This book provides an in-depth description of event-based systems, covering topics ranging from local event matching and distributed event forwarding algorithms, through a practical discussion of software engineering issues raised by the event-based style, to state-of-the-art research in event-based systems like composite event detection and security. The authors offer a comprehensive overview, and show the power of event-based architectures in modern system design, encouraging professionals to exploit this technique in next generation large-scale distributed applications like information dissemination, network monitoring, enterprise application integration, or mobile systems.

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Distributed event-based systems

Engineering context-aware systems and applications

Organic Computing (OC) and other research initiatives like Autonomic Computing or Proactive Computing have developed the vision of systems possessing life-like properties: they self-organize, adapt to their dynamically changing environments, and establish other so-called self-x properties, like self-healing, self-configuration, self-optimization, etc. What we are searching for in OC are methodologies and concepts for systems that allow to cope with increasingly complex networked application systems by introduction of self-x properties and at the same time guarantee a trustworthy and adaptive response to externally provided system objectives and control actions. Therefore, in OC, we talk about controlled self-organization.Although the terms self-organization and adaptivity have been discussed for years, we miss a clear definition of self-organization in most publications, which have a technically motivated background.In this article, we briefly summarize the state of the art and suggest a characterization of (controlled) self-organization and adaptivity that is motivated by the main objectives of the OC initiative. We present a system classification of robust, adaptable, and adaptive systems and define a degree of autonomy to be able to quantify how autonomously a system is working. The degree of autonomy distinguishes and measures external control that is exerted directly by the user (no autonomy) from internal control of a system which might be fully controlled by an observer/controller architecture that is part of the system (full autonomy). The quantitative degree of autonomy provides the basis for characterizing the notion of controlled self-organization. Furthermore, we discuss several alternatives for the design of organic systems.

Adaptivity and self-organization in organic computing systems

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 TSN-specific 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 proof-of-concept implementation and exemplary evaluation of TSN networks.

NeSTiNg: Simulating IEEE Time-sensitive Networking (TSN) in OMNeT++

In this position paper we present a conceptual vision of adaptation, a key feature of autonomic systems. We put some stress on the role of control data and argue how some of the programming paradigms and models used for adaptive systems match with our conceptual framework.

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A conceptual framework for adaptation

Networks in the automotive and aerospace area as well as in production facilities have to support time-critical (i.e., hard real-time) communication. For such applications, time-triggered Ethernet-based networking solutions provide the required timeliness, i.e., reliable packet delivery with deterministic latencies and low jitter. However, the routing and scheduling of the time-triggered traffic is an NP-hard problem. Hence, existing solutions to this problem make certain abstractions to reduce complexity if necessary. Nonetheless, such abstractions exclude feasible routing and scheduling options from the design space. Specifically, it is a typical approach to model routing and scheduling as separate problems, which are solved successively or with heuristic coupling. Therefore, we present a novel ILP formulation that can be used to jointly solve the routing and scheduling problem for time-triggered Ethernet networks. Using this formulation, it is possible to solve various scheduling problems that are infeasible when using a fixed shortest path routing with separate scheduling. Compared to a fixed load balanced routing with separate scheduling, schedules computed with our formulation offer lower communication latencies.

ILP-based joint routing and scheduling for time-triggered networks

Distributed publish/subscribe systems are usually deployed on top of an overlay network that enables complex routing strategies implemented in the application layer. Up to now, only little effort has been spent on the design of the broker overlay network assuming that it is either static or manually administered. As publish/subscribe systems are increasingly targeted at dynamic environments where client behavior and network characteristics vary over time, static overlay networks lead to suboptimal performance. In this paper, we present a self-organizing broker overlay infrastructure that adapts dynamically to achieve a better efficiency on both, the application and the network layer. This is obtained by taking network metrics as well as notification traffic into account.

Self-organizing broker topologies for publish/subscribe systems

On the Definitions of Self-Managing and Self-Organizing Systems

Future applications of the Industrial Internet of Things will increasingly depend on the timely exchange of information and data. Time-Sensitive Networking, which is currently being standardized, therefore extends switched Ethernet networks by realtime communication capabilities offering deterministic message delays. In its time-triggered communication variant, a network path needs to be planned for each realtime data flow and corresponding transmission time slots have to be reserved on the network links along that path. In this paper, we present the first joint mathematical model for path routing and time slot scheduling that combines multicast support with an individual transmission scheduling on each link along a flow's path. We provide a formalization as an Integer Linear Programming (ILP) problem and discuss several optimizations to significantly reduce the ILP solver's runtime without affecting the solution quality. In a thorough evaluation, we show the applicability of our approach and analyze the effects and trade-offs of different objective functions.

ILP-Based Routing and Scheduling of Multicast Realtime Traffic in Time-Sensitive Networks

Publish/subscribe systems are used increasingly often as a communication mechanism in loosely-coupled distributed applications. With their gradual adoption in mission critical areas, it is essential that systems are subjected to a rigorous performance analysis before they are put into production. However, existing approaches to performance modeling and analysis of publish/subscribe systems suffer from many limitations that seriously constrain their practical applicability. In this paper, we present a set of generalized and comprehensive analytical models of publish/subscribe systems employing different peer-to-peer and hierarchical routing schemes. The proposed analytical models address the major limitations underlying existing work in this area and are the first to consider all major performance-relevant system metrics including the expected broker and link utilization, the expected notification delay, the expected time required for new subscriptions to become fully active, as well as the expected routing table sizes and message rates. To illustrate our approach and demonstrate its effectiveness and practicality, we present a case study showing how our models can be exploited for capacity planning and performance prediction in a realistic scenario.

Helge Parzyjegla

Papers

ILP-based joint routing and scheduling for time-triggered networks

Self-organizing broker topologies for publish/subscribe systems

On the Definitions of Self-Managing and Self-Organizing Systems

ILP-Based Routing and Scheduling of Multicast Realtime Traffic in Time-Sensitive Networks

Stochastic performance analysis and capacity planning of publish/subscribe systems