Cisco Network Router User Manual page 37

Chapter 1 Introduction to PNNI
Figure 1-3
group 2 group 2
group 3
In a hierarchical PNNI network, logical levels are used to manage the portions of the PNNI database that
describe communications paths between individual peer groups. PNNI divides the entire network
database into manageable chunks, and the portions that describe communications between peer groups
are managed by LGNs that operate at levels above the lowest-level peer groups.
Within each level 56 peer group in
PNNI database that describes communication paths to all other nodes within the peer group. However,
individual peer group nodes do not exchange PTSEs with nodes outside their peer group. Instead, LGNs
are created during configuration to operate at level 40 and communicate with other level 40 nodes.
The level 40 nodes in
same way as do the lower level nodes. The level 40 LGN for each peer group in
peer group leader and provides summarized information to its child peer group about the other peer
groups represented at level 40. Each peer group leader also provides summarized peer group information
about its child peer group to the other peer group leaders at the same level. Peer Group 1, for example,
learns about 8 nodes: 4 physical nodes are in its own peer group, and 4 LGNs are actually representing
other peer groups.
To demonstrate how hierarchical networks support more nodes than single peer group networks,
consider the two-level example in
there are 5 peer groups, so each peer group will learn about 4 LGNs that will represent the other peer
groups. This allows each peer group to support up to 156 physical nodes (160 - 4 = 156). The hierarchical
network in
Part Number OL-3847-01 Rev. D0, April, 2004
Example Hierarchical PNNI Network Topology Showing a Two-Level Hierarchy
Peer Peer
Peer
Figure 1-3
Figure 1-3 can support 780 physical nodes (156 * 5 = 780).
Cisco PNNI Network Planning Guide for MGX and SES Products, Release 5
Peer group 1
PNNI networks
Figure 1-3, all the nodes exchange PTSEs to build and maintain a
are all part of the same level 40 peer group and exchange PTSEs in the
Figure 1-3. A single peer group can support 160 nodes. In
The Hierarchical PNNI Network Topology
Level 40
Peer peer
group 5 group 5
Level 56
Peer
group 4
Figure 1-3 is called a
Figure 1-3,
1-5