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U.S. versus Europe
We now analyze the distance ratios for paths in Europe and compare
these to the distance ratios for paths in the U.S. We consider paths
from the 17 U.S. sources to destinations in the LibWeb set and also
paths from the 3 European sources to destinations in the EuroWeb
set. Thus, all of these paths are contained either entirely within the
U.S. or entirely within Europe. We do not consider paths from
U.S. sources to European destinations (or vice versa) because the
distance ratio for such paths tends to be dominated by long
transatlantic links (which tends to push the ratio towards 1).
Figure 6:
CDF of distance ratio for paths within the U.S. and those within Europe.
![\begin{figure}
\centerline{\psfig{file=figs/USvsEurope.eps,height=3.0in,width=4.5in,angle=0}}
\vspace{-0.20in}
\textbf{}
\end{figure}](img11.png) |
In Figure 6, we show the distribution of the
distance ratio for three sources: Berkeley in the U.S., and Stockholm
(Sweden) and Bologna (Italy) in Europe. We observe that the distance
ratio tends to be larger for the European sources compared to
Berkeley, especially in the tail of the distribution. We attribute
this to three causes.
First, paths in Europe tend to traverse multiple regional or
national ISPs. The complex peering relationships between these ISPs
often results in convoluted paths. For instance, a path from Bologna
to a host in Salzburg, Austria traverses 3 ISPs - GARR (Italian
Academic and Research Network), Eqip/Infonet, and KPNQwest (a leading
pan-European ISP based in the Netherlands) - and passes through Milan
(Italy), Geneva (Switzerland), Paris (France), Amsterdam
(Netherlands), Frankfurt (Germany), and Vienna (Austria). The
linearized distance of the path is 2506 km whereas the geographic
distance between Bologna and Salzburg is only 383 km.
Second, in some cases the path from a European source to a European
destination passes through nodes in the U.S. For instance, a path from
Stockholm (Sweden) to Zagreb (Croatia) passes through a node in New
York City belonging to Teleglobe, a large international ISP. In the
event that the ISPs in Europe have better connectivity to ISPs in
U.S., it would be appropriate for them to route their traffic through
U.S. though the route may be more circuitous. Third, geographic
distances in Europe tend to be smaller than the ones in U.S. As in
the case of St Louis in Section 4.2.1,
small detours in routing can be particularly expensive in terms of the
distance ratio for paths between end-hosts in Europe.
Next: Temporal properties of routing
Up: Effect of geographic location
Previous: Multiple sources in different
Lakshminarayanan Subramanian
2002-04-14