DHT-assisted probabilistic exhaustive search in unstructured P2P networks

Existing replication strategies in unstructured P2P networks, such as square-root principle based replication, can effectively improve search efficiency. How to get optimal replication strategy, however, is not trivial. In this paper we show, through mathematical proof, that random replication strategy achieves the optimal results. By randomly distributing rather small numbers of item and query replicas in the unstructured P2P network, we can guarantee perfect search success rate comparable to exhaustive search with high probability. Our analysis also shows that the cost for such replication strategy is determined by the network size of a P2P system. We propose a hybrid P2P architecture which combines a lightweight DHT with an unstructured P2P overlay to address the problems of network size estimating and random peer sampling. We conduct comprehensive simulation to evaluate this design. Results show that our scheme achieves perfect search success rate with quite small overhead. ©2008 IEEE

Enabling technologies for decentralized interpersonal communication

In the recent years the Internet users have witnessed the emergence of Peer-to-Peer (P2P) technologies and applications. One class of P2P applications is comprised of applications that are targeted for interpersonal communication. The communication applications that utilize P2P technologies are referred to as decentralized interpersonal communication applications. Such applications are decentralized in a sense that they do not require assistance from centralized servers for setting up multimedia sessions between users. The invention of Distributed Hash Table (DHT) algorithms has been an important, but not an inclusive enabler for decentralized interpersonal communication. Even though the DHTs provide a basic foundation for decentralization, there are still a number of challenges without viable technological solutions. The main contribution of this thesis is to propose technological solutions to a subset of the existing challenges. In addition, this thesis also presents the preliminary work for the technological solutions. There are two parts in the preliminary work. In the first part, a set of DHT algorithms are evaluated from the viewpoint of decentralized interpersonal communication, and the second part gives a coherent presentation of the challenges that a decentralized interpersonal communication application is going to encounter in mobile networks. The technological solution proposals contain two architectures and two algorithms. The first architecture enables an interconnection between a decentralized and a centralized communication network, and the second architecture enables the decentralization of a set of legacy applications. The first algorithm is a load balancing algorithm that enables good scalability, and the second algorithm is a search algorithm that enables arbitrary searches. The algorithms can be used, for example, in DHT-based networks. Even though this thesis has focused on the decentralized interpersonal communication, some of the proposed technological solutions also have general applicability outside the scope of decentralized interpersonal communication