"uuid","repository link","title","author","contributor","publication year","abstract","subject topic","language","publication type","publisher","isbn","issn","patent","patent status","bibliographic note","access restriction","embargo date","faculty","department","research group","programme","project","coordinates"
"uuid:5c80616a-87ba-478d-8428-45f807f473f3","http://resolver.tudelft.nl/uuid:5c80616a-87ba-478d-8428-45f807f473f3","A network approach for power grid robustness against cascading failures","Wang, X.; Koc, Y.; Kooij, R.E.; Van Mieghem, P.","","2015","Cascading failures are one of the main reasons for blackouts in electrical power grids. Stable power supply requires a robust design of the power grid topology. Currently, the impact of the grid structure on the grid robustness is mainly assessed by purely topological metrics, that fail to capture the fundamental properties of the electrical power grids such as power flow allocation according to Kirchhoff’s laws. This paper deploys the effective graph resistance as a metric to relate the topology of a grid to its robustness against cascading failures. Specifically, the effective graph resistance is deployed as a metric for network expansions (by means of transmission line additions) of an existing power grid. Four strategies based on network properties are investigated to optimize the effective graph resistance, accordingly to improve the robustness, of a given power grid at a low computational complexity. Experimental results suggest the existence of Braess’s paradox in power grids: bringing an additional line into the system occasionally results in decrease of the grid robustness. This paper further investigates the impact of the topology on the Braess’s paradox, and identifies specific sub-structures whose existence results in Braess’s paradox in power grids. Careful assessment of the design and expansion choices of grid topologies incorporating the insights provided by this paper optimizes the robustness of a power grid, while avoiding the Braess’s paradox in the system.","","en","conference paper","RNDM","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Network Architectures and Services","","","",""
"uuid:d940cff1-457e-4c2c-afba-962c7d4400ec","http://resolver.tudelft.nl/uuid:d940cff1-457e-4c2c-afba-962c7d4400ec","Quantifying the robustness of metro networks","Wang, X.; Koç, Y.; Derrible, S.; Nasir Ahmad, Sk.; Kooij, R.E.","","2015","Metros (heavy rail transit systems) are integral parts of urban transportation systems. Failures in their operations can have serious impacts on urban mobility, and measuring their robustness is therefore critical. Moreover, as physical networks, metros can be viewed as network topological entities, and as such they possess measurable network properties. In this paper, by using network science and graph theoretical concepts, we investigate both theoretical and experimental robustness metrics (i.e., the robustness indicator, the effective graph conductance, and the critical thresholds) and their performance in quantifying the robustness of metro networks under random failures or targeted attacks. We find that the theoretical metrics quantify different aspects of the robustness of metro networks. In particular, the robustness indicator captures the number of alternative paths and the effective graph conductance focuses on the length of each path. Moreover, the high positive correlation between the theoretical metrics and experimental metrics and the negative correlation within the theoretical metrics provide significant insights for planners to design more robust system while accommodating for transit specificities (e.g., alternative paths, fast transferring).","","en","conference paper","Kyoto University - Japan Society of Transportation Engineering","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Network Architectures and Services","","","",""
"uuid:4437bbbb-39d6-4bd4-ae96-442f074da684","http://resolver.tudelft.nl/uuid:4437bbbb-39d6-4bd4-ae96-442f074da684","The Impact of the Topology on Cascading Failures in a Power Grid Model","Koç, Y.; Warnier, M.; Van Mieghem, P.; Kooij, R.E.; Brazier, F.M.T.","","2014","Cascading failures are one of the main reasons for large scale blackouts in power transmission grids. Secure electrical power supply requires, together with careful operation, a robust design of the electrical power grid topology. Currently, the impact of the topology on grid robustness is mainly assessed by purely topological approaches, that fail to capture the essence of electric power flow. This paper proposes a metric, the effective graph resistance, to relate the topology of a power grid to its robustness against cascading failures by deliberate attacks, while also taking the fundamental characteristics of the electric power grid into account such as power flow allocation according to Kirchoff Laws. Experimental verification on synthetic power systems shows that the proposed metric reflects the grid robustness accurately. The proposed metric is used to optimize a grid topology for a higher level of robustness. To demonstrate its applicability, the metric is applied on the IEEE 118 bus power system to improve its robustness against cascading failures.","","en","journal article","Elsevier","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Network Architectures & Services (NAS)","","","",""
"uuid:cb32eba2-0207-4ea2-855c-2047fd8fbaaa","http://resolver.tudelft.nl/uuid:cb32eba2-0207-4ea2-855c-2047fd8fbaaa","Graphs with given diameter maximizing the algebraic connectivity","Wang, H.; Kooij, R.E.; Van Mieghem, P.","","2010","We propose a class of graphs G?D(n1, n2, ..., nD+1), containing of a chain of D+1 cliques Kn1 , Kn2 , ..., KnD+1, where neighboring cliques are fully-interconnected. The class of graphs has diameter D and size N = ? 1?i?D+1ni. We prove that this class of graphs can achieve the maximal number of links, the minimum average hopcount, and more interestingly, the maximal of any Laplacian eigenvalue among all graphs with N nodes and diameter D. The algebraic connectivity is the eigenvalue of the Laplacian that has been studied most, because it features many interesting properties. We determine the graph with the largest algebraic connectivity among graphs with N nodes and diameter D ? 4. For other diameters, numerically searching for the maximum of any eigenvalue is feasible, because (a) the searching space within the class G?D(n1, n2, ..., nD+1) is much smaller than within all graphs with N nodes and diameter D; (b) we reduce the calculation of the Laplacian spectrum from a N × N to a (D +1)× (D + 1) matrix. The maximum of any Laplacian eigenvalue obtained either theoretically or by numerical searching is applied to (1) investigate the topological features of graphs that maximize different Laplacian eigenvalues; (2) study the correlation between the maximum algebraic connectivity amax(N, D) and N as well as D and (3) evaluate two upper bounds of the algebraic connectivity that are proposed in the literature.","graphs; algebraic connectivity; maximize; diameter","en","journal article","Elsevier","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Network Architectures & Services (NAS)","","","",""
"uuid:e986f176-d5cb-454e-b421-3076ebd19388","http://resolver.tudelft.nl/uuid:e986f176-d5cb-454e-b421-3076ebd19388","Techniques for measuring quality of experience","Kuipers, F.; Kooij, R.; De Vleeschauwer, D.; Brunnström, K.","","2010","Quality of Experience (QoE) relates to how users perceive the quality of an application. To capture such a subjective measure, either by subjective tests or via objective tools, is an art on its own. Given the importance of measuring users’ satisfaction to service providers, research on QoE took flight in recent years. In this paper we present an overview of various techniques for measuring QoE, thereby mostly focusing on freely available tools and methodologies.","","en","conference paper","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Network Architectures and Services","","","",""
"uuid:32776292-d65a-4010-b6ab-5990e1349206","http://resolver.tudelft.nl/uuid:32776292-d65a-4010-b6ab-5990e1349206","One Thousand Flowers in Delft: A Bottom-up approach to improve teaching international students","Brummelink, M.L.; Frantzeskaki, N.; Klaassen, R.G.; Blom, E.M.; Kooij, R.E.; Kroesen, J.O.; Stadler, D.I.; Van den Boogaard, M.E.D.","","2009","Delft University of Technology (DUT) is becoming more and more an international community. Since lectures on master level are all conducted in English, the numbers of students from foreign countries attending DUT are rising and international cooperation within educational projects is a necessity. To prepare educators for the continuing internationalization and globalization of education, a project named ‘One Thousand Flowers in Delft’ is launched at DUT. The key strength of this project is the bottom-up approach to internationalization. The Flowers project approach is a method to stimulate lecturers to turn the spotlights on internationalization in their own classrooms and to apply international skills, knowledge and attitudes in order to make these topics a more integrated part of the regular curriculum. This approach has proven itself over the years in ICT projects as an important motivational factor for lecturers, because it uses the challenges they themselves experience in class as a starting point. Instead of educational advisors prescribing lecturers what to improve on, lecturers come up with small-scale projects on topics they feel need improvement. The solutions participating lecturers find often turn out to be very valuable for a larger group of lecturers, since these solutions are rooted in and easily applicable to everyday education. In this paper, we will discuss the development and results of five Flowers and consider the possibilities the results have to offer other lecturers.","international students; intercultural communication; multicultural group work","en","conference paper","International Association for Technology, Education and Development","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Network Architectures and Services","","","",""
"uuid:e7944cb1-b333-4408-9e89-52dd10749fe7","http://resolver.tudelft.nl/uuid:e7944cb1-b333-4408-9e89-52dd10749fe7","That’s the way we want to learn!” ICT workshop at a primary school","Balch, C.; Kooij, R.; Leendertse, M.","","2009","Education is a key ingredient of any knowledge-based society, and ICT will be a key enabling factor to cope with the new strains on our education system. Recently TNO, the Dutch Organisation for Applied Scientific Research, experimented with different existing ICT technologies in a real-life primary classroom. Our ICT for education project had four main objectives. First, we wanted to investigate how we can tweak existing technologies to make them useful within an educational context. Second, we wanted to research the willingness of children to embrace ICT tools within their learning process. Third, we wanted to test whether it is feasible to develop ICT tools for education through participative research. And finally, we wanted the input from school management on practical ICT innovations in education. Our workshop consisted of six different educational activities. In this paper we describe these activities, as well as the feedback from the children, teacher and school director and we list the conditions for success for such a workshop. After discussing relevant follow-up activities we put the results of the workshop in a broader context.","ICT; games; mathematics; primary school.","en","conference paper","International Association for Technology, Education and Development","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Network Architectures and Services","","","",""
"uuid:0ffb67ab-3f9b-4458-9970-3abc6eaa85af","http://resolver.tudelft.nl/uuid:0ffb67ab-3f9b-4458-9970-3abc6eaa85af","A New Metric for Robustness with Respect to Virus Spread (Work in Progress)","Kooij, R.E.; Schumm, P.; Scoglio, C.; Youssef, M.","","2009","The robustness of a network is depending on the type of attack we are considering. In this paper we focus on the spread of viruses on networks. It is common practice to use the epidemic threshold as a measure for robustness. Because the epidemic threshold is inversely proportional to the largest eigenvalue of the adjacency matrix, it seems easy to compare the robustness of two networks. We will show in this paper that the comparison of the robustness with respect to virus spread for two networks actually depends on the value of the effective spreading rate ?. For this reason we propose a new metric, the viral conductance, which takes into account the complete range of values ? can obtain. In this paper we determine the viral conductance of regular graphs, complete bipartite graphs and a number of realistic networks.","robustness; virus spread; epidemic threshold; viral conductance.","en","conference paper","Springer","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Network Architectures and Services","","","",""
"uuid:0f1ff826-f1c9-48fa-b2ec-9a4b2b67a1d1","http://resolver.tudelft.nl/uuid:0f1ff826-f1c9-48fa-b2ec-9a4b2b67a1d1","Heterogenous protection in regular and complete bi-partite networks","Omic, J.S.; Kooij, R.E.; Van Mieghem, P.","","2009","We examine the influence of heterogeneous curing rates for a SIS model, used for malware spreading on the Internet, information dissemination in unreliable networks, and propagation of failures in networks. The topology structures considered are the regular graph which represents the homogenous network structures and the complete bi-partite graph which represents the hierarchical network structures. We find the threshold in a regular graph with m different curing rates. Further, we consider a complete bi-partite graph with 2 curing rates and find the threshold for any distribution of curing rates among nodes. In addition, we consider the optimization problem and show that the minimum sum of the curing rates that satisfies the threshold equation is equal to the number of links in the graph. The optimization problem is simplified by assuming fixed curing rates ?1, ?2 and optimization of the distribution of curing rates among different sets of nodes.","virus spread; epidemic threshold; heterogeneous networks","en","conference paper","Springer","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Network Architectures and Services","","","",""
"uuid:833962c9-63f2-471d-bfaf-8b9189efb63c","http://resolver.tudelft.nl/uuid:833962c9-63f2-471d-bfaf-8b9189efb63c","Impact of Advertisements during Channel Zapping on Quality of Experience","Godana, B.E.; Kooij, R.E.; Ahmed, O.K.","","2009","Nowadays various digital television services are available. However, the user of these services experiences longer delays than the traditional analog TV while switching from channel to channel. The digital TV operator usually displays a black screen with the channel number during zapping. However, it could be interesting for the TV viewer, if the operator displays a screen with information instead of just a black screen. This information may be an advertisement, information about the target channel, personalized content of the user etc. In this paper, we describe a subjective experiment where the Quality of Experience (QoE) of channel zapping was quantified, while displaying a random set of advertisement pictures during zapping. It is found that, for longer zapping times, advertisements give better QoE than the black screen. However, when zapping times are small,users prefer a black screen over a glance of an advertisement picture.","","en","conference paper","IARIA/IEEE","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Network Architectures and Services","","","",""
"uuid:0e1964b4-54e5-4e29-80a7-b609a1e21f75","http://resolver.tudelft.nl/uuid:0e1964b4-54e5-4e29-80a7-b609a1e21f75","Virus Spread in Networks","Van Mieghem, P.; Omic, J.; Kooij, R.","","2009","","virus spread; epidemic threshold; mean field theory; spectral radius; Markov theory","en","journal article","IEEE/ACM","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Network Architectures and Services","","","",""
"uuid:1c81bb88-338e-4d3f-8779-fd24bf4ddc77","http://resolver.tudelft.nl/uuid:1c81bb88-338e-4d3f-8779-fd24bf4ddc77","Model validation of channel zapping quality","Kooij, R.E.; Nicolai, F.; Ahmed, O.K.; Brunnström, K.","","2009","In an earlier paper we showed, that perceived quality of channel zapping is related to the perceived quality of download time of web browsing, as suggested by ITU-T Rec.G.1030. We showed this by performing subjective tests resulting in an excellent fit with a 0.99 correlation. This was what we call a lean forward experiment and gave the rule of thumb result that the zapping time must be less than 0.43 sec to be good ( > 3.5 on the MOS scale). To validate the model we have done new subjective experiments. These experiments included lean backwards zapping i.e. sitting in a sofa with a remote control. The subjects are more forgiving in this case and the requirement could be relaxed to 0.67 sec. We also conducted subjective experiments where the zapping times are varying. We found that the MOS rating decreases if zapping delay times are varying. In our experiments we assumed uniformly distributed delays, where the variance cannot be larger than the mean delay. We found that in order to obtain a MOS rating of at least 3.5, that the maximum allowed variance, and thus also the maximum allowed mean zapping delay, is 0.46 sec.","video quality; video metrics; standards; multimedia; subjective; objective","en","conference paper","SPIE","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Network Architectures and Services","","","",""
"uuid:f219628b-8878-453c-b0fe-d016745cbe47","http://resolver.tudelft.nl/uuid:f219628b-8878-453c-b0fe-d016745cbe47","Quantifying the Quality of Service of Streaming Media in Differentiated Services Networks","Agrawal, D.K.; Kleiberg, T.; Papp, S.; Kooij, R.E.; Van Mieghem, P.","","2007","Quality of Service (QoS) support in the current internet is indispensable because of QoS-sensitive real-time applications such as Voice-over-IP, IP-TV, video conferencing, online gaming etc. Since the introduction of the Differentiated Services (Diff-Serv) architecture there has been considerable work reported in literature on its performance evaluation. However, none of them have addressed the basic issue of quantification of QoS for supporting streaming media. The main contribution in this paper is the quantification of the QoS of streaming media in terms of Mean Opinion Score (MOS) values. A test bed has been implemented using off-the-shelf components. The experimental results and MOS values are used to show that in a DiffServ Assured Forwarding network architecture, with class based weighted fair queue scheduling discipline, the QoS of streaming media is not compromised when the load exceeds the reserved capacity, even in case of congestion.","","en","conference paper","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Network Architectures and Services","","","",""
"uuid:68b0690c-5bf3-4add-8daf-4176c1254eb4","http://resolver.tudelft.nl/uuid:68b0690c-5bf3-4add-8daf-4176c1254eb4","Modeling Ping Times in First Person Shooter Games","Degrande, N.; De Vleeschauer, D.; Kooij, R.E.; Mandjes, M.R.H.","","2006","In First Person Shooter (FPS) games the Round Trip Time (RTT), i.e., the sum of the network delay from client to server and the network delay from server to client, impacts the gamer’s performance considerably. Game client software usually has a built-in process to measure this RTT (also referred to as ping time), and therefore gamers do not want to connect to servers with a long ping time. This paper develops a methodology to evaluate the ping time in a scenario where gamers access a common gaming server over an access network, consisting of a link per user that connects this user to a shared aggregation node that in turn is connected to the gaming server via a bottleneck link. First, a model for the traffic the users and the server generate, is proposed based on experimental results of previous papers. It turns out that the characteristics of the (downstream) traffic from server to clients differ substantially from the characteristics of the client-to-server (upstream) traffic. Then, two queuing models are developed (one for the upstream and one for the downstream direction) and combined such that a quantile of the RTT can be calculated given all traffic and network parameters (packet sizes, packet inter-arrival times, link rate, network load,
). This methodology is subsequently used to assess the (quantile of the) RTT in a typical Digital Subscriber Line (DSL) access scenario. In particular, given the capacity dedicated to gaming traffic on the bottleneck link (between the aggregation node and gaming server), the number of gamers (or equivalently the gaming load the bottleneck link can support) is determined under the restriction that the quantile of the RTT should not exceed a predefined bound. It turns out that this tolerable load is surprisingly low in most circumstances. Finally, it is remarked that this conclusion depends to some extent on the details of the downstream traffic characteristics and that measurements reported in literature do not give conclusive evidence on the exact value of all parameters, such that, although the qualitative conclusion still remains valid, additional experiments could refine the detailed quantitative results.","On-line games; Round Trip Time; queuing model; analysis","en","conference paper","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Network Architectures and Services","","","",""
"uuid:acfb25f7-b4ef-4c90-9303-c1bc1ced0796","http://resolver.tudelft.nl/uuid:acfb25f7-b4ef-4c90-9303-c1bc1ced0796","Het Nederlands elftal als complex netwerk","Kooij, R.E.; Jamakovic, A.; Van Kesteren, F.; De Koning, T.C.M.; Theisler, I.B.; Veldhoven, P.","","","In de zomer van 2008, tijdens het Europees Kampioenschap voetbal in Zwitserland en Oostenrijk, zullen weer miljoenen mensen de verrichtingen van het Nederlands elftal op de voet volgen. Ondanks het feit dat voetbal razend populair is, bestaat er vanuit de wetenschappelijke wereld relatief weinig interesse voor voetbal. In dit artikel bestuderen we het Nederlands elftal vanuit het perspectief van complexe netwerken. In het Nederlands-elftalnetwerk, bestaat elk knooppunt uit een speler die ooit een officiële interland speelde. Twee knopen zijn met elkaar verbonden als de spelers in dezelfde interland hebben gespeeld. Het doel van dit artikel is het onderzoeken van topologische eigenschappen van het aldus verkregen Nederlandselftalnetwerk. Almerima Jamakovic en Rob Kooij zijn werkzaam als onderzoeker bij de faculteit van Elektrotechniek, Wiskunde en Informatica van de Technische Universiteit Delft; Rob Kooij werkt eveneens bij TNO Informatie- en Communicatietechnologie evenals de andere vier auteurs.","","en","journal article","Royal Dutch Mathematical Society","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Network Architectures and Services","","","",""
"uuid:e20b4727-94c3-48b3-bc1e-b20a397f51a7","http://resolver.tudelft.nl/uuid:e20b4727-94c3-48b3-bc1e-b20a397f51a7","On the Quality of Experience of SopCast","Fallica, B.; Lu, Y.; Kuipers, F.A.; Kooij, R.; Van Mieghem, P.","","","Peer-to-Peer (P2P) file sharing has become immensely popular in the Internet. Recently, there has been a growing interest in academic and commercial enviornments for live streaming using P2P technology. A number of new P2P digital television (P2PTV) applications have emerged. Such P2PTV applications are developed with proprietary technologies and the Quality of Experience (QoE) provided by them is not well known. Therefore, investigating their mechanisms, analyzing their performance, and measuring their quality are important for researchers, operators and end users. In this paper, we present results from a measurement study of a P2PTV application called SopCast, using both objective and subjective measurement technologies. The results obtained in our study reveal important design issues of SopCast and the QoE that the end users perceive.","","en","conference paper","IEEE","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Network Architectures and Services","","","",""