-
[show abstract]
[hide abstract]
ABSTRACT: In response to the high throughput needs of grid and cloud computing applications, several production networks have recently started to support advance reservation of dedicated circuits. An important open problem within this context is to devise advance reservation algorithms that can provide provable throughput performance guarantees independently of the specific network topology and arrival pattern of reservation requests. In this paper, we first show that the throughput performance of greedy approaches, which return the earliest possible completion time for each incoming request, can be arbitrarily worse than optimal. Next, we introduce two new online, polynomial-time algorithms for advance reservation, called BatchAll and BatchLim. Both algorithms are shown to be throughput-optimal through the derivation of delay bounds for 1 + ε bandwidth augmented networks. The BatchLim algorithm has the advantage of returning the completion time of a connection immediately as a request is placed, but at the expense of looser delay performance than BatchAll. We then propose a simple approach that limits path dispersion, i.e., the number of parallel paths used by the algorithms, while provably bounding the maximum reduction factor in the transmission throughput. We prove that the number of paths needed to approximate any flow is quite small and never exceeds the total number of edges in the network. Through simulation for various topologies and traffic parameters, we show that the proposed algorithms achieve reasonable delay performance, even at request arrival rates close to capacity bounds, and that three to five parallel paths are sufficient to achieve near-optimal performance.
IEEE/ACM Transactions on Networking 11/2011; · 2.03 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We characterize policies and prices for secondary spectrum provision whose profitability is insensitive to the demand curve. In more explicit terms, the paper provides a critical price value such that if secondary access is priced above that value then allowing secondary access is profitable for the licensee as long as the price generates secondary demand. Conversely, if the price does not generate demand then the licensee does not incur any operational cost due to secondary service. Hence such characterization serves as a guarantee that a spectrum licensee can strictly avoid revenue loss due to participation in spectrum trading.
New Frontiers in Dynamic Spectrum Access Networks (DySPAN), 2011 IEEE Symposium on; 06/2011
-
[show abstract]
[hide abstract]
ABSTRACT: Identifying codes have been proposed as an abstraction for implementing monitoring tasks such as indoor localization using wireless sensor networks. In this approach, sensors' radio coverage overlaps in unique ways over each identifiable region, according to the codewords of an identifying code. While connectivity of the underlying identifying code is necessary for routing data to a sink, existing algorithms that produce identifying codes do not guarantee such a property. As such, we propose a novel polynomial-time algorithm called ConnectID that transforms any identifying code into a connected version that is also an identifying code and is provably at most twice the size of the original. We evaluate the performance of ConnectID on various random graphs, and our simulations show that the connected codes generated are actually at most 25% larger than their non-connected counterparts.
Wireless Communications and Networking Conference (WCNC), 2011 IEEE; 05/2011
-
[show abstract]
[hide abstract]
ABSTRACT: We consider the problem of generating a connected robust identifying code of a graph, by which we mean a subgraph with two properties: (i) it is connected, (ii) it is robust identifying, in the sense that the (subgraph-) induced neighborhoods of any two vertices differ by at least 2r + 1 vertices, where r is the robustness parameter. This particular formulation builds upon a rich literature on the identifying code problem but adds a property that is important for some practical networking applications. We concretely show that this modified problem is NP-complete and provide an otherwise efficient algorithm for computing it for an arbitrary graph. We demonstrate a connection between the the sizes of certain connected identifying codes and error-correcting code of a given distance. One consequence of this is that robustness leads to connectivity of identifying codes.
Information Theory and Applications Workshop (ITA), 2011; 03/2011
-
[show abstract]
[hide abstract]
ABSTRACT: New architectures have recently been proposed and deployed to support end-to-end advance reservation of network resources. These architectures rely on the use a centralized scheduler, which may be unpractical in large or administratively heterogeneous networks. In this work, we explore and demonstrate the feasibility of implementing distributed solutions for advance reservation. We introduce a new distributed, distance-vector algorithm, called Distributed Advance Reservation (DAR), that provably returns the earliest time possible for setting up a connection between any two nodes. Our main findings in this context are the following: (i) we prove that widest path routing and path switching (i.e, allowing a connection to switch between different paths) are necessary to guarantee earliest scheduling; (ii) we propose a novel approach for loop-free distributed widest path routing, leveraging the recently proposed DIV framework. Our routing results directly extend to on-demand QoS routing problems.
Parallel & Distributed Processing (IPDPS), 2010 IEEE International Symposium on; 05/2010
-
[show abstract]
[hide abstract]
ABSTRACT: We consider a wireless provider who caters to two classes of customers, namely primary and secondary users. Primary users have long term contracts while secondary users are admitted and priced according to current availability of excess spectrum. Secondary users accept an advertised price with a certain probability defined by an underlying demand function. We analyze the problem of maximizing profit gained by admission of secondary users. Previous studies in the field usually assume that the demand function is known and that the call length distribution is also known and exponentially distributed. In this paper, we analyze more realistic settings where both of these quantities are unknown. Our main contribution is to derive near-optimal pricing strategies under such settings. We focus on occupancy-based pricing policies, which depend only on the total number of ongoing calls in the system. We first show that such policies are insensitive to call length distribution except through the mean. Next, we introduce a new on-line, occupancy-based pricing algorithm, called Measurement-based Threshold Pricing (MTP) that operates by measuring the reaction of secondary users to a specific price and does not require the demand function to be known. MTP optimizes a profit function that depends on price only. We prove that while the profit function can be multimodal, MTP converges to one of the local optima as fast as if the function were unimodal. Lastly, we provide numerical studies demonstrating the near-optimal performance of occupancy-based policies for diverse sets of call length distributions and demand functions and the quick convergence of MTP to near-optimal on-line profit.
INFOCOM, 2010 Proceedings IEEE; 04/2010
-
[show abstract]
[hide abstract]
ABSTRACT: We examine the problem of minimizing feedbacks in reliable wireless broadcasting, by pairing rateless coding with extreme value theory. Our key observation is that, in a broadcast environment, this problem resolves into estimating the maximum number of packets dropped among many receivers rather than for each individual receiver. With rateless codes, this estimation relates to the number of redundant transmissions needed at the source in order for all receivers to correctly decode a message with high probability. We develop and analyze two new data dissemination protocols, called Random Sampling (RS) and Full Sampling with Limited Feedback (FSLF), based on the moment and maximum likelihood estimators in extreme value theory. Both protocols rely on a single-round learning phase, requiring the transmission of a few feedback packets from a small subset of receivers. With fixed overhead, we show that FSLF has the desirable property of becoming more accurate as the receivers's population gets larger. Our protocols are channel agnostic, in that they do not require a-priori knowledge of (i.i.d.) packet loss probabilities, which may vary among receivers. We provide simulations and an improved full-scale implementation of the Rateless Deluge over-the-air programming protocol on sensor motes as a demonstration of the practical benefits of our protocols, which translate into about 30% latency and energy consumption savings.
INFOCOM, 2010 Proceedings IEEE; 04/2010
-
[show abstract]
[hide abstract]
ABSTRACT: As a result of perceived limitations of TCP/IP in supporting high-throughput applications, significant efforts have recently been devoted to develop alternative architectures based on the concept of advance channel reservation. In this paper, we develop a polynomial-time algorithmic framework, called graded channel reservation (GCR), to support the implementation of such architectures. This framework enables users to specify minimum bandwidth and duration requirements for their connections. Upon receiving a request, GCR returns the highest graded path, selected according to a general, multicriteria optimization objective. In particular, if the optimization criterion is delay, we prove that GCR returns the earliest time available to establish the connection. Thereafter, we present a generalization of GCR, called GCR<sub>switch</sub>, that is capable of supporting path switching throughout a connection. We present practical methods for minimizing or limiting the number of path switches. Through extensive simulations, we evaluate the performance of GCR and its variants under various topological settings and applications workload. Our results show that, for certain traffic parameters, optimized path selection combined with path switching can reduce the average delay of requests by an order of magnitude and increase the maximum sustainable load by as much as 50%.
IEEE/ACM Transactions on Networking 11/2009; · 2.03 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The erasure resilience of rateless codes, such as Luby-Transform (LT) codes, makes them particularly suitable to a wide variety of loss-prone wireless and sensor network applications, ranging from digital video broadcast to software updates. Yet, traditional rateless codes usually make no use of a feedback communication channel, a feature available in many wireless settings. As such, we generalize LT codes to situations where receiver(s) provide feedback to the broadcaster. Our approach, referred to as Shifted LT (SLT) code, modifies the robust soliton distribution of LT codes at the broadcaster, based on the number of input symbols already decoded at the receivers. While implementing this modification entails little change to the LT encoder and decoder, we show both analytically and through real experiments, that it achieves significant savings in communication complexity, memory usage, and overall energy consumption. Furthermore, we show that significant savings can be even achieved with a low number of feedback messages (on the order of the square root of the total number of input symbols) transmitted at a uniform rate. The practical benefits of Shifted LT codes are demonstrated through the implementation of a real over-the-air programming application for sensor networks, based on the Deluge protocol.
INFOCOM 2009, IEEE; 05/2009
-
[show abstract]
[hide abstract]
ABSTRACT: Network coding and cooperative diversity have each extensively been explored in the literature as a means to substantially improve the performance of wireless networks. Yet, little work has been conducted to compare their performance under a common framework. Our goal in this paper is to fill in this gap. Specifically, we consider a single-hop wireless network consisting of a base station and N receivers. We perform an asymptotic analysis, as N rarr infin, of the expected delay associated with the broadcasting of a file consisting of K packets. We show that if K is fixed, cooperation outperforms network coding, in the sense that the expected delay is proportional to K (and thus within a constant factor of the optimal delay) in the former case while it grows logarithmically with N in the latter case. On the other hand, if K grows with N at a rate at least as fast as (logN)<sup>r</sup>, for r Gt 1, then we show that the average delay of network coding is also proportional to K and lower than the average delay of cooperation if the packet error probability is smaller than 0.36. Our analytical findings are validated through extensive numerical simulations.
IEEE Transactions on Wireless Communications 05/2009; · 2.59 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Over-the-air programming (OAP) is a fundamental service in sensor networks that relies upon reliable broadcast for efficient dissemination. As such, existing OAP protocols become decidedly inefficient (with respect to energy, communication or delay) in unreliable broadcast environments, such as those with relatively high node density or noise. In this paper, we consider OAP approaches based on rateless codes, which significantly improve OAP in such environments by drastically reducing the need for packet rebroadcasting. We thus design and implement two rateless OAP protocols, rateless Deluge and ACKless Deluge, both of which replace the data transfer mechanism of the established OAP Deluge protocol with rateless analogs. Experiments with Tmote Sky motes on single-hop networks with packet loss rates of 7% show these protocols to save significantly in communication over regular Deluge (roughly 15-30% savings in the data plane, and 50-80% in the control plane), and multi-hop experiments reveal similar trends. Simulations further shows that our new protocols scale better than standard Deluge (in terms of communication and energy) to high network density. TinyOS code for our implementation can be found at http://nislab.bu.edu.
Information Processing in Sensor Networks, 2008. IPSN '08. International Conference on; 05/2008
-
[show abstract]
[hide abstract]
ABSTRACT: Recent deregulation initiatives enable cellular providers to sell excess spectrum for secondary usage. In this paper, we investigate the problem of optimal spot pricing of spectrum by a provider in the presence of both non-elastic primary users, with long-term commitments, and opportunistic, elastic secondary users. We first show that optimal pricing can be formulated as an infinite horizon average reward problem and solved using stochastic dynamic programming. Next, we investigate the design of efficient single pricing policies. We provide numerical and analytical evidences that static pricing policies do not perform well in such settings (in sharp contrast to settings where all the users are elastic). On the other hand, we prove that deterministic threshold pricing achieves optimal profit amongst all single-price policies and performs close to global optimal pricing. We characterize the profit regions of static and threshold pricing, as a function of the arrival rate of primary users. Under certain reasonable assumptions on the demand function, we show that the profit region of threshold pricing can be far larger than that of static pricing. Moreover, we also show that these profit regions critically depend on the support of the demand function rather than specific form of it. We prove that the profit function of threshold pricing is unimodal in price and determine a restricted interval in which the optimal threshold lies. These two properties enable very efficient computation of the optimal threshold policy that is far faster than that of the global optimal policy.
INFOCOM 2008. The 27th Conference on Computer Communications. IEEE; 05/2008
-
[show abstract]
[hide abstract]
ABSTRACT: Advance channel reservation is emerging as an important feature of ultra high-speed networks requiring the transfer of large files. In this paper, we present two new delay-competitive algorithms for advance reservation, called BatchAll and BatchLim. These algorithms are guaranteed to achieve optimal throughput performance, based on multi-commodity flow arguments. Unlike BatchAll, the BatchLim algorithm returns the completion time of a connection immediately as a request is placed, but at the expense of a slightly looser competitive ratio than that of BatchAll. We propose a simple approach that limits the number of parallel paths used by the algorithms while provably bounding the maximum reduction factor in the transmission throughput. We show that, although the number of different paths can be exponentially large, the actual number of paths needed to approximate the flow is quite small and proportional to the number of edges in the network. According to our simulations for a number of topologies, three to five parallel paths are sufficient to achieve close to optimal performance.
INFOCOM Workshops 2008, IEEE; 05/2008
-
[show abstract]
[hide abstract]
ABSTRACT: Rate adaptation plays a key role in determining the performance of wireless LANs. In this paper, we introduce a semi-Markovian framework to analyze the performance of two of the most popular rate adaptation algorithms used in wireless LANs, namely automatic rate fallback (ARF) and adaptive automatic rate fallback (AARF). Given our modeling assumptions, the analysis is exact and provides closed form expressions for the achievable throughput of ARF and AARF. We illustrate the benefit of our analysis by numerically comparing the throughput performance of ARF and AARF in two different channel regimes. The results show that neither of these algorithms consistently outperforms the other. We thus propose and analyze a new variant to AARF, called persistent AARF (or PAARF), and show that it achieves a good compromise between the two algorithms, often performing close to the best algorithm in each of the studied regimes.
Sensor, Mesh and Ad Hoc Communications and Networks, 2007. SECON '07. 4th Annual IEEE Communications Society Conference on; 07/2007
-
[show abstract]
[hide abstract]
ABSTRACT: We analyze the performance limits of data dissemination with multi-channel, single radio sensors. We formulate the problem of minimizing the average delay of data dissemination as a stochastic shortest path problem and show that, for an arbitrary topology network, an optimal control policy can be found in a finite number of steps, using value iteration or Dijsktra's algorithm. However, the computational complexity of this solution is generally prohibitive. We thus focus on two special classes of network topologies of practical interest, namely single-hop clusters and multi-hop cluster trees. For these topologies, we derive the structure of policies that achieve an average delay within a factor 1 + e of the optimal average delay, in networks with large number of nodes. Through simulation, we show that these policies perform close to optimal even for networks with small and moderate numbers of nodes. Our analysis and simulations reveal that multichannel data dissemination policies lead to a drastic reduction in the average delay, up to a factor as large as the total number of channels available, even though each node can communicate over only one channel at any point of time. Finally, we present the foundations of a methodology, based on extreme value theory, allowing the implementation of our near-optimal dissemination policies with minimal overhead.
INFOCOM 2007. 26th IEEE International Conference on Computer Communications. IEEE; 06/2007
-
[show abstract]
[hide abstract]
ABSTRACT: The next generation of grid applications demand fast and reliable transfers of extremely large volumes of data between distributed sites around the world. For example, the U.S. Department of Energy's Genomes to Life (GTL) project aims at supporting critical applications such as bioenergy production or microbial carbon recycling [1]. GTL studies relies on ultra high throughput connections between research laboratories and supercomputers for processing and analyzing massive amounts of data.
High-Speed Networks Workshop, 2007; 06/2007
-
[show abstract]
[hide abstract]
ABSTRACT: We study secondary pricing of spectrum in wireless cellular networks employing CDMA at the physical layer. We consider a primary license holder who aims to lease its spectrum within a certain geographic subregion of its own network. Such a transaction has two contrasting economic implications for the seller: On the one hand the seller obtains a revenue due to the exercised price, or rent, of the region. On the other hand, the seller incurs a cost due to (i) reduced spatial coverage of its network and (ii) possible interference from the leased region into the retained portion of its network. We formulate an optimization problem with the objective of profit maximization, and characterize its solutions based on a reduced load approximation that can be shown to be asymptotically exact. The form of optimal prices suggests charging the buyer per admitted call, in proportion with the interference it generates. The charged amount balances the corresponding loss of revenue incurred by the seller due to the influence of an admitted call. We numerically argue that this pricing approach yields better profit compared to some other simplistic techniques.
New Frontiers in Dynamic Spectrum Access Networks, 2007. DySPAN 2007. 2nd IEEE International Symposium on; 05/2007
-
[show abstract]
[hide abstract]
ABSTRACT: Network coding and cooperative diversity have each extensively been explored in the literature as a means to substantially improve the performance of wireless networks. Yet, little work has been conducted to compare their performance under a common framework. Our goal in this paper is to fill in this gap. Specifically, we consider a single-hop wireless network consisting of a base station and N receivers. We perform an asymptotic analysis, as N rarr infin, of the expected delay associated with the broadcasting of a file consisting of K packets. We show that if K is fixed, cooperation outperforms network coding, in the sense that the expected delay is proportional to K (and thus within a constant factor of the optimal delay) in the former case while it grows logarithmically with N in the latter case. On the other hand, if K grows with N at a rate at least as fast as (log N)<sup>r</sup>, for r > 1, then we show that the average delay of network coding is within a factor less than two of the optimal delay, no worse than the average delay of cooperation. Our analytical findings are validated through extensive numerical simulations.
Information Sciences and Systems, 2007. CISS '07. 41st Annual Conference on; 04/2007
-
[show abstract]
[hide abstract]
ABSTRACT: The request-to-send/clear-to-send (RTS/CTS) mechanism is widely used in wireless networks in order to avoid packet collisions and, thus, achieve high network throughput. In multihop settings, however, current implementations of the RTS/CTS mechanism may lead to interdependencies that unnecessarily prohibit nodes from transmitting over long periods of time. We refer to this problem as "false blocking." In this paper, we describe and analyze the false blocking problem in detail. We show that false blocking can lead to a significant performance degradation in a variety of topologies and, possibly, to network-wide congestion as well. We propose a backward-compatible solution to the false blocking problem, called the RTS validation. We model and analyze the performance of RTS validation under general traffic and topology settings and show that it achieves a considerable reduction in the probability of false blocking. Furthermore, we carry out extensive simulations that validate our analysis and show that the RTS validation stabilizes the throughput at high load and increases its peak value, sometimes by as much as 50%
IEEE Transactions on Vehicular Technology 04/2007; · 1.92 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We introduce a new algorithmic framework for advanced channel reservation in ultra high speed networks, called Graded Channel Reservation (GCR). GCR allows users to specify minimum bandwidth and duration requirements for their connections. GCR returns the highest graded path, selected according to a general, multi-criteria optimization objective. In particular, if the optimization criterion is delay, we prove that GCR returns the earliest time available to establish the connection. The computational complexity is polynomial in the size of the graph and the number of pending requests. We introduce a number of variants to GCR, including one that that provides the capability to switch between different paths during a connection. We present practical methods for minimizing or limiting the number of path switches. Through extensive simulations, we evaluate the performance of GCR and its variants under various topological settings and applications workload. Our results show that, for certain traffic parameters, optimized path selection combined with path switching can reduce the average delay of requests by an order of magnitude and increase the saturation throughput by as much as 50%. I.
Broadband Communications, Networks and Systems, 2006. BROADNETS 2006. 3rd International Conference on; 11/2006
