The value of vRtrPimLdpPmsiCGrpSrcJoinTimer indicates the time
interval before the Provider Edge (PE) router connected to the
source switches to the S-PMSI group.
After providing sufficient time for all PE's to join the S-PMSI, the
transmitting PE switches the given multicast stream to the S-PMSI.
The PE router connected to the source then starts encapsulating
traffic using the S-PMSI group.