| 1. |
- Aravind, Meera, et al.
(författare)
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An Event-Based Messaging Architecture for Vehicular Internet of Things (IoT) Platforms
- 2017
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Ingår i: Communications in Computer and Information Science, vol. 778. - Cham : Springer Verlag. - 9783319675961 ; , s. 37-46
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Konferensbidrag (refereegranskat)abstract
- Internet of Things (IoT) has revolutionized transportation systems by connecting vehicles consequently enabling their tracking, as well as monitoring of driver activities. Such an IoT platform requires a significant amount of data to be send from the on-board vehicle to the off-board servers, contributing to high network usage. The data can be send at regular intervals or in an event-based manner whenever relevant events occur. In interval-based approach, the data is send even if it is not relevant for reporting leading to a wastage of network resources, e.g., when the data does not change considerably compared to the previously sent value. In this paper, we investigate the possibility of using an event-based architecture to send data from the on-board system to the off-board system. The results show that our event-based architecture improves the accuracy of data available at the off-board system, by a careful selection of events. Moreover, we found that our event based architecture significantly decreases the frequency of sending messages, particularly during highway driving, leading to reduced average data transfer rates. Our results enable a customer to perform trade-offs between accuracy and data transfer rates.
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| 2. |
- Davis, Rob, et al.
(författare)
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Exact Speedup Factors and Sub-Optimality for Non-Preemptive Scheduling
- 2018
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Ingår i: Real-time systems. - : Springer Science and Business Media LLC. - 0922-6443 .- 1573-1383. ; , s. 208-246
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Tidskriftsartikel (refereegranskat)abstract
- Fixed priority scheduling is used in many real-time systems; however, both preemptive and non-preemptive variants (FP-P and FP-NP) are known to be sub-optimal when compared to an optimal uniprocessor scheduling algorithm such as preemptive Earliest Deadline First (EDF-P). In this paper, we investigate the sub-optimality of xed priority non-preemptive scheduling. Speci cally, we derive the exact processor speed-up factor required to guarantee the feasibility under FP-NP (i.e. schedulablability assuming an optimal priority assignment) of any task set that is feasible under EDF-P. As a consequence of this work, we also derive a lower bound on the sub-optimality of non-preemptive EDF (EDF-NP). As this lower bound matches a recently published upper bound for the same quantity, it closes the exact sub-optimality for EDF-NP. It is known that neither preemptive, nor non-preemptive xed priority scheduling dominates the other, in other words, there are task sets that are feasible on a processor of unit speed under FP-P that are not feasible under FP-NP and vice-versa. Hence comparing these two algorithms, there are non-trivial speedup factors in both directions. We derive the exact speed-up factor required to guarantee the FP-NP feasibility of any FP-P feasible task set. Further, we derive the exact speed-up factor required to guarantee FP-P feasibility of any constrained-deadline FP-NP feasible task set.
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| 3. |
- Desai, Nitin, 1986-, et al.
(författare)
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A Topology-specific Tight Worst-case Analysis of Strict Priority Traffic in Real-time Systems
- 2023
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Ingår i: IEEE Int. Conf. Emerging Technol. Factory Autom., ETFA. - : Institute of Electrical and Electronics Engineers Inc.. - 9798350339918
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Konferensbidrag (refereegranskat)abstract
- Tight end-to-end worst-case delay bounds for periodic traffic streams are essential for time sensitive networks. In this paper, we provide an algorithm to compute a tight (and accurate) end-to-end worst-case bound by considering distinct topological patterns and the manner in which streams enter and leave switches. This refined analysis uses non-preemptive, strict-priority arbitration mechanism commonly deployed in Ethernet switches. Compared to the state-of-the-art that considers all higher and equal priority interference as contributing to the worst-case bound, we present an analytical approach for computing a tighter worst-case delay bound and prove through discrete event simulations that only a certain number of equal-priority interference streams can actually affect the worst-case case. Our results enable efficient resource allocation and have implications for online re-configuration mechanisms for time-sensitive factory communication systems.
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| 4. |
- Desai, Nitin, 1986-
(författare)
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Designing safe and adaptive time-critical fog-based systems
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Safety-critical systems in industrial automation, avionics, or automotive domains demand correct, timely and predictable performance under all(including faulty) operating conditions. Fault-tolerance plays an important role in ensuring seamless system function even in the presence of failures. Typically such systems run hard real-time applications, and hence timing violations can result in hazards. Fog computing is an adaptive paradigm which distributes computation and communication along the cloud-IoT continuum to reduce communication latencies, making it more conducive to execute real-time applications. This requires enhancements to the network connecting various sub-systems to support timely delivery of safety-critical messages. Traditionally safety-critical systems are designed offline and are not re-configured during runtime. The inherent adaptive properties of fog computing systems make it susceptible to timeliness violations and can be a hindrance to safety guarantees. At the same time, adaptivity in terms of migrating computation and communication to different devices in the fog-cloud continuum can be used to make the system more fault-tolerant by suitable design approaches. In this work we provide design approaches geared towards achieving safety and predictability of critical applications that run on adaptive fog computing platforms. To this end, we start by performing a survey of safety considerations in a fog computing system and identifying key safety challenges. We then propose a design approach to improve predictability in an autonomous mobile robot use-case in a factory setting designed using the fog computing paradigm. We narrow our attention on time-sensitive networking (TSN) and propose a temporal redundancy-based fault tolerance approach for time-sensitive messages. Furthermore, we study the 802.1CB TSN protocol and suggest improvements to reduce network congestion owing to replicated frames.As a future work, we intend to also include the wireless aspects in the evaluation of timeliness guarantees for safety-critical applications. The emphasis will be on run-time failure scenarios and self-healing mechanisms based on online decisions taken in concert with offline guarantees.
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| 5. |
- Desai, Nitin, 1986-, et al.
(författare)
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MALOC : Building an adaptive scheduling and routing framework for rate-constrained TSN traffic
- 2022
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Ingår i: IEEE International Conference on Emerging Technologies and Factory Automation, ETFA. - : Institute of Electrical and Electronics Engineers Inc.. - 9781665499965
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Konferensbidrag (refereegranskat)abstract
- Time Sensitive Networking (TSN) is a set of standards aimed at providing real-time guarantees over existing Ethernet standards. Worst-case traversal time (WCTT) analyses of network traffic are traditionally used in schedulability and routing analyses to determine feasible routes for traffic streams. However, worst-case conditions happen quite rarely from a probabilistic perspective. The typical or average-case traversal times are easier to compute and can be used as an effective design tool for routing and scheduling. In this paper, we present "MaLoC"or Maximally Loaded Common links for routing and scheduling of rate-constrained (RC) traffic in time-sensitive networks (TSN). The proposed framework employs a fully decentralized approach to route and schedule generation with only switch-local information. We further provide a preliminary evaluation of the proposed approach using a simple network topology.
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| 6. |
- Dobrin, Radu, 1970-
(författare)
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Combining Off-line Schedule Construction and Fixed Priority Scheduling in Real-Time Computer Systems
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Datorer har blivit lika vanliga i samhället under de senaste 10 åren som vanliga mikrovågsugnar i hemmet. Förutom hem-PC som numera finns i nästan alla hushåll, är nästan all elekronik i hemmet (till exempel dvd-spelaren eller tv apparaten) eller i bilen, datorstyrt. I de enklaste fallen består dessa system av en dator och ett antal datorprogram som körs på den.I och med att dessa system blir allt mer avancerade så ökar kraven på datorns effektivitet också, till exempel hur många program kan köras på samma dator samtidigt, medan priserna på den färdiga produkten måste hållas så låga som möjligt för att kunna anpassas till marknaden.Vissa program i ett datorstyrt system är viktigare än andra att de utförs korrekt med avseende på både funktionalitet och tid. I bilar, till exempel, är det ytterst viktigt att datorprogrammen som styr airbagen eller bromsarna alltid fungerar som de ska, medan cd- äxlaren inte är så kritiskt för passagerarnas säkerhet. Både airbagen och cd-växlaren måste reagera på externa händelser (krock eller tryck på play knappen). Medan airbagen måste aktiveras inom en viss tidsintervall, dvs, inte före en krock, men inte för sent efter en krock heller, så spelar det ingen större roll om det tar en halv sekund extra mellan tiden man trycker på play knappen på cd:n och tiden när låten börjar spelas upp. Alla dessa system måste kunna koexistera utan att påverka varandra på ett negativt sätt, dvs, om cd-växlaren slutar fungera, får det inte påverka bromsarnas funktionalitet.I vissa system, är grunddesignen gjort på så sätt att det är svårt att lägga till ytterligare funktionalitet, oftast i form av nya datorprogram. Om man, till exempel, vill lägga till ett antisladd system i en bil, som kommer att styras av bil datorn, så måste man kunna vara säker på att resten av programmen som körs på samma dator, i synnerhet de kritiska delarna (till ex. airbag), fortfarande kommer att fungera felfritt. Å andra sidan, ju mera program man lägger till i systemet, desto svårare blir det för datorn att hantera dem. Detta leder oftast till behovet att förnya datorn till en kraftigare modell som ska lätt hantera de gamla programmen. Samtidigt så måste man fortfarande säkerställa att programmen fungerar korrekt. Att garantera att det nya systemet som består av en ny dator och de gamla programmen uppfyller kraven på korrekt funktionalitet, kan vara ett väldigt svår uppgift.I det här arbetet, vi förseslår metoder som gör det möjligt och lätt att utföra ovannämda uppgifter, dvs, att utöka funktionaliteten i befintliga datorsystem eller att uppgradera systemen medan den kritiska beteendet garanteras. Samtidigt, introducerar vi metoder for att förbättra efektiviteten i befintliga datorstyrda system som används i dagens läge i, till exempel, bil och flygindustrin.
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| 7. |
- Dobrin, Radu, 1970-, et al.
(författare)
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On fault-tolerant scheduling of time sensitive networks
- 2019
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Ingår i: OpenAccess Series in Informatics. - : Schloss Dagstuhl- Leibniz-Zentrum fur Informatik GmbH, Dagstuhl Publishing. - 9783959771191
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Konferensbidrag (refereegranskat)abstract
- Time sensitive networking (TSN) is gaining attention in industrial automation networks since it brings essential real-time capabilities at the data link layer. Though it can provide deterministic latency under error free conditions, TSN still largely depends on space redundancy for improved reliability. In many scenarios, time redundancy could be an adequate as well as cost efficient alternative. Time redundancy in turn will have implications due to the need for over-provisions needed for timeliness guarantees. In this paper, we discuss how to embed fault-tolerance capability into TSN schedules and describe our approach using a simple example.
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| 8. |
- Gutiérrez, Marina, et al.
(författare)
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Self-Configuration of IEEE 802.1 TSN Networks
- 2017
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Konferensbidrag (refereegranskat)abstract
- Configuration processes of real-time networks are costly both in terms of time and engineering effort and require the system to be shutdown during the reconfiguration phase thus resulting in significant down time as well. The convergence of IT/OT technologies is bringing a whole world of possibilities for the configuration and management of real-time networks for the automation industry. With software defined networking (SDN) features like the separation of the data and control plane and standards like IEEE 802.1 developed with the goal of adding deterministic capabilities to traditionally dynamic switched Ethernet networks, the plug and play paradigm is almost around the corner. In this paper, we go one step further and start looking into the self-configuration of real-time networks. To achieve that we propose to introduce a Configuration Agent in the network, an entity that continuously monitors the network to detect changes and automatically update the configuration to adapt to such changes while maintaining desired quality of service. We present here the complete framework for the Configuration Agent that will provide self-configuration capabilities to real-time networks. The proposed framework has IEEE 802.1 as its core, but also shows how the set of standards need to be extended in order to achieve the self-configuration requirements. Concretely we examine the role of existing communication protocols like NETCONF and OPC-UA and propose the essential ingredients (managed objects) for a YANG model for the learning aspects in the bridges, including different working modes.
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| 9. |
- Gutiérrez, M., et al.
(författare)
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Synchronization quality of IEEE 802.1AS in large-scale industrial automation networks.
- 2017
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Ingår i: Proceedings of the IEEE Real-Time and Embedded Technology and Applications Symposium, RTAS. - : Institute of Electrical and Electronics Engineers Inc.. - 9781509052691 ; , s. 273-282
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Konferensbidrag (refereegranskat)abstract
- Industry 4.0 and Industrial Internet of Things projects work towards adoption of standard IT technologies for real-time control networks in industrial automation. For this the IEEE 802.1 Time-Sensitive Networking (TSN) Task Group has developed and continues to develop a set of standards. One of these standards is the IEEE 802.1AS clock synchronization protocol. IEEE 802.1AS can be used to enable time-triggered communication as well as to coordinate distributed actions in industrial networks. In this paper we study the synchronization quality of IEEE 802.1AS and we are interested in whether the clocks can be synchronized with sufficiently low error such that the protocol can be used for demanding industrial automation applications. In particular, we study the protocol behavior in large-scale networks while considering critical implementation details. We report analytical worst-case results as well as probabilistic results based on simulations, that show that implementation details such as the PHY jitter and the clock granularity have a big impact on the time synchronization precision.
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| 10. |
- Markovic, Filip, 1992-, et al.
(författare)
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A Comparison of Partitioning Strategies for Fixed Points-based Limited Preemptive Scheduling
- 2019
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Ingår i: IEEE Transactions on Industrial Informatics. - 1551-3203 .- 1941-0050. ; 15:2, s. 1070-1081
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Tidskriftsartikel (refereegranskat)abstract
- The increasing industrial demand for handling complex functionalities has influenced the design of hardware architectures for time critical embedded systems, during the past decade. Multi-core systems facilitate the inclusion of many complex functionalities, while, at the same time, inducing cache related overheads, as well as adding partitioning complexity to the overall system schedulability. One of the efficient paradigms for controlling and reducing the cache related costs in real-time systems is Limited Preemptive Scheduling (LPS), with its particular instance Fixed Preemption Points Scheduling (LP-FPPS), that has been shown to outperform other alternatives as well as has been supported by and investigated in the automotive domain. With respect to the partitioning constraints, Partitioned Scheduling has been widely used to pre-runtime allocate tasks to specific cores, resulting in a predictable cache-related preemption delays estimations. In this paper we propose to integrate LP-FPPS and Partitioned Scheduling on fixed-priority multicore real-time systems in order to increase the overall system schedulability.We define a new joint approach for task partitioning and preemption point selection, that is based on the computation of the maximum blocking tolerance upon each allocation, thus being able to quantify the schedulability of the taskset on each processor. Furthermore, we investigate partitioning strategies based on different heuristics, i.e. First Fit Decreasing and Worst Fit Decreasing, and priority and density taskset orderings. The evaluation performed on randomly generated tasksets shows that in the general case, no single partitioning strategy fully dominates the others. However, the evaluation results reveal that certain partitioning strategies perform significantly better with respect to the overall schedulability for specific taskset characteristics. The results also reveal that the proposed partitioning strategies outperform Fully Preemptive and Non-Preemptive partitioned scheduling in terms of successful partitioning.
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