Fluctuation of the Download Network

The scaling behaviour of fluctuation for a download network we investigated a few years ago based upon Zhang's Econophysics web page is presented. A power law scaling, namely σ~ α exists between the dispersion σ and average flux of the download rates. The fluctuation exponent α is neither 1/2 nor 1, which were claimed as two universal fluctuation classes in previous publication, while it varies from 1/2 to 1 with the time window in which the download data are accumulated. The crossover behaviour of fluctuation exponents can be qualitatively understood by the external driving fluctuation model for a small-size system or a network traffic model which suggests congestion as the origin.