While traditional IP multicast schemes (RFC 1112) are scalable for
very large multicast groups, they have scalability issues with a very
large number of distinct multicast groups. This document describes
Xcast (Explicit Multi-unicast), a new multicast scheme with
complementary scaling properties: Xcast supports a very large number
of small multicast sessions. Xcast achieves this by explicitly
encoding the list of destinations in the data packets, instead of
using a multicast group address. This document discusses Xcast
concepts and options in several areas; it does not provide a complete
technical specification. This memo defines an Experimental Protocol
for the Internet community.