An integrated runtime QoS-aware middleware framework for distributed multimedia applications

Future-generation distributed multimedia applications are expected to be highly scalable to a wide variety of heterogeneous devices, and highly adaptive across wide-area distributed environments. This demands multiple stages of run-time support in QoS-aware middleware architectures, particularly, probing the performance of QoS parameters, instantiating the initial component configurations, and adapting to on-the-fly variations. However, few of the past experiences in related work have shown comprehensive run-time support in all of the above stages – they often design and build a middleware framework by focusing on only one of the run-time issues. In this paper, we argue that distributed multimedia applications need effective run-time middleware support in all these stages to be highly scalable and adaptive across a wide variety of execution environments. Nevertheless, the design of such a middleware framework should be kept as streamlined and simple as possible, leading to a novel and integrated run-time middleware platform to unify the probing, instantiation and adaptation stages. In addition, for each stage, the framework should enable the interaction of peer middleware components across host boundaries, so that the corresponding middleware function can be performed in a coordinated and coherent fashion. We present the design of such an integrated architecture, with a case study to illustrate how it is simple yet effective to monitor and configure complex multimedia applications.     

基于分布式主动代理的网络性能监测和发布系统

给出了一个新的网络性能监测和发布系统的设计。该系统的主要特点是使用了分布式主动代理技术,和传统的集中式网络性能监测系统及其它基于分布式代理技术的网络性能监测系统相比,使用分布式主动代理网络性能监测系统具有更高的安全性,数据采集的时间一致性也得到了保证。     

Autonomic configuration and recovery in a mobile agent‐based distributed event monitoring system

In this paper we present a framework for building policy‐based autonomic distributed agent systems. The autonomic mechanisms of configuration and recovery are supported through a distributed event processing model and a set of policy enforcement mechanisms embedded in an agent framework. Policies are event‐driven rules derived from the system's functional and non‐functional requirements. Agents in the network monitor the system state for policy violation conditions, generate appropriate events, and communicate them to other agents for cooperative filtering, aggregation, and handling. A set of agents perform policy enforcement actions whenever events signifying any policy violation conditions occur. Policies are defined using a specification framework based on XML. The policy enforcement agents interpret the policies given in XML. We illustrate the utility of this framework in the context of an agent‐based distributed network monitoring application. We also present an experimental evaluation of our approach. Copyright © 2006 John Wiley & Sons, Ltd.     

动态上下文环境下的实时分布式多媒体系统框架

伴随着多媒体采集和处理设备成本的不断降低,以及处理目标的不断复杂化,多媒体信息系统正朝着大规模数据分析和管理系统靠拢,因此如何有效支持实时分布式多媒体信息所需的实时采集、压缩、传输、处理、描述、反馈与存档,以及后期的浏览与检索,已经成为多媒体计算研究的重要问题。为了有效支持实时分布式多媒体信息的实时采集、传输、处理、描述、存档等的需要,在分析动态上下文环境下实时分布式多媒体系统对底层采集、压缩和传输以及信息的表达和存储的普遍需求的基础上,提出并实现了一个通用的实时分布式媒体信息处理框架,以便为实时分布多媒体系统提供基础服务支持。该框架包括软件平台和信息系统两部分。前者用于将逻辑功能与物理设备隔离开来,完成实时采集、压缩、传输和解压等功能;后者通过统一信息表达格式,将数据与特定的采集处理模块隔离开来,同时还提供了信息管理的功能,以便于用户后期检索。这两部分共同将多媒体系统所需要的实时采集、处理、压缩、描述、反馈与存档以及离线浏览与检索等服务融入一致、统一的框架中。基于该框架的会议系统的相关实验表明,该框架具有良好的开放性、可配置性和可扩展性。     

Mobile agent-enabled framework for structuring and building distributed systems on the internet

Mobile agent has shown its promise as a powerful means to complement and enhance existing technology in various application areas. In particular, existing work has demonstrated that MA can simplify the development and improve the performance of certain classes of distributed applications, especially for those running on a wide-area, heterogeneous, and dynamic networking environment like the Internet. In our previous work, we extended the application of MA to the design of distributed control functions, which require the maintenance of logical relationship among and/or coordination of proc- essing entities in a distributed system. A novel framework is presented for structuring and building distributed systems, which use cooperating mobile agents as an aid to carry out coordination and cooperation tasks in distributed systems. The framework has been used for designing various distributed control functions such as load balancing and mutual ex- clusion in our previous work. In this paper, we use the framework to propose a novel ap- proach to detecting deadlocks in distributed system by using mobile agents, which dem- onstrates the advantage of being adaptive and flexible of mobile agents. We first describe the MAEDD (Mobile Agent Enabled Deadlock Detection) scheme, in which mobile agents are dispatched to collect and analyze deadlock information distributed across the network sites and, based on the analysis, to detect and resolve deadlocks. Then the design of an adaptive hybrid algorithm derived from the framework is presented. The algorithm can dynamically adapt itself to the changes in system state by using different deadlock detec- tion strategies. The performance of the proposed algorithm has been evaluated using simulations. The results show that the algorithm can outperform existing algorithms that use a fixed deadlock detection strategy.     

Fault Management in Distributed Systems: A Policy-Driven Approach

Managing the availability and performance of a distributed system involves monitoring the behavior of the system, identifying system problems, and correcting those problems. Each of these tasks requires some expertise, such as an understanding of the mechanics of the underlying system components. As the size and complexity of these systems increases, and the number of distributed applications executing on these systems increases, managing the availability and performance of distributed systems becomes more difficult. Little research has focused on embedding systems management expertise into a management application for a distributed system. In this paper we describe a rule-based management application for a commercially available distributed computing environment that is capable of monitoring the distributed system, detecting system service-related performance and availability problems, and generating corrective actions to correct the problems.     

Enabling run-time composition and support for heterogeneous pervasive multi-agent systems

User needs-driven and computer-supported development of pervasive heterogeneous and dynamic multi-agent systems remains a great challenge for agent research community. This paper presents an innovative approach to composing, validating and supporting multi-agent systems at run-time. Multi-agent systems (MASs) can and should be assembled quasi-automatically and dynamically based on high-level user specifications which are transformed into a shared and common goal–mission. Dynamically generating agents could also be supported as a pervasive service. Heterogeneity of MASs refers to diverse functionality and constituency of the system which include mobile as well as host associated software agents. This paper proposes and demonstrates on-demand and just-in-time agent composition approach which is combined with run-time support for MASs. Run-time support is based on mission cost-efficiency and shared objectives which enable termination, generation, injection and replacement of software agents as the mission evolves at run-time. We present the formal underpinning of our approach and describe the prototype tool – called eHermes, which has been implemented using available agent platforms. Analysis and results of evaluating eHermes are presented and discussed.     

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.     

分布式监测信息系统架构设计及应用

分布式监测系统广泛应用于检测对象分散的大型工程项目,而信息系统是其中重要的组成部分．本文将信息系统分为内部信息系统和外部信息系统,内部信息系统负责数据汇集及管理,为数据库服务器系统架构设计,外部信息系统则利用原始监测数据,计算监测目标并将其呈现给用户．在内部信息系统中通过协调服务器实现现场服务器和数据服务器的有效联接,按照通用分布式监测系统功能将外部信息系统分为7个层次,针对不同监测系统构建其中具体功能模块及其关系．最后,基于该架构体系提出了分布式地铁隧道沉降监测信息系统模型,该系统也可广泛应用于其他分布式监测系统．     

WebWork: METEOR2's Web-Based Workflow Management System

METEOR₂ workflow management systems consist of both (1) design/build-time and (2) run-time/enactment components for implementing workflow applications. An enactment system provides the command, communication and control for the individual tasks in the workflow. Tasks are the run-time instances of intra- or inter-enterprise applications. We are developing three implementations of the METEOR₂ model: WebWork, OrbWork and NeoWork. This paper discusses WebWork, an implementation relying solely on Web technology as the infrastructure for the enactment system. WebWork supports a distributed implementation with participation of multiple Web servers. It also supports automatic code generation of workflow applications from design specifications produced by a comprehensive graphical designer. WebWork has been developed as a complement of its more heavyweight counterparts (OrbWork and NeoWork), with the goal of providing ease of workflow application development, installation, use and maintenance. At the time of this writing, WebWork has been installed by several of the LSDIS Lab's industrial partners for testing, evaluation and building workflow applications.     

一个基于CORBA和移动智能体的分布式网箱集成框架

文中分析了当前主流网管系统在体系结构上的缺陷,阐述了分布对象技术（CORBA）与移动智能体技术各自在网管领域的应用方法与优势。结合这些优势,给出了一个基于CORBA和移动智能体的分布式网管集成框架,并进一步通过实验模拟证实了其可行性。     

Formal approach to agent-based dynamic reconfiguration in Networks-On-Chip

A Network-On-Chip (NoC) platform is an emerging topology for large-scale applications. It provides a required number of resources for critical and excessive computations. However, the computations may be interrupted by faults occurring at run-time. Hence, reliability of computations as well as efficient resource management at run-time are crucial for such many-core NoC systems. To achieve this, we utilize an agent-based management system where agents are organized in a three-level hierarchy. We propose to incorporate reallocation and reconfiguration procedures into agents hierarchy such that fault-tolerance mechanisms can be executed at run-time. Task reallocation enables local reconfiguration of a core allowing it to be eventually reused in order to restore the original performance of communication and computations. The contributions of this paper are: (i) an algorithm for initial application mapping with spare cores, (ii) a multi-objective algorithm for efficient utilization of spare cores at run-time in order to enhance fault-tolerance while maintaining efficiency of communication and computations at an adequate level, (iii) an algorithm integrating the local reconfiguration procedure and (iv) formal modeling and verification of the dynamic agent-based NoC management architecture incorporating these algorithms within the Event-B framework.     

基于中间件的实时内存调度

在数据密集型实时监测系统中,任务需要通过分配内存来存储和处理动态变化的信息。该文提出了一种基于中间件的新型内存调度器,通过反馈驱动来调节实时任务的内存分配,与受控任务保持平滑的连接,开放结构允许系统设计人员增加或修改内存管理策略。测试结果表明,内存调度器引起的开销较小,能有效地协调资源共享冲突。     

Resource Reservation in Dynamic Real-Time Systems

This paper focuses on the problem of providing efficient run-time support to multimedia applications in a real-time system, where different types of tasks (characterized by different criticality) can coexist. Whereas critical real-time tasks (hard tasks) are guaranteed based on worst-case execution times and minimum interarrival times, multimedia tasks are served based on mean parameters. A novel bandwidth reservation mechanism (the constant bandwidth server) allows real-time tasks to execute in a dynamic environment under a temporal protection mechanism, so that each task will never exceed a predefined bandwidth, independently of its actual requests. The paper also discusses how the proposed server can be used for handling aperiodic tasks efficiently and how a statistical analysis can be applied to perform a probabilistic guarantee of soft tasks. The performance of the proposed method is compared with that of similar service mechanisms (dynamic real-time servers and proportional share schedulers) through extensive simulation experiments.     

A framework for synchronous delivery of time-dependent multimedia data

Multimedia data often have time dependencies that must be satisfied at presentation time. To support a general purpose multimedia information system, these timing relationships must be managed to provide utility to both the data presentation system and the multimedia author. Timing management encompasses specification, data representation, temporal access control, playout scheduling, and run-time intermedia synchronization. In this paper we describe the components of our framework for supporting time-dependent multimedia data encompassing these areas and how they are assembled into a unified system.     

Comparative analysis of two different middleware approaches for reconfiguration of distributed real-time systems

Software-based reconfiguration of distributed real-time systems is a complex problem with many sides to it ranging from system-wide concerns down to the intrinsic non-robust nature of the specific middleware layer and the used programming techniques. In a completely open distributed system, mixing reconfiguration and real-time is not possible; the set of possible target states can be very large threatening the temporal predictability of the reconfiguration process. Over the last years, middle ware solutions have appeared mainly for general purpose systems where efficient state transitions are sought for, but real-time properties are not considered. One of the few contributions to run-time software reconfiguration in distributed real-time environments has been the iLAND middleware, where the germ of a solution with high potential has been conceived and delivered in practice.¹ The key idea has been the fact that a set of bounds and limitations to the structure of systems and to their open nature needs to be imposed in order to come up with practical solutions. In this paper, the authors present the different sides of the problem of software reconfiguration from two complementary middleware perspectives comparing two strategies built inside distribution middleware. We highlight the lessons learned in the iLAND project aimed at service-based reconfiguration and compare it to our experience in the development of distributed real-time Java reconfiguration based on distributed tasks rescheduling. Authors also provide a language view of both solutions. Lastly, empirical results are shown that validate these solutions and compare them on the basis of different programming language realizations.     

Semantic technologies for open interaction systems

Open interaction systems play a crucial role in agreement technologies because they are software devised for enabling autonomous agents (software or human) to interact, negotiate, collaborate, and coordinate their activities in order to establish agreements and manage their execution. Following the approach proposed by the recent literature on agent environments those open distributed systems can be efficiently and effectively modeled as a set of correlated physical and institutional spaces of interaction where objects and agents are situated. In our view in distributed open systems, spaces are fundamental for modeling the fact that events, actions, and social concepts (like norms and institutional objects) should be perceivable only by the agents situated in the spaces where they happen or where they are situated. Institutional spaces are also crucial for their active functional role of keeping track of the state of the interaction, and for monitoring and enforcing norms. Given that in an open distributed and dynamic system it is fundamental to be able to create and destroy spaces of interaction at run-time, in this paper we propose to create them using Artificial Institutions (AIs) specified at design time. This dynamic creation is a complex task that deserves to be studied in all details. For doing that, in this paper, we will first define the various components of AIs and spaces using Semantic Web Technologies, then we will describe the mechanisms for using AIs specification for realizing spaces of interaction. We will exemplify this process by formalizing the components of the auction Artificial Institution and of the spaces created for running concrete auctions.     

A Suite of Tools for Debugging Distributed Autonomous Systems

This paper describes a set of tools that enables developers to log and analyze the run-time behavior of distributed control systems. A feature of the tools is that they can be applied to distributed systems. The logging tools enable developers to instrument C or C++ programs so that data indicating state changes can be logged automatically in a variety of formats. In particular, run-time data from distributed systems can be synchronized into a single relational database. Tools are also provided for visualizing the logged data. Analysis to verify correct program behavior is done using a new interval logic that is described in this paper. The logic enables system engineers to express temporal specifications for the autonomous control program that are then checked against the logged data. The data logging, visualization, and interval logic analysis tools are all fully implemented. Results are given from a NASA distributed autonomous control system application.     

A practical approach for active camera coordination based on a fusion-driven multi-agent system

In this paper, we propose a multi-agent system architecture to manage spatially distributed active (or pan-tilt-zoom) cameras. Traditional video surveillance algorithms are of no use for active cameras, and we have to look at different approaches. Such multi-sensor surveillance systems have to be designed to solve two related problems: data fusion and coordinated sensor-task management. Generally, architectures proposed for the coordinated operation of multiple cameras are based on the centralisation of management decisions at the fusion centre. However, the existence of intelligent sensors capable of decision making brings with it the possibility of conceiving alternative decentralised architectures. This problem is approached by means of a MAS, integrating data fusion as an integral part of the architecture for distributed coordination purposes. This paper presents the MAS architecture and system agents.