On the topology of multicast trees

The benefit derived from using multicast is seemingly dependent upon the shape of the distribution tree. In this paper, we attempt to accurately model interdomain multicast trees. 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 of 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.