280 research outputs found
Rational Fair Consensus in the GOSSIP Model
The \emph{rational fair consensus problem} can be informally defined as
follows. Consider a network of (selfish) \emph{rational agents}, each of
them initially supporting a \emph{color} chosen from a finite set .
The goal is to design a protocol that leads the network to a stable
monochromatic configuration (i.e. a consensus) such that the probability that
the winning color is is equal to the fraction of the agents that initially
support , for any . Furthermore, this fairness property must
be guaranteed (with high probability) even in presence of any fixed
\emph{coalition} of rational agents that may deviate from the protocol in order
to increase the winning probability of their supported colors. A protocol
having this property, in presence of coalitions of size at most , is said to
be a \emph{whp\,--strong equilibrium}. We investigate, for the first time,
the rational fair consensus problem in the GOSSIP communication model where, at
every round, every agent can actively contact at most one neighbor via a
\emph{pushpull} operation. We provide a randomized GOSSIP protocol that,
starting from any initial color configuration of the complete graph, achieves
rational fair consensus within rounds using messages of
size, w.h.p. More in details, we prove that our protocol is a
whp\,--strong equilibrium for any and, moreover, it
tolerates worst-case permanent faults provided that the number of non-faulty
agents is . As far as we know, our protocol is the first solution
which avoids any all-to-all communication, thus resulting in message
complexity.Comment: Accepted at IPDPS'1
Epidemic failure detection and consensus for extreme parallelism
Future extreme-scale high-performance computing systems will be required
to work under frequent component failures. The MPI Forum’s User
Level Failure Mitigation proposal has introduced an operation,
MPI Comm shrink, to synchronize the alive processes on the list of failed
processes, so that applications can continue to execute even in the presence
of failures by adopting algorithm-based fault tolerance techniques. This
MPI Comm shrink operation requires a failure detection and consensus
algorithm. This paper presents three novel failure detection and consensus
algorithms using Gossiping. Stochastic pinging is used to quickly detect
failures during the execution of the algorithm, failures are then disseminated
to all the fault-free processes in the system and consensus on the
failures is detected using the three consensus techniques. The proposed
algorithms were implemented and tested using the Extreme-scale Simulator.
The results show that the stochastic pinging detects all the failures in
the system. In all the algorithms, the number of Gossip cycles to achieve
global consensus scales logarithmically with system size. The second algorithm
also shows better scalability in terms of memory and network
bandwidth usage and a perfect synchronization in achieving global consensus.
The third approach is a three-phase distributed failure detection
and consensus algorithm and provides consistency guarantees even in very
large and extreme-scale systems while at the same time being memory and
bandwidth efficient
Randition: Random Blockchain Partitioning for Write Throughput
This paper proposes to support dynamic runtime partitioning of Tendermint, which is an in-development state machine replication algorithm that uses the blockchain model to provide Byzantine-fault tolerance. We call this variation Randition. We incorporate recent research from blockchain consensus and replicated state machine partitioning to allow Randition users to partition their blockchain for improved write performance at the cost of some Byzantine fault tolerance. We conduct an experiment to compare the raw write throughput of Randition and Tendermint. Finally, we discuss the experiment results and discuss further improvements to Randition
Design and performance study of algorithms for consensus in sparse, mobile ad-hoc networks
PhD ThesisMobile Ad-hoc Networks (MANETs) are self-organizing wireless networks that consist
of mobile wireless devices (nodes). These networks operate without the aid
of any form of supporting infrastructure, and thus need the participating nodes to
co-operate by forwarding each other’s messages. MANETs can be deployed when
urgent temporary communications are required or when installing network infrastructure
is considered too costly or too slow, for example in environments such as
battlefields, crisis management or space exploration.
Consensus is central to several applications including collaborative ones which a
MANET can facilitate for mobile users. This thesis solves the consensus problem in
a sparse MANET in which a node can at times have no other node in its wireless
range and useful end-to-end connectivity between nodes can just be a temporary
feature that emerges at arbitrary intervals of time for any given node pair.
Efficient one-to-many dissemination, essential for consensus, now becomes a challenge:
enough number of destinations cannot deliver a multicast unless nodes retain
the multicast message for exercising opportunistic forwarding. Seeking to keep storage
and bandwidth costs low, we propose two protocols. An eventually relinquishing
(}RC) protocol that does not store messages for long is used for attempting at consensus,
and an eventually quiescent (}QC) one that stops forwarding messages
after a while is used for concluding consensus. Use of }RC protocol poses additional
challenges for consensus, when the fraction, f
n, of nodes that can crash is:
1
4 f
n < 1
2 .
Consensus latency and packet overhead are measured through simulation indicating
that they are not too high to be feasible in MANETs. They both decrease
considerably even for a modest increase in network density.Damascus University
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