Cisco Systems Network Router manual Complex Node Representation

Chapter 1 Introduction to PNNI

The Hierarchical PNNI Network Topology

Figure 1-4 Simple Node Representation

Outside link 2

Outside link 1

Peer Group A

Outside link 3

Outside link 4

Other peer groups receive information about the outside links leading to the local peer group, but no internal peer group information is advertised to other peer groups. The advantage of simple node representation is that it keeps the PNNI database within each node smaller than that for complex node representation. Simple node representation also requires fewer resources on the LGN that represents the peer group. The disadvantage it that the true cost of crossing a peer group is hidden by simple node representation. In some networks, this can cause connections to be routed over less desirable routes.

Complex Node Representation

The alternative to simple node representation is complex node representation. When complex node representation is enabled for a LGN, the LGN presents additional information about the peer group it represents. Figure 1-5illustrates complex node representation.

Figure 1-5 Complex Node Representation

Outside link 2

Outside link 1

Peer Group A

Outside link 3

Nucleus

Spoke

Outside link 4

The default complex node representation presents the peer group as a node with multiple ports. A logical nucleus is calculated and logical spokes are created between the nucleus and the logical ports that terminate each outside link. When the LGN presents a complex node to other peer groups, those peer groups can pick the path to use through the local peer group. In contrast, when the simple node representation is used, remote peer groups can choose to communicate through the local peer group, but the remote group must rely on border nodes within the local peer group to determine the path within the local peer group.

	Cisco PNNI Network Planning Guide for MGX and SES Products, Release 5
Part Number OL-3847-01 Rev. D0, April, 2004		1-7