9,593 research outputs found
DSIM: A distributed simulator
Discrete event-driven simulation makes it possible to model a computer system in detail. However, such simulation models can require a significant time to execute. This is especially true when modeling large parallel or distributed systems containing many processors and a complex communication network. One solution is to distribute the simulation over several processors. If enough parallelism is achieved, large simulation models can be efficiently executed. This study proposes a distributed simulator called DSIM which can run on various architectures. A simulated test environment is used to verify and characterize the performance of DSIM. The results of the experiments indicate that speedup is application-dependent and, in DSIM's case, is also dependent on how the simulation model is distributed among the processors. Furthermore, the experiments reveal that the communication overhead of ethernet-based distributed systems makes it difficult to achieve reasonable speedup unless the simulation model is computation bound
Criticality of the Exponential Rate of Decay for the Largest Nearest Neighbor Link in Random Geometric Graph
Let n points be placed independently in d-dimensional space according to the
densities Let be the longest edge length for the nearest neighbor graph on
these points. We show that converges weakly to
the Gumbel distribution where We also show that the
strong law result, % \lim_{n \to \infty}
\frac{(\lambda^{-1}\log(n))^{1-1/\alpha}d_n}{\sqrt{\log \log n}} \to
\frac{d}{\alpha \lambda}, a.s. % Thus, the exponential rate of decay i.e.
is critical, in the sense that for where
as a.s. as Comment: Communicated to 'Stochastic Processes and Their Applications'. Sep.
11, 2006: replaced paper uploaded on Apr. 27, 2006 by a corrected version;
errors/corrections found by the authors themselve
Nonuniform random geometric graphs with location-dependent radii
We propose a distribution-free approach to the study of random geometric
graphs. The distribution of vertices follows a Poisson point process with
intensity function , where , and is a
probability density function on . A vertex located at
connects via directed edges to other vertices that are within a cut-off
distance . We prove strong law results for (i) the critical cut-off
function so that almost surely, the graph does not contain any node with
out-degree zero for sufficiently large and (ii) the maximum and minimum
vertex degrees. We also provide a characterization of the cut-off function for
which the number of nodes with out-degree zero converges in distribution to a
Poisson random variable. We illustrate this result for a class of densities
with compact support that have at most polynomial rates of decay to zero.
Finally, we state a sufficient condition for an enhanced version of the above
graph to be almost surely connected eventually.Comment: Published in at http://dx.doi.org/10.1214/11-AAP823 the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Achieving Non-Zero Information Velocity in Wireless Networks
In wireless networks, where each node transmits independently of other nodes
in the network (the ALOHA protocol), the expected delay experienced by a packet
until it is successfully received at any other node is known to be infinite for
signal-to-interference-plus-noise-ratio (SINR) model with node locations
distributed according to a Poisson point process. Consequently, the information
velocity, defined as the limit of the ratio of the distance to the destination
and the time taken for a packet to successfully reach the destination over
multiple hops, is zero, as the distance tends to infinity. A nearest neighbor
distance based power control policy is proposed to show that the expected delay
required for a packet to be successfully received at the nearest neighbor can
be made finite. Moreover, the information velocity is also shown to be non-zero
with the proposed power control policy. The condition under which these results
hold does not depend on the intensity of the underlying Poisson point process.Comment: to appear in Annals of Applied Probabilit
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