1) Multicast backbone 
Mbone (short for `multicast backbone`) was an experimental backbone for carrying IP multicast traffic on the Internet. It was developed in the early 1990s and required specialized hardware and software. Since the operators of most Internet routers have disabled IP multicast due to concerns regarding bandwidth tracking and billing, the Mbone was .....
Multicast Backbone [Internet]
Multicast backbone. The multicast backbone of the Internet. MBone is a virtual multicast network composed of multicast LANs and the point-to-point tunnels that interconnect them.