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Hot-potato versus Cold-potato routing
Finally, we investigate whether geographic information can be helpful
in assessing whether ISP routing policies in the Internet conform to
either hot-potato routing or cold-potato routing. In hot-potato
routing, an ISP hands off traffic to a downstream ISP as quickly as it
can. Cold-potato routing is the opposite of hot-potato routing where
an ISP carries traffic as far as possible on its own network before
handing it off to a downstream ISP. These two policies reflect
different priorities for the ISP. In the hot-potato case, the goal is
to get rid of traffic as soon as possible so as to minimize the amount
of work that the ISP's network needs to do. In the cold-potato case,
the goal is carry traffic on the ISP's network to the extent possible
so as to maximize the control that the ISP has on the end-to-end
quality of service. In general, an ISP's routing policy would lie
somewhere in between the extremes of hot-potato and cold-potato
routing.
Figure 14:
CDF of the fraction of the end-to-end path that lies within the first and second ISP networks in sequence.
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We consider the set of paths from U.S. sources to TVHosts. For each
path that traverses two or more major ISPs (with nationwide
backbones), we compute the fraction of the end-to-end path that lies
within the first major ISP (ISP1) and the second major ISP (ISP2) in
sequence. We use these fractions as measures of the amount of work
that these ISPs do in conveying packets end-to-end. The distributions
of these fractions is plotted in
Figure 14. We observe that the fraction of
the path that lies within the first ISP tends to be significantly
smaller than that within the second ISP. For instance, the median is
0.22 for the first ISP and 0.64 for the second ISP. This is consistent
with hot-potato routing behavior because the first ISP tends to
hand off traffic quickly to the second ISP who carries it for a much
greater distance.
Figure 14 also plots the distributions of
the path lengths in the case where the first ISP is Sprintlink. We
find that the difference between the ISP1 and ISP2 curves is even
greater in this case. Again, this is consistent with hot-potato
routing behavior on the part of Sprintlink for routes from academic
locations.
Next: Summary
Up: Impact of multiple ISPs
Previous: Distribution of ISP path
Lakshminarayanan Subramanian
2002-04-14