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Conclusions
In this paper, we have presented geography as a means for analyzing
various aspects of Internet routing. First, our analysis based on
extensive traceroute data shows the existence of many circuitous
routes in the Internet. From the end-to-end perspective, we observe
that the circuitousness of routes depends on the geographic and
network locations of the end-hosts. We also find that the minimum
delay along a path is more strongly correlated with the linearized
distance the path than it is with the geographic distance between the
end-points. This suggests that the circuitousness of a path does
impact its minimum delay characteristics, which is an important
end-to-end performance metric. In ongoing work, we are studying the
correlation between geography and network performance.
Second, a more careful examination shows that many circuitous paths
tend to traverse multiple major ISPs. Although many of these
major ISPs have points of presence in common locations,
the peering between them is restricted to specific geographic
locations, which causes the paths traversing multiple ISPs to be more
circuitous. We also found that intra-ISP paths are far less circuitous than
inter-ISP paths. An important requirement to reduce the circuitousness
of paths is for ISPs to have peering relationships at many geographic
locations.
Third, the fraction of the end-to-end path that lies within an ISP's
network varies widely from one ISP to another. Furthermore, when we
consider paths that traverse two or more major ISPs, we find that the
path generally traverses a significantly shorter distance in the first
ISP's network than in the second. This finding is consistent with the
hot-potato routing policy. Using geographic information, we are able
to quantify the degree to which an ISP's routing policy resembles
hot-potato routing.
Finally, our analysis of geographic fault tolerance of ISPs indicates
that the (IP-level) network topologies of many tier-1 ISPs exhibit
skewed degree distributions which may induce a low tolerance to the
failure of a single, critical geographic node. The combined topology
of multiple ISPs exhibits better fault tolerance characteristics,
assuming that the ISPs peer at all geographic locations that are in
common.
Next: Acknowledgments
Up: Geographic Properties of Internet
Previous: Failure of high connectivity
Lakshminarayanan Subramanian
2002-04-14