3,036 research outputs found
A Puff of Steem: Security Analysis of Decentralized Content Curation
Decentralized content curation is the process through which uploaded posts are ranked and filtered based exclusively on users\u27 feedback. Platforms such as the blockchain-based Steemit employ this type of curation while providing monetary incentives to promote the visibility of high quality posts according to the perception of the participants. Despite the wide adoption of the platform very little is known regarding its performance and resilience characteristics. In this work, we provide a formal model for decentralized content curation that identifies salient complexity and game-theoretic measures of performance and resilience to selfish participants. Armed with our model, we provide a first analysis of Steemit identifying the conditions under which the system can be expected to correctly converge to curation while we demonstrate its susceptibility to selfish participant behaviour. We validate our theoretical results with system simulations in various scenarios
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Valued Redundancy
Replicated objects increase distributed system performance and availability. An object is more valuable to the system if it contributes more to system performance (e.g. it is frequently accessed) and availability. Similarly, an object is less valuable if it is expensive to maintain (e.g. it is a large object). By replicating only the most valuable objects we use redundancy to maximize system performance and availability a t low cost. A simulation study of a distributed main-memory database shows substantial performance and availability gains with valued redundancy
Sustainable Fault-handling Of Reconfigurable Logic Using Throughput-driven Assessment
A sustainable Evolvable Hardware (EH) system is developed for SRAM-based reconfigurable Field Programmable Gate Arrays (FPGAs) using outlier detection and group testing-based assessment principles. The fault diagnosis methods presented herein leverage throughput-driven, relative fitness assessment to maintain resource viability autonomously. Group testing-based techniques are developed for adaptive input-driven fault isolation in FPGAs, without the need for exhaustive testing or coding-based evaluation. The techniques maintain the device operational, and when possible generate validated outputs throughout the repair process. Adaptive fault isolation methods based on discrepancy-enabled pair-wise comparisons are developed. By observing the discrepancy characteristics of multiple Concurrent Error Detection (CED) configurations, a method for robust detection of faults is developed based on pairwise parallel evaluation using Discrepancy Mirror logic. The results from the analytical FPGA model are demonstrated via a self-healing, self-organizing evolvable hardware system. Reconfigurability of the SRAM-based FPGA is leveraged to identify logic resource faults which are successively excluded by group testing using alternate device configurations. This simplifies the system architect\u27s role to definition of functionality using a high-level Hardware Description Language (HDL) and system-level performance versus availability operating point. System availability, throughput, and mean time to isolate faults are monitored and maintained using an Observer-Controller model. Results are demonstrated using a Data Encryption Standard (DES) core that occupies approximately 305 FPGA slices on a Xilinx Virtex-II Pro FPGA. With a single simulated stuck-at-fault, the system identifies a completely validated replacement configuration within three to five positive tests. The approach demonstrates a readily-implemented yet robust organic hardware application framework featuring a high degree of autonomous self-control
Detection and Prevention System towards the Truth of Convergence on Decision Using Aumann Agreement Theorem
AbstractThe Detection and Prevention system against many attacks has been formulated in Mobile ad hoc networks to secure the data and to provide the uninterrupted service to the legitimate clients. The formulation of opinion of neighbors or belief value or Trust value plays vital role in the detection system to avoid attacks. The attack detection system always extracts the behaviors of nodes to identify the attack patterns and prediction of future attacks. The False positives and false negatives plays vital role on identification of attackers accurately without any false positives and negatives .Our system uses the Aumann agreement theorem for convergence of Truth on opinion based on the bound of confidence value, such that truth consensus will maintained, The accuracy of system will be enhanced through this methodolog
Distributed Maintenance of Anytime Available Spanning Trees in Dynamic Networks
We address the problem of building and maintaining distributed spanning trees
in highly dynamic networks, in which topological events can occur at any time
and any rate, and no stable periods can be assumed. In these harsh
environments, we strive to preserve some properties such as cycle-freeness or
the existence of a root in each tree, in order to make it possible to keep
using the trees uninterruptedly (to a possible extent). Our algorithm operates
at a coarse-grain level, using atomic pairwise interactions in a way akin to
recent population protocol models. The algorithm relies on a perpetual
alternation of \emph{topology-induced splittings} and \emph{computation-induced
mergings} of a forest of spanning trees. Each tree in the forest hosts exactly
one token (also called root) that performs a random walk {\em inside} the tree,
switching parent-child relationships as it crosses edges. When two tokens are
located on both sides of a same edge, their trees are merged upon this edge and
one token disappears. Whenever an edge that belongs to a tree disappears, its
child endpoint regenerates a new token instantly. The main features of this
approach is that both \emph{merging} and \emph{splitting} are purely localized
phenomenons. In this paper, we present and motivate the algorithm, and we prove
its correctness in arbitrary dynamic networks. Then we discuss several
implementation choices around this general principle. Preliminary results
regarding its analysis are also discussed, in particular an analytical
expression of the expected merging time for two given trees in a static
context.Comment: Distributed Maintenance of Anytime Available Spanning Trees in
Dynamic Networks, Poland (2013
Permission-based fault tolerant mutual exclusion algorithm for mobile Ad Hoc networks
This study focuses on resolving the problem of mutual exclusion in mobile ad hoc networks. A Mobile Ad Hoc Network (MANET) is a wireless network without fixed
infrastructure. Nodes are mobile and topology of MANET changes very frequently and unpredictably. Due to these limitations, conventional mutual exclusion algorithms
presented for distributed systems (DS) are not applicable for MANETs unless they attach to a mechanism for dynamic changes in their topology.
Algorithms for mutual exclusion in DS are categorized into two main classes including token-based and permission-based algorithms. Token-based algorithms depend on circulation of a specific message known as token. The owner of the token has priority for entering the critical section. Token may lose during communications, because of link failure or failure of token host. However, the processes for token-loss detection and token regeneration are very complicated and time-consuming. Token-based algorithms are generally non-fault-tolerant (although some mechanisms are utilized to increase their level of fault-tolerance) because of common problem of single token as a single point of failure. On the contrary, permission-based algorithms utilize the permission of multiple nodes to guarantee mutual exclusion. It yields to high traffic when number of nodes is high. Moreover, the number of message transmissions and energy consumption increase in MANET by increasing the number of mobile nodes accompanied in every decision making cycle.
The purpose of this study is to introduce a method of managing the critical section,named as Ancestral, having higher fault-tolerance than token-based and fewer message
transmissions and traffic rather that permission-based algorithms. This method makes a tradeoff between token-based and permission-based. It does not utilize any token, that is similar to permission-based, and the latest node having the critical section influences
the entrance of the next node to the critical section, that is similar to token-based algorithms. The algorithm based on ancestral is named as DAD algorithms and
increases the availability of fully connected network between 2.86 to 59.83% and decreases the number of message transmissions from 4j-2 to 3j messages (j as number of nodes in partition).
This method is then utilized as the basis of dynamic ancestral mutual exclusion algorithm for MANET which is named as MDA. This algorithm is presented and evaluated for different scenarios of mobility of nodes, failure, load and number of nodes. The results of study show that MDA algorithm guarantees mutual exclusion,dead lock freedom and starvation freedom. It improves the availability of CS to minimum 154.94% and 113.36% for low load and high load of CS requests respectively
compared to other permission-based lgorithm.Furthermore, it improves response time up to 90.69% for high load and 75.21% for low load of CS requests. It degrades the
number of messages from n to 2 messages in the best case and from 3n/2 to n in the worst case. MDA algorithm is resilient to transient partitioning of network that is
normally occurs due to failure of nodes or links
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