3Com CoreBuilder 7000 Operation Manual page 72

72 C 4: P N - -N I (PNNI) V 1.0
HAPTER RIVATE ETWORK TO ETWORK NTERFACE ERSION
For information on the ATM address format, refer to "ATM Address
Format" on page 84 in the Management Guide.
Once the node is put into a group, the groups are linked and a hierarchy
is created. Each node and peer group has a specified level which is
indicated in its level indicator. The level indicator specifies the exact
number of significant bits that are used for the peer group ID and can
range from 0 to 104. The more levels, the more complex the network. It
is this level indicator that is used to create the hierarchy in the network.
Each peer group can have a peer group leader. The peer group leader is
responsible for passing summarized information about its group to higher
levels in the hierarchy. See "Peer Group Leader" on page 74 in the
Management Guide for details on how the peer group leader is chosen.
In addition to the peer group leader there is also a border node. These
nodes have at least one link that crosses the peer group boundary. These
nodes may be peer group leaders. It is the border node(s) that have
access to other nodes outside its peer group. All nodes within the group
will know that in order to route outside the group the border node must
be used.
The Lowest Level Hierarchy - A Flat Hierarchy
The lowest level hierarchy, or flat hierarchical representation, is shown in
Figure 16. In this example, each lowest level node has to maintain the
topology of the entire network, including information for every physical
link in the network and reachability information for every node on the
network. This could cause memory overload and lead to inefficient
routing as a result. Improvements in the CoreBuilder 7000 allow for easy
storage all of this information, reducing the risk of memory overload.
Furthermore, the CoreBuilder 7000 will easily adapt to a hierarchy when
one is built. A PNNI routing hierarchy, when implemented, will reduce
overhead and provide for more efficient routing.