Abstract

Peer-to-peer (P2P) systems are characterised by a wide disparity in peer resources and capabilities. In particular, a number of measurements on deployed P2P systems show that peer stability (e.g. uptime) varies by several orders of magnitude between peers. In this paper, we introduce a peer utility metric and construct a self-organising P2P topology based on this metric that allows the efficient discovery of stable peers in the system. We propose and evaluate a search algorithm and we show that it achieves significantly better performance than random walking. Our approach can be used by certain classes of applications to improve the availability and performance of system services by placing them on the most stable peers, as well as to reduce the amount of network traffic required to discover and use these services. As a proof-ofconcept, we demonstrate the design of a naming service on the gradient topology. 1

Abstract. Middleware supporting event-based communication is widely recognized as being well suited to mobile applications since it naturally accommodates a dynamically changing population of interacting entities and the dynamic reconfiguration of the connections between them. STEAM is an event-based middleware designed for use in ad hoc networks. STEAM differs from other event-based middleware in that its architecture does not rely on the presence of any separate infrastructure, event notification filters are distributed, and filtering may be applied to functional and non-functional attributes. In particular, filters may be applied to either the subject or the content of an event notification, or to non-functional attributes, such as location and time. Filters may be used to define geographical areas within which event notifications are valid, thereby bounding the propagation of these notifications. Such proximity-based filtering represents a natural way to filter events of interest in mobile applications. This paper describes the architecture and implementation of STEAM and its use of proximity-based filtering. In particular, we show how proximity-based filtering can be used to reduce the number of events delivered to collaborative mobile applications.

As event-based middleware is currently being applied for application component integration in a range of application domains, a variety of event services have been proposed to address different application requirements. This paper presents a survey of existing event systems structured as a taxonomy of distributed event-based programming systems. A taxonomy is a classification that allows different examples of some generic type to be systematically arranged in groups or categorised according to established criteria. The taxonomy presented in this paper is structured as a hierarchy of the properties of a distributed eventbased programming system and may be used as a framework to describe a distributed event-based programming system according to its properties. Our taxonomy identifies a set of fundamental properties of event-based programming systems and categorises them according to the event model and event service criteria. The event service is further classified according to its organisation and interaction model, as well as other functional and non-functional features. The event-based communication model is particularly useful in centralised and distributed applications that require one or more application components to react to a change in the state of another application component as it provides a one-to-many or many-to-many communication pattern [6][7][8][9]. Event-based communication is essentially asynchronous [10], [11] which results in a less tightly coupled communication relationship between application components compared to the traditional request/response communication model. Since it features anonymity, it is well suited for applications consisting of a possibly large number of anonymously interacting components, without having to rely on centralised control. Such communities of cooperating components are exploited in distributed systems where independent application components establish communication relationships dynamically over time in an unpredictable fashion. Index TermsEvent-based middleware is currently being applied for application component integration in many application domains including finance, telecommunications, smart environments, multimedia, avionics, health care, and entertainment [1,2,[12][13][14][15][16][17][18][19]. Moreover, with the widespread deployment and use of wireless technology, where communication relationships amongst heterogeneous application components [10] are established very dynamically during the lifetime of the components, event-based middleware will become even more prevalent as it addresses important application requirements of the wireless and hence mobile computing domain, including avoidance of long-lasting and hence potentially expensive connections, hiding of communication latency due to decoupled interaction phases, omission of centralised control, and heterogeneity. Both mobility and wireless networking represent key enabling technologies underlying the vision of ubiquitous computing, where interconnected computers will be embedded in a wide...

Recently sophisticated protocols for routing in ad hoc networks have been proposed, but there is still little work on service discovery in such volatile environments. In this paper a mobile agent-based scheme for service discovery in ad hoc networks is introduced. Mobile agents are traveling through the network, collecting the dynamically changing service information. The travel route and the number of travel agents are adjusted according to the information state and the change of network topology. In a quantitative analysis the proposed algorithm is compared with the flooding scheme. The usefulness of the approach is proved by an implementation for mobile devices using J2ME and Bluetooth.

This paper suggests a revision of the commonly used model of acceptance of technical tools (TAM) for analyzing employees' attitudes towards ICT-enabled public sector organizational transformation. TAM models focus too much on technology acceptance ignoring employees' resistance to change and the reasons for innovation failure. Empirical research has shown the importance to consider these factors in organizational change projects. Basing on the example of the implementation of an electronic record system in the state (Land) Brandenburg (Germany), the paper applies a quantitative methodology for addressing the question: To what extent can other factors, besides software-problems, explain the employees' resistance to change towards the implementation of the electronic record system? The results of our analysis show that in addition to the construct 'technology acceptance model' the variables: fear of losing work autonomy or in other words discretion, the perceived quality of information and the social influence significantly affect resistance to change. Long term analysis of the introduction of electronic systems in public organizations would improve the explanation power of our model enabling to examine the particular importance of these factors in different phases of the innovation process and to create appropriate interventions.

As event-based middleware is currently being applied for application component integration in a range of application domains, a variety of event services have been proposed to address different application requirements. This paper presents a survey of existing event systems structured as a taxonomy of distributed event-based programming systems. A taxonomy is a classification that allows different examples of some generic type to be systematically arranged in groups or categorised according to established criteria. The taxonomy presented in this paper is structured as a hierarchy of the properties of a distributed eventbased programming system and may be used as a framework to describe a distributed event-based programming system according to its properties. Our taxonomy identifies a set of fundamental properties of event-based programming systems and categorises them according to the event model and event service criteria. The event service is further classified according to its organisation and interaction model, as well as other functional and non-functional features. The event-based communication model is particularly useful in centralised and distributed applications that require one or more application components to react to a change in the state of another application component as it provides a one-to-many or many-to-many communication pattern [6][7][8][9]. Event-based communication is essentially asynchronous [10], [11] which results in a less tightly coupled communication relationship between application components compared to the traditional request/response communication model. Since it features anonymity, it is well suited for applications consisting of a possibly large number of anonymously interacting components, without having to rely on centralised control. Such communities of cooperating components are exploited in distributed systems where independent application components establish communication relationships dynamically over time in an unpredictable fashion. Index TermsEvent-based middleware is currently being applied for application component integration in many application domains including finance, telecommunications, smart environments, multimedia, avionics, health care, and entertainment [1,2,[12][13][14][15][16][17][18][19]. Moreover, with the widespread deployment and use of wireless technology, where communication relationships amongst heterogeneous application components [10] are established very dynamically during the lifetime of the components, event-based middleware will become even more prevalent as it addresses important application requirements of the wireless and hence mobile computing domain, including avoidance of long-lasting and hence potentially expensive connections, hiding of communication latency due to decoupled interaction phases, omission of centralised control, and heterogeneity. Both mobility and wireless networking represent key enabling technologies underlying the vision of ubiquitous computing, where interconnected computers will be embedded in a wide...

Abstract-Efficient use and re-use of traffic data depends on an ITS architecture that enables information sharing across a wide variety of intelligent transportation systems and applications. Existing ITS architectures, such as KAREN or the National ITS architecture, can be used to develop systems within a given framework thereby facilitating such intersystem integration. However, these architectures typically include assumptions regarding the overall organization of system functionality that prohibit integration of previously deployed systems without major reengineering. This paper presents a framework for an ITS architecture that has been designed for integrating novel as well as existing intelligent transportation systems and applications. The iTransIT framework supports a number of possible systems interaction paradigms and proposes a layered data model to facilitate data exchange between systems with diverse service requirements and functional organizations. These data layers are defined within a common context model, may be distributed across multiple systems, and exploit the overlapping temporal and spatial aspects of information generated and used by both legacy and future systems.