Showing papers by "Nigel Davies published in 1998"

Exploiting Context in HCI Design for Mobile Systems

Abstract: The last five years has seen a shift in the nature of mobile computers. The development of increasingly powerful laptop computer systems has been mirrored by the production of a range of small computational devices. The increased prominence of these devices outlined a number of distinct research challenges. These challenges have tended to focus on extending the utility of these devices using new forms of interaction; techniques to overcome display limitations or improvements in the general ergonomics of these devices. The merging of these devices with existing telecommunication services and the production of devices that offer connections to other systems presents yet another set of research challenges in terms of the development of cooperative multi-user applications.

L 2 imbo: a distributed systems platform for mobile computing

Abstract: Mobile computing environments increasingly consist of a range of supporting technologies offering a diverse set of capabilities to applications and end-systems. Such environments are characterised by sudden and dramatic changes in the quality-of-service (QoS) available to applications and users. Recent work has shown that distributed systems platforms can assist applications to take advantage of these changes in QoS and, more specifically, facilitate applications to adapt to their environment. However, the current state-of-the-art in these platforms reflects their fixed network origins through their choice of synchronous connection-oriented communications paradigms. In this paper we argue that these paradigms are not well suited to operation in the emerging mobile environments. Furthermore, we offer an alternative programming paradigm based on tuple spaces which, we believe, offers a number of benefits within a mobile context. The paper presents the design, implementation and evaluation of a new platform based on this paradigm.

Developing a Context Sensitive Tourist Guide

Abstract: The GUIDE project is investigating the provision of context-sensitive mobile multimedia computing support for city visitors. In essence, the project is developing systems and application-level support for hand-portable multimedia end-systems which provide information to visitors as they navigate an appropriately networked city. The endsystems being developed are context-sensitive, i.e. they have knowledge of their users and of their environment including, most importantly, their physical location. This information is used to tailor the system's behaviour in order to provide users with an intelligent visitor guide.

Supporting adaptive multimedia applications through open bindings

Abstract: In order to support multimedia applications in mobile environments, it will be necessary for applications to be aware of the underlying network conditions and also to be able to adapt their behaviour and that of the underlying platform. This paper focuses on the role of middleware in supporting such adaptation. In particular, we investigate the role of open implementation and reflection in the design of middleware platforms such as CORBA. The paper initially extends CORBA with the concept of explicit binding, where path of communication between objects is represented as first class objects. We then introduce the concept of open bindings which support inspection and adaptation of the path of communications. An implementation of open bindings is described, based on the Ensemble protocol suite from Cornell University.

Supporting Collaboration in Mobile-Aware Groupware

Abstract: This paper builds on the experiences gained from the extensive work carried out during the MOST project [MOST,95]. This project investigated the use of mobile technologies to support multimedia collaboration between highly mobile field engineers in the safety critical domain of the U.K. power distribution industry. The MOST team developed a prototype distributed groupware application which was arguably the first collaborative mobile application ever built that was capable of adaption in a mobile environment [Cheverst,94]. The application was designed as an expandable toolkit comprising a number of modules including a shared GIS module. This module enabled groups of field engineers to perform spatially-aware collaboration by supporting the display and annotation of network schematics across groups. The MOST application was evaluated by real end-users in a trial scenario using the GSM service for communications. This evaluation provided a valuable set of implications regarding the development of distributed groupware in conjunction with mobile technologies.

Developing Interfaces for Collaborative Mobile Systems

Abstract: This paper describes the issues encountered when developing user interfaces for collaborative multimedia applications designed for operation in unreliable mobile networking environments. To provide end-users with some degree of dependability applications need to provide increased levels of user-awareness in order to enable users to adapt their style of interaction to match the current quality of communications. The application described in this paper achieves this by presenting users with graphical feedback when the constraints imposed by the network violate the collaborating groups' various communications requirements. Because traditional distributed development platforms tend to mask detailed network information from reaching the application the development platform was enhanced to enable the flow of information between the network and application level services and vice versa.

Supporting adaptive video applications in mobile environments

Abstract: The transmission of digital video over wireless networks is becoming a reality: it is now possible to construct working prototype systems which illustrate the benefits to be accrued from the integration of mobile computing and digital video. However, systems which deploy video in mobile environments must be able to adapt to changes in the quality of service of their underlying communications channel. The authors focus on the practical applications and implications of supporting adaptive video in mobile environments. In particular, we describe a testbed which supports multicast transmission of stored and live video sequences over both WaveLAN and GSM technologies. The testbed employs H.263 and MPEG encoding techniques and enables clients to freely roam between heterogeneous networks while maintaining video connectivity.

A CORBA-based Proxy Architecture for Mobile Multimedia Applications

Abstract: In many cases users of mobile computers wish to have the same applications running and to have access to the same information as they would when connected to a fixed network. Such transparency is difficult to realise given the differences in the fundamental characteristics of wired and wireless links. These differences, apparent in variations in parameters such as delay, throughput and error rate can have a significant impact on demanding applications such as those which exploit multimedia communications. To overcome these problems, application requirements have to be adapted to match the capabilities of the wireless communication link. One general method of achieving this is the introduction of one or more proxies between the distributed components. This paper presents a generalised architecture for installing and managing proxies in the network in order to enable applications to continue operation in the face of variations in quality of service. The developed architecture is based on the CORBA standard to improve flexibility and acceptance.

Software architecture for adaptive distributed multimedia systems

Abstract: To support multimedia applications in mobile environments, it will be necessary for applications to be aware of the underlying network conditions and also to be able to adapt their behaviour and that of the underlying platform. This paper focuses on the role of middleware in supporting such adaptation. In particular, we investigate the role of open implementation and reflection in the design of middleware platforms such as CORBA. The paper initially extends CORBA with the concept of explicit binding, where path of communication between objects is represented as first class objects. We then introduce the concept of open bindings which support inspection and adaptation of the path of communications. An implementation of open bindings for adaptive continuous-media interaction is described using the example of adaptive video-on-demand for mobile environments.

Supporting video in heterogeneous mobile environments

Abstract: High quality digital wireless networks and advances in multimedia compression schemes now permit the transmission of video streams over mobile networks. This opens up video communications to a new range of mobile users. We present our experiences of integrating very-low-bit-rate video encoding into a heterogeneous mobile environment as part of an ongoing project to provide multimedia support for the emergency services. This paper focuses on the features required to enable open working between a variety of applications, end-systems and networks and the performance of a very low bit rate encoder.

An asynchronous distributed systems platform for heterogeneous environments

Abstract: Since its introduction over a decade ago the tuple space paradigm has attracted interest from the distributed systems community. Despite being developed for shared memory parallel architectures, the simplicity and elegance of the model has led researchers to attempt to realise it in loosely coupled distributed environments. This paper argues that these attempts have largely failed due to their selection of inappropriate target domains, lack of multicast support and failure to operate in heterogeneous environments. We present the design and implementation of a new tuple space platform engineered using IP multicast. The platform is designed to support complex distributed applications such as groupware and mobile applications, operates over a range of end-systems and networks and offers performance comparable to existing RPC based platforms even in tests designed to benefit the RPC paradigm.

Software architecture for adaptive distributive multimedia systems.

Abstract: To support multimedia applications in mobile environments, it will be necessary for applications to be aware of the underlying network conditions and also to be able to adapt their behaviour and that of the underlying platform. This paper focuses on the role of middleware in supporting such adaptation. In particular, we investigate the role of open implementation and reflection in the design of middleware platforms such as CORBA. The paper initially extends CORBA with the concept of explicit binding, where path of communication between objects is represented as first class objects. We then introduce the concept of open bindings which support inspection and adaptation of the path of communications. An implementation of open bindings for adaptive continuous-media interaction is described using the example of adaptive video-on-demand for mobile environments.

Supportin Adaptive Video tions in Mobile Environments

Abstract: The transmission of digital video over wireless networks is becoming a reality: it is now possible to construct working prostrate the benefits to be accrued from the integration of mobile totype sys computing and digital video. However, systems which deploy video in mobile environments must be able to adapt to changes in the quality of service of their underlying communications channel. In this article the authors focus on the practical applications and implications of supporting adaptive video in mobile environments. In particular, we describe a testbed which supports multicast transmission of stored and live video sequences over both WaveLAN and GSM technologies. The testbed employs H.263 and MPEG encoding techniques and enables clients to freely roam between heterogeneous networks while maintaining video connectivity. ABS explores the issue of mobile video adaptation in more detail and presents a brief summary of existing work in the area from a computer science perspective. The section after that describes our testbed in depth. We then present an analysis of our experiences of developing and using the testbed, and the last section contains our concluding remarks.