368 research outputs found
On Space-Time Capacity Limits in Mobile and Delay Tolerant Networks
We investigate the fundamental capacity limits of space-time journeys of
information in mobile and Delay Tolerant Networks (DTNs), where information is
either transmitted or carried by mobile nodes, using store-carry-forward
routing. We define the capacity of a journey (i.e., a path in space and time,
from a source to a destination) as the maximum amount of data that can be
transferred from the source to the destination in the given journey. Combining
a stochastic model (conveying all possible journeys) and an analysis of the
durations of the nodes' encounters, we study the properties of journeys that
maximize the space-time information propagation capacity, in bit-meters per
second. More specifically, we provide theoretical lower and upper bounds on the
information propagation speed, as a function of the journey capacity. In the
particular case of random way-point-like models (i.e., when nodes move for a
distance of the order of the network domain size before changing direction), we
show that, for relatively large journey capacities, the information propagation
speed is of the same order as the mobile node speed. This implies that,
surprisingly, in sparse but large-scale mobile DTNs, the space-time information
propagation capacity in bit-meters per second remains proportional to the
mobile node speed and to the size of the transported data bundles, when the
bundles are relatively large. We also verify that all our analytical bounds are
accurate in several simulation scenarios.Comment: Part of this work will be presented in "On Space-Time Capacity Limits
in Mobile and Delay Tolerant Networks", P. Jacquet, B. Mans and G. Rodolakis,
IEEE Infocom, 201
On the Throughput-Delay Trade-off in Georouting Networks
We study the scaling properties of a georouting scheme in a wireless
multi-hop network of mobile nodes. Our aim is to increase the network
capacity quasi linearly with while keeping the average delay bounded. In
our model, mobile nodes move according to an i.i.d. random walk with velocity
and transmit packets to randomly chosen destinations. The average packet
delivery delay of our scheme is of order and it achieves the network
capacity of order . This shows a practical
throughput-delay trade-off, in particular when compared with the seminal result
of Gupta and Kumar which shows network capacity of order and
negligible delay and the groundbreaking result of Grossglausser and Tse which
achieves network capacity of order but with an average delay of order
. We confirm the generality of our analytical results using
simulations under various interference models.Comment: This work has been submitted to IEEE INFOCOM 201
Information Propagation Speed in Mobile and Delay Tolerant Networks
Recent research has highlighted the necessity of developing routing protocols for mobile ad hoc networks where end-to-end multi-hop paths may not exist and communication routes may only be available through time and mobility. Depending on the context, these networks are commonly referred as Intermittently Connected Mobile Networks (ICNs) or Delay/Disruption Tolerant Networks (DTNs). Conversely, little is known about the inherent properties of such networks, and consequently, performance evaluations are often limited to comparative simulations (using mobility models or actual traces). The goal of this paper is to increase our understanding of possible performances of DTNs. After introducing our formal model, we use analytical tools to derive theoretical upper-bounds of the information propagation speed in wireless mobile networks. We also present some numerical simulations to illustrate the accuracy of the bounds in numerous scenarios
Blockchain moderated by empty blocks to reduce the energetic impact of crypto-moneys
While cryptocurrencies and blockchain applications continue to gain
popularity, their energy cost is evidently becoming unsustainable. In most
instances, the main cost comes from the required amount of energy for the
Proof-of-Work, and this cost is inherent to the design. In addition, useless
costs from discarded work (e.g., the so-called Forks) and lack of scalability
(in number of users and in rapid transactions) limit their practical
effectiveness.
In this paper, we present an innovative scheme which eliminates the nonce and
thus the burden of the Proof-of-Work which is the main cause of the energy
waste in cryptocurrencies such as Bitcoin. We prove that our scheme guarantees
a tunable and bounded average number of simultaneous mining whatever the size
of the population in competition, thus by making the use of nonce-based
techniques unnecessary, achieves scalability without the cost of consuming a
large volume of energy. The technique used in the proof of our scheme is based
on the analogy of the analysis of a green leader election. The additional
difference with Proof-of-Work schemes (beyond the suppression of the nonce
field that is triggering most of the waste), is the introduction of (what we
denote as) "empty blocks" which aim are to call regular blocks following a
staircase set of values. Our scheme reduces the risk of Forks and provides
tunable scalability for the number of users and the speed of block generation.
We also prove using game theoretical analysis that our scheme is resilient to
unfair competitive investments (e.g., "51 percent" attack) and block nursing.Comment: preliminary version appeared in CryBlock'2019, The IEEE 2nd Workshop
on Cryptocurrencies and Blockchains for Distributed Systems (co-located with
INFOCOM 2019), April 29th, 2019. Paris, France. Green Mining: toward a less
energetic impact of cryptocurrencies, P. Jacquet and B. Mans, IEEE Press, 6
page
Bandwidth Reservation in Multihop Wireless Networks: Complexity and Mechanisms
We show that link interferences in wireless networks make multihop bandwidth reservation in such an environment an NP-complete problem. This is in sharp contrast to bandwidth reservation in wireline networks where efficient polynomial algorithms exist. We also consider the problem of slot allocation according to bandwidth requirements in a wireless slotted environment. In the context of Mobile Ad Hoc Networks, we propose simple heuristics applicable to the OLSR routing protocol in order to find routes that satisfies requirements without impairing the performance of other connections
Information Propagation Speed in Mobile and Delay Tolerant Networks
The goal of this paper is to increase our understanding of the fundamental
performance limits of mobile and Delay Tolerant Networks (DTNs), where
end-to-end multi-hop paths may not exist and communication routes may only be
available through time and mobility. We use analytical tools to derive generic
theoretical upper bounds for the information propagation speed in large scale
mobile and intermittently connected networks. In other words, we upper-bound
the optimal performance, in terms of delay, that can be achieved using any
routing algorithm. We then show how our analysis can be applied to specific
mobility and graph models to obtain specific analytical estimates. In
particular, in two-dimensional networks, when nodes move at a maximum speed
and their density is small (the network is sparse and surely
disconnected), we prove that the information propagation speed is upper bounded
by ( in the random way-point model, while it is upper bounded by
for other mobility models (random walk, Brownian motion).
We also present simulations that confirm the validity of the bounds in these
scenarios. Finally, we generalize our results to one-dimensional and
three-dimensional networks
Highway Vehicular Delay Tolerant Networks: Information Propagation Speed Properties
International audienceIn this paper, we provide a full analysis of the information propagation speed in bidirectional vehicular delay tolerant networks such as roads or highways. The provided analysis shows that a phase transition occurs concerning the information propagation speed, with respect to the vehicle densities in each direction of the highway. We prove that under a certain threshold, information propagates on average at vehicle speed, while above this threshold, information propagates dramatically faster at a speed that increases quasi-exponentially when the vehicle density increases. We provide the exact expressions of the threshold and of the average information propagation speed near the threshold, in case of finite or infinite radio propagation speed. Furthermore, we investigate in detail the way information propagates under the threshold, and we prove that delay tolerant routing using cars moving on both directions provides a gain in propagation distance, which is bounded by a sub-linear power law with respect to the elapsed time, in the referential of the moving cars. Combining these results, we thus obtain a complete picture of the way information propagates in vehicular networks on roads and highways, which may help designing and evaluating appropriate VANET routing protocols. We confirm our analytical results using simulations carried out in several environments (The One and Maple)
Characterizing the Energy Trade-Offs of End-to-End Vehicular Communications using an Hyperfractal Urban Modelling
We characterize trade-offs between the end-to-end communication delay and the
energy in urban vehicular communications with infrastructure assistance. Our
study exploits the self-similarity of the location of communication entities in
cities by modeling them with an innovative model called "hyperfractal". We show
that the hyperfractal model can be extended to incorporate road-side
infrastructure and provide stochastic geometry tools to allow a rigorous
analysis. We compute theoretical bounds for the end-to-end communication hop
count considering two different energy-minimizing goals: either total
accumulated energy or maximum energy per node. We prove that the hop count for
an end-to-end transmission is bounded by where
is the fractal dimension of the mobile nodes process.
This proves that for both constraints the energy decreases as we allow choosing
routing paths of higher length. The asymptotic limit of the energy becomes
significantly small when the number of nodes becomes asymptotically large. A
lower bound on the network throughput capacity with constraints on path energy
is also given. We show that our model fits real deployments where open data
sets are available. The results are confirmed through simulations using
different fractal dimensions in a Matlab simulator
Blockchain moderated by empty blocks to reduce the energetic impact of crypto-moneys
International audienceWhile cryptocurrencies and blockchain applications continue to gain popularity, their energy cost is evidently becoming unsustainable. In most instances, the main cost comes from the required amount of energy for the Proof-of-Work, and this cost is inherent to the design. In addition, useless costs from discarded work (e.g., the so-called Forks) and lack of scalability (in number of users and in rapid transactions) limit their practical effectiveness. In this paper, we present an innovative scheme which eliminates the nonce and thus the burden of the Proof-of-Work which is the main cause of the energy waste in cryptocurrencies such as Bitcoin. We prove that our scheme guarantees a tunable and bounded average number of simultaneous mining whatever the size of the population in competition, thus by making the use of nonce-based techniques unnecessary, achieves scalability without the cost of consuming a large volume of energy. The technique used in the proof of our scheme is based on the analogy of the analysis of a green leader election. The additional difference with Proof-of-Work schemes (beyond the suppression of the nonce field that is triggering most of the waste), is the introduction of (what we denote as) "empty blocks" which aim are to call regular blocks following a staircase set of values. Our scheme reduces the risk of Forks and provides tunable scalability for the number of users and the speed of block generation. We also prove using game theoretical analysis that our scheme is resilient to unfair competitive investments (e.g., "51 percent" attack) and block nursing
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