In Figure 2, we illustrate the distribution of inter-node round trip times between nodes in the three data sets. The King measurements were limited to a maximum of 800ms. The data exhibit one important characteristic: spread. The application-level, Azureus round trip times spread across four orders-of-magnitude, while the inter-DNS, King data set spreads across three. In theory, this is not a harbinger of higher embedding error; in practice, however, as Hong et al. have shown, the error between nodes whose distance is near the middle of the latency distribution tends to be the lowest : with longer tails to this distribution, there are more edges to be inaccurate. (We found ICMP measurements exhibit a similarly wide distribution; see Section 7.5.) This wide spread is a warning sign that Azureus will have higher error than a system with a narrower round trip time distribution.
Jonathan Ledlie 2007-02-23