| 1. |
- Aysan, Hüseyin, et al.
(författare)
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A Cascading Redundancy Approach for Dependable Real-Time Systems
- 2009
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Ingår i: Proceedings - 15th IEEE International Conference on Embedded and Real-Time Computing Systems and Applications, RTCSA 2009. - 9780769537870 ; , s. 467-476
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Konferensbidrag (refereegranskat)abstract
- Dependable real-time systems typically consist of tasks of multiple criticality levels and scheduling them in a fault-tolerantmanner is a challenging problem. Redundancy in the physical and temporal domains for achieving fault tolerance has been often dealt independently based on the types of errors one needs to tolerate. To our knowledge, there had been no work which tries to integrate fault tolerant scheduling and multiple redundancy mechanisms. In this paper we propose a novel cascading redundancy approach within a generic fault tolerant scheduling framework. The proposed approach is capable of tolerating errors with a wider coverage (with respect to error frequency and error types) than time and space redundancy in isolation, allows tasks with mixed criticality levels, is independent of the scheduling technique and, above all, ensures that every critical task instance can be feasibly replicated in both time and space.
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| 2. |
- Aysan, Hüseyin, et al.
(författare)
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A Generalised Error Model and Schedulability Guarantees for Dependable Real-Time Systems
- 2011
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Ingår i: Proceedings of the 1st International Workshop on Dependable and Secure Industrial and Embedded Systems (WORDS).
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Konferensbidrag (refereegranskat)abstract
- The fundamental requirement for the design of effective and efficient fault-tolerance mechanisms in dependable real-time systems is a realistic and applicable model of potential faults, their manifestations and consequences. Fault and error models also need to be evolved based on the changes in the environments of usage or even based on technological advances. In this paper we propose a novel probabilistic burst error model in lieu of the commonly used simplistic fault assumptions. We introduce an approach to reason about real-time systems schedulability under the proposed error model in a probabilistic manner. We first present a sufficient analysis that accounts for the worst case interference caused by error bursts on the response times of tasks scheduled under the fixed priority scheduling (FPS) policy. Further, we identify potential sources of pessimism in the calculations and propose an algorithm that refines the results.
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| 3. |
- Aysan, Hüseyin, et al.
(författare)
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A Generalized Task Allocation Framework for Dependable Real-Time Systems
- 2007
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Ingår i: Proceedings of the Work-In-Progress (WIP) session of the 19th Euromicro Conference on Real-Time Systems (ECRTS 07).
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Konferensbidrag (refereegranskat)abstract
- In this paper, we present a general framework which allows the designer to specify a wide range of criteria for allocation. Major factors considered as part of our framework are mixed criticalities of tasks, schedulability, power consumption, fault-tolerance, and dependability requirements in addition to typical functional aspects such as memory constraints. This being a global optimization problem, we are forced to use meta-heuristic algorithms, and we were able to represent these requirements in a very intuitive manner by the usage of energy functions in simulated annealing. We envision the proposed methodology as a quite simple, scalable, as well as computationally effective solution covering a wide range of system architectures and solution spaces.
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| 4. |
- Aysan, Hüseyin, et al.
(författare)
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Adding the Time Dimension to Majority Voting Strategies
- 2008
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Ingår i: Proceedings of the Work-In-Progress (WIP) session of the 14th IEEE Real-Time and Embedded Technology and Applications Symposium (RTAS'08), St. Louis, MO, United States. ; , s. 69-73
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Konferensbidrag (refereegranskat)
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| 5. |
- Aysan, Hüseyin, et al.
(författare)
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Efficient Fault Tolerant Scheduling on Controller Area Network (CAN)
- 2010
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Ingår i: Proceedings of the 15th IEEE International Conference on Emerging Technologies and Factory Automation, ETFA 2010. - Bilbao, Spain. ; , s. Art.nr 5641318-
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Konferensbidrag (refereegranskat)abstract
- Dependable communication is becoming a critical factor due to the pervasive usage of networked embedded systems that increasingly interact with human lives in many real-time applications. Controller Area Network (CAN) has gained wider acceptance as a standard in a large number of industrial applications, mostly due to its efficient bandwidth utilization, ability to provide real-time guarantees, as well as its fault-tolerant capability. However, the native CAN fault-tolerant mechanism assumes that all messages transmitted on the bus are equally critical, which has an adverse impact on the message latencies, results in the inability to meet user defined reliability requirements, and, in some cases, even leads to violation of timing requirements. As the network potentially needs to cater to messages of multiple criticality levels (and hence varied redundancy requirements), scheduling them in an efficient fault-tolerant manner becomes an important research issue. We propose a methodology which enables the provision of appropriate guarantees in CAN scheduling of messages with mixed criticalities. The proposed approach involves definition of fault-tolerant feasibility windows of execution for critical messages, and off-line derivation of optimal message priorities that fulfill the user specified level of fault-tolerance.
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| 6. |
- Aysan, Hüseyin, et al.
(författare)
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Error Modeling in Dependable Component-based Systems
- 2008
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Ingår i: Proceedings - International Computer Software and Applications Conference. - 9780769532622 ; , s. 1309-1314
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Konferensbidrag (refereegranskat)abstract
- Component-Based Development (CBD) of software, with its successes in enterprise computing, has the promise of being a good development model due to its cost effectiveness and potential for achieving high quality of components by virtue of reuse. However, for systems with dependability concerns, such as real-time systems, a major challenge in using CBD consists of predicting dependability attributes, or providing dependability assertions, based on the individual component properties and architectural aspects. In this paper, we propose a framework which aims to address this challenge. Specifically, we present a revised error classification together with error propagation aspects, and briefly sketch how to compose errormodels within the context of Component-Based Systems (CBS). The ultimate goal is to perform the analysis on a given CBS, in order to find bottle-necks in achieving dependability requirements and to provide guidelines to the designer on the usage of appropriate error detection and fault tolerance mechanisms.
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| 7. |
- Aysan, Hüseyin, 1982-
(författare)
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Fault-Tolerance Strategies and Probabilistic Guarantees for Real-Time Systems
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ubiquitous deployment of embedded systems is having a substantial impact on our society, since they interact with our lives in many critical real-time applications. Typically, embedded systems used in safety or mission critical applications (e.g., aerospace, avionics, automotive or nuclear domains) work in harsh environments where they are exposed to frequent transient faults such as power supply jitter, network noise and radiation. They are also susceptible to errors originating from design and production faults. Hence, they have the design objective to maintain the properties of timeliness and functional correctness even under error occurrences. Fault-tolerance plays a crucial role towards achieving dependability, and the fundamental requirement for the design of effective and efficient fault-tolerance mechanisms is a realistic and applicable model of potential faults and their manifestations. An important factor to be considered in this context is the random nature of faults and errors, which, if addressed in the timing analysis by assuming a rigid worst-case occurrence scenario, may lead to inaccurate results. It is also important that the power, weight, space and cost constraints of embedded systems are addressed by efficiently using the available resources for fault-tolerance. This thesis presents a framework for designing predictably dependable embedded real-time systems by jointly addressing the timeliness and the reliability properties. It proposes a spectrum of fault-tolerance strategies particularly targeting embedded real-time systems. Efficient resource usage is attained by considering the diverse criticality levels of the systems' building blocks. The fault-tolerance strategies are complemented with the proposed probabilistic schedulability analysis techniques, which are based on a comprehensive stochastic fault and error model.
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| 8. |
- Aysan, Hüseyin, et al.
(författare)
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Fault Tolerant Scheduling on Control Area Network (CAN) :
- 2010
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Ingår i: ISORC Workshops 2010 - 2010 13th IEEE International Symposium on Object/Component/Service-Oriented Real-Time Distributed Computing Workshops, Vol. 2. ; , s. 226-232
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Konferensbidrag (refereegranskat)abstract
- Dependable communications is becoming a critical factor due to the pervasive usage of networked embedded systems that increasingly interact with human lives in one way or the other in many real-time applications. Though many smaller systems are providing dependable services employing uniprocesssor solutions, stringent fault containment strategies etc., these practices are fast becoming inadequate due to the prominence of COTS in hardware and component based development(CBD) in software as well as the increased focus on building 'system of systems'. Hence the repertoire of design paradigms, methods and tools available to the developers of distributed real-time systems needs to be enhanced in multiple directions and dimensions. In future scenarios, potentially a network needs to cater to messages of multiple criticality levels (and hence varied redundancy requirements) and scheduling them in a fault tolerant manner becomes an important research issue. We address this problem in the context of Controller Area Network (CAN), which is widely used in automotive and automation domains, and describe a methodology which enables the provision of appropriate scheduling guarantees. The proposed approach involves definition of fault-tolerant windows of execution for critical messages and the derivation of message priorities based on earliest deadline first (EDF).
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| 9. |
- Aysan, Hüseyin, et al.
(författare)
-
FT-Feasibility in Fixed Priority Real-Time Scheduling
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Real-time systems typically have to satisfy complex requirements mapped to the timing attributes of the tasks that are eventually guaranteed by the underlying scheduler. These systems consist of a mix of hard and soft tasks with varying criticalities as well as associated fault tolerance (FT) requirements. Often time redundancy techniques are preferred in many embedded applications and hence it is extremely important to devise appropriate methodologies for scheduling real-time tasks under fault assumptions. Additionally, the relative criticality of tasks could undergo changes during the evolution of the system. Hence scheduling decisions under fault assumptions have to reflect all these important factors in addition to the resource constraints.In this paper we propose a framework for 'FTfeasibility', i.e., to provide a priori guarantees that all critical tasks in the system will meet their deadlines even in case of faults. Our main objective here is to ensure FTfeasibility of all critical tasks in the system and do so with minimal costs and without any fundamental changes in the scheduling paradigm. We demonstrate its applicability in scenarios where the FT strategy employed is re-execution of the affected tasks or an alternate action upon occurrence of transient faults or software design faults. We analyse a feasible set of tasks and propose methods to adapt it to varying FT requirements without modifications to the underlying scheduler. We do so by reassigning task attributes to achieve FT-feasibility while keeping the costs minimised.
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| 10. |
- Aysan, Huseyin, et al.
(författare)
-
Improving Reliability of Real-Time Systems through Value and Time Voting
- 2013
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Konferensbidrag (refereegranskat)abstract
- Critical systems often use N-modular redundancy to tolerate faults in subsystems. Traditional approaches to N-modular redundancy in distributed, loosely-synchronised, real-time systems handle time and value errors separately: a voter detects value errors, while watchdog-based health monitoring detects timing errors. In prior work, we proposed the integrated Voting on Time and Value (VTV) strategy, which allows both timing and value errors to be detected simultaneously. In this paper, we show how VTV can be harnessed as part of an overall fault tolerance strategy and evaluate its performance using a well-known control application, the Inverted Pendulum. Through extensive simulations, we compare the performance of Inverted Pendulum systems which employs VTV and alternative voting strategies to demonstrate that VTV better tolerates well-recognised faults in this realistically complex control problem.
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