http://www.rfc-editor.org/rfc/rfc5015.txt
RFC 5015: Bidirectional Protocol Independent Multicast (BIDIR-PIM), M. Handley, I. Kouvelas, T. Speakman, L. Vicisano2007-10-01T23:00:00-00:00This document discusses Bidirectional PIM (BIDIR-PIM), a variant of PIM Sparse-Mode that builds bidirectional shared trees connecting multicast sources and receivers. Bidirectional trees are built using a fail-safe Designated Forwarder (DF) election mechanism operating on each link of a multicast topology. With the assistance of the DF, multicast data is natively forwarded from sources to the Rendezvous-Point (RP) and hence along the shared tree to receivers without requiring source-specific state. The DF election takes place at RP discovery time and provides the route to the RP, thus eliminating the requirement for data-driven protocol events. [STANDARDS-TRACK]