protocol-independent multicast (PIM)

Protocol-independent multicast (PIM) is a set of four specifications that define modes of Internet multicasting to allow one-to-many and many-to-many transmission of information.

The four modes are:

  • sparse mode (SM)
  • dense mode (DM)
  • source-specific multicast (SSM)
  • bidirectional.

The most common mode in PIM is the sparse mode. It is used for transmission of data to nodes in multiple Internet domains, where it is expected that only a small proportion of the potential nodes will actually subscribe. Dense mode, in contrast to sparse mode, is used when it is expected that a large proportion of the potential nodes will subscribe to the multicast. In source-specific multicast, paths (also called trees) originate (or are rooted) at a single, defined source, whereas bidirectional PIM is not source-specific.

The term "protocol independent" means that PIM can function by making use of routing information supplied by a variety of communications protocols. In information technology, a protocol is a defined set of rules that end points in a circuit or network employ to facilitate communication.

This was last updated in April 2007

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