Showing papers by "Nigel Davies published in 1995"

A Network Emulator to Support the Development of Adaptive Applications

Abstract: Mobile applications must operate in environments in which the network connectivity, input/output devices, power and contextual information available to them may all vary. Applications which react to changes in these parameters in order to ensure continuing service to the user are termed adaptive applications and have recently emerged as an area of intense research activity. In this paper we describe the design and implementation of a network emulator which facilitates research in this field by allowing applications to be exposed to user controlled fluctuations in network service. The emulator can be used with any application which uses UDP and requires only minimal changes to the application or, it may be used with applications written using the ANSAware distributed systems platform in which case no changes are necessary to the application. The design and implementation of the emulator are described in this paper as our experiences of using the emulator to model three distinct types of wireless network: GSM, an analogue cellular service and a simple shared radio channel. The source code for the emulator is freely available and instructions on obtaining the code are also included.

Experiences of using RM-ODP to build advanced mobile applications

Abstract: Significant advances have been made in recent years in tackling the problem of heterogeneity in distributed systems with ISO/ITU-T standards for a Reference Model for Open Distributed Processing (RM-ODP) now approaching international agreement. It is important, however, that such standards are responsive to new developments in computer and communications technologies. This paper reports on experiences of applying RM-ODP technology and mobile communications in supporting field workers in the electricity industry. The results of the study show that the framework provided by RM-ODP offers a strong basis for the development of mobile applications. Particular benefits are gained from the object-oriented modelling approach, the model of selective distribution transparency and the concept of QoS-managed bindings in RM-ODP. However, our experiences indicate that care must be taken in the development of RM-ODP compliant platforms particularly with respect to the communications infrastructure.

Distributed systems support for mobile applications

Abstract: Future computer environments will include mobile computers which will either be disconnected, weakly interconnected by low speed wireless networks such as GSM, or fully interconnected by high speed networks ranging from Ethernet to ATM. Two key characteristics of such environments are: a heterogeneous processing environment; and rapid and massive fluctuations in the quality of service provided by the underlying communication infrastructure. The first of these issues, i.e. heterogeneity, can be addressed by exploiting emerging distributed systems standards such as the International Standards Organisation Reference Model for Open Distributed Processing (RM-ODP), the Open Software Foundation's Distributed Computing Environment (OSF-DCE) or the Object Management Group's Common Object Request Broker Architecture (OMG-CORBA). Such standards provide applications with uniform computational models for accessing services and enables them to operate over a variety of processor/operating system configurations. The second of these issues, QoS fluctuations, is, we believe, one of the most fundamental problems in the field of mobile computing. We consider this issue and propose extensions to emerging distributed systems standards to support mobile computing.

A Collaborative Multimedia Application for a Mobile Environment

Abstract: With recent advances in portable computers and wireless networks, it is now feasible to provide sophisticated IT support for a range of mobile workers in areas such as the police, ambulance services and the utilities industries. However, to date, such support has been limited to providing remote access to central facilities such as e-mail and databases. This paper focuses on extending this level of support to include collaborative applications requiring multimedia communications. Such applications make considerable demands on the underlying systems infrastructure. More specifically, the paper discusses the role of such collaborative multimedia applications in supporting field workers in the electricity industry. A prototype conferencing application is described which enables field engineers to jointly view and annotate network diagrams and maps produced by a Geographical Information System. Voice communications is also provided to enable discussions to take place. The underlying distributed systems platform is also presented. The application has been successfully demonstrated over GSM.