Browsing by Author "Pedreiras, Paulo"
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- Comparing Admission Control Architectures for Real-Time EthernetPublication . Alvarez, Ines; Moutinho, Luis; Pedreiras, Paulo; Bujosa, Daniel; Proenza, Julian; Almeida, LuisIndustry 4.0 and Autonomous Driving are emerging resource-intensive distributed application domains that deal with open and evolving environments. These systems are subject to stringent resource, timing, and other non-functional constraints, as well as frequent reconfiguration. Thus, real-time behavior must not preclude operational flexibility. This combination is motivating ongoing efforts within the Time Sensitive Networking (TSN) standardization committee to define admission control mechanisms for Ethernet. Existing mechanisms in TSN, like those of AVB, its predecessor, follow a distributed architecture that favors scalability. Conversely, the new mechanisms envisaged for TSN (IEEE 802.1Qcc) follow a (partially) centralized architecture, favoring short reconfiguration latency. This paper shows the first quantitative comparison between distributed and centralized admission control architectures concerning reconfiguration latency. Here, we compare AVB against a dynamic real-time reconfigurable Ethernet technology with centralized management, namely HaRTES. Our experiments show a significantly lower latency using the centralized architecture. We also observe the dependence of the distributed architecture in the end nodes' performance and the benefit of having a protected channel for the admission control transactions.
- Enhancing MQTT with Real-Time and Reliable Communication ServicesPublication . Almeida, Luis; Shahri, Ehsan; Pedreiras, PauloMQTT is an application-layer protocol that eventually became popular in the Internet of Things (IoT) and Industrial IoT (IIoT) thanks to its simplicity and effective publisher-subscriber messaging model that enables its use in embedded resource-constrained devices. However, MQTT features a limited set of Quality-of-Service classes addressing exclusively message delivery, impairing its use in IIoT applications subject to timeliness requirements. This limitation of MQTT has been addressed in the literature, but with focus on the broker real-time operation, only. This paper adds to the state-of-the-art, by proposing a set of extensions to the MQTT protocol grounded on Software-Defined Networking (SDN) that enable, at the network level, attaining real-time communication services. Simulation results validate the benefits of the proposed extensions.
- Holistic Analysis for Fork-Join Distributed Tasks supported by the FTT-SE ProtocolPublication . Martínez, Ricardo Garibay; Nelissen, Geoffrey; Ferreira, Luís Lino; Pedreiras, Paulo; Pinho, Luís MiguelThis paper presents a holistic timing analysis for fixed-priority fork-join Parallel/Distributed tasks (P/D tasks) over a Flexible Time Triggered - Switched Ethernet (FTT-SE) network. The holistic approach considers both time-triggered and eventtriggered tasks/messages.
- Improved Holistic Analysis for Fork–Join Distributed Real-Time Tasks Supported by the FTT-SE ProtocolPublication . Garibay-Martínez, Ricardo; Nelissen, Geoffrey; Lino Ferreira, Luis; Pedreiras, Paulo; Pinho, Luis MiguelModern distributed real-time embedded applications have high processing requirements associated with strict deadlines. For some applications, such constraints cannot be fulfilled by existing single-core embedded platforms. A solution is to parallelize the execution of the applications, by allowing networked nodes to distribute their workload to remote nodes with spare capacity. In that context, this paper presents a holistic timing analysis for fixed-priority fork-join parallel/distributed tasks. Furthermore, we extend the holistic approach to consider the interaction between parallel threads and messages interchanged through a flexible time triggered switched Ethernet network, and we show how the pessimism on the worst case response time computation of such tasks can be reduced by considering the pipeline effect that occurs in such distributed systems. To evaluate the performance and correctness of the holistic model, this paper includes a numerical evaluation based on a real automotive application. The obtained results show that the proposed method is effective in distributing the load by different nodes, allowing a significant reduction of the worst case response time of the tasks. Moreover, the paper also reports an implementation of the model on a Linux library, called parallel/distributed real-time, as well as the corresponding results obtained on a real testbed. The obtained results are in accordance with the predictions of the holistic timing analysis.
- On the adequacy of SDN and TSN for Industry 4.0Publication . Silva, Luis; Pedreiras, Paulo; Fonseca, Pedro; Almeida, LuisIndustry 4.0, Industrial Internet of Things, Cyber-Physical Production Systems and Smart Factories are closely related emerging concepts expected to drive significant improvements in industrial production systems, with gains in efficiency, cost and customer satisfaction. These concepts are intimately associated with highly distributed and cooperative architectures that rely, naturally, on the network infrastructure. However, traditional industrial communication technologies hardly provide the required level of integration, flexibility and performance. Seeking a solution to this mismatch, we assess two technologies that appeared recently in the industrial realm, namely IEEE 802.1 Time-Sensitive Networking (TSN) and Software-Defined Networking (SDN). TSN and SDN are fundamentally different, thus having distinct strengths and weaknesses. This paper reviews their fundamental operation principles, evaluating them qualitatively against the specific requirements posed by Industry 4.0.
- A Real-Time Software Defined Networking Framework for Next-Generation Industrial NetworksPublication . Moutinho, Luis; Pedreiras, Paulo; Almeida, LuisIndustry 4.0 brings in a whole set of new requirements to engineering industrial systems, with notorious impact at the networking layer. A key challenge posed by Industry 4.0 is the operational flexibility needed to support on-the-fly reconfiguration of production cells, stations, and machines. At the networking layer, this flexibility implies dynamic packet handling, scheduling, and dispatching. SoftwareDefined Networking (SDN) provides this level of flexibility in the general Local Area Network (LAN) domain. However, its application in the industry has been hindered by a lack of support for real-time services. This paper addresses this limitation, proposing an extended SDN OpenFlow framework that includes realtime services, leveraging existing real-time data plane Ethernet technologies. We show the OpenFlow enhancements, a real-time SDN controller, and experimental validation and performance assessment. Using a proof-of-concept prototype with 3 switches and cycles of 250µs, we could achieve 1µs jitter on timetriggered traffic and a reconfiguration time between operational modes below 10ms