高带宽组播网络端到端时延测量及分析

随着IP组播技术的飞速发展,用户对多媒体视频流的需求的增加导致IP组播网络的性能下降。为解决IP组播性能测量中网络延迟问题,在高速校园网中,根据RFC标准文档中定义的组播性能测试指标和测试方法,实现精确测量组播网络的端到端时延,并且利用时钟同步原理对测量结果进行时钟频差分析。其创新之处在于将线性规划算法应用到对测量模型进行分析的过程中。通过在高速校园网中的测量结果表明,通过所提出算法对测量结果进行修正后可以得到准确的端到端网络时延。该研究为在校园网中推广组播流媒体应用打下基础,更有利于发现网络瓶颈,为未来网络构建奠定基础。     

Test workload measurement and reliability analysis for large commercial software systems

This paper characterizes the testing environment for large commercial software systems, matches reliability model assumptions with the application environment, examines alternative test workload measurements that capture software usage information during testing, and uses two such measurements, test runs and transactions, as our usage dependent time measurements in reliability modeling. Our previous research using test runs, execution time, and test input information for reliability analysis and improvement is extended to ensure better test workload measurements for reliability assessment and prediction. This paper also identifies conditions under which different test workload measurements are appropriate, and presents reliability modeling results using these measurements in several products developed in the IBM Software Solutions Toronto Laboratory.     

控制系统的SDG模型描述及故障传播分析

讨论了控制系统的符号有向图(SDG)模型描述和故障在控制系统中的传播方式及分析方法.该方法按控制回路信息流向的正反推理,分析初始和稳态响应的故障传递规律,通过基本单元的组合可以扩展到各类控制系统的SDG描述和故障传播分析.以锅炉水位控制系统为例,验证了该方法的有效性.     

Integrating workload balancing and fault tolerance in distributed stream processing system

World Wide Web - Distributed Stream Processing Engine (DSPE) is designed for processing continuous streams so as to achieve the real-time performance with low latency guaranteed. To satisfy such...     

The reliability of general vague fault-tree analysis on weapon systems fault diagnosis

An algorithm of vague fault-tree analysis is proposed in this paper to calculate fault interval of system components from integrating expert's knowledge and experience in terms of providing the possibility of failure of bottom events. We also modify Tanaka et al's definition and extend the new usage on vague fault-tree analysis in terms of finding most important basic system component for managerial decision-making. In numerical verification, the fault of automatic gun is presented as a numerical example. For advanced experiment, a fault tree for the reactor protective system is adopted as simulation example and we compare the results with other methods. This paper also develops vague fault tree decision support systems (VFTDSS) to generate fault-tree, fault-tree nodes, then directly compute the vague fault-tree interval, traditional reliability, and vague reliability interval.     

Runtime latency detection and analysis

Detecting latency‐related problems in production environments is usually carried out at the application level with custom instrumentation. This is enough to detect high latencies in instrumented applications but does not provide all the information required to understand the source of the latency and is dependent on manually deployed instrumentation. The abnormal latencies usually start in the operating system kernel because of contention on physical resources or locks. Hence, finding the root cause of a latency may require a kernel trace. This trace can easily represent hundreds of thousands of events per second. In this paper, we propose and evaluate a methodology, efficient algorithms, and concurrent data structures to detect and analyze latency problems that occur at the kernel level. We introduce a new kernel‐based approach that enables developers and administrators to efficiently track latency problems in production and trigger actions when abnormal conditions are detected. The result of this study is a working scalable latency tracker and an efficient approach to perform stateful tracing in production. Copyright © 2016 John Wiley & Sons, Ltd.     

支持低延迟通信与容错的计算资源共享环境构建

提出与描述了支持低延迟通信与容错的计算资源共享环境LF-CRSE (low latency and fault tolerance CRSE),LF-CRSE提出了节点功能角色的观点,由客户端功能节点、任务服务器、工作机服务提供器、工作机节点组成,形成一个可扩展的分布式网络体系结构.采用了任务缓存、任务预获取和任务服务器端计算等策略保证了通信过程的低延迟开销.在应用上利用分支界限模式的任务划分,使LF-CRSE支持主-从模式和分-治模式的灵活编程模型.通过工作机端的心跳消息和面向子任务的容错方式保证了LF-CRSE的正确性.测试过程选择了具有数据依赖的分布式旅行商问题,实验结果表明,LF-CRSE的加速比随着工作机的增加稳定提高,在低延迟通信和容错特性上也具有良好的性能.     

烧结矿取制样品称量数据采集系统的通讯故障分析

简要介绍重钢新区1、2#烧结矿取制样品称量数据采集系统,针对实际使用过程因通讯故障导致该系统不能正常运行案例,进行故障分析,查找原因,提出改进措施,可以有效保证该系统的顺行,为指导烧结矿生产,提升烧结矿品质,打下坚实基础.     

Analyzing scalability of parallel systems with unbalanced workload

This paper presents a new formulation of the isoefficiency function which can be applied to parallel systems executing balanced or unbalanced workloads. This new formulation allows analyzing the scalability of parallel systems under either balanced or unbalanced workloads. Finally, the validity of this new metric is evaluated using some synthetic benchmarks. The experimental results allow assessing the importance of considering the unbalanced workloads while analyzing the scalability of parallel systems.     

数据库系统交易型负载自适应管理

数据库系统的负载自适应是指数据库系统通过对负载的过滤和控制有效利用系统资源去满足负载性能要求的过程。自治数据库系统负载管理框架（Autonomic Workload Management Framework,AWMF）是一种负载自适应的总体框架,给出了负载自适应的基本组件和主要工作过程。研究AWMF对交易型负载（Transactional Workload）的有效性,提出了基于查询成本（Query Cost）的交易型负载的排队网络模型,以该模型作为性能预测部件实现了AWMF的原型实现——查询调度器,通过实验验证了AWMF对交易型负载的有效性。     

Effect of network latency on load sharing in distributed systems

Distributed computing systems consist of computers interconnected by communications links. In such systems, Load sharing is an important technique used to improve system performance in which jobs are transferred from overloaded nodes to underloaded ones. However, due to the ubiquitous and inescapable presence of network latencies, various pitfalls arise which can adversely affect the beneficial effects of job transfer.In this paper, we present an investigation into the effect of network latency on load sharing. The notions of Transfer Pair, and Load-Sharing Window are rigorously defined. A general expression for the probability distribution function of the Load-Sharing Window is derived. A class of rules, called quantile rules, is introduced and their role in avoiding unproductive job redistribution in spite of network latency, as well as to make multiple job transfers, is explained. The general technique is applied to the specific case of a distributed computing system consisting of M/M/1 queues. For this case, an expression for the mean of the Load-Sharing Window is derived. Numerical computations are presented, and their significance discussed.     

Intelligent scheduling processes and controlling workload in computing systems

Methods and algorithms of adaptive scheduling processes and workload control in computing systems are considered.     

On the impact of network latency on distributed systems design

Research in distributed database systems to date has assumed a “variable cost” model of network response time. However, network response time has two components: transmission time (variable with message size) and latency (fixed). This research improves on existing models by incorporating a “fixed plus variable cost” model of the network response time. In this research, we: (1) develop a distributed database design approach that incorporates a “fixed plus variable cost”, network response time function; (2) run a set of experiments to create designs using this model, and (3) evaluate the impact the new model had on the design in various types of networks. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of varying the threshold of alarm systems and workload on human performance

The purpose of this research was to investigate the effects of varying the threshold of alarm systems and workload on human response to alarm signals and performance on a complex task. A receiver operating characteristic (ROC) curve was selected to reflect the sensitivity of the alarm system. The threshold of the alarm system was manipulated by changing the value of beta along the ROC curve. A total of 84 students participated in experiment 1 and 48 students participated in experiment 2. Participants performed a compensatory-tracking, a resource management and a monitoring task. As expected, results showed that participants responded significantly faster to true alarm signals when they were using the system with the highest threshold under low-workload conditions. Results also indicated that changing the threshold of the alarm system had a significant effect on overall performance and this effect was greater under high-workload conditions. However, contrary to expectations, the highest level of performance was achieved by setting the threshold at a low level. Results from both experiments revealed that the advantage of faster alarm reaction time as a result of increasing the system's threshold was lost because of its increased probability of missed events.     

Effects of varying the threshold of alarm systems and workload on human performance

The purpose of this research was to investigate the effects of varying the threshold of alarm systems and workload on human response to alarm signals and performance on a complex task. A receiver operating characteristic (ROC) curve was selected to reflect the sensitivity of the alarm system. The threshold of the alarm system was manipulated by changing the value of beta along the ROC curve. A total of 84 students participated in experiment 1 and 48 students participated in experiment 2. Participants performed a compensatory-tracking, a resource management and a monitoring task. As expected, results showed that participants responded significantly faster to true alarm signals when they were using the system with the highest threshold under low-workload conditions. Results also indicated that changing the threshold of the alarm system had a significant effect on overall performance and this effect was greater under high-workload conditions. However, contrary to expectations, the highest level of performance was achieved by setting the threshold at a low level. Results from both experiments revealed that the advantage of faster alarm reaction time as a result of increasing the system's threshold was lost because of its increased probability of missed events.     

ADS-B延迟时间计算方法的可行性分析

广播式自动相关监视(ADS-B)的延迟时间对监视精度有较大的影响,为了提高ADS-B的监视精度,提出一种精确计算每个ADS-B报文延迟时间的方法。根据ADS-B报文的接收时间和报文内容,可计算两相邻报文的时间间隔和对应报文中飞机两相邻位置的时间间隔,通过对两种时间间隔求差可得到ADS-B两相邻报文的延迟时间差,在初始报文中或者间隔一定时间发送飞机位置测量时刻的条件下,可计算其后所有报文的延迟时间,从而对延迟时间进行修正。最后在15min、25min和45min的ADS-B报文中分别随机选取1架飞机的报文利用Excel对该方法的可行性进行了分析。分析结果表明,采用该方法ADS-B的监视精度得到了很大的提高,在场面滑行的情况下,监视精度小于10m,满足场面监视的需要。     

Performance bounds for distributed systems with workload variabilities and uncertainties

Bounding techniques for queuing network models used to analyze the performance of parallel and distributed computer systems accept single values as model inputs. Uncertainties or variabilities in service demands may exist in many types of systems. Using models with a single aggregate mean value for each parameter for such systems can lead to inaccurate or even incorrect results. This paper proposes to use histograms for characterizing model parameters that are associated with uncertainty and/or variability. The adaptation of the well-known asymptotic bounds as well as balanced job bounds for single class queuing networks to histogram parameters is presented in the paper.