基于Axis的Web服务身份验证策略管理

Web服务身份验证策略是Web服务安全的重要组成部分。针对当前Web服务身份验证策略管理、部署中策略交互协调的问题,提出根据客户端安全级别进行Web服务身份验证策略管理,同时提出方法以动态协调当前服务策略。验证策略查询服务作为策略选择的核心部分,为客户端和服务器端提供策略查询以实现动态调用相应的策略。根据这一方法,基于J2EE的相关技术,实现在Axis上的验证策略管理。并且支持动态策略的部署,增加了系统的灵活性和扩展性。     

基于Petri网的Web服务注册方法的研究与实现

为了使Petri网理论与方法在服务组合相关问题中得到实际应用,从软件实现的角度,解决面向Web服务组合的Petri网的自动生成问题,本文提出了基于Petri网的Web服务注册方法.首先根据已建立的领域本体来规范Web服务各参数的定义,然后依据Web服务的输入输出参数绘制其相应的Petri网,同时对Web服务Petri网中的库所元素添加语义标记,进而得到Web服务的PNML(Petrinetwork markup language)+OWL(ontology web language)描述,最后将Web服务相关信息及其PNML+OWL文件上传至服务器端进行注册和存储,为Web服务组合的Petri网自动生成提供了基础,并通过机票查询原子Web服务与旅游查询复合Web服务对本文方法进行了具体说明.     

Android学习平台中Web Service架构的实现与研究

Android手机软件开发是远程教育学习平台的重要内容,手机通常以终端的形式出现,大量的数据被保存在服务器端,手机通过网络,使用Web Service服务与服务器端进行通讯,交流数据.因此,Web Service架构的研究与实现具有重要意义.本文详细研究了Android学习平台中Web Service的设计与实现方案.     

基于双线性对的乐观Mix-net协议

提出了一种新的基于双线性对的乐观Mix-net协议。利用双线性对工具简化了密钥管理,在不同的协议会话中服务器端不用重新生成密钥,并且当前会话不会为其他会话提供解密预言机服务。采用了“哑元追踪法”保证混洗过程的完整性,简化了正确性证明的构造。对ElGamal联合解密过程做了优化,降低了每个服务器节的指数运算量。在没有服务器作弊的情况下,对输入密文组的混洗和解密速度比其他可公开验证的Mix-net方案高得多。     

基于Agent会话的自适应Web服务交互

基于Agent的Web服务集成框架中的每个Agent代理一个服务,将服务集成流程映射为Agent会话协议,通过Agent会话体现服务交互的自适应,从而发现和恢复服务集成中的错误,使得系统具有一定的容错能力,实现服务交互的自适应.     

基于ASP的Web数据库应用设计与实现

新一代的开发动态交互网页技术(ASP)给Web开发者提供了一个灵活、易用的开发环境。本文介绍了用于创建动态Web页面的ASP技术的特点、对象以及实现方式,分析了利用ASP的ADO组件实现Web与数据库互连和处理数据库数据的具体方法。ADO与ASP结合,作用在服务器端,通过OLEDB提供者存取、操纵各种关系型及非关系型数据库,通过执行SQL命令,让用户在浏览器画面中输入、更新和删除站点服务器的数据库信息,并给出了实现数据库查询的实例。最后介绍了“同学录应用系统”的实现方法。     

基于本体的语义Web服务注册平台研究

提出了一种基于本体的语义Web服务注册模型,结合Jena实现语义Web服务的语义查询和推理.应用元模型互操作框架(MFI)中的本体注册元模型标准,以实现与其他注册模型的语义互操作,并给出了一个基于该模型的语义Web服务注册平台.     

Web Service在Android开发中的应用研究

在移动客户端操作系统是Android并且服务端通过Web Service提供编程接口的情况下,实现了客户端与服务器端的信息交互。本文主要依托车辆检验系统中的手持安卓终端和Web服务通信过程为例,对Android客户端和Web Service结合构建可扩展、易于维护的应用系统提供了高效的方法。     

基于策略的Web服务实时性能评价与验证

面向服务的架构(SOA)通过标准Internet协议实现了异构平台上的服务动态集成.然而,开放网络环境的不稳定性和不确定性,给Web服务在线质量评价带来一定的困难.Web服务的测试只能给出测试环境下的服务评价,不能评价服务的真实运行情况,因此服务实时监测对服务运行状态追踪及异常检测具有重要的意义.本文基于服务系统的协同监测,采用原子服务和组合服务多种时间特性定义了Web服务的性能评价模型.在该模型的基础上,提出了一种基于策略的服务在线质量评价与验证方法,给出了基于WS-Policy的策略描述,实现了原型系统,并通过对实验服务的在线监测数据,分析了方法的有效性及性能代价.     

Django框架Web数据查询分页技术研究

为了探索Django框架下Web数据查询分页的实现方法及性能,本文先对Web数据查询分页的执行过程和在其它框架下常用的分页方法进行了分析研究.在此基础上,提出了在Web服务层和在数据库服务层分页两种方案在Django框架下实现的几种具体方法,分别是利用缓存和Sessions实现在Web服务层分页,利用存储过程和自定义Manager方法实现在数据库服务层分页.最后,对这几种实现方法进行了测试比较,发现在网站数据量较小时几种方法性能差别不大,当数据量较大时在数据库服务层分页方法性能较为优越.     

ZGLS: a novel flat quorum-based and reliable location management protocol for VANETs

In location management services, a destination advertises its position attributes to a set of vehicles called location servers while, a source obtains these attributes from such location servers to track destination. The location management techniques in VANET have been categorized into flooding-based, flat hashing-based, hierarchical hashing-based and hierarchical quorum-based techniques. In flooding-based location service, destination information is flooded to the entire network which results into high congestion, low throughput and non-scalable network. In flat hashing, a global hash function is applied to compute location servers of each destination which results into higher delay, drop and signaling overhead in large VANETs. In hierarchical hashing, global hash function computes location servers of destination in hierarchical order. It therefore suffers from handover signaling between servers, high load on the top hierarchy and location query delay when source and destination are apart. In hierarchical quorum-based, location servers are identified cluster-wise and therefore it also suffers from the problems similar to hierarchical techniques. To overcome these problems, ZoomOut Geographic Location Service (ZGLS) protocol is proposed which introduces flat quorum-based location management service. In contrast to the aforementioned techniques, the novelty of ZGLS lies in the fact that it has shifted the location server role from hashing-based or clustering-based geographic areas to few 1-hop neighbours, called relatives. The proposed protocol creates a chain of relatives to provide positioning and tracking service. To evaluate signalling overhead, timeliness and the reliability of update and query packets, ZGLS is compared with RLSMP and HRHLS through ns-2 simulations. The results reveal that ZGLS stands out as a better choice for large-scale sparse and dense VANETs.     

一种改进的分布式Web服务注册管理模型研究

目前比较流行的Web服务注册管理模型UDDI存在实际使用情况较差的问题.主要原因在于:集中式的管理导致其随着服务数量的增加变得较难管理和维护;另一方面,目前UDDI只能提供基于关键字的目录查找,造成了服务查找有效性较差的问题.文中提出了一种改进的分布式服务注册管理模型(pUDDI),利用分布式结构和Web服务池机制减轻Web服务注册中心的负担和提高注册库中服务查找的有效性.     

Estimation‐Based Load‐Balancing with Admission Control for Cluster Web Servers

The growth of the World Wide Web and web‐based applications is creating demand for high performance web servers to offer better throughput and shorter user‐perceived latency. This demand leads to widely used cluster‐based web servers in the Internet infrastructure. Load balancing algorithms play an important role in boosting the performance of cluster web servers. Previous load balancing algorithms suffer a significant performance drop under dynamic and database‐driven workloads. We propose an estimation‐based load balancing algorithm with admission control for cluster‐based web servers. Because it is difficult to accurately determine the load of web servers, we propose an approximate policy. The algorithm classifies requests based on their service times and tracks the number of outstanding requests from each class in each web server node to dynamically estimate each web server load state. The available capacity of each web server is then computed and used for the load balancing and admission control decisions. The implementation results confirm that the proposed scheme improves both the mean response time and the throughput of clusters compared to rival load balancing algorithms and prevents clusters being overloaded even when request rates are beyond the cluster capacity.     

An adaptive load balancing scheme for web servers

This paper describes an overload control scheme for web servers which integrates admission control and load balancing. The admission control mechanism adaptively determines the client request acceptance rate to meet the web servers' performance requirements while the load balancing or client request distribution mechanism determines the fraction of requests to be assigned to each web server. The scheme requires no prior knowledge of the relative speeds of the web servers, nor the work required to process each incoming request. Copyright © 2002 John Wiley & Sons, Ltd.     

基于云的域名解析服务模型

针对现行域名解析系统存在各种性能和安全上的问题(例如,查询延迟、更新延迟、易受DoS攻击等),提出了一种新型的、可增量部署的、和现行DNS兼容的、具有更好性能的域名解析服务模型。此服务模型基于云技术,利用云及其网络架构来发布DNS记录,响应用户的域名解析请求,提供域名解析服务。在此服务模型中,云的节点服务器实现了域名解析器和权威域名服务器的功能,域名的权威DNS记录被发布到各节点服务器,DNS查询结果直接由节点服务器返回给用户(现行的DNS则需要访问多级域名服务器来完成对域名解析器中未缓存的DNS记录的解析)。理论分析和实验证明,此服务模型与现行的各种域名解析服务相比,其DNS查询延迟、更新延迟、故障应变能力、可靠性等各方面性能都有显著提高。     

Measuring the size of the Internet via importance sampling

Measuring the size of the Internet via Monte Carlo sampling requires probing a large portion of the Internet protocol (IP) address space to obtain an accurate estimate. However, the distribution of information servers on the Internet is highly nonuniform over the IP address space. This allows us to design probing strategies based on importance sampling for measuring the prevalence of an information service on the Internet that are significantly more effective than strategies relying on Monte Carlo sampling. We present thorough analysis of our strategies together with accurate estimates for the current size of the Internet Protocol Version 4 (IPv4) Internet as measured by the number of publicly accessible web servers and FTP servers.     

Apache集群在多媒体内容播控管理平台上的应用

随着终端用户的增加,多媒体内容播控管理平台对高访问量、高并发的需求越来越高。本文首先介绍了Apache集群的原理,然后将其应用于多媒体内容播控管理平台中,通过均衡负载,减轻了服务器的负担,提高了响应速度。     

Multirate scheduling of VBR video traffic in ATM networks

One of the major attractions of asynchronous transfer mode (ATM) networks for transporting bursty video traffic is its ability to exploit the multiplexing gains of packet switching while providing quality of service guarantees. Unfortunately, most of the multiplexing mechanisms proposed in the literature fail to exploit the multiplexing gains of ATM. We propose a multirate service mechanism that allows a session to be served at different rates at different times. Applications generating bursty data, such as variable bit-rate (VBR) video, can take advantage of multirate service by requesting a high rate of service for brief periods of bursty arrivals and a much lower rate of service for all other times. Consequently, the applications can improve their delay performance without reserving a high bandwidth for the entire duration of the sessions. Furthermore, the scheduler can multiplex the peaks and the lulls in service rates of different sessions and improve the utilization of the system. Using MPEG video traces from a number of applications, we show that multirate servers outperform single-rate PGPS (packet-by-packet generalized processor sharing) servers and CBR (constant bit-rate) servers in terms of number of connections admitted, while providing the same level of service guarantees. We also investigate the performance of multirate service when service quality need not be guaranteed. We refer to this as predictive service. We propose a measurement-based admission control procedure for predictive service, and show that it helps increase the size of the admissible region even further     

一个面向Internet的分布式信息检索系统模型

随着Internet上的用户急剧增加,如何快速地处理查询请求已成为面向Internet的信息检索系统急需解决的问题.文中提出了一个面向Internet的分布式信息检索系统模型(Fastresponse).在该系统模型中,针对当前分布式信息检索系统在可获得性、可靠性、可扩展性、查询服务智能性等方面存在的一些问题,我们提出了对服务器和文档进行两级调度;系统需要时动态招募备份服务器;对子服务器群中和子服务器群间的服务器进行两级监控;根据用户的要求自动重组服务器等一些新的管理策略,有效地解决了上述方面存在的问题,从而可以更好地处理用户的查询请求.