PIM operates in two basic modes: sparse mode and dense mode. In addition, PIM can operate in sparse-dense mode, with some multicast groups configured as dense mode (flood-and-prune, [S,G] state) and others configured as sparse mode (explicit join to rendezvous point [RP], [*,G] state).
PIM drafts also establish a mode known as PIM source-specific mode, or PIM SSM. In PIM SSM there is only one specific source for the content of a multicast group within a given domain.