Sparse multicast

Protocol-Independent Multicast (PIM) is a family of multicast for (IP) networks that provide one-to-many and many-to-many distribution of data over a LAN, WAN or the Internet. It is termed protocol-independent because PIM does not include its own topology discovery mechanism, but instead uses routing information supplied by other . PIM is not dependent on a specific unicast routing protocol; it can make use of any unicast routing protocol in use on the network. PIM does not build its own routing tables. PIM uses the unicast routing table for reverse path forwarding.

There are four variants of PIM:

PIM-SM is commonly used in IPTV systems for routing multicast streams between VLANs, Subnets or local area networks.

There are two PIM versions. The versions are not directly compatible though may coexist on the same network. Network equipment may implement both versions. PIMv2 has the following improvements over PIMv1: A single RP is used per group. RP discovery is accomplished by a Bootstrap Router (BSR). Groups are either sparse or dense mode; Interfaces can be either. General improvements to protocol flexibility and efficiency.

Protocol Independent Multicast - Sparse-Mode (PIM-SM) is a for efficiently routing (IP) packets to multicast groups that may span wide-area and inter-domain internets. The protocol is named protocol-independent because it is not dependent on any particular unicast routing protocol for topology discovery, and sparse-mode because it is suitable for groups where a very low percentage of the nodes (and their routers) will subscribe to the multicast session. Unlike earlier dense-mode multicast routing protocols such as DVMRP and dense multicast routing which flooded packets across the network and then pruned off branches where there were no receivers, PIM-SM explicitly constructs a tree from each sender to the receivers in the multicast group.

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