分布式对象中间件技术研究

中间件是处于操作系统和应用层之间的一个软件层,由于它可以简化基于分布式系统的开发应用,成为目前软件工程中的热点。在对中间件简单概述基础上,讨论了分布式对象中间件的层次结构和发展现状,最后通过对目前主流分布式对象中间件技术的分析和比较,从4个方面给出了中间件技术的发展趋势,它们是接口的标准化、体系结构的构件化、开放化和可配置化以及使用的简单化。     

A context-aware middleware for real-time semantic enrichment of distributed multimedia metadata

This paper investigates the problem of the real-time integration and processing of multimedia metadata collected by a distributed sensor network. The discussed practical problem is the efficiency of the technologies used in creating a Knowledge Base in real-time. Specifically, an approach is proposed for the real-time, rule-based semantic enrichment of lower level context features with higher-level semantics. The distinguishing characteristic is the provision of an intelligent middleware-based architecture on which low level components such as sensors, feature extraction algorithms, data sources, and high level components such as application-specific ontologies can be plugged. Throughout the paper, Priamos, a middleware architecture based on Semantic Web technologies is presented, together with a stress-test of the system’s operation under two test case scenarios: A smart security surveillance application and a smart meeting room application. Performance measurements are conducted and corresponding results are exposed.     

Dynamic end-to-end QoS management middleware for distributed multimedia systems

In this paper, we present a separable, reusable middleware solution that provides coordinated, end-to-end QoS management over any type of service component, and can use existing (legacy) QoS management solutions (by using wrappers) in a distributed multimedia system. Our middleware solution incorporates strategic and tactical QoS managers, and supports protocols and messages between tactical managers and managed application components, and between QoS managers in the management hierarchy. Strategic QoS managers take a global view of QoS provided by a set of application components within the manager's policy domain. Tactical QoS managers provide local control over application components. We introduce the concept of QoS policy domains to scope the authority of a strategic QoS manager. We describe how the management hierarchy is dynamically configured and reconfigured based on runtime needs of the application.     

PressBase : a presentation synchronization database for distributed multimedia systems

Multimedia presentations are the basic objects of multimedia databases. Since a multimedia presentation is not an instant display of a query result, the control knowledge (or synchronization requirements) has to be incorporated into the database and necessary precautions have to be taken for a lengthy presentation. Active databases provide a mechanism for incorporation of control knowledge by using event-condition-action (ECA) rules. In this paper, we describe how multimedia synchronization can be handled within a database using ECA rules. We present a prototype presentation synchronization database, named as PressBase, for distributed multimedia systems. We have adopted one of the synchronization models, SynchRuler, and then incorporated into a relational database system.     

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.     

Supporting interactive presentation for distributed multimedia applications

In this paper we present IMP, a platform to support the authoring and run-time management of interactive multimedia applications in distributed environments. The multi-level platform model encourages slot-in extensibility to cater for the evolving environment. We illustrate with our prototype platform built above the Cambridge multimedia environment. The authoring model emphasises reusability, tailorability and use of environment features in a uniform way. We have shown the validity of our approach by constructing a variety of application types.     

Transformation and exchange of multimedia objects in distributed multimedia systems

One of the challenges in the design of a distributed multimedia system is devising suitable specification models for various schemas in different levels of the system. Another important research issue is the integration and synchronization of heterogeneous multimedia objects. In this paper, we present our models for multimedia schemas and transformation algorithms. They transform high-level multimedia objects into schemas that can be used to support the presentation and communication of the multimedia objects. A key module in the system is the Object Exchange Manager (OEM). In this paper, we present the design and implementation of the OEM module, and discuss in detail the interaction between the OEM and other modules in a distributed multimedia system.     

A model for secure multimedia document database system in a distributed environment

The Internet provides a universal platform for large-scale distribution of information and supports inter-organizational services, system integration, and collaboration. Use of multimedia documents for dissemination and sharing of massive amounts of information is becoming a common practice for Internet-based applications and enterprises. With the rapid proliferation of multimedia data management technologies over the Internet, there is growing concern about security and privacy of information. Composing multimedia documents in a distributed heterogeneous environment involves integrating media objects from multiple security domains that may employ different access control policies for media objects. In this paper, we present a security model for distributed document management system that allows creation, storage, indexing, and presentation of secure multimedia documents. The model is based on a time augmented Petri-net and provides a flexible, multilevel access control mechanism that allows clearance-based access to different levels of information in a document. In addition, the model provides detailed multimedia synchronization requirements including deterministic and non-deterministic temporal relations and incomplete timing information among media objects.     

PLUS: a probe-loss utilization streaming mechanism for distributed multimedia presentation systems

We present a new flow and congestion control scheme, PLUS (Probe-Loss Utilization Streaming protocol), for distributed multimedia presentation systems. This scheme utilizes probing of the network situation and an effective adjustment mechanism to data loss to support multimedia presentations. The proposed scheme is also designed to scale with increasing number of PLUS-based streaming traffic and to live in harmony with TCP-based traffic. The novelty of the PLUS protocol is that it utilizes the knowledge of its future bottleneck bandwidth in probing the current network situation. This can be achieved by a priori knowledge of the multimedia data before a presentation is requested by a client. Compression schemes like MPEG introduce dependencies on media units. I frames are needed to successfully decode P and B frames, and P frames are needed to decode B frames. A loss of an I or P frame automatically eliminates dependent media units. Our probing scheme increases the successful transmission of critical I and P packets without the overhead of error-correction-schemes. Probing is done using B-frame packets. The advantage is that we use data packets as probe packets. With the PLUS protocol we address the need to avoid congestion rather than react to it. Experiments demonstrate the effectiveness of the approach in utilizing network resources and decreasing loss ratios.     

Spatio-temporal composition of distributed multimedia objects forvalue-added networks

The overall process necessary to perform spatial and temporal data composition for a distributed multimedia information system is addressed. With respect to delays introduced through the network, it is found that temporal composition can be most suitably achieved at the workstation. Spatial composition is most effectively performed in a hierarchical fashion as dictated by the availability of system resources. The subsequent composition methodology combines spatial and temporal composition as a network service. Database organizations and data distributions are also investigated, and spatial and temporal composition functions and their composition into the network architecture are discussed. The issue of mapping the composition process onto the network resources as a value-added service is also addressed     

A dynamic Petri net model for iterative and interactive distributed multimedia presentation

Object Composition Petri Nets, Priority Petri Nets, Dynamic OCPN, and Enhanced P-Nets have extended the original Petri Net to achieve the modeling of media synchronization and asynchronous user interactions during multimedia playback. The dynamic Petri Net (DPN) has been conceptualized to tackle existing problems in these two areas of modeling distributed multimedia systems. DPN features dynamic modeling elements which allows iteration and hence is able to reduce graph sizes of synchronous playback models while allowing greater details to be shown. DPN also introduces asynchronous event handling techniques that are powerful and effective. DPN was used in the design and modeling of a multimedia orchestration tool which is a typical representation of an application that works in a distributed multimedia system.     

Buffer model and management in distributed multimedia presentation systems

The delivery of continuous and synchronous multimedia data from a database (or file) server to multiple destinations over a network presents new challenges in the area of buffer management. Many factors that were not considered in conventional buffer management must be examined. In this paper, we investigate the principles of buffer model and management for multimedia data presentations in distributed systems. The primary goal is to minimize the response time of multimedia presentations while ensuring that all continuity and synchronization requirements are satisfied. A framework for buffer model and management is introduced. Minimum buffering requirements at both client and server sides to guarantee the continuity and synchrony of the presentation of multimedia data are examined. A prefetching and replacement strategy which satisfies these requirements is then offered. These principles and techniques provide users with the full range of information required to develop a distributed system for multimedia presentations.     

SuiteSound: a system for distributed collaborative multimedia

SuiteSound, a programming environment with integrated support for multimedia, is discussed. SuiteSound is built in the Suite object-based system on a conventional UNIX operating system. SuiteSound objects incorporate multimedia by creating flows and filters. Flows are streams of multimedia data moving through a sequence of objects. They bridge the gap between objects representing the state of an entity at a discrete point in time and space and continuous media such as live audio or video. Filters are intermediate objects between the source and destination of a flow. They take flow as input, perform one of several operations such as multiplex-in, multiplex-out, gain control, or silence deletion on it, and send the resulting flow to its destination. In effect, they provide a virtual device interface for the application programmer that is uniform and independent of any physical device. The design and implementation of SuiteSound on the Sun SparcStation are described. Experiments performed to determine the network and CPU load of the sound tool are reviewed     

CMSNS: a communication middleware for social networking and networked multimedia systems

Multimedia Tools and Applications - In this paper, we propose a communication middleware for social networking services (CMSNS) in order to reduce the development effort and to support high...     

Dermi: a new distributed hash table-based middleware framework

We disscus about Dermi: a new distributed hash table-based middleware framework. Decentralized event remote method invocation (Dermi) is a peer-to-peer (P2P), decentralized event-based object middleware framework built on top of a structured overlay network. Using an event-notification service as the principal building block, Dermi makes three innovative contributions: P2P call abstractions, distributed interception, and a decentralized object-location service. We describe how to use these three pillars to build a wide variety of global-scale distributed applications and argue that Dermi is a solid foundational technology for future wide-area distributed component infrastructures.     

Response time driven multimedia data objects allocation forbrowsing documents in distributed environments

Distributed information processing, in many WWW applications, requires access to and the transfer and synchronization of large multimedia data objects (MDOs) across the communication network. Moreover, end users expect very fast response times and high QoS. Since the transfer of large MDOs across the communication network contributes to the response time observed by the end users, the problem of allocating these MDOs so as to minimize the response time is challenging. This problem becomes more complex in the context of hypermedia documents, in which the MDOs need to be synchronized during presentation to the end users. The basic problem of data allocation in distributed database environments is NP-complete. Therefore, there is a need to pursue and evaluate solutions based on heuristics which generate near-optimal MDO allocation. We address this problem by: (1) conceptualizing this problem by using a navigational model to represent hypermedia documents and their access behavior by end users, and by capturing the synchronization requirements on MDOs, (2) formulating the problem by developing a base case cost model for response time and generalizing it to incorporate user interaction and buffer memory constraints, (3) designing two algorithms to find near-optimal solutions for allocating MDOs of the hypermedia documents while adhering to the synchronization requirements, and (4) evaluating the trade-off between the time complexity to obtain the solution and the solution quality by comparing the solutions generated by the algorithms with the optimal solutions generated through an exhaustive search     

A support platform for distributed multimedia applications

Abstract

Considerable progress has been made in the development of technologies to support distributed multimedia computing, such that there is now a wide range of pilot applications under development. The design of support systems which help in the development of multimedia applications is therefore an emerging area of research. This paper discusses the requirements of distributed multimedia applications with respect to their support environments. A number of experimental systems are then described which intend to provide the necessary facilities for multimedia applications. Particular focus is placed on the Lancaster system which provides multimedia support for open distributed systems.     

一种分布式SCADA消息中间件设计方案测控技术与仪器仪表

随着分布式SCADA系统在铁路牵引供电应用的不断推广,SCADA系统节点之间以及与其他异构系统之间进行消息数据传递面临着效率降低、接口不统一等问题。针对此问题,提出一种基于发布/订阅模式的分布式SCADA消息中间件的设计方案,该方案使用了N-Tree结构将系统消息进行逻辑区域划分,设计了一套完善的消息传递与反馈处理机制,方案中利用Quorum-Based改进型算法确保了分布式节点的消息一致性。实践及仿真实验证明,本方案提高了SCADA系统的消息传递效率,降低了分布式系统的运行负载和通信开销。