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Archive for February, 2012

MSc/MRes in Web Science and new course on Complex Networks & Web

February 28th, 2012 Shi Zhou Comments off

The Media Futures group of UCL Computer Science Department will offer a new MSc/MRes programme on the Web Science starting from September 2012.

Dr. Shi Zhou will teach a new core module on Complex Networks & Web.

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Article in IEEE Circuits and Systems Magazine

February 28th, 2012 Shi Zhou Comments off

Our paper on modelling network traffic fluctuations is recently published in the IEEE Circuit and Systems Magazine.

Circuits and Systems Magazine, IEEE

Title: Traffic Fluctuations on Weighted Networks

Authors: Yichao Zhang, Shi Zhou, et al.

Abstract: Traffic fluctuation has so far been studied on unweighted networks. However, many real traffic systems are better represented and understood as weighted networks, where nodes and links are assigned some weight values representing their physical properties such as capacity and delay. Here, we introduce a general random diffusion (GRD) model to investigate the traffic fluctuations on weighted networks, where a random walk’s choice of route is affected not only by the number of links a node has, but also by the weights of individual links. We obtain analytical solutions that characterize the relation between the average traffic and the fluctuations through nodes and links. Our analysis is supported by results of extensive numerical simulations. We observe that the value ranges of the average traffic and the fluctuations, through nodes or links, increase dramatically with the level of heterogeneity in link weights. This highlights the key role that link weight plays in traffic fluctuation and the necessity to study traffic fluctuations on weighted networks.

Traffic
Fluctuations
on Weighted

Network

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IEEE International Conference on Communications (ICC) 2012

February 28th, 2012 Shi Zhou Comments off

We will present our latest work on modelling the Internet routing at the IEEE ICC’2012, which is the flagship annual conference of the IEEE Communications Society.

ICC 2012

Title: Valley-free violation in Internet routing – Analysis based on BGP Community data

Authors: Vasileios Giotsas and Shi Zhou

Abstract: The valley-free rule defines patterns of routing paths that allow the Internet Autonomous Systems (AS) to minimize their routing costs through selective announcement of BGP routes. The valley-free rule has been widely perceived as a universal property of the Internet BGP routing that is only violated due to transient configuration errors. Analysing the valley-free violations is important for a better understanding of BGP behaviour and inter-domain routing. This requires knowledge of the business relationships between ASes. The ground-truth data of AS relationships are not publicly available. Previous algorithms have inferred AS relationships based on the assumption that AS paths should be valley-free. Such inference results are biased and cannot provide an objective assessment of the valley-free rule. Instead we extract the AS relationships directly from routing polices encoded in the BGP Community attribute. We are able to extract the business relationship of more than 30% of AS links based on BGP data collected from the RouteViews and RIPE RIS repositories in June 2011. We use our inferred AS relationships to analyse the valley-free violations in BGP routing. We reveal that the non valley-free paths are significantly more frequent than previously reported. As many as one fifth of AS paths in IPv6 BGP updates are valley paths. A substantial portion of these valley paths are persistent during the whole month of measurement. These observations strongly indicate that the valley paths are not merely a result of BGP misconfigurations. Instead they are the outcome of complex business relationships and deliberate policies by ASes using distinct unconventional models.

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