TCP/IP Tutorial and Technical Overview - IBM Redbooks

from the delivery tree. The inefficiencies associated with flooding is minimal. This
configuration is also appropriate when:
► Senders and receivers are in close proximity to each other.
► There are few senders and many receivers.
► The volume of multicast traffic is high.
► The stream of multicast traffic is constant.
Unlike DVMRP, PIM-DM does not support tunnels to transmit multicast traffic
through non-multicast capable networks. Therefore, the network administrator
must ensure that each device connected to the end-to-end path is
multicast-enabled.
6.7.2 PIM sparse mode
The PIM-SM protocol uses a variant of the center-based tree algorithm. In a
PIM-SM network, a rendezvous point (RP) is analogous to the center point
described in the algorithm. Specifically, an RP is the location in the network
where multicast senders connect to multicast receivers. Receivers join a tree
rooted at the RP. Senders register their existence with the RP. Initially, traffic
from the sender flows through the RP to reach each receiver.
The benefit of PIM-SM is that unlike DVMRP and PIM-DM networks, multicast
data is blocked from a network segment unless a downstream device specifically
asks to receive the data. This has the potential to significantly reduce the amount
of traffic traversing the network. It also implies that no pruning information is
maintained for locations with no receivers. This information is maintained only in
devices connected to the multicast delivery tree. Because of these benefits,
PIM-SM is currently the most popular multicast routing protocol used in the
Internet.
Chapter 6. IP multicast 263