Measurement testbed

We used 20 geographically distributed hosts as the sources for our traceroutes. 17 of these hosts were located in the U.S. (Figure 1) while 3 were located in Europe (at Stockholm (Sweden), Bologna (Italy), and Budapest (Hungary)). The geographical diversity in source locations enables us to study the variations in routing properties as seen from different vantage points. For logistical reasons, it was convenient for us to locate the traceroute sources on university campuses. 18 out of the 20 traceroute sources fell into this category. Furthermore, 9 of the 15 university locations we considered in the U.S. were connected by the Internet2 backbone [19]. To add some diversity, we had one source in Berkeley, CA connected to a home cable modem network (in addition to a host at the University of California at Berkeley) and another in Seattle, WA connected to the Microsoft Research network (in addition to a host at the University of Washington at Seattle). These two pairs of sources allow us to study (albeit to a limited extent²) what impact, if any, the nature of the source's connectivity has. The destination set for the traceroutes comprised several thousand hosts. These destinations hosts fell into 4 categories:

1. UnivHosts: 265 Web servers and other hosts located on university campuses in the U.S. The hosts were distributed across 44 of the 50 states in the U.S.
2. LibWeb: 1,205 Web servers of public libraries [21] distributed across 49 states in the U.S. We also ensured that the distribution of the geographic locations of these libraries is not skewed.
3. TVHosts: 3,100 client hosts in the U.S. that connected to an on-line TV program guide. A majority of these clients were located on non-academic networks such as America Online (AOL).
4. EuroWeb: 1,092 Web servers [23] distributed across 25 countries in Europe.

For ease of exposition, we sometimes refer to UnivHosts, LibWeb, and TVHosts as the U.S. hosts and EuroWeb as the European hosts. This diverse set of destination hosts enables us to investigate the properties of Internet routing in the context of a large set of ISPs. In all, we traced approximately 84,000 end-to-end paths between our traceroute sources and the destination hosts during October-December 2000. Our data is available online at [27].