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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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3. The RP-based delivery tree can reflect suboptimal routes to some receivers.<br />

To optimize these connections, the router can create a source-based<br />

multicast delivery tree. Figure 6-12 shows this function.<br />

Figure 6-12 Establishing a source-based delivery tree<br />

4. After the router receives multicast packets through both the source-based<br />

delivery tree <strong>and</strong> the RP-based delivery tree, PIM prune messages are sent<br />

toward the RP to prune this branch of the tree. When complete, multicast data<br />

from the source flows only through the source-based delivery tree.<br />

Figure 6-13 shows this function.<br />

Figure 6-13 Eliminating the RP-based delivery tree<br />

The switch to the source-based tree occurs after a significant number of packets<br />

have been received from the source. To implement this policy, the router<br />

monitors the quantity of packets received through the RP-based delivery tree.<br />

When this data rate exceeds a configured threshold, the device initiates the<br />

change.<br />

Chapter 6. <strong>IP</strong> multicast 265

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