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  • 1
    Language: English
    In: ACM SIGBED Review, 15 August 2018, Vol.15(3), pp.7-12
    Description: Safety-critical Ethernet-based networks are receiving significant attention in avionics, automotive and industrial domains. Time-Triggered Ethernet (TTEthernet AS6802) provides safety-critical transmission guarantees via a high priority, time-triggered (TT) traffic class and a lower priority, rate-constrained (RC) traffic class. TT traffic is transmitted between synchronized nodes of a TTEthernet network in offline scheduled TT transmission windows. In this work, we analyze the impact of different placement strategies for these TT transmission windows on end-to-end delay and jitter of RC messages on the same path segment. We show that, depending on the placement of TT transmission windows in a schedule, the end-to-end delay and jitter of RC messages can vary significantly. We further introduce link-based offsets, a new placement strategy for TT transmission windows which allows to reduce the impact of TT transmission windows on RC traffic. In this strategy offsets are applied to all TT transmission windows in a physical link schedule to reduce the amount of time that an RC message on the same physical link is delayed by TT traffic. The link-based offsets strategy can be implemented in the TTEthernet scheduler and does not require hardware modifications. We show that the link-based offset strategy can reduce the end-to-end delay and jitter of RC traffic, and evaluate our claims using an 〈i〉OMNET++〈/i〉 simulation.
    Keywords: Rate-Constrained Traffic ; Scheduling ; Time-Triggered Networks ; Time-Triggered Traffic ; Engineering
    E-ISSN: 1551-3688
    Source: BIBSAM:2015-2018 (ACM Digital Library)
    Source: Jisc Collections:Digital Library:2017-2019 (ACM Digital Library)
    Source: ACM Digital Library (Association for Computing Machinery)
    Source: KESLI (ACM Digital Library)
    Source: SHEDL- 2014 (ACM Digital Library)
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  • 2
    Language: English
    In: ACM SIGBED Review, 03 November 2016, Vol.13(4), pp.55-60
    Description: Time-triggered networks are widely used for safety-critical applications. Being offline scheduled, flexibility and adaptivity typically come at the price of very low resource utilization, if possible at all. In this paper, we present the Stacked Scheduling Approach (SSA) for time-triggered networks to enable mode changes and implicit adaptation in such networks by enabling reuse of network bandwidth reservations. We describe SSA in detail and conduct a case study to show that SSA can be implemented in COTS time-triggered network hardware and validate the approach by implementing an example in a COTS TTEthernet network.
    Keywords: Mode Changes ; Scheduling ; Time-Triggered Networks ; Engineering
    ISSN: ACM SIGBED Review
    E-ISSN: 1551-3688
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  • 3
    Language: English
    In: Journal of Systems Architecture, May 2018, Vol.85-86, pp.14-27
    Description: Modern safety critical systems require certification in order to guarantee correct operation before system deployment. The certification process requires rigorous verification and validation, the efforts for which can be greatly reduced by using resource partitioning. However, Lackorzyński et al. demonstrated that bandwidth reservation for event-triggered (ET) activities in partitioned systems may lead to significant bandwidth loss. In contrast, the online admission of ET activities can prevent bandwidth losses. However, the state-of-the-art approaches for online admission of ET activities fail to fulfill the requirements of safety critical systems as they do not support (i) partitioning, (ii) the industrial mixed-criticality task model or (iii) non-preemptive task execution. In this paper, we present job-shifting algorithm for online admission of non-preemptive aperiodic tasks in partitioned time-triggered environment. Our approach circumvents the bandwidth loss issue with partitioning, and provides guarantees similar to the bandwidth reservation technique such that the certification process of safety critical systems need not be modified. Our approach can be implemented on top of variety of hypervisors and can provide lower response-times for aperiodic tasks. Through evaluation, we demonstrate that our approach efficiently utilizes processor bandwidth and only incurs small scheduling overheads.
    Keywords: Real-Time Systems ; Scheduling Algorithms ; Mixed-Criticality ; Hierarchic Scheduling ; Online Aperiodic Admission ; Computer Science
    ISSN: 1383-7621
    E-ISSN: 1873-6165
    Source: ScienceDirect Journals (Elsevier)
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  • 4
    Language: English
    In: Mobile Networks and Applications, 2018, Vol.23(4), pp.817-827
    Description: Typical communication networks for closed-loop control application in factory automation are designed to grant short cycle times, precise synchronicity in the microseconds range and high reliability with low packet error rates. However, new requirements for greater flexibility and scalability can only be fulfilled in combination with wireless networks. Therefore, cascaded communication networks with combinations of wired and wireless subnetworks will arise. However, combining heterogeneous communication protocols will lead to additional latencies. In order to reduce their influence on the real-time behavior of the overall network as far as possible, this latency must be completely known to the application and minimized as far as possible. In this paper, we analyze one additional source of latencies resulting from frame conversion for different subnetworks. With an abstract network model we introduce, we are able to analyze the timing independent of a specific protocol implementation. Using this, we are able to show different existing frame conversion concepts with their properties regarding latency and jitter. By simulating a typical network for automation technology and a currently developed wireless real-time communication network, we were able to verify our investigations.
    Keywords: Industrial ethernet ; Closed-loop control ; Wireless communication ; Cascaded network ; ParSec ; Latency
    ISSN: 1383-469X
    E-ISSN: 1572-8153
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  • 5
    Description: One of the primary sources of unpredictability in modern multi-core embedded systems is contention over shared memory resources, such as caches, interconnects, and DRAM. Despite significant achievements in the design and analysis of multi-core systems, there is a need for a theoretical framework that can be used to reason on the worst-case behavior of real-time workload when both processors and memory resources are subject to scheduling decisions. In this paper, we focus our attention on dynamic allocation of main memory bandwidth. In particular, we study how to determine the worst-case response time of tasks spanning through a sequence of time intervals, each with a different bandwidth-to-core assignment. We show that the response time computation can be reduced to a maximization problem over assignment of memory requests to different time intervals, and we provide an efficient way to solve such problem. As a case study, we then demonstrate how our proposed analysis can be used to improve the schedulability of Integrated Modular Avionics systems in the presence of memory-intensive workload. Comment: Accepted for publication in the IEEE Real-Time Systems Symposium (RTSS) 2018 conference
    Keywords: Computer Science - Distributed, Parallel, And Cluster Computing
    Source: Cornell University
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  • 6
    Language: English
    In: Proceedings of the 23rd International Conference on real time and networks systems, 04 November 2015, pp.309-318
    Description: In this paper, we consider scheduling of non-preemptive and independent periodic tasks with implicit deadlines on uniprocessor systems. We assume 〈b〉loose-harmonic〈/b〉 task sets with periods being integer multiples of the smallest period. This problem is known to be NP-Hard. Recently, two online non-work-conserving scheduling algorithms called Precautious-RM (P-RM) and lazy P-RM (LP-RM) have been introduced to guarantee schedulability of special cases of 〈i〉harmonic〈/i〉 task sets. In this paper, we provide new sufficient schedulability tests for P-RM and LP-RM. Then, by introducing a new algorithm called efficient Precautious-RM (EP-RM), we increase the number of schedulable loose-harmonic task sets in comparison with P-RM by letting the tasks share the priorities. We prove that the new test dominates the schedulability tests for P-RM. Moreover, we show that if the ratio of two consecutive periods is greater than or equal to 3, P-RM, LP-RM, and EP-RM are able to schedule any task set satisfying the necessary conditions of schedulability. We present results from a simulation study, showing the efficiency of the algorithm.
    ISBN: 9781450335911
    ISBN: 1450335918
    Source: ACM Digital Library (Association for Computing Machinery)
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  • 7
    Language: English
    In: 2011 Visual Communications and Image Processing (VCIP), November 2011, pp.1-4
    Description: In this paper, we propose a novel method for real- time stream adaptation of live MPEG-4 Visual advanced simple profile (ASP) and simple profile (SP) bit streams to limited and varying network bandwidth. The proposed method operates by dropping higher order AC DCT coefficients present in blocks. Unlike frame dropping, the proposed method delivers finer granularity during adaptation and therefore smaller resource under-utilization. Furthermore, to optimize the resource utilization and consequently the perceptive video quality, the method attempts to represent the adapted block with the least possible number of bits. The low computation requirements of the proposed method qualifies its application to adaptation of live streams. Additionally, the method can be applied for other constrained resources as well (e.g. CPU bandwidth). Implementation and case study of the proposed method show that, on an average, a bit rate reduction of up to 50% and a decoding time speedup up to 20% are achieved when compared with that of the original bitstream. Results also affirm the efficiency in resource usage.
    Keywords: Bandwidth ; Transform Coding ; Digital Signal Processing ; Streaming Media ; Discrete Cosine Transforms ; Decoding ; Resource Management
    ISBN: 9781457713217
    ISBN: 1457713217
    Source: IEEE Conference Publications
    Source: IEEE Xplore
    Source: IEEE Journals & Magazines 
    Source: IEEE eBooks
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  • 8
    Language: English
    In: Proceedings of the Conference on design, automation and test in europe, 12 March 2012, pp.578-581
    Description: Target sensitive tasks have an execution window for feasibility and must execute at a target point in time for maximum utility. In the gravitational task model, a task can express a target point, and the utility decay as a function of the deviation from this point. A method called 〈i〉equilibrium〈/i〉 approximates the schedule with maximum utility accrual based on an analogy with physical pendulums. In this paper, we propose a scheduling algorithm for this task model to schedule periodic tasks. The basic idea of our solution is to combine the equilibrium with Earliest Deadline First (EDF) in order to reuse EDF's well studied timeliness analysis. We present simulation results and an example multimedia application to show the benefits of our solution.
    Keywords: Engineering
    ISBN: 9783981080186
    ISBN: 3981080181
    Source: ACM Digital Library (Association for Computing Machinery)
    Source: KESLI (ACM Digital Library)
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  • 9
    Language: English
    In: Proceedings of the 2011 ACM Symposium on applied computing, 21 March 2011, pp.742-747
    Description: The gravitational task model allows target sensitive applications (e.g. multimedia and control) to express target points for maximum utility, and a utility decay as a function of the deviation from these points. The compromise among their deviations for maximized utility is calculated based on a physical pendulum analogy. However, in an overloaded system a compromise among all jobs does not necessarily incur in maximized utility. In this paper we propose an overload handling mechanism for the gravitational task model which accounts for both system load and target sensitivity of applications. This mechanism considers the trade-off between aborting and shifting the execution of a job for resulting increased utility accrual and improved resource usage. The heuristic to abort jobs is based on their utility and amount of consumed resources. An aborted job does not yield any utility, but frees resources that can be exploited by other jobs for increased utility accrual. A multimedia case study shows that our mechanism reduces frame display jitter and improves resource usage.
    Keywords: Adaptivity ; Overload ; Scheduling ; Target Sensitivity ; Utility ; Computer Science
    ISBN: 9781450301138
    ISBN: 1450301134
    Source: ACM Digital Library (Association for Computing Machinery)
    Source: KESLI (ACM Digital Library)
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  • 10
    Language: English
    In: 2013 IEEE 19th International Conference on Embedded and Real-Time Computing Systems and Applications, August 2013, pp.165-174
    Description: Slot shifting is a method to combine time-triggered and event-triggered scheduling of real-time systems. It analyzes offline constructed scheduling tables for the amount and location of unused resources, called spare capacities, which are used to accommodate event-triggered activities, such as aperiodic tasks. Spare capacities are efficiently represented to indicate available resources and the flexibility to shift offline scheduled tasks while maintaining their feasibility with respect to their original timing constraints. In this paper, we study the overhead costs involved in the practical implementation of slot shifting. We present results from measurements on the cycle accurate multi-processor systems-on-chip simulator MPARM, which indicate the execution time and memory costs of the various steps of online slot shifting for the ARM architecture. These allow a designer to select configurations and trade-offs for the implementation. We present the insights gained which lead to a redesign of the original algorithm.
    Keywords: Runtime ; Schedules ; Scheduling ; Algorithm Design and Analysis ; Hardware ; Heuristic Algorithms ; Servers
    ISSN: 2325-1271
    ISSN: 15332306
    Source: IEEE Conference Publications
    Source: IEEE Xplore
    Source: IEEE Journals & Magazines 
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