The interplay between structural connections and emerging information flow in the human brain remains an open research problem. A recent study observed global patterns of directional information flow in empirical data using the measure of transfer entropy. For higher frequency bands, the overall direction of information flow was from posterior to anterior regions whereas an anterior-to-posterior pattern was observed in lower frequency bands. In this study, we applied a simple Susceptible-Infected-Susceptible (SIS) epidemic spreading model on the human connectome with the aim to reveal the topological properties of the structural network that give rise to these global patterns. We found that direct structural connections induced higher transfer entropy between two brain regions and that transfer entropy decreased with increasing distance between nodes (in terms of hops in the structural network). Applying the SIS model, we were able to confirm the empirically observed opposite information flow patterns and posterior hubs in the structural network seem to play a dominant role in the network dynamics. For small time scales, when these hubs acted as strong receivers of information, the global pattern of information flow was in the posterior-to-anterior direction and in the opposite direction when they were strong senders. Our analysis suggests that these global patterns of directional information flow are the result of an unequal spatial distribution of the structural degree between posterior and anterior regions and their directions seem to be linked to different time scales of the spreading process.

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We have analyzed the measurements of end-to-end Voip packets by tracing UDP packets between 12 testboxes in the Netherlands. We show that voice probes experience low delay and loss in the network. Moreover, we find that the reordering of packets has virtually no impact on the voice quality in our experiments. To determine the quality of Voip calls over time, we have monitored the end-to-end packet delay, and packet loss over 10 days. The experimental results indicate that the networks in the Netherlands can continuously achieve a high voip quality.@en

Application layer (AL) multicast protocols emerged, and in large number, as a response to the slow deployment op IP multicast. However, the gain of different AL multicast mechanisms, in terms of resources consumption over unicast, is questionable. In this paper, we investigate the efficiency of AL multicast protocol NICE, in terms of the number of hops a packet traverses on its path toward the destinations. We propose four alternative algorithms for the creation of NICE overlay and compare their efficiency to the efficiency of unicast, IP multicast, and another two previously evaluated AL multicast, and another two previously evaluated AL multicast protocols (MCAN and Scribe). Further, we investigate the influance of the underlying topology awareness on the efficiency. Our analysis has been performed via simulations, as well as via measurements on the PlanetLab network. We show that the NICE structure achieves better results than MCAN and Scribe.@en

The Internet is a collection of networks that use the TCP/IP suite of protocols. It has a huge impact on human activity. There are currently hundreds of millions of computers connected to the Internet, generating several petabytes traffic a day. Internet is still growing rapidly. However, the Internet today is not yet precisely characterized. One reason for this is that it is dynamic, constantly changing in size, traffic load, and application types. Recently, there has been a lot of effort put into various aspects of Internet measurements. These are important to the scientists as they provides crucial, fundamental knowledge about Internet structure and performance, and, at the same time, these measurements have added value for Internet Service Providers (ISPs) in terms of service monitoring and for management purposes. Results obtained so far in Internet measurements are very encouraging. Significant progress has been made in many fields (e.g., we now understand the topology of Web much better than before), but there are still many aspects of the Internet¿s structure, workload, and applications that are unexplored. This thesis addresses several unanswered questions about the performance of the Internet at the network and the application layer. To mention a few: 1. How can we model the Internet infrastructure, and how can this be measured? 2. How does IPv6 compare to IPv4 in terms of delay and loss performance and how has performance evolved over the past few years? 3. How can we evaluate user application performance through Internet measurements? 4. Is there any method to estimate network distance based on reduced or incomplete measurements (e.g., delay and hopcount)? We intend to address these questions by measuring the Internet and analyzing empirical evidence obtained from Internet data. In this thesis, we show that accurate measurements not only enhance our understanding of the current Internet, but can also lead to recommendations for improvements on both the network infrastructure and network protocols.@en

To provide high quality service to future internet applications, IPv6 performance measurements are needed. However, to the best of our knowledge, IPv6 delay and loss performance evolution and their impact on applications have not been studied on a large scale. In this paper, we have analyzed more than 600 end-to-end IPv6 paths between about 26 testboxes of RIPE NCC over the past two years, and compared the delay and loss performance evolution in IPv6 with their IPv4 counterparts. We present and discuss the measurement methodology, and we provide evidence that IPv6 network has a higher delay and loss evolution than IPv4. Finally, based upon our measurements, we asses the the perceived quality of three real-life applications: VoIP, Video-over-IP and data communication services based upon TCP.@en

IPv6 provides an expanded address space to satisfy the future Internet requirements. In this paper we compare and analyze one-month measurements of the end-to-end IPv6 delay and hopcount between 26 testboxes of the RIPE TTM project with the corresponding parts in IPv4 network. By comparing IPv6 and IPv4 paths, we focus on problems that are only present in the IPv6 paths. In those poorly performing IPv6 paths, we run traceroute with the path maximum transmission unit (MTU) discovery to identify the problems and their causes.@en