14,821 research outputs found
Fault-Tolerant Consensus in Unknown and Anonymous Networks
This paper investigates under which conditions information can be reliably
shared and consensus can be solved in unknown and anonymous message-passing
networks that suffer from crash-failures. We provide algorithms to emulate
registers and solve consensus under different synchrony assumptions. For this,
we introduce a novel pseudo leader-election approach which allows a
leader-based consensus implementation without breaking symmetry
Efficient Synchronous Byzantine Consensus
We present new protocols for Byzantine state machine replication and
Byzantine agreement in the synchronous and authenticated setting. The
celebrated PBFT state machine replication protocol tolerates Byzantine
faults in an asynchronous setting using replicas, and has since been
studied or deployed by numerous works. In this work, we improve the Byzantine
fault tolerance threshold to by utilizing a relaxed synchrony
assumption. We present a synchronous state machine replication protocol that
commits a decision every 3 rounds in the common case. The key challenge is to
ensure quorum intersection at one honest replica. Our solution is to rely on
the synchrony assumption to form a post-commit quorum of size , which
intersects at replicas with any pre-commit quorums of size . Our
protocol also solves synchronous authenticated Byzantine agreement in expected
8 rounds. The best previous solution (Katz and Koo, 2006) requires expected 24
rounds. Our protocols may be applied to build Byzantine fault tolerant systems
or improve cryptographic protocols such as cryptocurrencies when synchrony can
be assumed
The Impact of RDMA on Agreement
Remote Direct Memory Access (RDMA) is becoming widely available in data
centers. This technology allows a process to directly read and write the memory
of a remote host, with a mechanism to control access permissions. In this
paper, we study the fundamental power of these capabilities. We consider the
well-known problem of achieving consensus despite failures, and find that RDMA
can improve the inherent trade-off in distributed computing between failure
resilience and performance. Specifically, we show that RDMA allows algorithms
that simultaneously achieve high resilience and high performance, while
traditional algorithms had to choose one or another. With Byzantine failures,
we give an algorithm that only requires processes (where
is the maximum number of faulty processes) and decides in two (network)
delays in common executions. With crash failures, we give an algorithm that
only requires processes and also decides in two delays. Both
algorithms tolerate a minority of memory failures inherent to RDMA, and they
provide safety in asynchronous systems and liveness with standard additional
assumptions.Comment: Full version of PODC'19 paper, strengthened broadcast algorith
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A Dose Relationship Between Brain Functional Connectivity and Cumulative Head Impact Exposure in Collegiate Water Polo Players.
A growing body of evidence suggests that chronic, sport-related head impact exposure can impair brain functional integration and brain structure and function. Evidence of a robust inverse relationship between the frequency and magnitude of repeated head impacts and disturbed brain network function is needed to strengthen an argument for causality. In pursuing such a relationship, we used cap-worn inertial sensors to measure the frequency and magnitude of head impacts sustained by eighteen intercollegiate water polo athletes monitored over a single season of play. Participants were evaluated before and after the season using computerized cognitive tests of inhibitory control and resting electroencephalography. Greater head impact exposure was associated with increased phase synchrony [r (16) > 0.626, p < 0.03 corrected], global efficiency [r (16) > 0.601, p < 0.04 corrected], and mean clustering coefficient [r (16) > 0.625, p < 0.03 corrected] in the functional networks formed by slow-wave (delta, theta) oscillations. Head impact exposure was not associated with changes in performance on the inhibitory control tasks. However, those with the greatest impact exposure showed an association between changes in resting-state connectivity and a dissociation between performance on the tasks after the season [r (16) = 0.481, p = 0.043] that could also be attributed to increased slow-wave synchrony [F (4, 135) = 113.546, p < 0.001]. Collectively, our results suggest that athletes sustaining the greatest head impact exposure exhibited changes in whole-brain functional connectivity that were associated with altered information processing and inhibitory control
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