Abstract: The “small world” phenomenon, i.e., the fact that the
global social network is strongly connected in the sense
that every two persons are inter-related through a small
chain of friends, has attracted research attention and has
been strongly related to the results of the social
psychologistĘs Stanley Milgram experiments; properties
of social networks and relevant problems also emerge in
peer-to-peer systems and their study can shed light on
important modern network design properties.
In this paper, we have experimentally studied greedyrouting algorithms, i.e., algorithms that route information
using “long-range” connections that function as
shortcuts connecting “distant” network nodes. In
particular, we have implemented greedyrouting
algorithms, and techniques from the recent literature in
networks of line and grid topology using parallelization
for increasing efficiency. To the best of our knowledge, no
similar attempt has been made so far
Abstract: The study of the path coloring problem is motivated by the allocation of optical bandwidth to communication requests in all-optical networks that utilize Wavelength Division Multiplexing (WDM). WDM technology establishes communication between pairs of network nodes by establishing transmitter-receiver paths and assigning wavelengths to each path so that no two paths going through the same fiber link use the same wavelength. Optical bandwidth is the number of distinct wavelengths. Since state-of-the-art technology allows for a limited number of wavelengths, the engineering problem to be solved is to establish communication minimizing the total number of wavelengths used. This is known as the wavelength routing problem. In the case where the underlying network is a tree, it is equivalent to the path coloring problem.
We survey recent advances on the path coloring problem in both undirected and bidirected trees. We present hardness results and lower bounds for the general problem covering also the special case of sets of symmetric paths (corresponding to the important case of symmetric communication). We give an overview of the main ideas of deterministic greedy algorithms and point out their limitations. For bidirected trees, we present recent results about the use of randomization for path coloring and outline approximation algorithms that find path colorings by exploiting fractional path colorings. Also, we discuss upper and lower bounds on the performance of on-line algorithms.
Abstract: Direct routing is the special case of bufferless routing where N packets, once injected into the network, must be routed along specific paths to their destinations without conflicts. We give a general treatment of three facets of direct routing: (i) Algorithms. We present a polynomial time greedy algorithm for arbitrary direct routing problems whch is worst-case optimal, i.e., there exist instances for which no direct routing algorithm is better than the greedy. We apply variants of this algorithm to commonly used network topologies. In particular, we obtain near-optimal routing time using for the tree and d-dimensional mesh, given arbitrary sources and destinations; for the butterfly and the hypercube, the same result holds for random destinations. (ii) Complexity. By a reduction from Vertex Coloring, we show that Direct Routing is inapproximable, unless P=NP. (iii) Lower Bounds for Buffering. We show the existence of routing problems which cannot be solved efficiently with direct routing. To solve these problems, any routing algorithm needs buffers. We give nontrivial lower bounds on such buffering requirements for general routing algorithms.
Abstract: Through recent technology advances in the eld of wireless energy transmission, Wireless Rechargeable Sensor Networks
(WRSN) have emerged. In this new paradigm for
WSNs a mobile entity called Mobile Charger (MC) traverses
the network and replenishes the dissipated energy of sensors.
In this work we rst provide a formal denition of the charging
dispatch decision problem and prove its computational
hardness. We then investigate how to optimize the tradeo
s of several critical aspects of the charging process such
as a) the trajectory of the charger, b) the dierent charging
policies and c) the impact of the ratio of the energy
the MC may deliver to the sensors over the total available
energy in the network. In the light of these optimizations,
we then study the impact of the charging process to the
network lifetime for three characteristic underlying routing
protocols; a greedy protocol, a clustering protocol and an
energy balancing protocol. Finally, we propose a Mobile
Charging Protocol that locally adapts the circular trajectory
of the MC to the energy dissipation rate of each sub-region
of the network. We compare this protocol against several
MC trajectories for all three routing families by a detailed
experimental evaluation. The derived ndings demonstrate
signicant performance gains, both with respect to the no
charger case as well as the dierent charging alternatives; in
particular, the performance improvements include the network
lifetime, as well as connectivity, coverage and energy
Abstract: We propose local mechanisms for efficiently marking the broader network region around obstacles, for data propagation to early enough avoid them towards near-optimal routing paths. In particular, our methods perform an online identification of sensors lying near obstacle boundaries,which then appropriately emit beacon messages in the network towards establishing efficient obstacle avoidance paths. We provide a variety of beacon dissemination schemes that satisfy different trade-offs between protocol overhead and performance. Compared to greedy, face routing and trustbased methods in the state of the art, our methods achieve significantly shorter propagation paths, while introducing much lower overhead and converging faster to near-optimality.
Abstract: We propose local mechanisms for efficiently marking the
broader network region around obstacles, for data propagation
to early enough avoid them towards near-optimal
routing paths. In particular, our methods perform an online
identification of sensors lying near obstacle boundaries,
which then appropriately emit beacon messages in the network
towards establishing efficient obstacle avoidance paths.
We provide a variety of beacon dissemination schemes that
satisfy different trade-offs between protocol overhead and
performance. Compared to greedy, face routing and trustbased
methods in the state of the art, our methods achieve
significantly shorter propagation paths, while introducing
much lower overhead and converging faster to near-optimality.
Abstract: This research further investigates the recently introduced
(in ) paradigm of radiation awareness in ambient environments with abundant heterogeneous wireless networking
from a distributed computing perspective. We call radiation
at a point of a wireless network the total amount of electromagnetic quantity the point is exposed to; our denition incorporates the eect of topology as well as the time domain
and environment aspects. Even if the impact of radiation to
human health remains largely unexplored and controversial,
we believe it is worth trying to understand and control, in
a way that does not decrease much the quality of service
oered to users of the wireless network.
In particular, we here focus on the fundamental problem
of ecient data propagation in wireless sensor networks, try-
ing to keep latency low while maintaining at low levels the
radiation cumulated by wireless transmissions. We rst propose greedy and oblivious routing heuristics that are radiation aware. We then combine them with temporal back-o
schemes that use local properties of the network (e.g. number of neighbours, distance from sink) in order to spread" radiation in a spatio-temporal way. Our proposed radiation
aware routing heuristics succeed to keep radiation levels low,
while not increasing latency.