The MBone, now sometimes called the Multicast Internet, is an arranged use of a portion of the Internet for Internet Protocol (IP) multicasting (sending files - usually audio and video streams - to multiple users at the same time somewhat as radio and TV programs are broadcast over airwaves). Although most Internet traffic is unicast (one user requesting files from one source at another Internet address), the Internet's IP protocol also supports multicasting, the transmission of data packets intended for multiple addresses. Since most IP servers on the Internet do not currently support the multicasting part of the protocol, the MBone was set up to form a network within the Internet that could transmit multicasts. The MBone was set up in 1994 as an outgrowth of earlier audio multicasts by the Internet Engineering Task Force (IETF) and has multicast a number of programs, including some well-publicized rock concerts.
The MBone consists of known servers (mostly on UNIX workstations) that are equipped to handle the multicast protocol. Tunneling is used to forward multicast packets through routers on the network that don't handle multicasting. An MBone router that is sending a packet to another MBone router through a non-MBone part of the network encapsulates the multicast packet as a unicast packet. The non-MBone routers simply see an ordinary packet. The destination MBone router unencapsulates the unicast packet and forwards it appropriately. The MBone consists of a backbone with a mesh topology which is used by servers that redistribute the multicast in their region in a star topology. The MBone network is intended to be global and includes nodes in Europe.
The channel bandwidth for MBone multicasts is 500 kilobits per second and actual traffic is from 100-300 kilobits depending on content. MBone multicasts usually consist of streaming audio and video.