R.E. Kooij

Virus spread in networks

The influence of the network characteristics on the virus spread is analyzed in a new-the <i>N</i> -intertwined Markov chain-model, whose only approximation lies in the application of mean field theory. The mean field approximation is quantified in detail. The <i>N</i> -intertwined model has been compared with the exact 2^N-state Markov model and with previously proposed ldquohomogeneousrdquo or ldquolocalrdquo models. The sharp epidemic threshold tau_c , which is a consequence of mean field theory, is rigorously shown to be equal to tau_c = 1/(lambda_max(<i>A</i>)) , where lambda_max(<i>A</i>) is the largest eigenvalue-the spectral radius-of the adjacency matrix <i>A</i> . A continued fraction expansion of the steady-state infection probability at node <i>j</i> is presented as well as several upper bounds.

Predicting the perceived quality of a first person shooter: the Quake IV G-model

This paper describes the development of an end-to-end quality measurement method that allows us to quantify the perceived quality of Interactive Gaming, with an emphasis on the so-called First Person Shooter (FPS) game Quake IV. We conducted a number of subjective experiments to quantify the impact of network parameters on the perceived quality of this recent FPS game. Making use of a multi-dimensional regression analysis we developed the Quake IV G-model which enables us to predict a gamers Quake IV quality rating (expressed in a Mean Opinion Score) based on measured ping and jitter values. Our G-model shows a very high correlation (R = 0.98) with the subjective data.

Assessing the Quality of Experience of SopCast

Recently, there has been a growing interest in academic and commercial environments 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. Their traffic characteristics and the Quality of Experience (QoE) provided by them are not well known. Therefore, investigating their mechanisms, analysing their performance, and measuring their quality are important objectives for researchers, developers and end users. In this paper, we present results from a measurement study of a BitTorrent-like P2PTV application called SopCast, using both objective and subjective measurement technologies. The results obtained in our study reveal the characteristics and important design issues of SopCast, as well as the QoE that the end users perceive.

On the Quality of Experience of SopCast

Peer-to-Peer (P2P) file sharing has become immensely popular in the Internet. Recently, there has been a growing interest in academic and commercial environments 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.

Robustness of networks against viruses: the role of the spectral radius

In this paper we study the spectral radius of a number of real-life networks. This study is motivated by the fact that the smaller the spectral radius, the higher the robustness of a network against the spread of viruses. First we study how well-known upper bounds for the spectral radius of graphs match to the spectral radii of the social network of the Dutch soccer team, the Dutch roadmap network, the network of the observable part of the Internet graph at the IP-level and the autonomous system level. Secondly, we compare the spectral radius for these real-life networks with those of commonly used complex network models

Impact of Advertisements during Channel Zapping on Quality of Experience

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.

A New Metric for Robustness with Respect to Virus Spread

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 bi-partite graphs and a number of realistic networks.

Model validation of channel zapping quality

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.

Quantifying the quality of service of streaming media in differentiated services networks

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 gaining 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.

The minimal spectral radius of graphs with a given diameter

The spectral radius of a graph (i.e., the largest eigenvalue of its corresponding adjacency matrix) plays an important role in modeling virus propagation in networks.In fact, the smaller the spectral radius, the larger the robustness of a network against the spread of viruses.Among all connected graphs on n nodes the path Pn has minimal spectral radius.However, its diameter D, i.e., the maximum number of hops between any pair of nodes in the graph, is the largest possible, namely D = n - 1.In general, communication networks are designed such that the diameter is small, because the larger the number of nodes traversed on a connection, the lower the quality of the service running over the network.This leads us to state the following problem: which connected graph on n nodes and a given diameter D has minimal spectral radius?In this paper we solve this problem explicitly for graphs with diameter D .{1, 2, . n 2 ., n - 3, n - 2, n - 1}.Moreover, we solve the problem for almost all graphs on at most 20 nodes by a computer search.