Most multicast backbone providers have links that show that they mBGP with peers and offer MSDP as well. This allows for the customer on one providers network to access a source on another providers network. Of course there are issues with the 5 bit overlap in multicast address space, but it does work. There are commercial companies that have registered/reserved particular addresses for their applications as well. While I think that today the amount of multicast traffic is low, it will continue to increase. On Sat, 9 Jun 2001, Deepak Jain wrote:

When multicast enabling a network, am I wrong in assuming that the routers will only multicast to their direct, end-user connections and peers (like an access router will only offer streams to its direct connections)? I am trying to figure out what advantages multicast-enabling a backbone has when the majority of customers are not multicast-peers of their upstream routers.