Donald F. Towsley

University of Massachusetts Amherst, Amherst Center, Massachusetts, United States

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Publications (235)75.59 Total impact

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    ABSTRACT: We study the emergence of long-range connectivity in multilayer networks (also termed multiplex, composite and overlay networks) obtained by merging the connectivity subgraphs of multiple percolating instances of an underlying backbone network. Multilayer networks have applications ranging from studying long-range connectivity in a communication or social network formed with hybrid technologies, a transportation network connecting the same cities via rail, road and air, in studying outbreaks of flu epidemics involving multiple viral strains, studying temporal flow of information in dynamic networks, and potentially in studying conductivity properties of graphene-like stacked lattices. For a homogenous multilayer network---formed via merging $M$ random site-percolating instances of the same graph $G$ with single-layer site-occupation probability $q$---we argue that when $q$ exceeds a threshold $q_c(M) = \Theta(1/\sqrt{M})$, a spanning cluster appears in the multilayer network. Using a configuration model approach, we find $q_c(M)$ exactly for random graphs with arbitrary degree distributions, which have many applications in mathematical sociology. For multilayer percolation in a general graph $G$, we show that $q_c/\sqrt{M} < q_c(M) < \sqrt{-\ln(1-p_c)}/{\sqrt{M}}, \forall M \in {\mathbb Z}^+$, where $q_c$ and $p_c$ are the site and bond percolation thresholds of $G$, respectively. We show a close connection between multilayer percolation and mixed (site-bond) percolation, since both provide a smooth bridge between pure-site and pure-bond percolations. We find excellent approximations and bounds on layered percolation thresholds for regular lattices using the aforesaid connection, and provide several exact results (via numerical simulations), and a specialized bound for the multilayer kagome lattice using a site-to-bond transformation technique.
    02/2014;
  • Upendra Sharma, Prashant Shenoy, Donald F. Towsley
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    ABSTRACT: In this paper we present a simple and effective approach for resource provisioning to achieve a percentile bound on the end to end response time of a multi-tier application. We, at first, model the multi-tier application as an open tandem network of M/G/1-PS queues and develop a method that produces a near optimal application configuration, i.e, number of servers at each tier, to meet the percentile bound in a homogeneous server environment -- using a single type of server. We then extend our solution to a K-server case and our technique demonstrates a good accuracy, independent of the variability of service-times. Our approach demonstrates a provisioning error of no more than 3% compared to a 140% worst case provisioning error obtained by techniques based on an M/M/1-FCFS queue model. In addition, we extend our approach to handle a heterogenous server environment, i.e., with multiple types of servers. We find that fewer high-capacity servers are preferable for high percentile provisioning. Finally, we extend our approach to account for the rental cost of each server-type and compute a cost efficient application configuration with savings of over 80%. We demonstrate the applicability of our approach in a real world system by employing it to provision the two tiers of the java implementation of TPC-W -- a multi-tier transactional web benchmark that represents an e-commerce web application, i.e. an online bookstore.
    Proceedings of the 9th international conference on Autonomic computing; 09/2012
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    Yan Cai, Patrick P. C. Lee, Weibo Gong, Donald F. Towsley
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    ABSTRACT: Traffic burstiness is known to be undesirable for a router as it increases the router’s queue length and hence the queueing delays of data flows. This poses a security problem in which an attacker intentionally introduces traffic burstiness into routers. We consider a correlation attack, whose fundamental characteristic is to correlate multiple attack flows to generate synchronized small attack bursts, in an attempt to aggregate the bursts into a large burst at a target router.In this paper, we develop an analytical, fluid-based framework that models how the correlation attack disrupts router queues and how it can be mitigated. Using Poisson Counter Stochastic Differential Equations (PCSDEs), our framework captures the dynamics of a router queue for special cases and gives the closed-form average router queue length as a function of the inter-flow correlation. To mitigate the correlation attack, we apply our analytical framework to model different pacing schemes including Markov ON–OFF pacing and rate limiting, which are respectively designed to break down the inter-flow correlation and suppress the peak rates of bursts. We verify that our fluid models conform to packet-level ns2 simulation results.
    Computer Networks 01/2011; 55:734-747. · 1.23 Impact Factor
  • Pinghui Wang, Xiaohong Guan, Weibo Gong, Donald F. Towsley
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    ABSTRACT: We present a new virtual indexing method for estimating host connection degrees for high speed links. It is based on the virtual connection degree sketch where a compact sketch of network traffic is built by generating the associated virtual bitmaps for each host. Each virtual bitmap consists of a fixed number of bits selected randomly from a shared bit array by a new method for recording the traffic flows of the corresponding host. The shared bit array is efficiently utilized by all hosts since its every bit is shared by the virtual bitmaps of multiple hosts. To reduce the “noise” contaminated in a host's virtual bitmaps due to sharing, we propose a new method to generate the “filtered” bitmap used to estimate host connection degree. Furthermore, it can be easily implemented in parallel and distributed processing environments. The experimental and testing results based on the actual network traffic show that the new method is accurate and efficient.
    INFOCOM 2011. 30th IEEE International Conference on Computer Communications, Joint Conference of the IEEE Computer and Communications Societies, 10-15 April 2011, Shanghai, China; 01/2011
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    Cagatay Capar, Dennis Goeckel, Donald F. Towsley
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    ABSTRACT: The capability of nodes to broadcast their message to the entire wireless network when nodes employ cooperation is considered. We employ an asymptotic analysis using an extended random network setting and show that the broadcast performance strongly depends on the path loss exponent of the medium. In particular, as the size of the random network grows, the probability of broadcast in a one-dimensional network goes to zero for path loss exponents larger than one, and goes to a nonzero value for path loss exponents less than one. In two-dimensional networks, the same behavior is observed for path loss exponents above and below two, respectively.
    IEEE Transactions on Information Theory 01/2011; abs/1104.3209. · 2.62 Impact Factor
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    ABSTRACT: One of the challenges of wireless networks is to pro- vide a reliable end-to-end path between two end hosts in the face of link and node outages. These can occur due to fluctuations in channel quality, node movement, or node failure. One mechanism that has been proposed is based on multipath routing , the idea being to establish two or more paths between the end hosts so that they always have a path between them with high probability in the face of outages. This naturally raises the question of how to discover these paths in an unknown, random wireless network to enable robust multipath routing. In order to answer this question, we model a random wireless network as a 2D spatial Poisson process. Based on the results of percolation highways in Franceschetti, et al. (1), we present accurate conditions that enable robust multipath routing. If the number of hops of a path between the end hosts is n, then there exists a path between them in a strip of width proportional to log n. More precisely, there exist C log n disjoint paths in a strip of width a(C,p ) · log n, where p is the probability that characterizes the availability of an individual wireless communication link. We derive tight bounds for the function a(C,p ). This provides a useful guideline for the establishment of multiple paths in a real wireless network, namely that the width should grow logarithmically in the number of hops on the path between the hosts.
    INFOCOM 2011. 30th IEEE International Conference on Computer Communications, Joint Conference of the IEEE Computer and Communications Societies, 10-15 April 2011, Shanghai, China; 01/2011
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    Peter B. Key, Laurent Massoulié, Donald F. Towsley
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    ABSTRACT: In this paper, we investigate the benefits that accrue from the use of multiple paths by a session coupled with rate control over those paths. In particular, we study data transfers under two classes of multipath control, coordinated control where the rates over the paths are determined as a function of all paths, and uncoordinated control where the rates are determined independently over each path. We show that coordinated control exhibits desirable load balancing properties; for a homogeneous static random paths scenario, we show that the worst-case throughput performance of uncoordinated control behaves as if each user has but a single path (scaling like log(log(N) )/ log(N) where N is the system size, measured in number of resources), whereas coordinated control yields a worstcase throughput allocation bounded away from zero. We then allow users to change their set of paths and introduce the notion of a Nash equilibrium. We show that both coordinated and uncoordinated control lead to Nash equilibria corresponding to desirable welfare maximizing states, provided in the latter case, the rate controllers over each path do not exhibit any round-trip time (RTT) bias (unlike TCP Reno). Finally, we show in the case of coordinated control that more paths are better, leading to greater welfare states and throughput capacity, and that simple path reselection polices that shift to paths with higher net benefit can achieve these states.
    Commun. ACM. 01/2011; 54:109-116.
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    ABSTRACT: The workloads in modern Chip-multiprocessors (CMP) are becoming increasingly diversified, creating different resource demands on hardware substrate. It is necessary to allocate hardware resources based on the needs of the workloads in order to improve ...
    SIGMETRICS 2011, Proceedings of the 2011 ACM SIGMETRICS International Conference on Measurement and Modeling of Computer Systems, San Jose, CA, USA, 07-11 June 2011 (Co-located with FCRC 2011); 01/2011
  • SIGMETRICS 2010, Proceedings of the 2010 ACM SIGMETRICS International Conference on Measurement and Modeling of Computer Systems, New York, New York, USA, 14-18 June 2010; 06/2010
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    ABSTRACT: We identify privacy risks associated with releasing network datasets and provide an algorithm that mitigates those risks. A network dataset is a graph representing entities connected by edges representing relations such as friendship, communication or shared activity. Maintaining privacy when publishing a network dataset is uniquely challenging because an individual’s network context can be used to identify them even if other identifying information is removed. In this paper, we introduce a parameterized model of structural knowledge available to the adversary and quantify the success of attacks on individuals in anonymized networks. We show that the risks of these attacks vary based on network structure and size and provide theoretical results that explain the anonymity risk in random networks. We then propose a novel approach to anonymizing network data that models aggregate network structure and allows analysis to be performed by sampling from the model. The approach guarantees anonymity for entities in the network while allowing accurate estimates of a variety of network measures with relatively little bias.
    The VLDB Journal 01/2010; 19:797-823. · 1.40 Impact Factor
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    Jian Tan, Wei Wei, Bo Jiang, Ness B. Shroff, Donald F. Towsley
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    ABSTRACT: Parallelism has often been used to improve the reliability and efficiency of a variety of different engineering systems. In this paper, we quantify the efficiency of parallelism in systems that are prone to failures and exhibit power law processing durations. We focus on the context of transmitting a data unit in communication networks, where parallelism can be achieved by multipath transmission (e.g., multipath routing). We investigate two types of transmission schemes: redundant and split transmission techniques. We find that the power-law transmission delay phenomenon still persists with multipath transmission. In particular, we show that when the transmission delays of each path are characterized by the same power law, redundant multipath transmission can only result in a constant factor performance gain, while order gains are possible when the delays are light tailed. We further compare the performance of redundant transmission and split transmission, and show that there is no clear winner. Depending on the packet size distribution properties and the manner in which splitting is performed, one scheme results in greater performance over the other. Specifically, split transmission is effective in mitigating power law delays if the absolute value of the logarithm of the packet size probability tail is regularly varying with positive index, and becomes ineffective if the above quantity is slowly varying. Based on our analysis, we develop an optimal split transmission strategy, and show that this strategy always outperforms redundant transmission.
    SIGMETRICS 2010, Proceedings of the 2010 ACM SIGMETRICS International Conference on Measurement and Modeling of Computer Systems, New York, New York, USA, 14-18 June 2010; 01/2010
  • Zhiguo Ding, Kin K. Leung, Dennis Goeckel, Donald F. Towsley
    IEEE Transactions on Communications. 01/2010; 58:2425-2435.
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    ABSTRACT: Peer-to-peer swarming is one of the de facto solutions for distributed content dissemination in today’s Internet. By leveraging resources provided by clients, swarming systems reduce the load on and costs to publishers. However, there is a limit to how much cost savings can be gained from swarming; for example, for unpopular content peers will always depend on the publisher in order to complete their downloads. In this paper, we investigate such a dependence of peers on a publisher. For this purpose, we propose a new metric, namely swarm self-sustainability. A swarm is referred to as self-sustaining if all its blocks are collectively held by peers; the self-sustainability of a swarm is the fraction of time in which the swarm is self-sustaining. We pose the following question: how does the self-sustainability of a swarm vary as a function of content popularity, the service capacity of the users, and the size of the file? We present a model to answer the posed question. We then propose efficient solution methods to compute self-sustainability. The accuracy of our estimates is validated against simulations. Finally, we also provide closed-form expressions for the fraction of time that a given number of blocks is collectively held by peers.
    Perform. Eval. 01/2010; 67:1243-1258.
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    ABSTRACT: In a number of network scenarios (including military settings), mobile nodes are clustered into groups, with nodes within the same group exhibiting significant correlation in their movements. Mobility models for such networks should reflect this group structure. In this paper, we consider the problem of identifying the number of groups, and the membership of mobile nodes within groups, from a trace of mobile nodes. We present two clustering algorithms to determine the number of groups and their identities: k-means chain and spectral clustering. Different from traditional k-means clustering, k-means chain identifies the number of groups in a dynamic graph, using a chaining process to keep track of group trajectories over the entire trace. The second approach uses spectral clustering, which uses similarities between node pairs to cluster nodes into groups. We show that the number of groups and node membership can be accurately extracted from traces, particularly when the number of groups is small.
    Proceedings of the 6th International Wireless Communications and Mobile Computing Conference, IWCMC 2010, Caen, France, June 28 - July 2, 2010; 01/2010
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    Bruno F. Ribeiro, Donald F. Towsley
    Proceedings of the 10th ACM SIGCOMM Conference on Internet Measurement 2010, Melbourne, Australia - November 1-3, 2010; 01/2010
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    Sudarshan Vasudevan, Dennis Goeckel, Donald F. Towsley
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    ABSTRACT: We investigate the scalability of a class of algorithms that exploit the dynamics of wireless fading channels to achieve secret communication in a large wireless network of n randomly located nodes. We describe a construction in which nodes transmit artificial noise to suppress eavesdroppers whose locations are unknown and ensure secrecy of messages transported across the network. Under a model in which eavesdroppers operate independently and under appropriate conditions on the achievable per-node throughput Ψ(n), we show that the network can tolerate Ω((1⁄√n(n))2c) eavesdroppers while ensuring that the aggregate rate at which eavesdroppers intercept packets goes to 0, where c is a constant such that 0 c n(n))1ε) antennas, ∀ε > 0. We also establish sufficient conditions on the number of eavesdroppers to achieve a non-zero throughput in our construction.
    Proceedings of the 11th ACM Interational Symposium on Mobile Ad Hoc Networking and Computing, MobiHoc 2010, Chicago, IL, USA, September 20-24, 2010; 01/2010
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    ABSTRACT: Streaming movies over the Internet has become increasingly popular in recent years as an alternative to mailing DVDs to a customer. In this paper we investigate the environmental- and energy-related impacts of these two methods of movie content delivery. We compare the total energy consumed and the carbon footprint impact of these two delivery methods and find that the non-energy optimized streaming of a movie through the Internet consumes approximately 78% of the energy needed to ship a movie, but has a carbon footprint that is approximately 100% higher. However, by taking advantage of recently proposed "greening of IT" techniques in the research literature for the serving and transmission of the movie, we find that the energy consumption and carbon footprint of streaming can be reduced to approximately 30% and 65% respectively of that of shipping. We also consider how this tradeoff may change in the future.
    Proceedings of the 1st ACM SIGCOMM Workshop on Green Networking 2010, New Delhi, India, August 30, 2010; 01/2010
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    ABSTRACT: Many emerging information processing applications require applying various fork and join type operations such as correlation, aggregation, and encoding/decoding to data streams in real-time. Each operation will require one or more simultaneous input data streams and produce one or more output streams, where the processing may shrink or expand the data rates upon completion. Multiple tasks can be co-located on the same server and compete for limited resources. Effective in-network processing and resource management in a distributed heterogeneous environment is critical to achieving better scalability and provision of quality of service. In this paper, we study the distributed resource allocation problem for a synchronous fork and join processing network, with the goal of achieving the maximum total utility of output streams. Using primal and dual based optimization techniques, we propose several decentralized iterative algorithms to solve the problem, and design protocols that implement these algorithms. These algorithms have different strengths in practical implementation and can be tailored to take full advantage of the computing capabilities of individual servers. We show that our algorithms guarantee optimality and demonstrate through simulation that they can adapt quickly to dynamically changing environments.
    INFOCOM 2010. 29th IEEE International Conference on Computer Communications, Joint Conference of the IEEE Computer and Communications Societies, 15-19 March 2010, San Diego, CA, USA; 01/2010
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    ABSTRACT: This work investigates reciprocity in peer-to-peer systems. The scenario is one where users arrive to the network with a set of contents and content demands. Peers exchange contents to satisfy their demands, following either a direct reciprocity principle ( I help you and you help me ) or indirect reciprocity principle ( I help you and someone helps me ). First, we prove that any indirect reciprocity schedule of exchanges, in the absence of relays, can be replaced by a direct reciprocity schedule, provided that users (1) are willing to download undemanded content for bartering purposes and (2) use up to twice the bandwidth they would use under indirect reciprocity. Motivated by the fact that, in the absence of relays, the loss of efficiency due to direct reciprocity is at most two, we study various distributed direct reciprocity schemes through simulations, some of them involving a broker to facilitate exchanges.
    INFOCOM 2010. 29th IEEE International Conference on Computer Communications, Joint Conference of the IEEE Computer and Communications Societies, 15-19 March 2010, San Diego, CA, USA; 01/2010
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    ABSTRACT: This work proposes and studies the properties of a hybrid sampling scheme that mixes independent uniform node sampling and random walk (RW)-based crawling. We show that our sampling method combines the strengths of both uniform and RW sampling while minimizing their drawbacks. In particular, our method increases the spectral gap of the random walk, and hence, accelerates convergence to the stationary distribution. The proposed method resembles PageRank but unlike PageRank preserves time-reversibility. Applying our hybrid RW to the problem of estimating degree distributions of graphs shows promising results.
    Algorithms and Models for the Web-Graph - 7th International Workshop, WAW 2010, Stanford, CA, USA, December 13-14, 2010. Proceedings; 01/2010

Publication Stats

12k Citations
75.59 Total Impact Points

Institutions

  • 1985–2012
    • University of Massachusetts Amherst
      • • School of Computer Science
      • • Department of Electrical and Computer Engineering
      Amherst Center, Massachusetts, United States
  • 2002–2008
    • Microbiology Department at UMass Amherst
      Amherst Center, Massachusetts, United States
    • Northrop Grumman
      Falls Church, Virginia, United States
  • 2005
    • Cancer Research UK Cambridge Institute
      Cambridge, England, United Kingdom
  • 2002–2005
    • Columbia University
      • Department of Electrical Engineering
      New York City, New York, United States
  • 2003
    • University of Florida
      Gainesville, Florida, United States
    • Politecnico di Torino
      Torino, Piedmont, Italy
  • 2001
    • University of Bologna
      • Department of Computer Science and Engineering DISI
      Bologna, Emilia-Romagna, Italy
  • 1999
    • AT&T Labs
      Austin, Texas, United States
  • 1995–1998
    • The Chinese University of Hong Kong
      • Department of Computer Science and Engineering
      Hong Kong, Hong Kong
  • 1997
    • University of Nice-Sophia Antipolis
      Nice, Provence-Alpes-Côte d'Azur, France
  • 1996
    • The American University of Rome
      Roma, Latium, Italy