Taxonomy of P2P Applications

Peer-to-peer (p2p) networks have gained immense popularity in recent years and the number of services they provide continuously rises. Where p2p-networks were formerly known as file-sharing networks, p2p is now also used for services like VoIP and IPTV. With so many different p2p applications and services the need for a taxonomy framework rises. This paper describes the available p2p applications grouped by the services they provide. A taxonomy framework is proposed to classify old and recent p2p applications based on their characteristics

Optimally Efficient Prefix Search and Multicast in Structured P2P Networks

Searching in P2P networks is fundamental to all overlay networks. P2P networks based on Distributed Hash Tables (DHT) are optimized for single key lookups, whereas unstructured networks offer more complex queries at the cost of increased traffic and uncertain success rates. Our Distributed Tree Construction (DTC) approach enables structured P2P networks to perform prefix search, range queries, and multicast in an optimal way. It achieves this by creating a spanning tree over the peers in the search area, using only information available locally on each peer. Because DTC creates a spanning tree, it can query all the peers in the search area with a minimal number of messages. Furthermore, we show that the tree depth has the same upper bound as a regular DHT lookup which in turn guarantees fast and responsive runtime behavior. By placing objects with a region quadtree, we can perform a prefix search or a range query in a freely selectable area of the DHT. Our DTC algorithm is DHT-agnostic and works with most existing DHTs. We evaluate the performance of DTC over several DHTs by comparing the performance to existing application-level multicast solutions, we show that DTC sends 30-250% fewer messages than common solutions

Fluid learning: vision for lifelong learning in 2030

This paper provides a vision of what we term ‘fluid learning’ through which autonomous learners make choices about their own learning. This vision is critical because it equips European citizens to live in a global context where knowledge and work is changing so rapidly that people have to learn continually. Fluid learning is suited to a world that has seen a radical change in cultural perceptions of learner agency and learner-teacher roles, associated with changes in technology. After completing compulsory education, the focus of each learner moves from learning pre-defined knowledge to filling gaps between areas of knowledge, integrating different areas of expertise, as well as learning new knowledge. People do not turn automatically to formal institutions for large blocks of learning. Instead they consider it natural to make use of open learning resources and open courses, making their own decisions about what to learn, when and how. Learners naturally employ open learning practices, creating new knowledge for future learners to benefit from. They expect to contribute to the learning of others as well as learning themselves, viewing themselves as the experts in their own situation. In some cases they may elect to take a short formal course, but this is always for a specific reason rather than as a cultural norm. Rather than managing multiple identities in the different groups/communities to which they belong, they see their unique identity as a unifying factor that integrates their activities in various groups, including work and leisure groups that they move easily between. In doing so they accrue new knowledge, integrating it with their current understanding, such that their expertise changes dynamically to match their current needs. The vision requires significant cultural change in European society by 2030

Uncertainty and risk: politics and analysis

In environmental and sustainable development policy issues, and in infrastructural megaprojects and issues of innovative medical technologies as well, public authorities face emergent complexity, high value diversity, difficult-to-structure problems, high decision stakes, high uncertainty, and thus risk. In practice, it is believed, this often leads to crises, controversies, deadlocks, and policy fiascoes. Decision-makers are said to face a crisis in coping with uncertainty. Both the cognitive structure of uncertainty and the political structure of risk decisions have been studied. So far, these scientific literatures exist side by side, with few apparent efforts at theoretically conceptualizing and empirically testing the links between the two. Therefore, this exploratory and conceptual paper takes up the challenge: How should we conceptualize the cognitive structure of uncertainty? How should we conceptualize the political structure of risk? How can we conceptualize the link(s) between the two? Is there any empirical support for a conceptualization that bridges the analytical and political aspects of risk? What are the implications for guidelines for risk analysis and assessment

Designing for interaction

At present, the design of computer-supported group-based learning (CS)GBL) is often based on subjective decisions regarding tasks, pedagogy and technology, or concepts such as ‘cooperative learning’ and ‘collaborative learning’. Critical review reveals these concepts as insufficiently substantial to serve as a basis for (CS)GBL design. Furthermore, the relationship between outcome and group interaction is rarely specified a priori. Thus, there is a need for a more systematic approach to designing (CS)GBL that focuses on the elicitation of expected interaction processes. A framework for such a process-oriented methodology is proposed. Critical elements that affect interaction are identified: learning objectives, task-type, level of pre-structuring, group size and computer support. The proposed process-oriented method aims to stimulate designers to adopt a more systematic approach to (CS)GBL design according to the interaction expected, while paying attention to critical elements that affect interaction. This approach may bridge the gap between observed quality of interaction and learning outcomes and foster (CS)GBL design that focuses on the heart of the matter: interaction