Protocol Independent Multicast

Protocol Independent Multicast ( PIM ) is a method in network technology that allows dynamic routing of multicast packets on the Internet. Unlike traditional methods such as DVMRP or MOSPF PIM is still efficient even in highly dispersed participants or multicast groups and at extremely heterogeneous network infrastructure. For this reason, PIM is probably the only one still used multicast routing method.

PIM differs between the two modes of operation, dense- mode and sparse mode.

Dense -Mode

In the so-called dense- mode, the initiation of a multicast generates a broadcast to all known multicast groups. One speaks here of a "push " model. Then the router from the multicast log off in whose subnets there are no takers ( so-called pruning ). The dense- mode is therefore only suitable for networks with low subscriber density and complexity.

The Dense - Mode is used in large networks is no longer applicable, since in addition to the network load can also troubleshoot would be too costly.

Sparse -mode

For networks with very high subscriber density or large scattering of the participants on different subnets of the sparse -mode is employed. This includes the agreement of a rendezvous point router that receives multicast publications. Other routers may ask whether multicasts are received for appropriate stakeholders at this rendezvous point. If this is the case, give the rendezvous point between the sender and the multicast router in the subnet, an interested subscriber is a connection. This mode causes the network sections downstream of the rendezvous point a huge load. By using Switchover SPT ( Shortest Path Tree or minimum tree spanning ), a last-hop router after the first received packet to establish a direct connection to the multicast sender and thus relieve the network, since now the network portion of route with the lowest cost is used.