Analyzing network bandwidths of ISP topologies having power-law degree distributions

Recent measurement studies on Internet topology show that the connectivities of nodes exhibit a power–law attribute. That is, the probability p(k) that a node is connected to k other nodes follows p(k) ∼ k −γ. However, even if the degree distributions of some topologies are the same, more detailed characteristics are often quite different. For example, ISP topologies had a much higher cluster coefficient than the other topologies attained with conventional modeling methods, and more importantly, these differences greatly affect methods of network control. Thus, for studies of higher–layer protocols such as routing and flow controls, more detailed information of ISP networks are required. One of our main motivations in this thesis is to investigate the link bandwidths of actual ISP topologies, and then gives some reasonings being that. For this purpose, in this thesis, we measure topologies and link bandwidths of two Japanese ISPs. The results of measurements show that the degree distribution of ISP networks shows power-law attribute. That is, the most of nodes have few outgoing links, while few nodes have many outgoing links. We next measure bandwidths of all the links on each Japanese ISP topology. The results show that the high band-width links are located at Tokyo. Furthermore, nodes that have a high bandwidth link also have a lot of outgoing links, which is different from discussions given by other researcher's works where high bandwidth links are connected to lower-degree nodes. Following this observation, we present a geographical model to give a realistic bandwidth distribution of links, and we demonstrate that the geographical model certainly reproduces the link bandwidths of ISP networks.