Cabletron Systems 04-0053-01 User Manual

SmartSwitch ATM User Guide   3-7

PNNI Routing

Multi-level PNNI Topology  

Connectivity is now established between the two peer groups. For example, if LANE services are running on a switch 
within peer group A, LANE clients can exist in group B. The clients in group B will traverse the link between the two 
groups, find the LANE server in group A, and join the ELAN. Figure 3-2 shows a logical representation of the 
topology created in the example. 

Figure 3-2 Logical representation of connectivity between groups A and B

3.2.2

Physical Connections Between Peer Groups

Keep in mind that the two PGL switches (switches SWA3 and SWB3) do not have to be directly connected to each 
other for the two peer groups to maintain connectivity. PGLs can find each other through any physical link that 
connects the two groups. For example, if a second physical link is made between two other switches in groups A and 
B (for instance, between SWA1 and SWB2), and if the physical link between the PGLs is removed, the PGLs will 
reestablish their connectivity across the second physical link.

Adding Higher-level Peer Groups

Adapting the process in the example above, more sophisticated PNNI topologies can be created. For example, to 
establish connectivity with other parent groups at level 72, do the following:

Make a physical connection between any two switches represented in the separate parent groups.

Peer Group A

Level 80

Peer Group B

Level 80

Level 72

Logical link

Physical Link

SWA1

SWA2

SWB1

SWB2

Logical Group Nodes 

for Peer Groups A and B

Peer Group Leader

Peer Group Leader

Parent Group of

Group A and B

Outside Uplink in 

 command

N/A Horizontal Link to/from LGN in 

 command