On a PIM Dense Mode domain, a branch was previously pruned and a new receiver appears that needs traffic immediately. Which PIM message causes the upstream neighbor to resume forwarding multicast down that branch without waiting for the next periodic refresh?

In PIM Dense Mode, when a new receiver appears on a previously pruned branch, a PIM Graft message is sent upstream. This message immediately notifies the upstream router that the branch needs to rejoin the multicast distribution tree and begin receiving traffic, bypassing the normal prune timeout and periodic refresh cycle. PIM Join messages are used in PIM Sparse Mode to explicitly request traffic. PIM Prune messages are used to stop traffic from flowing down a branch. PIM Register messages are used by designated routers to register sources with a Rendezvous Point in PIM Sparse Mode.