Lectures notes for 2010 - KTH

Protocol-Independent Multicast (PIM)
Two modes:
• PIM-dense mode (PIM-DM) [8]
• Dense mode is an implementation of RPF and prune/graft strategy
• Relies on unicast routing tables providing an optimal path
• However, it is independent of the underlying unicast protocol
• PIM-sparse mode (PIM-SM) [7]
• Sparse mode is an implementation of CBT where join points are called “rendezvous points”
• A given router may know of more than one rendezvous point
• Simpler than CBT as there is no need for acknowledgement of a join message
• Can switch from group-shared tree to source-based tree if there is a dense cluster far from
the nearest rendezvous point
The adjectives “dense” and “sparse: refer to the density of group members in the
Internet. Where a group is send to be dense if the probability is high that the area
contains at least one group member. It is send to be sparse if that probability is
low.
Maguire Protocol-Independent Multicast (PIM) 8: 45 of 78
maguire@kth.se 2010.03.21 Internetworking/Internetteknik