IMDEA Networks Institute Digital Repository
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Providing Service Guarantees in 802.11e EDCA WLANs with Legacy Stations
Get PDFAlthough the EDCA access mechanism of the 802.11e standard supports legacy DCF stations, the presence of DCF stations in the WLAN jeopardizes the provisioning of the service guarantees committed to the EDCA stations. The reason is that DCF stations compete with Contention Windows (CWs) that are predefined and cannot be modified, and as a result, the impact of the DCF stations on the service received by the EDCA stations cannot be controlled. In this paper, we address the problem of providing throughput guarantees to EDCA stations in a WLAN in which EDCA and DCF stations coexist. To this aim, we propose a technique
that, implemented at the Access Point (AP), mitigates the impact of DCF stations on EDCA by skipping with a certain probability the Ack reply to a frame from a DCF station. When missing the Ack, the DCF station increases its CW, and thus, our technique allows us to have some control over the CWs of the legacy DCF stations. In our approach, the probability of skipping an Ack frame is dynamically adjusted by means of an adaptive algorithm. This algorithm is based on a widely used controller from classical control theory, namely a Proportional Controller. In order to find an adequate configuration of the controller, we conduct a control-theoretic analysis of the system. Simulation results show that the proposed approach is effective in providing throughput guarantees to EDCA stations in
presence of DCF stations.TRUEpu
Exploiting concurrency to improve latency and throughput in a hybrid storage system
Get PDFThis paper considers the problem of how to improve
the performance of hybrid storage system employing solid state
disks and hard disk drives. We utilize both initial block allocation
as well as migration to reach “Wardrop equilibrium”, in which
the response times of different devices equalize. We show that
such a policy allows adaptive load balancing across devices of
different performance. We also show that such a policy exploits
parallelism in the storage system effectively to improve throughput and latency simultaneously. We implemented a prototype
in Linux and evaluated it in multiple workloads and multiple
configurations. The results show that the proposed approach
improved both the latency of requests and the throughput
significantly, and it adapted to different configurations of the
system under different workloads.TRUEpu
Game Theory Application to Interdomain Routing
Get PDFThis thesis proposes a game theoretic analysis of interdomain routing. In the two following chapters we try to capture some of the intricacies of the current Internet routing protocol, the Border Gateway Protocol (BGP).
The first chapter of the thesis paper presents a survey of recent adv ances in the application of game theory to model the behaviour of interdomain routing. In these models, the
participants of the interdomain routing game are represented as strategic agents seeking to improve their benefits through the manipulation of the interdomain routing protoco l BGP.
The main results achieved over the last few years in this field include models to an alyze the stability of the interdomain routing and the design of mechanisms that guarantee BGP to be incentive-compatible with or without monetary transfers. However, over the last years, the research community has been deeply concerned about
the scalability issues that the Internet routing is facing. As the Internet popularity grows, so do the network resources needed in order to sustain its worldwide availability. In the second chapter of this thesis we consider a commons model in which the Global Routing
Table (GRT) is a public resource. We use this model to study the economic incentives the ASes have for deaggregating their assigned address blocks. We evaluate the efficiency of the global routing system, the properties of the game equilibria and we examine its relation
to the social welfare point of the considered game setup. We find that the str ategy adopted by the ASes in the interdomain is not an overall optimum strategy and it leads to an inefficient exploitation of the common resource. Therefore, we prove that the GRT, just like any common natural resource, “remorselessly generates tragedy”, following Hardin’s game theoretic analysis on the tragedy of the commons. Finally, we introduce in the model a pricing
mechanism that aims to avoid the tragedy of the Internet routing commons.Telematics EngineeringUniversidad Carlos III de Madrid, Spainpu
Opportunistic Information Dissemination in Mobile Ad-hoc Networks: The Profit of Global Synchrony
Get PDFPublished in: DISC'10 Proceedings of the 24th international conference on Distributed computing
Springer-Verlag Berlin, Heidelberg ©2010
Distributed Computing
Lecture Notes in Computer Science Volume 6343
ISBN:3-642-15762-9 978-3-642-15762-2The topic of this paper is the study of Information Dissemination in Mobile Ad-hoc Networks by means of deterministic protocols. We characterize the connectivity resulting from the movement, from failures and from the fact that nodes may join the computation at different times with two values, α and β, so that, within α time slots, some node that has the information must be connected
to some node without it for at least β time slots. The protocols studied are classified into three classes: oblivious (the transmission schedule of a node is only a
function of its ID), quasi-oblivious (the transmission schedule may also depend on a global time), and adaptive.
The main contribution of this work concerns negative results. Contrasting the lower and upper bounds derived, interesting complexity gaps among protocolclasses are observed. More precisely, in order to guarantee any progress towards solving the problem, it is shown that β must be at least n − 1 in general, but that β ∈ Ω(n
2 / log n) if an oblivious protocol is used. Since quasi-oblivious protocols can guarantee progress with β ∈ O(n), this represents a significant gap, almost linear in β, between oblivious and quasi-oblivious protocols. Regarding
the time to complete the dissemination, a lower bound of Ω(nα + n3/ log n)is proved for oblivious protocols, which is tight up to a polylogarithmic factor because a constructive O(nα + n 3 log n) upper bound exists for the same class. It is also proved that adaptive protocols require Ω(nα + n 2), which is optimal given that a matching upper bound can be proved for quasi-oblivious protocols.
These results show that the gap in time complexity between oblivious and quasioblivious, and hence adaptive, protocols is almost linear. This gap is what we call the profit of global synchrony, since it represents the gain the network obtains from global synchrony with respect to not having it.TRUEpu
A Simple Analytical Model for the Energy-Efficient Activation of Access Points in Dense WLANs
Get PDFEnergy efficient networks are becoming a hot research topic,
and the networking community is increasingly devoting its
attention to the identification of approaches to save energy in the networks of today. However, the networks of tomorrow
will require built-in energy efficiency capabilities, so that
new design techniques based on network models that account for energy efficiency are called for.
One of the simplest approaches to obtain energy efficiency
is based on the activation of network resources on demand,
thus avoiding to always power on all the resources that are
necessary to serve users during peak traffic periods.
In this paper we both present a simple analytical model
to determine the effectiveness of policies that activate APs
(Access Points) in dense WLANs (Wireless LANs) according
to the actual user demands, and quantify the performance
that is achieved by such policies in terms of energy savings
and QoS (Quality of Service). Numerical results show that,
in the configurations that we studied, energy savings up to
87% are possible during low traffic periods, with hardly any
sacrifice in QoSTRUEpu
Exploiting microscopic spectrum opportunities in cognitive radio networks via coordinated channel access
Get PDFUnder the current opportunistic spectrum access (OSA) paradigm, a common belief is that a cognitive radio (CR) can use a
channel only when this channel is not being used by any neighboring primary radio (PR). Therefore, the existence of a spectrum
opportunity hinges on the absence of active cochannel PRs in a macroscopic region. In this paper, we propose the concept of
microscopic spectrum opportunity and show that CRs can still utilize this type of opportunities without interfering with active cochannel
PRs, even when these PRs are close to them. As a result, a channel may at the same time present different levels of availability to
different CRs. Channel access needs to be carefully coordinated between these CRs to avoid collisions, and more importantly, ensure
efficient utilization of the spectrum opportunity from a network’s standpoint. In this paper, we formulate the coordinated channel access
as a joint power/rate control and channel assignment optimization problem, with the objective of maximizing the sum-rate achieved by
the cognitive radio network (CRN). We develop both centralized and distributed algorithms to solve this problem. Our simulation results
show that even when accounting for the implementation overhead, significant throughput gain is achieved under our designs.TRUEpu
Improving QoE using a Novel Multipath Routing based on Source and Intermediate Node Forwarding
No full textISBN: 978-0-7695-3940-9TRUEpu
Resource utilization mechanism for multi-rate ultrawide band networks
Get PDFUltra-wideband (UWB) communications has
emerged as a burgeoning technology for high data rate wireless
personal area networks (WPANs). In this paper, we propose
a novel resource utilization mechanism (RUM) for improving
the throughput in multi-rate UWB-based WPANs. RUM is
intended to remedy a critical issue in both unicast and multicast
transmissions. In unicast (single- and multi-hop), the connectivity
of a source-destination pair is defined by the ability to overhear
control messages (e.g., route requests, request-to-send/clear-tosend, etc.). These messages are usually sent at a low transmission
rate to extend their reachability, hence a node can directly
communicate with faraway destinations. Such destinations
cannot be reliably reached by high transmission rates. This
leads to a long channel reservation time and hence a high
blocking probability for prospective reservations and low network
throughput. In the case of multicast, the maximum transmission
rate is bottlenecked by the farthest destination. RUM exploits
opportunistic-relaying and time-spreading techniques to improve
link reliability and increase the transmission rate, and hence
network throughput. Simulations are used to demonstrate the
performance gain of RUM.TRUEpu
