Distribution occurs through the use of multicasting technology.
Unicasting is the normal way we use the Internet. One host sends a packet of information to another host. Multicasting occurs when one host sends a packet of information to a group of hosts. At the end of tunnels are workstation-class machines, typically, supported by IP multicast operating systems. IP multicast packets are encapsulated for transmission through tunnels, so that they look like normal unicast datagrams to intervening routers and subnets.