一个基于CORBA的分布式网管系统模型ACORBA-BasedModelfor

新一代的分布式网管系统应具有良好的可扩展性、可集成性等特征。本文分析了当前主流网管系统的不足之后,给出了基于ＣＯＲＢＡ的分布式网管系统模型,并进一步阐述了分布对象技术（ＣＯＲＢＡ）在网管领域的应用优劣。     

基于CORBA的分布式系统自适应容错模型的研究

一、引言分布式系统需要可靠性保证,例如在线支付系统对安全性提出了很高的要求。因此,分布式系统必须提供可靠性机制,支持关键业务。容错技术是分布式系统运行过程中可靠性保证的重要手段,冗余资源是实现容错的根本保证。单一的容错策略仅适用于特定的应用和特定的系统,无法适应系统状态的动态变化,支持广泛的分布式应用。系统的容错模型应该能够智能地根据外部运行环境的变化,选择合适的容错策略,以便在保证系统可靠性的前提下提高系统资源利用率。自适应容错可以在分布式系统中的各个层次中实现。基于操作系统的自适应容错强烈地依赖于特定的操作系统,系统可移植性差;而在应用程序中实现自适应容错又加重了开     

Robust Adaptive Metrics for Deadline Assignment in Distributed Hard Real-Time Systems

Distributed real-time applications usually consist of several component tasks and must be completed by its end-to-end (E-T-E) deadline. As long as the E-T-E deadline of an application is met, the strategy used for dividing it up for component tasks does not affect the application itself. One would therefore like to slice each application E-T-E deadline and assign the slices to component tasks so as to maximize the schedulability of the component tasks, and hence the application. Distribution of the E-T-E deadline over component tasks is a difficult and important problem since there exists a circular dependency between deadline distribution and task assignment. We propose a new deadline-distribution scheme which has two major improvements over the best scheme known to date. It can distribute task deadlines prior to task assignment and relies on new adaptive metrics that yield significantly better performance in the presence of high resource contention. The deadline-distribution problem is formulated for distributed hard real-time systems with relaxed locality constraints, where schedulability analysis must be performed at pre-run-time, and only a subset of the tasks are constrained by pre-assignment to specific processors. Although it is applicable to any scheduling policy, the proposed deadline-distribution scheme is evaluated for a non-preemptive, time-driven scheduling policy. Using extensive simulations, we show that the proposed adaptive metrics deliver much better performance (in terms of success ratio and maximum task lateness) than their non-adaptive counterparts. In particular, the simulation results indicate that, for small systems, the adaptive metrics can improve the success ratio by as much as an order of magnitude. Moreover, the new adaptive metrics are found to exhibit very robust performance over a large variety of application and architecture scenarios.     

基于CORBA技术的高可用舰船信息处理系统

舰船信息处理面临着大数据量、复杂应用环境和平台异构化等趋势,本文设计了基于CORBA的高可用舰船信息处理系统,利用CORBA所具有的平台及语言无关的特点,屏蔽平台之间的差异,实现了异构平台间通信;并运用Ora-cle数据库的Advanced Replication功能实现了系统的双机热备和负载均衡,提高了系统的可用性。     

基于CORBA的分布式数据库监控系统研究与实现

针对当前分布式数据库性能监控软件在实时监测、提前预警、灵活性和二次开发等方面存在的一些问题,设计并实现了一种基于CORBA的分布式Oracle数据库监控系统.系统采用基于层次的内容呈现方式,并通过预测模型方法有效降监控引起的网络流量.实际应用证明,该系统能够在多层次多粒度上对分布式Oracle数据库系统和服务器资源情况进行持续地实时监控,能对潜在故障进行提前预警,能对被监控系统进行全面分析,还具有一定的远程处理功能.     

CORBA分布式系统中网络分割协议可行度分析

对象管理组织(OMG)颁布的容错CORBA通过对象冗余的方式实现容错。但容错CORBA(FT-CORBA)没有对网络分割的问题提供解决方法,即在网络分割的情况下,由于分割子网之间无法传递最新的复制对象状态,导致网络处于不断重复获取复制对象状态的阶段,操作不能继续执行,从而大大降低了系统的可执行性。通过在CORBA中间件中添加附件,在原有的容错机制上,根据对象一致性的要求分级,对不同等级的对象一致性对象采取不同的容错措施来提高系统的可执行性。并对网络分割为3个子网和10个子网的情况下进行了可行度分析验证。当网络分割情况不严重,即使所有子网都没有包含大部分网络节点时,改进的容错机制仍有较好的可执行度。当网络分割成的子网数比较多,网络的可行度与单个子网包含整个分布式系统节点数的多少有关,如果没有一个子网包含分布式系统中大部分节点时,网络的可行度仍然非常低,但仍优于改进前分布式系统的可行度。整个改进机制添加在中件间附件中,无需改变原有的ORB代码。     

Metrics for Action-labelled Quantitative Transition Systems

This paper defines action-labelled quantitative transition systems as a general framework for combining qualitative and quantitative analysis. We define state-metrics as a natural extension of bisimulation from non-quantitative systems to quantitative ones. We then prove that any single state-metric corresponds to a bisimulation and that the greatest state-metric corresponds to bisimilarity. Furthermore, we provide two extended examples which show that our results apply to both probabilistic and weighted automata as special cases of action-labelled quantitative transition systems.     

Approximation Metrics for Discrete and Continuous Systems

Established system relationships for discrete systems, such as language inclusion, simulation, and bisimulation, require system observations to be identical. When interacting with the physical world, modeled by continuous or hybrid systems, exact relationships are restrictive and not robust. In this paper, we develop the first framework of system approximation that applies to both discrete and continuous systems by developing notions of approximate language inclusion, approximate simulation, and approximate bisimulation relations. We define a hierarchy of approximation pseudo-metrics between two systems that quantify the quality of the approximation, and capture the established exact relationships as zero sections. Our approximation framework is compositional for a synchronous composition operator. Algorithms are developed for computing the proposed pseudo-metrics, both exactly and approximately. The exact algorithms require the generalization of the fixed point algorithms for computing simulation and bisimulation relations, or dually, the solution of a static game whose cost is the so-called branching distance between the systems. Approximations for the pseudo-metrics can be obtained by considering Lyapunov-like functions called simulation and bisimulation functions. We illustrate our approximation framework in reducing the complexity of safety verification problems for both deterministic and nondeterministic continuous systems     

Timers for Distributed Systems

We deal with temporal aspects of distributed systems, introducing and studying a new model called timed distributed π-calculus. This model extends distributed π-calculus with timers, transforming the communication channels into temporary resources. Distributed π-calculus describes located interactions between processes with restricted access to resources. We introduce time constraints by considering timeout timers for channels. Combining these timers with types and locations, we provide a formal framework able to describe complex systems with constraints on time and on resource access. Its typing system and operational semantics are presented. It is proved that the passage of time does not interfere with the typing system. The new model is proved to be sound by using a method based on subject reduction.     

一种基于机群的分布式数据采集系统

提出了一种基于机群的分布式数据采集系统，即采用任务调度中心、机群管理中心、采集代理多层次结构实现分布式数据采集；同时提出了机群的3种分配策略、管理中心选择机制及采集代理的设计方案。实验结果表明：该文所提出的方法适用于大规模网络的数据采集，能更加有效地提高数据采集的速度，解决传统的采集方法在大规模网络中所存在的数据传输负载过重和数据处理的瓶颈问题，在数据采集领域具有很好的应用前景，具有一定的应用价值。     

基于复杂网络的大型软件系统度量

随着软件系统规模的不断增大,如何度量面向对象大规模软件系统成为一个亟待解决的问题.近年来迅速发展的复杂网络理论为解决该问题提供了一个新的视角.介绍了大规模软件系统中的复杂网络现象,从元素级、模块级、网络级3个不同的粒度提出基于复杂网络的软件系统的各种度量;实现了大型Java程序复杂网络描述和度量工具JPAC.JPAC可用于分析大型Java系统的结构,并计算基于复杂网络的各度量值.     

并行计算系统度量指标综述

系统度量指标的研究一直是并行系统和应用设计的重要问题。本文首先通过对国内外并行计算系统度量指标的分析,将当前并行计算系统度量指标分为单一的计算性能度量指标和多要素综合的高效能度量指标两种。其次,总结了这些度量指标的研究现状,并指出这些度量指标研究中存在的一些问题以及需要考虑的难点。由于并行计算系统正在逐渐从"高性能"走向"高效能",本文主要考虑当前大规模并行计算系统的可靠性和能耗要素对系统的影响,从系统可扩展角度建立了可靠并行加速比和能耗并行加速比模型,并进一步扩展为度量并行计算系统效能的综合指标模型。最后指出了未来并行计算系统度量的研究方向。     

Dynamic Configuration for Distributed Systems

Dynamic system configuration is the ability to modify and extend a system while it is running. The facility is a requirement in large distributed systems where it may not be possible or economic to stop the entire system to allow modification to part of its hardware or software. It is also useful during production of the system to aid incremental integration of component parts, and during operation to aid system evolution. The paper introduces a model of the configuration process which permits dynamic incremental modification and extension. Using this model we determine the properties required by languages and their execution environments to support dynamic configuration. CONIC, the distributed system which has been developed at Imperial College with the specific objective of supporting dynamic configuration, is described to illustrate the feasibility of the model.     

分布参数系统的能控性

本文对一个控制量以分布方式在作用于系统的齐次项的同时,也作用于系统导数项的一阶分布参数系统讨论能控性问题。     

Detecting Distributed Denial-of-Service Attacks Using Kolmogorov Complexity Metrics

This paper describes an approach to detecting distributed denial of service (DDoS) attacks that is based on fundamentals of Information Theory, specifically Kolmogorov Complexity. A theorem derived using principles of Kolmogorov Complexity states that the joint complexity measure of random strings is lower than the sum of the complexities of the individual strings when the strings exhibit some correlation. Furthermore, the joint complexity measure varies inversely with the amount of correlation. We propose a distributed active network-based algorithm that exploits this property to correlate arbitrary traffic flows in the network to detect possible denial-of-service attacks. One of the strengths of this algorithm is that it does not require special filtering rules and hence it can be used to detect any type of DDoS attack. We implement and investigate the performance of the algorithm in an active network. Our results show that DDoS attacks can be detected in a manner that is not sensitive to legitimate background traffic.This research has been funded by the Defense Advanced Research Projects Agency (DARPA) contract F30602-01-C-0182 and managed by the Air Force Research Laboratory (AFRL) Information Directorate.General Electric Global Research Center, Niskayuna, New York.     

一种面向分布式系统的程序设计模式

分布式系统的程序设计模式主要包括多线程模式和事件驱动模式,其中事件驱动模式占据了主导地位。本文讨论了这两种模式的不足,以及Coroutine模式相对它们的优点,并认为Coroutine模式是最适合分布式系统的程序设计模式。本文在此基础上提出了Libresync,它是一个基于Coroutine模式的分布式系统基础支持库。它既能给应用开发带来非常清晰的控制流程,又具有很高的灵活性和表达力,性能也能满足大多数需求。     

Checkpointing and Rollback-Recovery for Distributed Systems

We consider the problem of bringing a distributed system to a consistent state after transient failures. We address the two components of this problem by describing a distributed algorithm to create consistent checkpoints, as well as a rollback-recovery algorithm to recover the system to a consistent state. In contrast to previous algorithms, they tolerate failures that occur during their executions. Furthermore, when a process takes a checkpoint, a minimal number of additional processes are forced to take checkpoints. Similarly, when a process rolls back and restarts after a failure, a minimal number of additional processes are forced to roll back with it. Our algorithms require each process to store at most two checkpoints in stable storage. This storage requirement is shown to be minimal under general assumptions.