Integrated Task and Message Scheduling in Time-Triggered Aeronautic Systems

This thesis presents generation techniques for task and message configurations in time-triggered IMA architectures. The commonality among the given techniques is the problem of integrated task and message scheduling for time-triggered networks. The proposed approaches allow the automatic generation of task and message schedules, which comprises certain system requirements. Our first approach solves the task and message scheduling problem by regarding it as a graph problem. We present an off-line scheduling algorithm that traverses the precedence graph. The approach integrates task scheduling at system level and message scheduling at communication level by iteratively traversing the given precedence graph. The algorithm incorporates backtracking and path extension functionality, guaranteeing the consistency of the developed schedule. The main advantage of the algorithm is that it scales up well even for large avionics applications. Furthermore, this thesis extends ongoing research into task and message scheduling based on time-triggered networks by first using model checking techniques for solving this kind of problem. We demonstrate that state-of-the-art model checking and bounded model checking techniques can be used to compute a schedule that fulfills certain system requirements. Therefore, we introduce an approach that adopts the principle of symbolic state space exploration to schedule synthesis and provides a symbolic encoding which makes it possible to guarantee an optimal solution with respect to minimizing the system’s end-to-end latency. A developed heuristic approach extends this approach in order to increase scalability by preventing from an exhaustive search through a guided, weight-based state-space exploration. The developed approaches are implemented in a framework for scheduling synthesis. This framework enables the generation and investigate certain system configurations in terms of complexity. This is done by using a complexity evaluation approach, which is developed is this thesis.Diese Arbeit präsentiert Techniken zur Generierung von integrierten Task- und Message Konfigurationen für zeitgesteuerte IMA Architekturen. Den präsentierten Ansätzen liegt das Problem der Erzeugung von integrierten Task und Message Schedules für zeitgesteuerte Netzwerke zugrunde. Die entwickelten Ansätze generieren dabei automatisch integrierte Task und Message Schedules, die speziellen Systemanforderungen genügen. Unser erster Ansatz löst das Task und Message Scheduling Problem mittels Transformierung in ein Graphen - Problem. Ein Algorithmus wird entwickelt, der den Abhängigkeitsgraphen durchläuft und dabei sowohl das Task Scheduling auf Systemebene, als auch das Message Scheduling auf Kommunikationsebene einbezieht. Der präsentierte Ansatz arbeitet iterativ und enthält Überprüfungs- und Pfad-Erweiterungs-Funktionalität, die die zeitliche Konsistenz des entwickelten Schedules garantieren. Einer der Vorteile dieses Ansatzes ist die Skalierbarkeit, die es ermöglicht, auch größere aeronautische Architekturen zu untersuchen und entsprechende Konfigurationen bereitzustellen. Ein zweiter Ansatz beschreibt und löst erstmals das gegebene Problem mit Hilfe von Model - Checking Techniken. Diese Arbeit zeigt, dass aktuelle Model - Checking und Bounded Model - Checking Techniken genutzt werden können, um integrierte Task und Message Schedules zu berechnen, die speziellen Systemeigenschaften genügen. Wir präsentieren einen Ansatz, der das Prinzip der Zustandsraumexploration zur Scheduling Synthese nutzt. Dazu entwickeln wir eine symbolische Kodierung, die es nicht nur ermöglicht gültige Konfigurationen zu finden, sondern auch solche, die optimal sind bezüglich der Minimierung der Ende-zu-Ende Latenz. Zusätzlich präsentieren wir einen heuristischen Ansatz, der es erlaubt, die Skalierbarkeit deutlich zu verbessern, indem er das Problem der erschöpfenden Suche einschränkt. Die entwickelte Heuristik führt dabei eine gesteuerte, gewichtsbasierte Erkundung des Zustandsraumes durch. Die entwickelten Ansätze sind in einem Framework zur Scheduling Synthese implementiert. Dieses Framework erlaubt die Generierung von geeigneten System Konfigurationen als auch Komplexitätsuntersuchung für verschiedene Systemarchitektur - Szenarien. Dazu wird ein Ansatz zur Evaluierung von Komplexitätsuntersuchungen entwickelt

Scheduling & routing time-triggered traffic in time-sensitive networks

The application of recent advances in computing, cognitive and networking technologies in manufacturing has triggered the so-called fourth industrial revolution, also referred to as Industry 4.0. Smart and flexible manufacturing systems are being conceived as a part of the Industry 4.0 initiative to meet the challenging requirements of the modern day manufacturers, e.g., production batch sizes of one. The information and communication technologies (ICT) infrastructure in such smart factories is expected to host heterogeneous applications ranging from the time-sensitive cyber-physical systems regulating physical processes in the manufacturing shopfloor to the soft real-time analytics applications predicting anomalies in the assembly line. Given the diverse demands of the applications, a single converged network providing different levels of communication guarantees to the applications based on their requirements is desired. Ethernet, on account of its ubiquity and its steadily growing performance along with shrinking costs, has emerged as a popular choice as a converged network. However, Ethernet networks, primarily designed for best-effort communication services, cannot provide strict guarantees like bounded end-to-end latency and jitter for real-time traffic without additional enhancements. Two major standardization bodies, viz., the IEEE Time-sensitive Networking (TSN) Task Group (TG) and the IETF Deterministic Networking (DetNets) Working Group are striving towards equipping Ethernet networks with mechanisms that would enable it to support different classes of real-time traffic. In this thesis, we focus on handling the time-triggered traffic (primarily periodic in nature) stemming from the hard real-time cyber-physical systems embedded in the manufacturing shopfloor over Ethernet networks. The basic approach for this is to schedule the transmissions of the time-triggered data streams appropriately through the network and ensure that the allocated schedules are adhered with. This approach leverages the possibility to precisely synchronize the clocks of the network participants, i.e., end systems and switches, using time synchronization protocols like the IEEE 1588 Precision Time Protocol (PTP). Based on the capabilities of the network participants, the responsibility of enforcing these schedules can be distributed. An important point to note is that the network utilization with respect to the time-triggered data streams depends on the computed schedules. Furthermore, the routing of the time-triggered data streams also influences the computed transmission schedules, and thus, affects the network utilization. The question however remains as to how to compute transmission schedules for time-triggered data streams along with their routes so that an optimal network utilization can be achieved. We explore, in this thesis, the scheduling and routing problems with respect to the time-triggered data streams in Ethernet networks. The recently published IEEE 802.1Qbv standard from the TSN-TG provides programmable gating mechanisms for the switches enabling them to schedule transmissions. Meanwhile, the extensions specified in the IEEE 802.1Qca standard or the primitives provided by OpenFlow, the popular southbound software-defined networking (SDN) protocol, can be used for gaining an explicit control over the routing of the data streams. Using these mechanisms, the responsibility of enforcing transmission schedules can be taken over by the end systems as well as the switches in the network. Alternatively, the scheduling can be enforced only by the end systems or only by the switches. Furthermore, routing alone can also be used to isolate time-triggered data streams, and thus, bound the latency and jitter experienced by the data streams in absence of synchronized clocks in the network. For each of the aforementioned cases, we formulate the scheduling and routing problem using Integer Linear Programming (ILP) for static as well as dynamic scenarios. The static scenario deals with the computation of schedules and routes for time-triggered data streams with a priori knowledge of their specifications. Here, we focus on computing schedules and routes that are optimal with respect to the network utilization. Given that the scheduling problems in the static setting have a high time-complexity, we also present efficient heuristics to approximate the optimal solution. With the dynamic scheduling problem, we address the modifications to the computed transmission schedules for adding further or removing already scheduled time-triggered data streams. Here, the focus lies on reducing the runtime of the scheduling and routing algorithms, and thus, have lower set-up times for adding new data streams into the network