A method of operating a network node in PIM-SM (Protocol Independent Multicast-Sparse Mode) is disclosed. In one embodiment, a Rendezvous Point Tree (RPT) to Shortest Path Tree (SPT) switch over process is initiated after the packet flow rate of the RPT data stream is compared against a predetermined threshold using a reverse rate limiting technique. If the packet flow rate of the RPT data stream exceeds the threshold, further analysis can be performed to decide whether the RPT to SPT switch over process should be initiated. Otherwise, if the packet flow rate does not exceed a predetermined threshold, the network node continues to receive multicast packets via the RPT until the predetermined threshold is reached.