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Paths from a single source
We consider paths from our traceroute sources in U.S. universities to
two varied set of end-hosts: UnivHosts and TVHosts.
Many of the hosts in UnivHosts (including our sources)
connect to the Internet2 high-speed backbone via a local GigaPOP. So
much of the wide-area path between our sources and a host in
UnivHosts traverses the Internet2 backbone. On the other hand, TVHosts
is a more diverse set that includes hosts located in various
commercial networks (AOL, MSN, @Home, etc.) as well as university
campuses. So the wide-area paths from our sources to the
hosts in TVHosts typically traverse one or more commercial ISP
backbones.
Figure 3:
CDF of distance ratio for paths from UC Berkeley to UnivHosts and TVHosts.
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This difference between the two groups of destination hosts is
reflected in the cumulative distribution function (CDF) of the
distance ratio for the two cases. As Figure 3
shows (for source in UC Berkeley), the distance ratio is close to 1
for many of the destinations. The ratio is 1.1 or less (corresponding
to a linearized distance that exceeds the end-to-end geographic
distance by no more than 10%) for 55% of the destinations in
UnivHosts and 45% in TVHosts. This finding is consistent with the
rich Internet connectivity of the San Francisco Bay Area (where UC
Berkeley is located). The area includes several public Internet
exchanges (e.g., MAE-West, PAIX, etc.) as well as private peering
points. So a path from the UC Berkeley host to a destination host is
often (but not always) able to transition to the latter's ISP within
the SF bay area itself. So there is little need to take a detour
through another city just to transition to the destination's ISP.
There is a far more pronounced difference between the UnivHosts and
TVHosts cases if we look at the tail of the distribution. For
instance, at the 90th percentile mark, the distance ratio is 1.41 in
the case of UnivHosts but 1.72 in the case of TVHosts; in other words,
the detour is 1.75 times as large for TVHosts destinations as it is
for UnivHosts (72% versus 41%). The paths to some of the hosts in
TVHosts tend to be more circuitous because they traverse multiple
commercial ISPs whose peering relationships may cause detours in the
end-to-end path. We discuss this issue in more detail in Section
5. We observe qualitatively the same trends for other
university sources as well; i.e., the distance ratio tends to be
smaller for paths leading to UnivHosts compared to TVHosts.
Next: Multiple sources in the
Up: Effect of network location
Previous: Effect of network location
Lakshminarayanan Subramanian
2002-04-14