As peer‐to‐peer (P2P) applications become more mature and demanding, there is a need for the underlying technologies to provide more adaptive characteristics, according to the application's requirements. In this paper, we present K‐Umbrella, a K‐ary distributed hash table (DHT), which allows us to efficiently route through the use of a fixed‐size routing table. By controlling a number of parameters, our algorithm is able to trade‐off between efficiency, fault‐tolerance and decentralisation according to the application's requirements. Through a detailed analysis of our algorithms and an extensive set of simulations, we will show that our protocol is able to offer an improved alternative to current DHT algorithms. Copyright © 2007 John Wiley & Sons, Ltd.

This article presents the AVATON system. AVATON aims at providing citizens with ubiquitous user-friendly services, offering personalized, location-aware (GSM Association, 2003), tourism-oriented multimedia information related to the area of the Aegean Volcanic Arc. Towards this end, a uniform architecture is adopted in order to dynamically release the geographic and multimedia content to the end users through enhanced application and network interfaces, targeting different device technologies (mobile phones, PDAs, PCs, and TV sets). Advanced positioning techniques are applied for those mobile user terminals that support them.

The technical and ethical issues of these systems proved to be their weak point. Systems that have no central point of control and distribute functions among all users seem better fit for sharing and distributing content. A solution has been proposed in the form of distributed hashtables (DHTs). This article proposes an alternative architecture for content distribution based on a new DHT routing scheme. The proposed architecture is well structured and self-organized in such a way as to be fault-tolerant and highly efficient. It provides users with content distribution and discovery capabilities on top of an overlay network. The novelty of our proposed architecture lies in its routing table which is maintained by each node and is of constant size, as opposed to other algorithms that are proportional to the network’s size (usually O(logN)). All operations in our architecture are of O(logbN) steps (entry, publishing, and lookups) and degrade gracefully as up-to-date information of the routing table decreases due to numerous node failures.

This article presents a location-based multimedia content delivery system (LMCDS) for monitoring purposes, which incorporates media processing with a decision support system and positioning techniques for providing the appropriate content to the most suitable users, in respect to user profile and location, for monitoring purposes. This system is based on agent technology (Hagen & Magendanz, 1998) and aims to promote the social welfare, by increasing the overall situation awareness and efficiency in emergency cases and in areas of high importance. Such a system can be exploited in many operational (public or commercial) environments and offers increased security at a low cost.

This article presents the AVATON system. AVATON aims at providing citizens with ubiquitous user-friendly services, offering personalized, location-aware (GSM Association, 2003), tourism-oriented multimedia information related to the area of the Aegean Volcanic Arc. Towards this end, a uniform architecture is adopted in order to dynamically release the geographic and multimedia content to the end users through enhanced application and network interfaces, targeting different device technologies (mobile phones, PDAs, PCs, and TV sets). Advanced positioning techniques are applied for those mobile user terminals that support them.