IMDEA Networks Institute Digital Repository
Not a member yet
1915 research outputs found
Sort by
The impact of mobility on the geocasting problem in mobile ad-hoc networks: Solvability and cost
Get PDFWe present a model of a mobile ad-hoc network in which nodes can move arbitrarily on the plane with some bounded speed. We show that without any assumption on some topological stability, it is impossible to solve the geocast problem deterministically despite connectivity and no matter how slowly the nodes move. Moreover, even if each
node maintains a stable connection with each of its neighbors for some period of time, it is impossible to solve the geocast problem if nodes move too fast.
Additionally, we give a tradeoff lower bound which shows that the faster the nodes can move on a monodimensional space, the more costly it would be to solve the geocast problem. We provide geocasting algorithms for the case where nodes move in one dimension and also when they can move on the plane (i.e., in two dimensions). We prove correctness of our algorithms by giving exact bounds on the speed of movement. Our analysis helps understand the impact of speed of nodes, firstly, on geocasting solvability and, secondly, on the cost of geocasting.TRUEpu
Collision-Free Operation in Wireless Ad-Hoc Networks
Get PDFIn some wireless ad-hoc networks it is not possible to rely on carrier-sense mechanisms to prevent collisions. In this article we suggest a MAC protocol that reaches collision-free operation in sparse ad-hoc wireless networks when all the stations are saturated. The basic idea is to
use a random backoff after failed transmissions and a deterministic back-off after successful transmissions. Each of the participating stations can configure its own backoff parameter after collecting information from its neighborhood. Then the system enters in a transient-state until collision-free operation is reached. We assess the duration of the transient-state and other performance metrics for an example scenario and finally we discuss two options to incorporate reception acknowledgements.TRUEpu
Unbounded Contention Resolution in Multiple-Access Channels
Get PDFA frequent problem in settings where a unique resource must
be shared among users is how to resolve the contention that arises when all of them must use it, but the resource allows only for one user each time. The application of efficient solutions for this problem spans a myriad of settings such as radio communication networks or databases. For the case where the number of users is unknown, recent work has yielded fruitful results for local area networks and radio networks, although either a (possibly loose) upper bound on the number of users needs to be known [7], or the solution is suboptimal [2], or it is only implicit [11] or embedded [6] in other problems, with bounds proved only asymptotically. In this paper, under the assumption that collision detection or information on the number of contenders is not available, we present a novel protocol for contention resolution in radio networks, and we recreate a protocol previously used for other problems [6, 11], tailoring the constants for our needs. In contrast with previous work, both protocols are proved to be optimal up to a small constant factor and with high probability for big enough number of contenders. Additionally, the protocols are evaluated and contrasted with the previous work by extensive simulations. The evaluation shows that the complexity bounds obtained by the analysis are rather tight, and that both protocols proposed have small and predictable complexity for many system sizes (unlike previous proposals).TRUEpu
Reducing Costs and Pollution in Cellular Networks
Get PDFCellular wireless networks are expected to provide high-quality audio and video services while enabling fast and low-cost Internet access to mobile users. The need for green cost-efficient networks is twofold: reduce the service price and preserve the environment. In this work, we discuss the various strategies that help reduce infrastructure costs, power costs, and greenhouse gas
(GHG) emissions with no impairments on the quality of network services. These strategies range over a wide area from enhancing the electronics, to developing new energy-aware radio access protocols, to deploying enhanced base stations with tunable capacity. To reduce both
capital and operational expenditures, and the GHG footprint, manufacturers propose new compact installation with lightweight antenna systems, very efficient power amplifiers, and efficient hardware and software. The resulting economy can be up to 50 percent or more by reducing the electricity bill, sparing the use of air conditioning, and deploying compact sites that would
seldom require maintenance. Recent scientific publications confirm that a very high gain could be achieved by optimizing the use of base stations proactively, and huge additional improvements could be obtained by optimizing power saving mechanisms by leveraging traffic statistics.TRUEpu
Brief Announcement: Algorithmic Mechanisms for Internet-Based Computing under Unreliable Communication
Get PDFThis work, using a game-theoretic approach, considers
Internet-based computations, where a master processor assigns, over the Internet, a computational task to a set of untrusted worker processors, and collects their responses. In particular, we consider a framework where
altruistic, malicious, and rational workers co-exist, the communication between the master and the workers is not reliable, and that workers could be unavailable. Within this framework, we design algorithmic mechanisms that provide appropriate incentives to rational workers to
act correctly, despite the malicious’ workers actions and the unreliability of the network.TRUEpu
Distributed Bottleneck Flow Control in Mobile Ad Hoc Networks
No full textFlow control in mobile ad hoc networks (MANETs) encounters more challenges than flow control in conventional wired networks, such as channel bandwidth variation, medium
contention, and frequent re-routing. Without proper flow control, serious network performance degradation in MANETs has been reported in recent studies. In this paper, we
introduce a distributed bottleneck flow control technique in MANETs. The proposed scheme uses a distributed flow control mechanism that has been used in both bottleneck flow control and bandwidth balancing in Distributed-Queue-Dual-Bus (DQDB) in wired networks. It extends bandwidth balancing to operate in a mobile wireless environment. Extensive simulations demonstrate that our flow control scheme is effective and can provide max-min fairness as well as improve Quality of Service (QoS) for flows in MANETs.TRUEpu
DNS64: DNS Extensions for Network Address Translation from IPv6 Clients to IPv4 Servers
Get PDFDNS64 is a mechanism for synthesizing AAAA records from A records. DNS64 is used with an IPv6/IPv4 translator to enable client-server communication between an IPv6-only client and an IPv4-only server, without requiring any changes to either the IPv6 or the IPv4 node, for the class of applications that work through NATs. This document specifies DNS64, and provides suggestions on how it should be deployed in conjunction with IPv6/IPv4 translators.Internet Engineering Task Force (IETF)pu
A Control Theoretic Approach to Distributed Optimal Configuration of 802.11 WLANs
Get PDFThe optimal configuration of the contention parameters of a WLAN depends on the network conditions in terms of number of stations and the traffic they generate. Following this observation, a considerable effort in the literature has been devoted to the design of distributed algorithms that optimally configure the WLAN parameters based on current conditions. In this paper we propose a novel algorithm that, in contrast to previous proposals which are mostly based on heuristics, is sustained by mathematical foundations from multivariable control theory. A key advantage of the algorithm over existing approaches is that it is compliant with the 802.11 standard and can be implemented with current wireless cards without introducing any changes into the hardware or firmware. We study the performance of our proposal by means of theoretical
analysis, simulations and a real implementation. Results show that the algorithm substantially outperforms previous approaches in terms of throughput and delay.TRUEpu
Highway Capacity Benefits from Using Vehicle-to-Vehicle Communication and Sensors for Collision Avoidance
No full textISSN : 1090-3038
Print ISBN: 978-1-4244-8328-0Several automobile manufacturers are offering assisted driving systems that use sensors to automatically brake automobiles to avoid collisions. Before extensively deploying these systems, we should determine how they will affect highway capacity. The goal of this paper is to compare the highway capacity when using sensors alone and when using sensors and vehicle-to-vehicle communication. To achieve this goal, the rules for using both technologies to prevent collisions are proposed, and highway capacity is estimated based on these rules. We show that both technologies can increase highway capacity. The increase in capacity is a function of the fraction of the vehicles that use a technology. If all of the vehicles use sensors alone, the increase in highway capacity is about 43%. While if all of the vehicles use both sensors and vehicle-to-vehicle communication, the increase is about 273%.TRUEpu