The paper describes an approach to building adaptable realtime command and control (C2) systems. In particular it presents an overview of the Adaptable real-timedistributedobject Management (ARTDOM) project in prog...
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The paper describes an approach to building adaptable realtime command and control (C2) systems. In particular it presents an overview of the Adaptable real-timedistributedobject Management (ARTDOM) project in progress at the MITRE Corporation. This project is currently developing realtime extensions for the Common object Request Broker Architecture (CORBA) Trading objectservice. The goal of the project is to demonstrate how current C2 systems can be more easily upgraded and made more adaptable by using emerging distributedcomputing technology. This goal is being accomplished by investigating and developing realtime middleware that is reflexive (i.e., capable of examining its current state and processing demands) and self adapting (i.e., capable of reconfiguring itself based on its reflective findings).
We investigate issues related to building highly available World Wide Web (WWW) servers on workstation clusters. We present a novel architecture that includes a dynamic Domain Name System (DNS) and a WWW server based ...
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We investigate issues related to building highly available World Wide Web (WWW) servers on workstation clusters. We present a novel architecture that includes a dynamic Domain Name System (DNS) and a WWW server based on passive object replication. This architecture allows us to reduce the service down-time of a WWW server without impacting on the Hyper Text Transfer Protocol (HTTP) protocol (and thus on the WWW client software). We implement this architecture in our department and we show some experimental results that analyze, given a batch of HTTP requests, the average response time to a request and the average time of WWW service unavailability due to object crashes.
The Common object Request Broker Architecture (CORBA) is a widely-accepted, standardized open system integration framework based on distributedobject technologies, which has been successfully used for implementation ...
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The Common object Request Broker Architecture (CORBA) is a widely-accepted, standardized open system integration framework based on distributedobject technologies, which has been successfully used for implementation of open Web services. CORBA is focused on facilitating general computing environments and does not explicitly address quality-of-service parameters neither for its communication links nor its endsystems. However efforts like the real-time CORBA Special Interest Group (SIG) at OMG and the "pluggable protocols" proposal will ultimately lead to support of quality-of-service properties for CORBA communication links. We concentrate on architectural approaches for fault-tolerant, highly available endsystems. We present the Observer approach for implementation of reliable CORBA clients. Consensus protocols based on the Composite objects technique is our solution for constructing CORBA servers with high predictability regarding timely and reliable method execution. Our middleware uses commercial off-the-shelf (COTS) technology and aims at conversion of legacy applications into reliable Web-services. We present Java-based Web-interfaces to the Balancing Robots soft real-time simulation. Also, we demonstrate a fault-tolerant version of the Netscape Navigator based on our Observer technique.
Multimedia applications require support for quality of service (QoS). The need for reusable and maintainable code also means that these kinds of applications are developed in a distributedobject system. To address th...
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Multimedia applications require support for quality of service (QoS). The need for reusable and maintainable code also means that these kinds of applications are developed in a distributedobject system. To address the support of QoS in middleware, we propose a lightweight model to manage QoS constraints in this kind of environment. This model is based on two types of objects: micro-QoS managers (/spl mu/QoS-Mngrs) and resource managers (R-Mngrs). A /spl mu/QoS-Mngr is associated with an application, and it handles the QoS contract, the QoS mapping and the QoS monitoring. Each R-Mngr is responsible for QoS management for a specific resource, including admission control, real-time scheduling and monitoring. The /spl mu/QoS-Mngrs and the R-Mngrs co-operate, using the middleware, to ensure end-to-end QoS management. This paper focuses on the R-Mngrs and it gives an overview of our implementation on a CORBA platform in the context of a video-on-demand (VOD) application.
In a distributed system, replication of components, such as objects, is a well known way of achieving availability. For increased availability, crashed and disconnected components must be replaced by new components on...
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In a distributed system, replication of components, such as objects, is a well known way of achieving availability. For increased availability, crashed and disconnected components must be replaced by new components on available spare nodes. In this context, we address the problem of reconfiguring a group after the group as an entity has failed. Such a failure is termed a group failure which, for example, can be the crash of every component in the group or the group being partitioned into minority islands. The solution assumes crash-proof storage, and eventual recovery of crashed nodes and healing of partitions. It guarantees that: (i) the number of groups reconfigured after a group failure is never more than one, and (ii) the reconfigured group contains a majority of the components which were members just before the group failed, so that the loss of state information due to group failure is minimal. The protocol is efficient in terms of communication rounds and use of stable store, during both normal operations and reconfiguration after a group failure.
Adaptive QoS systems are attractive for multimedia services that are accessed via the Internet or mobile computers. An important feature of an adaptive QoS system is that it allows application programs to specify the ...
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Adaptive QoS systems are attractive for multimedia services that are accessed via the Internet or mobile computers. An important feature of an adaptive QoS system is that it allows application programs to specify the QoS level desired, and at the system to set the level according to the resources available. With an adaptive QoS system, the user should specify not only the target QoS, but also a QoS range to minimize the quality degradation resulting from resource shortages. The paper introduces QoSPath as an extensible object model for specifying, translating, and arbitrating QoS in adaptive QoS systems. The QoSPath model herein lets users and application programs specify their QoS preference by setting QoSPoints in a QoSPath, each of which specifies an objective QoS level against a subjective utility value. With the QoSPath model, a simple QoS preference can be specified by a few parameters, while more detailed specifications can be given by providing more information, thus the model offers both the simple and descriptive QoS specifications. It is designed to be flexible in that new QoS formats and translation modules can be easily defined with only a minimum knowledge of other parts of a system. It therefore separates the functions of QoS specification, translation/inverse-translation and arbitration.
We propose a new Web documentation database as a supporting environment of the Multimedia Micro-University project. The design of this database facilitates a Web documentation development paradigm that we have propose...
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We propose a new Web documentation database as a supporting environment of the Multimedia Micro-University project. The design of this database facilitates a Web documentation development paradigm that we have proposed earlier. From a script description to its implementation as well as testing records, the database and its interface allow the user to design Web documents as virtual courses to be used in a Web-savvy virtual library. The database supports object reuse and sharing, as well as referential integrity and concurrence. In order to allow real-time course demonstration, we also propose a simple course distribution mechanism, which allows the pre-broadcast of course materials. The system is implemented as a three-tier architecture which runs under MS Windows and other platforms.
distributed applications are difficult to build and maintain and are even more difficult when the applications are distributed over wide-area networks. distributedobjectcomputing middleware has emerged to simplify t...
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ISBN:
(纸本)0818684321
distributed applications are difficult to build and maintain and are even more difficult when the applications are distributed over wide-area networks. distributedobjectcomputing middleware has emerged to simplify the building of distributed applications by hiding implementation details behind functional interfaces. However critical applications have non-functional requirements, such as real-rime performance, dependability, or security, that are as important as the functional requirements, but are also hidden by the middleware. Because current distributedobject middleware doesn't support these aspects of critical applications, application developers often find themselves bypassing the distributedobject systems, effectively gaining little or no advantage from the middleware. We have developed Quality objects (QuO), a framework for including Quality of service (QoS) in distributedobject applications. QuO supports the specification of QoS contracts between clients and service providers, runtime monitoring of contracts, and adaptation to changing system conditions. A crucial aspect of QuO is a suite of Quality Description Languages for describing states of QoS, system elements that need to be monitored to measure the current QoS, and notification and adaptation to trigger when the state of QoS in the system changes. This paper gives a brief overview of QuO and describes the syntax and semantics of CDL, the component of QDL for describing QoS contracts.
Many engineers are still reluctant to adopt advanced object-oriented technologies (such as high modularity: dynamic binding, automatic garbage collection, etc.) for embedded systems with real-time constraints, because...
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ISBN:
(纸本)0818684321
Many engineers are still reluctant to adopt advanced object-oriented technologies (such as high modularity: dynamic binding, automatic garbage collection, etc.) for embedded systems with real-time constraints, because of their supposed inefficiency. We set ourselves into the context of building telecommunication systems with a standard object-oriented analysis and design approach. We describe how we use relevant design patterns, followed with an implementation in a pure object-oriented language (Eiffel) to conciliate the needed efficiency with the benefits of the object-oriented approach - flexibility dynamic configurability maintenability portability, etc. We discuss a case study. based on the implementation of SMDS (Switched Multi-megabits Data service) servers featuring high-throughput and low-delay transmissions and respecting the real-time constraints of SMDS.
The confluence of computers, communications, and databases is quickly creating a global virtual database where many applications require real-time access to both temporally accurate and multimedia data. This is partic...
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ISBN:
(纸本)0818684321
The confluence of computers, communications, and databases is quickly creating a global virtual database where many applications require real-time access to both temporally accurate and multimedia data. This is particularly true in military and intelligence applications, but these required features are needed in many commercial applications as well. We are developing a distributed database, called BeeHive, which could offer features along different types of requirements: real-time, fault-tolerance, security, and quality-of service for audio and video. Support of these features and potential trade-offs between them could provide a significant improvement in performance and functionality over current distributed database and object management systems. In this paper, we present a high level design for BeeHive architecture and sketch the design of the BeeHive object Model (BOM) which extends object-oriented data models by incorporating time and other features into objects.
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