Biblio

The popularity of P2P (Peer-To-Peer) systems is increased tremendously due to massive increase in the Internet based applications. Initially, P2P systems were mainly designed for wired networks but today people are using more wireless networks and therefore these systems are gaining popularity. There are many wireless networks available today and WMNs (Wireless Mess Networks) are gaining popularity due to hybrid structure. People are using structured P2P systems-based applications within perimeter of a WMN. Structured P2P WMNs will assist the community to fetch the relevant information to accomplish their activities. There are inherent challenges in the structured P2P network and increased in wireless environment like WMNs. Structured P2P systems suffer from many challenges like lack of content availability, malicious content distribution, poor search scalability, free riding behaviour, white washing, lack of a robust trust model etc. Whereas, WMNs have limitations like mobility management, bandwidth constraint, limited battery power of user's devices, security, maintenance etc. in remote/ forward areas. We exploit the better possibility of content availability and search scalability in this paper. We propose replication schemes based on the popularity of content for structured P2P system applications in community based WMNs. The analysis of the performance shows that proposed scheme performs better than the existing replication scheme in different conditions.

Atomic multicast is a communication primitive that delivers messages to multiple groups of processes according to some total order, with each group receiving the projection of the total order onto messages addressed to it. To be scalable, atomic multicast needs to be genuine, meaning that only the destination processes of a message should participate in ordering it. In this paper we propose a novel genuine atomic multicast protocol that in the absence of failures takes as low as 3 message delays to deliver a message when no other messages are multicast concurrently to its destination groups, and 5 message delays in the presence of concurrency. This improves the latencies of both the fault-tolerant version of classical Skeen's multicast protocol (6 or 12 message delays, depending on concurrency) and its recent improvement by Coelho et al. (4 or 8 message delays). To achieve such low latencies, we depart from the typical way of guaranteeing fault-tolerance by replicating each group with Paxos. Instead, we weave Paxos and Skeen's protocol together into a single coherent protocol, exploiting opportunities for white-box optimisations. We experimentally demonstrate that the superior theoretical characteristics of our protocol are reflected in practical performance pay-offs.

We seek to answer the following question: To what extent can we deduplicate replicated storage? To answer this question, we design ReDup, a secure storage system that provides users with strong integrity, reliability, and transparency guarantees about data that is outsourced at cloud storage providers. Users store multiple replicas of their data at different storage servers, and the data at each storage server is deduplicated across users. Remote data integrity mechanisms are used to check the integrity of replicas. We consider a strong adversarial model, in which collusions are allowed between storage servers and also between storage servers and dishonest users of the system. A cloud storage provider (CSP) could store less replicas than agreed upon by contract, unbeknownst to honest users. ReDup defends against such adversaries by making replica generation to be time consuming so that a dishonest CSP cannot generate replicas on the fly when challenged by the users. In addition, ReDup employs transparent deduplication, which means that users get a proof attesting the deduplication level used for their files at each replica server, and thus are able to benefit from the storage savings provided by deduplication. The proof is obtained by aggregating individual proofs from replica servers, and has a constant size regardless of the number of replica servers. Our solution scales better than state of the art and is provably secure under standard assumptions.

Real world wireless networks usually have diverse connectivity characteristics. Although existing works have identified replication as the key to the successful design of routing protocols for these networks, the questions of when the replication should be used, by how much, and how to distribute packet copies are still not satisfactorily answered. In this paper, we investigate the above questions and present the design of the Hybrid Routing Protocol (HRP). We make a key observation that delay correlations can significantly impact performance improvements gained from packet replication. Thus, we propose a novel model to capture the correlations of inter-contact times among a group of nodes. HRP utilizes both direct delays feedback and the proposed model to estimate the replication gain, which is then fed into a novel regret-minimization algorithm to dynamically decide the amount of packet replication under unknown network conditions. We evaluate HRP through extensive simulations. We show that HRP achieves up to 3.5x delivery ratio improvement and up to 50% delay reduction, with comparable and even lower overhead than state-of-art routing protocols.