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Geographic fault tolerance of ISPs
An important component of studying Internet routing is to understand
its fault tolerance aspects. Fault tolerance of a network is normally
studied at the granularity of router or link failures. However such a
failure model does not capture the fact that two seemingly independent
routers can be susceptible to correlated failures.
We ask the question: what is the tolerance of an ISP's network to a
total network failure in a geographic region, i.e., a failure
that affects all paths traversing the region? We refer to such a
failure as a geographic failure. Potential reasons for such a
failure include natural calamities such as earthquakes or power
blackouts.
By using the geographic location information of the routers, we can
identify routers that are co-located and thereby construct a
geographic topology of an ISP. In this topology, each geographic
region is associated with a node and an edge between two nodes
signifies the existence of at least one long-haul backbone link that
connects the corresponding geographic regions.
We obtained the geographic topologies for 9 of the 13 major ISPs
listed in Section 3.4.1 from the CAIDA MapNet site
[24]. These are: AT&T, Cable and Wireless, Sprintlink,
Genuity, Qwest, PSINet, UUNet, Verio and Exodus. Many of these
topologies are obtained from information published at the ISPs' Web
sites and are between 6-12 months out of date. Although it may be
possible to construct an ISP's geographic topology using extensive
traceroute measurements, it would be hard to assess the completeness
of the constructed topology. Hence we restrict ourselves to the
geographic topologies obtained from CAIDA. However, as acknowledged by
CAIDA [24], it is possible that these topologies may
themselves be incomplete. This may be due to limited tracing or the
presence of backup paths in routing. We will perform our analysis
under the assumption that these topologies are reasonably complete and
only have a few missing links.
Subsections
Next: Degree distributions
Up: Geographic Properties of Internet
Previous: Summary
Lakshminarayanan Subramanian
2002-04-14