Avaya Configuring IP Multicasting and Multimedia Services Manual do Utilizador descarregar pdf (Página 201)

Customizing Protocol Independent Multicast

117355-D Rev 00

6-15

How the RP Switches to the Shortest-Path Tree

The following steps, which are illustrated in Figure 6-5, describe how the RP

switches from the shared tree to the shortest-path tree when it has downstream

group members:

A source directly attached to a LAN sends a multicast packet to a group. The

DR (first-hop router) encapsulates each packet in a register message and sends

a unicast message directly to the RP for distribution down the shared tree.

The RP decapsulates each register message and forwards native multicast

messages downstream to all members on the shared tree.

If the data rate of the source packet exceeds the data rate threshold configured

on the RP, the RP immediately sends a join message toward the DR of the

source to establish a shortest-path tree between itself and the source.

All intermediate routers along the path to the source add a new entry to their

multicast forwarding tables for the new (source-group) pair. This entry

establishes a delivery path that all intermediate routers can use to forward

subsequent messages from the source to the RP.

After the source’s DR receives the join message from the RP, it sends native

multicast packets toward the RP on the shortest-path tree.

Upon receiving these multicast packets, the RP immediately sends a

downstream group members.

For information about configuring an RP to switch to an SPT, see “Modifying the

Rendezvous Point Threshold” on page 6-21.

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Avaya Configuring IP Multicasting and Multimedia Services Manual do Utilizador Página 201