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  • 1.
    Eriksson, Emil
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Pacifici, Valentino
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Efficient Distribution of Visual Processing Tasks in Multi-camera Visual Sensor Networks2015In: Multimedia & Expo Workshops (ICMEW), 2015 IEEE International Conference on, IEEE conference proceedings, 2015, 1-6 p.Conference paper (Refereed)
    Abstract [en]

    Multi-camera visual sensor networks (VSNs) require large computational resources in order to perform visual analysis in real-time. One way to match the computational needs is to augment the VSN with dedicated processing nodes that do in-network processing, but this requires careful allocation of loads from the sensor nodes in order to ensure low processing times. In this paper we formulate the problem of load allocation and completion time minimization in a VSN as an optimization problem. We propose a distributed algorithm for load allocation, and evaluate its performance in terms of completion time and convergence compared to a Greedy algorithm. Simulations show that the proposed algorithm converges faster, but at the cost of increased completion times. Nonetheless, combined with appropriate coordination, the proposed algorithm achieves low completion times at low complexity.

  • 2.
    Josilo, Sladana
    et al.
    KTH, School of Electrical Engineering (EES), Network and Systems engineering.
    Pacifici, Valentino
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Dan, György
    Distributed algorithms for content placement in hierarchical cache networks2017In: Computer Networks, ISSN 1389-1286, E-ISSN 1872-7069, Vol. 125, 160-171 p.Article in journal (Refereed)
    Abstract [en]

    The growing popularity of mobile multimedia content and the increase of wireless access bitrates are straining backhaul capacity in mobile networks. A cost-effective solution to reduce the strain, enabled by emerging all-IP 4G and 5G mobile backhaul architectures, could be in-network caching of popular content during times of peak demand. Motivated by the potential benefits of caching in mobile backhaul networks, in this paper we formulate the problem of content placement in a hierarchical cache network as a binary integer programming problem. We provide a polynomial time solution when the link costs are induced by a potential and we propose a 2-approximation algorithm for the general case. The 2-approximation requires full information about the network topology and the link costs, as well as about the content demands at the different caches, we thus propose two distributed algorithms that are based on limited information on the content demands. We show that the distributed algorithms terminate in a finite number of steps, and we provide analytical results on their approximation ratios. We use simulations to evaluate the proposed algorithms in terms of the achieved approximation ratio and computational complexity on hierarchical cache network topologies as a model of mobile backhaul networks.

  • 3. Lehrieder, F.
    et al.
    Pacifici, Valentino
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    On the benefits of P2P cache capacity allocation2011In: Proceedings of the 2011 23rd International Teletraffic Congress, ITC 2011, 2011, 312-313 p.Conference paper (Refereed)
    Abstract [en]

    Peer-to-peer (P2P) systems are responsible for a large fraction of inter-ISP transit traffic in the Internet. Hence, many Internet service providers (ISPs) have deployed P2P caches to decrease their P2P related transit traffic. In our work we consider the problem of allocating the limited upload capacity of a P2P cache between a set of overlay swarms. The goal of cache capacity allocation is to increase the amount of transit traffic that can be saved using the cache. Our preliminary results are based on analytical models and simulations and show that cache capacity allocation is a promising means of improving the efficiency of P2P caches. We are currently validating our results via experiments on Planet-Lab.

  • 4.
    Pacifici, Valentino
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Bandwidth and Storage Allocation for Operator-owned Content Management Systems2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The demand for Internet-based visual content delivery has increased significantly in recent years, triggered mainly by the widespread use of Internet enabled smartphones and portable devices, and by the availability of super HD content.As a consequence, live and on-demand video content has become the most important source of network traffic in mobile and fixed networks alike.In order to be able to efficiently deliver the increasing amount of video traffic, network operators have started to deploy caches and operator-owned CDNs. These solutions do not only reduce the amount of transit traffic of the operators but they may also improve the customers' quality of experience, through bringing the video content closer to customers. Nevertheless, their efficiency is determined by the algorithms and protocols used to allocate resources, both in terms of storage and bandwidth. The work in this thesis addresses the allocation of these two resources for operator-owned content management systems.

    In the first part of the thesis we consider a cache maintained by a single network operator. We investigate how caching at a network operator affects the content distribution system as a whole, and consequently, the efficiency of content delivery. We propose a model of the decision process undertaken by a network operator that aims at optimizing the efficiency of a cache by actively managing its bandwidth. We design different algorithms that aim at approximating the optimal cache bandwidth allocation and we evaluate them through extensive simulations and experiments. We show that active cache bandwidth allocation can significantly increase traffic savings.

    We then consider the potential interaction among caches maintained by different network operators.We consider the problem of selfish replication on a graph as a modelof network operators that individually deploy replication systems, and try to leverage their peering agreements so as to minimize the traffic through their transit providers. We use game-theoretical tools to investigate the existence of stable and efficient allocations of content at the network operators. We show that selfish myopic updates of content allocations at different network operators lead the system to a stable state, and that the convergence speed depends on the underlying network topology. In addition, we show that interacting operator-owned caches can reach a stable content allocation without coordination, but coordination leads to more cost efficient content allocations.

  • 5.
    Pacifici, Valentino
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Distributed Caching Algorithms for Interconnected Operator CDNs2016In: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 35, no 2, 380-391 p.Article in journal (Refereed)
    Abstract [en]

    Fixed and mobile network operators increasingly deploy managed content distribution networks (CDNs) with the objective of reducing the traffic on their transit links and to improve their customers' quality of experience. As network operator managed CDNs (nCDNs) become commonplace, operators will likely provide common interfaces to interconnect their nCDNs for mutual benefit, as they do with peering today. In this paper, we consider the problem of using distributed algorithms for computing a cache allocation for nCDNs. We show that if every network operator aims to minimize its cost and bilateral payments are not allowed, then it may be impossible to compute a cache allocation. For the case when bilateral payments are possible, we propose two distributed algorithms, the aggregate value compensation and the object value compensation algorithms, which differ in terms of the level of parallelism they allow and in terms of the amount of information exchanged between nCDNs. We prove that the algorithms converge, and we propose a scheme to ensure ex-post individual rationality. Simulations performed on a real autonomous system-level network topology and synthetic topologies show that the algorithms have geometric rate of convergence, and scale well with the graphs' density and the nCDN capacity.

  • 6.
    Pacifici, Valentino
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Resource Allocation in Operator-owned Content Delivery Systems2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Live and on-demand video content have become the most important source of network traffic in mobile and fixed networks in recent years. In order to be able to efficiently deliver the increasing amount of video content, network operators have started to deploy caches and operator-owned CDNs. These solutions do not only reduce the amount of transit traffic of the operators but they may also improve the customers' quality of experience, through bringing the video content closer to customers. Nevertheless, their efficiency is determined by the algorithms and protocols used to allocate resources, both in terms of storage and bandwidth. The work in this thesis proposes and analyses algorithms for the allocation of these two resources for operator-owned content management systems. In the first part of the thesis we consider a cache maintained by a single network operator. We formulate the problem of content caching in a mobile backhaul as an integer program and we show that there exists an efficient centralized solution to the problem. Due to the prohibitive space complexity of the centralized algorithm, we propose two distributed approximations based on local information on the content demands. We then consider the problem of managing cache bandwidth so as to minimize the traffic cost of content delivery and we propose various approximations of the optimal stationary policy. We then consider the interaction among content management systems maintained by different network operators. First, we consider the problem of selfish replication on a graph as a model of network operators that use their caches to prefetch popular content, and try to leverage their peering agreements so as to minimize the traffic through their transit providers. We design efficient distributed algorithms that compute a stable content allocation through selfish myopic updates of content allocations at different network operators. We show that, if the cost function is neighbor-specific, network operators need bilateral payments to compute a stable content allocation that is individually rational. We then consider the problem of coordinated caching in a network of autonomous systems engaged in content-level peering. We investigate whether interacting operator-owned caches need explicit coordination in order to reach a stable content allocation efficiently. Beyond the theoretical contributions made to the analysis of player-specific graphical congestion games and their generalizations, the results in thesis provide guidelines for the design of protocols for standalone and for interconnected operator-owned content management systems.

  • 7.
    Pacifici, Valentino
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    A Game Theoretic Analysis of Selfish Content Replication on Graphs2011In: 7th Swedish National Computer Networking Workshop (SNCNW), 2011, 2011Conference paper (Refereed)
    Abstract [en]

    Replication games are a model of the problem of content placement in computer and communication systems, when the participating nodes maketheir decisions such as to maximize their individualutilities. In this paper we consider replication gamesplayed over arbitrary social graphs; the social graphmodels limited interaction between the players due to,e.g., the network topology. We show that in replicationgames there is an equilibrium object placement forarbitrary social graphs. Nevertheless, if all nodes followa myopic strategy to update their object placementsthen they might cycle arbitrarily long before reachingan equilibrium if the social graph is non-complete. Wegive sufficient conditions under which such cycles do notexist, and propose an efficient distributed algorithm toreach an equilibrium over a non-complete social graph.

  • 8.
    Pacifici, Valentino
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Content-peering Dynamics of Autonomous Caches in a Content-centric Network2013In: 2013 Proceedings IEEE Infocom, IEEE Computer Society, 2013, 1079-1087 p.Conference paper (Refereed)
    Abstract [en]

    Autonomous systems are likely to play a similar role in a content-centric Internet as they do today. Thus, the content-centric Internet will be a network of cache networks, each of them optimized for local performance. In this paper we consider ASs that maintain peering agreements with each other for mutual benefit, and engage in content-level peering in order to leverage each others' cache contents. We propose a game theoretical model of the interaction and the coordination between the caches managed by peering ASs. We address the questions of whether stable and efficient content-level peering can be implemented without explicit coordination between the neighboring ASs or alternatively, whether the interaction needs to rely on explicit announcements of content reachability in order for the system to be stable. We show that without coordination content-peering can lead to stable but inefficient cache configurations. For the case of coordination we show that in order to efficiently reach a stable cache configuration, the ASs need to follow an ex-ante irrational algorithm, which is, however, ex-post rational. We validate our analytical results using simulations on the measured peering topology of more than 600 ASs.

  • 9.
    Pacifici, Valentino
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Convergence in Player-Specific Graphical Resource Allocation Games2012In: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 30, no 11, 2190-2199 p.Article in journal (Refereed)
    Abstract [en]

    As a model of distributed resource allocation in networked systems, we consider resource allocation games played over a influence graph. The influence graph models limited interaction between the players due to, e. g., the network topology: the payoff that an allocated resource yields to a player depends only on the resources allocated by her neighbors on the graph. We prove that pure strategy Nash equilibria (NE) always exist in graphical resource allocation games and we provide a linear time algorithm to compute equilibria. We show that these games do not admit a potential function: if there are closed paths in the influence graph then there can be best reply cycles. Nevertheless, we show that from any initial allocation of a resource allocation game it is possible to reach a NE by playing best replies and we provide a bound on the maximal number of update steps required. Furthermore we give sufficient conditions in terms of the influence graph topology and the utility structure under which best reply cycles do not exist. Finally we propose an efficient distributed algorithm to reach an equilibrium over an arbitrary graph and we illustrate its performance on different random graph topologies.

  • 10.
    Pacifici, Valentino
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Coordinated Selfish Distributed Caching for Peering Content-centric Networks2016In: IEEE/ACM Transactions on Networking, ISSN 1063-6692, E-ISSN 1558-2566, Vol. PP, no 99, 1-12 p.Article in journal (Refereed)
  • 11.
    Pacifici, Valentino
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Coordinated Selfish Distributed Caching for Peering Content-Centric Networks2016In: IEEE/ACM Transactions on Networking, ISSN 1063-6692, E-ISSN 1558-2566, Vol. 24, no 6, 3690-3701 p.Article in journal (Refereed)
    Abstract [en]

    A future content-centric Internet would likely consist of autonomous systems (ASes) just like today’s Internet. It would thus be a network of interacting cache networks, each of them optimized for local performance. To understand the influence of interactions between autonomous cache networks, in this paper, we consider ASes that maintain peering agreements with each other for mutual benefit and engage in content-level peering to leverage each others’ cache contents. We propose a model of the interaction between the caches managed by peering ASes. We address whether stable and efficient content-level peering can be implemented without explicit coordination between the neighboring ASes. We show that content-level peering leads to stable cache configurations, both with and without coordination. However, peering Internet Service Providers (ISPs) that coordinate to avoid simultaneous updates converge to a stable configuration more efficiently. Furthermore, if the content popularity estimates are inaccurate, content-level peering is likely to lead to cost efficient cache allocations. We validate our analytical results using simulations on the measured peering topology of more than 600 ASes.

  • 12.
    Pacifici, Valentino
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Distributed Algorithms for Content Allocation in Interconnected Content Distribution Networks2015In: Proc. of IEEE Infocom, IEEE , 2015Conference paper (Refereed)
    Abstract [en]

    Internet service providers increasingly deploy internal CDNs with the objective of reducing the traffic on their transit links and to improve their customers' quality of experience. Once ISP managed CDNs (nCDNs) become commonplace, ISPs would likely provide common interfaces to interconnect their nCDNs for mutual benefit, as they do with peering today. In this paper we consider the problem of using distributed algorithms for computing a content allocation for nCDNs. We show that if every ISP aims to minimize its cost and bilateral payments are not allowed then it may be impossible to compute a content allocation. For the case of bilateral payments we propose two distributed algorithms, the aggregate value compensation (AC) and the object value compensation (OC) algorithms, which differ in terms of the level of parallelism they allow and in terms of the amount of information exchanged between nCDNs. We prove that the algorithms converge, and we propose a scheme to ensure ex-post individual rationality. Simulations performed on a real AS-level network topology and synthetic topologies show that the algorithms have geometric rate of convergence, and scale well with the graphs' density and the nCDN capacity.

  • 13.
    Pacifici, Valentino
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Selfish Content Replication on Graphs2011In: ITC '11 Proceedings of the 23rd International Teletraffic Congress, ITCP , 2011, 119-126 p.Conference paper (Refereed)
    Abstract [en]

    Replication games are a model of the problem of content placement in computer and communication systems, when the participating nodes make their decisions such as to maximize their individual utilities. In this paper we consider replication games played over arbitrary social graphs; the social graph models limited interaction between the players due to, e.g., the network topology. We show that in replication games there is an equilibrium object placement for arbitrary social graphs. Nevertheless, if all nodes follow a myopic strategy to update their object placements then they might cycle arbitrarily long before reaching an equilibrium if the social graph is non-complete. We give sufficient conditions under which such cycles do not exist, and propose an efficient distributed algorithm to reach an equilibrium over a non-complete social graph.

  • 14.
    Pacifici, Valentino
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Stable Content-peering of Autonomous Systems in a Content-centric Network2013Conference paper (Refereed)
    Abstract [en]

    A future content-centric Internet would likely consistof autonomous systems (ASes) just like today’s Internet. It wouldthus be a network of interacting cache networks, each of themoptimized for local performance. To understand the influence ofinteractions between autonomous cache networks, in this paperwe consider ASes that maintain peering agreements with eachother for mutual benefit, and engage in content-level peering toleverage each others’ cache contents. We propose a model of theinteraction and the coordination between the caches managed bypeering ASes. We address whether stable and efficient contentlevel peering can be implemented without explicit coordinationbetween the neighboring ASes in order for the system to bestable. We show that content-level peering leads to stable cacheconfigurations, and that avoiding simultaneous updates by peeringISPs provides faster and more cost efficient convergence to a stableconfiguration. We validate our analytical results using simulationson the measured peering topology of more than 600 ASes.

  • 15.
    Pacifici, Valentino
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Josilo, Sladjana
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Distributed Algorithms for Content Caching in Mobile Backhaul Networks2016In: Proceedings of the 28th International Teletraffic Congress, ITC 2016, Institute of Electrical and Electronics Engineers (IEEE), 2016, 313-321 p., 7809666Conference paper (Refereed)
    Abstract [en]

    The growing popularity of mobile multimedia content and the increase of wireless access bitrates are straining backhaul capacity in mobile networks. A cost-effective solution to reduce the strain, enabled by emerging all-IP 4G and 5G mobile backhaul architectures, could be in-network caching of popular content during times of peak demand. In this paper we formulate the problem of content caching in a mobile backhaul as a binary integer programming problem, and we propose a 2-approximation algorithm for the problem. The 2-approximation requires full information about the network topology and the link costs, as well as about the content demands at the different caches, we thus propose two distributed algorithms that are based on limited information on the content demands. We show that the distributed algorithms terminate in a finite number of steps, and we provide analytical results on their approximation ratios. We use simulations to evaluate the proposed algorithms in terms of the achieved approximation ratio and computational complexity on realistic mobile backhaul topologies.

  • 16.
    Pacifici, Valentino
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Lehrieder, Frank
    University of Wurzburg.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Cache Bandwidth Allocation for P2P File Sharing Systems to Minimize Inter-ISP Traffic2016In: IEEE/ACM Transactions on Networking, ISSN 1063-6692, E-ISSN 1558-2566, Vol. 24, no 1, 437-448 p.Article in journal (Refereed)
    Abstract [en]

    Many Internet service providers (ISPs) have deployed peer-to-peer (P2P) caches in their networks in order to decrease costly inter-ISP traffic. A P2P cache stores parts of the most popular contents locally, and if possible serves the requests of local peers to decrease the inter-ISP traffic. Traditionally, P2P cache resource management focuses on managing the storage resource of the cache so as to maximize the inter-ISP traffic savings. In this paper we show that, when there are many overlays competing for the upload bandwidth of a P2P cache, then in order to maximize the inter-ISP traffic savings the cache's upload bandwidth should be actively allocated among the overlays. We formulate the problem of P2P cache bandwidth allocation as a Markov decision process, and propose three approximations to the optimal cache bandwidth allocation policy. We use extensive simulations and experiments to evaluate the performance of the proposed policies, and show that the bandwidth allocation policy that prioritizes swarms with a small ratio of local peers to all peers in the swarm can improve the inter-ISP traffic savings in BitTorrent-like P2P systems by up to 30 to 60 percent.

  • 17.
    Pacifici, Valentino
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Lehrieder, Frank
    University of Würzburg.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Cache Capacity Allocation for BitTorrent-like Systems to Minimize Inter-ISP Traffic2012In: IEEE  International Conference on Computer Communications (INFOCOM), 2012, 2012, 1512-1520 p.Conference paper (Refereed)
    Abstract [en]

    Many Internet service providers (ISPs) have deployed peer-to-peer (P2P) caches in their networks in order to decrease costly inter-ISP traffic. A P2P cache stores parts of the most popular contents locally, and if possible serves the requests of local peers to decrease the inter-ISP traffic. Traditionally, P2P cache resource management focuses on managing the storage resource of the cache so as to maximize the inter-ISP traffic savings. In this paper we show that when there are many overlays competing for the upload bandwidth of a P2P cache then in order to maximize the inter-ISP traffic savings the cache’s upload bandwidth should be actively allocated among the overlays. We formulate the problem of P2P cache bandwidth allocation as a Markov decision process, and describe two approximations to the optimal cache bandwidth allocation policy. Based on the insights obtained from the approximate policies we propose SRP, a priority-based allocation policy for BitTorrent-like P2P systems. We use extensive simulations to evaluate the performance of the proposed policies, and show that cache bandwidth allocation can improve the inter-ISP traffic savings by up to 30 to 60 percent. We validate the results via BitTorrent experiments on Planet-lab.

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