Dan Chalmers

A survey of quality of service in mobile computing environments

The specification and management of quality of service (QoS) is important in networks and distributed computing systems, particularly to support multimedia applications. The advent of portable laptop computers, palmtops, and personal digital assistants with integrated communication capabilities facilitates mobile computing. This article is a survey of QoS concepts and techniques for mobile distributed computing environments. The requirements of current and future mobile computing are examined and the services required to support mobility are discussed. Generic concepts of QoS specification and management are overviewed followed by an analysis of the QoS work specific to mobile computing environments.

The state of peer-to-peer simulators and simulations

In this paper, we discuss the current situation with respect to simulation usage in P2P research, testing the available P2P simulators against a proposed set of requirements, and surveying over 280 papers to discover what simulators are already being used. We found that no simulator currently meets all our requirements, and that simulation results are generally reported in the literature in a fashion that precludes any reproduction of results. We hope that this paper will give rise to further discussion and knowledge sharing among those of the P2P and network simulation research communities, so that a simulator that meets the needs of rigorous P2P research can be developed

Map adaptation for users of mobile systems

Display characteristics, network Quality of Service, and the user’s current task all exhibit a wide range of variation when users interact with mobile and ubiquitous devices. It is desirable to enable applications to adapt to these variations. The user’s experience in interacting with the application can be significantly enhanced by adapting the data presented. However, we find that naive degradation of data can quickly result in an unacceptable presentation. In this paper we present a means of describing compound documents and preferences according to the semantics of the data, and an algorithm for performing a selection amongst the offered data based on these descriptions. Our model of the user’s preferences is more descriptive than most common specifications used for Webbased applications. These have been implemented for a map viewing application, along with application level network resource management. We present test results for adapting to network bandwidth and a download deadline. We show the technique is applicable over two orders of magnitude in bandwidth variation, and successful in meeting deadlines. By degrading the data presented in sympathy with the user’s needs, the degradation has less impact on the user for any given benefit in download time than arbitrary selection.

QoS and Context Awareness for Mobile Computing

Systems must support context awareness for mobile applications to permit adaptation to heterogeneity of hosts and networks, and variations in the users environment. We believe that context aware management of resources provides the most reliable basis for managing the non-deterministic behaviour of mobile systems.

A framework for contextual mediation in mobile and ubiquitous computing applied to the context-aware adaptation of maps

Context has many aspects, which may vary widely, such as the device, environment and user. The perception of data in different contexts also varies widely. We present a new, flexible approach to meeting needs and limits arising from context: contextual mediation. In this paper limits are defined as goals over managed system resources. These can be met by the selection of data, taking into account preferences over its semantic and syntactic properties. The specification of this selection is presented in detail and the supporting framework is described. We illustrate our description with examples from a context-aware map application and present experimental results and experiences which demonstrate that contextual mediation enhances the usability of the application in restrictive contexts of use.

Reconciling privacy and security in pervasive computing: the case for pseudonymous group membership

In this paper, we outline an approach to the identification of entities for access control that is based on the membership of groups, rather than individuals. By using group membership as a level of indirection between the individual and the system, we can increase privacy and provide incentives for better behaviour. Privacy comes from the use of pseudonyms generated within the group and which can be authenticated as belonging to the group. The incentives for better behaviour come from the continuous nature of groups - members may come and go, but the group lives on, and groups are organised so as to ensure group-longevity, and prevent actions which may harm the groups reputation. We present a novel pseudonym generation mechanism suitable for use in groups without a centralised administration. Finally, we argue that the use of group membership as the basis for formulating policies on interaction is more efficient for disconnected operation, facilitating proxies and the efficient storage of revoked membership and distrusted organisations within bloom filters for small memory footprints.

Sensing and Systems in Pervasive Computing

Focus on issues and principles in context awareness, sensor processing and software design (rather than sensor networks or HCI or particular commercial systems).Designed as a textbook, with readings and lab problems in most chapters.Focus on concepts, algorithms and ideas rather than particular technologies.

Composing software services in the pervasive computing environment: Languages or APIs?

The pervasive computing environment will be composed of heterogeneous services. In this work, we have explored how a domain specific language for service composition can be implemented to capture the common design patterns for service composition, yet still retain a comparable performance to other systems written in mainstream languages such as Java. In particular, we have proposed the use of the method delegation design pattern, the resolution of service bindings through the use of dynamically adjustable characteristics and the late binding of services as key features in simplifying the service composition task. These are realised through the Scooby language, and the approach is compared to the use of APIs to define adaptable services.

The Fans United will Always be Connected: Building a Practical DTN in a Football Stadium

Football stadia present a difficult environment for the deployment of digital services, due to their architectural design and the capacity problems from the numbers of fans. A delay tolerant network (DTN) is a viable solution to this problem. We present preliminary results from deploying an Android app building an ad hoc network amongst the attendees at matches at Brighton and Hove Albion’s AMEX stadium, so as to share the available capacity and supply digital services to season ticket holders. We describe the protocol, how we engaged our users in service design so that the app was attractive to use and the problems we encountered in using Android. Initial results show that there is interest in the services provided and that the DTN is successful in providing connectivity.

Are your friends who they say they are?: data mining online identities

How sure are you that your friends are who they say they are? In real life, unless you are the target of some form of espionage, you can usually be fairly certain that you know whom your friends are because you have a history of shared interests and experiences. Likewise, most people can tell, just by using common sense, if someone is trying to sell them on a product, idea, or candidate. When we interact with people face-to-face, we reevaluate continuously whether something just seems off based on body language and other social and cultural cues.