4,235 research outputs found
Reaching Approximate Byzantine Consensus in Partially-Connected Mobile Networks
We consider the problem of approximate consensus in mobile networks
containing Byzantine nodes. We assume that each correct node can communicate
only with its neighbors and has no knowledge of the global topology. As all
nodes have moving ability, the topology is dynamic. The number of Byzantine
nodes is bounded by f and known by all correct nodes. We first introduce an
approximate Byzantine consensus protocol which is based on the linear iteration
method. As nodes are allowed to collect information during several consecutive
rounds, moving gives them the opportunity to gather more values. We propose a
novel sufficient and necessary condition to guarantee the final convergence of
the consensus protocol. The requirement expressed by our condition is not
"universal": in each phase it affects only a single correct node. More
precisely, at least one correct node among those that propose either the
minimum or the maximum value which is present in the network, has to receive
enough messages (quantity constraint) with either higher or lower values
(quality constraint). Of course, nodes' motion should not prevent this
requirement to be fulfilled. Our conclusion shows that the proposed condition
can be satisfied if the total number of nodes is greater than 3f+1.Comment: No. RR-7985 (2012
Iterative Approximate Consensus in the presence of Byzantine Link Failures
This paper explores the problem of reaching approximate consensus in
synchronous point-to-point networks, where each directed link of the underlying
communication graph represents a communication channel between a pair of nodes.
We adopt the transient Byzantine link failure model [15, 16], where an
omniscient adversary controls a subset of the directed communication links, but
the nodes are assumed to be fault-free.
Recent work has addressed the problem of reaching approximate consen- sus in
incomplete graphs with Byzantine nodes using a restricted class of iterative
algorithms that maintain only a small amount of memory across iterations [22,
21, 23, 12]. However, to the best of our knowledge, we are the first to
consider approximate consensus in the presence of Byzan- tine links. We extend
our past work that provided exact characterization of graphs in which the
iterative approximate consensus problem in the presence of Byzantine node
failures is solvable [22, 21]. In particular, we prove a tight necessary and
sufficient condition on the underlying com- munication graph for the existence
of iterative approximate consensus algorithms under transient Byzantine link
model. The condition answers (part of) the open problem stated in [16].Comment: arXiv admin note: text overlap with arXiv:1202.609
Self-stabilising Byzantine Clock Synchronisation is Almost as Easy as Consensus
We give fault-tolerant algorithms for establishing synchrony in distributed
systems in which each of the nodes has its own clock. Our algorithms
operate in a very strong fault model: we require self-stabilisation, i.e., the
initial state of the system may be arbitrary, and there can be up to
ongoing Byzantine faults, i.e., nodes that deviate from the protocol in an
arbitrary manner. Furthermore, we assume that the local clocks of the nodes may
progress at different speeds (clock drift) and communication has bounded delay.
In this model, we study the pulse synchronisation problem, where the task is to
guarantee that eventually all correct nodes generate well-separated local pulse
events (i.e., unlabelled logical clock ticks) in a synchronised manner.
Compared to prior work, we achieve exponential improvements in stabilisation
time and the number of communicated bits, and give the first sublinear-time
algorithm for the problem:
- In the deterministic setting, the state-of-the-art solutions stabilise in
time and have each node broadcast bits per time
unit. We exponentially reduce the number of bits broadcasted per time unit to
while retaining the same stabilisation time.
- In the randomised setting, the state-of-the-art solutions stabilise in time
and have each node broadcast bits per time unit. We
exponentially reduce the stabilisation time to while each node
broadcasts bits per time unit.
These results are obtained by means of a recursive approach reducing the
above task of self-stabilising pulse synchronisation in the bounded-delay model
to non-self-stabilising binary consensus in the synchronous model. In general,
our approach introduces at most logarithmic overheads in terms of stabilisation
time and broadcasted bits over the underlying consensus routine.Comment: 54 pages. To appear in JACM, preliminary version of this work has
appeared in DISC 201
Parameter-independent Iterative Approximate Byzantine Consensus
In this work, we explore iterative approximate Byzantine consensus algorithms
that do not make explicit use of the global parameter of the graph, i.e., the
upper-bound on the number of faults, f
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