We propose a new multicast protocol called REUNITE. The key idea of REUNITE is to use recursive unicast trees to implement multicast service. REUNITE does not use class D IP addresses.Instead, both group identification and data forwarding are based on unicast IP addresses. Compared with existing IP multicast protocols, REUNITE has several unique properties. First, only routers that are acting as multicast tree branching points for a group need to keep multicast forwarding state of the group. All other non-branching-point routers simply forward data packets by unicast routing. In addition, REUNITE can be incrementally deployed in the sense that it works even if only a subset of the routers implement the protocol. Furthermore, REUNITE supports load balancing and graceful degradation such that when a router does not have resources (forwarding table entry, buffer space, processing power) to support additional multicast groups, the branching can be automatically migrated to other less loaded routers. Finally, sender access control can be easily supported in REUNITE. Although in REUNITE, routers in a multicast tree still need to maintain control path state, we discuss a variant of REUNITE in which routers do not need to maintain any control path state. However, this is achieved at the expense of having two additional protocol message types, and a slightly more complex protocol.

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