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IFIP/ACM International Conference on distributed Systems Platforms and Open distributed Processing, Middleware 2000

作者： Blair, Gordon S. Blair, Lynne Issarny, Valérie Tuma, Petr Zarras, Apostolos Distributed Multimedia Research Group Computing Department Lancaster University Bailrigg LancasterLA1 4YR United Kingdom Solidor Research Group NRIA-Rocquencourt Domaine de Voluceau Rocquencourt - BP 105 Chesnay Cédex78153 Le France Distributed Systems Research Group Department of Software Engineering Charles University Prague Czech Republic

ISBN: (纸本)3540673520

Future middleware platforms will need to be more configurable in order to meet the demands of a wide variety of application domains. Furthermore, we believe that such platforms will also need to be reconfigurable, for example to enable systems to adapt to changes in the underlying systems infrastructure. A number of technologies are emerging to support this level of configurability and re-configurability, most notably middleware platforms based on the concepts of open implementation and reflection. One problem with this general approach is that widespread changes can often be made to the middleware platform, potentially jeopardizing the integrity of the overall system. This paper discusses the role of software architecture in maintaining the overall integrity of the system in such an environment. More specifically, the paper discusses extensions to the Aster framework to support the re-configuration of a reflective (component-based) middleware platform in a constrained manner. The approach is based on i) the formal specification of a range of possible component configurations, ii) the systematic selection of configurations based on a given set of non-functional properties, and iii) the orderly re-configuration between configurations, again based on formally specified rules. © Springer-Verlag Berlin Heidelberg 2000.

关键词： Software architecture

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A principled approach to supporting adaptation in distributed mobile environments

A principled approach to supporting adaptation in distribute...

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IEEE International Workshop on Software Engineering for Parallel and distributed Systems

作者： Blair Coulson Andersen Clarke Costa Duran Parlavantzas Saikoski University of Tromsø Norway Distributed Multimedia Research Group Department of Computing Lancaster University Lancaster UK

To support multimedia applications in mobile environments, it is necessary for applications to be aware of the underlying environmental conditions, and also to be able to adapt their behaviour and that of the underlying platform as such conditions change. Many existing distributed systems platforms support such adaptation only in a rather ad-hoc manner. This paper presents a principled approach to supporting adaptation through the use of reflection. More specifically, the paper introduces a language-independent, component-based reflective architecture featuring a per-component meta-space, the use of meta-models to structure the meta-space, and a consistent use of component graphs to represent composite components. The paper also reports on a quality-of-service management framework, providing sophisticated support for monitoring and adaptation functions. Finally, the paper describes a prototype implementation of this architecture using the object-oriented programming language Python.

关键词： Adaptive systems

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ATM QoS support via output port controllers

ATM QoS support via output port controllers

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IEEE International Conference on Communications (ICC)

作者： Yap Ma Tit Simon Fong D. Hutchison School of Applied Science Nanyang Technological University Singapore Distributed Multimedia Research Group Department of Computing Lancaster University Lancaster UK

The challenge in building an ATM switch, especially in the area of QoS control, lies in the design of the port controllers. By combining port reconfiguration, cell scheduling and connection admission control, a programmable QoS controller at the output port of the non-blocking, output-buffered reconfigurable ATM switch is proposed. In such a switch, the output port is the only point of contention that can cause possible QoS degradations due to excessive queueing delays. Cell scheduling is used as an essential mechanism for attaining meaningful differentiated QoS behaviour. The QoS controller combines per-connection buffer management with a table-driven cell scheduler to achieve a broad range of QoS behaviour. This paper reports the simulation results of our study on (i) the effects of different traffic characteristics, and (ii) the effects of slot algorithms in the cell scheduler, on the QoS performance.

关键词： Switches Asynchronous transfer mode Bit rate Traffic control Admission control Degradation Scheduling algorithm Fabrics Delay effects Buildings

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The role of software architecture in constraining adaptation incomponent-based middleware platforms 00

The role of software architecture in constraining adaptation...

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IFIP/ACM International Conference on distributed systems platforms

作者： Gordon S. Blair Lynne Blair Valéie Issarny Petr Tuma Apostolos Zarras Distributed Multimedia Research Group Computing Department Lancaster University Bailrigg Lancaster LA1 4YR U.K. Solidor Research Group INRIA-Rocquencourt Domaine de Voluceau Rocquencourt - BP 105 78153 Le Chesnay Cédex France Distributed Systems Research Group Department of Software Engineering Faculty of Mathematics and Physics Charles University Prague Czech Republic

ISBN: (纸本)9783540673521

Future middleware platforms will need to be more configurable in order to meet the demands of a wide variety of application domains. Furthermore, we believe that such platforms will also need to be re-configurable, for example to enable systems to adapt to changes in the underlying systems infrastructure. A number of technologies are emerging to support this level of configurability and re-configurability, most notably middleware platforms based on the concepts of open implementation and reflection. One problem with this general approach is that widespread changes can often be made to the middleware platform, potentially jeopardizing the integrity of the overall system. This paper discusses the role of software architecture in maintaining the overall integrity of the system in such an environment. More specifically, the paper discusses extensions to the Aster framework to support the re-configuration of a reflective (component-based) middleware platform in a constrained manner. The approach is based on i) the formal specification of a range of possible component configurations, ii) the systematic selection of configurations based on a given set of non-functional properties, and iii) the orderly re-configuration between configurations, again based on formally specified rules.

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The support of mobile-awareness in collaborative groupware

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Personal and Ubiquitous computing 1999年第1-2期3卷 33-42页

作者： Cheverst, Keith Blair, Gordon Davies, Nigel Friday, Adrian Distributed Multimedia Research Group Department of Computing Lancaster University Lancaster LA1 4YR United Kingdom

This paper explores the need for mobile-awareness in groupware designed for use in a mobile environment. The motivation for providing this additional form of awareness is that current groupware tends to assume a reliable and constant quality of communications that does not exist in a mobile environment. The implications of making this false assumption are twofold: first, systems that enforce certain ordering and reliability semantics across all operations can suffer drastic performance penalties;second, users are given insufficient awareness of (and control over) the effect of the unreliable communications environment on their collaboration. The support of mobile-awareness implies providing users with appropriate and sufficient inforraation to adapt their behaviour (and the behaviour of the system) in response to changes in the quality of group communications available. To support the development of mobile-aware groupware we have built a flexible Quality of Service (QoS)-based group service capable of providing group-oriented feedback to application level services. © Springer-Verlag London Ltd.

关键词： groupware

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LARA: A prototype system for supporting high performance active networking

LARA: A prototype system for supporting high performance act...

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1st International Working Conference on Active Networks, IWAN 1999

作者： Cardoe, R. Finney, J. Scott, A.C. Shepherd, W.D. Distributed Multimedia Research Group Computing Department Lancaster University Lancaster United Kingdom

ISBN: (纸本)3540662383

There are a number of alternative directions in which active networking is progressing, each of which have their own advantages and disadvantages. This paper presents the Lancaster Active Router Architecture (LARA), as a means to integrate these distinct active network environments in a single system, to allow increased flexibility in network programming. There are a number of issues involved in accomplishing this, including scalability, resource management, performance and security. The remainder of this paper describes our prototype composite hardware/software solution, which takes the first steps towards tackling these issues. © Springer-Verlag Berlin Heidelberg 1999.

关键词： Active networks

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Next generation middleware: Requirements, architecture, and prototypes 7

Next generation middleware: Requirements, architecture, and ...

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7th IEEE Workshop on Future Trends of distributed computing Systems, FTDCS 1999

作者： Eliassen, Frank Andersen, Anders Blair, Gordon S. Costa, Fabio Coulson, Geoff Goebel, Vera Hansen, Øivind Kristensen, Tom Plagemann, Thomas Rafaelsen, Hans Ole Saikoski, Katia B. Yu, Weihai Department of Informatics University of Oslo Norway Distributed Multimedia Research Group Computing Department Lancaster University United Kingdom Department of Computer Science University of Tromsø Norway Faculty of Engineering Agder College Grimstad Norway

ISBN: (纸本)076950468X

Middleware technologies such as CORBA or Java RMI have proved their suitability for "standard" client-server applications. However, challenges from existing and new types of applications, including support for multimedia real-time requirements and mobility seems to indicate the need for defining a new architecture for open distributed systems. The new architecture should be designed from the beginning with flexibility and adaptability in mind. This can be achieved by defining an open engineering middleware platform that is run time configurable and allows inspection and adaptation of the underlying components. This paper proposes a next generation middleware architecture that conforms to requirements as indicated above. This architecture is characterised by being open, and adaptable based on the principle of reflection. The paper also reports on some existing research prototypes with a focus towards their suitability as next generation middleware. © 1999 IEEE.

关键词： Middleware

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'Caches in the air': disseminating tourist information in the GUIDE system

'Caches in the air': disseminating tourist information in th...

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IEEE Workshop on Mobile computing Systems and Applications (WMCSA)

作者： N. Davies K. Cheverst K. Mitchell A. Friday Distributed Multimedia Research Group Department of Computing Lancaster University Lancaster UK

The paper describes work carried out as part of the GUIDE project at Lancaster University. The overall aim of the project is to develop a context-sensitive tourist guide for visitors to the city of Lancaster. Visitors are equipped with portable GUIDE units which in turn provide interactive services and dynamically tailored Web based information, reflecting the visitor's preferences and environmental context. In contrast to existing tourist systems, all information in GUIDE is obtained dynamically using a city-wide wireless network infrastructure. We focus on the design of the GUIDE information model. The model presented is novel by virtue of the fact that it enables both geographic and contextual information to be captured. The paper also describes our development of an efficient broadcast mechanism which enables visitors' requests for information to be serviced quickly despite the wireless communications infrastructure employed.

关键词： Cities and towns Geographic Information Systems Access protocols Multimedia systems Multimedia computing distributed computing Telephony Electronic mail LAN interconnection Wireless communication

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Meta-signalling for open network control

Meta-signalling for open network control

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IEEE Conference on Open Architectures and Network Programming

作者： C. Edwards D.G. Waddington D. Hutchison Distributed Multimedia Research Group Computing Department Lancaster University Lancaster UK

distributed applications have wide ranging requirements. Message-based applications must now co-exist with multimedia-based applications that often require precise bounds on the delivery of data. A single best effort service is no longer sufficient. Attempts at supporting a wide variety of applications have come from different directions, and have inevitably led to a scenario where one is better at supporting a certain type of application than the other. What is clear is that different network services and different protocol stacks are required in order to satisfy the needs of the emerging variety of application types. This paper discusses an approach to providing seamless integration for different network control mechanisms, providing access to network services in a clear and consistent manner. We build on the previously defined Open Service Model and introduce the idea of meta-signalling, used to negotiate end-to-end network requirements. We employ the Internet Protocol as a means for signalling control information, and object technology as a mechanism for providing distributed resource management. We look at the requirements for a signalling protocol, notably reliability, low bit rate and low delay, and consider how in the context of an IP network we can provide a level of quality of service for signalling messages.

关键词： Internet Switches Communication system control Access protocols IP networks Quality of service Transport protocols Streaming media Asynchronous transfer mode Programming environments

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The role of reflection in supporting dynamic QoS management functions

The role of reflection in supporting dynamic QoS management ...

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International Workshop on Quality of Service

作者： G.S. Blair A. Andersen L. Blair G. Coulson Distributed Multimedia Research Group Department of Computing Lancaster University Lancaster UK

In previous papers, the authors have reported on the design and implementation of reflective middleware platforms. The aim of this paper is to consider the implications of such an architecture for the area of quality of service (QoS) management. More specifically, the paper describes how critical QoS management functions can be incorporated into our reflective middleware platform, with particular emphasis on the dynamic QoS management functions of QoS monitoring and adaptation. It is argued that the reflective approach leads to a natural and highly flexible implementation of such QoS management functions (and indeed the approach offers considerable benefits over more conventional approaches).

关键词： Reflection Quality of service Protocols Middleware Multimedia computing distributed computing Computer architecture Quality management Monitoring Inspection

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