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Peer-to-Peer Algorithms in Wireless Ad-Hoc Networks for Disaster Management – GRK-Wiki

Peer-to-Peer Algorithms in Wireless Ad-Hoc Networks for Disaster Management

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This dissertation addresses the challenge of reaching efficiency, scalability and fault-tolerance by P2P algorithms for resource-limited and irregular WAHNs where a spatially correlated group of nodes may crash simultaneously. In particular, we consider a fault-tolerant replication scheme for data-centric storage for supplying data survivability and a self-organized, efficient calculation of localized data aggregates for solving the consensus problem.

There exists a variety of algorithms that address issues of scalability, fault tolerance and self-organization in wired networks. However, they are inadequate for the addressed systems, as physical communication in WAHNs causes’ bottleneck in Peer-to-Peer algorithms designed for the wired systems. Moreover, replication in wired P2P algorithms that abstract from geographical location of replicas cannot supply data survivability in DM scenarios in WAHNs.

Incorporating information on geographical location of nodes is a recognized way to increase the efficiency and scalability of P2P applications in wireless networks. Locally available positions of nodes are used in existing solutions for location-aware WAHNs to reduce the communication overhead. However, information on the geographical area covered by the network is required for tasks of data and replica allocation in the target disaster scenarios.

We propose to efficiently construct new position information in a location-aware WAHN, where each node knows its own location and location of its direct neighbors. The new information are: 1) network area, which expresses the geographical area covered by the network, and 2) group membership, where each node belongs to exactly one group that is placed over the area of a maximum defined size. This new position information enable the use of the existing, scalable P2P data store in WAHNs (Geographical Hash Table), allow design of efficient fault-tolerant replication for the assumed fault model, increase efficiency of georouting and replica search, and allow to limit the geographical extent of activity of any distributed application, as we show using an example of data aggregation protocol.

Proposed protocols tolerate message loss and use local broadcast only. They are evaluated by simulation over irregular topologies following the node placement of the existing, large wireless ad-hoc networks, which contain both very sparse and very dense network parts. The protocols can be used in disaster management and environmental applications that collect, store and process data with use of wireless ad-hoc networks.

Supervisor: Prof. Dr. Alexander Reinefeld

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