Impact of multiple ISPs

Our analysis in Section 4 focused on the characteristics of the end-to-end path from a source to a destination. The end-to-end path typically traverses multiple autonomous systems (ASes). Some of the ASes are stub networks such as university or corporate networks (where the source and destination nodes may be located) whereas others are ISP networks. The relationships between these networks is often complex. There are customer-provider relationships (such as those between a university network and its ISP or between a regional ISP and a nationwide ISP) and peering relationships (such as those between two nationwide ISPs). A stub network may be multi-homed (i.e., be connected to multiple providers). Two nationwide ISPs may peer with each other at multiple locations (e.g., San Francisco and New York). These complex interconnections between the individual networks have an impact on end-to-end routing. In this section, we show that geography can indeed be used as a means to analyze these complex interconnections. Specifically, we investigate the following questions: (a) are Internet paths within individual ISP networks as circuitous as end-to-end paths?, (b) what impact does the presence of multiple ISPs have on the circuitousness of the end-to-end path?, (c) what is the distribution of the path length within individual ISP networks, and (d) can geography shed light on the issue of hot-potato versus cold-potato routing?