No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
A Framework for Re-use and Maintenance of Quality of Service Mechanisms in Distributed Object Systems.
Abstract
Quality of service (QoS) management is a popular demand on distribution infrastructures. We present MAQS, a generic framework for QoS management based on standard CORBA middleware. The framework facilitates the specification and generation of QoS-enabled client/server applications. Architectural support for re-use and maintenance of implementations of QoS mechanisms is one of our main objectives. Our approach is based on the aspect-oriented programming paradigm. We discuss the design of the framework and how AOP facilitates the re-use and maintenance of QoS components
... MASQ uses aspect-oriented programming ideas to weave QoS with the application objects [Geihs01B]. This is done with the MICO CORBA ORB. ...
The ability to control the Quality of Service (QoS) characteristics of
distributed systems is essential for their success. The QoS characteristics that we consider in this thesis are performance characteristics (response time and throughput) and availability characteristics (uptime, mean-timebetween-disruptions and mean-time-to-repair). The research presented in this thesis can be used to develop commercial QoS mechanisms that improve the QoS of component-middleware-based applications.
... Durch die flexiblen Kombinationsmöglichkeiten von Sinks, Kanälen und Proxies ist es relativ einfach Mehrkategoriedienstgüten umzusetzen. In [9] wurde gezeigt, dass Mechanismen auf Anwendungs-und Transportebene ausreichend sind, um ein Vielzahl von Dienstgütekategorien zu unterstützen. ...
Das Erbringen von Dienstg¨ ute (Quality of Service) ist heute eine wichtige Forderung an verteilte Infrastrukturen. In den letzten Jahren wurden verschiedene Ans ¨ atze unter- sucht, Dienstg¨ uteerbringung in Verteilungsplattformen - in- besondere in objekt-orientierte Middleware - zu integrie- ren. Dabei erwies sich die Integration als problematisch. Einerseits setzt Dienstg¨ uteerbringung Wissen ¨ uber die Ver- teilung und die Manipulation der Nachrichten ¨ ubertragung voraus, andererseits ist Verteilungstransparenz das zentrale Ziel beim Einsatz von Middleware. Außerdem greifen Me- chanismen zur Dienstg¨ uteerbringung an vielen verschiede- nen Stellen einer verteilten Anwendung und sind deshalb nur schwer vom Anwendungscode selbst zu trennen. In diesem Beitrag stellen wir unseren Ansatz zur Integra- tion von Dienstgute in .NET Remoting - der Verteilungs- plattform von .NET - vor. Wir zeigen, wie verschiedene Eigenschaften und F¨ ahigkeiten des .NET Rahmenwerkes, zur Dienstg¨ uteintegration genutzt werden k¨ onnen und die- se im Vergleich zu existierenden Losungen stark vereinfa- chen. Beim Entwurf von DotQoS haben wir auf Erkenntnis- se unserer Arbeit an MAQS, einem Dienstguterahmenwerk f¨ ur CORBA, aufgebaut.
This paper describes an approach centered on aspect oriented programming (AOP) for controlling the synchronization of distributed multimedia systems. AOP fosters separation of concerns between application objects and synchronization aspects, which naturally arise as cross-cutting concerns. Aspect modularization and encapsulation contribute to re-usability and maintenance of both application components and control mechanisms. The paper illustrates the use of AOP technologies through the construction and evaluation of a real-time quality of service (QoS) filter regulating the QoS at the receiver-side of a multimedia system over the Internet. Aspects are programmed using AspectJ. Particular aspects are exploited for testing the temporal behavior of the synchronized system. Execution experiments make use of Java Media Framework which provides the presentation system.
The concern for Quality of Service (QoS) management in middleware has been an area of active research for many years. We present a novel QoS management framework for .NET, called DotQoS, which adds generic QoS management to .NET in an architecturally conforming way. It is shown how built-in .NET features such as reflection, interception, and custom meta-data facilitate the QoS integration. Throughout the paper we compare the design and implementation of DotQoS to a CORBA-based QoS framework that we developed in a previous project. Our experience with the two frameworks reveals general insights into the principles of middleware QoS engineering.
197 pages Mobile networked devices become more and more pervasive. By embedding such devices into everyday items, pervasive computing systems will emerge in the near future. Current approaches for such systems are based on the model of Smart Environments. In such environments, a preinstalled hardware infrastructure enhances a spatial area, e.g., a room or house, and enables it to coordinate multiple mobile devices present in the environment to cooperatively provide services to the users. However, such systems rely on the presence of such an expensive infrastructure and do not work in areas without it. This restricts the deployment of pervasive computing systems severely. Therefore, in this work we propose another model for pervasive computing systems, the so-called Smart Peer Group model. A Smart Peer Group consists of a number of interconnected mobile devices that discover each other dynamically and form a spontaneous composition of devices. Coordination is provided by the participating devices themselves and no external infrastructure is needed. This results in a highly flexible system that can be used at any time and anywhere. The development of such systems is a non trivial task, due to the high level of dynamism, the potentially high resource constraintness, and the unpredictable nature of Smart Peer Groups. In this dissertation, we present the Smart Peer Group model and analyze the specific characteristics of this system class. In addition, we propose a number of concepts and algorithms to develop Smart Peer Group-based Pervasive Computing systems. A communication middleware for Smart Peer Groups is presented, which offers means to cope with resource-poor specialized devices and shields application developers from fluctuating network connectivities. Furthermore, a service discovery system for such systems is developed, which allows unused devices to temporarily deactivate themselves in order to save energy without loosing the ability to discover new services or to be discovered by others. The presented concepts and algorithms are evaluated in different scenarios using an analytical and an experimental evaluation.
Quality-of-Service (QoS) enhanced service-oriented systems are becoming more important due to the need to support various demands of different application do- mains. Such rising importance and inadequate exist- ing solutions necessitate a finer feature-level develop- ment support that can promote systematic verification of more robust QoS features. Consequently, this paper proposes a systematic methodology to develop versatile or adaptive QoS features in service-oriented systems built for decentralised environments such as peer-to- peer and mobile networks. Keywords: Decentralised service-oriented system, adaptive quality, verification, methodology.
Quality of service (QoS) management has become an important requirement for middleware platforms and distributed applications. Early QoS engineering attempts focused on single-category extensions to standard middleware. In recent years generic middleware frameworks have been proposed in order to facilitate multicategory QoS management. Our experience with such a framework has revealed that QoS management cannot be shielded from the applications. Applications need to be designed in a QoS-aware manner and application QoS requirements need to be translated into appropriate middleware extensions. Therefore we propose a comprehensive, model-driven development process for QoS-enabled distributed applications on top of QoS-enhanced middleware platforms. Our approach builds on OMG's Model-Driven Architecture (MDA). We demonstrate the mapping from the platform-independent to the platform-specific model, and we show how the design approach is applied targeting a .NET-based QoS-enabled middleware.
In this paper we present a model-driven approach to the composition of QoS mechanisms. The support of multiple QoS categories as well as runtime adaptation requires the ability to change the message path of a middleware on the fly This leads to a new set of problems regarding the composition of individual mechanisms to a functioning message path. Especially the order in which messages are passed through the QoS mechanisms is of great importance. We show how QoS mechanisms and their composition constraints can be modeled using the UML. Furthermore, a mapping from these UML models to our NET Remoting based QoS management framework DotQoS is presented.
This article outlined the requirements, characteristics, and performance of an ideal price-setting mechanism. These prices could be computed in a completely decentralized manner. Decentralized price computation provides a high degree of protection against disruption due to network failure and congestion. Furthermore, with decentralized computing, the informational and computational requirements of price-computing mechanisms are minimal. One of the most significant benefits of this approach is...
Modelling and implementing distributed systems leads often to the same problems. By ignoring partial failures, dynamic changes in bandwiths, security issues etc. object-orientation provides a very well suited abstraction. But when actually dealing with the aspects arising from the distribution, former clear designs loose their elegance. Little or none support is provided by current implementations.
DCOM (Distributed Component Object Model) and CORBA (Common Object Request Broker Architecture) are two popular distributed object models. In this paper, we make architectural comparison of DCOM and CORBA at three different layers: basic programming architecture, remoting architecture, and the wire protocol architecture. A step-by-step description of remote object activation and method invocation is provided to demonstrate the similarities and differences of the two frameworks. A primary goal is for people who are already familiar with one model to quickly understand the basic architecture of the other. 1.
. Distributed object middleware, such as CORBA, hides systemand network-specific characteristics of objects behind functional interface specifications. This simplifies development and maintenance of distributed objects, contributing to their growing acceptance. Critical applications have Quality of Service (QoS) requirements, however, such as real-time performance, dependability, or security, that are hidden by middleware. Because of this, application developers often bypass distributed object systems, thus gaining little or no advantage from the middleware. We have developed Quality Objects (QuO), a framework for developing distributed applications with QoS requirements. QuO provides a set of aspect languages, called Quality Description Languages (QDL), for specifying possible QoS states, the system resources and mechanisms for measuring and controlling QoS, and behavior for adapting to changing levels of available QoS at runtime. This paper describes QuO's aspect languages, their usa...
form only given on an article discussing Aspect-oriented programming.
Many real-time application domains can benefit from flexible and open distributed architectures, such as those defined by the CORBA specification. CORBA is an architecture for distributed object computing being standardized by the OMG. Although CORBA is well-suited for conventional request/response applications, CORBA implementations are not yet suited for real-time applications due to the lack of key quality of service (QoS) features and performance optimizations.This paper makes three contributions to the design of real-time CORBA systems. First, the paper describes the design of TAO, which is our high-performance, real-time CORBA 2.0-compliant implementation that runs on a range of OS platforms with real-time features including VxWorks, Chorus, Solaris 2.x, and Windows NT. Second, it presents TAO's real-time scheduling service that can provide QoS guarantees for deterministic real-time CORBA applications. Finally, the paper presents performance measurements that demonstrate the effects of priority inversion and non-determinism in conventional CORBA implementations and how these hazards are avoided in TAO.
Quality of Service (QoS) integration is a growing demand on nowadays networks and distributed systems. While QoS has originally been a domain of networking protocols and multimedia applications, a generalized view includes all aspects related to service quality that a client experiences. Object-oriented middleware like CORBA, DCOM or Java/RMI are popular but the current standards lack means for QoS integration. Some efforts have been made to integrate QoS in such middleware. But so far, all of them are restricted to specialized QoS categories like real-time, fault-tolerance or multimedia. A general approach is still missing. In this paper we present an approach how QoS definitions for a broad variety of QoS categories can be integrated into CORBA.
The suitability of the object-oriented programming model for implementing distributed systems has lead to middleware platforms,
such as CORBA, DCOM, and Java/RMI. Originally, these middleware systems aimed at distribution transparency for application
programmers. However, distributed systems are exposed to system issues, such as dynamic performance changes or partial errors,
which prevent complete distribution transparency. Quality of Service (QoS) management addresses these system issues. The goal
is to add QoS management to the interactions between clients and services. Support for QoS management in distributed object
systems is a hot topic of current research which poses a number of open questions: How is QoS integrated with the object model
that emphasizes encapsulation and information hiding? Can one build generic support frameworks for multiple QoS categories,
in contrast to specialized, single category systems, such as TAO, Electra, Eternal, DOORS among others. Can QoS be viewed
as an aspect in the sense of Aspect Oriented Programming (AOP) or are other classifications more appropriate? This ECOOP-workshop
has discussed the open questions and aimed at a summary of the state of the art in the field. The workshop stimulated discussions
about how next generation QoS management facilities can be built into object infrastructures.
Quality of service (QoS) management is an increasing demand on distribution infrastructures. While most of the existing QoS management architectures support a fixed set of QoS only, larger distributed systems encounter a variety of QoS requirements. This leads to a mix of different platforms and increased interoperability and management efforts. Generic QoS management could help to reduce this effort and provide flexibility towards new application requirements. We have developed a generic QoS management architecture based on CORBA. We present the motivations and requirements for the architecture, and we discuss the necessary extensions to the CORBA
Large computer networks such as corporate intranets and the
Internet are inherently heterogeneous due to such factors as
increasingly rapid technological change, engineering trade-offs,
accumulation of legacy systems over time, and varying system costs.
Unfortunately, such heterogeneity makes the development and maintenance
of applications that make the best use of such networks difficult. The
Common Object Request Broker Architecture specification created by the
Object Management Group provides a stable model for distributed
object-oriented systems that helps developers cope with heterogeneity
and inevitable change. Applications written to the CORBA standard are
abstracted away from underlying networking protocols and transports,
instead relying on object request brokers to provide a fast and flexible
communication and object activation substrated. The abstractions
provided by CORBA ORBs are currently serving as the basis for
applications in a wide variety of problem domains, including
telecommunications, finance, medicine, and manufacturing, running on
platforms ranging from mainframes down to test and measurement
equipment. This article first provides an overview of the Object
Management Architecture, then describes in detail the CORBA component of
that architecture, and concludes with a description of the OMG
organization along with some of its current and future work
this paper we discuss four major problems we have observed in our developing and deploying wide-area distributed object applications and middleware. First, most programs are developed ignoring the variable wide area conditions. Second, when application programmers do try to handle these conditions, they have great difficulty because these harsh conditions are different from thost of the local objects they are used to dealing with. Third, IDL hides information about the tradeoffs any implementation of an object must make. Fourth, there is presently no way to systematically reuse current technology components which deal with these conditions, so code sharing becomes impractical.
The Common Object Request Broker Architecture, Rev. 2.3
- Management Object
- Group
Workshop on quality of service in distributed object systems
- C Becker
- J Zinky