Multicast is a transmission service that simultaneously delivers packets from a sender to a group of receivers. The set of receivers form a multicast group logically identi?ed by a unique multicast address. In a network with network level multicast support (e.g. IP) a copy of each packet is transmitted once on each link of a directed tree rooted at the sender with the receivers as leaves. In the public Internet, IP Multicast in an extension to the basic routing and forwarding model, endowed with its own address space, signaling (IGMP), and routing protocols (MOSPF, DVMRP, PIM).