Abstract. Context-aware computing is a central concept in ubiquitous computing and many suggestions for context-aware technologies and applications have been proposed. There is, however, little evidence on how these concepts and technologies play out in a real-world setting. In this paper we describe and discuss our experiences from an ongoing deployment of a suite of context-aware technologies and applications in a hospital environment, including a context-awareness infrastructure, a location tracking system, and two context-aware applications running on interactive wall displays and mobile phones. Based on an analysis of the use of these systems, we observe that many of the ideas behind context-aware computing are valid, and that the context-aware applications are useful for clinicians in their work. By reflecting on the nature of the designed context-aware technologies, we present a model which states that the triggering of context-awareness actions depend upon the accuracy of the sensed context information, the degree to which you know which action to perform in a given situation, and the consequence of performing the action.

Abstract. Gossip-based information dissemination protocols are considered easy to deploy, scalable and resilient to network dynamics. Loadbalancing is inherent in these protocols as the dissemination work is evenly spread among all nodes. Yet, large-scale distributed systems are usually heterogeneous with respect to network capabilities such as bandwidth. In practice, a blind load-balancing strategy might significantly hamper the performance of the gossip dissemination.This paper presents HEAP, HEterogeneity-Aware gossip Protocol, where nodes dynamically adapt their contribution to the gossip dissemination according to their bandwidth capabilities. Using a continuous, itself gossip-based, approximation of relative bandwidth capabilities, HEAP dynamically leverages the most capable nodes by increasing their fanout, while decreasing by the same proportion that of less capable nodes. HEAP preserves the simple and proactive (churn adaptation) nature of gossip, while significantly improving its effectiveness. We extensively evaluate HEAP in the context of a video streaming application on a testbed of 270 PlanetLab nodes. Our results show that HEAP significantly improves the quality of the streaming over standard homogeneous gossip protocols, especially when the stream rate is close to the average available bandwidth.

Abstract. Contemporary object-oriented programming seeks to enable distributed computing by accessing remote objects using blocking remote procedure calls. This technique, however, suffers from several drawbacks because it relies on the assumption of stable network connections and synchronous method invocations. In this paper we present an approach to support distributed programming, which rely on local object replicas keeping themselves synchronized using an underlying peer-to-peer infrastructure. We have termed our approach Peer-to-peer Distributed Shared Objects (PDSO). This PDSO approach has been implemented in the DOLCLAN framework. An evaluation demonstrates that DOLCLAN can be utilized to create a real distributed collaborative system for ad-hoc collaboration in hospitals, which demonstrates that the approach can support the creation of non-trivial distributed applications for pervasive computing.

Contemporary distributed collaborative systems tend to utilize either a client-server or a pure peer-to-peer paradigm. A client-server solution may potentially spawn direct connections between the clients to offload the server thereby creating a hybrid architecture. A pure peer-to-peer paradigm may on the other hand fully eliminate the need for a server. However, some situations call for the strengths of both approaches without relying on either of them. A system might both be used in environments where an infrastructure is present and in environments where it is not. In this paper we present an architecture and early implementation of a system capable of adapting to its operating environment, choosing the best fit combination of the client-server and peerto-peer architectures. The architecture creates a seamless integration between a centralized hybrid architecture and a decentralized architecture, relying on what we have termed Peer-to-peer Distributed Shared Objects (PDSO). The proposed solution has been implemented and early evaluation has begun. Furthermore, the approach has been utilized to create a real distributed collaborative system for collaboration in hospitals.

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