USC LBL CISCO CISCO UCL UMICH USC USC Traditional multicast routing mechanisms (e.g. DVMRP and MOSPF [1][2]) were intended for use within regions where groups are widely represented or bandwidth is universally plentiful. When group members, and senders to those group members, are distributed sparsely across a wide area, these schemes are not efficient; data packets or membership report information are periodically sent over many links that do not lead to receivers or senders, respectively. This characteristic lead the Internet community to investigate multicast routing architectures that efficiently establish distribution trees across wide-area internets, where many groups are sparsely represented and where bandwidth is not uniformly plentiful due to the distances and multiple administrations traversed. Efficiency is evaluated in terms of the state, control message processing, and data packet processing required across the entire network in order to deliver data packets to the members of the group.