A Decentralized Computational Infrastructure for Grid-Based Parallel Asynchronous Iterative Applications

Parallel asynchronous iterative algorithms relax synchronization and communication requirements, and can potentially extend Desktop Grids beyond embarrassingly parallel applications to support a broader class of parallel iterative applications. This paper presents the design and implementation of CometG, a decentralized (peer-to-peer) computational infrastructure that extends Desktop Grid environments to support these applications. CometG provides a decentralized and scalable tuple space, efficient communication and coordination support, and application-level abstractions that can be used to implement Desktop Grid applications based on parallel asynchronous iterative algorithms using the master-worker/BOT paradigm. The deployment and evaluations of CometG and a CometG-based application in a wide-area environment using the PlanetLab [7] test bed, as well as a campus network are presented.     

WCL: A co-ordination language for geographically distributed agents

In this paper a tuple space based co-ordination language, and a run-time system which supports it, is described. The co-ordination language is called WCL, and it is designed to support agent co-ordination over the Internet between agents which are geographically distributed. WCL uses tuple spaces as used in Linda. WCL provides a richer set of primitives than traditional tuple space based systems, and provides asynchronous and synchronous tuple space access, bulk tuple primitives, and streaming primitives which, as a whole, provide a complete framework more suited to co-ordination over the Internet compared with the Linda primitives. The primitives emphasise efficiency and location transparency (of data and agents) and this is exploited in the current run-time system used to support WCL. The run-time system described in this paper is distributed and uses location transparency and dynamic analysis of tuple space usage to migrate tuple spaces around the distributed system. Some initial experimental results are given which demonstrate the performance gains of using the tuple space migration. The paper motivates the inclusion of many of the primitives, and demonstrates how a well designed set of primitives provides performance and efficiency. The JavaSpace primitives are used as an example of how the choice of primitives can detrimentally affect the efficiency of the language, and exclude required co-ordination constructs.     

Mobile Agent Coordination for Distributed Network Management

Mobile agents are a promising technology to face the problems raised by the increasing complexity and size of today's networks. In particular, in the area of network management, mobile agents can lead to a fully distributed paradigm to overcome the limits of traditional centralized approaches. A basic requirement for the management of a complex network is the definition of high-level and flexible models to coordinate the accesses to the resources—data and services—provided by the network nodes. On this basis, this paper describes the MARS coordination architecture for mobile agents. MARS is based on the definition of programmable tuple spaces associated with the network nodes: mobile agents can access the local resources and services via the tuple space, thus adopting a standard and high-level interface. The network administrator—via mobile agents—can dynamically program the behavior of the tuple space in reaction to the agents' access to the tuple space, thus leading to a flexible network model. Several examples show the effectiveness of the MARS approach in supporting network management activities.     

Coordinating Mobile Agents by the XML-Based Tuple Space

This paper presents Xspace,a programmable coordination paradigm for Internet applications based on mobile agents.The Xspace system fully exploits the advantages of the XML language and Linda-like coordination.It supports XML documents as tuple fields and multiple matching routines implementing different relations among XML documents,including those given by XML query languages,The Xspace uses Java as the implementation language;it is based on object-oriented XMLized tuple spaces to implement a portable and programmable coordination paradigm for mobile agents.The dsign and implementation procedures of Xspace are described in this paper,Experiment and performance evaluation are also made.Finally,some conclusinos and remarks are given.     

Data Privacy in Tuple Space Based Mobile Agent Systems

More recently, distributed variants of tuple spaces have been proposed to exploit the Linda model for programming distributed applications over wide area networks, possibly exploiting code mobility. However, the flexibility of the shared tuple space model opens possible security holes; it basically provides no access protection to the shared data. In this paper we investigate some possible scenarios where mobile agents can benefit from our cryptographic tuple space based framework, CryptoKlava, and sketch how to possibly implement such agents in order to keep the privacy of items collected by the mobile agent during its itinerary. The functionalities of the framework are general enough to be applied to other Java frameworks using multiple distributed tuples spaces possibly dealing with code mobility.     

Two approaches for an adaptive multimedia transfer service for mobile environments

Mobile environments are characterized by varying locations and network access points of end users, by varying levels of network QoS and often also by limited connectivity and reliability. These aspects have to be considered specifically for distributed multimedia applications, typically involving large amounts of data and specific QoS requirements. This article presents concepts and experiences concerning adaptive services for asynchronous multimedia transmission in mobile environments. We describe two different approaches to solve the problems of adaptation to variable network QoS using generic mechanisms. The first approach takes advantage of a mobile queuing service and is based on our former work on a support platform for mobile computing (see Schill and Kümmel. Mobile Computing Special Issue of Distributed Systems Engineering Journal 1995; 128–41; Schill et al. Proceedings of IMC 96 Workshop on Information Visualization and Mobile Computing. Zentrum für graphische Datenverarbeitung, February 1996). The second approach uses the mobile agent paradigm in the context of an application partitioning model to gain flexibility and maintainability (see Schill et al. In: Papaioannou, Minar, editors, Proceedings. Mobile Agents in the Context of Competition and Cooperation (MAC3), a workshop at Autonomous Agents '99, 1999. p. 34–41.). Both approaches exploit software-based conversion to adapt multimedia data according to bandwidth availability. Decoupling of communication peers with automatic notifications about communication actions helps to address disconnection problems.     

Supporting fault-tolerant parallel programming in Linda

Linda is a language for programming parallel applications whose most notable feature is a distributed shared memory called tuple space. While suitable for a wide variety of programs, one shortcoming of the language as commonly defined and implemented is a lack of support for writing programs that can tolerate failures in the underlying computing platform. This paper describes FT-Linda, a version of Linda that addresses this problem by providing two major enhancements that facilitate the writing of fault-tolerant applications: stable tuple spaces and atomic execution of tuple space operations. The former is a type of stable storage in which tuple values are guaranteed to persist across failures, while the latter allows collections of tuple operations to be executed in an all-or-nothing fashion despite failures and concurrency. The design of these enhancements is presented in detail and illustrated by examples drawn from both the Linda and fault-tolerance domains. An implementation of FT-Linda for a network of workstations is also described. The design is based on replicating the contents of stable tuple spaces to provide failure resilience and then updating the copies using atomic multicast. This strategy allows an efficient implementation in which only a single multicast message is needed for each atomic collection of tuple space operations     

EMMA: Epidemic Messaging Middleware for Ad hoc networks

The characteristics of mobile environments, with the possibility of frequent disconnections and fluctuating bandwidth, have forced a rethink of traditional middleware. In particular, the synchronous communication paradigms often employed in standard middleware do not appear to be particularly suited to ad hoc environments, in which not even the intermittent availability of a backbone network can be assumed. Instead, asynchronous communication seems to be a generally more suitable paradigm for such environments. Message oriented middleware for traditional systems has been developed and used to provide an asynchronous paradigm of communication for distributed systems, and, also for some specific mobile computing systems recently. In this paper, we present our experience in designing, implementing, and evaluating Epidemic Messaging Middleware for Ad hoc networks (EMMA), an adaptation of Java Message Service (JMS) for mobile ad hoc environments, discussing in detail the design challenges and the solutions that have been adopted.

Light-Weight Currency Management Mechanisms in Mobile and Weakly-Connected Environments

This paper discusses the currency management mechanisms used in Deno, an object replication system designed for use in mobile and weakly-connected environments. Deno primarily differs from previous work in implementing an asynchronous weighted-voting scheme via epidemic information flow, and in committing updates in an entirely decentralized fashion, without requiring any server to have complete knowledge of system membership.We first give an overview of Deno, discussing its voting scheme, proxy mechanism, basic API, and commit performance. We then focus on the issue of currency management. Although there has been much work on currency management in synchronous, strongly-connected environments, this issue has not been explored in asynchronous, weakly-connected environments. We present currency management mechanisms, based on peer-to-peer currency exchanges, that enable light-weight replica creation, retirement, and currency redistribution while maintaining the correctness of the underlying consistency protocol. We also demonstrate that peer-to-peer currency exchanges can be used to exponentially converge to arbitrary target currency distributions, without the need for any server to have global system information.     

Providing data confidentiality against malicious hosts in Shared Data Spaces

This paper focuses on the protection of the confidentiality of the data space content when Shared Data Spaces are deployed in open, possibly hostile, environments. In previous approaches, the data space content was protected against access from unauthorised application components by means of access control mechanisms. The basic assumption is that the hosts (and their administrators) where the data space is deployed have to be trusted. When such an assumption does not hold, then encryption schemes can be used to protect the data space content from malicious hosts. However, such schemes do not support searching on encrypted data. As a consequence, performing retrieval operations is very expensive in terms of resource consumption. Moreover, in these schemes applications have to share secret keys requiring a very complex key management. In this paper, we present a novel encryption scheme that allows tuple matching on completely encrypted tuples. Since the data space does not need to decrypt tuples to perform the search, tuple confidentiality can be guaranteed even when the data space is deployed on malicious hosts (or an adversary gains access to the host). Our scheme does not require authorised components to share keys for inserting and retrieving tuples. Each authorised component can encrypt, decrypt, and search encrypted tuples without knowing other components’ keys. This is beneficial inasmuch as it simplifies the task of key management. An implementation of an encrypted data space based on this scheme is described and some preliminary performance results are given.     

移动对等网络支撑平台MOBIPEER的设计与实现

支撑平台是对软件的开发、运行和管理提供核心机制支持的基础设施。移动对等网络研究中支撑平台的实现是核心技术难点。介绍了MOBIPEER的设计与实现,在对移动对等网络支撑平台的主要功能进行归纳和分类之后,着重讨论了实现中的若干关键技术,最后基于该平台开发了即时消息应用。结果表明MOBIPEER能够为移动对等网络研究提供良好的实践基础。     

Programming mobile context-aware applications with TOTAM

In tuple space approaches to context-aware mobile systems, the notion of context is defined by the presence or absence of certain tuples in the tuple space. Existing approaches define such presence either by collocation of devices holding the tuples or by replication of tuples across all devices. We show that both approaches can lead to an erroneous perception of context. Collocation ties the perception of context to network connectivity which does not always yield the expected result. Tuple replication can cause that a certain context is perceived even if the device has left the context a long time ago. We propose a tuple space approach in which tuples themselves carry a predicate that determines whether they are in the right context or not. We present a practical API for our approach and show its use by means of the implementation of various mobile applications. Benchmarks show that our approach can lead to a significant increase in performance compared to other approaches.     

Mobile-Process-Based Parallel Simulation

Our focus is on the novel use of a process-oriented methodology in software systems for parallel simulation on distributed memory. To the best of our knowledge, the few existing systems which adopt a process view strictly use message passing to effect process interaction in distributed-memory settings. As a result, these systems avoid scenarios in which processes directly access passive but shared components. This can restrict the manner in which a system is modeled and hinder the phase of distributed model construction. In this paper, we propose an approach which utilizes mobile processes in distributed-memory simulation systems. The approach entails the migration of a requesting process with its timestamp to the remote site hosting the requested passive object. Major advantages of this approach include one-time transmission, fixed communication topology, and increased locality of reference. Empirical results based on lightweight processes show that the mobile process paradigm can be as efficient as the message-passing paradigm.     

The Esperanto Broker: a communication platform for nomadic computing systems

There is an increasing demand for middleware for nomadic computing applications. Owing to the inherent characteristics of such environments, these platforms have to address two fundamental issues: (i) device disconnections and the limitations of wireless networks may force users to experience short periods of service unavailability; and (ii) the complexity to design and develop next‐generation mobile computing applications. This paper proposes the Esperanto Broker (EB), a communication platform that addresses mobility issues via an integrated approach, i.e. at data‐link, network, and middleware levels. Decoupling interactions are achieved via a tuple‐space underlying infrastructure. To support developers with advanced services, the EB enhances the distributed objects computing model providing the abstraction for the communication paradigms standardized by the W3C. Esperanto applications can be modeled as sets of objects that are distributed over mobile devices, which communicate via remote method invocations (RMIs). RMIs natively implement pull and push models, in both one‐to‐one and one‐to‐many multiplicity. The paper focuses on the EB design issues, essential aspects of the implementation, and performance evaluations of the implemented prototype. Copyright © 2006 John Wiley & Sons, Ltd.     

基于分布对象技术的移动中间件

基于JavaRMI技术的移动中间件存在一定程度的局限性。文中以中间件、分布对象计算和移动计算等相关领域的技术为背景,提出了基于分布对象技术的移动中间件MMDO(MobileMiddlewareBasedonDistributedObject),该体系结构包括:动态可定制的基础核心、通用移动Agent平台、异步消息服务、动态资源发现和移动用户安全注册。MMDO能够解决移动中间件研究存在的Java效率问题,同时拓展了移动服务,给移动应用提供更好的支撑环境。最后,给出仿真测试结果,证明了MMDO的有效性。     

支持时间无关激活的分布对象中间件异步模型

时间无关的异步激活方式对于大规模分布式应用、移动应用和企业应用集成都具有重要意义．目前的分布对象中间件虽然支持回调和轮询两种异步机制，但是都不支持时间无关的异步激活方式．针对这一问题，本文基于国防科学技术大学计算机学院在分布对象中间件Starbus平台异步模型方面的研究成果，提出了一种新的异步模型RAAM(Router Agent based Asynchronous Model)，该模型能够支持消息的异步传递和时间无关的激活方式，同时对消息的服务质量提供了很好的支持．在自主研发的分布计算平台Starbus异步子系统中实现了RAAM模型，并与相关工作进行了比较．     

Analysing trade-offs in frameworks for the design of smart environments

ABSTRACT

Smart Interactive Experiences (SIEs) are usage situations enabled by the Internet of Things that empower users to interact with the surrounding environment. The goal of our research is to define methodologies and software environments to support the design of SIEs; more specifically, we focus on design paradigms suitable for experts of given domains, who however might not be experts in technology. In this context, this paper discusses some trade-offs that we identified between six different dimensions that characterise the quality of software environments for SIE design. The trade-offs emerged from the analysis of data collected in an experimental study that compared three different design paradigms to understand in which measure each paradigm supports the creative process for SIE design. After reporting on the study procedure and the data analyses, the paper illustrates how the resulting trade-offs led us to identify alternatives for SIE design paradigms, and to structure on their basis a modular architecture of a software platform where the strengths of the three paradigms can be exploited flexibly, i.e. depending on the constraints and the requirements characterising specific design situations.     

基于U-P2P元组空间知识协作模式的中越跨语言查询扩展

针对中国与东盟国家在知识共享过程中的语言障碍问题, 详细阐述跨语言查询扩展元组空间的逻辑结构, 提出U-P2P网络模式下元组空间知识协作的分布式中、越跨语言查询扩展模型。在此基础上, 增加查询扩展代理peer的动作语言规则的定义和元组元操作指令集, 依据强化学习算法提出一种基于加权矩阵的自适应路由选择/查询机制。在Gnutella环境下的实验表明, 相对于传统的集中式查询而言, 该模型对中越两种语言之间的快速翻译和扩展查询具有较好的准确率和召回率, 在不同知识领域的运用中具有通用性和可扩充性。     

Indoor scene recognition by a mobile robot through adaptive object detection

Mobile robotics has achieved notable progress, however, to increase the complexity of the tasks that mobile robots can perform in natural environments, we need to provide them with a greater semantic understanding of their surrounding. In particular, identifying indoor scenes, such as an Office or a Kitchen, is a highly valuable perceptual ability for an indoor mobile robot, and in this paper we propose a new technique to achieve this goal. As a distinguishing feature, we use common objects, such as Doors or furniture, as a key intermediate representation to recognize indoor scenes. We frame our method as a generative probabilistic hierarchical model, where we use object category classifiers to associate low-level visual features to objects, and contextual relations to associate objects to scenes. The inherent semantic interpretation of common objects allows us to use rich sources of online data to populate the probabilistic terms of our model. In contrast to alternative computer vision based methods, we boost performance by exploiting the embedded and dynamic nature of a mobile robot. In particular, we increase detection accuracy and efficiency by using a 3D range sensor that allows us to implement a focus of attention mechanism based on geometric and structural information. Furthermore, we use concepts from information theory to propose an adaptive scheme that limits computational load by selectively guiding the search for informative objects. The operation of this scheme is facilitated by the dynamic nature of a mobile robot that is constantly changing its field of view. We test our approach using real data captured by a mobile robot navigating in Office and home environments. Our results indicate that the proposed approach outperforms several state-of-the-art techniques for scene recognition.