IP multicast is a technique that allows packets to be simultaneously transmitted over internet2 (it is not deployed in the commercial internet) to a selected set of destinations. Standard Internet traffic requires a separate set of packets for each destination. IP multicast allows for one set of packets to be sent to multiple destinations. This is accomplished through the use of multicast trees, based on a reverse path routing where clients request a stream, and the packets are replicated by routers within the network. Rather than having to send a single stream to every client, with multicast the host only sends one stream into the network, where it is replicated and "broadcast" to all subscribers.
