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
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.
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| Cisco PNNI Network Planning Guide for MGX and SES Products, Release 5 |
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