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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 but fixed, recent work has yielded fruitful results for local area networks and radio networks, although either the solution is suboptimal or a (possibly loose) upper bound on the number of users needs to be known.
In this paper, we present the first (two) protocols for contention resolution in radio networks that are asymptotically optimal (with high probability), work without collision detection, and do not require information about the number of contenders. The protocols are evaluated and contrasted with the previous work by extensive simulations. These show that the complexity bounds obtained by the analysis are rather tight, and that the two protocols proposed have small and predictable complexity for all system sizes (unlike previous proposals).Institute IMDEA Networkspu
Brief Announcement: Opportunistic Information Dissemination in Mobile Ad-Hoc Networks: - Adaptiveness vs. Obliviousness and Randomization vs. Determinism
Get PDFIn the context of Mobile Ad-hoc Networks (MANET), we
study the problem of disseminating a piece of information, initially held by a source node, to some subset of nodes. We use a model of MANETs that is well suited for dynamic networks and opportunistic communication. We assume that network nodes are placed in a plane where they can move with bounded speed; they may start, crash and recover at different times; and they communicate in a collision-prone single channel. In this setup informed and uninformed nodes may be disconnected for some time, but eventually some informed-uninformed pair must be connected long enough to communicate. We show negative and positive results for
different types of randomized protocols, and we contrast them with our previous deterministic results.TRUEpu
Architecture and Abstractions for Environment and Traffic Aware System-Level Coordination of Wireless Networks
Get PDFThis paper presents a system level approach to interference management in an infrastructure based wireless network with full frequency reuse. The key idea is to use loose base station coordination that is tailored to the spatial load
distribution and the propagation environment to exploit the
diversity in a user population’s sensitivity to interference. System architecture and abstractions to enable such coordination are developed for both the downlink and the uplink cases, which present differing interference characteristics. The basis for the approach is clustering and aggregation of traffic loads into classes of users with similar interference sensitivities that enable
coarse grained information exchange among base stations with
greatly reduced communication overheads. The paper explores
ways to model and optimize the system under dynamic traffic
loads where users come and go resulting in interference induced performance coupling across base stations. Based on extensive system-level simulations, we demonstrate load-dependent reductions in file transfer delay ranging from 20-80% as compared to a simple baseline not unlike systems used in the field today, while simultaneously providing more uniform coverage. Average savings in user power consumption of up to 75% is achieved. Performance results under heterogeneous spatial loads illustrate the importance of being traffic and environment aware.TRUEpu
Principles of Distributed Systems - 15th International Conference, OPODIS 2011, Toulouse, France, December 13-16, 2011. Proceedings
No full textThis book constitutes the refereed proceedings of the 15th International Conference on Principles of Distributed Systems, OPODIS 2011, held in Toulouse, France, in December 2011. The 26 revised papers presented in this volume were carefully reviewed and selected from 96 submissions. They represent the current state of the art of the research in the field of the design, analysis and development of distributed and real-time systems.TRUEpu
B-Neck: A Distributed and Quiescent Max-min Fair Algorithm
Get PDFThe problem of fairly distributing the capacity of a network among a set of sessions has been widely studied. In
this problem, each session connects via a single path a source and a destination, and its goal is to maximize its assigned transmission rate (i.e., its throughput). Since the links of the network have limited bandwidths, some criterion has to be defined to fairly distribute their capacity among the sessions. A popular criterion is max-min fairness that, in short, guarantees that each session i gets a rate !i such that no sessions can increase !s without causing another session s! to end up with a rate !s! < !s. Many max-min fair algorithms have been proposed, both centralized and distributed. However, to our knowledge, all proposed distributed algorithms require control data being continuously transmitted to recompute the max-min fair rates when needed (because none of them has mechanisms to detect convergence to the max-min fair rates). In this paper we propose B-Neck, a distributed max-min fair algorithm that is also quiescent. This means that, in absence of changes (i.e., session arrivals or departures), once the maxmin rates have been computed, B-Neck stops generating network traffic. Quiescence is a key design concept of B-Neck, because B-Neck routers are capable of detecting and notifying changes in the convergence conditions of max-min fair rates. As far as
we know, B-Neck is the first distributed max-min fair algorithm that does not require a continuous injection of control traffic to compute the rates. The correctness of B-Neck is formally proved, and extensive simulations are conducted. In them, it is shown that B-Neck converges relatively fast and behaves nicely in presence of sessions arriving and departing.TRUEpu
Performance Evaluation of IEEE 802.11aa MAC Enhancements for Robust Audio Video Streaming
Get PDFVideo traffic is foreseen to account for the majority of the Internet traffic in the near future. While the demand of video transmission keeps growing, the vast majority of wireless equipment deployed in the home environment, based on IEEE 802.11, does not support robust multicast transmission that video applications require. In order to cope with the increasing demand of multimedia traffic, the IEEE 802.11aa Task Group is standardizing new mechanisms that allow the efficient transmission of unicast/multicast multimedia flows in Wireless LAN. In this thesis, we provide analytical models for the throughput of new mechanisms proposed by the Task Group and we validate them through simulation. We also study the reliability via simulation, providing insight into new methods included in the standard to handle group addressed frames.Telematics EngineeringUniversidad Carlos III de Madrid, Spainpu
Energy Efficient File Distribution
No full textThe Internet is growing very rapidly. With it, the
total energy consumption of the devices required to keep it
functioning properly to meet the demand. While a tremendous
amount of research has been done to reduce the energy consumption of the devices, this paper focuses on file distribution mechanism from an energy point of view. We model and characterize the energy consumed in the file distribution from one host to several clients. We derive lower bounds on the energy required for distribution and subsequently design algorithms that achieve these lower bounds proving that upto 50% energy savings are possible in the best case. Moreover, our scheme are efficient with respect to the time required to finish the process. In addition to the theoretical results, we also discuss some potential scenarios where our schemes can be applied in practice.Telematics EngineeringUniversidad Carlos III de Madrid, Spainpu
IEEE 802.21 and Proxy Mobile IPv6: A network controlled mobility solution
Get PDFIP Mobility has been deeply investigated in the past years and standardization bodies (e.g., IETF, 3GPP and IEEE) have specified a wide suite of protocols enabling seamless mobility across heterogeneous wireless access technologies. However, such mobility helping technologies are not yet widely spread as compared to other emerging technologies like WiFi hotspots. This paper aims at filling this gap between research and real deployments by specifying and implementing a scheme for mobility support in wireless heterogeneous environments. In our solution, mobility management is achieved via the Proxy Mobile IPv6 protocol while optimized handover control is provided by the integration of the IEEE 802.21 framework with Proxy Mobile IPv6. The paper also includes the performance evaluation of the proposed platform, shows results obtained through live experiments on the field.TRUEpu
VoIPiggy: Implementation and evaluation of a mechanism to boost voice capacity in 802.11 WLANs
Get PDFSupporting voice traffic in existing WLANs results extremely inefficient, given the large overheads of the protocol operation and the need to prioritize this traffic over, e.g., bulky transfers. In this thesis we propose a simple scheme to improve the efficiency of WLANs when voice traffic is present. The mechanism is based on piggybacking voice frames from one direction of the voice call over the acknowledgments for the frames on the other direction, which reduces both frame overheads and time spent in contentions. We evaluate its performance by means of analysis and in a large-scale testbed consisting on 30 commercial off-the-shelf devices. The experimental results follow those from the analytical model, obtaining dramatic performance improvements in both voice-only and mixed
voice-and-data scenarios.Telematics EngineeringUniversidad Carlos III de Madrid, Spainpu
