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.

A.It is used only for directly connected subnets or aggregate routes
B.It can only be used with LDP.
C.It is only used when two or more labels are stacked.
D.It enables the Edge LSR to request a label pop operation from Its upstream neighbors
E.It is requested through TDP using a special label value that is also called the implicit-null value.
F.It is requested through LDP using a special label value that is also called the implicit-null value.