Scheduling of Overload-Tolerant Computation and Multi-Mode Communication in Real-Time Systems

Real-time tasks require sufficient resources to meet deadline constraints. A component should provision sufficient resources for its workloads consisting of tasks to meet their deadlines. Supply and demand bound functions can be used to analyze the schedulability of workloads. The demand-bound function determines the maximum required computational units for a given workload and the supply-bound function determines the minimum possible resources supplied to the workload. A component will experience an overload if it receives fewer resources than required. An overload will be transient if it occurs for a bounded amount of time. Most work concentrates on designing components that avoid overloads by over-provisioning resources even though some computational units such as control system components can tolerate transient overloads. Overload-tolerant components can utilize resources more efficiently if over-provisioning of resources can be avoided. First, this dissertation presents the design of an efficient periodic resource model for scheduling computation of components that can tolerate transient overloads under the Earliest Deadline First (EDF) scheduling policy. We propose a periodic resource model for overload-tolerant components to address three problems: (1) characterize overloads and determine metrics of interest (i.e., delay), (2) derive a model to compute a periodic resource supply for a given workload and a worst-case tolerable delay, and (3) find a periodic resource supply for given control system specifications with a worst-case delay. The derived periodic resource supply can be used to derive an overload-tolerant component interface. Overload-tolerant real-time components can connect with each other in a distributed manner and thus require communication scheduling for reliable and guaranteed transmissions. Moreover, applications may require multi-mode communication for efficient data transmission. Second, this dissertation discusses communication schedules for multi-mode distributed components. Since distributed multi-mode applications are prone to suffer from delays incurred during mode changes, good communication schedules have low average mode-change delays. A key problem in designing multi-mode communication in real-time systems is the generation of schedules to move away the complexity of schedule design from the developer. We propose a mechanism to generate multi-mode communication schedules using optimization constraints associated with timing requirements. We illustrate a workflow from specifications to the generation of communication schedules through a real-time video monitoring case-study. Experimental analysis for the case-study demonstrates that schedules generated using the proposed method reduce the average mode-change delay compared to a randomized algorithm and the well-known EDF scheduling policy. Finally, this thesis discusses the synthesis of schedules for computation and communication to achieve not only performance but also separation of concerns for reducing complexity and increasing safety. To integrate overload-tolerant components using real-time communication, we derive specifications of component interfaces using the characterization of overloads and the proposed periodic resource model. The generation of communication schedules uses the specifications of interfaces which include timing requirements of possible transient overloads. A walk-through case-study explains the steps necessary to generate communication schedules using component interfaces. The interfaces provide safety through isolation of transient overload-tolerant components and the generated communication schedules provide high performance as a result of their low average mode-change delay

A Taxonomy for Management and Optimization of Multiple Resources in Edge Computing

Edge computing is promoted to meet increasing performance needs of data-driven services using computational and storage resources close to the end devices, at the edge of the current network. To achieve higher performance in this new paradigm one has to consider how to combine the efficiency of resource usage at all three layers of architecture: end devices, edge devices, and the cloud. While cloud capacity is elastically extendable, end devices and edge devices are to various degrees resource-constrained. Hence, an efficient resource management is essential to make edge computing a reality. In this work, we first present terminology and architectures to characterize current works within the field of edge computing. Then, we review a wide range of recent articles and categorize relevant aspects in terms of 4 perspectives: resource type, resource management objective, resource location, and resource use. This taxonomy and the ensuing analysis is used to identify some gaps in the existing research. Among several research gaps, we found that research is less prevalent on data, storage, and energy as a resource, and less extensive towards the estimation, discovery and sharing objectives. As for resource types, the most well-studied resources are computation and communication resources. Our analysis shows that resource management at the edge requires a deeper understanding of how methods applied at different levels and geared towards different resource types interact. Specifically, the impact of mobility and collaboration schemes requiring incentives are expected to be different in edge architectures compared to the classic cloud solutions. Finally, we find that fewer works are dedicated to the study of non-functional properties or to quantifying the footprint of resource management techniques, including edge-specific means of migrating data and services.Comment: Accepted in the Special Issue Mobile Edge Computing of the Wireless Communications and Mobile Computing journa

Designing application software in wide area network settings

Progress in methodologies for developing robust local area network software has not been matched by similar results for wide area settings. The design of application software spanning multiple local area environments is examined. For important classes of applications, simple design techniques are presented that yield fault tolerant wide area programs. An implementation of these techniques as a set of tools for use within the ISIS system is described

5GAuRA. D3.3: RAN Analytics Mechanisms and Performance Benchmarking of Video, Time Critical, and Social Applications

5GAuRA deliverable D3.3.This is the final deliverable of Work Package 3 (WP3) of the 5GAuRA project, providing a report on the project’s developments on the topics of Radio Access Network (RAN) analytics and application performance benchmarking. The focus of this deliverable is to extend and deepen the methods and results provided in the 5GAuRA deliverable D3.2 in the context of specific use scenarios of video, time critical, and social applications. In this respect, four major topics of WP3 of 5GAuRA – namely edge-cloud enhanced RAN architecture, machine learning assisted Random Access Channel (RACH) approach, Multi-access Edge Computing (MEC) content caching, and active queue management – are put forward. Specifically, this document provides a detailed discussion on the service level agreement between tenant and service provider in the context of network slicing in Fifth Generation (5G) communication networks. Network slicing is considered as a key enabler to 5G communication system. Legacy telecommunication networks have been providing various services to all kinds of customers through a single network infrastructure. In contrast, by deploying network slicing, operators are now able to partition one network into individual slices, each with its own configuration and Quality of Service (QoS) requirements. There are many applications across industry that open new business opportunities with new business models. Every application instance requires an independent slice with its own network functions and features, whereby every single slice needs an individual Service Level Agreement (SLA). In D3.3, we propose a comprehensive end-to-end structure of SLA between the tenant and the service provider of sliced 5G network, which balances the interests of both sides. The proposed SLA defines reliability, availability, and performance of delivered telecommunication services in order to ensure that right information is delivered to the right destination at right time, safely and securely. We also discuss the metrics of slicebased network SLA such as throughput, penalty, cost, revenue, profit, and QoS related metrics, which are, in the view of 5GAuRA, critical features of the agreement.Peer ReviewedPostprint (published version

Simulating Real-Time Aspects of Wireless Sensor Networks

Wireless Sensor Networks (WSNs) technology has been mainly used in the applications with low-frequency sampling and little computational complexity. Recently, new classes of WSN-based applications with different characteristics are being considered, including process control, industrial automation and visual surveillance. Such new applications usually involve relatively heavy computations and also present real-time requirements as bounded end-to- end delay and guaranteed Quality of Service. It becomes then necessary to employ proper resource management policies, not only for communication resources but also jointly for computing resources, in the design and development of such WSN-based applications. In this context, simulation can play a critical role, together with analytical models, for validating a system design against the parameters of Quality of Service demanded for. In this paper, we present RTNS, a publicly available free simulation tool which includes Operating System aspects in wireless distributed applications. RTNS extends the well-known NS-2 simulator with models of the CPU, the Real-Time Operating System and the application tasks, to take into account delays due to the computation in addition to the communication. We demonstrate the benefits of RTNS by presenting our simulation study for a complex WSN-based multi-view vision system for real-time event detection

Adaptive Quality of Service Control in Distributed Real-Time Embedded Systems

An increasing number of distributed real-time embedded systems face the critical challenge of providing Quality of Service (QoS) guarantees in open and unpredictable environments. For example, such systems often need to enforce CPU utilization bounds on multiple processors in order to avoid overload and meet end-to-end dead-lines, even when task execution times deviate significantly from their estimated values or change dynamically at run-time. This dissertation presents an adaptive QoS control framework which includes a set of control design methodologies to provide robust QoS assurance for systems at different scales. To demonstrate its effectiveness, we have applied the framework to the end-to-end CPU utilization control problem for a common class of distributed real-time embedded systems with end-to-end tasks. We formulate the utilization control problem as a constrained multi-input-multi-output control model. We then present a centralized control algorithm for small or medium size systems, and a decentralized control algorithm for large-scale systems. Both algorithms are designed systematically based on model predictive control theory to dynamically enforce desired utilizations. We also introduce novel task allocation algorithms to ensure that the system is controllable and feasible for utilization control. Furthermore, we integrate our control algorithms with fault-tolerance mechanisms as an effective way to develop robust middleware systems, which maintain both system reliability and real-time performance even when the system is in face of malicious external resource contentions and permanent processor failures. Both control analysis and extensive experiments demonstrate that our control algorithms and middleware systems can achieve robust utilization guarantees. The control framework has also been successfully applied to other distributed real-time applications such as end-to-end delay control in real-time image transmission. Our results show that adaptive QoS control middleware is a step towards self-managing, self-healing and self-tuning distributed computing platform

Evaluation of Burst Failure Robustness of Control Systems in the Fog

This paper investigates the robustness of control systems when a controller is run in a Fog environment. Control systems in the Fog are introduced and a discussion regarding relevant faults is presented. A preliminary investigation of the robustness properties of a MinSeg case study is presented and commented. The discussion is then used to outline future lines of research