http://www.rfc-editor.org/rfc/rfc2362.txt
RFC 2362: Protocol Independent Multicast-Sparse Mode (PIM-SM): Protocol Specification, D. Estrin, D. Farinacci, A. Helmy, D. Thaler, S. Deering, M. Handley, V. Jacobson, C. Liu, P. Sharma, L. Wei1998-06-01T23:00:00-00:00This document describes a protocol for efficiently routing to multicast groups that may span wide-area (and inter-domain) internets. This memo defines an Experimental Protocol for the Internet community. It does not specify an Internet standard of any kind. Discussion and suggestions for improvement are requested.