Modeling the Branching Characteristics and
	      Efficiency Gains in Global Multicast Trees

	       Robert C. Chalmers and Kevin C. Almeroth
		    Department of Computer Science
		       University of California
		     Santa Barbara, CA 93106-5110
		    {robertc,almeroth}@cs.ucsb.edu


In this paper, we investigate two issues.  First, what level of
efficiency gain does multicast offer over unicast?  Second, how does
the shape of multicast trees impact multicast efficiency?  We address
the first issue by developing a metric to measure multicast efficiency
for a number of real and synthetic datasets.  We find that group sizes
as small as 20 to 40 receivers offer a 60-70% reduction in the number
of links traversed compared to separately delivered unicast streams.
Addressing the second issue, we have found that almost all multicast
trees have similar characteristics in terms of key parameters such as
depth, degree frequency and average degree.  A final contribution of
our work is that we have taken multicast group membership data and
multicast path data and compiled datasets which can be used to
generate large, realistic multicast trees.