Modularity and Extreme Edges of the Internet

TL;DR

This paper analyzes the spectral properties of Internet networks to reveal their modular structure, identifying extreme edges like Russia and US military sites, and proposes a new measure for network modularity based on diffusion modes.

Contribution

It introduces a spectral analysis approach to identify Internet modules and proposes a novel measure of modularity based on participation ratios of slow decaying modes.

Findings

Internet exhibits a modular structure with extreme edges like Russia and US military sites.

Participation ratio of slow modes is about 10 times larger than in a random network.

Approximately 30% of nodes participate in the slowest decaying modes.

Abstract

We study the spectral properties of a diffusion process taking place on the Internet network focusing on the slowest decaying modes. These modes allow us to identify an underlying modular structure of the Internet roughly corresponding to individual countries. For instance in the slowest decaying mode the diffusion current flows from Russia towards US military sites. These two regions thus constitute the extreme edges of the Internet. Quantitatively the modular structure of the Internet manifests itself in approximately 10 times larger participation ratio of its slow decaying modes compared to the null model - a random scale-free network. We propose to use the fraction of nodes participating in slow decaying modes as a general measure of the modularity of a network. For the 100 slowest decaying modes of the Internet we measured this fraction to be around 30%. Finally we suggest, that the degree of isolation of an individual module can be assessed by comparing its participation in different diffusion modes. Using the proportionality of response as a criterion we find that the independent module approximation works well for the Internet.