Nortel business policy switch 2000, User Manual

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108 Chapter 2 Network configuration
208700-C
Redundant cascade stacking feature
Business Policy Switches allow you to connect up to 8 units into a redundant
cascade stack. If any single unit fails or if a cable is accidently disconnected, other
units in the stack remain operational, without interruption.
Figure 16 shows an example of how a stack configuration reacts to a failed or
powered-down unit in the stack configuration:
1 As shown in Figure 16 , unit 3 becomes nonoperational.
This result can be due to a failed unit or simply because the unit was powered
down.
2 Unit 2 and unit 4, directly upstream and downstream from unit 3, sense the
loss of link signals from unit 3.
a Units 2 and 4 automatically loop their internal stack signals (A and B).
b The Cas Up LED for unit 2 and the Cas Dwn LED for unit 4 turn on
(amber) to indicate that the stack signals are looped.
3
The remaining stack units remain connected.
Although the example shown in Figure 16 shows a failed unit causing the stack to
loop signals at the points of failure (A and B), the system reacts the same way if a
cable is removed.