Cisco Systems Network Router manual Peer group

Chapter 1 Introduction to PNNI

The Hierarchical PNNI Network Topology

Note Hierarchical PNNI networks are not supported on Cisco MGX 8850 switches before Release 2.1.60, and they are not supported on the SES PNNI Controller before Release 1.1.60.

Figure 1-2 Example Hierarchical PNNI Network Topology Showing Multiple Peer Groups

Peer group 2

Peer group 5

Peer group 1

Peer	Peer
group 3	group 4
	PNNI networks

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Notice that the only difference between the single peer group in Figure 1-1and the hierarchical PNNI network in Figure 1-2is the grouping of the nodes. This grouping of the nodes creates smaller PNNI databases within the nodes in each peer group and reduces the PNNI processing requirements in each node. This grouping also provides room to add more nodes in each of the groups.

In a hierarchical network, the database for each peer group is smaller because the peer group collects, stores and processes PTSEs for only those nodes in the same peer group. The nodes within a peer group do receive information on other peer groups, but the information is summarized. From the perspective of an individual peer group, other peer groups appear to be single nodes. Nodes within one peer group do not receive PTSEs from other peer groups and therefore do not collect, store, and process information about all the individual nodes and links in other peer groups.

The Cisco switches described in this guide support up to 32 visible peer groups in one network. (The specifications for Cisco switches are described in Table 2-1in Chapter 2, “Interoperability and Performance Planning.”) A visible peer group is a peer group with which the local peer group can communicate. Because each visible peer group appears as a logical group node (LGN), each visible peer group reduces the available node count for a peer group. For example, if the local peer group discovers 32 visible peer groups, the node count for the local peer group is reduced to 128 (160 - 32 = 128).

Figure 1-3demonstrates why a multiple peer group PNNI network is called a hierarchical PNNI network.

	Cisco PNNI Network Planning Guide for MGX and SES Products, Release 5
1-4	Part Number OL-3847-01 Rev. D0, April, 2004