PIM-SM
Protocol Independent Multicast - sparse mode
draft-ietf-pim-sm-v2-new-xx
Obsoletes RFC 2362
BSR removed from PIM spec.
explicit join: assumes everyone does not want the data
uses unicast  routing table for RPF checking
data and joins are forwarded to RP for initial rendezvous
all routers in a PIM domain must have RP mapping
when load exceeds threshold forwarding swaps to shortest path tree (default
is first packet)
state increases (not everywhere) as number of sources and number of
groups increase
source-tree state is refreshed when data is forwarded and with Join/Prune
control messages