Control-Based Adaptive Middleware for Real-Time Image Transmission over Bandwidth-Constrained Networks

Real-time image transmission is crucial to an emerging class of distributed embedded systems operating in open network environments. Examples include avionics mission replanning over Link-16, security systems based on wireless camera networks, and online collaboration using camera phones. Meeting image transmission deadlines is a key challenge in such systems due to unpredictable network conditions. In this paper, we present CAMRIT, a Control-based Adaptive Middleware framework for Real-time Image Transmission in distributed real-time embedded systems. CAMRIT features a distributed feedback control loop that meets image transmission deadlines by dynamically adjusting the quality of image tiles. We derive an analytic model that captures the dynamics of a distributed middleware architecture. A control-theoretic methodology is applied to systematically design a control algorithm with analytic assurance of system stability and performance, despite uncertainties in network bandwidth. Experimental results demonstrate that CAMRIT can provide robust real-time guarantees for a representative application scenario.     

Designing and Rightsizing the Information System Architecture

Information system design and sizing constitute a complex, top-down process that tailors the technology architecture to application requirements. Practitioners usually tackle this top-down process by focusing on individual design aspects, such as data or specific applications, and by relying on their previous experiences to compare alternative architectural solutions. Acquisition costs are usually accounted for, but related operating and maintenance costs are often neglected or underestimated. The complexity of optimizing individual design problems leads researchers to avoid a global optimization perspective and, thus, the IS architecture is usually a result of the juxtaposition of multiple local optima.This paper takes an overall perspective on the cost minimization problem of information system design to achieve a better trade-off between cost and performance over the whole expected life of the technology architecture. A comprehensive design methodology is discussed as an integrating framework that accounts for all categories of costs, including design, implementation, maintenance, and operation, to achieve a globally cost-minimizing solution.     

分布、实时、容错一体化设计方法研究

针对分布式航天器系统的运行环境和特点，对嵌入式系统在空间环境、实时、容错、分布上的需求进行了分析，提出了分布、实时、容错一体化的嵌入式系统设计方法，从满足实时要求下的实时容错能力、免疫与自愈相结合的综合容错能力、单节点的容错与节点间容错相结合的分布容错能力和多种容错方法集成等4个方面，对设计方法进行了阐述。     

Achieving jitter-free and predictable real-time control by accurately timed computer peripherals

Contemporary real-time computers are unable to manipulate external parallel processes simultaneously, and their response times are generally unpredictable, resulting in jitter of the corresponding sampled data systems. It is shown that these problems can be easily solved by endowing process control computers with input/output facilities, working fully in parallel, and making use of exact time specifications. The required system functions are compiled, the design of the additional hardware components is given, and the real-time operating system support is discussed. As a by-product, the exact timing feature of input/output operations opens a new way of synchronising the access of multiple tasks to shared peripherals, which is based on the dimension time.     

分布式实时操作系统消息机制的设计与实现

随着数字信号处理技术的迅猛发展,针对并行数字信号处理(DSP)应用自主开发了一个满足用户需要的高性能分布式实时操作系统--腾飞分布式实时操作系统(TF-RTOS).消息机制用于线程间的通信,是操作系统中的重要部分.在开发TF-RTOS过程中,从消息命令包、消息队列、消息传递过程和消息原语这4个方面设计并实现了一种直接消息传递的消息机制,该消息机制具有简化线程间通信、增强系统功能、提高系统性能的特点.     

Design of a real-time knowledge-based controller with applications in hydraulic turbine generator systems

Issues in the design and implementation of a real-time Knowledge-Based Controller (KBC) have been investigated. The design objective of such a controller is to maintain overall system stability and performance not only during normal, but also contingency, conditions. A general structure for such controllers is proposed. It consists of four major components: a knowledge base, a real-time inference engine, information processing algorithms, and a distributed controller. The functions of each individual component, as well as the relationship among them, are considered. The proposed design methodology is applied to synthesize a real-time knowledge-based controller for a hydraulic turbine governor.     

Modular abstractions for verifying real-time distributed systems

In this work we present a verification methodology for real-time distributed systems, based on their modular decomposition into processes. Given a distributed system, each of its components is reduced by abstracting away from details that are irrelevant for the required specification. The abstract components are then composed to form an abstract system to which a model checking procedure is applied. The abstraction relation and the specification language guarantee that if the abstract system satisfies a specification, then the original system satisfies it as well.The specification languageRTL is a branching-time version of the real-time temporal logicTPTL presented in Alur and Henzinger [1]. Its model checking is linear in the size of the system and exponential in the size of the formula. Two notions of abstraction for real-time systems are introduced, each preserving a sublanguage ofRTL.     

Feedback utilization control in distributed real-time systems with end-to-end tasks

An increasing number of distributed real-time systems face the critical challenge of providing quality of service guarantees in open and unpredictable environments. In particular, such systems often need to enforce utilization bounds on multiple processors in order to avoid overload and meet end-to-end deadlines even when task execution times are unpredictable. While recent feedback control real-time scheduling algorithms have shown promise, they cannot handle the common end-to-end task model where each task is comprised of a chain of subtasks distributed on multiple processors. This paper presents the end-to-end utilization control (EUCON) algorithm that adaptively maintains desired CPU utilization through performance feedbacks loops. EUCON is based on a model predictive control approach that models utilization control on a distributed platform as a multivariable constrained optimization problem. A multi-input-multi-output model predictive controller is designed based on a difference equation model that describes the dynamic behavior of distributed real-time systems. Both control theoretic analysis and simulations demonstrate that EUCON can provide robust utilization guarantees when task execution times deviate from estimation or vary significantly at runtime.     

Experimental evaluation of linear time-invariant models for feedback performance control in real-time systems

In recent years a new class of soft real-time applications operating in unpredictable environments has emerged. Typical for these applications is that neither the resource requirements nor the arrival rates of service requests are known or available a priori. It has been shown that feedback control is very effective to support the specified performance of dynamic systems that are both resource insufficient and exhibit unpredictable workloads. To efficiently use feedback control scheduling it is necessary to have a model that adequately describes the behavior of the system. In this paper we experimentally evaluate the accuracy of four linear time-invariant models used in the design of feedback controllers. We introduce a model (DYN) that captures additional system dynamics, which a previously published model (STA) fails to include. The accuracy of the models are evaluated by validating the models with regard to measured data from the controlled system and through a set of experiments where we evaluate the performance of a set of feedback control schedulers tuned using these models. From our evaluations we conclude that second order models (e.g., DYN) are more accurate than first order models (e.g. STA). Further we show that controllers tuned using second order models perform better than controllers tuned using first order models.     

The COMPLEX methodology for UML/MARTE Modeling and design space exploration of embedded systems

The design of embedded systems is being challenged by their growing complexity and tight performance requirements. This paper presents the COMPLEX UML/MARTE Design Space Exploration methodology, an approach based on a novel combination of Model Driven Engineering (MDE), Electronic System Level (ESL) and design exploration technologies. The proposed framework enables capturing the set of possible design solutions, that is, the design space, in an abstract, standard and graphical way by relying on UML and the standard MARTE profile. From that UML/MARTE based model, the automated generation framework proposed produces an executable, configurable and fast performance model which includes functional code of the application components. This generated model integrates an XML-based interface for communication with the tool which steers the exploration. This way, the DSE loop iterations are efficiently performed, without user intervention, avoiding slow manual editions, or regeneration of the performance model. The novel DSE suited modelling features of the methodology are shown in detail. The paper also presents the performance model generation framework, including the enhancements with regard the previous simulation and estimation technology, and the exploration technology. The paper uses an EFR vocoder system example for showing the methodology and for demonstrative results.     

A critique of unix

The UNIX operating system enjoys an ever increasing popularity throughout the computing community; there will be 1.4 million UNIX licences distributed by 1985, rising at a rate of about 400,000 per annum. With universal acceptance of a system comes a dangerously high degree of inertia. Consider the analogous area of programming languages, where there has been great resistance to change, despite major advancements. This paper presents a critique of UNIX, based on three areas which we consider to be of vital importance to future operating systems. These areas are operating system structures and design, programming support environments and distributed computing. The criticisms presented are in no way intended to discredit UNIX. UNIX compares favourably with most of the present generation of operating systems. The intention is to highlight deficiencies in the state of the art in operating system design.     

Monitoring and debugging distributed realtime programs

In this paper we describe the design and implementation of an integrated monitoring and debugging system for a distributed real-time computer system. The monitor provides continuous, transparent monitoring capabilities throughout a real-time system's lifecycle with bounded, minimal, predictable interference by using software support. The monitor is flexible enough to observe both high-level events that are operating system- and application-specific, as well as low-level events such as shared variable references. We present a novel approach to monitoring shared variable references that provides transparent monitoring with low overhead. The monitor is designed to support tasks such as debugging realtime applications, aiding real-time task scheduling, and measuring system performance. Since debugging distributed real-time applications is particularly difficult, we describe how the monitor can be used to debug distributed and parallel applications by deterministic execution replay.     

Traffic-aware stress testing of distributed real-time systems based on UML models using genetic algorithms

This paper presents a model-driven, stress test methodology aimed at increasing chances of discovering faults related to network traffic in distributed real-time systems (DRTS). The technique uses the UML 2.0 model of the distributed system under test, augmented with timing information, and is based on an analysis of the control flow in sequence diagrams. It yields stress test requirements that are made of specific control flow paths along with time values indicating when to trigger them. The technique considers different types of arrival patterns (e.g., periodic) for real-time events (common to DRTSs), and generates test requirements which comply with such timing constraints. Though different variants of our stress testing technique already exist (that stress different aspects of a distributed system), they share a large amount of common concepts and we therefore focus here on one variant that is designed to stress test the system at a time instant when data traffic on a network is maximal. Our technique uses genetic algorithms to find test requirements which lead to maximum possible traffic-aware stress in a system under test. Using a real-world DRTS specification, we design and implement a prototype DRTS and describe, for that particular system, how the stress test cases are derived and executed using our methodology. The stress test results indicate that the technique is significantly more effective at detecting network traffic-related faults when compared to test cases based on an operational profile.     

Concurrent intelligent rapid prototyping environment

Rapid prototyping technology enables rapid production of complex objects directly from a computer-aided design model without involving any tooling or conventional part programming. This has created a new set of problems associated with part design, process planning, support design and value engineering analysis of rapid prototyping parts. In this paper, a methodology for resolving these problems is described, which uses concurrent engineering, distributed blackboard, value engineering, knowledge-based and feature-based technologies. The functionality, design methodology and knowledge representation techniques of a concurrent intelligent rapid prototyping system for stereolithography form the main focus of this paper.     

Design of a Remote Procedure Call system for object-oriented distributed programming

This paper describes the design of an RPC system for building object-oriented distributed software systems. The general requirements for such a system are to provide mechanisms for supporting inheritance, polymorphism, dynamic binding, and modular development in implementing distributed software systems. This paper presents the functionalities of this RPC system to support these general requirements. It also briefly describes the experiences with two previous versions of this system and how they led to the design of the final system. This system was implemented as a part of the programming environment of the Nexus distributed operating system. © 1998 John Wiley & Sons, Ltd.     

Design and Verification of Distributed Recovery Blocks with CSP

A case study on the application of Communicating Sequential Processes (CSP) to the design and verification of fault-tolerant real-time systems is presented. The distributed recovery block (DRB) scheme is a design technique for the uniform treatment of hardware and software faults in real-time systems. Through a simple fault-tolerant real-time system design using the DRB scheme, the case study illustrates a paradigm for specifying fault-tolerant software and demonstrates how the different behavioural aspects of a fault-tolerant real-time system design can be separately and systematically specified, formulated, and verified using an integrated set of formal techniques based on CSP.     

Methods for the Development of Distributed Real-Time Embedded Systems Using VDM

The development of distributed real-time embedded systems presents a signi-ffcant practical challenge both because of the complexity of distributed computation and because of the need to rapidly assess a wide variety of design alternatives in early stages when requirements are often volatile. Formal methods can address some of these challenges but are often thought to require greater initial investment and longer development cycles than is desirable for the development of noncritical systems in highly competitive markets.In this paper we propose an approach that takes advantage of formal modelling and analysis technology in a lightweight way, making signi cant use of readily available tools. We describe an incremental approach in which detail is progressively added to abstract system-level speci cations of functional and timing properties via intermediate models that express system architecture, concurrency and distribution. The approach is illustrated using a modelof a home automation system. The models are expressed using the Vienna Development Method (VDM) and are validated primarily by scenario-based tests.     

User-level Real-Time Network System on Microkernel-based Operating Systems

This paper presents the design and implementation of a user-level real-time network system in Real-Time Mach. Traditional network systems for microkernel based operating systems, which tend to focus on high performance and flexibility, are not suitable for real-time communication. Our network system provides a framework for implementing real-time network protocols which require to bound protocol processing time, and it is suitable for implementing on microkernel based operating systems. In this paper, we especially focus on the aspects to avoid the priority inversion problem in order to make network systems more preemptable and predictable. We also describe the feasibility of our network system for building distributed multimedia systems.     

Mobile agent-enabled framework for structuring and building distributed systems on the internet

Mobile agent has shown its promise as a powerful means to complement and enhance existing technology in various application areas. In particular, existing work has demonstrated that MA can simplify the development and improve the performance of certain classes of distributed applications, especially for those running on a wide-area, heterogeneous, and dynamic networking environment like the Internet. In our previous work, we extended the application of MA to the design of distributed control functions, which require the maintenance of logical relationship among and/or coordination of proc- essing entities in a distributed system. A novel framework is presented for structuring and building distributed systems, which use cooperating mobile agents as an aid to carry out coordination and cooperation tasks in distributed systems. The framework has been used for designing various distributed control functions such as load balancing and mutual ex- clusion in our previous work. In this paper, we use the framework to propose a novel ap- proach to detecting deadlocks in distributed system by using mobile agents, which dem- onstrates the advantage of being adaptive and flexible of mobile agents. We first describe the MAEDD (Mobile Agent Enabled Deadlock Detection) scheme, in which mobile agents are dispatched to collect and analyze deadlock information distributed across the network sites and, based on the analysis, to detect and resolve deadlocks. Then the design of an adaptive hybrid algorithm derived from the framework is presented. The algorithm can dynamically adapt itself to the changes in system state by using different deadlock detec- tion strategies. The performance of the proposed algorithm has been evaluated using simulations. The results show that the algorithm can outperform existing algorithms that use a fixed deadlock detection strategy.     

面向并行图像处理的实时分布式操作系统的设计与实现

针对多片TMS320C64 DSP构成的多计算机体系结构的实时图像识别系统，设计并实现了面向并行图像处理的实时分布式操作系统PIPORTDOS（Parallel image processing-oriented real-time distributed operating system）．PIPORTDOS基于微内核体系结构，包括硬件抽象层、系统核心层、分布式消息通信机制和系统服务层四个层次．其多任务内核实现了基于优先级的抢先式调度、任务闻的同步和通信原语、实时的中断处理以及面向应用的缓存管理机制．为了实现对分布式并行图像处理的支持，PIPORTDOS采用了基于消息传递（Message Passing）的方式，并在实现中充分考虑了上层图像处理算法的应用需求以及DSP的硬件功能．相关性能指标表明，本文设计实现的PIPORTDOS完全可以满足系统的强实时性要求．在功能上也能适应算法对不同并行结构的需求．