实时CORBA端到端调度的研究

当前，对实时CORBA作端到端调度分析的研究还比较少．本文在进行分析了对实时CORBA作端到端调度分析的研究基础上，提出了一种新的方法，旨在提高系统的并发程度，从而提高系统的可调度性。     

End-to-end latency characterization of task communication models for automotive systems

Real-Time Systems - Different communication models have been historically adopted in the automotive domain for allowing concurrent tasks to coordinate, interact and synchronize on a shared memory...     

FAD and SPA: End-to-end link-level loss rate inference without infrastructure

It is highly desirable and important for end users, with no special privileges, to identify and pinpoint faults inside the network that degrade the performance of their applications. However, existing tools are inaccurate to infer the link-level loss rates and have large diagnosis granularity. To address these problems, we propose a suite of user-level diagnosis approaches in two categories: (1) the diagnosis tool needs to be deployed only at the source and (2) the tool has to be deployed at both source and destination. For the former, we propose two fragmentation aided diagnosis approaches (FAD), Algebraic FAD and Opportunistic FAD, which use IP fragmentation to enable accurate link-level loss rate inference. For the latter category, we propose Striped Probe Analysis (SPA) which significantly improves the diagnosis granularity over those of the source-only approaches. Internet experiments are applied to evaluate each individual scheme (including an improved version of the state-of-the-art tool, Tulip [R. Mahajan, N. Spring, D. Wetherall, T. Anderson, User-level internet path diagnosis, in: ACM SOSP, 2003]) and various hybrid approaches. The results indicate that our approaches dramatically outperform existing work (especially for diagnosis granularity). But more importantly, we show that combination of different individual approaches (e.g. OFAD + Tulip or OFAD + SPA) provide not only the best performance but also smooth tradeoff among deployment requirement, diagnosis accuracy and granularity.     

一种基于FPGA的容错嵌入式系统设计

在FPGA内部使用各种IP软核搭建了完整的嵌入式系统,实现了用三个MicroBlaze CPU软核进行表决的三模冗余容错方案。同时对μC／OS—Ⅱ操作系统以及应用程序进行改进,在程序的内部加入了错误检测和校正(EDAC)、函数堆栈保护等容错功能。通过实验证明,该系统减小了器件本身和内存模块受到的SEU(Single Event Upset)影响。     

End-to-end analysis of distributed video-on-demand systems

The focus of the research presented in this paper is the end-to-end analysis of a distributed Video-on-Demand (VoD) system. We analyze the distributed architecture of a VoD system to design global request handling and admission control strategies and evaluate them using global metrics. The performance evaluation methodology developed in this paper helps in determining efficient ways of using all resources in the VoD architecture within the constraints of providing guaranteed high quality service to each request. For instance, our simulation results show that request handling policies based on limited redirection of blocked requests to other resources perform better than load sharing policies. We also show that request handling policies based on redirection have simpler connection establishment semantics than load sharing policies and, therefore, are easily incorporated into reservation or signaling protocols.     

Design and evaluation of a fault-tolerant mobile-agent system

The mobile agents create a new paradigm for data exchange and resource sharing in rapidly growing and continually changing computer networks. In a distributed system, failures can occur in any software or hardware component. A mobile agent can get lost when its hosting server crashes during execution, or it can get dropped in a congested network. Therefore, survivability and fault tolerance are vital issues for deploying mobile-agent systems. This fault tolerance approach deploys three kinds of cooperating agents to detect server and agent failures and recover services in mobile-agent systems. An actual agent is a common mobile agent that performs specific computations for its owner. Witness agents monitor the actual agent and detect whether it's lost. A probe recovers the failed actual agent and the witness agents. A peer-to-peer message-passing mechanism stands between each actual agent and its witness agents to perform failure detection and recovery through time-bounded information exchange; a log records the actual agent's actions. When failures occur, the system performs rollback recovery to abort uncommitted actions. Moreover, our method uses checkpointed data to recover the lost actual agent.     

End-to-end reliability of service oriented applications

As organizations move towards adopting a service oriented architecture that permits the coexistence of multiple technology environments, an increasing number of applications will be developed through the assembly of existing software components with standard web service interfaces. These components with web service interfaces may be available in-house, or may be supplied or hosted by external vendors. The use of multiple services, possibly utilizing different technologies, providers, locations, and sources, has implications for the end-to-end reliability of these applications to support a business process. Selecting the best service for individual tasks in a business process does not guarantee the most effective overall solution, particularly if criteria other than functional characteristics are employed. This paper examines reliability issues associated with applications developed within service oriented architecture. It develops a measure for deriving end-to-end application reliability, and develops a model to help select appropriate services for tasks in the business process which accommodate the redundant and overlapping functionality of available services and planned redundancy in task support to satisfy the reliability requirement of the resulting application. A genetic algorithm approach is adopted to select promising services to assemble the application using end-to-end reliability as the criterion of interest. An application to a real-world business process illustrates the effectiveness of the approach.     

End-to-end testing of IP QoS mechanisms

Voice quality provides a valid metric for testing the effectiveness of quality-of-service mechanisms in preserving the quality of voice streams in IP network traffic     

Reconfiguration and analysis of a fault-tolerant circular butterflyparallel system

The butterfly parallel system has a regular and simple interconnection pattern, making it suitable for VLSI or WSI implementation. The authors propose an effective fault-tolerant technique for the circular butterfly parallel system to ensure its rigid full butterfly structure even in the presence of failures, addressing reconfiguration in detail. The resulting butterfly system has L levels, involves (1/log₂ L)% spare processing elements (PEs), and approximately 50% additional links. The reconfiguration process of the design in response to any operational fault is easy and can be performed in a distributed manner. The reliability and layout of this proposed design are evaluated analytically. This design, due to its specific configuration, exhibits significant improvement in reliability while taking only moderately more layout area     

Closure and convergence: a foundation of fault-tolerant computing

The authors formally define what it means for a system to tolerate a class of faults. The definition consists of two conditions. The first is that if a fault occurs when the system state is within the set of legal states, the resulting state is within some larger set and, if faults continue to occur, the system state remains within that larger set (closure). The second is that if faults stop occurring, the system eventually reaches a state within the legal set (convergence). The applicability of the definition for specifying and verifying the fault-tolerance properties of a variety of digital and computer systems is demonstrated. Using the definition, the authors obtain a simple classification of fault-tolerant systems. Methods for the systematic design of such systems are discussed     

TETRA系统端-端加密机制研究

数字集群系统TETRA提供空中接口加密和端-端加密以实现通信的机密性。该文研究了TETRA的端-端加密机制及其优缺点。分析了基于分组密码算法IDEA设计的端-端加密系统。     

An operating system for a fault-tolerant multiprocessor controller

The development of an operating system that is a central component of a fault-tolerant multiprocessor is described. The operating system, while relatively simple and small, supports multitasking and multiprocessing, as well as both self-diagnostics and cross-diagnostics for fault detection. In the event of a fault, the system permits rapid reconfiguration in a manner that retains processing for the highest-priority tasks. Since the hardware needed to provide fault tolerance is available when there are no faults, the operating system can utilize this excess capacity to accomplish lower-priority tasks during normal operation. This approach yields graceful degradation in response to faults in the system components     

Heuristic fault-tolerant routing strategies for a multiprocessor network

We examine the suitability of three heuristic search algorithms (Greedy Constructive Scheme, Best First Search and A^*) for use as routing strategies on a faulty multiprocessor network. Our search space is a simulated 5 × 5 × 5 (125-node) multiprocessor mesh network. Each virtual node comprises a processor and a communications switch supporting explicit message backtracking. Their performances are compared for up to 20% of randomly generated faulty links. The results show that heuristic search algorithms can be implemented as fault-tolerant routing strategies and that the modified Best First Search routing strategy performed consistently better with significantly less degradation than the Greedy Constructive Scheme and the A^* strategies.     

Active leave behavior of members in a fault-tolerant group

With the fast development of network applications, there are more asynchronous distributed systems and more requirements for fault tolerance. Asynchrony means there is no upper bound for either message transfer or operation execution. Active replication is an effective means to enhance fault tolerant capability in distributed systems. A key component in a system is replicated and all the replicas make up of a fault-tolerant group. Members in such a group execute all client requests and then re…     

A fault-tolerant real-time multiprocessor with a built-in recovery mechanism

The architecture of a fault-tolerant multiprocessor with a rollback recovery mechanism is described. Fault-tolerance is attained owing to restarts of faulty processes of computations or their definite parts after detecting failures. An error occurring during the interaction of some processes leads to the multistep reconstruction of the entire computational process. An estimate of the efficiency of the proposed fault-tolerant technology is given.Translated from Kibernetika i Sistemnyi Analiz, No. 5, pp. 169–176, September–October 2004.     

Actuator fault-tolerant control design: Demonstration on a three-tank-system

Fault-tolerant control or reconfigurable control systems are generally based on a nominal control law associated with a fault detection and isolation module. A general review of techniques dealing with this problem is given and a new fault-tolerant control approach is presented. This method is based on the on-line estimation of an eventual fault and the addition of a new control law to the nominal control law in order to reduce the fault effect once this fault is detected and isolated. The performances of this method depend on the time delay between the occurrence of the fault and its detection and isolation. A modified approach is then proposed in order to avoid the problems generated by delays, false alarms or non-detection inherent to diagnosis techniques. These methods are applied to a pilot plant and their performances are compared and discussed.     

Machine checked proofs of the design of a fault-tolerant circuit

We describe a formally verified implementation of the “Oral Messages” algorithm of Pease, Shostak and LamportJ. ACM (1980)27, 228–234;ACM TOPLAS (1982)4, 382–401. An abstract implementation of the algorithm is proved to achieve interactive consistency in the presence of faults. This abstract characterisation is then mapped down to a hardware level implementation which inherits the fault-tolerant characteristics of the abstract version. All steps in the proof were checked with the Boyer-Moore theorem prover. A significant result of this work is the demonstration of a fault-tolerant device that is formally specified and the development of an implementation proved correct with respect to this specification. A significant simplifying assumption is that the redundant processors behave synchronously. We also describe a mechanically checked proof that the Oral Messages algorithm is “optimal” in the sense that no algorithm which achieves agreement via similar message passing can tolerate a larger proportion of faulty processors.     

Piranha: a CORBA tool for high availability

Despite the most careful planning, system applications can be dogged by unexpected failures. Our firm is keenly aware of the need for availability. To help meet that need, I developed an experimental CORBA-based restart service and monitor called Piranha, which both monitors and manages distributed applications to help systems attain high availability. First, Piranha acts as a network monitor that reports failures through a graphical user interface. Second, Piranha acts as a manager: it automatically restarts failed CORBA objects, replicates stateful objects (objects that maintain an internal set of values) on-the-fly, migrates objects from one host to another and enforces predefined replication degrees-numbers of copies-on groups of objects. As a backdrop to the discussion of Piranha's design and implementation, this article first examines the ways in which a CORBA ORB should support availability. I then explain how Piranha affords availability