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PNNI in an ATM Network
893-01006-C
4-21
Multilevel Designated Transit Lists
The Centillion 50/100 switches support multilevel designated transit lists.
Multilevel DTLs include peer groups in different levels of the PNNI hierarchy,
which means that end stations connected to Centillion 50/100 switches in separate
peer groups can communicate over PNNI.
Figure 4-8
shows three peer groups (A, B, and C). End station Z can talk to end
station Y because switch 2 in peer group A and switch 3 in peer group B create a
third peer group (C) that allows peer groups A and B to communicate.
Figure 4-8. Multilevel Hierarchy of Centillion 50/100 Switches
Switch 2 is the peer group leader of peer group A and C. Switch 2 cannot be the
peer group leader of B because a switch cannot be the peer group leader of another
peer group on the same level.
Communication between end stations in different peer groups is accomplished
using a multilevel DTL, which includes nodes in different levels of the PNNI
hierarchy. The DTL of the path from station Z to station Y would be: 1-2-C-3-4.
The DTL is considered multilevel because it includes peer group C (a higher-level
peer group).
Note:
A Centillion 50/100 or Model 5000BH switch cannot be a peer group
leader or border node.
Peer group leader
for A and C
2
C
8853EA
1
3
AB
4
Peer group
leader for B
yz