Abstract. In the real world, cities exist because of external economies associated with the geographic concentration of firms within a city. Of course, such a geographic proximity with input providers and consumers, would at first reduce transportation costs. But why cities, information cities, i.e. large agglomerations of people and economic activity emerge in the virtual world? In the Internet, transportation costs are zero. Web sites can easily be reached from anybody and everywhere with no particular cost. In these conditions of equal access distance, one would rather expect a smooth web geography with a relatively even distribution of visitors per site. However, the web economy illustrates strong agglomeration trends with a very small number of web sites capturing a large segment of the web population and the most of virtual economic activity. This paper attempts to provide a sound basis for the dynamics of population concentration in the web under increasing returns.
We discuss a parallel implementation of an agent-based simulation. Our approach allows to adapt a sequential simulator for largescale simulation on a cluster of workstations. We target discrete-time simulation models that capture the behavior of WWW. The real-world phenomena of emerged aggregated behavior of the Internet population is studied. The system distributes data among workstations, which allows large-scale simulations infeasible on a stand-alone computer. The model properties cause traffic between workstations proportional to partition sizes. Network latency is hidden by concurrent simulation of multiple users. The system is implemented in Mozart that provides multithreading, dataflow variables, component-based software development, and network-transparency. Currently we can simulate up to 10 6 Web users on 10 4 Web sites using a cluster of 16 computers, which takes few seconds per simulation step, and for a problem of the same size, parallel simulation offers speedups between 11 and 14.
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