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The benefit derived from using multicast is seemingly dependent upon the shape of the distribution tree. We attempt to model interdomain multicast trees accurately. We measure a number of key parameters, such as depth, degree frequency, and average degree, for a number of real and synthetic data sets. We find that interdomain multicast trees actually do share a common shape at both the router and autonomous system levels. Furthermore, we develop a characterization of multicast efficiency which reveals that group sizes as small as 20 to 40 receivers offer a 55%-70% reduction in the total number of links traversed when compared to separately delivered unicast streams. A final contribution of our work consists in a number of data sets, compiled from multicast group membership and path data, that can be used to generate large sample trees, representative of the current multicast infrastructure.
Date of Publication: Feb 2003