A.PIM join messages are sent every 60 seconds to refresh the upstream router’s mroute state for the multicast tree.
B.Routers send a PIM join acknowledgement in response to each PIM join message received from a downstream router.
C.PIM join messages are only sent when the multicast distribution tree is first being established.
D.PIM join messages are sent every three minutes to refresh the upstream router’s mroute state for the multicast tree.

A.The source must send a PIM Register message to the rendezvous point （RP）
B.The source must first join the multicast group using IGMP before sending
C.The source must perform a Request to Send （RTS） and Clear to Send （CTS） handshake with the PIM designated router （DR）
D.No control plane signaling needs to be performed；the source can simply begin sending on the local subnet