基于代理的移动事务处理模型

在移动计算环境中，为了支持断连操作，一方面，需要在移动客户端上进行数据缓存；另一方面，在重新连接后，移动客户端上的暂时事务需要在服务器上重新执行，这使得事务的一致性很难得到保障。扩展嵌套事务的概念并提出了一种模型，通过在事务执行机制中加入移动代理，使事务执行时数据的一致性在频繁断连状态下能满足应用要求。     

移动计算中断连操作性能的改善方法

在移动计算环境中,如果移动客户机与固定主机的读/写、写/写冲突机率很高,则暂态事务在固定主机上成功提交的概率就很低,大量的暂态事务就会夭折,这将浪费大量的服务器资源和通信资源,降低了整个系统的性能。为了提高暂态事务重提交的成功概率,我们提出按概率提交暂态事务的方法。该方法在冲突频率非常高的场合,能够节省移动客户机的传送开销、减轻固定主机的负担,提高事务的吞吐量。     

网格事务服务和事务处理机制的研究

提出了网格服务环境中基于移动Agent的网格事务服务和事务处理机制,能够支持动态网格事务的处理.研究了网格事务服务的架构、算法和事务处理机制.基于Agent的网格事务服务能够提供动态的事务管理能力,为网格服务投入到商业应用提供了有力的支持.     

基于代理的移动数据库研究

近年来,无线技术的发展促进了移动计算的研究,但是多数移动数据库系统使用传统的客户机/服务器模式或单代理模式处理移动查询,进而产生了数据大量迁移的问题。文章提出了一种基于多移动代理技术的移动数据库查询处理模型,旨在减少处理过程中的数据迁移量,提高移动环境下查询分布式异构数据库的性能。     

MOHO“移动”办公新概念

以往“移动”办公的概念是两种方式：将办公所需的功能尽可能的缩小,迷你化乃至集成到一个很小的,可以随身携带的设备上,此之谓基于设备的“移动”办公,典型代表如PDA、商务通等。还有另外一种“移动”办公,是基于网络的,用户要利用笔记本电脑或者台式PC机通过INTERNET联接到相关的服务器来获得相应的办公的功能。这两种“移动”办公的可谓各有千秋,在不同的层次上满足了人们对于在“移动”中处理日常办公事务的需要,但是,人们在享受这些功能给工作带来的便利的同时,也不免有一些遗憾,那就是,什么时候才能够有一种解决方案可以做到真正的“随时随地,无限沟通”,充分享受到和固定办公室一样的便利呢？     

一种基于移动计算环境的并发控制策略

针对移动计算环境中传统的并发控制机制并不足以支持移动事务执行的问题,提出一种新的事务管理机制以提高移动事务的处理效率.文中着重研究移动事务的并发控制机制,提出了一种基于动态计时器机制的并发控制策略.该策略主要是在锁管理器中添加动态计时器,通过调整事务执行队列以及动态的分配事务执行时间,达到减少事务的重启次数,提高事务提交率的目的.性能测试表明,所提出的并发控制策略能提高移动计算环境下事务的成功率.     

一个Web服务事务处理模型：结构、算法和事务补偿

事务处理是web，服务能否用于电子商务的关键技术之一．Web服务事务处理必须提供协调短事务和长事务的能力。本文提出了一个能够同时处理原子事务和聚合事务的模型，研究了其协调算法、状态转换及恢复机制．聚合事务允许候选者独立提交，并使用补偿事务来撤销已提交的子事务所带来的影响，可以较好地满足Web服务环境下对长事务的要求，为Web服务投入商用提供了有力支持．     

诺基亚移动软交换全球用户突破10亿并且持续增长

近日,诺基亚在全球的总移动软交换（MSS）容量实现大幅提升,用户数量突破10亿大关。该统计数字基于客户使用流量,且仅对实际操作中的用户容量进行统计,结果代表通过诺基亚西门子通信MSS系统进行连接的活跃用户数量。迄今为止,若包括每日移动运营的缓冲容量,诺基亚西门子通信交付的总MSS容量已逾15亿人。     

浅论移动办公系统中无线接入技术的应用

随着经济全球化趋势发展以及中国加入WTO后,中国电信市场的政府管制力度逐渐衰弱,电信市场更加开放,电信行业竞争也愈演愈烈。国内各大公众电信营运企业在经营理念以及管理模式上都必须要有更高层次的跨越以适应国内外电信市场环境的要求,从而在电信运营商的国际竞争中处于领先地位。目前大多数电信运营商都通过MSS(Management Supporting System)系统的建设,让企业在其发展过程中,逐步整理以及固化现有流程,以高效的现代信息化措施推进标准化的信息分析和业务流程,提高企业的管理效率以及执行力水平,加强企业核心竞争力,促进企业战略目标的贯彻实施,从而使企业在日益激烈的市场竞争中立于不败之地,向成为国际一流的电信企业的目标迈进。作为MSS系统建设的重要组成部分,移动办公是一种全新理念,意在通过WAP、COMAIX、WALN等多种无线方式接入,为一些高端商务人士提供自由自在的工作方式和无处不在的办公环境。提升办公效率,改善办公方式,增大办公空间。本文重点研究无线接入技术在移动办公系统中的应用,并且提出几种行之有效的措施。     

一个Web服务事务处理模型:结构、算法和事务补偿

事务处理是Web服务能否用于电子商务的关键技术之一.Web服务事务处理必须提供协调短事务和长事务的能力.本文提出了一个能够同时处理原子事务和聚合事务的模型,研究了其协调算法、状态转换及恢复机制.聚合事务允许候选者独立提交,并使用补偿事务来撤销已提交的子事务所带来的影响,可以较好地满足Web服务环境下对长事务的要求,为Web服务投入商用提供了有力支持.     

一种可靠高效的回卷恢复实现方法

本文针对现有用户级进程检查点实现中的线程挂起点不确定性问题提出一种基于线程自挂的解决方案.另外,为了降低分布式回卷恢复开销,本文提出一个多线程化的回卷恢复实现基架.基于所提回卷恢复策略,开发了一个回卷恢复试验床WINDAR.试验结果表明,多线程化实现策略能够显著提高悲观消息日志协议性能.     

Performance evaluation of rollback-recovery techniques in computerprograms

Rollback recovery is a backward error recovery technique used to recover from temporary faults in database and process control systems. Rollback in process control systems is generally constrained by deadlines, thereby requiring a dynamic insertion of rollback points. This is in contrast to rollback recovery in database systems in which rollback points are inserted at equidistant intervals. A simple model based on a semi-Markov process is developed to study the performance of rollback recovery strategies. Using this model, the mean program completion time is obtained for both database and process control systems when rollback recovery is implemented. The analytic results obtained by the semi-Markov model are compared with the simulation results by means of extensive computer simulations     

基于分块消息日志的回卷恢复策略

本文给出了一种基于分块消息日志的回卷恢复协议,建立了其性能模型,评估了协议的平均开销.分块消息日志方法是一种可配置的一般化方法,悲观消息日志方法和协同检查点方法是其两个特例.性能分析结果表明,协议配置参数具有可优化特性,采用分块消息日志策略能够优化协议性能.     

An efficient optimistic message logging scheme for recoverable mobile computing systems

A number of checkpointing and message logging algorithms have been proposed to support fault tolerance of mobile computing systems. However, little attention has been paid to the optimistic message logging scheme. Optimistic logging has a lower failure-free operation cost compared to other logging schemes. It also has a lower failure recovery cost compared to the checkpointing schemes. This paper presents an efficient scheme to implement optimistic logging for the mobile computing environment. In the proposed scheme, the task of logging is assigned to the mobile support station so that volatile logging can be utilized. In addition, to reduce the message overhead, the mobile support station takes care of dependency tracking and the potential dependency between mobile hosts is inferred from the dependency between mobile support stations. The performance of the proposed scheme is evaluated by an extensive simulation study. The results show that the proposed scheme requires a small failure-free overhead and the cost of unnecessary rollback caused by the imprecise dependency is adjustable by properly selecting the logging frequency.     

Disconnected Processes, Mechanisms and Architecture for Mobile E-Business

With the tremendous advances in hand-held computing and communication capabilities, rapid proliferation of mobile devices, and decreasing device costs, we are seeing a growth in mobile e-business in various consumer and business markets. In this paper, we present a novel architecture and framework for end-to-end mobile e-business applications (e.g., point of sales). The architecture takes into consideration disconnection, application context, synchronization, transactions and failure recovery modes to provide mobile users with seamless and transparent access to business transactions and business-context specific data. In our architecture, we consider a novel business process design based on state-machines and event management to handle disconnection, resource limitations and failures. We designed, implemented and deployed a system for mobile e-business on clients (e.g., PDAs and PocketPCs) integrated with private exchanges and sell-side servers. The state-machine model with failure recovery mechanisms enables handling of one-to-many and many-to-one disconnections in large mobile e-business environments. The e-business framework on mobile clients is implemented based on J2ME, Webservices, and open XML standards. A detailed performance study of commerce transactions was done on different mobile client devices with diverse computing, memory and storage capabilities. We compare the performance of a purchasing application and the middleware on various devices such as PDAs and Laptops. We demonstrated that for small devices with limited capability the performance is reasonable. For devices with more computing capability, the response time is excellent.     

WOB:一种新的文件检查点设置策略

实现分布/并行系统容错的基础是单进程检查点设置和卷回恢复技术,而对进程活动文件状态进行保存和恢复则是这种技术的重要方面.本文提出的延迟写策略,实现了对用户文件的检查点设置,有效地解决了在发生故障时用户文件内容与进程全局状态的不一致问题.它对用户通明,并且通过优化设置内存缓冲区大小、时延隐藏等手段,使得这种策略在空间开销、正常运行时间、恢复时间等性能指标上优于其它方法.     

移动数据库中移动Agent技术的应用与研究

目前，移动数据库技术的研究与应用是数据库领域和移动计算领域的一个研究热点。首先介绍了移动数据库和移动Agent的特点，分析了基于移动Agent的移动数据库体系结构，最后提出一种基于移动Agent的移动查询处理模型并叙述了其实现过程。     

Associativity-Based Routing for Ad Hoc Mobile Networks

This paper presents a new, simple and bandwidth-efficient distributed routing protocol to support mobile computing in a conference size ad-hoc mobile network environment. Unlike the conventional approaches such as link-state and distance-vector distributed routing algorithms, our protocol does not attempt to consistently maintain routing information in every node. In an ad-hoc mobile network where mobile hosts (MHs) are acting as routers and where routes are made inconsistent by MHs' movement, we employ an associativity-based routing scheme where a route is selected based on nodes having associativity states that imply periods of stability. In this manner, the routes selected are likely to be long-lived and hence there is no need to restart frequently, resulting in higher attainable throughput. Route requests are broadcast on a per need basis. The association property also allows the integration of ad-hoc routing into a BS-oriented Wireless LAN (WLAN) environment, providing the fault tolerance in times of base stations (BSs) failures. To discover shorter routes and to shorten the route recovery time when the association property is violated, the localised-query and quick-abort mechanisms are respectively incorporated into the protocol. To further increase cell capacity and lower transmission power requirements, a dynamic cell size adjustment scheme is introduced. The protocol is free from loops, deadlock and packet duplicates and has scalable memory requirements. Simulation results obtained reveal that shorter and better routes can be discovered during route re-constructions.     

移动医疗商业介入路径研究

首先,分析移动医疗发展的现状,指出中国移动医疗行业面临巨大的机遇.其次,对比分析传统医疗行业产业链和移动医疗产业链,指出移动医疗具有良好的行业发展前景.然后,具体分析移动医疗的三大类群用户和产业链,指出可产生增值效益的商业模式对移动医疗行业至关重要.最后,通过对国外成熟的移动医疗商业模式的分析,提出中国可发展的未来移动医疗商业模式.     

战术通信移动性管理

简述民用移动通信移动管理现状，进而对其技术进行分析与综合。在此基础上重点讨论军事上战术通信移动管理的必要性、特点与初步设想。