Sparse multicast
|
|
Sparse mode multicast is one mode which multicast can use to construct a tree for sending packets to the multicast subscribers. Its opposite is dense multicast.
Sparse mode is ideal for groups where a very low percentage of the nodes (and their routers) will subscribe to the multicast.
One router will designate itself as the rendezvous point (RP), and all routers must explicitly join through the RP. The RP will send IGMP join messages through the routers between it and the source. Once the other routers which need to receive those group packets have subscribed, the RP will unsubscribe to that multicast group, unless it also needs to forward packets to another router or node.
Additionally, the routers will use reverse-path forwarding to ensure that there are no loops for packet forwarding among routers that wish to receive multicast packets.