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1915 research outputs found
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A network-based localized mobility solution for Distributed Mobility Management
Get PDFInternet traffic has increased steeply in recent years, due in great part to social platforms and peer-to-peer networks. In addition, users' wireless access represents an ever-growing portion of such demand, thus posing a paradigm shift in the flow of Internet information, for which most deployed architectures are not prepared for.TRUEpu
Thwarting inside jamming attacks on wireless broadcast communications
Get PDFWe address the problem of jamming-resistant broadcast communications under an internal threat model. We propose a
time-delayed broadcast scheme (TDBS), which implements
the broadcast operation as a series of unicast transmissions, distributed in frequency and time. TDBS does not rely on commonly shared secrets, or the existence of jamming immune control channels for coordinating broadcasts. Instead, each node follows a unique pseudo-noise (PN) frequency hopping sequence. Contrary to conventional PN sequences designed for multi-access systems, our sequences exhibit high correlation to enable broadcast. Moreover, their design limits the information leakage due to the exposure of a subset of sequences by compromised nodes. We map the problem of constructing such PN sequences to the 1-factorization problem for complete graphs. Our evaluation results show that TDBS can maintain broadcast communications in the presence of inside jammers.TRUEpu
Deployment and evaluation of a real wireless multi-hop heterogeneous vehicular network: lessons learned
No full textInternet access and communications may occur in very different scenarios and with a wide variety of devices. Above all, there is a raising trend for mobility: users want to be able to communicate anytime, anywhere. How would our lives change if the communication devices were our own vehicles? Although it could seem to be science fiction, there have been huge advances in research in the field of vehicular communications lately, leading to new standardization proposals, such as a medium access control layer specifically suited for vehicular networks: the IEEE 802.11p.
Vehicular networks are very likely to become a reality not too far to come, and there are a plethora of research works in the literature. However, the research community is still
lacking practical experience in evaluating vehicular communication mechanisms in real life scenarios. With the goal of gaining insights into practical issues of vehicular networks, we have deployed an experimental platform and assessed the suitability of existing hardware and software tools. This platform comprises heterogeneous wireless access technologies, namely the ones that will be most likely present in a vehicular scenario: 3G and IEEE 802.11. In order to be able to discover and face real problems when experimenting with a vehicular communication protocol, we have chosen a vehicular routing optimization mechanism for
vehicular networks, called VARON, which was developed and extensively simulated, but not implemented and tested yet in a real vehicular scenario. The physical deployment of this prototype has brought out some issues concerning the wireless links and the hindrances of current IEEE 802.11 technology for its use in vehicular environments.
This master thesis gathers the lessons learned in the process and the challenges to be faced in such a demanding deployment, thus paving the way for near future experimentation.Telematics EngineeringUniversidad Carlos III de Madrid, Spainpu
Measuring BitTorrent Ecosystem: Techniques, Tips and Tricks
Get PDFBitTorrent is the most successful peer-to-peer application.
In the last years the research community has studied
the BitTorrent ecosystem by collecting data from real BitTorrent swarms using different measurement techniques. In this paper we present the first survey of these techniques that constitutes a first step in the design of future measurement techniques and tools for analyzing large scale systems. The techniques are classified into Macroscopic, Microscopic and Complementary. Macroscopic
techniques allow to collect aggregated information of torrents and present a very high scalability being able to monitor up to hundreds of thousands of torrents in short periods of time. Rather, Microscopic techniques operate at the peer level and focus on understanding performance aspects such as the peers’ download rates. They offer a higher granularity but do not scale as well as the Macroscopic techniques. Finally, Complementary techniques utilize recent extensions to the BitTorrent protocol in
order to obtain both aggregated and peer level information. The paper also summarizes the main challenges faced by the research community to accurately measure the BitTorrent ecosystem such as accurately identifying peers or estimating peers’ upload rates. Furthermore, we provide possible solutions to address the described challenges.TRUEpu
Performance evaluation of a tree-based routing and address autoconfiguration for vehicle-to-Internet communications
Get PDFVehicular ad hoc networks have proven to be quite
useful for broadcast alike communications between nearby cars, but can also be used to provide Internet connectivity from vehicles. In order to do so, vehicle-to-Internet routing and IP address autoconfiguration are two critical pieces. TREBOL is a tree-based and configurable protocol which benefits from the inherent tree-shaped nature of vehicle to Internet traffic to reduce the signaling overhead while dealing efficiently with the vehicular
dynamics. This paper experimentally evaluates the performance of TREBOL using a Linux implementation under lab-controlled realistic scenarios, including real vehicular traces obtained in the region of Madrid.TRUEpu
FLAVIA: Towards a Generic MAC for 4G Mobile Cellular Networks
Get PDFThe future 4th generation IMT-Advanced standards for 3GPP and IEEE 802.16 are LTE-A and IEEE 802.16m, respectively. While at a detailed level IEEE 802.16m and 3GPP LTE-A seem to be significantly different, on a conceptual and functional level both technologies use similar approaches for medium access and radio resource management and are very similar at the PHY layer. In this paper, we analyse both technologies with the goal of finding common functional subsets which can be used as building blocks for a generic and extensible MAC for future mobile cellular networks. To this end, we propose a systematic categorization into services, interfaces, functions and primitives as a first step towards achieving generic architecture.TRUEpu
Control-Theoretic Adaptive Mechanisms for Performance Optimization of IEEE 802.11 WLANs: Design, Implementation and Experimental Evaluation
Get PDF“Premio extraordinario de doctorado Universidad Carlos III de Madrid – Curso 2011/2012”. PhD Thesis defended on March 18th, 2011, in Madrid, Spain. The prize was awarded on November 27th, 2012The media access control (MAC) layer of the IEEE 802.11 standard specifies a set of parameters that regulate the behavior of the wireless stations when accessing the channel. Although the standard defines a set of recommended values for these parameters, they are statically set and do not take into account the current conditions in the wireless local area network (WLAN) in terms of, e.g., number of contending stations and the traffic they generate, which results in suboptimal performance. In this thesis we propose two novel control theoretic approaches to optimally configure the WLAN parameters based on the dynamically observed network conditions: a Centralized Adaptive Control (CAC)algorithm, whereby the access point (AP) computes the configuration that maximizes performance and signals it to the active stations, and a Distributed Adaptive Control(DAC) algorithm, which is independently employed by each station with the same goal.
In contrast to previous proposals, which are mostly based on heuristics, our approaches build upon (i) analytical models of the WLAN performance, used to derive the optimal
point of operation of the IEEE 802.11 protocol, and (ii) mathematical foundations from single- and multi-variable control theory, used to design the mechanisms that drive the
WLAN to this point of operation. Another key advantage of the proposed algorithms over existing approaches is that they are compliant with the IEEE 802.11 standard and can be
implemented with current wireless cards without introducing any modifications into their hardware and/or firmware. We show by means of an exhaustive performance evaluation study that our algorithms maximize the WLAN performance in terms of throughput and delay under a wide set of network conditions, substantially outperforming the standard
recommended configuration as well as previous adaptive proposals.
Finally, we present our experiences with implementing the proposed adaptive algorithms in a real IEEE 802.11 testbed and discuss the implementation details of the building blocks that comprise these mechanisms. We evaluate their performance by conducting extensive measurements, considering different network conditions in terms of number of nodes, transmission power employed and traffic generated. Based on the obtained results, we provide valuable insights on the performance of the distributed and centralized algorithms and discuss the suitability of these schemes for real deployments.Telematics EngineeringUniversidad Carlos III de Madrid, Spainpu
A resource allocation framework for scalable video broadcast in cellular networks
Get PDFFrom the issue entitled "Special Issue: Wireless and Personal Communications"Video streaming is one of the most important applications that will make use of the high data rates offered by 4G networks. The current video transport techniques are already very advanced, and the more immediate problems lie in the joint optimization of video coding, AL-FEC, and PHY rate selection with the goal of enhancing the user perceived quality. In this work we provide an analysis of video broadcast streaming services for different combinations of layered coding and AL-FEC, using a realistic LTE PHY layer. Our simulation results show that the scalable content adaptation given by Scalable Video Coding (SVC) and the scheduling flexibility offered by the 3G-LTE MAClayer provide a good match for enhanced video broadcast services for next generation cellular networks. Our proposed solution is compared to baseline algorithms
and broadcast systems based on H.264/AVC streaming solutions. We emphasize the system quality improvement
brought by our solution and discuss implications for a wide-scale practical deployment.TRUEpu
Bisection Width of Multidimensional Product Graphs
Get PDFIn this paper we will provide two general results that allow to obtain upper and lower bounds on the bisection width of a product graph as a function of some properties of
its factor graphs. The most interesting contribution of this paper is the exact value of the bisection width of a d-dimensional torus, as this problem has been open for almost 20 years [2]. Our work is partially based on the work by Azizo�glu and E�gecio�glu. In [1] they study the relation between the isoperimetric number and the bisection width of diff�erent product networks and obtained and exact value for the bisection width of the d-dimensional array studying it as a product of paths. Similarly, we have been able to provide a lower and an upper bound for the bisection width of product graphs whose factor graphs have the same maximal congestion with multiplicity r, for the former case, or the same central cut, for the latter one.
The general results provided are used to obtain exact bounds on the bisection width of several product graphs. The factor graphs used are paths, rings, complete binary
trees (CBTs), and extended trees (which are CBTs with the leaves connected as a path). Then, we show that the Cartesian product of rings (i.e., the torus) of sizes k1 � : : : � kd has bisection width 2 Pei =1 Ci, where Ci = Qdj =i+1 kj for i 2 [1; e], and e being the lowest dimension with an even number of vertices. (If there is no such dimension, e = d.). Additionally, we show that the Cartesian product of a mixture of XTs and rings has the
same bisection width. (When all factor graphs are XTs, e = d.) Finally, we show that the Cartesian product of a mixture of CBTs and paths has bisection width Pei =1 Ci. (When all factor graphs are CBTs, e = d.)TRUEpu
Unrevealing the structure of live BitTorrent Swarms: methodology and analysis
Get PDFBitTorrent is one of the most popular application
in the current Internet. However, we still have little knowledge about the topology of real BitTorrent swarms and how the traffic is actually exchanged among peers. This paper addresses fundamental questions regarding the topology of live BitTorrent swarms. For this purpose we have collected the evolution of the graph topology of 250 real torrents from its birth during a period of 15 days. Using this dataset we first demonstrate that real BitTorrent swarms are neither random graphs nor small world
networks. Furthermore, we will see how some factors such as the torrent popularity affect the swarm topology. Secondly, the paper proposes a novel methodology in order to infer the clustered peers in real BitTorrent swarms, something that was not possible so far. Finally, we dedicate special effort to demonstrate that current BitTorrent swarms are experiencing a marked locality phenomenon at the overlay construction level (or connectivity graph). This locality effect is even more pronounced when we consider the exchange traffic relationships between peers. This suggests that an important portion of the BitTorrent traffic is currently confined within the ISPs. This opens a discussion
regarding the relative gain of the locality solution proposed so far.TRUEpu