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介绍了W eb服务QoS的度量方法,基于提出的服务质量模型,给出集成服务中在资源使用方面作了改进的局部服务选择算法,针对其不足提出一种全局W eb服务集成路径选择的数学模型,并给出求解算法。此数学模型在QoS参数方面具有可扩展性,为服务集成的QoS分析,集成路径的确定提供了一个合适的决策框架。 相似文献
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一种面向服务的网格作业管理机制 总被引:14,自引:0,他引:14
开放网格服务体系结构(OGSA)的出现表明让网格资源以服务形式提供标准化的接口已成为趋势,然而目前的网格作业管理系统主要针对以程序形式提交的批处理类型作业,其管理的资源对象和调度目标主要面向科学计算,在基于服务的网格环境下远不能满足应用的需求:一方面,用户的使用模式从批处理为主转向带有交互性质的服务访问模式;另一方面,不同的应用对服务质量(QoS)有着不同级别的需求,为了解决这些问题,提出了一种面向服务的作业管理机制,它作为用户访问网格资源(服务)的代理,为用户提供透明的、与资源物理位置无关的并带有会话支持的作业服务接口。还引入了服务水平协议(SLA)的概念来表示用户需求的不同网格服务级别,作业管理系统则根据可定制的服务水平实现配置(SLAP)将sIA中规定的各项QoS特性映射到具体的作业管理行为,该作业管理机制已应用于织女星网格系统软件中,并能够为基于服务网格的应用提供灵活有效的支持。 相似文献
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一种基于QoS的服务构件组合方法 总被引:18,自引:1,他引:18
在面向服务的架构中,如何利用已有的服务构件组装成新的服务成为当前此领域的一个研究热点.该文以构件化嵌入式操作系统Liquid为背景,给出了一种基于QoS的服务构件组合方法,在满足组合服务的功能需求同时,满足其QoS需求.文章详细给出了所涉及的服务模型、QoS模型以及构件选择基本算法.为使此服务构件组合方法适应于动态变化的系统环境,该文进一步对构件选择基本算法进行优化,给出了构件选择的启发和协商算法.最后通过实验,比较和分析三种算法的性能. 相似文献
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一种基于QoS的网格服务选择机制 总被引:1,自引:0,他引:1
开放网格服务体系结构OGSA提出了网格服务的概念,为网格资源的虚拟化管理给出了一条有效途径。当前网格系统对于网格服务的支持主要集中在服务的功能发现与调用部分,缺乏对服务的非功能属性的管理支持。服务的非功能属性如服务的响应时间、价格、可靠性等对于用户来说非常重要,体现着用户对网格服务的QoS需求。基于QoS的服务选择机制能够对网格服务的QoS模型进行管理和度量,对于用户提出的QoS需求,服务匹配算法能够为用户选择满足需求倾向的服务。 相似文献
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考虑有向无环图(DAG)描述的组合服务模型,提出了一种新的组合服务QoS度量方法——基于拓扑序列归约的Web服务QoS度量方法(QCMTSR).其借鉴迭代归约度量方法中的基本结构及Q6计算公式,定义了DAG图中的两类基本结构,串归约结构和并归约结构,并给出了两种基本结构的QoS属性计算公式;通过逐步归约DAG图拓扑序列中的每个节点,直至最后一个节点的QoS属性值就是组合服务的各QoS属性的度量结果.从理论上证明了QCMTSR算法适用于所有DAG描述的组合服务,并实验证明QCMTSR算法对可靠性和可用性能够更准确的度量. 相似文献
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考虑有向无环图 (DAG)描述的组合服务模型,提出了一种新的组合服务QoS度量方法--基于拓扑序列归约的Web服务QoS度量方法(QCMTSR)。其借鉴迭代归约度量方法中的基本结构及QoS计算公式,定义了DAG图中的两类基本结构,串归约结构和并归约结构,并给出了两种基本结构的QoS属性计算公式;通过逐步归约DAG图拓扑序列中的每个节点,直至最后一个节点的QoS属性值就是组合服务的各QoS属性的度量结果。从理论上证明了QCMTSR算法适用于所有DAG描述的组合服务,并实验证明QCMTSR算法对可靠性和可用性能够更准确的度量。 相似文献
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Architectures based on a non-blocking fabric, such as a crosspoint switch, are attractive for use in high-speed LAN switches, IP routers, and ATM switches. When operating at the highest speed, memory bandwidth limitations dictate that queues be placed at the input of the switch. But it is well known that input-queueing can lead to low throughput, and does not allow the control of latency through the switch. This is in contrast to output-queueing which maximizes throughput and permits the accurate control of packet latency through scheduling. We ask the question: Can a switch with combined input and output queueing be designed to behave identically to an output-queued switch? In this paper, we prove that if the switch uses virtual output queueing and has an internal speedup of just four, it is possible for it to behave identically to an output-queued switch, regardless of the nature of the arriving traffic. Our proof is based on a novel scheduling algorithm, called Most Urgent Cell First. We find that with a speedup of four the most urgent cell first algorithm (or MUCFA) enables perfect emulation of a FIFO output-queued switch, i.e. one in which packets depart in the same order that they arrived. We extend this result to show that with a small modification, the MUCFA algorithm enables perfect emulation of a variety of output scheduling policies, including strict priorities and weighted fair-queueing. This result makes possible switches that perform as if they were output-queued, yet use memories that run more slowly. 相似文献
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Shareable data services providing consistency guarantees, such as atomicity (linearizability), make building distributed systems easier. However, combining linearizability with efficiency in practical algorithms is difficult. A reconfigurable linearizable data service, called Rambo, was developed by Lynch and Shvartsman. This service guarantees consistency under dynamic conditions involving asynchrony, message loss, node crashes, and new node arrivals. The specification of the original algorithm is given at an abstract level aimed at concise presentation and formal reasoning about correctness. The algorithm propagates information by means of gossip messages. If the service is in use for a long time, the size and the number of gossip messages may grow without bound. This paper presents a consistent data service for long-lived objects that improves on Rambo in two ways: it includes an incremental communication protocol and a leave service. The new protocol takes advantage of the local knowledge, and carefully manages the size of messages by removing redundant information, while the leave service allows the nodes to leave the system gracefully. The new algorithm is formally proved correct by forward simulation using levels of abstraction. An experimental implementation of the system was developed for networks-of-workstations. The paper also includes selected analytical and preliminary empirical results that illustrate the advantages of the new algorithm. 相似文献
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服务器负载均衡技术研究 总被引:13,自引:1,他引:12
负载均衡是建立在网络结构之上的一种调度策略,能有效的扩展服务器带宽和增加吞吐量,增强网络数据处理能力。根据实际层次不同,对负载均衡技术进行了分类,从应用范围、运行原理等角度分析并比较了常用的负载均衡技术和算法,展望了负载均衡的发展。 相似文献
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熊熙 《网络安全技术与应用》2010,(6):61-64
随着互联网的迅速普及和广泛应用,网络信息资源的数量及网站设计的复杂度也呈急剧增长趋势。如今,针对用户特性并向用户提供个性化服务已经成为计算机技术的研究热点之一。本文首先简述了Web日志挖掘的相关概念和具体实现过程,然后重点讲述了Web日志挖掘的关键技术。最后采用了用户群体聚类算法与Web页面聚类算法相结合实现挖掘用户访问模式,并针对个性化服务的应用和发展方向进行了研究和分析。 相似文献
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F. Leclerc J-Y. Potvin J.Y. Potvin 《International Transactions in Operational Research》1997,4(5-6):391-400
Decisions regarding the dispatch of transportation vehicles for servicing customer requests is mostly based on human expertise. In this paper, genetic algorithms are proposed as a means to support vehicle dispatchers in the context of a courier or express mail service. Vehicle dispatching is first modeled as a multiattribute choice problem. Then, a genetic algorithm is used to find a weighting scheme for the attributes that best reproduces the expert's decision process. Numerical results are reported on data collected from an operations day of a courier service company. 相似文献
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为了充分体现服务质量(QoS)的不确定性和用户偏好的模糊性,本文将模糊集理论引入基于QoS的Web服务组合中,将不适合精确表示的QoS属性和用户偏好等信息用三角模糊数表示.然后基于权重和法计算模糊总目标,通过设计新的模糊数比较方法,改写Pareto支配关系,将基于模糊数比较的单目标优化问题转化为多目标优化问题,并设计模糊多目标遗传算法(FMOGA)求得Pareto最优解集.该方法不仅能够得到更加贴近实际情况的优化解,同时也解决了多属性决策方法无法对大量候选服务进行全局优化的问题.最后通过实验验证了该算法的有效性和优越性. 相似文献
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We consider the management of FIFO buffers for network switches providing differentiated services. In each time step, an arbitrary
number of packets arrive and only one packet can be sent. The buffer can store a limited number of packets and, due to the
FIFO property, the sequence of sent packets has to be a subsequence of the arriving packets. The differentiated service model
is abstracted by attributing each packet with a value according to its service level. A buffer management strategy can drop
packets, and the goal is to maximize the sum of the values of sent packets.
For only two different packet values, we introduce the account strategy and prove that this strategy achieves an optimal competitive
ratio of
if the buffer size tends to infinity and an optimal competitive ratio of
for arbitrary buffer sizes. For general packet values, the simple preemptive greedy strategy (PG) is studied. We show that
PG achieves a competitive ratio of
which is the best known upper bound on the competitive ratio of this problem. In addition, we give a lower bound of
on the competitive ratio of PG which improves the previously known lower bound. As a consequence, the competitive ratio of
PG cannot be further improved significantly.
Supported by the DFG grant WE 2842/1. A preliminary version of this paper appeared in Proceedings of the 14th Annual European
Symposium on Algorithms (ESA), 2006. 相似文献