in a mobile context

Recent advances in wireless and portable devices technologies have opened new opportunities for innovative services that can be accessed by mobile users in highly dynamic environments, through a combination of ad-hoc and infrastructure based communication networks. Such services cover a large variety of application domains including information and entertainment (voice and video streaming, online gaming, contextual information services, etc.), as well as safety and dependability critical services (hazard warning, safety and traffic management for transportation systems, assisted living support systems and healthcare monitoring, crisis management, etc.). This fast growing area poses some significant challenges from the dependability evaluation point of view. The main challenge concerns the quantification of dependability characteristics taking into account the combined effects of faults affecting the mobile nodes and their communication, and the mobility of these nodes. In particular, the development of quantitative assessment strategies with realistic mobility patterns and failure models is needed to provide a faithful validation of the quality of service provided by these applications.

Our research in this context covers two complementary evaluation approaches:

  1. model-based evaluation using analytical and simulation techniques and
  2. experimental measurements.

Model–based evaluation is well suited to support the comparative analysis of architectural solutions at the design stage based on the assessment of system level dependability properties such as reliability, availability and safety. Our contributions concern the development of modeling approaches that are well suited to master the complexity of the target systems and to capture the behavior of the system that results from the occurrence of failures and recovery actions and from the mobility of the users. The proposed models are based on generalized stochastic Petri nets (GSPNs) and Stochastic Activity Networks (SAN). Also, simulations have been performed to estimate some connectivity characteristics in dynamic mobile scenarios, in particular for vehicular applications. Three case studies have been investigated:

  • a) a distributed application using cooperative backups on mobile nodes [Courtes 2008, Courtes et al 2007] (Figure 1),
  • b) a replication service for applications running on ad-hoc networks [Matthiessen et al 2007], and c) an automated highway system based on platooning [Hamouda et al 2009b].

Another complementary approach that is particularly relevant to improve the accuracy of dependability assessments in mobile environments, concerns the development of experimental techniques based on laboratory testbeds (the ARUM platform) or on the analysis of data collected from real life systems. Such experiments can provide a realistic estimation of some parameters that are used in analytical models such as connectivity rates or specific failure rates that are pertinent in a mobile setting, along with their associated distributions. In particular, our research aims at developing new fault injection techniques to analyze the behavior of mobile systems in the presence of faults.
Two major difficulties need to be addressed: i) what new types of faults and failures are induced by mobility, and ii) how to inject faults in a mobile device or in a location-aware system. To address these difficulties, we recently began the development of a laboratory-scale platform to experimentally evaluate and validate resilience mechanisms of mobile ubiquitous systems (https://www.laas.fr/ARUM/wiki/) [Killijian et al 2008, Killijian et al 2009]
(Figure 2). It scales the physical dimensions of a real-life mobile system into ones that are practical for experimentation in a laboratory environment. By changing scale, we plan to emulate systems of different sizes, from networks of communicating road vehicles, down to nanorobots injected into the blood systems to perform surgery. The platform will serve as the basis for the development of new fault injection tools and techniques.

This research has been partially carried out in the context of the HIDENETS European project “Highly Dependable ip-based Networks and Services”, the ReSIST European network of excellence “Resilience for Survivability in IST”, and the MOSAIC research project (Mobile System Availability, Integrity and Confidentiality) partially funded by the French national research program on Security and Informatics (ACI & SI).
 

Figure 1: Cooperative backup on mobile devices using ad-hoc networks (automobile context)


Figure 2: The ARUM platform for the validation of ubiquitous mobile systems

Publications

[Roy et al. 2009] M. Roy, M-O. Killijian. A platform for Experimenting with Mobile Algorithms in a Laboratory. 28th Annual ACM Symposium on Principles of Distributed Computing, PODC 2009.

[Killijian et al. 2009] M. O. Killijian, M. Roy, G. Severac, C. Zanon, Data backup for mobile nodes : a cooperative middleware and experimentation platform, Workshop on Architecting Dependable Systems and Networks (WADS), The 39th IFIP/IEEE International Conference on Dependable Systems and Networks (DSN-2009), Estoril (Portugal), 29 June 2009, 6p. 

[Hamouda et al. 2009a] O. Hamouda, M. Kaâniche , E. V. Matthiesen, J. G. Rasmussen, H. P. Schwefel,Connectivity dynamics in vehicular freeway scenariosThe 2nd IEEE International Workshop on ITS for Ubiquitous Roads (UBIROADS'2009)IEEE GIIS 2009, Hammamet (Tunisia), 26 June 2009, 15p. 

[Hamouda et al. 2009b] O. Hamouda, M. Kaâniche , K. Kanoun, Safety modeling and evaluation of automated highway systems, The 2009 IFIP/IEEE International Conference on Dependable Systems and Networks (DSN-2009), Estoril (Portugal), 29 June -2 July 2009, pp. 73-82. 

[Killijian et al. 2008] M. O. Killijian, D. Powell, M. Roy, G. Severac, Experimental Evaluation of ubiquitous systems : Why and how to reduce WiFi communication range, 2nd International Conference on Distributed Event-Based Systems (DEBS 2008), Rome (Italy), 1-4 July 2008, 2p. 

[Matthiesen et al. 2008] E. V. Matthiesen, O. Hamouda, M. Kaâniche, H. P. Schwefel, Dependability evaluation of a replication service for mobile applications in dynamic ad-hoc networks5th International Service Availability Symposium (ISAS-2008), Tokyo (Japan), 19-21 May 2008, 20p

[Courtes 2008] L. Courtes, Cooperative data backup for mobile devices, PhD Thesis, Institut National Polytechnique de Toulouse, LAAS-Report 08776, 15 December 2008, http://tel.archives-ouvertes.fr/tel-00196822/fr/

[Courtes et al. 2007] L. Courtes, O. Hamouda, M. Kaâniche, M. O. Killijian, D. Powell, Dependability evaluation of cooperative backup strategies for mobile devices, 13th Pacific Rim International Symposium on Dependable Computing (PRDC 2007), Melbourn (Australia), 17-19 December 2007, pp.139-146. 

Contact: Marc-Olivier Killijian