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  • 1.
    Al-Zubaidy, Hussein
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Network and Systems engineering. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Dán, György
    KTH, School of Electrical Engineering (EES), Network and Systems engineering. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Flierl, Markus
    KTH, School of Electrical Engineering (EES), Information Science and Engineering. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Reliable Video Streaming With Strict Playout Deadline in Multihop Wireless Networks2017In: IEEE transactions on multimedia, ISSN 1520-9210, E-ISSN 1941-0077, Vol. 19, no 10, 2238-2251 p.Article in journal (Refereed)
    Abstract [en]

    Motivated by emerging vision-based intelligent services, we consider the problem of rate adaptation for high-quality and low-delay visual information delivery over wireless networks using scalable video coding. Rate adaptation in this setting is inherently challenging due to the interplay between the variability of the wireless channels, the queuing at the network nodes, and the frame-based decoding and playback of the video content at the receiver at very short time scales. To address the problem, we propose a low-complexity model-based rate adaptation algorithm for scalable video streaming systems, building on a novel performance model based on stochastic network calculus. We validate the analytic model using extensive simulations. We show that it allows fast near-optimal rate adaptation for fixed transmission paths, as well as cross-layer optimized routing and video rate adaptation in mesh networks, with less than 10% quality degradation compared to the best achievable performance.

  • 2.
    Al-Zubaidy, Hussein Mohammed
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Performance of in-network processing for visual analysis in wireless sensor networks2015In: Proceedings of 2015 14th IFIP Networking Conference, IFIP Networking 2015, IEEE conference proceedings, 2015Conference paper (Refereed)
    Abstract [en]

    Nodes in a sensor network are traditionally used for sensing and data forwarding. However, with the increase of their computational capability, they can be used for in-network data processing, leading to a potential increase of the quality of the networked applications as well as the network lifetime. Visual analysis in sensor networks is a prominent example where the processing power of the network nodes needs to be leveraged to meet the frame rate and the processing delay requirements of common visual analysis applications. The modeling of the end-to-end performance for such networks is, however, challenging, because in-network processing violates the flow conservation law, which is the basis for most queuing analysis. In this work we propose to solve this methodological challenge through appropriately scaling the arrival and the service processes, and we develop probabilistic performance bounds using stochastic network calculus. We use the developed model to determine the main performance bottlenecks of networked visual processing. Our numerical results show that an end-to-end delay of 2-3 frame length is obtained with violation probability in the order of 10-6. Simulation shows that the obtained bounds overestimates the end-to-end delay by no more than 10%.

  • 3. Andersson, G.
    et al.
    Esfahani, P. M.
    Vrakopoulou, M.
    Margellos, K.
    Lygeros, J.
    Teixeira, André
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Cyber-security of SCADA systems2012In: 2012 IEEE PES Innovative Smart Grid Technologies, ISGT 2012, IEEE , 2012, 6175543- p.Conference paper (Refereed)
    Abstract [en]

    After a general introduction of the VIKING EU FP7 project two specific cyber-attack mechanisms, which have been analyzed in the VIKING project, will be discussed in more detail. Firstly an attack and its consequences on the Automatic Generation Control (AGC) in a power system are investigated, and secondly the cyber security of State Estimators in SCADA systems is scrutinized.

  • 4. Araldo, Andrea
    et al.
    Dan, György
    KTH, School of Electrical Engineering (EES), Network and Systems engineering.
    Rossi, Dario
    Stochastic Dynamic Cache Partitioning for Encrypted Content Delivery2016In: Proceedings of the 28th International Teletraffic Congress, ITC 2016, IEEE Press, 2016, Vol. 1, 139-147 p.Conference paper (Refereed)
    Abstract [en]

    In-network caching is an appealing solution to cope with the increasing bandwidth demand of video, audio and data transfer over the Internet. Nonetheless, an increasing share of content delivery services adopt encryption through HTTPS, which is not compatible with traditional ISP-managed approaches like transparent and proxy caching. This raises the need for solutions involving both Internet Service Providers (ISP) and Content Providers (CP): by design, the solution should preserve business-critical CP information (e.g., content popularity, user preferences) on the one hand, while allowing for a deeper integration of caches in the ISP architecture (e.g., in 5G femto-cells) on the other hand. In this paper we address this issue by considering a content-oblivious ISP-operated cache. The ISP allocates the cache storage to various content providers so as to maximize the bandwidth savings provided by the cache: the main novelty lies in the fact that, to protect business-critical information, ISPs only need to measure the aggregated miss rates of the individual CPs and do not need to be aware of the objects that are requested, as in classic caching. We propose a cache allocation algorithm based on a perturbed stochastic subgradient method, and prove that the algorithm converges close to the allocation that maximizes the overall cache hit rate. We use extensive simulations to validate the algorithm and to assess its convergence rate under stationary and non-stationary content popularity. Our results (i) testify the feasibility of content-oblivious caches and (ii) show that the proposed algorithm can achieve within 10% from the global optimum in our evaluation.

  • 5. Baroffio, L.
    et al.
    Canclini, A.
    Cesana, M.
    Redondi, A.
    Tagliasacchi, M.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Eriksson, Emil
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Ascenso, J.
    Monteiro, P.
    Demo: Enabling image analysis tasks in visual sensor networks2014In: Proceedings of the 8th ACM/IEEE International Conference on Distributed Smart Cameras, ICDSC 2014, Association for Computing Machinery (ACM), 2014, a46- p.Conference paper (Refereed)
    Abstract [en]

    This demo showcases some of the results obtained by the GreenEyes project, whose main objective is to enable visual analysis on resource-constrained multimedia sensor networks. The demo features a multi-hop visual sensor network operated by BeagleBones Linux computers with IEEE 802.15.4 communication capabilities, and capable of recognizing and tracking objects according to two different visual paradigms. In the traditional compress-then-analyze (CTA) paradigm, JPEG compressed images are transmitted through the network from a camera node to a central controller, where the analysis takes place. In the alternative analyze-then-compress (ATC) paradigm, the camera node extracts and compresses local binary visual features from the acquired images (either locally or in a distributed fashion) and transmits them to the central controller, where they are used to perform object recognition/tracking. We show that, in a bandwidth constrained scenario, the latter paradigm allows to reach better results in terms of application frame rates, still ensuring excellent analysis performance.

  • 6.
    Barreto, Sergio
    et al.
    EPFL.
    Pignati, Marco
    EPFL.
    Dán, György
    KTH, School of Electrical Engineering (EES), Network and Systems engineering.
    Paolone, Mario
    EPFL.
    Le Boudec, Jean-Yves
    EPFL.
    Undetectable PMU Timing-Attack on Linear State-Estimation by UsingRank-1 Approximation2016In: IEEE Transactions on Smart Grid, ISSN 1949-3053, E-ISSN 1949-3061Article in journal (Refereed)
    Abstract [en]

    Smart-grid applications based on synchrophasor measurements have recently been shown to be vulnerable to timing attacks. A fundamental question is whether timing attacks could remain undetected by bad-data detection algorithms used in conjunction with state-of-the-art situational-awareness state estimators. In this paper, we analyze the detectability of timing attacks on linear state-estimation. We show that it is possible to forge delay attacks that are undetectable. We give a closed form for an undetectable attack; it imposes two phase offsets to two or more synchrophasor-based measurement units that can be translated to synchrophasors’ time delays. We also propose different methods for combining two-delays attacks to produce a larger impact. We simulate the attacks on a benchmark powertransmission grid, we show that they are successful and can lead to physical grid damage. To prove undetectability, we use classic bad-data detection techniques such as the largest normalized residual and the 2-test.

  • 7.
    Barreto, Sergio
    et al.
    EPFL.
    Shereen, Ezzeldin
    KTH, School of Electrical Engineering (EES), Network and Systems engineering.
    Pignati, Marco
    EPFL.
    Dán, György
    KTH, School of Electrical Engineering (EES), Network and Systems engineering.
    Le Boudec, Jean-Yves
    EPFL.
    Paolone, Mario
    EPFL.
    A Continuum of Undetectable Timing-Attacks on PMU-based Linear State-Estimation2017Conference paper (Refereed)
  • 8. Carlsson, N.
    et al.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Mahanti, A.
    Arlitt, M.
    A longitudinal characterization of local and global BitTorrent workload dynamics2012In: 13th International Conference on Passive and Active Measurement (PAM), 2012, Springer Berlin/Heidelberg, 2012, Vol. 7192 LNCS, 252-262 p.Conference paper (Refereed)
    Abstract [en]

    Workload characterization is important for understanding how systems and services are used in practice and to help identify design improvements. To better understand the longitudinal workload dynamics of chunk-based content delivery systems, this paper analyzes the BitTorrent usage as observed from two different vantage points. Using two simultaneously collected 48-week long traces, we analyze the differences in download characteristics and popularity dynamics observed locally at a university campus versus at a global scale. We find that campus users typically download larger files and are early adopters of new content, in the sense that they typically download files well before the time at which the global popularity of the files peak. The noticeable exception is music files, which the campus users are late to download. We also find that there typically is high churn in the set of files that are popular each week, both locally and globally, and that the most popular files peak significantly later than their release date. These findings provide insights that may improve the efficiency of content sharing locally, and thus increase the scalability of the global system.

  • 9.
    Carlsson, Niklas
    et al.
    Linkoping University.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Eager, Derek
    University of Saskatchewan .
    Mahanti, Anirban
    NICTA.
    Tradeoffs in cloud and peer-assisted content delivery systems2012In: 2012 IEEE 12th International Conference on Peer-to-Peer Computing, P2P 2012, IEEE , 2012, 249-260 p.Conference paper (Refereed)
    Abstract [en]

    With the proliferation of cloud services, cloud-based systems can become a cost-effective means of on-demand content delivery. In order to make best use of the available cloud bandwidth and storage resources, content distributors need to have a good understanding of the tradeoffs between various system design choices. In this work we consider a peer-assisted content delivery system that aims to provide guaranteed average download rate to its customers. We show that bandwidth demand peaks for contents with moderate popularity, and identify these contents as candidates for cloud-based service. We then consider dynamic content bundling (inflation) and cross-swarm seeding, which were recently proposed to improve download performance, and evaluate their impact on the optimal choice of cloud service use. We find that much of the benefits from peer seeding can be achieved with careful torrent inflation, and that hybrid policies that combine bundling and peer seeding often reduce the delivery costs by 20% relative to only using seeding. Furthermore, all these peer-assisted policies reduce the number of files that would need to be pushed to the cloud. Finally, we show that careful system design is needed if locality is an important criterion when choosing cloud-based service provisioning.

  • 10. Carra, D.
    et al.
    Strufe, T.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Karnstedt, M.
    Topic 7: Peer-to-peer computing (Introduction)2013In: Lecture Notes in Computer Science, 2013, 353- p.Conference paper (Refereed)
    Abstract [en]

    In Peer-to-peer (P2P) systems computers form an overlay network and share their resources (storage, CPU, bandwidth) to implement a service on top of the Internet. P2P computing has a great potential for creating systems that are selforganizing, efficient, and scalable, but it also faces many challenges: dynamic peer arrivals and departures, which may be correlated (e.g., flash crowd effects, or software failures), high variability of resources, and resource heterogeneity. This topic provides a forum for researchers to present new contributions to P2P systems, technologies, middleware, and applications that address key research issues and challenges.

  • 11. Casetti, C.
    et al.
    Cesana, M.
    Filippini, I.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Marsh, I.
    Context-aware information dissemination in vehicular networks2011In: EURO-NGI Conf. Next Gener. Internet Networks, NGI - Proc., 2011Conference paper (Refereed)
    Abstract [en]

    With the proliferation of mobile devices and vehicular onboard-units mobility is becoming a key factor in determining the performance of networked systems: both the performance of the infrastructure (e.g., the amount of control traffic) and the performance perceived by the end-users (e.g., access latency, throughput) are influenced by mobility. Mobility, as a manifestation of the physical world, transforms content distribution systems into cyber-physical systems. The efficient design and operation of cyber-physical systems, in general, requires an understanding of the characteristics and of the interactions between the components of the system.

  • 12.
    Chatzidrossos, Ilias
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Playout Adaptation in Peer-to-Peer Systems Under Churn2012In: 2012 19th International Packet Video Workshop, PV 2012, IEEE , 2012, 119-124 p.Conference paper (Refereed)
    Abstract [en]

    We address the problem of playout adaptation in peer-to-peer streaming systems. We propose two algorithms for playout adaptation: one coordinated and one distributed. The algorithms dynamically adapt the playback delay of the peers so that the playout miss ratio is maintained within a predefined interval. We validate the algorithms and evaluate their performance through simulations under various churn models. We show that playout adaptation is essential in peer-to-peer systems when the system size changes. At the same time, our results show that distributed adaptation performs well only if the peers in the overlay have similar playback delays. Thus, some form of coordination among the peers is necessary for distributed playout adaptation in peer-to-peer streaming systems.

  • 13.
    Chatzidrossos, Ilias
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktória
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Delay and playout probability trade-off in mesh-based peer-to-peer streaming with delayed buffer map updates2009In: Peer-to-Peer Networking and Applications, ISSN 1936-6442, Vol. 3, no 3, 208-221 p.Article in journal (Refereed)
    Abstract [en]

    In mesh-based peer-to-peer streaming systemsdata is distributed among the peers according tolocal scheduling decisions. The local decisions affecthow packets get distributed in the mesh, the probabilityof duplicates and consequently, the probabilityof timely data delivery. In this paper we proposean analytic framework that allows the evaluation ofscheduling algorithms. We consider four solutions inwhich scheduling is performed at the forwarding peer,based on the knowledge of the playout buffer contentat the neighbors. We evaluate the effectiveness of thesolutions in terms of the probability that a peer can playout a packet versus the playback delay, the sensitivityof the solutions to the accuracy of the knowledge of theneighbors’ playout buffer contents, and the scalabilityof the solutions with respect to the size of the overlay.We also show how the model can be used to evaluatethe effects of node arrivals and departures on the overlay’sperformance.

  • 14.
    Chatzidrossos, Ilias
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktória
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Server Guaranteed Cap: an incentive mechanism for maximizing streaming quality in heterogeneous overlays2010In: NETWORKING 2010, PROCEEDINGS / [ed] Crovella M; Feeney LM; Rubenstein D; Raghavan SV, 2010, 315-326 p.Conference paper (Refereed)
    Abstract [en]

    We address the problem of maximizing the social welfare in a peer-to-peel streaming overlay given a fixed amount of server upload capacity. We show that peers' selfish behavior leads to an equilibrium that is suboptimal in terms of social welfare, because selfish peers are interested in forming clusters and exchanging data among themselves In order to increase the social welfare we propose a novel incentive mechanism: Server Guaranteed Cap (SGC), that uses the server capacity as an incentive for high contributing peers to upload to low contributing ones We prove that SGC is individually rational anti incentive compatible We also show that under very general conditions, there exists exactly one server capacity allocation that maximizes the social welfare under SGC, hence simple gradient based method can be used to find the optimal allocation

  • 15.
    Chatzidrossos, Ilias
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Legout, Arnaud
    INRIA, FRANCE.
    Small-world Streaming: Network-aware Streaming Overlay Construction Policies for a Flat Internet2011Manuscript (preprint) (Other academic)
    Abstract [en]

    Recent measurements indicate that the peering agreements betweenAutonomous Systems (AS) are flattening the AS level topology of theInternet. The transition to a more flat AS topology opens up for newpossibilities for proximity-aware peer-to-peer overlay construction. Inthis paper we consider the problem of the construction of overlays  forlive peer-to-peer streaming  that leverage peering connections tothe maximum extent possible, and investigate how a limited number ofoverlay connections over transit links should be chosen such as tomaximize the streaming performance. We define a set of transit overlaylink establishment policies that leverage topological characteristics ofthe AS graph. We evaluate their performance over regular AS topologiesusing extensive simulations, and show that the performance difference between the policies can be up to an order of magnitude. Thus, it is possible to maximize the system performance by leveraging the characteristics of the AS graph. Based on our results we also argue that the average loss probability is not an adequate measure of the performance of proximity-aware overlays.  We confirm our findings via simulations over a graph of the peering AS topology of over 600 ASs obtained from a large measurement data set.

  • 16.
    Dan, György
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture, Telecommunication Systems Laboratory, TSLab.
    Internet Video Transmission2006Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The Internet has rapidly evolved from being a scientific experiment to a commercial network connecting millions of hosts that carries traffic generated by a large amount of applications with diverse requirements. Its architecture was however designed to enable efficient point-to-point delivery of bulk data, and can not provide statistical guarantees on the timely delivery of delay sensitive data such as streaming and real-time multimedia. Thus, applications that require low loss probabilities in today's Internet have to use some end-to-end error recovery mechanism. For delay sensitive applications the introduced latency by the applied schemes has to be low as well. Traffic control functions such as delay limited shaping and forward error correction (FEC), and multiple description coding (MDC) have been proposed for variable bitrate video. Their major drawback is, however, that it is difficult to predict their efficiency, as it depends on many factors like the characteristics of the stream itself, the characteristics of the traffic in the network and the network parameters. Consequently, it is difficult to decide which control mechanisms to employ, how to combine them and to choose the right parameters (e.g. block length, code rate) for optimal performance.

    In this thesis we present results on the efficiency of traffic control functions and MDC for video transmission based on mathematical models and simulations. We investigate the efficiency of delay limited traffic shaping and the trade-offs in the joint use of traffic shaping and forward error correction. We identify the packet size distribution of the traffic in the network as an additional factor that may influence the efficiency of FEC, and present a thorough analysis of its possible effects. We present an analytical comparison of MDC versus media-dependent FEC and media-independent FEC, and based on the results we conclude that MDC is a promising error control solution for multimedia communications with very strict delay bounds in an environment with bursty losses. We combine the analytical results with traces from measurements performed on the Internet to evaluate how efficient these error control schemes are under real loss patterns. We compare the efficiency of MDC and media-dependent FEC in the presence of channel estimation errors; we propose a new rate allocation method, which is robust to mis-estimations of the channel state and which improves error resilience on non-stationary channels. Finally we present an analytical model of the performance of an end-point-based multimedia streaming architecture based on multiple distribution trees and forward error correction, and analyze the behavior of the architecture for a large number of nodes.

  • 17. Danyek, Gyula
    et al.
    Dán, András M.
    Budapest University of Technology and Economics.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Kisvölcsey, Jenő
    Budapest University of Technology and Economics.
    The Aim and a New Instrument for Residual Current Measurement in Ground Current Compensated Networks2002In: Elektrotechnika, Vol. 95, no 2, 53-55 p.Article in journal (Refereed)
  • 18.
    Dán, András M.
    et al.
    Budapest University of Technology and Economics.
    Dán, György
    Budapest University of Technology and Economics.
    Rios, Sebastian M.
    Universidad Pontifica Catolica de Chile.
    Improved Method for Flicker Evaluation1999In: Conference on  Electric Power Engineering, 1999Conference paper (Refereed)
  • 19.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Cache-to-Cache: Could ISPs Cooperate to Decrease Peer-to-Peer Content Distribution Costs?2011In: IEEE Transactions on Parallel and Distributed Systems, ISSN 1045-9219, E-ISSN 1558-2183, Vol. 22, no 9, 1469-1482 p.Article in journal (Refereed)
    Abstract [en]

    We consider whether cooperative caching may reduce the transit traffic costs of Internet service providers (ISPs) due to peer-to-peer (P2P) content distribution systems. We formulate two game-theoretic models for cooperative caching, one in which ISPs follow their selfish interests, and one in which they act altruistically. We show the existence of pure strategy Nash equilibria for both games, and evaluate the gains of cooperation on various network topologies, among them the AS level map of Northern Europe, using measured traces of P2P content popularity. We find that cooperation can lead to significant improvements of the cache efficiency with little communication overhead even if ISPs follow their selfish interests.

  • 20.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Cooperative Caching and Relaying Strategies for Peer-to-peer Content Delivery2008In: International Workshop on Peer-to-peer Systems, 2008Conference paper (Refereed)
    Abstract [en]

    Peer-to-peer content distribution has becomea major source of bandwidth costs for Internet serviceproviders (ISPs). One way for ISPs to decrease these costsis to deploy caches for p2p traffic. To make efficient useof the caches, in this paper we propose a cooperativecaching and relaying scheme that is compatible with theexisting business relations between ISPs. We formulate theproblem of cooperative caches as a resource allocationproblem, and show that it is related to the problemof r-configuration studied in graph theory. We proposea distributed algorithm to solve the resource allocationproblem, and show that cooperation leads to significantgains compared to non-cooperative caching.

  • 21.
    Dán, György
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Traffic Control for VBR Video in Packet Switched Networks2004Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The best effort service offered by the Internet is notsatisfactory for the transmission of loss and delay sensitivedata, such as real-time voice and video. In order to provideservice guarantees at reasonably high load levels, additionalcontrol functions haveto be employed in the network. Theintroduction of these functions is a critical issue, as severalaspects have to be taken into account, like scalability,economic feasibility and compliance with the end-to-endargument, one of the basic principles underlying the currentInternet architecture. To fulfill these requirements controlfunctions should be put at the network edge, while the core ofthe network should be kept simple to maintain the flexibilityof the network.

    The endpoint measurement-based admission control schemesproposed recently follow this principle. Most of theseadmission control schemes, however, suffer from limitedgranularity, namely, the QoS guarantees (packet loss, delay anddelay jitter) within a service class are the same for allstreams. Quality differentiation thus either requires qualityspecific service classes, which is in contradiction to theend-to-end argument, or the use of additional traffic controlfunctions at the network edge.

    Such additional control functions can decrease the packetloss probability given by the admission control to a levelrequired by the application by introducing additional delay.Delay limited shaping can be used to decrease the burstiness ofthe streams and thus their packet loss probability at the priceof increased delay. Forward error correction can be used torecover from losses within the network while incurringincreased delay and some overhead.

    This thesis gives an evaluation of how the different controlfunctions can work together to improve transmission quality,and thus the perceived visual quality. The effects of the jointuse of the control functions shaping and forward errorcorrection are evaluated, and the optimal allocation of thedelay is investigated. An exact mathematical model of thepacket loss process for multimedia traffic is presented, andits applicability is evaluated.

  • 22.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Bobba, Rakesh B.
    University of Illinois at Urbana-Champaign.
    Gross, George
    University of Illinois at Urbana-Champaign.
    Campbell, Roy H.
    University of Illinois at Urbana-Champaign.
    Cloud Computing for the Power Grid: From Service Composition to Assured Clouds2013In: Proceedings of the 5th USENIX Workshop on Hot Topics in Cloud Computing (HotCloud), June 2013, 2013Conference paper (Refereed)
    Abstract [en]

    The electric power industry is one of the few industries where cloud computing has not yet found much adoption, even though electric power utilities rely heavily on communications and computation to plan, operate and analyze power systems. In this paper we explore the reasons for this phenomenon. We identify a variety of power system applications that could benefit from cloud computing. We then discuss the security requirements of these applications, and explore the design space for providing the security properties through application layer composition and via assured cloud computing. We argue that a combination of these two approaches will be needed to meet diverse application requirements at a cost that can justify the use of cloud computing.

  • 23.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Carlsson, N.
    Centralized and distributed protocols for tracker-based dynamic swarm management2013In: IEEE/ACM Transactions on Networking, ISSN 1063-6692, E-ISSN 1558-2566, Vol. 21, no 1, 297-310 p.Article in journal (Refereed)
    Abstract [en]

    With BitTorrent, efficient peer upload utilization is achieved by splitting contents into many small pieces, each of which may be downloaded from different peers within the same swarm. Unfortunately, piece and bandwidth availability may cause the file-sharing efficiency to degrade in small swarms with few participating peers. Using extensive measurements, we identified hundreds of thousands of torrents with several small swarms for which reallocating peers among swarms and/or modifying the peer behavior could significantly improve the system performance. Motivated by this observation, we propose a centralized and a distributed protocol for dynamic swarm management. The centralized protocol (CSM) manages the swarms of peers at minimal tracker overhead. The distributed protocol (DSM) manages the swarms of peers while ensuring load fairness among the trackers. Both protocols achieve their performance improvements by identifying and merging small swarms and allow load sharing for large torrents. Our evaluations are based on measurement data collected during eight days from over 700 trackers worldwide, which collectively maintain state information about 2.8 million unique torrents. We find that CSM and DSM can achieve most of the performance gains of dynamic swarm management. These gains are estimated to be up to 40% on average for small torrents.

  • 24.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Carlsson, Niklas
    Linköping University.
    Dynamic Content Allocation for Cloud-assisted Service of Periodic Workloads2014In: INFOCOM, 2014 Proceedings IEEE, IEEE conference proceedings, 2014, 853-861 p.Conference paper (Refereed)
    Abstract [en]

    Motivated by improved models for content workloadprediction, in this paper we consider the problem of dynamiccontent allocation for a hybrid content delivery system thatcombines cloud-based storage with low cost dedicated serversthat have limited storage and unmetered upload bandwidth. Weformulate the problem of allocating contents to the dedicatedstorage as a finite horizon dynamic decision problem, and showthat a discrete time decision problem is a good approximation forpiecewise stationary workloads. We provide an exact solution tothe discrete time decision problem in the form of a mixed integerlinear programming problem, propose computationally feasibleapproximations, and give bounds on their approximation ratios.Finally, we evaluate the algorithms using synthetic and measuredtraces from a commercial music on-demand service and giveinsight into their performance as a function of the workload characteristics.

  • 25.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Carlsson, Niklas
    Linköping University.
    Dynamic Swarm Management for Improved BitTorrent Performance2009In: International Workshop on Peer-to-peer Systems, USENIX , 2009Conference paper (Refereed)
    Abstract [en]

    BitTorrent is a very scalable _le sharing protocol that utilizes the upload bandwidth of peers to of_oad the original content source. With BitTorrent, each _le is split into many small pieces, each of which may be downloaded from different peers. While BitTorrent allows peers to effectively share pieces in systems with suf_cient participating peers, the performance can degrade if participation decreases. Using measurements of over 700 trackers, which collectively maintain state information of a combined total of 2.8 million unique torrents, we identify many torrents for which the system performance can be signi_cantly improved by re-allocating peers among the trackers. We propose a light-weight distributed swarm management algorithm that manages the peer torrents while ensuring load fairness among the trackers. The algorithm achieves much of its performance improvements by identifying and merging small swarms, for which the performance is more sensitive to _uctuations in the peer participation, and allows load sharing for large torrents.

  • 26.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Carlsson, Niklas
    Linköping University.
    Power-law revisited: A Large Scale Measurement Study of P2P Content Popularity2010In: International Workshop on Peer-to-peer Systems, 2010Conference paper (Refereed)
    Abstract [en]

    The popularity of contents on the Internet is oftensaid to follow a Zipf-like distribution. Different measurementstudies showed, however, signicantly different distributions dependingon the measurement methodology they followed. Weperformed a large-scale measurement of the most popular peerto-peer (P2P) content distribution system, BitTorrent, over elevenmonths. We collected data on a daily to weekly basis from 500 to 800 trackers, with information about 40 to 60 millionpeers that participated in the distribution of over 10 milliontorrents. Based on these measurements we show how fundamentalcharacteristics of the observed distribution of content popularitychange depending on the measurement methodology and thelength of the observation interval. We show that while short-termor small-scale measurements can conclude that the popularity ofcontents exhibits a power-law tail, the tail is likely exponentiallydecreasing, especially over long time intervals.

  • 27.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Carlsson, Niklas
    Linköping University.
    Chatzidrossos, Ilias
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Efficient and Highly Available Peer Discovery: A Case for Independent Trackers and Gossiping2011In: IEEE Conference on Peer-to-peer Computing, IEEE , 2011, 290-299 p.Conference paper (Refereed)
    Abstract [en]

    Abstract—Tracker-based peer-discovery is used in most commercial peer-to-peer content distribution systems, as it provides performance benefits compared to distributed solutions, and facilitates the control and monitoring of the overlay. But a tracker is a central point of failure, and its deployment and maintenance incur costs; hence an important question is how high tracker availability can be achieved at low cost. We investigate highly available, low overhead peer discovery, using independent trackers and a simple gossip protocol. This work is a step towards understanding the trade-off between the overhead and the achievable peer connectivity in highly available distributed overlay-management systems for peer-to-peer content distribution. We propose two protocols that connect peers in different swarms efficiently with a constant, but tunable, overhead. The two protocols, Random Peer Migration (RPM) and Random Multi-Tracking (RMT), employ a small fraction of peers in a torrent to virtually increase the size of swarms. We develop analytical models of the protocols based on renewal theory, and validate the models using both extensive simulations and controlled experiments. We illustrate the potential value of the protocols using large-scale measurement data that contains hundreds of thousands of public torrents with several small swarms, with limited peer connectivity. We estimate the achievable gains to be up to 40% on average for small torrents.

  • 28.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Chatzidrossos, Illias
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    On the performance of error-resilient end-point-based multicast streaming2006In: 2006 14TH IEEE INTERNATIONAL WORKSHOP ON QUALITY OF SERVICE, PROCEEDINGS, 2006, 160-168 p.Conference paper (Refereed)
    Abstract [en]

    In this paper we propose an analytical model of a resilient end-node multicast streaming architecture based on multiple minimum-depth-trees that employs path diversity and forward error correction for improved resilience to node churns and packet losses. We study the performance of the architecture in the presence of packet losses and dynamic node behavior. We show that for a given redundancy the probability that an arbitrary node possesses a packet is high as long as the loss probability in the network is below a certain threshold. After reaching the threshold the packet possession probability suddenly drops; the rate decrease gets faster as the number of nodes in the overlay grows. The value of the threshold depends on the ratio of redundancy and on the number of the distribution trees. We study the overlay structure in the presence of node dynamics and conclude that stability can be achieved only if the root node serves a large number of nodes simultaneously.

  • 29.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    An analytical study of Low Delay Multi-tree-based Overlay Multicast2007In: P2P-TV '07 Proceedings of the 2007 workshop on Peer-to-peer streaming and IP-TV, 2007, 352-357 p.Conference paper (Refereed)
    Abstract [en]

    In this paper we propose an analytical model that describes the temporal evolution of the end-to-end loss characteristics for live multicast streaming. We consider push-based architectures combined with retransmissions and forward error correction (FEC). We use the model to identify the primary sources of delay in overlay multicast, and to investigate the possible ways of decreasing the required playback delay. Based on the results we argue that in order to achieve good quality with low playback delays independent of the overlay's size, these systems have to adjust the FEC code rate dynamically. Our findings show that the available upload capacity is the key to efficient overlay multicast with low delay bounds.

  • 30.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Delay bounds and scalability for overlay multicast2008In: AD HOC AND SENSOR NETWORKS, WIRELESS NETWORKS, NEXT GENERATION INTERNET, PROCEEDINGS, 2008, Vol. 4982, 227-239 p.Conference paper (Refereed)
    Abstract [en]

    A large number of peer-to-peer streaming systems has been proposed and deployed in recent years. Yet, there is no clear understanding of how these systems scale and how multi-path and multihop transmission, properties of all recent systems, affect the quality experienced by the peers. In this paper we present an analytical study that considers the relationship between delay and loss for general overlays: we study the trade-off between the playback delay and the probability of missing a packet and we derive bounds on the scalability of the systems. We use an exact model of push-based overlays to show that the bounds hold under diverse conditions: in the presence of errors, under node churn, and when using forward error correction and various retransmission schemes.

  • 31.
    Dán, György
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Fodor, Viktoria
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    On the efficiency of shaping live video streams2002In: Proceedings of the 2002  international symposium on performance evaluation of computer and telecommunications systems, 2002Conference paper (Refereed)
    Abstract [en]

    In this work the efficiency of shaping live video streams is considered. We propose low complexity shaping algorithms adequate for real-time operation and supporting applications with a wide range of delay tolerance. The effect of shaping is investigated considering video streams multiplexed at an output link with a small buffer to absorb packet scale congestion. The advantage of using small buffers when transmitting video streams is the limited delay and delay variation. Consequently, we concentrate on the loss characteristics to evaluate the performance of the proposed solutions. We present mathematical analysis based on fluid flow modeling and the theory of large deviations and confirm the results with simulation.

  • 32.
    Dán, György
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Fodor, Viktoria
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Quality differentiation with source shaping and forward error correction2003In: Interactive Multimedia On Next Generation Networks / [ed] Ventre, G; Canonico, R, 2003, 222-233 p.Conference paper (Refereed)
    Abstract [en]

    The transmission of video traffic over the Internet is a fundamental issue of network design. Video applications require quality of service guarantees from the network in terms of limited packet loss, end-to-end delay, and delay variation. The question of today's research and development is how to provide these guarantees considering the architecture of the present Internet. In the last years a variety of admission control schemes based on per-hop or end-to-end measurements has been suggested to control delay and loss sensitive streams with very little or no support at the routers. Most of these solutions, however, have to apply the same acceptance threshold for all streams, a significant limitation considering the diverse quality requirements of the applications. In this work we investigate how source shaping and forward error correction (FEC) can be used together to achieve application specific quality differentiation in terms of end-to-end delay and packet loss probability. While source shaping and FEC have been proposed independently to decrease the probability of packet loss due to buffer overflow, their joint use has not been studied before. As the two control functions use the same scarce resource, end-node delay, and their efficiency to decrease loss probability is proportional to the introduced delay but with a decreasing marginal gain, combining the two a better performance can be achieved than by using only one of them. The performance evaluation focuses on the optimal delay allocation for shaping and FEC, such that the loss probability is minimized. We investigate how shaping can be used to substitute FEC redundancy and the sensitivity of the quality differentiation to the background traffic characteristics.

  • 33.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    A rate-distortion based comparison of media-dependent FEC and MDC for real-time audio2006In: 2006 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS, VOLS 1-12, 2006, Vol. 3, 1002-1007 p.Conference paper (Refereed)
    Abstract [en]

    Applications that require low loss probabilities in today's Internet have to employ some end-to-end error-recovery mechanism. For interactive applications with strict delay constraints, the delay introduced by the applied schemes has to be low as well. In this paper we compare two schemes proposed for error recovery for real-time audio applications: media-dependent forward error correction (MD-FEC) and multiple description coding (MDC). We conclude that MDC always performs better than MD-FEC, and that the stationary loss probability plays a key role in the choice of the optimal parameters for these schemes. Combining the analytical results with the loss characteristics of measured traces of VoIP calls we conclude that in the current Internet these schemes give considerable gains for streams with a high code rate only, and for these streams MDC can decrease the average distortion significantly better than MD-FEC.

  • 34.
    Dán, György
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Fodor, Viktoria
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Karlsson, Gunnar
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Analysis of the Packet Loss Process for Multimedia Traffic2004In: Intl. Conference on Telecommunication Systems Modeling and Analysis, 2004Conference paper (Refereed)
    Abstract [en]

    In the case of multimedia traffic, like VBR video, the average loss probability is not sufficient to investigate the effects of loss on perceived visual quality, but it is difficult to analytically model the queuing behavior for such traffic. It has been shown that in the case of realtime communications, for which small buffers are used for delay reasons, short range dependence dominates the loss process and so the Markovmodulated Poisson process (MMPP) might be a reasonable source model. In this paper we present an exact mathematical model for the loss process of an MMPP+M/D/1/K queue; we validate it via simulations and compare it to other mathematical models, like the MMPP+M/M/1/K and the Gilbert model, and to simulations with real MPEG-4 video traces. We conclude that the other models give accurate results only in a small set of network scenarios, while our model can capture the loss process of VBR video sufficiently well in most cases. This makes it possible to analyze the effects of forward error correction on transmission quality in various network scenarios.

  • 35.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Are multiple descriptions better than one?2005In: NETWORKING 2005: NETWORKING TECHNOLOGIES, SERVICES, AND PROTOCOLS; PERFORMANCE OF COMPUTER AND COMMUNICATION NETWORKS; MOBILE AND WIRELESS COMMUNICATIONS SYSTEMS / [ed] Boutaba, R; Almeroth, K; Puigjaner, R; Shen, S; Black, JP, 2005, 684-696 p.Conference paper (Refereed)
    Abstract [en]

    In this paper we compare three schemes proposed for error recovery for real-time multimedia applications: media-dependent forward error correction (MD-FEC) proposed for real-time audio, media-independent forward error correction (MI-FEC) proposed for real-time video and the recently re-discovered multiple description coding (MDC). We provide a detailed queueing analysis for these schemes considering bursty traffic sources, and combine results from information theory and queueing theory to analyze their performance bounds. We conclude that MDC always performs better than MD-FEC, and that the average loss probability plays a key role in the choice of the optimal parameters. We also show that MDC outperforms MI-FEC if packet losses are highly correlated, like in the current Internet and the available delay for error control is low.

  • 36.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    On the asymptotic behavior of end-point-based multicast streaming2006In: 2006 International Zurich Seminar on Communications: Access - Transmission - Networking, Proceedings, NEW YORK: IEEE , 2006, 66-69 p.Conference paper (Refereed)
    Abstract [en]

    In this paper we propose an analytical model of a resilient, tree-based end-node multicast streaming architecture that employs path diversity and forward error correction for improved resilience to node churns and packet losses. We show that this architecture can distribute data to nodes arbitrarily far away from the root of the trees as long as the loss probability is lower than a certain threshold, but the probability of packet reception suddenly drops to zero once this threshold is exceeded. The value of the threshold depends on the ratio of redundancy and on the number of the distribution trees.

  • 37.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    On the stability of end-point-based multimedia streaming2006In: NETWORKING 2006: NETWORKING TECHNOLOGIES, SERVICES, AND PROTOCOLS; PERFORMANCE OF COMPUTER AND COMMUNICATION NETWORKS; MOBILE AND WIRELESS COMMUNICATIONS SYSTEMS / [ed] Boavida F, Plagemann T, Stiller B; Westphal C, Monteiro E, Berlin: Springer-Verlag Berlin , 2006, 678-690 p.Conference paper (Refereed)
    Abstract [en]

    In this paper we propose an analytical model of a resilient, tree-based end-node multicast streaming architecture that employs path diversity and forward error correction for improved resilience to node churns and packet losses. Using the model and via simulations we study the performance of this architecture in the presence of packet losses and dynamic node behavior. We show that the overlay can distribute data to nodes arbitrarily far away from the root of the trees as long as the loss probability is lower than a certain threshold, but the probability of packet reception suddenly drops to zero once this threshold is exceeded. The value of the threshold depends on the ratio of redundancy and on the number of the distribution trees. Using the model and simulations we show that correlated and inhomogeneous losses slightly worsen the overlay's performance. We apply the model to study the effects of dynamic node behavior and compare its results to simulations.

  • 38.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Packet size distribution: An aside?2005In: QUALITY OF SERVICE IN MULTISERVICE IP NETWORKS, PROCEEDINGS, 2005, Vol. 3375, 75-87 p.Conference paper (Refereed)
    Abstract [en]

    For multimedia traffic like VBR video, knowledge of the average loss probability is not sufficient to determine the impact of loss on the perceived visual quality and on the possible ways of improving it, for example by forward error correction (FEC) and error concealment. In this paper we investigate how the packet size distribution affects the packet loss process, the distribution of the number of packets lost in a block of packets and the related FEC performance. We present an exact mathematical model for the loss process of an MMPP + M/E-r/1/K queue and compare the results of the model to simulations performed with various other packet size distributions (PSDs), among others, the measured PSD from an Internet backbone. We conclude that the packet size distribution affects the packet loss process and thus the efficiency of FEC. This conclusion is mainly valid in access networks where a single multimedia stream might affect the multiplexing behavior. The results show that analytical models of the PSD matching the first three moments (mean,variance and skewness) of the empirical PSD can be used to evaluate the performance of FEC in real networks. We also conclude that the exponential PSD, though it is not a worst case scenario, is a good approximation for the PSD of today's Internet to evaluate FEC performance.

  • 39.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fodor, Viktória
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Delay Asymptotics and Scalability for Peer-to-Peer Live Streaming2009In: IEEE Transactions on Parallel and Distributed Systems, ISSN 1045-9219, E-ISSN 1558-2183, Vol. 20, no 10, 1499-1511 p.Article in journal (Refereed)
    Abstract [en]

    A large number of peer-to-peer streaming systems have been proposed and deployed in recent years. Yet, there is no clear understanding of how these systems scale and how multipath and multihop transmission, properties of all recent systems, affect the quality experienced by the peers. In this paper, we present an analytical study that considers the relationship between delay and loss for general overlays: we study the trade-off between the playback delay and the probability of missing a packet and we derive bounds on the scalability of the systems. We present an exact model of push-based overlays and show that the bounds hold under diverse conditions: in the presence of errors, under node churn, and when using forward error correction and various retransmission schemes.

  • 40.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktória
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Communication Networks.
    Stability and performance of overlay multicast systems employing forward error correction2010In: Performance evaluation (Print), ISSN 0166-5316, Vol. 67, no 2, 80-101 p.Article in journal (Refereed)
    Abstract [en]

    The two main sources of impairment in overlay multicast systems are packet losses and node churn. Yet, little is known about their effects on the data distribution performance. In this paper we develop an analytical model of a large class of peer-to-peer streaming architectures based on decomposition and non-linear recurrence relations. We analyze the stability properties of these systems using fixed-point analysis. We derive bounds on the probability that nodes in the overlay receive an arbitrary packet of the stream. Based on the model, we explain the effects of the overlay's size, node heterogeneity, loss correlations and node churn on the overlay's performance. Our findings lead us to the definition of an overlay structure with improved stability properties. We show how and under what conditions overlays can benefit from the use of error control solutions, prioritization and taxation schemes. Based on our results, we identify the components that are needed to achieve good data distribution performance in multi-tree-based overlay multicast.

  • 41.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktória
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Chatzidrossos, Ilias
    KTH, School of Electrical Engineering (EES), Communication Networks.
    On the performance of multiple-tree-based peer-to-peer live streaming2007In: INFOCOM 2007, VOLS 1-5, 2007, 2556-2560 p.Conference paper (Refereed)
    Abstract [en]

    In this paper we propose and analyze a generalized multiple-tree-based overlay architecture for peer-to-peer live streaming that employs multipath transmission and forward error correction. We give mathematical models to describe the stability properties of the overlay and evaluate the error recovery in the presence of node dynamics and packet losses. We show how the stability of the overlay improves with the proper allocation of the outgoing bandwidths of the peers among the trees without compromising its error correcting capability.

  • 42.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktória
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Chatzidrossos, Ilias
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Streaming performance in multiple-tree-based overlays2007In: NETWORKING 2007: Ad Hoc and Sensor Networks, Wireless Networks, Next Generation Internet, Proceedings / [ed] Akyildiz, IF; Sivakumar, R; Ekici, E; DeOliveira, JC; McNair, J, 2007, 617-627 p.Conference paper (Refereed)
    Abstract [en]

    In this paper we evaluate the data transmission performance of a generalized multiple-tree-based overlay architecture for peer-to-peer live streaming that employs multipath transmission and forward error correction. We give mathematical models to describe the error recovery in the presence of packet losses. We evaluate the data distribution performance of the overlay, its asymptotic behavior, the stability regions for the data transmission, and analyze the system behavior around the stability threshold. We argue that the composed measure of the mean and the variance of the packet possession probability can support adaptive forward error correction.

  • 43.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES).
    Fodor, Viktória
    KTH, School of Electrical Engineering (EES).
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES).
    On the effects of the packet size distribution on FEC performance2006In: Computer Networks, ISSN 1389-1286, E-ISSN 1872-7069, Vol. 50, no 8, 1104-1129 p.Article in journal (Refereed)
    Abstract [en]

    For multimedia traffic like VBR video, knowledge of the average loss probability is not sufficient to determine the impact of loss on the perceived visual quality and on the possible ways of improving it, for example by forward error correction (FEC) and error concealment. In this paper we investigate how the packet size distribution affects the packet loss process, i.e., the probability of consecutive losses and the distribution of the number of packets lost in a block of packets and the related FEC performance. We present an exact mathematical model for the loss process of an MMPP + MMPP/Er/1/K queue and compare the results of the model to simulations performed with various other packet size distributions (PSDs), among others, the measured PSD from an Internet backbone. The results show that analytical models of the PSD matching the first three moments (mean, variance and skewness) of the empirical PSD can be used to evaluate the performance of FEC in real networks. We conclude that the exponential PSD, though it is not a worst case scenario, is a good approximation for the PSD of today's Internet to evaluate FEC performance. We also conclude that the packet size distribution affects the packet loss process and thus the efficiency of FEC mainly in access networks where a single multimedia stream might affect the multiplexing behavior. We evaluate how the PSD affects the accuracy of the widely used Gilbert model to calculate FEC performance and conclude that the Gilbert model can capture loss correlations better if the CoV of the PSD is high.

  • 44.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES).
    Fodor, Viktória
    KTH, School of Electrical Engineering (EES).
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES).
    On the effects of the packet size distribution on the packet loss process2006In: Telecommunications Systems, ISSN 1018-4864, E-ISSN 1572-9451, Vol. 32, no 1, 31-53 p.Article in journal (Refereed)
    Abstract [en]

    Real-time multimedia applications have to use forward error correction (FEC) anderror concealment techniques to cope with losses in today's best-effort Internet. The efficiency of these solutions is known however to depend on the correlation between losses in the media stream. In this paper we investigate how the packet size distribution affects the packet loss process, that is, the distribution of the number of lost packets in a block, the related FEC performance and the average loss run length. We present mathematical models for the loss process of the MMPP+M/D/1/K and the MMPP+M/M/1/K queues; we validate the models via simulations, and compare the results to simulation results with an MPEG-4 coded video trace. We conclude that the deterministic packet size distribution (PSD) not only results in lower stationary loss probability than the exponential one, but also gives a less correlated loss process, both at a particular average link load and at a particular stationary loss probability as seen by the media stream.Our results show that for applications that can only measure the packet loss probability, the effects of the PSD on FEC performance are higher in access networks, where a single multimedia stream might affect the multiplexing behavior. Our results show that the effects of the PSD on FEC performance are higher in access networks, where a single multimedia stream might affect the multiplexing behavior and thus can improve the queuing performance by decreasing the variance of its PSD.

  • 45.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fodor, Viktória
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Robust source-channel coding for real-time multimedia2008In: Multimedia Systems, ISSN 0942-4962, E-ISSN 1432-1882, Vol. 13, no 5-6, 363-377 p.Article in journal (Refereed)
    Abstract [en]

    Multimedia applications operating in today's Internet have to employ some form of error resilience to cope with losses. For interactive applications with strict delay constraints the latency introduced by these schemes has to be low as well. Furthermore the parameters of the applied scheme have to be set based on measurements in a possibly rapidly changing environment. In this paper we propose a robust method, called min-max-α, for optimal source-channel code rate allocation to deal with time-varying packet channels and channel state estimation errors. We evaluate its performance when used with forward error correction and multiple description coding in both stationary and non-stationary environments. We show that on a stationary channel robust rate allocation is suboptimal in terms of mean distortion, but it achieves a lower variance, while on a non-stationary channel it prevents severe degradation of the quality. We apply the proposed rate allocation method to motion compensated video and show that it performs better on a non-stationary channel than minimization of the mean distortion proposed earlier.

  • 46.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Hossfeld, Tobias
    Oechsner, Simon
    Cholda, Piotr
    Stankiewicz, Rafal
    Papafili, Ioanna
    Stamoulis, George D.
    Interaction Patterns between P2P Content Distribution Systems and ISPs2011In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 49, no 5, 222-230 p.Article in journal (Refereed)
    Abstract [en]

    Peer-to-peer (P2P) content distribution systems are a major source of traffic in the Internet, but the application layer protocols they use are mostly unaware of the underlying network in accordance with the layered structure of the Internet's protocol stack. Nevertheless, the need for improved network efficiency and the business interests of Internet service providers (ISPs) are both strong drivers toward a cross-layer approach in peer-to-peer protocol design, calling for P2P systems that would in some way interact with the ISPs. Recent research shows that the interaction, which can rely on information provided by both parties, can be mutually beneficial. In this article we first give an overview of the kinds of information that could potentially be exchanged between the P2P systems and the ISPs, and discuss their usefulness and the ease of obtaining and exchanging them. We also present a classification of the possible approaches for interaction based on the level of involvement of the ISPs and the P2P systems, and we discuss the potential strengths and the weaknesses of these approaches.

  • 47.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Khan, Muhammadaltamash A.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Characterization of SURF and BRISK interest point distribution for distributed feature extraction in visual sensor networks2015In: IEEE transactions on multimedia, ISSN 1520-9210, E-ISSN 1941-0077, Vol. 17, no 5, 591-602 p., 7047857Article in journal (Refereed)
    Abstract [en]

    We study the statistical characteristics of SURF and BRISK interest points and descriptors, with the aim of supporting the design of distributed processing across sensor nodes in a resource -constrained visual sensor network (VSN). Our results show high variability in the density, the spatial distribution , and the octave layer distribution of the interest points. The high variability implies that balancing the processing load among the sensor nodes is a very challenging task, and obtaining a priori information is essential, e.g., through prediction. Our results show that if a priori information is available about the images, then Top-$M$ interest point selection, limited , octave-based processing at the camera node, together with area-based interest point detection and extraction at the processing nodes, can balance the processing load and limit the transmission cost in the network. Complete interest point detection at the camera node with optimized descriptor extraction delegation to the processing nodes in turn can further decrease the transmission load and allow a better balance of the processing load among the network nodes.

  • 48.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Lui, King-Shan
    The University of Hong-Kong.
    Tabassum, Rehana
    University of Illinois at Urbana-Champaign.
    Zhu, Quanyan
    University of Illinois at Urbana-Champaign.
    Nahrstedt, Klara
    University of Illinois at Urbana-Champaign.
    SELINDA: A Secure, Scalable and Light-Weight Data Collection Protocol for Smart Grids2013In: 2013 IEEE International Conference on Smart Grid Communications (SmartGridComm), 2013, 480-485 p.Conference paper (Refereed)
    Abstract [en]

    Security in the smart grid is a challenge as an increasing number of sensors and measurement devices are connected to the power grid. General purpose security protocols are not suitable for providing data security to devices with limited memory, computational power and network connectivity. In this paper, we develop a secure and light-weight scalable security protocol that allows a power system operator (PO) to collect data from measurement devices (MDs) using data collectors (DCs). The security protocol trades off between computations and device memory requirements and provides flexible association between DC and MDs. These features allow data to be securely transferred from MDs to PO via mobile or untrustworthy DCs. We analyze the complexity and security of the protocol and validate its performance using experiments. Our results confirm that our proposed protocol collects data in a secure, fast and efficient manner.

  • 49.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Stealth attacks and protection schemes for state estimators in power systems2010In: 2010 1st IEEE International Conference on Smart Grid Communications, SmartGridComm 2010, IEEE , 2010, 214-219 p.Conference paper (Refereed)
    Abstract [en]

    State estimators in power systems are currently used to, for example, detect faulty equipment and to route power flows. It is believed that state estimators will also play an increasingly important role in future smart power grids, as a tool to optimally and more dynamically route power flows. Therefore security of the estimator becomes an important issue. The estimators are currently located in control centers, and large numbers of measurements are sent over unencrypted communication channels to the centers. We here study stealthy false-data attacks against these estimators. We define a security measure tailored to quantify how hard attacks are to perform, and describe an efficient algorithm to compute it. Since there are so many measurement devices in these systems, it is not reasonable to assume that all devices can be made encrypted overnight in the future. Therefore we propose two algorithms to place encrypted devices in the system such as to maximize their utility in terms of increased system security. We illustrate the effectiveness of our algorithms on two IEEE benchmark power networks under two attack and protection cost models.

  • 50.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Ekstedt, Mathias
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Björkman, Gunnar
    Challenges in Power System Information Security2012In: IEEE Security and Privacy, ISSN 1540-7993, E-ISSN 1558-4046, Vol. 10, no 4, 62-70 p.Article in journal (Refereed)
    Abstract [en]

    Achieving all-encompassing component-level security in power system IT infrastructures is difficult, owing to its cost and potential performance implications.

123 1 - 50 of 110
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