IEEE 802.1 Time-sensitive Networking (TSN) enables real-time communication with deterministically bounded network delay and jitter over standard IEEE 802.3 networks ("Ethernet"). In particular, TSN specifies a time-triggered scheduling mechanism in IEEE Std 802.1Qbv implemented by switches to control when outgoing queues get access to switch ports. Besides this time-triggered scheduling mechanism, other scheduling mechanisms can be active in the network at the same time including priority queuing and a credit-based shaper. Moreover, further supporting mechanisms such as the possibility to interrupt frames already in transmission (frame preemption) are specified by the TSN standards. Overall, this leads to a complex network infrastructure transporting both, real-time and non-real-time traffic in one converged network, making it hard to analyze the behavior of converged networks. To facilitate the analysis of TSN networks, we present TSNspecific extensions to the popular OMNeT++/INET framework for network simulations in this paper including, in particular, the time-triggered scheduling mechanism of IEEE Std 802.1Qbv. Besides the design of the TSN simulator, we present a proofof-concept implementation and exemplary evaluation of TSN networks.
Networked control systems (NCS) have attracted considerable attention in recent years. While the stabilizability and optimal control of NCS for a given communication system has already been studied extensively, the design of the communication system for NCS has recently seen an increase in more thorough investigation. In this paper, we address an optimal scheduling problem for a set of NCS sharing a dedicated communication channel, providing performance bounds and asymptotic stability. We derive a suboptimal scheduling policy with dynamic state-based priorities calculated at the sensors, which are then used for stateless priority queuing in the network, making it both scalable and efficient to implement on routers or multi-layer switches. These properties are beneficial towards leveraging existing IP networks for control, which will be a crucial factor for the proliferation of wide-area NCS applications. By allowing for an arbitrary number of concurrent transmissions, we are able to investigate the relationship between available bandwidth, transmission rate, and delay. To demonstrate the feasibility of our approach, we provide a proofof-concept implementation of the priority scheduler using real networking hardware.
Converged networks support applications with completely different (real-time) requirements. The communication paradigms offered in converged networks are predominantly treated as separate entities from the perspective of traffic engineering, e.g., time-triggered traffic for closed-loop control systems, shaped traffic for multimediastreaming applications, and best-effort traffic for non-time-critical IT applications. However, there are scenarios where applications benefit from considering time-triggered messages and non-timetriggered messages as complemental components of a single traffic flow. These applications have the property that time-triggered transmissions guarantee basic functionality (e.g., stability of a control system), and additional non-time-triggered transmissions improve the application's performance. We present how to model these so-called complemental traffic flows for this type of application using a traffic metric for the description of the non-time-triggered traffic part. Furthermore, we show that complemental flows are suitable for traffic engineering by presenting two different approaches for the problem of optimized joint routing and scheduling in converged networks with mixed integer linear programming. In our evaluations, we use an exemplary min-max objective for the joint routing and scheduling problem which yields an average reduction of the peak value of the traffic metric by 20-30% over constraint-based approaches. CCS CONCEPTS • Networks → Network algorithms; • Computer systems organization → Real-time systems.
Data processing tasks are increasingly spread across the internet to account for the spatially distributed nature of many data sources. In order to use network resources efficiently, subtasks need to be distributed in the network so data can be filtered close to the data sources. Previous approaches to this operator placement problem relied on various heuristics to constrain the complexity of the problem. In this paper, we propose two generic integer constrained problem formulations: a topology aware version which provides a placement including the specific network links as well as an end-to-end delay aware version which relies on the routing capabilities of the network. A linear programming relaxation for both versions is provided which allows exact and efficient solution using common solvers.
In this paper, we present a communication abstraction for Networked Control Systems that is characterized by a slotted transmission classification model. We discuss, how such a model can be implemented over local area networks by using IEEE Time Sensitive Networking methods. Furthermore, it is shown how asymptotic stability can be analyzed for linear systems that communicate over such a network. Based on the stability result, a controller design procedure is derived that takes the information captured in the network model into account. Further topics and related open problems that are implicated by the proposed model are briefly discussed as an outlook.
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