Avaya Configuring IP Multicasting and Multimedia Services Manual de usuario descargar pdf (Pagina 194)

Configuring IP Multicasting and Multimedia Services

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117355-D Rev 00

Shared Trees and Shortest-Path Trees

PIM uses shared trees and shortest-path trees (SPTs) to deliver data packets to

group members in a PIM domain. The following sections describe both types of

trees.

Shared Trees

By default, group members in a PIM domain receive data from sources across a

shared tree. A shared tree consists of a set of paths that connect all members of a

multicast group to its RP. PIM creates a shared tree when sources and receivers

send messages toward the RP. The DR for the source sends register messages, and

the DR for the receiver sends join/prune messages. Typically, multicast groups

that consist of a large number of low-data-rate sources use shared trees to

conserve network resources. A source discovery advertisement application is an

example of a low-data-rate source.

Shortest-Path Trees

In general, the shared tree provides an efficient method of forwarding multicast

traffic from the source to receivers in a PIM domain. However, when the source

begins to send multicast traffic at a high rate, the router can switch from the shared

tree to a shortest-path tree (SPT) to create a more direct route between itself and

the source.

You use SPTs when you want sources and receivers to distribute data at a high

rate. Typically, multicast groups that consist of a large number of high-data-rate

sources use SPTs. For more information, see “How the RP Switches to the

Shortest-Path Tree” on page 6-15 and “How the Last-Hop Router Switches to the

Shortest-Path Tree” on page 6-17.

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Avaya Configuring IP Multicasting and Multimedia Services Manual de usuario Pagina 194