Dynamic host-group/multidestination routing for multicast sessions

Multicast routing research efforts have mostly focused on the host-group model in which multicast packets are addressed to a host group. Another multicast routing approach uses multidestination addressing, where a multicast packet carries a list of the unique (unicast) addresses of all the group members. This form of routing uses limited or no additional state beyond the existing unicast routing tables. It, therefore, scales well with the number of multicast sessions but does not scale well with the multicast group size and, in fact, requires the size of the group to be below a certain threshold. In this paper, we envision a future scenario in which both host-group and multidestination addressing routing approaches coexist within the Internet. We develop a dynamic routing context for this scenario wherein a multicast session can adapt among different routing configurations depending on the multicast group size and how this size changes over time. We consider three routing options: 1) a single multi-destination addressed flow - suitable for small-group sessions, 2) multiple multi-destination addressed flows - suitable for medium-group sessions and 3) a single host-group addressed flow - suitable for large-group sessions. Our work is concerned with the development and evaluation of protocols that allow a multicast session to dynamically switch among these three routing options as the size of the session changes.