Cisco Systems Network Router manual 4-11, 2 Farthest Node Branching

Chapter 4 Planning Intermediate Route Selection

Additional Routing Features in MGX and SES Nodes

The farthest-node branch option is a PNNI enhancement that allows PNNI to use network links more efficiently. Figure 4-2demonstrates farthest-node branching.

Figure 4-2 Farthest Node Branching

Switch 1 1 SVC

Root

4 SVCs

Switch 2		Party 1
	Leaf	Party 2
		Party 3
		Party 4

Switch 3 Leaf 1,	Party 5
Leaf 2,	Party 6
Leaf 3,	Party 7
Leaf 4,	Party 8

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In Figure 4-2, Switch 2 supports branching and Switch 3 does not. When PNNI sets up the P2MP connection to parties 1 through 4, it determines that the Switch 2 outgoing interface supports branching, so PNNI establishes 1 SVC between Switch 1 and 2.

Switch 3 in Figure 4-2does not support branching, so Switch 1, which does support branching, establishes 4 SVCs to Switch 3. The destination for each SVC must be a leaf, so four leaf end points are established on Switch 3, one for each party. The four leaf end points can be on one interface, or they can be spread out on multiple interfaces. A leaf end point is an SVC endpoint.

Farthest-node branching is a PNNI feature that takes advantage of branching when it is available. Switch 1 could have originated a separate connection for each party on Switch 2, but this would have required 4 SVCs instead of 1, and all four would be carrying the same data. Farthest node branching improves network efficiency by reducing the number of SVCs required for P2MP connections and by reducing the bandwidth requirements for P2MP connections.

Previous software releases disabled branching with the branching restricted option. This option is now set by default to enable branching. If the network includes a node that does not support branching, the farthest branching node from the root creates an SVC for every downstream party.

Note This release does not support the P2MP leaf-initiated join feature, and leaf endpoints cannot use a P2MP connection to communicate with other leaf endpoints.

	Cisco PNNI Network Planning Guide for MGX and SES Products, Release 5
Part Number OL-3847-01 Rev. D0, April, 2004		4-11