A configurable RMI mechanism for sharing distributed Java objects

Many distributed programming environments have been designed to support distributed shared objects over the Internet. Most of these environments (Java RMI and CORBA, for example), support client-server applications where distributed objects reside on servers, which execute all methods (remote or local) invoked on the objects. Traditional client-server models do not support client-side object caching and the local access it provides. We believe that object caching is critical to distributed applications, especially over the Internet, where latency and bandwidth are highly variable. We have developed a configurable and efficient remote method invocation mechanism that provides the same interface as Java RMI, while extending its functionality so that shared objects can be cached on the accessing nodes. The mechanism, called Javanaise, is based on the caching of clusters, which are groups of interdependent Java objects. We have implemented a prototype consisting of a preprocessor that generates the required proxy classes from the application interfaces and a run-time environment that uses system classes to manage the consistency of cluster replicas cached on client nodes. We describe the motivation for the work, the design choices made for the Javanaise clustering mechanism, the implementation principles for managing Javanaise clusters, and the results from three experiments that compare the performance of Javanaise with Java RMI     

基于GPRS网络的强一致性两级缓存系统框架

无线移动环境中缓存的主要目的是减少对无线带宽资源的占用和节省电池能量,然而移动无线终端的漫游与经常断开连接又给缓存内容的一致性带来了一系列新的问题。本文针对目前运行的GPRS网络,提出了在用户端（移动终端）和GPRS骨干网中添加验证服务器VS（Validation Server）对数据进行两级缓存的系统框架和缓存强一致性策略。该框架简化了无线移动环境下维护缓存一致性的复杂性,有效地降低了对无线带宽的占用和数据库服务器的负载,支持移动终端断开连接的时间任意和在一个公众陆地移动通信网PLMN网内的漫游,具有很强的实用性。     

嵌入式智能无线接入点系统的设计

该文提出了一种支持蓝牙、IEEE802.11b和GPRS三种不同的无线接入方式的智能无线接入点(AP)系统的实现方案。设计了在嵌入式Linux平台上智能无线AP的软硬件,重点讨论了蓝牙WPAN与Internet/GPRS以及WLAN的互连。     

Bluetooth-assisted context-awareness in educational data networks

In this paper, we propose an auxiliary location network, to support user-independent context-awareness in educational data networks; for example, to help visitors in a museum. We assume that, in such scenarios, there exist service servers that need to be aware of user location in real-time. Specifically, we propose the implementation of a Bluetooth Location Network (BLN). The BLN is composed of small wireless nodes, which establish an spontaneous network topology at system initialization, and interact with Bluetooth-enabled user terminals (WLAN or GPRS PDAs, or WAP phones) or independent Bluetooth modems (badges). The BLN may coexist with any data protocol (IP over IEEE 802.11b or GPRS, WAP). We do not impose specialized terminal programming for location purposes, since we rely on basic Bluetooth signaling (responses to inquiry cycles). We evaluate BLN feasibility in two real educational scenarios, a school and a museum.     

MobiPADS: a reflective middleware for context-aware mobile computing

Traditionally, middleware technologies, such as CORBA, Java RMI, and Microsoft's DCOM, have provided a set of distributed computing services that essentially abstract the underlying network services to a monolithic "black box." In a mobile operating environment, the fundamental assumption of middleware abstracting a unified distributed service for all types of applications operating over a static network infrastructure is no longer valid. In particular, mobile applications are not able to leverage the benefits of adaptive computing to optimize its computation based on current contextual situations. In this paper, we introduce the Mobile Platform for Actively Deployable Service (MobiPADS) system. MobiPADS is designed to support context-aware processing by providing an executing platform to enable active service deployment and reconfiguration of the service composition in response to environments of varying contexts. Unlike most mobile middleware, MobiPADS supports dynamic adaptation at both the middleware and application layers to provide flexible configuration of resources to optimize the operations of mobile applications. Within the MobiPADS system, services (known as mobilets) are configured as chained service objects to provide augmented services to the underlying mobile applications so as to alleviate the adverse conditions of a wireless environment.     

JDCS:实现高性能计算的分布式计算系统

分布对象计算技术提供了充分利用现有网络资源的有效途径。JavaRMI是当前比较成熟的一种分布对象技术,它提供了使用Java对象的简单和直接的方法。该文建立基于JavaRMI方法的适用于高性能计算的分布式计算系统JDCS。在JDCS中由网络上的计算结点构成服务器池,为用户提供高性能的计算服务。实现结果表明该系统可以获得较高的加速比。     

分布对象平台Java RMI和CORBA的对比研究

文章对开发基于Java的分布式应用程序的两种分布对象技术—————JavaRMI和CORBA的功能和效率进行了对比和分析。CORBA具有良好的语言中立性,定义有功能较强的各种服务,适合于规模较大,需要与其他语言集成的系统,它的缺点是开发过程较为繁琐,Java的一些先进特性无法在远程调用的界面上使用。RMI与Java语言结合得十分紧密,开发方便,支持对象传值,但它不太适合需要异种语言集成的场合。     

Java分布式计算技术的分析与比较

一、多层体系结构的应用系统传统的应用系统基本上是单一结构或C/S结构的系统,这种结构的应用系统其构造和维护一般很难,即使是简单的改动也需要对整个系统进行重编译和测试,因此越来越多的分布式应用系统开始采用多层体系结构。三层体系结构的分布式应用系统运行于多台计算机上。一般地,三层结构的应用系统包括用户界面层、事务逻辑层和数据存储层:     

Java-centric distributed computing

The Java language and platform provide a base for distributed computing that changes several conventional assumptions. In particular, the Java Virtual Machine allows a group of Java-enabled machines to be treated as a homogeneous group rather than a heterogeneous group, despite possible differences in the machine architectures and underlying operating systems. Java also makes it possible to safely and dynamically load code in a running Java process. Together, these features allow a system to invoke methods on remote objects, which can move code associated with language-level objects from the calling process to the process called and vice versa. Combining these qualities with a language-centric design not only significantly simplifies traditional RPC systems, it adds functionality that was previously not possible. We designed Java Remote Method Invocation (RMI) to support pure-Java distributed objects in a seamless manner. RMI allows calls to be made between Java objects in different virtual machines, even on different physical machines     

无线Mesh网络在矿井通信中的应用

针对矿井的特殊环境给出一种无线Mesh网络建网方案。该网络支持多媒体数据传输,实现了无线IP电话在网络层的接入和漫游。给出矿井全覆盖无线通信网络、无线中继及无线路由的设计。在实际环境中对实验网络进行了测试,检测网络配置参数的相互关联性,用于指导具体的矿井无线Mesh网络设计和组网。     

基于Java的RMI技术的研究与应用

Java语言因其突出的简单性、可移植性、安全性和支持并发机制的程序设计等优良特性,使它成为基于Internet网络应用开发的首选语言。其价值主要体现在强大的开发分布式网络应用的能力上,而RMI则是开发纯Java的网络分布式应用系统的核心解决方案。通过对Java RMI分布式应用程序实例的分析,给出了Java RMI分布式应用程序的实现和运行方法,为Java语言应用开发人员提供参考。     

Switching supports for stateful object remoting on network processors

Distributed object-oriented environments have become important platforms for parallel and distributed service frameworks. Among distributed object-oriented software, .NET Remoting provides a language layer of abstractions for performing parallel and distributed computing in .NET environments. In this paper, we present our methodologies in supporting .NET Remoting over meta-clustered environments. We take the advantage of the programmability of network processors to develop the content-based switch for distributing workloads generated from remote invocations in .NET. Our scheduling mechanisms include stateful supports for .NET Remoting services. In addition, we also propose scheduling policy to incorporate work-flow models as the models are now incorporated in many of tools of grid architectures. The result of our experiment shows that the improvement of EFT is from 5% to 21% when compared to ETT and is from 8% to 34% when compared to RR while the stateful task ratio is 50%. Our schemes are effective in supporting the switching of .NET Remoting computations over meta-cluster environments.     

Qos-aware Middleware for Mobile Multimedia Communications

Next generation wireless communications system will be required to support the seamless delivery of voice, video and data with high quality. Delivering hard Quality of Service (QOS) assurances in the wireless domain is complex due to large-scale mobility requirements, limited radio resources and fluctuating network conditions. To address this challenge we are developing mobiware, a QOS-aware middleware platform that contains the complexity of supporting multimedia applications operating over wireless and mobile networks. Mobiware is a highly programmable software platform based on the latest distributed systems technology (viz. CORBA and Java). It is designed to operate between the application and radio-link layers of next generation wireless and mobile systems. Mobiware provides value-added QOS support by allowing mobile multimedia applications to operate transparently during handoff and periods of persistent QOS fluctuation.     

Optimization of QoS parameters using scheduling techniques in heterogeneous network

Multimedia applications in wireless communication have been increased in recent years. A variety of wireless access technologies is introduced for various needs. The abundant increase in mobile computing devices and different networking systems leads to the support of user’s mobility on heterogeneous network. In general, the roaming users migrate between two different wireless technologies and their service must be supported by vertical handover (HO). Since the roaming users expect a rapid handover experience while switching from one wireless network to another, the handover operation must be enhanced by the networks. Various wireless technologies such as wireless LAN, Worldwide Interoperability for Microwave Access (WiMAX), and the 3G Partnership Project (3GPP) are interlaced to support many wireless services in rural, urban, and global scenarios. Moreover, quality of service (QoS) has become more significant in many applications where wireless network resources are utilized. In this paper, a handover management scheme is proposed for QoS enhancement in roaming users between WiMAX and WLAN by subscribers of networks belonging to the 3GPP standards. The proposed algorithms genetic queuing, proportionally fair queuing, and WiMAX aware load balancing are analyzed in the scheduling process during handover. The simulation is implemented using NS–2 and the experimental results are obtained for the proposed algorithms and compared with the standard scheme.     

A Java-centric Distributed Object-based Paradigm for Surveillance Services and Visual Message Exchange

Building an effective surveillance system on the Internet is an interesting application involving the interoperability of heterogeneous computing environments and the challenge of orchestrating the exchange of different visual message types in a unified manner. In this paper, we propose a distributed object-based paradigm to achieve this by applying the so-called bridging technologies for supporting distributed surveillance services. This paradigm integrates emerging technologies of the next-generation Internet-based applications ranging from wireless transmission at the network infrastructure level, to multi-tier, client/server, and RMI/CORBA at the architecture level, and to Java-centric, delegation-based visual user interfaces, and object web-based user interfaces at the system design level. The experimental results show that objects in the paradigm can efficiently cross the boundaries of different platforms, operating systems, programming languages, and visual message types. The DSS paradigm establishes a firm basis for supporting a variety of potentially cost-effective applications in a plug-and-play manner.     

Software architecture design for streaming Java RMI

In recent years, network streaming becomes a highly popular research topic in computer science due to the fact that a large proportion of network traffic is occupied by multimedia streaming. In this paper we present novel methodologies for enhancing the streaming capabilities of Java RMI. Our streaming support for Java RMI includes the pushing mechanism, which allows the servers to push data in a streaming fashion to the client site, and the aggregation mechanism, which allows the client site to make a single remote invocation to gather data from multiple servers that keep replicas of data streams and aggregate partial data into a complete data stream. In addition, our system also allows the client site to forward local data to other clients. Our framework is implemented by extending the Java RMI stub to allow custom designs for streaming buffers and controls, and by providing a continuous buffer for raw data in the transport layer socket. This enhanced framework allows standard Java RMI services to enjoy streaming capabilities. In addition, we propose aggregation algorithms as scheduling methods in such an environment. Preliminary experiments using our framework demonstrate its promising performance in the provision of streaming services in Java RMI layers.     

基于分离式MAC架构的WLAN漫游认证机制研究

根据分离式MAC架构WLAN的结构特点,提出了一种新的漫游切换认证方案,减少了切换时无线用户的重新认证时间,满足了VOIP等实时业务的需要。     

Unix环境下基于RMI的分布式计算研究与实践

在分析远程过程调用（RPC）原理的基础上，引入Java远程方法调用（RMI）的概念，并详细讨论了Java RMI的体系结构和运作机制。还给出了一个Unix环境下的分布计算示例。     

Roaming across wireless local area networks using SIM-based authentication protocol

Wireless local area networks provide high speed data transferring rate to a mobile device. And it is crucial to integrate together two critical issues, the authentication and roaming in heterogeneous networks. For this, Tsai and Chang proposed a SIM-based authentication mechanism for wireless local area networks in 2006. Tsai and Chang's scheme provides an integration method of mobile cellular networks and wireless local area networks. Unfortunately, we found that there are some weaknesses existing in their scheme. In this paper, we propose an improved version for a user roaming in heterogeneous networks. Besides, we also proposed a mobile IP model to provide a better efficiency for a mobile user in WLAN environment.     

整合SSL协议的Java RMI的研究与设计

Java RMI机制是分布式技术的一种理想解决方案,其目标是使得网络中任意节点上的应用都可以透明的访问存在于网络上的其它节点上的远程对象.但是默认的RMI机制并不提供认证和加密传输,其安全机制还存在一定隐患.介绍了JavaRMI机制的运行机理,详细阐述了整合SSL协议的Java RMI的方案,设计了整合SSL协议的安全RMI接口,并通过实例的设计与运行,验证了其可行性.