Gerência da largura de banda para garantir QoS adaptável em redes sem fio ad hoc

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico.As redes sem fio apresentam um novo paradigma computacional que tem como função principal prover aos usuários o acesso permanente à rede independente de sua localização física. Com a diminuição dos custos dos dispositivos portáteis e o aumento da sua capacidade surgiu um novo conceito chamado redes ad hoc, onde a comunicação é feita diretamente entre os computadores móveis. Neste trabalho são descritas as características fundamentais das redes ad hoc. Assim como as principais tendências para garantir a qualidade de serviço nas redes sem fio, considerando as características: transmissão pouco confiável, largura de banda limitada e alta taxa de erros. No trabalho é proposto um mecanismo para manter QoS adaptável sobre o princípio de gerência da largura de banda em redes sem fio de topologia ad hoc. Também foi desenvolvido um software que permite simular ambientes de redes ad hoc, fazendo as conexões em conformidade com o critério do mecanismo proposto. Para a validação realizaram-se várias experiências que permitiram provar as vantagens do mecanismo. Naquelas redes onde o mecanismo de QoS adaptável foi usado, obteve-se melhor aproveitamento do canal de transmissão, ao mesmo tempo que maior quantidade de conexões eram aceitas

Coordinated adaptation for adaptive context-aware applications

The ability to adapt to change is critical to both mobile and context-aware applications. This thesis argues that providing sufficient support for adaptive context-aware applications requires support for coordinated adaptation. Specifically, the main argument of this thesis is that coordinated adaptation requires applications to delegate adaptation control to an entity that can receive state information from multiple applications and trigger adaptation in multiple applications. Furthermore, coordination requires support for reconfiguration of the adaptive behaviour and user involvement. Failure to support coordinated adaptation is shown to lead to poor system and application performance and insufficient support for user requirements. An investigation of the existing state-of-the-art in the areas of adaptive and context- aware systems and an analysis of the limitations of existing systems leads to the establishment of a set of design requirements for the support of coordinated adaptation. Specifically, adaptation control should be decoupled from the mechanisms implementing the adaptive behaviour of the applications, applications should externalise both state information and the adaptive mechanisms they support and the adaptation control mechanism should allow modifications without the need for re-implementation of either the application or the support platform. This thesis presents the design of a platform derived from the aforementioned re- quirements. This platform utilises a policy based mechanism for controlling adaptation. Based on the particular requirements of adaptive context-aware applications a new pol- icy language is defined derived from Kowalsky’s Event Calculus logic programming formalism. This policy language allows the specification of policy rules where condi- tions are defined through the expression of temporal relationships between events and entities that represent duration (i.e. fluents). A prototype implementation of this design allowed the evaluation of the features offered by this platform. This evaluation reveals that the platform can support coordinated adaptation with acceptable performance cost.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Architektur vernetzter Systeme. Seminar

This technical report comprises student papers within assignments for the seminar ``Architektur vernetzter Systeme\u27\u27. It took place at the Institute of Telematics of the University of Karlsruhe in summer 1999. Main topics for discussion contained CORBA extensions, tools and systems for mobile applications and also optimization concepts for large distributed systems

Improving Context Recognition In Ubiquitous Computing Environments

Ziel dieser Arbeit ist es, kontextverarbeitende Anwendungen einer ubiquitären Informationsumgebung, systematisch umzustrukturieren und zu erweitern, so dass eine signifikante Verbesserung in der Erkennung von Kontexten erreicht werden kann. Dazu wurde das Konzept des systematischen Kontextmanagements eingeführt, das eine neue Schicht innerhalb kontextverarbeitender Systeme bildet. Voraussetzung für effiziente Qualitätssicherungsmechanismen ist eine systematische und formale Ausgestaltung der Repräsentation, Verarbeitung und Kommunikation von Kontexten. Ein solches formales Modell einer ubiquitären Informationsumgebung wurde hier eingeführt. Es bildet die Grundlage des Qualitätsmanagements für Kontexte. Der zentrale Beitrag dieser Arbeit ist ein Qualitätsmanagementsystem für Kontexte auf der Basis von Kontextattributen. Attribute sind dabei allgemeine Eigenschaften von Kontextdaten, welche von der semantischen Bedeutung, die Kontexte für die Anwendungen einer ubiquitären Informationsumgebung haben, unabhängig sind. Das vorgestellte Modell definiert vier solche Attribute: das Kontextalter, die räumliche Herkunft des Kontextes, die Verlässlichkeit der Kontextinformation und die informationelle Abhängigkeit von Kontexten. Für jedes dieser Attribute werden konkrete Algorithmen und Verfahren eingeführt, welche die quantitative Beurteilung der Qualität einer Kontextinformation erlauben. Diese werden innerhalb der neu eingeführten Kontextmanagementschicht in einem Qualitätsfilter umgesetzt. Durch die Filterkomponente erhalten alle Artefakte die Möglichkeit, dynamisch die eingehenden Kontexte auf der Basis ihrer Qualitätsmaße zu filtern und so ihre eigene Dienstqualität zu verbessern. Im Ergebnis konnte, durch das hier vorgestellte Kontextmanagementsystem, eine Verbesserung der Erkennungsrate von Artefakten einer ubiquitären Informationsumgebung um bis zu 48% nachgewiesen werden.The goal of this work was to gain a significant improvement of context recognition rates of applications in ubiquitous computing environments by systematically restructuring and enhancing them. To reach this goal the concept of "Systematic Context Management" was introduced that forms a new processing layer in context sensitive systems. Systematic and formal definitions of context representation, context processing and context communication are required to build efficient quality management mechanisms. Such a formal model of a ubiquitous computing environment is introduced in this thesis. It represents the basis of a quality management system for context data. The central contribution of this work is a quality management system for contexts on basis of Context Attributes. Context Attributes are general attributes of context data that are independent from the semantically meaning of the context for an application in a ubiquitous computing environment. The presented model defines four Context Attributes: context age, spatial origin of contexts, context reliability and informational interdependence of contexts. For each of these attributes concrete algorithms and methods have been developed that allow for the quantitative assessment of context quality. These algorithms and methods are implemented in a quality-filter that is part of the newly introduced context management layer. With this filter component artefacts gain the ability to dynamically filter contexts on basis of their quality allowing for an improvement of the service quality of those artefacts. As a result of this work, it was possible to prove that by the introduction of the context management system developed in this thesis, the context recognition rate of artefacts in a ubiquitous computing environment can be improved by up to 48%

Programmable Mobile Networks

Existing mobile systems (e.g., mobile IP, mobile ATM and third generation cellular systems) lack the intrinsic architectural flexibility to deal with the complexity of supporting adaptive mobile applications in wireless and mobile environments. We believe that there is a need to develop alternative network architectures from the existing ones to deal with the demands placed on underlying mobile signaling, adaptation management and wireless transport systems in support of new mobile services, e.g. interactive multimedia and web access. In this paper we present the design, implementation and evaluation of mobiware, a middleware technology that enables the introduction of new services in mobile networks. Mobiware provides a toolkit that service providers can utilize to build services that can dynamically exploit the intrinsic scalable properties of mobile multimedia applications in response to time-varying mobile network conditions. Based on an open programmable networking paradigm, mobiware runs on mobile devices, wireless access points and mobile-capable switch/routers providing a set of open programmable interfaces and distributed objects for adaptive mobile networking. Mobiware is software-intensive and is built on CORBA and Java distributed object technologies. The source code for mobiware v1.0 is freely available (comet.columbia.edu/mobiware) for experimentation