Multicast

Multicast is similar to broadcast where there is one sender and multiple receivers. The difference is that with multicast the receiver can opt-in to a specific multicast group. Routers and switches need multicast support in order to effectively switch multicast content to a station that opted in per IGMP packets. Multicast support on the Internet has always lagged behind somewhat probably due to the fact that the costs of a multicaster are quite low to reach lots of receivers as compared to a broadcaster serving multiple unicast streams. The people in power are just terrified that someone else has a message better than them. This is exactly the same reason that the upload speed of home DSL is capped at a small percentage of the download speed. Don't expect to see global or even continent wide multicast support anytime soon.