Abstract. Various peer-to-peer (P2P) architectures for ad-hoc networks have been proposed over the last few years. Most of them are unstructured and use some form of flooding to locate content, because the physical constraints of the underlying network make the construction of arbitrary application-layer overlays impractical. In this paper, we study the problem of applying distributed hash tables (DHT) to ad-hoc networks. Our approach to efficiently lookup content in such networks exploits physical proximity of peers when establishing and maintaining the DHT based routing tables. The efficiency of our method is demonstrated by simulation of large networks.
Abstract. Research on Wireless Sensor Networks (WSNs) has developed highly optimized software environments fitting the limited hardware resource constraints of Motes. Unfortunately, these environments suffer from relatively complex programming models. Nowadays well known languages such as Java and optimized JVMs become available and simplify the application development for the Motes. Thus, we developed the Freemote Emulator which is a Java based emulator providing a lightweight emulation tool for emerging Java based Motes. It runs experiments in real time mixing real and emulated nodes. Its layered architecture and a set of predefined code templates allow developers to quickly produce runnable code for real and emulated nodes as well as predefined scenarios to help the newcomers to introduce into the system and WSNs. Our emulator provides as well a useful visualization tool based on a parametrizable slow down feature that helps to understand complex WSN behaviours and to debug tricky implementation problems. Finally, a single emulation can run on several computers, thus allowing programmers to conduct experiments with a pretty large number of emulated and real nodes.
The most important characteristics of mobile ad-hoc networks (MANETs) such as broadcast and multihop communication, limited resources (particularly energy) and physical proximity are often ignored in solutions being proposed for information lookup and distribution. Thus, many lookup approaches rely on unstructured algorithms using flooding techniques, while content distribution mechanisms frequently generate inefficient multicast trees without considering the presence of nodes that are involved only as relays and are not interested in the distributed content. In this chapter, the authors present a multicast algorithm designed to build efficient multicast trees in MANETs that strive to limit the number of relay nodes and transmissions required. This distribution infrastructure relies on a lightweight distributed hash table (DHT) specifically adapted to MANETs, and exploits the physical proximity of nodes and broadcast communication. The algorithmic efficiency and scalability are evaluated by means of simulations for various network sizes and configurations.
Multicast trees are used in a variety of applications, such as publish/subscribe systems or content distribution networks. Existing algorithms for ad-hoc networks typically produce multicast trees requiring many nodes to act as relays even though they are not part of the multicast group. In this paper, we propose an algorithm for building efficient multicast trees that strives to minimize the number of non-member relay nodes and the number of transmissions required to reach all the group members, and to balance the degree of members when acting as internal nodes of the multicast tree. Our algorithm relies upon a lightweight distributed hash table (DHT) to construct and optimize the multicast trees. We evaluate the efficiency and scalability of our algorithm by simulations with various network configurations and sizes.
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