54,592 research outputs found
The Cost of Global Broadcast in Dynamic Radio Networks
We study the single-message broadcast problem in dynamic radio networks. We
show that the time complexity of the problem depends on the amount of stability
and connectivity of the dynamic network topology and on the adaptiveness of the
adversary providing the dynamic topology. More formally, we model communication
using the standard graph-based radio network model. To model the dynamic
network, we use a generalization of the synchronous dynamic graph model
introduced in [Kuhn et al., STOC 2010]. For integer parameters and
, we call a dynamic graph -interval -connected if for every
interval of consecutive rounds, there exists a -vertex-connected stable
subgraph. Further, for an integer parameter , we say that the
adversary providing the dynamic network is -oblivious if for constructing
the graph of some round , the adversary has access to all the randomness
(and states) of the algorithm up to round .
As our main result, we show that for any , any , and any
, for a -oblivious adversary, there is a distributed
algorithm to broadcast a single message in time
. We further show that even for large interval -connectivity,
efficient broadcast is not possible for the usual adaptive adversaries. For a
-oblivious adversary, we show that even for any (for any constant ) and for any , global broadcast in -interval -connected networks requires at least
time. Further, for a oblivious adversary,
broadcast cannot be solved in -interval -connected networks as long as
.Comment: 17 pages, conference version appeared in OPODIS 201
Distributed Connectivity Decomposition
We present time-efficient distributed algorithms for decomposing graphs with
large edge or vertex connectivity into multiple spanning or dominating trees,
respectively. As their primary applications, these decompositions allow us to
achieve information flow with size close to the connectivity by parallelizing
it along the trees. More specifically, our distributed decomposition algorithms
are as follows:
(I) A decomposition of each undirected graph with vertex-connectivity
into (fractionally) vertex-disjoint weighted dominating trees with total weight
, in rounds.
(II) A decomposition of each undirected graph with edge-connectivity
into (fractionally) edge-disjoint weighted spanning trees with total
weight , in
rounds.
We also show round complexity lower bounds of
and
for the above two decompositions,
using techniques of [Das Sarma et al., STOC'11]. Moreover, our
vertex-connectivity decomposition extends to centralized algorithms and
improves the time complexity of [Censor-Hillel et al., SODA'14] from
to near-optimal .
As corollaries, we also get distributed oblivious routing broadcast with
-competitive edge-congestion and -competitive
vertex-congestion. Furthermore, the vertex connectivity decomposition leads to
near-time-optimal -approximation of vertex connectivity: centralized
and distributed . The former moves
toward the 1974 conjecture of Aho, Hopcroft, and Ullman postulating an
centralized exact algorithm while the latter is the first distributed vertex
connectivity approximation
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