基于可信QoS的路径查找及负载均衡策略研究

Web服务是云计算中资源调用的有效方式。单一Web服务功能往往有限,只能完成特定任务。服务组合则可以将多种Web服务形成有效的调用序列,实现更为强大的功能。服务发布量以及服务请求量的迅速激增带来了新的安全问题。首先,现有的服务组合方案均以服务质量(QoS)为依据进行Web服务选择,但服务质量通常由服务发布者提供,存在服务发布者发布虚假QoS值诱骗用户的欺诈现象;其次,传统的服务组合方案只生成一条最优路径,当恶意请求持续访问时,会造成某服务节点瘫痪,甚至整个服务组合系统失效。因此,针对服务质量恶意欺诈的问题,文章提出一种可信的QoS计算模型,根据Web服务发布者的信用综合评估服务质量;针对单一最优路径无法满足大量请求的问题,文章提出一种路径发现和负载均衡的多路径方法。仿真结果表明,文章提出的方法不仅能提高服务组合的成功率,满足用户的需求,而且能找到更多的服务组合方案执行。     

一种基于多维服务质量的局部最优服务选择模型

全局最优和局部最优是服务选择的两种策略.现有的全局最优服务选择算法提供端对端约束下最优单解而非可接受的多解,既无法充分体现用户偏好和服务个性,也不利于激励服务提供者优化服务质量.首先,在引入序数效用函数作为局部服务排序的数值尺度的基础上,提出一种基于多维服务质量的局部最优服务选择模型MLOMSS(Multi-QoS based Local Opti mal Model of Service Selection),为自动选取优质服务提供重要依据.然后,构造客观赋权模式、主观赋权模式和主客观赋权模式来确定各服务质量属性的权重,既体现用户偏好和服务质量的客观性,又有助于快速生成聚合服务链.最后,通过语义Web服务集成平台SEWSIP(Semantic Enable Web Serv-ice Integration Platform)证明MLOMSS模型的有效性和灵活性.     

面向应用的服务匹配模型研究

在面向应用的服务组装平台中,服务匹配是服务组装的重要前提。分析现有服务匹配模型,在异构服务统一描述的基础上,提出适合于异构服务组装平台的服务匹配模型。该模型由功能匹配和非功能匹配（服务质量匹配）两阶段组成,引进具有替代性质的相似函数来度量服务的功能相似程度,并采用可扩展的QoS模型选择质量最优者,能从查全率和查准率两方面提高服务检索的质量。     

基于改进的自适应遗传算法的GIS服务组合研究

摘要针对当前GIS系统中集成应用模型时存在的数据和功能冗余、模型难以复用等问题,将GIS应用模型分解为子模型,与GIS功能一起,以服务的方式提供给用户,并对这些GIS服务定义服务质量(QoS);最后,提出了一种基于改进的自适应遗传算法(MAGA)的服务组合方法,以实现GIS服务组合的全局优化。     

一种多参数的Web服务选择方法

随着服务计算的快速发展，如何快速而准确地找到最优的Web服务组合是众多挑战中最重要的一项。提出了一种基于二阶隐马尔可夫模型（HMM）的服务选择方法。该方法使用服务质量（QoS）参数去区分具有相同功能的Web服务，并且选择一组最优的Web服务来执行用户请求。通过考虑两个QoS参数-吞吐量和响应时间，该方法能够解决根据设定的阈值来衡量Web服务质量的问题。通过构建的模型和算法，方法能够选择出最优的Web服务以满足用户的需求。仿真实验验证了所提出的方法是有效的。     

融合服务聚类与协作相似度的服务替换方法

当前服务替换方法多关注于替换服务与失效服务在功能和质量层面的匹配,缺乏对两者协作关系的考量。针对上述问题,提出一种融合服务聚类与协作关系的服务替换方法。首先,利用服务之间的组合关系构建服务协作图谱,基于node2vec进行序列采样并生成协作向量,进而计算服务之间的协作相似度。然后,通过引入服务簇缩减替换时的服务查找空间,从功能和质量层面快速构建候选替换服务集合。最后,在候选替换服务集合中综合服务质量评分和协作相似度实现可替换服务的择优推荐。实验证明该方法可以有效提高服务替换的效率与合理性。     

一种基于权重的云服务搜索算法

云计算技术迅猛发展,众多云服务的功能和服务质量有所不同。针对这种情况,提出一种服务权重计算方法。算法通过分析组合服务和原子服务的关系,结合服务实例的可靠性、新鲜度和负载度,计算服务实例权重值并排行,获得最优实例提供服务。数据分析和仿真实验表明,算法有效选择当前最优服务实例,提高云平台的可用性、效率和鲁棒性。     

二层组播QoS最优生成树

具有一对多特性的组播数据大量涌入以太网,对网络服务质量提出了更高的要求.二层域中生成树协议在选择根桥时没有考虑其对组播服务质量的影响.从二层组播接收者的角度出发,提出了二层组播QoS最优生成树的概念,从理论上证明了组播源位于最优生成树的根桥上时,组播能达到最优的服务质量.而且,最优生成树对于经过根桥的单播也能达到最优的服务质量.最后,给出的最优根桥逼近查找算法可以作为生成树算法的补充.通过对比实验,验证了该算法的有效性、可靠性和可扩展性.     

异构融合网络中服务质量控制仿真

针对当前网络服务质量控制方法中存在的用户满意度低和服务延迟长问题,提出基于蚁群算法的异构融合网络中服务质量控制方法。定义网络服务质量效用函数,结合质量参数层与使用者感知层关键质量参数定量评价网络服务质量,引入网络服务延迟约束条件,构建异构融合网络中服务质量控制目标函数。基于网络资源ID查询资源目前状态信息,初始化网络各资源点信息素,并计算任务分配概率值,更新局部信息素,直到任务队列中的任务均被分配至资源处理处为止。判断任务成功解决与否,假设任务没有被成功解决,则重新调度网络资源,并将任务重新排列在等待队列中。实时更新全局信息素和网络中各个节点可信度,以此综合评价此次资源调度,假设调度方案满足网络服务质量控制目标函数,则将该调度方案当作最优网络服务质量控制方案;反之,则不断更新当前解,直到得到最优网络服务质量控制方案。实验结果表明,该方法用户满意度高、服务延迟短。     

Strategic logistics outsourcing: An integrated QFD and fuzzy AHP approach

This paper develops an integrated approach, combining quality function deployment (QFD), fuzzy set theory, and analytic hierarchy process (AHP) approach, to evaluate and select the optimal third-party logistics service providers (3PLs). In the approach, multiple evaluating criteria are derived from the requirements of company stakeholders using a series of house of quality (HOQ). The importance of evaluating criteria is prioritized with respect to the degree of achieving the stakeholder requirements using fuzzy AHP. Based on the ranked criteria, alternative 3PLs are evaluated and compared with each other using fuzzy AHP again to make an optimal selection. The effectiveness of proposed approach is demonstrated by applying it to a Hong Kong based enterprise that supplies hard disk components. The proposed integrated approach outperforms the existing approaches because the outsourcing strategy and 3PLs selection are derived from the corporate/business strategy.     

基于QoS 随机性和信任评价的全局动态服务组合

由于Internet环境的开放性和动态性,导致Web服务质量稳定性较差,进而严重影响服务组合的准确度.为此,提出一种基于QoS随机性和信任评价的全局动态服务组合方法.首先,剔除导致客观QoS不稳定的异常值,并估计其真实值;然后,分析服务提供商和用户的信任度,聚合计算主观QoS评价值;最后,结合主、客观QoS约束条件,构建全局动态服务组合优化模型,求解最优组合服务.基于真实和仿真数据的实验结果表明,所提出的方法能够显著提高服务组合的稳定性和准确度.     

An analytical approach to providing controllable differentiated quality of service in Web servers

Provisioning quality of service (QoS) in Web servers has gained immense importance because Web servers are a major part of the Internet. To deliver the pledged QoS, Web service providers need control over the allocation of the resources in their Web servers. Control is also necessary for reaching the optimal resource allocation through proper service differentiation. In this paper, we propose and investigate an analytic approach that enables the service providers to deploy a differentiated service policy that offers this control. The proposed service policy is configurable by tunable control parameters. We devise the relationships between the performance measures and these parameters by adopting a unique queuing theoretic approach. Once these relationships are established, we describe how these parameters can be set to their most appropriate values depending on the objectives of the service providers. We illustrate the usefulness of our approach by conducting the analysis on a real Web trace.     

基于软件定义网络的媒体分发网络的接入控制

针对软件定义网络（SDN）环境下的媒体分发网络的接入控制问题,提出了一种综合考虑服务节点和传输链路服务性能优化问题的接入控制方案。该方案利用SDN控制器对路由器的直接管控和对全网的感知能力,对应用层上服务节点服务性能和网络层上服务节点到用户之间的传输链路的服务性能进行联合优化,减少了链路拥塞对数据传输和用户服务质量的影响。首先,为SDN服务系统的接入控制过程建立部分可观Markov决策过程（POMDP）模型;然后,使用基于观测的随机策略作为系统的接入控制策略;最后,通过策略梯度算法对接入控制策略进行优化,求解出模型的最优策略。仿真结果表明,与尽力而为的服务策略相比,基于POMDP模型的最优接入控制策略使系统性能提高了10%,验证了所提方法的有效性。     

A QoS-driven approach for service-oriented device anycasting in ubiquitous environments

The vision of pervasive computing is to let users enjoy ICT-enabled services in an “any time, anywhere, on any device” manner. It aims to supply ubiquitous services through communications among a set of devices deployed in a ubiquitous environment. Due to the diverse QoS needs of different kinds of ubiquitous services and users, it is a critical challenge to select an optimal set of devices with the objective of achieving service-specific QoS goals like low packet loss, short packet delay, and high energy efficiency. In this paper, the problem is first formulated as the service-oriented device anycasting problem (SDAP) and then proved as an NP-complete problem. By adopting a tree-based service representation model, Basu et al. proposed the dynamic task-embedding anycasting (DTA) approach. This approach effectively solves the SDAP in a distributed way. However, the service quality is likely sacrificed because the tree scheme does not sufficiently describe a ubiquitous service. In this paper, we propose a novel approach called the service-oriented device anycasting (SDA) approach that adopts a graph-based service representation model called the service profile (SP). By introducing a layered structure into the SP, the SDA approach can reach a compromise between service quality and computational complexity. In addition, the QoS-driven utility function is proposed to quantify service quality by matching the capabilities of heterogeneous devices to various QoS needs. Finally, the simulation results show that the SDA approach outperforms the DTA approach by saving roughly 20% of device energy and prolonging the network lifetime. Packet loss and packet delay are also improved by roughly 25% and 8%, respectively. The advantage of the SDA approach is more obvious in environments with highly mobile devices and multiple users.     

A time-aware Bayesian approach for optimal manufacturing service recommendation in distributed manufacturing environments

With the growing emergence of distributed collaborative manufacturing systems, the utilization of service-oriented manufacturing to offer seamless access to a variety of complex, distributed and dynamic manufacturing resources has become a challenging issue. This paper presents a novel time-aware probabilistic Bayesian approach for recommending a few optimal manufacturing services based on the user preference for an initial manufacturing service. The Bayesian approach operates over a comprehensive, formal representation of manufacturing services, which adds the time-aware probability of satisfied service execution in manufacturing service ontology to take into account the statistical nature of the dynamic manufacturing environment. The Bayesian approach is useful because it infers a few top ranked hypotheses of manufacturing service that have the largest probability as the optimal selection in a specified context of user preference. A prototype system is built and validated with an illustrative example from manufacturing industry to demonstrate the feasibility of the proposed approach for optimal service recommendation.     

一种高效的服务组合优化算法

随着功能性属性相同而非功能性属性各异的Web服务的大量涌现,如何在服务组合业务流程中为各个任务选择相应的组件服务以达到组合服务的QoS(quality of service)最大化,并在此基础上满足不同用户的需求,已成为了国内外研究的热点.由于该问题的复杂性(NP-hard),目前存在的大多数方法都并不十分适合需要相对精确、实时决策的Web服务组合系统.因此,本文提出了一种基于凸包构建的组合服务优化算法(CM-HEU)用以解决QoS感知的服务组合优化问题.CM-HEU首先通过对组合服务中的每组任务进行凸包构建,以减少搜索空间.然后通过对初始解向量的多次升级和一次降级操作以达到全局优化的目标.实验表明:相对于现阶段存在的一些主流方法,CM-HEU不仅能得到一个比较理想的结果,并且具有良好的效率.     

A hybrid approach based on SERVQUAL and fuzzy TOPSIS for evaluating transportation service quality

Managing service quality is vital to retain customer satisfaction and augment revenues for any business organization. Often it is difficult to assess service quality due to lack of quantifiable measures and limited data. In this paper, we present a hybrid approach based on SERVQUAL and fuzzy TOPSIS for evaluating service quality of urban transportation systems. The proposed approach consists of three steps. The first step involves development of a SERVQUAL based questionnaire to collect data for measuring transportation service quality. The participants provide linguistic assessments to rate the service quality criteria and the alternatives. In step 2, the linguistic ratings are combined through fuzzy TOPSIS to generate an overall performance score for each alternative. The alternative with the highest score is finally chosen. In step 3, sensitivity analysis is conducted to evaluate the influence of criteria weights on the decision making process.The strength of the proposed approach is its practical applicability and ability to provide solution under partial or lack of quantitative information. An application of the proposed approach for evaluation of service quality of metro in Montreal is provided.     

Service composition model and method in cloud manufacturing

This study optimizes service composition on the basis of task requirements to solve the problem of multitask corresponding multi-service selection. First, the basic path structure and the implementation steps of cloud manufacturing (CMfg) service composition are analyzed, and service composition is divided into four patterns. Second, the quality of service (QoS) index system of service composition is proposed by combining the six goals of time, composability, quality, usability, reliability, and cost; the calculation expressions of QoS under different composition structures are listed; and the mathematical model of CMfg service composition is established. Then, the weight of each index value in QoS evaluation is determined using an improved fuzzy comprehensive evaluation method. Finally, the optimal selection scheme of service composition is proposed by using gray relational analysis method(GM), and the validity of the optimal selection scheme is verified by an example of mold manufacturing.