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  • 1.
    Auvert, Marine
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Hjalmarsson, Håkan
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Johansson, Karl H.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Karlsson, Gunnar
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    On Router Control for Congestion Avoidance2002Conference paper (Refereed)
    Abstract [en]

    This short paper deals with active queue management for computer networks. The goal is to develop control mechanisms for routers in heterogeneous networks that reduce traffic fluctuations. The proposed control strategy operates with local information (such as estimated arrival rates) and actively use the buffers to smooth traffic, and thus it avoids the buildup and propagation of traffic bursts.

  • 2. Baldantoni, Luca
    et al.
    Lundqvist, Henrik
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Karlsson, Gunnar
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Adaptive End-to-End FEC for Improving TCP Performance over Wireless Links2004In: 2004 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS, 2004, p. 4023-4027Conference paper (Refereed)
    Abstract [en]

    TCP is a reliable transport protocol that has been tuned to perform well in networks where packet losses occur mostly because of congestion. However, wireless networks are different: TCP responds both to congestion-based and error-based losses by invoking a congestion control algorithm and reducing the sending rate, resulting in degraded end-to-end performance for wireless systems. We investigate a new end-to-end approach for improving TCP performance over lossy links by using adaptive, end-to-end forward error correction (FEC) for recovering losses and consequently avoiding the TCP back-off behaviour. Of course there is a clear trade-off between the capacity consumed by FEC and the gain achieved in the overall throughput. An adaptive algorithm is needed to calculate the optimum ratio of redundancy given the state of the connection. The sender uses feedback information from the receiver to dynamically tune the FEC parameters. Through simulations we evaluate the performance of TCP with end-to-end FEC in mixed wired and wireless networks. The simulation results show in different scenarios that the throughput can be significantly improved by adding end-to-end FEC to TCP. However, compared to other improved TCP variants such as Westwood+ the performance is not improved, hence a direct modification of TCP congestion control appears to be more efficient than adding end-to-end FEC.

  • 3. Barcelo-Ordinas, Jose M.
    et al.
    Casetti, Claudio
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Sargento, Susana
    Information Mobility: a New Paradigm for Wireless Content Dissemination2009In: EUWIT: 2009 EUROPEAN WIRELESS TECHNOLOGY CONFERENCE, 2009, p. 100-103Conference paper (Refereed)
    Abstract [en]

    Content distribution networks are nowadays becoming a mature technology. Nevertheless, content delivery research in ad hoc networks has dealt with overlay applications, information querying and data broadcasting techniques. The aim of this paper is to explore and discuss content delivery in wireless ad hoc networks and to state challenges and reference models for this kind of networks. The concept of Information Mobility is introduced to point out that the contents are being stored in mobile nodes and that the contents move and replicate before being accessed. The network considered is a wireless ad hoc network with sparse connectivity and limited infrastructure support.

  • 4. Briat, C.
    et al.
    Yavuz, E.A
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Jönsson, Ulf T.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    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.
    The Conservation of Information, Towards an Axiomatized Modular Modeling Approach to Congestion Control2015In: IEEE/ACM Transactions on Networking, ISSN 1063-6692, E-ISSN 1558-2566, Vol. 23, no 3, p. 851-865Article in journal (Refereed)
    Abstract [en]

    We derive a modular fluid-flow network congestion control model based on a law of fundamental nature in networks: the conservation of information. Network elements such as queues, users, and transmission channels and network performance indicators like sending/acknowledgment rates and delays are mathematically modeled by applying this law locally. Our contributions are twofold. First, we introduce a modular metamodel that is sufficiently generic to represent any network topology. The proposed model is composed of building blocks that implement mechanisms ignored by the existing ones, which can be recovered from exact reduction or approximation of this new model. Second, we provide a novel classification of previously proposed models in the literature and show that they are often not capable of capturing the transient behavior of the network precisely. Numerical results obtained from packet-level simulations demonstrate the accuracy of the proposed model.

  • 5.
    Briat, Corentin
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Jönsson, Ulf
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    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.
    Nonlinear state-dependent delay modeling and stability analysis of internet congestion control2010In: 49TH IEEE CONFERENCE ON DECISION AND CONTROL (CDC), 2010, p. 1484-1491Conference paper (Refereed)
    Abstract [en]

    It is shown that the queuing delay involved in the congestion control algorithm is state-dependent and does not depend on the current time. Then, using an accurate formulation for buffers, networks with arbitrary topologies can be built. At equilibrium, our model reduces to the widely used setup by Paganini et al. Using this model, the delay-derivative is analyzed and it is proved that the delay time-derivative does not exceed one for the considered topologies. It is then shown that the considered congestion control algorithm globally stabilizes a delay-free single buffer network. Finally, using a specific linearization result for systems with state-dependent delays from Cooke and Huang, we show the local stability of the single bottleneck network.

  • 6.
    Briat, Corentin
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Jönsson, Ulf T.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    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.
    Yavuz, Emre Altug
    KTH, School of Electrical Engineering (EES), Communication Networks.
    An axiomatic fluid-flow model for congestion control analysis2011In: 2011 50th IEEE Conference on Decision and Control andEuropean Control Conference (CDC-ECC), 2011, p. 3122-3129Conference paper (Refereed)
    Abstract [en]

    An axiomatic model for congestion control isderived. The proposed four axioms serve as a basis for theconstruction of models for the network elements. It is shownthat, under some assumptions, some models of the literature canbe recovered. A single-buffer/multiple-users topology is finallyderived and studied for illustration.

  • 7.
    Briat, Corentin
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Yavuz, Emre A.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    A conservation-law-based modular fluid-flow model for network congestion modeling2012In: 2012 Proceedings - IEEE INFOCOM, IEEE Computer Society, 2012, p. 2050-2058Conference paper (Refereed)
    Abstract [en]

    A modular fluid-flow model for network congestion analysis and control is proposed. The model is derived from an information conservation law stating that the information is either in transit, lost or received. Mathematical models of network elements such as queues, users, and transmission channels, and network description variables, including sending/ acknowledgement rates and delays, are inferred from this law and obtained by applying this principle locally. The modularity of the devised model makes it sufficiently generic to describe any network topology, and appealing for building simulators. Previous models in the literature are often not capable of capturing the transient behavior of the network precisely, making the resulting analysis inaccurate in practice. Those models can be recovered from exact reduction or approximation of this new model. An important aspect of this particular modeling approach is the introduction of new tight building blocks that implement mechanisms ignored by the existing ones, notably at the queue and user levels. Comparisons with packet-level simulations corroborate the proposed model.

  • 8.
    Briat, Corentin
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Yavuz, Emre A.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Impact of Queueing Delay Estimation Error on Equilibrium and Its Stability2011In: NETWORKING 2011, PT II, 2011, p. 356-367Conference paper (Refereed)
    Abstract [en]

    Delay-based transmission control protocols need to separate round-trip time (RTT) measurements into their constituting parts: the propagation and the queueing delays. We consider two means for this; the first is to take the propagation delay as the minimum observed RTT value, and the second is to measure the queueing delay at the routers and feed it back to the sources. We choose FAST-TCP as a representative delay-based transmission control protocol for analysis and study the impact of delay knowledge errors on its performance. We have shown that while the first method destroys fairness and the uniqueness of the equilibrium, the stability of the protocol can easily be obtained through tuning the protocol terms appropriately. Even though the second technique is shown to preserve fairness and uniqueness of the equilibrium point, we have presented that unavoidable oscillations can occur around the equilibrium point.

  • 9.
    Burden, Tony
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Cohen, Ian
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Dodd, D.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Online tutoring2006In: SEFI 2006 - 34th Annual Conference: Engineering Education and Active Students, Uppsala universitet, 2006Conference paper (Refereed)
    Abstract [en]

    Tutoring has been a central part of the educational system at the long established universities of Cambridge and Oxford in the UK. Previously, at most two students could be tutored in the mathematical sciences, one on each side of the supervisor. Today in the age of computing and Internet, any number of students, in principal, could be supervised at a distance, as each student will be sitting in front of his or her own computer. This paper describes an attempt to carry out tutoring in the subject area of mechanics in small groups and at a distance, i.e. the tutors and the students communicate via an Internet based e-meeting system rather being present in the same physical room. This is used at a KTH (Sweden) mechanics distance course supported with tutoring from AUT (New Zealand) and the reverse tutoring of students at a regular mechanics course at AUT tutored from KTH.

  • 10.
    Chen, Zhaofei
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Yavuz, Emre A.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Demo of a collaborative music sharing system2012In: MobiOpp'12 - Proceedings of the 3rd ACM International Workshop on Mobile Opportunistic Networks, New york: ACM , 2012, p. 77-78Conference paper (Refereed)
    Abstract [en]

    We demonstrate a wireless real-time music-sharing application that lets users play music directly from their mobiles through a jukebox. We have designed and implemented the application by using a previously developed content-centric opportunistic networking middleware. The jukebox plays the music file that is first in its playlist by streaming it in real-time from the publishing user device. All users can observe the collaboratively formed playlist on their mobiles in real-time. The application shows the usefulness of our middleware and demonstrates a new form of situated applications. The application handles churn and garbage collection after departed users.

  • 11.
    Chen, Zhaofei
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Yavuz, Emre Altug
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    What a juke! A collaborative music sharing system2012In: 2012 IEEE International Symposium on a World of Wireless, Mobile and Multimedia Networks, WoWMoM 2012 - Digital Proceedings, IEEE , 2012, p. 6263751-Conference paper (Refereed)
    Abstract [en]

    The fast spreading of smart mobile devices has changed the way people create and share multimedia contents. A recently proposed idea is to distribute contents opportunistically when devices are within each other's communication range. In this work we have seized this idea and designed and implemented a real-time music-sharing application that allows people to share a sound system for collective listening. The system utilizes a content-centric opportunistic networking middleware. The application provides an interface for users to play audio files stored in their own mobile devices through a shared jukebox that is within direct communication range. The jukebox plays the audio file that is first in queue in its playlist by streaming it from the publishing user device. All devices synchronize with the jukebox so that the users can observe the contents of the playlist on their displays in real-time. This paper presents the idea and motivation for such a system as well as its design and evaluation.

  • 12.
    Chupisanyarote, Sanpetch
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Kouyoumdjieva, Sylvia
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Helgason, Ólafur
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Caching in opportunistic networks with churn2012In: 2012 9th Annual Conference on Wireless On-Demand Network Systems and Services, WONS 2012, IEEE Communications Society, 2012, p. 39-42Conference paper (Refereed)
    Abstract [en]

    In this paper we examine opportunistic content distribution. We design and evaluate a caching strategy where a node will fetch and share contents on behalf of other nodes, although the contents are not of its own interest. We propose three caching options for improving the use of network resources: relay request on demand, hop-limit, and greedy relay request. The proposed strategies are implemented in the OMNeT++ simulator and evaluated on mobility traces from Legion Studio that have churn. We also compare our strategies with a strategy from the literature. The results are analyzed and they show that the use of opportunistic caching for a community of nodes may enhance the performance marginally while overhead increases significantly.

  • 13.
    Danielis, Peter
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Kouyoumdjieva, Sylvia T.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    DiVote: A Distributed Voting Protocol for Mobile Device-to-Device Communication2016In: Proceedings of the 28th International Teletraffic Congress, ITC 2016, 2016, Vol. 1, p. 69-77Conference paper (Refereed)
    Abstract [en]

    Distributed aggregation algorithms have traditionally been applied to environments with no or rather low rates of node churn. The proliferation of mobile devices in recent years introduces high mobility and node churn to these environments, thus imposing a new dimension on the problem of distributed aggregation in terms of scalability and convergence speed. To address this, we present DiVote, a distributed voting protocol for mobile device-to-device communication. We investigate a particular use case, in which pedestrians equipped with mobile phones roam around in an urban area and participate in a distributed yes/no poll, which has both spatial and temporal relevance to the community. Each node casts a vote and collects votes from other participants in the system whenever in communication range; votes are immediately integrated into a local estimate. The objective of DiVote is to produce a precise mapping of the local estimate to the anticipated global voting result while preserving node privacy. Since mobile devices may have limited resources allocated for mobile sensing activities, DiVote utilizes D-GAP compression. We evaluate the proposed protocol via extensive trace-driven simulations of realistic pedestrian behavior, and demonstrate that it scales well with the number of nodes in the system. Furthermore, in densely populated areas the local estimate of participants does not deviate by more than 3% from the global result. Finally, in certain scenarios the achievable compression rate of DiVote is at least 19% for realistic vote distributions.

  • 14. Danielis, Peter
    et al.
    Kouyoumdjieva, Sylvia T.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Network and Systems engineering. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    UrbanCount: Mobile Crowd Counting in Urban Environments2017In: 2017 8th IEEE Annual Information Technology, Electronics and Mobile Communication Conference (IEMCON) / [ed] Chakrabarti, S Saha, HN, Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 640-648Conference paper (Refereed)
    Abstract [en]

    Surveillance, management and estimation of spontaneous crowd formations in urban environments, e.g., during open-air festivals or rush hours, are necessary measures for city administration. Most solutions that implement these measures however require additional costly hardware installations (e.g., installation of observation cameras) and infrastructure support, and often pose privacy concerns. In this work, we present UrbanCount, a fully distributed crowd counting protocol for cities with high crowd densities. UrbanCount relies on mobile device-to-device communication to perform crowd estimation. Each node collects crowd size estimates from other participants in the system whenever in communication range and immediately integrates these estimates into a local estimate. The objective of UrbanCount is to produce a precise mapping of the local estimate to the anticipated global result while preserving node privacy. We evaluate the proposed protocol via extensive tracedriven simulations of synthetic and realistic mobility models. Furthermore, we investigate the dependency between accuracy and density, and demonstrate that in dense environments the local estimate does not deviate by more than 2% for synthetic and 7% for realistic scenarios. Index Terms-Crowd counting,

  • 15. Domingo-Pascual, Jordi
    et al.
    Karlsson, Gunnar
    KTH.
    QofIS 20042006In: Computer Communications, ISSN 0140-3664, E-ISSN 1873-703X, Vol. 29, no 7, p. 799-800Article in journal (Other academic)
  • 16.
    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, p. 160-168Conference 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.

  • 17.
    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, p. 1002-1007Conference 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.

  • 18.
    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.

  • 19.
    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, p. 684-696Conference 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.

  • 20.
    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, p. 66-69Conference 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.

  • 21.
    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, p. 678-690Conference 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.

  • 22.
    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, p. 75-87Conference 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.

  • 23.
    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, p. 1104-1129Article 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.

  • 24.
    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, p. 31-53Article 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.

  • 25.
    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, p. 363-377Article 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.

  • 26. Fortetsanakis, G.
    et al.
    Papadopouli, Maria
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Dramitinos, M.
    Yavuz, Emre A.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    To subscribe, or not to subscribe: Modeling and analysis of service paradigms in cellular markets2012In: 2012 IEEE International Symposium on Dynamic Spectrum Access Networks, DYSPAN 2012, IEEE , 2012, p. 189-200Conference paper (Refereed)
    Abstract [en]

    Traditionally customers subscribe to specific providers and are served by accessing base stations (BSs) of the network of their provider. Inevitably subscribers with relatively 'high' usage pattern and data-rate requirements are subsidized by the ones with lower usage and data-rates. As the wireless technology advances, a diverse set of services will be available. This paper introduces the 'flex service' paradigm that allows a customer to dynamically access BSs of different providers based on various criteria, such as profile, network conditions, and offered prices. 'Flex users' can select the appropriate provider and BS on a per-session basis. This work considers a diverse customer population with respect to their demand, their preference on data-rate over price, their tolerance on the blocking probabilities of their sessions, and their willingness to pay for certain services. Users can dynamically decide to buy a long-term subscription or become flex users. In this paper, we develop a rich framework for modeling and analysis of such markets in different spatio-temporal scales. We analyze the evolution of markets with the flex service paradigm, focusing on whether it can improve the quality-of-service (QoS), social welfare, flexibility and further enhance the competition among providers. The main contribution of this paper is detailed modeling and indepth performance analysis of such complex markets, in different spatial and temporal scales. It considers the perspective of clients, providers, and regulators. It demonstrates the benefits of markets with the flex service paradigm and compares them with the ones that only offer subscription contracts.

  • 27.
    Fu, Jing
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Hagsand, Olof
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    An analysis of Queueing Behavior in Network Processor Systems2006In: 4th Swedish National Computer Networking Workshop, SNCNW 2006, Luleå, Sweden, 2006Conference paper (Refereed)
  • 28.
    Fu, Jing
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Hagsand, Olof
    KTH, School of Computer Science and Communication (CSC).
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Improving and Analyzing LC-Trie Performance for IP-Address Lookup2007In: Journal of Networks, ISSN 1796-2056, E-ISSN 1796-2056, Vol. 2, no 3, p. 18-27Article in journal (Refereed)
    Abstract [en]

    IP-address lookup is a key processing function of Internet routers. The lookupis challenging because it needs to perform a longest prefix match. In this paper, wepresent our modifications to an efficient lookup algorithm, the LC-trie, based ona technique called prefix transformation. Thereafter, the LC-trie’s performance isanalyzed for both the original and our modified algorithm using real and syntheticallygenerated traces. The performance study includes trie search depth, prefixvector access behavior, cache behavior and packet lookup time. The study is basedboth on experiments and a model for packet lookup time. The results show thatthe modified algorithm requires only 30% of the lookup time of the original algorithm.In particular, the modified algorithm is capable of performing 60 millionpacket lookups per second on a Pentium 4, 2.8 GHz, computer for a real traffictrace. Further, the results show that the performance is about five times better onthe real trace compared to a synthetically generated network trace. This illustratesthat the choice of traces may have a large influence on the results when evaluatinglookup algorithms.

  • 29.
    Fu, Jing
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Hagsand, Olof
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Performance Evaluation and Cache Behavior of LC-Trie for IP-Address Lookup2006In: Proc. of IEEE 2006 Workshop on High Performance Switching and Routing (HPSR 2006), IEEE , 2006, p. 29-35Conference paper (Refereed)
    Abstract [en]

    Many IP-address lookup software algorithms use a trie-like data structure to perform longest prefix match. LC-trie is an efficient algorithm that uses level compression and path compression on tries. By using realistic and synthetically generated traces, we study the performance of the LC-trie algorithm. Our study includes trie search depth, prefix vector access behavior, cache behavior, and packet lookup service time. The results show that for a realistic traffic trace, the LC-trie algorithm is capable of performing 20 million packet lookups per second on a Pentium 4, 2.8 GHz computer, which corresponds to a 40 Gb/s link for average sized packets. Further, the results show that LC-trie performs up to five times better on the realistic trace compared to a synthetically generated network trace. This illustrates that the choice of traces may have a large influence on the results when evaluating lookup algorithms.

  • 30.
    Fu, Jing
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Hagsand, Olof
    KTH, School of Computer Science and Communication (CSC), Numerical Analysis and Computer Science, NADA.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Communication Networks.
    Queueing Behavior and Packet Delays in Network Processor Systems2007In: 15th IEEE International Symposium on Modeling, Analysis, and Simulation of Computer and Telecommunication Systems: Bogazici Univ, Dept Comp Engn, Istanbul, TURKEY, OCT 24-26, 2007 / [ed] Caglayan M. U.; Field AJ; Gelenbe E., 2007, p. 217-224Conference paper (Refereed)
    Abstract [en]

    Network processor systems provide the performance of ASICs combined withthe programmability of general-purpose processors. One of the main challengesin designing these systems is the memory subsystem used when forwarding andqueueing packets. In this work, we study the queueing behavior and packet delaysin a network processor system which works as a router. We introduce a systemmodel and a simulation tool based on the model. Using the simulation tool, bothbest-effort and diffserv IPv4 forwarding were modeled and tested using real-worldand synthetically generated packet traces. The results on queueing behavior havebeen used to dimension various queues, and can be used as guidelines for designingmemory subsystems and queueing disciplines. In particular, a system withsmall queue sizes has been proposed. The results on packet delays also show thatour diffserv setup provides good service differentiation for best-effort and prioritypackets. Finally, the study reveals that the choice of traces has a large impact onthe results when evaluating router and switch architectures.

  • 31.
    Fu, Jing
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sjödin, Peter
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Convergence of intra-domain routing with centralized control2008In: AD HOC AND SENSOR NETWORKS, WIRELESS NETWORKS, NEXT GENERATION INTERNET, PROCEEDINGS, 2008, Vol. 4982, p. 518-529Conference paper (Refereed)
    Abstract [en]

    The decentralized control scheme for routing in current IP networks has been questioned, and a centralized routing scheme has been proposed as an alternative. In this paper, we compare the convergence of centralized control scheme with decentralized link-state routing protocols. We first identify the components of the convergence time. Thereafter, we study how to achieve fast routing convergence in networks with centralized control. In particular, we analyze how to distribute forwarding information efficiently. Finally, we perform simulation studies on the convergence time for both real and synthetic network topologies, and study the impact of control element location, link weights, and number of failures on the convergence time. The results show that the centralized control scheme can provide faster routing convergence than link-state routing protocols.

  • 32.
    Fu, Jing
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Sjödin, Peter
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture, Telecommunication Systems Laboratory, TSLab.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Intra-Domain Routing Convergence with Centralized Control2009In: Computer Networks, ISSN 1389-1286, E-ISSN 1872-7069, Vol. 53, no 18, p. 2985-2996Article in journal (Refereed)
    Abstract [en]

    The decentralized control scheme for routing in current IP networks has been questioned, and a centralized routing scheme has been proposed as an alternative. In this paper, we compare the convergence of centralized control scheme with decentralized link-state routing protocols. We first review the architectural advantages and challenges of centralized control. Thereafter, we identify and discuss the components of the convergence time in both schemes. We present how to achieve fast routing convergence in networks with centralized control. in particular, we analyze how to distribute forwarding information efficiently. Finally, we perform simulation studies on the convergence time for both real and synthetic network topologies and study the impact of control element location, link weights, and number of failures on the convergence time. The results show that the centralized control scheme can provide faster routing convergence than link-state routing protocols.

  • 33.
    Fu, Jing
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Sjödin, Peter
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture, Telecommunication Systems Laboratory, TSLab.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Loop-Free Updates of Forwarding Tables2008In: IEEE Transactions on Network and Service Management, ISSN 1932-4537, Vol. 5, no 1, p. 22-35Article in journal (Refereed)
    Abstract [en]

    When the forwarding paths in an IP network change due to a link failure or a link weight modification, the forwarding tables in the routers may need to be updated. Each of these updates may cause transient loops if they are not performed in an appropriate order. In this paper, we propose an order to update the forwarding tables that avoids transient loops for non-urgent changes. The order is obtained by studying the changes in the forwarding tables, therefore it can be used in networks running any routing protocols, and for any type of forwarding path changes. After presenting the order, we prove that it is correct, and present an efficient algorithm to compute the order. Thereafter, we present several algorithms for performing forwarding table updates in accordance with the order. We also discuss how the update algorithms can be applied to both networks with centralized control and decentralized routing protocols. Finally, we study the update algorithms’ performance on several network topologies and with varying parameter settings and for several types of forwarding path changes.

  • 34.
    Fu, Jing
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Communication Networks.
    Sjödin, Peter
    KTH, School of Information and Communication Technology (ICT).
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Communication Networks.
    Traffic Engineering and Routing in IP Networks with Centralized Control2008In: Lecture Notes in Computer Science, ISSN 0302-9743, E-ISSN 1611-3349, Vol. 4982, p. 633-641Article in journal (Refereed)
    Abstract [en]

    There have been research initiatives in centralized control recently, which advocatethat the control of an autonomous system (AS) should be performed in acentralized fashion. In this paper, we propose an approach to perform traffic engineeringand routing in networks with centralized control, named LP-redirect.LP-redirect is based on an efficient formulation of linear programming (LP) thatreduces the number of variables and constraints. As LP is not fast enough for runtimerouting, LP-redirect uses a fast scheme to recompute routing paths when anetwork topology changes. The performance evaluation of LP-redirect shows thatit is more efficient in both traffic engineering and computation than an approachusing optimized link weights. In addition, LP-redirect is suitable for runtime trafficengineering and routing.

  • 35.
    Fu, Jing
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Sjödin, Peter
    KTH, School of Information and Communication Technology (ICT).
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Communication Networks.
    Two Stage IP-address Lookup in Distributed Routers2008In: Proc. of IEEE INFOCOM High-Speed Netwworks Workshop, 2008Conference paper (Refereed)
    Abstract [en]

    IP-address lookup is the primary processing functionof Internet routers. While a wide range of algorithms havebeen developed to perform lookups, very few of them havethe distributed architecture of current and future routers inconsideration. To support rapidly increasing high data rates,packet processing in commercial routers today are divided intoan ingress and an egress part, with the lookup performed at theingress. In the lookup, the egress line card, the outgoing interfaceand the nexthop address of a given packet are determined. In thispaper, we propose an alternative scheme to perform the lookupby dividing the task, which is named two-stage lookup scheme.In the lookup, the ingress determines the egress only, then it is upto the egress to determine the outgoing interface and the nexthopaddress. Based on our analysis and experimental study, weconclude that the proposed scheme has several advantages in bothhardware lookup technologies and software lookup algorithms.In particular, it provides significantly more efficient high-speedpacket lookup.

  • 36.
    Hagsand, Olof
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Más, Ignacio
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Marsh, Ian
    Swedish Institute of Computer Science.
    Karlsson, Gunnar
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Self-Admission Control for IP Telephony using Early Quality Estimation2004In: Lecture Notes in Computer Science, ISSN 0302-9743, E-ISSN 1611-3349, Vol. 3042, p. 381-391Article in journal (Refereed)
    Abstract [en]

    If quality of service could be provided at the transport or the application layer, then it might be deployed simply by software upgrades, instead of requiring a complete upgrade of the network infrastructure. In this paper, we propose a self-admission control scheme that does not require any network support or external monitoring schemes. We apply the admission control scheme to IP telephony as it is an important application benefiting from admission control. We predict the quality of the call by observing the packet loss over a short initial period using an in-band probing mechanism. The quality prediction is then used by the application to continue or to abort the call. Using over 9500 global IP telephony measurements, we show that it is possible to accurately predict the quality of a call. Early rejection of sessions has the advantage of saving valuable network resources plus not disturbing the on-going calls.

  • 37.
    Helgason, Olafur Ragnar
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    On the effect of cooperation in wireless content distribution2008In: 2008 FIFTH ANNUAL CONFERENCE ON WIRELESS ON DEMAND NETWORK SYSTEMS AND SERVICES, NEW YORK: IEEE , 2008, p. 141-148Conference paper (Refereed)
    Abstract [en]

    In this paper we propose continuous time Markov chain models that capture the dynamics of content spreading in a disruption tolerant wireless content distribution system. We use our models to study the effect of cooperation among the mobile nodes and how limited node resources, such as battery lifetime and confined storage, affect the content distribution process. Based on our models and numerical results we deduce that limiting the number of times a node shares each content entry is a good method to conserve energy while at the same time only slightly reducing system performance. Our study also suggests that the effect of assisting nodes is greatest for content channels with few subscribers. For promoting fairness in distributing channels and giving new channels a chance to spread, assisting nodes should therefore solicit and help in spreading less popular channels.

  • 38.
    Helgason, Ólafur
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Kouyoumdjieva, Sylvia T.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Does Mobility Matter?2010In: WONS 2010: SEVENTH INTERNATIONAL CONFERENCE ON WIRELESS ON-DEMAND NETWORK SYSTEMS AND SERVICES, NEW YORK: IEEE , 2010, p. 9-16Conference paper (Refereed)
    Abstract [en]

    In modern society, wireless devices are commonly carried by humans. The wireless communication is therefore affected by pedestrian mobility in urban outdoor and indoor spaces which is the scenario we consider in this work. Many of the mobility models currently used for evaluating wireless communication systems have poor resemblance to reality. Although advances have recently been made, there is still a lack of understanding on which elements of mobility affect system performance. In the civil-engineering field of transport and urban planning there exist advanced pedestrian mobility models, used for designing and dimensioning public spaces for pedestrian crowds and emergency evacuation. These models capture micro-mobility of pedestrians better than most mobility models used in mobile networking since the application domain requires that they realistically capture node interactions with its physical environment as well as other nodes. In this work we use Legion Studio, a commercial simulator, to explore which elements of pedestrian mobility are important with respect to system performance and how sensitive the connectivity metrics of nodes are to input mobility parameters. These studies give insight into whether relatively simple mobility models suffice for evaluating wireless systems. Furthermore, they contribute to our understanding of which parameters are important for modelling mobility and the accuracy in which these parameters need to be estimated to give dependable results.

  • 39.
    Helgason, Ólafur
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Kouyoumdjieva, Sylvia T.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Opportunistic Communication and Human Mobility2014In: IEEE Transactions on Mobile Computing, ISSN 1536-1233, E-ISSN 1558-0660, Vol. 13, no 7, p. 1597-1610Article in journal (Refereed)
    Abstract [en]

    Many mobility models currently used for evaluating wireless communication systems have weak resemblance to reality and there is a lack of understanding on which characteristics of human mobility affect system performance. In particular, most current mobility models assume a free flow of nodes and do not consider how mobility is affected by interactions with other persons and with the physical environment. They also assume a closed system, not considering the effect of node arrival and departure. The structure of space in which the mobility occurs is either not considered at all, or only in a limited way. In this work, we address human pedestrian mobility for evaluation of wireless communication to determine which of the aforementioned aspects need to be captured and to what level of detail. We focus on opportunistic communication in the form of ad-hoc and delay-tolerant networks. For the evaluation, we use mobility models from the field of transportation and urban planning that are used for designing and dimensioning public spaces for comfort and safety of pedestrians in rush hour and emergency evacuation. The models capture micro-mobility of pedestrians better than most mobility models used in mobile networking since the application domain requires realistic representation of node interactions with the physical environment and with other nodes. Our results show that the free flow assumption used in most models does not have a significant performance impact. We also conclude that performance is not very sensitive to accurate estimation of the probability distributions of mobility parameters such as speed and arrival process. Our results, however, suggest that it is important to capture the scenario and space in which mobility occurs since these may affect performance significantly.

  • 40.
    Helgason, Ólafur
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Kouyoumdjieva, Sylvia T.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Pajevic, Ljubica
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Yavuz, Emre A.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    A Middleware for Opportunistic Content Distribution2016In: Computer Networks, ISSN 1389-1286, E-ISSN 1872-7069Article in journal (Refereed)
    Abstract [en]

    In this work we present a middleware architecture for a mobile peer-to-peer content distribution system. Our architecture allows wireless content dissemination between mobile nodes without relying on infrastructure support. In addition, it supports the dissemination of contents between the wireless ad-hoc domain and the wired Internet. In the ad-hoc domain, contents are exchanged opportunistically when nodes are within communication range. Applications access the service of our platform through a publish/subscribe interface and therefore do not have to deal with low-level opportunistic networking issues or matching and soliciting of contents. Our middleware consists of three key components. A content structure that facilitates dividing contents into logical topics and allows efficient matching of content lookups and downloading under sporadic node connectivity. A solicitation protocol that allows nodes to solicit content meta-information in order to discover contents available at a neighboring node and to download content entries disjointedly from different nodes. An API that allows applications to access the system services through a publish/subscribe interface. In this work we present the design and implementation of our middleware and describe a set of applications that use the services provided by our middleware. We also assess the performance of the system using our Android implementation as well as a simulation implementation for large-scale evaluation.

  • 41.
    Helgason, Ólafur Ragnar
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Legendre, F.
    Lenders, V.
    May, M.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Performance of opportunistic content distribution under different levels of cooperation2010In: 2010 European Wireless Conference, Lucca, 2010, Vol. EW 2010, p. 903-910Conference paper (Refereed)
    Abstract [en]

    In this paper, we study the performance of opportunistic content distribution in a delay-tolerant network (DTN). Our primary interest is the benefit of node cooperation on the content dissemination and we investigate thoroughly how different levels of cooperation affect the content delivery delay. The evaluation is based on two complementary approaches, analytical stochastic models (Markov chains) and simulations that use real-world contact traces with high time resolution. These two independent approaches show agreeing results on the qualitative behavior of the system. Our major finding is that node collaboration - even if limited - dramatically improves performance compared to non-cooperation. In particular, we find that limiting the number of times a node shares a content item gives only a slightly worse performance than under unlimited cooperation. Besides, we find that a critical number of nodes is necessary to disseminate content efficiently. Eventually, based on the analytic model we also find that the details of the mobility show little effect on the delivery time when the nodes cooperate.

  • 42.
    Helgason, Ólafur
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Yavuz, Emre A.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Kouyoumdjieva, Sylvia
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Pajevic, Ljubica
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    A mobile peer-to-peer system for opportunistic content-centric networking2010In: Proceedings of the 2nd ACM SIGCOMM Workshop on Networking, Systems, and Applications on Mobile Handhelds, MobiHeld '10, Co-located with SIGCOMM 2010, 2010, p. 21-26Conference paper (Refereed)
    Abstract [en]

    In this work we present a middleware architecture for a mobile peer-to-peer content distribution system. Our architecture allows wireless content dissemination between mobile nodes without relying on infrastructure support. Contents are exchanged opportunistically when nodes are within communication range. Applications access the service of our platform through a publish/subscribe interface and therefore do not have to deal with low-level opportunistic networking issues or matching and soliciting of contents. Our architecture consists of three key components. A content structure that facilitates dividing contents into logical topics and allows for efficient matching of content lookups and downloading under sporadic node connectivity. A solicitation protocol that allows nodes to solicit content meta-information in order to discover contents available at a neighboring node and to download content entries disjointedly from different nodes. An API that allows applications to access the system services through a publish/subscribe interface. In this work we describe the design and implementation of our architecture. We also discuss potential applications and present evaluation results from profiling of our system.

  • 43. Jonsson, K. V.
    et al.
    Helgason, Ólafur Ragnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    A gateway for wireless broadcasting2007In: Proceedings of 2007 ACM CoNEXT Conference: 3rd International Conference on Emerging Networking EXperiments and Technologies, 2007, Vol. CoNEXTConference paper (Refereed)
    Abstract [en]

    Ad-hoc wireless peer-to-peer methods are an important and viable alternative to the more traditional infrastructure based ones for distributing contents among a population of users. The PodNet project is a ongoing effort to create a broadcasting system for delay-tolerant content, in which peer nodes exchange contents opportunistically when within range, and their mobility acts as a complementary mechanism for the dissemination. This paper introduces the design of a Pod-Net node. In particular, the special case of a gateway, which bridges the infrastructure world of the Internet and the adhoc domain, is considered.

  • 44.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Radio- och tv-avgiften och internet: Teknik, lag, tolkning och domar2013Report (Other academic)
    Abstract [sv]

    Sedan i februari har Radiotjänst AB en tolkning där man hävdar att internetansluten dator, mobiltelefon och datorplatta är en se som en tv-mottagare och därmed är innehavaren skyldig att betala radio- och tv-avgift. Tolkningen har skapat debatt och upprördhet bland allmänheten, exempelvis bland de som valt att inte ha tv-mottagare och som nu retroaktivt anses avgiftskyldiga för utrustning de införskaffat före Radiotjänst nytolkning.

    Jag har deltagit i debatten eftersom det är en teknisk definition som bestämmer vad som anses vara en tv-mottagare. I den här rapporten sammanfattar jag de artiklar och den video som jag tidigare publicerat och jag utökar mitt resonemang för att belysa frågeställning från olika perspektiv. Bland annat granskar jag Radiotjänsts påstående på webben, argumenten i en dom från förvaltningsrätten i Luleå från den 24 juni samt den efterföljande domen i samma ärende som överklagats till kammarrätten i Sundsvall. Jag tar även upp en dom från förvaltningsrätten som avser en äldre dator som blivit befriad från avgiften.

    Jag finner att Radiotjänsts tolkning saknar stöd i lagstiftningen och i förarbetena. Tolkningen baseras på selektivt urval av längre resonemang och är tekniskt felaktig. Motsvarande problem finns i de domar som jag tar upp. Min slutsats är att en tv-mottagare är enbart definierad med avseende på rundradioutsändning i marknät och satellitnät och över olika former av kabel-tv- och IPTV-nät. Detta utesluter dock inte Radiotjänst från att ta ut radio- och tv-avgift från de som tar del av utsändningarna i öppna internetsändningar, men avgiften kan inte följa innehav av någon utrustning. Betald avgift skulle exempelvis kunna krävas för tillgång till tv-sändningarna. Det kan styrkas med hjälp av inloggning.

  • 45.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    The IP in IP-TV: The networking aspects2007In: Proceedings 2007: WIC Midwintermeeting on IP-Television, 2007, Vol. IP-TV, p. 83-97Conference paper (Refereed)
  • 46.
    Karlsson, Gunnar
    et al.
    KTH, Superseded Departments (pre-2005), Microelectronics and Information Technology, IMIT.
    Almeroth, Kevin
    Univ Calif Santa Barbara, Dept Comp Sci, Santa Barbara, CA 93106 USA..
    Fall, Kevin
    Intel Res Berkeley, Berkeley, CA USA..
    May, Martin
    ETH, Comp Engn & Networks Lab, Zurich, Switzerland..
    Yates, Roy
    Rutgers State Univ, WINLAB, Piscataway, NJ USA..
    Delay and disruption tolerant wireless communication2008In: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 26, no 5, p. 745-747Article in journal (Other academic)
  • 47.
    Karlsson, Gunnar D.
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Lenders, Vincent
    May, Martin
    Delay-tolerant broadcasting2007In: IEEE transactions on broadcasting, ISSN 0018-9316, E-ISSN 1557-9611, Vol. 53, no 1, p. 369-381Article in journal (Refereed)
    Abstract [en]

    There are many asynchronous communication situations for which the prevalent continuous connectivity paradigm, is not needed. Communication with a fair delay tolerance may instead be provided by intermittent store-and-forwarding between nodes. This paper proposes a design for an open, receiver-driven broadcasting system that relies on delay-tolerant forwarding of data chunks through mobility of wireless nodes. The system provides public broadcast channels, which may be openly used for both transmission and reception. We show by analysis and simulation under benchmark mobility models that a delay-tolerant broadcast channel has both a sufficiently high throughput and reach to be interesting as a competitive alternative to the regulated wireless broadcast channel. The analysis is based on a queuing model to study the interactions among the mobile nodes in a street. The simulations complement this analysis for mobile nodes moving on a square according to benchmark mobility models. Finally, we present the design of, and experiences with, a proof-of-concept prototype.

  • 48.
    Karlsson, Gunnar
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Janson, Sverker
    Swedish Institute of Computer Science.
    How to create blended learning: Guidelines for improved teaching with flipped classroom and active learning2015Report (Other academic)
    Abstract [en]

    In this report we present guidelines for developing and giving courses that blend online and in-class instruction, offering a simple default based on the Flipped Classroom and Peer Instruction teaching models and use of a web-based teaching platform. The guidelines naturally fall into two parts, developing new courses and giving already developed courses.

  • 49.
    Karlsson, Gunnar
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Lenders, V.
    May, M.
    Delay-tolerant broadcasting2006In: Proceedings of ACM SIGCOMM 2006: Conference on Applications, Technologies, Architectures, and Protocols for Computer Communication, Pisa, 2006, Vol. 2006, p. 197-204Conference paper (Refereed)
    Abstract [en]

    There are many asynchronous communication situations for which the prevalent continuous connectivity paradigm is not needed. Communication with a fair delay tolerance may instead be provided by intermittent store-and-forwarding between nodes. This paper proposes a design for an open, receiver-driven broadcasting system that relies on delay-tolerant forwarding of data chunks through mobility of wireless nodes. The system provides public broadcast channels, which can be openly used for both transmission and reception. We show by simulation under benchmark mobility models that a delay-tolerant broadcast channel has both a sufficiently high throughput and reach to be interesting as a competitive alternative to the regulated wireless broadcast channel. We also present the design of, and experiences with, a proof-of-concept prototype.

  • 50.
    Karlsson, Gunnar
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Lundqvist, Henrik
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Más Ivars, Ignacio
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Single-Service Quality Differentiation2004In: 2004 Twelfth IEEE International Workshop on Quality of Service, IWQoS 2004: Montreal, Ont.; 7 June 2004 through 9 June 2004, 2004, p. 265-272Conference paper (Refereed)
    Abstract [en]

    This paper proposes a scheme for quality of service differentiation for single-service networks that is based on the use of two separate forms of traffic control at the transport layer: Streams are controlled by means of probe-based admission control and elastic flows are controlled by TCP. The controls allow separation of traffic into two distinct service classes. The stream class is designed to provide a consistent quality for interactive audiovisual communication, as favored by human perception. It is responsive to load variations as an aggregate through blocking of sessions, while TCP is responsive on the flow level. Streams can be isolated against disturbances from probes and TCP flows by means of error-control coding. We show that the two traffic controls can coexist without starvation, and the proposed scheme might thus provide a first step towards differentiated services end-to-end.

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