1,721,017 research outputs found
Brief announcement: When you don't trust clients: Byzantine proposer fast Paxos
No full textState machine replication is a general approach for constructing fault-tolerant services, and a key protocol underlying state machine replication is consensus. The set of Byzantine failures is so large that it has been applied for masking the effects of compromised systems, and so Byzantine-tolerant consensus has been used to construct systems that are meant to ameliorate the effect of compromise (see [1] among others). In the Byzantine model, there is no trust among processes: any process can behave in an arbitrarily faulty manner. However, in multi-site systems, processes in the same administrative domain typically have a measure of mutual trust. This is because such processes share fate: for example, if a process in a domain is compromised, then other processes-perhaps all of them-can be compromised as well, and the local services they rely upon may be compromised. In [4], this observation was used to argue for the Mutually Suspicious Domain (MSD) model, in which there is mutual trust between processes in a domain, but no trust for inter-domain communication, i.e., processes within a domain must protect itself from possible uncivil behavior from processes in other domains. © 2011 Springer-Verlag
When you don't trust clients: Byzantine proposer fast Paxos
No full textWe derive a consensus protocol for a hybrid failure model. In this model, clients are Byzantine faulty and servers are crash faulty. We argue that this model is well suited to environments where the servers run within one administrative domain, and the clients run outside of this domain. Our consensus protocol, which is derived from crash Paxos, provides low latency for client requests, tolerates any number of (Byzantine) faulty clients, up to 1/3 (crash) faulty servers, and does not rely on computing costly signatures in the common case. It can be used to build state machine replication that provides a highly available service. © 2012 IEEE
Proving Redundancy In Decentralized Storage Networks
Get PDFProof of Storage (PoS) is a scheme that proves the data is stored honestly. PoS is the general term for a collection of related proofs. Such as proof of retrievability and proof of data possession. In recent years, various PoS variants have been proposed, each with advantages. However, there is no protocol for auditing between peers without involving third-party auditors. This thesis proposes a protocol which allows auditing between peers without third-part involved. The protocol is fully implemented with Go coding language and deployed on the Swarm test network. The designed protocol is mainly based on proof of retrievability, proof of data possession and proof of replication. The proposed protocol uses a challenge-response protocol to send messages between nodes in a decentralised file storage system. Experiments show that our idea is feasible.
After experimenting with different test nodes, the results show that the efficiency of our proposed protocol is related to the number of redundant data chunks owned by the challenger and prover in the same network.
If either challenger or prover holds a relatively small amount of data chunks, our proposed protocol will have better performance
The Case for Reconfiguration without Consensus: Comparing Algorithms for Atomic Storage
Get PDFWe compare different algorithms for reconfigurable atomic storage in the data-centric model. We present the first experimental evaluation of two recently proposed algorithms for reconfiguration without consensus and compare them to established algorithms for reconfiguration both with and without consensus.
Our evaluation reveals that the new algorithms offer a significant improvement in terms of latency and overhead for reconfiguration without consensus. Our evaluation also shows that reconfiguration without consensus, can obtain similar results to that of consensus-based reconfiguration, which relies on a stable leader. Moreover, the new algorithms also substantially reduces the overhead compared to consensus-based reconfiguration without a leader.
While our analysis confirms our intuition that batching reconfiguration requests serves to reduce the overhead of reconfigurations, our evaluation also shows that it is equally important to separate reconfigurations from read and write operations. Specifically, we found that using read and write operations to assist in completing concurrent reconfigurations is in fact detrimental to the reconfiguration performance
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Non-hierarchical dynamic protocol composition in Jgroup/ARM
No full textProtocol composition is a common approach to structure generic protocols used by networked applications, and typically a vertically layered approach is taken. This paper presents an alternative approach, where the protocol composition is a weakly-coupled set of protocol modules organized in a non-hierarchical structure. Protocol modules are dynamically constructed at runtime. The approach is designed for systems that involves multiple communicating entities and multicast style interactions are supported, making the approach suitable for building reliable network applications. The main advantage of the approach is that modules in the same composition communicate by direct interaction, whereas other frameworks typically use a vertically layered protocol stack, forcing all messages/events to pass through all intermediate layers introducing unnecessary delays.
A Framework for Experimental Validation and Performance Evaluation in Fault Tolerant Distributed System
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