基于多类顾客排队网络的Exp-RAID系统性能评价模型

针对RAID在线扩展系统这一典型的存储系统混合负载访问问题,采用多类顾客闭合排队网络(multi-customer closed queueing network, MCQN)对系统建立性能评价模型.推广了平均值分析(MVA)方法使之适应多类型负载的需求,并采用这一方法对模型进行了理论计算.通过将计算结果与实际系统性能的测试结果进行对比可以表明,建立的模型基本上反映了真实系统的性能变化趋势,通过对模型的分析,可以发现系统的瓶颈资源,预测系统某个部件性能的变化对整个系统的影响程度.     

基于WAN的网络软RAID系统性能的研究

当前绝大多数网络存储系统都是通过高速网络进行连接的。论文设计并构建了基于低速WAN的网络软RAID系统(NSRAID),研究了广域网环境下影响网络存储系统性能的主要因素。同时,以网络负载的角度分析了远程存储节点数、网络存储协议和数据布局方式影响系统性能的内在原因。在此基础上,针对广域网不同的网络性能提出了提高网络软RAID系统性能的方法。     

基于分层排队网络模型的分布式系统性能评价

关于并发或分布式系统的性台匕评价是一个广泛研究的课题,提供有效的数学理论工具、直观的模型描述方法和有效的模型分析方法,是系统性能评价所面临的关键问题。传统的性能模型——排队网络模型已很难分析这样复杂的系统,分层排队网络（Layered Queueing Net,LQN）模型是排队网络模型的扩展,可以用来分析相互依赖任务间的冲突。介绍了分层排队网络模型的原理及研究现状,并以DBMS为例,建立了DBMS的分层排队网络模型。     

不同任务粒度下校验式IP-SWAN系统的性能评价模型

在不同的任务粒度下,RAID5结构的 IP-SWAN 系统的请求数据流动有很大的不同。在详细分析了校验式IP-SWAN 系统在读任务、大数据写任务和小数据写任务下的数据流程的基础上,建立了 IP-SWAN 系统的闭合排队网络模型,研究了在不同任务类型和粒度下系统各个部件服务需求的计算方法,并采用 MVA 分析法在理论上对 IP-SWAN 系统的吞吐量进行了计算。实验测试结果表明,理论模型的数值计算结果与实验结果基本一致,能够反映实际系统性能的变化趋势。     

IP存储广域网的I/O响应时间分析

以往对网络存储系统的性能分析大都集中在定性研究,定量分析模型很少。在分析基于iSCSI协议的IP存储广域网(IP-SWAN)的数据传输流程的基础上,建立了该系统的Petri网模型。利用Petri网模型的特点,在理论上计算了IP-SWAN系统的I/O响应时间,并分析了各参数对系统性能的影响,提出了改进IP-SWAN系统性能的方法。     

IP存储广域网性能分析模型

通过对数据传输流程的分析，建立了IP存储广域网的排队网络模型．在此基础上，提出了IP存储广域网的性能边界分析模型．实验结果发现，实测性能在理论性能边界范围之内，理论性能边界反映了实测性能的变化趋势．对模型的分析表明，IP WAN的性能是限制IP存储广域网最大性能的关键因素，提高缓存命中率、链路带宽和降低传播延迟将提高IP存储广域网的最大性能．     

基于排队网络的流水线模拟器任务缓存新分析模型

流水线软件模拟器是嵌入式微处理器软件仿真系统的关键技术,提出对嵌入式微处理器流水线仿真系统的排队网络建模与缓存大小分析方法.对SPARC-V8流水线模拟器建立M/M/1/N型排队网络模型,分析指令到达及服务阻塞机制.为了解决模型计算中的阻塞问题,在排队网络模型中增加"保持节点",得到扩展的等价排队网络模型.采用近似计算迭代算法,得到系统性能评价指标,并建立排队网络节点性能关系曲线,确定各功能模块的任务缓存大小.根据得出的任务缓存计算值设置流水线软件模拟器实际缓存大小,实验表明模型计算数据与实际运行数据基本一致.该评价方法对嵌入式微处理器流水线仿真系统的建模与性能分析具有重要的指导意义.     

网络光盘库模型的建立和分析*

网络存储技术的广泛应用为近线存储设备应用于海量存储系统提供了新思路,而网络光盘库正是一种利用网络存储技术的新的存储方式。研究了可以通过IP网络接入海量存储系统中的网络光盘库的排队网络模型,并对其进行了仿真模拟,为光盘库在海量存储系统中的应用、设计和性能优化提供理论方法和实验依据。     

子阵列数据布局方法在网络存储中的应用

RAID的高性能源于无差异磁盘组的并行工作。但受网络等因素的影响，网络存储阵列系统中各个磁盘的性能是有差异的，这直接导致系统并行度的降低。现有的研究大都是通过改变RAID中数据单元和校验单元的布局方式来平衡磁盘间的差异。该文根据不同存储应用的特点，提出了子阵列数据布局方法来解决这一问题，显著提高了网络存储系统的性能。     

离散事件动态系统的分析和优化：排队网络模型方法（上）

排队网络是离散事件动态系统的一个有效模型,本文全面地介绍了基于排队网络模型的各种分析方法.包括随机分析法、运行分析法,平均值分析法、近似分析法、仿真法和摄动分析法.并介绍了排队网络理论在 FMS 中的应用.     

The Analysis and Performance of Multi-Rate Service in Distributed Video-on-Demand Systems

In this paper, we develop an end-to-end analysis of a distributed Video-on-Demand (VoD) system that includes an integrated model of the server and the network subsystems with analysis of its impact on client operations. The VoD system provides service to a heterogeneous client base at multiple playback rates. A class-based service model is developed where an incoming video request can specify a playback rate at which the data is consumed on the client. Using an analytical model, admission control conditions at the server and the network are derived for multi-rate service. We also develop client buffer requirements in presence of network delay bounds and delay jitter bounds using the same integrated framework of server and network subsystems. Results from an extensive simulation show that request handling policies based on limited redirection of blocked requests to other resources perform better than load sharing policies. The results also show that downgrading the service for blocked requests to a lower bitrate improves VoD system performance considerably. Combining the downgrade option with restrictions on access to high bitrate request classes is a powerful tool for manipulating an incoming request mix into a workload that the VoD system can handle.     

基于排队网络的VoIP信令解析系统性能分析

基于软件性能模型的软件性能评估可以应用在软件研发周期的早期阶段,以便对软件系统的行为进行定量分析。该文给出一种应用排队网络模型对VoIP信令解析软件体系结构性能的评估方法。该方法的基本思想是：从基于UML描述的活动图导出多类排队网络性能模型,通过统计分析将得出的性能参数反馈给UML软件体系结构模型,不断完善体系结构设计。模型提供的统计性能评估方法克服了受限估计离散事件分析的局限性。     

STATE FEEDBACK CONTROLLER DESIGN OF NETWORKED CONTROL SYSTEMS WITH PARAMETER UNCERTAINTY AND STATE‐DELAY

This paper is concerned with the controller design of networked control systems. The continuous time plant with parameter uncertainty and state delay is studies. A new model of the networked control system is provided under consideration of the nonideal network conditions. In terms of the given model, a controller design method is proposed based on a delay dependent approach. The maximum allowable synthetical bounds related with the discarded data packet and network‐included delay and the feedback gain of a memoryless controller can be derived by solving a set of linear matrix inequalities for the stabilizablity of the networked control system based on Lyapunov functional method. An example is given to show the effectiveness of our method.     

Bounds on performance of nonstationary continuous-time filters under modelling uncertainty

A method for obtaining quantitative measures of the performance of non-stationary Kalman type filters for time-varying, linear, continuous-time systems with modelling errors is described. The performance measures consist of upper and lower bounds on the trace of the estimation error covariances (the mean squared error) of suboptimal filters. Errors in system configuration, noise statistics, and prior information are treated and the resulting bounds are expressed in terms of the model matrices and the range of errors in these matrices.     

Input-to-state stability for networked control systems via an improved impulsive system approach

This paper presents a novel impulsive system approach to input-to-state stability (ISS) analysis of networked control systems (NCSs) with time-varying sampling intervals and delays. This approach is based upon the new idea that an NCS can be viewed as an interconnected hybrid system composed of an impulsive subsystem and an input delay subsystem. A new type of time-varying discontinuous Lyapunov-Krasovskii functional, which makes full use of the information on the piecewise-constant input and the bounds of the network delays, is introduced to analyze the ISS property of NCSs. Linear matrix inequality based sufficient conditions are derived for ISS of NCSs with respect to external disturbances. When applied to the approximate tracking problem for NCSs, the derived ISS result provides bounds on the steady-state tracking error. Numerical examples are provided to show the efficiency of the proposed approach.     

Generalized load sharing for packet-switching networks. I. Theory and packet-based algorithm

In this paper, we propose a framework to study how to effectively perform load sharing in multipath communication networks. A generalized load sharing (GLS) model has been developed to conceptualize how traffic is split ideally on a set of active paths. A simple traffic splitting algorithm, called packet-by-packet weighted fair routing (PWFR), has been developed to approximate GLS with the given routing weight vector by transmitting each packet as a whole. We have developed some performance bounds for PWFR and found that PWFR is a deterministically fair traffic splitting algorithm. This attractive property is useful in the provision of service with guaranteed performance when multiple paths can be used simultaneously to transmit packets which belong to the same flow. Our simulation studies, based on a collection of Internet backbone traces, reveal that PWFR outperforms two other traffic splitting algorithms, namely, packet-by-packet generalized round robin routing (PGRR), and packet-by-packet probabilistic routing (PPRR).     

Tracking control for sampled‐data systems with uncertain time‐varying sampling intervals and delays

In this paper, a solution to the approximate tracking problem of sampled‐data systems with uncertain, time‐varying sampling intervals and delays is presented. Such time‐varying sampling intervals and delays can typically occur in the field of networked control systems. The uncertain, time‐varying sampling and network delays cause inexact feedforward, which induces a perturbation on the tracking error dynamics, for which a model is presented in this paper. Sufficient conditions for the input‐to‐state stability (ISS) of the tracking error dynamics with respect to this perturbation are given. Hereto, two analysis approaches are developed: a discrete‐time approach and an approach in terms of delay impulsive differential equations. These ISS results provide bounds on the steady‐state tracking error as a function of the plant properties, the control design and the network properties. Moreover, it is shown that feedforward preview can significantly improve the tracking performance and an online extremum seeking (nonlinear programming) algorithm is proposed to online estimate the optimal preview time. The results are illustrated on a mechanical motion control example showing the effectiveness of the proposed strategy and providing insight into the differences and commonalities between the two analysis approaches. Copyright © 2009 John Wiley & Sons, Ltd.     

Simulation based optimization of stochastic systems with integer design variables by sequential multipoint linear approximation

Optimization problems are considered for which objective function and constraints are defined as expected values of stochastic functions that can only be evaluated at integer design variable levels via a computationally expensive computer simulation. Design sensitivities are assumed not to be available. An optimization approach is proposed based on a sequence of linear approximate optimization subproblems. Within each search subregion a linear approximate optimization subproblem is built using response surface model building. To this end, N simulation experiments are carried out in the search subregion according to a D-optimal experimental design. The linear approximate optimization problem is solved by integer linear programming using corrected constraint bounds to account for any uncertainty due to the stochasticity. Each approximate optimum is evaluated on the basis of M simulation replications with respect to objective function change and feasibility of the design. The performance of the optimization approach and the influence of parameters N and M is illustrated via two analytical test problems. A third example shows the application to a production flow line simulation model. Received April 28, 2000