René Meier

Exploiting Proximity in Event-Based Middleware for Collaborative Mobile Applications

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.

Discovery of stable peers in a self-organising peer-to-peer gradient topology

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-of-concept, we demonstrate the design of a naming service on the gradient topology.

A framework for integrating existing and novel intelligent transportation systems

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 inter-system 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.

On Event-Based Middleware for Location-Aware Mobile Applications

As mobile applications become more widespread, programming paradigms and middleware architectures designed to support their development are becoming increasingly important. The event-based programming paradigm is a strong candidate for the development of mobile applications due to its inherent support for the loose coupling between components required by mobile applications. However, existing middleware that supports the event-based programming paradigm is not well suited to supporting location-aware mobile applications in which highly mobile components come together dynamically to collaborate at some location. This paper presents a number of techniques including location-independent announcement and subscription coupled with location-dependent filtering and event delivery that can be used by event-based middleware to support such collaboration. We describe how these techniques have been implemented in STEAM, an event-based middleware with a fully decentralized architecture, which is particularly well suited to deployment in ad hoc network environments. The cost of such location-based event dissemination and the benefits of distributed event filtering are evaluated.

Primary-Context Model and Ontology: A Combined Approach for Pervasive Transportation Services

Advanced pervasive transportation services aim to improve the safety and efficiency of public and private transportation facilities, while reducing operating costs and improving the travel experience for drivers, passengers and other travellers. In order to achieve these goals, such services require access to context information from a myriad of distributed, heterogeneous intelligent transportation systems. A context management scheme that models information in a standard fashion is essential to support information sharing between individual systems, and higher-level information reasoning. This paper presents an ontology-based spatial context model, which takes a combined approach to modelling context information utilised by pervasive transportation services: the primary-context model facilitates interoperation across independent intelligent transportation systems, whereas the primary-context ontology enables pervasive transportation services to reason about shared context information and to react accordingly. The independently defined, distributed information is correlated based on its primary-context: location, time, identity, and quality of service. The primary-context model and ontology have been evaluated by modelling a car park system for a smart parking space locator service

Using aggregation for adaptive super-peer discovery on the gradient topology

Peer-to-peer environments exhibit a very high diversity in individual peer characteristics ranging by orders of magnitude in terms of uptime, available bandwidth, and storage space. Many systems attempt to exploit this resource heterogeneity by using the best performing and most reliable peers, called super-peers, for hosting system services. However, due to inherent decentralisation, scale, dynamism, and complexity of P2P environments, self-managing super-peer selection is a challenging problem. In this paper, decentralised aggregation techniques are used to reduce the uncertainty about system properties by approximating the peer utility distribution allowing peers to calculate adaptive thresholds in order to discover appropriate super-peers. Furthermore, a heuristic search algorithm is described that allows super-peers, above a certain utility threshold, to be efficiently discovered and utilised by any peer in the system.

High-bandwidth mesh-based overlay multicast in heterogeneous environments

In this paper we present MeshCast, a peer-to-peer (p2p) multicast protocol for applications requiring high bandwidth (such as live video streaming) from a server to a large number of receivers. Traditional tree-based approaches to overlay multicast inefficiently utilise the outgoing bandwidth of participating nodes and poorly adapt to node membership churn. In contrast, MeshCast is based on Chainsaw mesh-based approach to data delivery that better utilises bandwidth and provides excellent adaptation properties. In this paper we identify properties that enable mesh-based overlay multicast protocols to better utilise the available bandwidth and consequently support higher data stream rates in heterogeneous environments. MeshCast uses a gossip-based algorithm to adapt the overlay to peer heterogeneity, while still preserving the advantages of a mesh-based overlay. Our experiments show that MeshCast can support 68% higher stream rates and provides a 22% improvement in buffering delay over the recently proposed Chainsaw protocol for a heterogeneous node bandwidth distribution.

Communication paradigms for mobile computing

The widespread deployment and use of wireless data communications causes the need for middleware to interconnect the components that comprise a mobile application. Middleware for mobile computing must deal with the increased complexity that comes with a dynamically changing population of application components and the resulting dynamic reconfiguration of the connections between these components. This paper presents an overview of two communication paradigms that are well suited as the basis for middleware for mobile computing, namely the event-based communication model and proximity-based group communication.

Proximity-based service discovery in mobile ad hoc networks

Existing approaches to service discovery have been developed primarily for environments with a fixed network backbone and typically rely on centralized components being accessible to potential service clients at any given time. The characteristic lack of a designated service infrastructure in combination with the highly dynamic nature of the underlying network topology renders such discovery mechanisms unsuitable for mobile ad hoc environments. This paper presents an approach to the discovery of ad hoc services that exploits the fact that the relevance of such services is often limited to specific geographical scopes. Service providers define the areas (proximities) in which their services are available. Clients register interest in specific services and are subsequently informed whenever they enter a proximity within which these services are available. Since ad hoc services can be stationary or may be moving with the location of their mobile providers our approach supports discovery of services with fixed locations as well as of those that migrate with their providers. Our approach has been implemented as a push-based proximity discovery service and its evaluation demonstrates that it is well suited for highly dynamic networks as it maintains neither routes nor overlay network topologies.

Towards real-time middleware for vehicular ad hoc networks

Applications of inter-vehicle and vehicle-to-roadside communication that make use of vehicular ad hoc networks (VANETs) will often require reliable communication that provides guaranteed real-time message propagation. This paper describes an event-based middleware, called RT-STEAM. Unlike other event systems, RT-STEAM does not rely on a centralized event broker or look-up service while still supporting event channels providing hard real-time event delivery. RT-STEAM event filtering can be based on subject, content and/or proximity. To guarantee real-time communication, we exploit proximity-based event propagation to guarantee real-time constraints within the defined proximities only. The proximity within which real-time guarantees are available is adapted to maintain time bounds while allowing changes to membership and topology, typical of VANETs. This Space-Elastic Model of real-time communication is the first to directly address adaptation in the space domain to guarantee real-time constraints.